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context: tag/antimatter/ question: Can one bit of light bounce off another bit of light? | Yes, one bit of light can bounce off another bit of light, but not directly, and the effect is very rare. Light is made out of small quantum objects called photons. When you turn on a lamp, the light bulb begins creating and emitting trillions upon trillions of photons. Photons are in a class of quantum particles known as bosons. Bosons are special because many bosons can occupy the exact same quantum state at the same time. Light being made of bosons is what makes a laser beam possible. A laser beam is a collection of many photons all in the same quantum state. In contrast, particles that are not bosons cannot occupy the same state at the same time. This is one of the effects that keeps the atoms in an object from collapsing to a single point. The principle that dictates that non-bosons cannot be in the same state is called the Pauli Exclusion Principle. Non-bosons are also called fermions. The fact that bosons such as light can occupy the same state means that they don't get in each other's way. Also, light dominantly interacts with objects that have electric charge. Since light itself does not have electric charge, one photon cannot directly interact with another photon. Instead, they just pass right through each other without being affected. Because they are bosons and because they carry no electric charge, one photon cannot directly bounce off another photon. If you point one jet of water towards another jet of water, then at the point where they cross you will get a mess of water spraying all over due to the collisions. In contrast, if you shine one light beam such that it crosses another light beam, they will just pass through each other unaffected. However, two photons heading towards each other can indeed collide indirectly. The process goes like this. A photon can spontaneously degenerate into a particle with mass and its antiparticle in a process known as pair production. In this process, the energy of the photon is completely transformed into the mass of the two particles. For example, a photon can turn into an electron and an anti-electron. If two photons head towards each other and they both turn into electron/anti-electron pairs at about the same time, then these particles can interact. The anti-electron from one photon will collide with an electron from the other photon, and turn back to light. The same thing happens to the other anti-electron and electron. The overall effect is that you get two photons going into the interaction and you get two photons coming out of the interaction, so it looks like the photons simply bounced off each other. In a sense, the one bit of light did indeed bounce off the other bit of light, but only indirectly by transforming into other particles. This interaction is shown in the diagram. The red squiggles represent photons, the e+ blue lines are anti-electrons (positrons), and the e- blue lines are electrons. A photon comes from the left of the diagram and decays into an electron and an anti-electron. At the same time, another photon comes from the right and turns into an electron and an anti-electron. Each anti-electron collides with an electron, they mutually annihilate and turn back into a new photon. Photon-photon scattering is therefore possible through an indirect mechanism, but it is rare. There are two reasons that it is rare. First, light can only turn into other particles if it has enough energy to create the mass needed for the new particles, according to E = mc2. Because c is such a huge number, it takes a large amount of energy to make a little bit of mass. In order to turn into an electron and an anti-electron, the photon must have at least as much energy as the equivalent energy of their combined masses. Only gamma rays (one step higher than X-rays) have enough energy to do this. Secondly, the photons have to transform at just the right moment in order for the new particles from both photons to collide. For both of these reasons, light-light scattering is very rare. In fact, light-light scattering has never been conclusively observed. All the steps in light-light scattering have been observed (pair production and pair annihilation), so that we know that it is possible. The whole effect is just so rare that it has never been observed. However, the Large Hadron Collider (LHC) has both the ability to create high-energy light, and the ability to create a lot of it, making the rarity of light-light scattering more manageable. It is only a matter of time before the LHC observes light bouncing off light. |
context: tag/antimatter/ question: Does the negative mass of antimatter mean that it's gravitationally repelled from stars? | Antimatter does not have negative mass. In our universe, there is no such thing as negative mass. Mass only comes in positive form. In contrast, electric charge can be positive or negative. The nonexistence of negative mass has profound consequences. First, gravity is always attractive and never repulsive. Presumably, if negative mass existed, it would be repelled by objects with positive mass such as the earth or sun. A cup made out of negative mass would fall up and not down when you let it go. As interesting as this sounds, negative mass does not exist, so heavier objects always fall down. Second, the lack of negative mass means that gravitational fields can never be shielded, blocked, or canceled. In contrast, electric charge comes in both positive and negative varieties. An electric field created by a positively charged object can therefore be blocked by a wall of negative charges. This is the principle used in metal shielding, which keeps the microwaves in a microwave oven from cooking everything in the kitchen. But there is no negative mass to cancel out gravity. If negative mass did exist, you could use it as a form of anti-gravity. If you built a floor on earth out of negative mass of sufficient size, then people above that floor would feel no gravity and would float around. Again, negative mass does not exist, so genuine anti-gravity is not possible. Gravity permeates every cell of every creature, and into the deepest dungeon with the thickest walls. Antimatter is a physical entity with positive mass that is identical to regular matter in every way except that the charge and some other properties are flipped. Every bit of matter in the universe has a potential antimatter counterpart. Every fundamental particle of regular matter has an antimatter version. For instance, the antimatter version of the electron is the positron. Electrons and positron have the exact same mass, the same spin, and the same charge magnitude. The only difference is that electrons are negatively charged and positrons are positively charged (positrons should not be confused with protons which are completely different particles) and a few other properties are flipped. When an electron meets a positron, they annihilate each other and their combined mass is converted completely into energy in the form of gamma rays. This effect is used routinely in medical PET scans. In general, antimatter annihilates its regular matter version when they meet. Antimatter can be thought of as regular matter traveling backwards in time. In this picture, a particle-antiparticle annihilation event can be thought of as a forward-time-traveling particle being knocked by gamma rays so that it becomes the same particle, but just traveling backwards in time. Note that this time travel concept applies only to specific antimatter events that obey the conservation of energy and does not open up the possibility for humans to travel back in time, which would violate the conservation of energy. Although antimatter comes in very small quantities in our universe, it is not as exotic or unnatural as once thought. Every minute of every day, high energy cosmic rays from distant supernovas are slamming into earth's atmosphere and creating a very small amount of antimatter. Also, the natural radioactive decay that takes place constantly in earth's rocks creates small amounts of antimatter. But this antimatter does not stick around for long because it quickly bumps up against regular matter and destroys itself in the process. |
context: tag/antimatter/ question: How can you tell a black hole made out of antimatter from a black hole made out of matter? | According to our current understanding, there is no way to distinguish an antimatter black hole from a regular-matter black hole. In fact, there is no difference between an antimatter black hole and a regular-matter black hole if they have the same mass, charge, and angular-momentum. First of all, antimatter is just like regular matter except that its charge and some other properties are flipped. Antimatter has positive mass just like regular matter and experiences gravity the same way. Antimatter is exotic in the sense of being very rare in our universe, but it is not exotic in how it obeys the laws of physics. An antimatter cookie would look just like a regular-matter cookie. Therefore, adding the concept of antimatter to the discussion does not really lead to anything new or exotic. We could just as easily ask, "what is the difference between a black hole made of hydrogen and a black hole made of helium?" The answer is that there is no difference (as long as the total mass, charge, and angular-momentum are the same). According to the No-Hair Theorem, a black hole has the interesting property that all information and structure that falls into a black hole becomes trapped from the rest of the universe, and perhaps even destroyed, except for its effect on the total mass, charge, and angular momentum of the black hole. The overall mass of a black hole is what determines the strength of its gravity. When scientists talk about large or small black holes, they are actually talking about the mass of the black hole. Large black holes have more mass, more gravity, and therefore more effect on their surroundings. When matter falls into a black hole, it increases the overall mass of the black hole. The overall electric charge of a black hole determines the strength of the electric field that it creates. When matter with electric charge of the same polarity as the black hole falls in, it increases the charge of the black hole. The overall angular momentum of a black hole describes how fast it is spinning. When matter falls into a black hole with a swirling motion (as opposed to falling straight in), it can increase the black hole's total angular momentum if the matter swirls in the same direction, or decrease the black hole's total angular momentum if it swirls in the opposite direction. In the book The Nature of Space and Time by Stephen Hawking and Roger Penrose, Hawking states: The no-hair theorem, proved by the combined work of Israel, Carter, Robinson, and myself, shows that the only stationary black holes in the absence of matter fields are the Kerr solutions. These are characterized by two parameters, the mass M and the angular momentum J. The no-hair theorem was extended by Robinson to the case where there was an electromagnetic field. This added a third parameter Q, the electric charge... What the no-hair theorems show is that a large amount of information is lost when a body collapses to form a black hole. The collapsing body is described by a very large number of parameters. These are the types of matter and the multipole moments of the mass distribution. Yet the black hole that forms is completely independent of the type of matter and rapidly loses all the multipole moments except the first two: the monopole moment, which is the mass, and the dipole moment, which is the angular momentum. We don't know exactly what goes on in a black hole. The matter inside a black hole could be condensed down to an indistinguishable blob. Or the matter could retain some structure but remain trapped in the black hole by the black hole's intense gravity. The problem is that a black hole's center is so small that the theory of General Relativity, which describes gravitational effects, becomes inaccurate. We need quantum theory to accurately describe physics on the very small scale. But we have not yet developed a correct theory of quantum gravity. Therefore, we won't have a good idea of what goes on inside a black hole until we have an accurate theory of quantum gravity. The fact that the inside of black holes is shielded from all experimental observations makes the task even more difficult. |
context: tag/antimatter/ question: Is there any difference between antimatter, dark matter, dark energy, and degenerate matter? | Yes. Although the names sound vague and almost fictional, the types of matter called antimatter, dark matter, dark energy, and degenerate matter are all different, specific entities that really exist in our universe. Antimatter is just regular matter with a few properties flipped, such as the electric charge. For example, the antimatter version of an electron is a positron. They both have the same mass, but have opposite electric charge. Antimatter is not as exotic as science fiction makes it out to be. For starters, antimatter has regular mass and accelerates in response to forces just like regular matter. Also, antimatter is gravitationally attracted to other forms of matter just like regular matter. For every particle that exists, there is an antimatter counterpart (some particles such as photons are their own anti-particles). What makes antimatter unique is that when antimatter comes in contact with its regular matter counterpart, they mutually destroy each other and all of their mass is converted to energy. This matter-antimatter mutual annihilation has been observed many times and is a well-established principle. In fact, medical PET scans routinely use annihilation events in order to form images of patients. Antimatter is therefore only distinct from regular matter in that it annihilates when meeting regular matter. For instance, a proton and a positron are somewhat similar. They both have regular mass. They both have a positive electric charge of the same strength. They both have a quantum spin of one half. But when a proton meets an electron, it forms a stable hydrogen atom. When a positron meets an electron, they destroy each other. The key difference is that a positron is antimatter and a proton is not. Antimatter is very rare in our universe compared to regular matter, but there are small amounts of antimatter all over the place in the natural world, including inside your body. Antimatter is created by many types of radioactive decay, such as by the decay of potassium-40. When you eat a banana, you are eating trace amounts of antimatter-producing atoms. The amount is so small, that it does not really affect your health. But it is still there. Why doesn't antimatter build up in your body? The key is that our universe is mostly made of regular matter, so antimatter cannot stick around for very long. Very soon after antimatter is created, it bumps into regular matter and gets destroyed again. Antimatter is also produced by lightning and cosmic rays. It is well understood by physicists, and is predicted by standard particle physics theories. Dark matter is matter that does not interact electromagnetically, and therefore cannot be seen using light. At the same time, dark matter does interact gravitationally and can therefore be "seen" through its gravitational effect on other matter. It is common throughout the universe and helps shape galaxies. In fact, recent estimates put dark matter as five times more common than regular matter in our universe. But because dark matter does not interact electromagnetically, we can't touch it, see it, or manipulate it using conventional means. You could, in principle, manipulate dark matter using gravitational forces. The problem is that the gravitational force is so weak that you need planet-sized masses in order to gravitationally manipulate human-sized objects. There remains much unknown about dark matter since it is so hard to detect and manipulate. Dark matter is not predicted or explained by standard particle physics theories but is a crucial part of the Big Bang model. Dark energy is an energy on the universal scale that is pushing apart galaxies and causing the universe to expand at an increasing rate. Like dark matter, dark energy is poorly understood and is not directly detectable using conventional means. Several lines of evidence make it clear that our universe is expanding. Not only that, our universe is expanding at an increasing rate. Dark energy is the name of the poorly understood mechanism that drives this accelerating expansion. While dark matter tends to bring matter together, dark energy tends to push matter apart. Dark energy is weak and mostly operates only on the intergalactic scale where gravitational attraction of dark matter and regular matter is negligible. Dark energy is thought to be spread thinly but evenly throughout the entire universe. Dark energy is also not predicted or explained by standard particle physics theories but is included in modern versions of the Big Bang model. Dark energy may have a connection with the vacuum energy predicted by particle physics, but the connection is currently unclear. Degenerate matter is regular matter that has been compressed until the atoms break down and the particles lock into a giant mass. Degenerate matter acts somewhat like a gas in that the particles are not bound to each other, and somewhat like a solid in that the particles are packed so closely that they cannot move much. A white dwarf star is mostly composed of electrons compressed into a state of degenerate matter. A neutron star is mostly composed of degenerate neutrons. Further compression of a neutron star may transform it to a quark star, which is a star composed of quarks in a degenerate state. But not enough is known about quarks to determine at present whether quark stars really exist or are even possible.
These concepts are summarized in the list below. Regular Matter Antimatter Dark Matter Dark Energy Degenerate Matter |
context: tag/atom/ question: Are there nuclear reactions going on in our bodies? | Yes, there are nuclear reactions constantly occurring in our bodies, but there are very few of them compared to the chemical reactions, and they do not affect our bodies much. All physical objects are made of molecules. A molecule is a series of atoms linked together by chemical (electromagnetic) bonds. Inside each atom is a nucleus which is a collection of protons and neutrons linked together by nuclear bonds. Chemical reactions are the making, breaking, and rearranging of bonds between atoms in molecules. Chemical reactions do not change the nuclear structure of any atoms. In contrast, nuclear reactions involve the transformation of atomic nuclei. Most of the processes surrounding us in our daily life are chemical reactions and not nuclear reactions. All of the physical processes that take place to keep a human body running (blood capturing oxygen, sugars being burned, DNA being constructed,etc.) are chemical processes and not nuclear processes. Nuclear reactions do indeed occur in the human body, but the body does not use them. Nuclear reactions can lead to chemical damage, which the body may notice and try to fix. There are three main types of nuclear reactions: Note that nuclear fission and radioactive decay overlap a little bit. Some types of radioactive decay involve the spitting out of nuclear fragments and could therefore be seen as a type of fission. For the purposes of this article, "fission" refers to large-scale nucleus fragmentation events that can clearly not be classified as radioactive decay. Nuclear fusion requires high energy in order to be ignited. For this reason, nuclear fusion only occurs in stars, in supernovas, in nuclear fusion bombs, in nuclear fusion experimental reactors, in cosmic ray impacts, and in particle accelerators. Similarly, nuclear fission requires high energy or a large mass of heavy, radioactive elements. For this reason, significant nuclear fission only occurs in supernovas, in nuclear fission bombs, in nuclear fission reactors, in cosmic ray impacts, in particle accelerators, and in a few natural ore deposits. In contrast, radioactive decay happens automatically to unstable nuclei and is therefore much more common. Every atom has either a stable nucleus or an unstable nucleus, depending on how big it is and on the ratio of protons to neutrons. Nuclei with too many neutrons, too few neutrons, or that are simply too big are unstable. They eventually transform to a stable form through radioactive decay. Wherever there are atoms with unstable nuclei (radioactive atoms), there are nuclear reactions occurring naturally. The interesting thing is that there are small amounts of radioactive atoms everywhere: in your chair, in the ground, in the food you eat, and yes, in your body. Radioactive decay produces high-energy radiation that can damage your body. Fortunately, our bodies have mechanisms to clean up the damage caused by radioactivity and high-energy radiation before they become serious. For the average person living a normal life, the amount of radioactivity in his body is so small that the body has no difficulty repairing all the damage. The problem is when the radioactivity levels (the amount of nuclear reactions in and around the body) rise too high and the body cannot keep up with the repairs. In such cases, the victim experiences burns, sickness, cancer, and even death. Exposure to dangerously high levels of radioactivity is rare and is typically avoided through government regulation, training, and education. Common causes of human exposure to high radioactivity include: Note that if you have a single medical scan performed that requires drinking or being injected with a radioactive tracer, you do indeed end up with more nuclear reactions in your body than normal, but the level is still low enough to not be dangerous, and therefore was not included on this list. Low levels of radioactive atoms are constantly accumulating in every person. The ways we end up with radioactive atoms in our bodies include: eating food that naturally contains small amounts of radioactive isotopes, breathing air that naturally contains small amounts of radioactive isotopes, and being bombarded with cosmic rays that create radioactive atoms in our bodies. The most common natural radioactive isotopes in humans are carbon-14 and potassium-40. Chemically, these isotopes behave exactly like stable carbon and potassium. For this reason, the body uses carbon-14 and potassium-40 just like it does normal carbon and potassium; building them into the different parts of the cells, without knowing that they are radioactive. In time, carbon-14 atoms decay to stable nitrogen atoms and potassium-40 atoms decay to stable calcium atoms. Chemicals in the body that relied on having a carbon-14 atom or potassium-40 atom in a certain spot will suddenly have a nitrogen or calcium atom. Such a change damages the chemical. Normally, such change are so rare, that the body can repair the damage or filter away the damaged chemicals. The textbook Chemistry: The Practical Science by Paul B. Kelter, Michael D. Mosher and Andrew Scott states: Whereas potassium-39 and potassium-41 possess stable nuclei, potassium-40 is radioactive. This means that when we consume a banana, we get a measurable amount of radioactive potassium-40. How much? The natural abundance of potassium-40 is only 0.012%, or approximately 1 atom in 10,000. A typical banana has approximately 300 mg of potassium. Therefore, with each banana that we eat, we ingest approximately 0.036 mg of radioactive potassium-40.
The natural occurrence of carbon-14 decay in the body is the core principle behind carbon dating. As long as a person is alive and still eating, every carbon-14 atom that decays into a nitrogen atom is replaced on average with a new carbon-14 atom. But once a person dies, he stops replacing the decaying carbon-14 atoms. Slowly the carbon-14 atoms decay to nitrogen without being replaced, so that there is less and less carbon-14 in a dead body. The rate at which carbon-14 decays is constant and well-known, so by measuring the relative amount of carbon-14 in a bone, archeologists can calculate when the person died. All living organisms consume carbon, so carbon dating can be used to date any living organism, and any object made from a living organism. Bones, wood, leather, and even paper can be accurately dated, as long as they first existed within the last 60,000 years. This is all because of the fact that nuclear reactions naturally occur in living organisms. |
context: tag/atom/ question: Are two atoms of the same element identical? | No. Two atoms of the same chemical element are typically not identical. First of all, there is a range of possible states that the electrons of an atom can occupy. Two atoms of the same element can be different if their electrons are in different states. If one copper atom has an electron in an excited state and another copper atom has all of its electrons in the ground state, then the two atoms are different. The excited copper atom will emit a bit of light when the electron relaxes back down to the ground state, and the copper atom already in the ground state will not. Since the states of the electrons in an atom are what determine the nature of the chemical bonding that the atom experiences, two atoms of the same element can react differently if they are in different states. For instance, a neutral sodium atom (say, from a chunk of sodium metal) reacts with water much more violently than an ionized sodium atom (say, from a bit of salt). Chemists know this very well. It's not enough to say what atoms are involved if you want to fully describe and predict a reaction. You have to also specify the ionization/excitation states of the electrons in the atoms. Even if left alone, an atom often does not come with an equal number of protons and electrons. But what if two atoms of the same element both have their electrons in the same states. Then are they identical? No, they are still not identical. Two atoms of the same element and in the same electronic state could be traveling or rotating at different speeds, which affects their ability to chemically bond. Slower moving atoms (such as the atoms in solid iron) have time to form stable bonds, while faster moving atoms (such as the atoms in liquid iron) cannot form such stable bonds. A slow moving tin atom acts differently from a rapidly moving tin atom. But what if two atoms of the same element both have their electrons in the same states, and the atoms are both traveling and rotating at the same speed. Then are they identical? No. Although two such atoms are essentially chemically identical (they will chemically react in the same way), they are not completely identical. There's more to the atom than the electrons. There's also the nucleus. The nucleus of an atom contains neutrons and protons bonded tightly together. The same chemical element can have a different number of neutrons and still be the same element. We refer to the atoms of the same element with different numbers of neutrons as "isotopes". While the particular isotope involved does not affect how an atom will react chemically, it does determine how the atom will behave in nuclear reactions. The most common nuclear reaction on earth is radioactive decay. Some isotopes decay very quickly into other elements and emit radiation, while other isotopes do not. If you are doing carbon dating, the fact that a carbon-12 atom is not identical to a carbon-14 atom is essential to the dating process. Simply counting the number of carbon atoms in a sample will not give you any information about the age of a sample. You will have to count the number of different isotopes of carbon instead. But what if two atoms are the same element, have electrons in the same state, are traveling and rotating at the same speed, and have the same number of neutrons; then are they identical? No. Just like the electrons, the neutrons and protons in the nucleus can be in various excited states. In addition, the nucleus as a whole can rotate and vibrate at various speeds. Therefore, even if all else is identical, two gold atoms can have their nuclei in different excited states and behave differently in nuclear reactions. To state the case succinctly, it is very hard to have two atoms of the same element be exactly identical. In fact, succeeding in coaxing a group of atoms to be very close to identical was worthy of a Nobel Prize. With that said, don't think that atoms have individual identities beyond what has been mentioned here. If two carbon atoms are in the exact same molecular, atomic, electronic and nuclear states, then those two carbon atoms are identical, no matter where they came from or what has happened to them in the past. |
context: tag/atom/ question: Can sound waves generate heat? | Yes, sound waves can generate heat. In fact, sound waves almost always generate a little bit of heat as they travel and almost always end up as heat when they are absorbed. Sound and heat are both macroscopic descriptions of the movement of atoms and molecules. Sound is the ordered movement of atoms and molecules in rapid waving patterns. Heat is the disordered, random, movement of atoms and molecules. Therefore, all you have to do in order to turn sound into heat is transform some of the ordered movement of the atoms and molecules into disordered movement. This effect always happens to some extent. This effect happens a lot whenever the sound wave encounters irregularities as it travels. For instance, dust particles in air are irregularities that randomly interfere with the vibrating motion of some of the air molecules that make up the sound wave. The dust particles mess up some of the ordered motion, and therefore convert some of the sound to heat. As another example, the rough surface of an object constitutes a collection of irregularities that the sound wave encounters. Therefore, when a sound wave hits a rough surface, the motion of the air molecules gets scrambled up a bit. Note that the air molecules already have a motion that is somewhat disordered. In other words, air through which sound is traveling already contains some amount of heat. When some of the sound wave is converted to heat, the motion of the air molecules becomes more disordered and the amount of heat increases. The ordered movement of atoms is also made more disorderly when sound travels through acoustically absorbent materials. Materials can be made absorbent by embedding an array of little irregularities directly into the material, such as air bubbles. For this reason, materials that are soft and porous, like cloth, are good at converting sound to heat. The sound is said to be "absorbed" or "lost" when it is converted to heat inside a material. Even without irregularities, a material can be highly absorbent if the atoms and molecules that make up the material cannot slide past each other smoothly. In this case, an atom or molecule that is trying to participate in the ordered vibrational motion of the sound wave roughly slides past the neighboring atoms or molecules that are off to the side, such that motion gets diverted in sideways directions rather than continuing in the forward direction as part of the sound wave. The ordered motion therefore becomes disordered. You can think of it as a kind of internal friction that all materials posses to some extent. In this way, some of the sound energy is converted to thermal energy. All materials, even air, have some amount of resistance to smooth atomic/molecular sliding and therefore are somewhat absorbent to sound. In summary, sound waves always generate a little heat as they travel and they ultimately almost always end up completely as heat when they are absorbed by materials. However, the amount of energy carried by sound waves is very small, so that the amount of heat they generate is typically insignificant. In short, cranking up the volume on your speakers is a terrible way to try to heat up your room. Yelling at your soup does indeed warm it up, but the amount is far too small to be noticeable. |
context: tag/atom/ question: Can the decay half-life of a radioactive material be changed? | Yes, the decay half-life of a radioactive material can be changed. Radioactive decay happens when an unstable atomic nucleus spontaneously changes to a lower-energy state and spits out a bit of radiation. This process changes the atom to a different element or a different isotope. Since radioactive decay is a spontaneous event, you may think that the half-life of the decay process is completely fixed and cannot be altered by outside influences. However, this statement is not completely true. First of all, it is worth pointing out that the time when an individual radioactive atom decays is completely random. It is impossible to predict when an individual radioactive atom will decay. The half-life of a certain type of atom does not describe the exact amount of time that every single atom experiences before decaying. Rather, the half-life describes the average amount of time it takes for a large group of atoms to reach the point where half of the atoms have decayed. The half-life of a radioactive material can be changed using time dilation effects. According to relativity, time itself can be slowed down. Everything that experiences time can therefore be given a longer effective lifetime if time is dilated. This can be done in two ways. Traveling at a speed close to the speed of light causes time to slow down significantly, relative to the stationary observer. For instance, a number of radioactive atoms shot through a tube at high speed in the lab will have their half-life lengthened relative to the lab because of time dilation. This effect has been verified many times using particle accelerators. Time can also be dilated by applying a very strong gravitational field. For instance, placing a bunch of radioactive atoms near a black hole will also extend their half-life relative to the distant observer because of time dilation. The half-life of radioactive decay can also be altered by changing the state of the electrons surrounding the nucleus. In a type of radioactive decay called "electron capture", the nucleus absorbs one of the atom's electrons and combines it with a proton to make a neutron and a neutrino. The more the wavefunctions of the atom's electrons overlap with the nucleus, the more able the nucleus is to capture an electron. Therefore, the half-life of an electron-capture radioactive decay mode depends slightly on what state the atom's electrons are in. By exciting or deforming the atom's electrons into states that overlap less with the nucleus, the half-life can be increased. Since the chemical bonding between atoms involves the deformation of atomic electron wavefunctions, the radioactive half-life of an atom can depend on how it is bonded to other atoms. Simply by changing the neighboring atoms that are bonded to a radioactive isotope, we can change its half-life. However, the change in half-life accomplished in this way is typically small. For instance, a study performed by B. Wang et al and published in the European Physical Journal A was able to measure that the electron capture half-life of beryllium-7 was made 0.9% longer by surrounding the beryllium atoms with palladium atoms. In addition to altering the chemical bonds, the half-life can be altered by simply removing electrons from the atom. In the extreme limit of this approach, all of the electrons can be ripped off of a radioactive atom. For such an ion, there are no longer any electrons available to capture, and therefore the half-life of the electron capture radioactive decay mode becomes infinite. Certain radioactive isotopes that can only decay via the electron capture mode (such as rubidium-83) can be made to never decay by ripping off all the electrons. Other types of radioactive decay besides electron capture have also been found to have the decay half-life depend on the state of the surrounding electrons, but the effects are smaller. The change in half-life due to changing the electron environment is generally very small, typically much less than 1%. Lastly, the half-life of a radioactive material can be changed by bombarding it with high-energy radiation. This should not come as a surprise since radioactive decay is a nuclear reaction, and inducing other nuclear reactions at the same time as the decay can interfere with it. However, at this point, you don't really have stand-alone radioactive decay. Rather, you have nuclear reaction soup, so this approach may not really count as "changing the half-life". When reference books list values for the half-life of various materials, they are really listing the half-life for the material when its atoms are at rest, in the ground state, and in a particular chemical bonding configuration. Note that most changes to the half-life of radioactive materials are very small. Furthermore, large changes to a half-life require elaborate, expensive, high-energy equipment (e.g. particle accelerators, nuclear reactors, ion traps). Therefore, outside of specialized labs, we can say that as a good approximation radioactive decay half-lives don't change. For instance, carbon dating and geological radiometric dating are so accurate because decay half-lives in nature are so close to constant. |
context: tag/atom/ question: Do atoms ever actually touch each other? | The answer depends on what you mean by "touch". There are three possible meanings of touch at the atomic level: 1) two objects influence each other, 2) two objects influence each other significantly, or 3) two objects reside in the exact same location. Note that the everday concept of touch (i.e the hard boundaries of two objects exist at the same location) makes no sense at the atomic level because atoms don't have hard boundaries. Atoms are not really solid spheres. They are fuzzy quantum probability clouds filled with electrons spread out into waving cloud-like shapes called "orbitals". Like a cloud in the sky, an atom can have a shape and a location without having a hard boundary. This is possible because the atom has regions of high density and regions of low density. When we say that an atom is sitting at point A, what we really mean is that the high-density portion of the atom's probability cloud is located at point A. If you put an electron in a box (as is done in quantum dot lasers), that electron is only mostly in the box. Part of the electron's wavefunction leaks through the walls of the box and out to infinity. This makes possible the effect of quantum tunneling, which is used in scanning tunneling microscopes. With the non-solid nature of atoms in mind, let us look at each of the possible meanings of touching. 1. If "touching" is taken to mean that two atoms influence each other, then atoms are always touching. Two atoms that are held a mile apart still have their wavefunctions overlapping. The amplitude of one atom's wavefunction at the point where it overlaps with the other atom's center will be ridiculously small if they are a mile apart, but it will not be zero. In principle, two atoms influence each other no matter where they are in the universe because they extend out in all directions. In practice, if two atoms are more than a few nanometers apart, their influence on each other typically becomes so small that it is overshadowed by the influence of closer atoms. Therefore, although two atoms a mile apart may technically be touching (if we define touching as the overlap of atomic wavefunctions), this touching is typically so insignificant that it can be ignored. What is this "touching"? In the physical world, there are only four fundamental ways for objects to influence each other: through the electromagnetic force, through the strong nuclear force, through the weak nuclear force, and through the force of gravity. Neutrons and protons that make up the nucleus of an atom are bound to each other and undergo reactions via the two nuclear forces. The electrons that make up the rest of the atom are bound to the nucleus by the electromagnetic force. Atoms are bound into molecules, and molecules are bound into everyday objects by the electromagnetic force. Finally, planets (as well as other large astronomical objects) and macroscopic objects on the planet's surface are bound together by gravity. If two atoms are held a meter apart, they are touching each other through all four fundamental forces. However, for typical atoms, the electromagnetic force tends to dominate over the other forces. What does this touching lead to? If two atoms are too far apart, their interaction is too weak compared to other surrounding bodies to amount to anything. When the two atoms get close enough, this interaction can lead to many things. The entire field of chemistry can be summed up as the study of all the interesting things that happen when atoms get close enough to influence each other electromagnetically. If two atoms are non-reactive and don't form covalent, ionic, or hydrogen bonds, then their electromagnetic interaction typically takes the form of the Van der Walls force. In the Van der Walls effect, two atoms brought close to each other induce electric dipole moments in each other, and these dipoles then attract each other weakly through electrostatic attraction. While the statement that "all atoms on the planet are always touching all other atoms on the planet" is strictly true according to this definition of touching, it is not very helpful. Instead, we can arbitrarily define an effective perimeter that contains most of the atom, and then say that any part of the atom that takes extends beyond that perimeter is not worth noticing. This takes us to our next definition of touching. 2. If "touching" is taken to mean that two atoms influence each other significantly, then atoms do indeed touch, but only when they get close enough. The problem is that what constitutes "significant" is open to interpretation. For instance, we can define the outer perimeter of an atom as the mathematical surface that contains 95% of the atom's electron mass. As should be obvious at this point, a perimeter that contains 100% of the atom would be larger than the earth. With 95% of the atom's electron probability density contained in this mathematical surface, we could say that atoms do not touch until their 95% regions begin to overlap. Another way to assign an effective edge to an atom is to say it exists halfway between two atoms that are covalently bonded. For instance, two hydrogen atoms that are covalently bonded to each other to form an H2 molecule have their centers separated by 50 picometers. They can be thought of as "touching" at this separation. In this approach, atoms touch whenever they are close enough to potentially form a chemical bond. 3. If "touching" is taken to mean that two atoms reside in the exact same location, then two atoms never touch at room temperature because of the Pauli exclusion principle. The Pauli exclusion principle is what keeps all the atoms in our body from collapsing into one point. Interestingly, at very low temperatures, certain atoms can be coaxed into the exact same location. The result is known as a Bose-Einstein condensate. Again, atoms never touch in the everyday sense of the word for the simple reason that they don't have hard boundaries. But in every other sense of the word "touch" that has meaning at the atomic level, atoms certainly touch. |
context: tag/atom/ question: Does an atom have a color? | The answer really depends on how you define "having a color". The term "color" refers to visible light with a certain frequency, or a mixture of visible light frequencies. Therefore, the word "color" describes the frequency content of any type of visible light. Anytime visible light is present, we can describe it as having a certain color. With this in mind, there are many different ways an object can reflect or emit visible light. Thus, there are many ways an object can "have a color". While a single, isolated, atom can reflect or emit visible light in several of these ways, it does not participate in all the ways. If you define "having a color" very narrowly such that it only includes certain mechanisms, then atoms do not have color. If you define "having a color" more broadly, then atoms do have a color. Let us look at the different ways an object can reflect or emit visible light and apply each one to an atom. 1. Bulk reflection, refraction, and absorptionThe most common, everyday manner in which objects can send visible light to our eyes is through bulk reflection, refraction, and absorption. These three effects are all part of the same physical mechanism: the interaction of an external beam of light with many atoms at the same time. When white light, which contains all colors, hits the surface of a red apple, the light waves that are orange, yellow, green and blue get absorbed by the atoms in the apple's skin and converted to heat, while the red waves are mostly reflected back to our eyes. Some of the light is also transmitted through the apple skin and bent slightly as it goes through. We call this bent transmission of light "refraction". Some materials such as glass transmit a lot of the light while other materials such as apples transmit very little. The key point here is that traditional reflection, refraction, and absorption constitute a bulk phenomenon where each ray of light interacts with dozens to millions of atoms at the same time. This makes sense when you consider that visible light has a wavelength that is about a thousand times bigger than atoms. Visible light waves have a wavelength from 400 nanometers to 700 nanometers, depending on the color. In contrast, atoms have a width of about 0.2 nanometers. This discrepancy is why you can't see individual atoms using an optical microscope. The atoms are far smaller than the light you are trying to use to see them. The color of an object that results from traditional bulk reflection, refraction, and absorption is therefore a result of how several atoms are bound together and arranged, and not a result of the actual color of individual atoms. For example, take carbon atoms and bind them into a diamond lattice, and you get a clear diamonds. In contrast, take carbon atoms and bind them into hexagonal planes and you get gray graphite. The nature of the bonds between many atoms is what determines the traditional color of a material and not the type of atoms themselves. If you have no bonds at all between any atoms, you get a monoatomic gas, which is invisible (at least according to traditional reflection, refraction, and absorption). The color of most of the everyday objects around us, from apples to pencils to chairs, arises from traditional bulk reflection, refraction, and absorption. This mechanism of light delivery is so common and intuitive that we could define "having a color" narrowly to only include this mechanism. With this narrow definition in mind, therefore, a single atom is too small to have a color. 2. Thermal radiationHeat up a bar of iron enough and it glows red. You could therefore say that the color of a hot iron bar is glowing red. The red color of the iron bar in this case, however, is due to thermal radiation, which is a mechanism that is very different from bulk reflection, refraction, and absorption. In the mechanism of thermal radiation, the atoms of an object knock into each other so violently that they emit light. More accurately, the collisions cause the electrons and atoms to be excited to higher energy states, and then the electrons and atoms emit light when they transition back down to lower energy states. Since the collisions due to thermal motion are random, they lead to a wide range of energy excitations. As a result, the thermal radiation emitted contains many colors that span a broad band of frequencies. The interesting thing about thermal radiation is that its color is more a result of the temperature of the object and less a result of the material of the object. Every solid material glows red if you can get it to the right temperature without it evaporating or chemically reacting. The key to thermal radiation is that it is an emergent property of the interaction of many atoms. As such, a single atom cannot emit thermal radiation. So even if we expand the definition of "having a color" to include thermal radiation, individual atoms still have no color. 3. Rayleigh scatteringMore informatively called "long-wavelength scattering", Rayleigh scattering is when light does bounce off of single atoms and molecules. But because the light is so much bigger than the atoms, Rayleigh scattering is not really the "bouncing" of a light wave off of a small particle such as an atom, but is more a case of immersing the particle in the electric field of the light wave. The electric field induces an oscillating electric dipole in the particle which then radiates. Because the mechanism is so different, Rayleigh scattering of white light off of small particles always creates the same broad range of colors, with blue and violet being the strongest. The color of Rayleigh scattering is always the same (assuming the incident light is white) and is mostly independent of the material of the scattering object. Therefore, a single atom does have a color in the sense that it participates in Rayleigh scattering. For example, earth's atmosphere is composed mostly of small oxygen molecules (O2) and nitrogen molecules (N2). These molecules are far enough apart that they act like single, isolated molecules. When the daytime white sunlight hits isolated air molecules, it scatters according to Rayleigh scattering, turning the sky whitish-bluish-violet. The fact that we can see the daytime sky attests to the fact that small, individual molecules can exhibit some form of color. While we are talking about small molecules when it comes to the sky, the same principle applies to single atoms. Properly understood, the color in Rayleigh scattering belongs more to the interaction itself than to the actual types of atoms involved. Just because the sky is blue does not necessarily mean that nitrogen atoms are blue. Raman scattering is much rarer than Rayleigh scattering, but is nearly identical in the context of this discussion. Raman scattering is different in that some of the energy of the incident light is lost internally to the particle so that the scattered light is shifted lower in frequency. 4. Gas DischargeGas discharge (e.g. a Neon light) is perhaps the mechanism that would best fit the notion of an individual atom "having a color". Gas discharge is what happens when you take pure atoms, isolate them from each other in a low-density gas state and then excite them using an electric current. When the atoms de-excite, they emit visible light. The key here is that a particular atom can only being excited, de-excited, and emit light in certain ways. This leads to the color of an atom during gas discharge being very strongly tied to the type of atom involved. The frequency spectrum of an atom during gas discharge is considered the color "fingerprint" of that particular type of atom. For instance, true neon signs are always red because neon atoms themselves are red under gas discharge. Argon atoms are lavender under gas discharge, while sodium atoms are yellow and mercury atoms are blue. Many of the colors generated by "Neon" lights are attained by mixing different gases together. The "flame test" used in chemistry to detect certain atoms is essentially a less-controlled, less-pure version of a gas discharge lamp. Note that florescence (such as in a florescent light bulb), phosphorescence, and gas laser emission are all similar to gas discharge in that they involve exciting electrons in single atoms or simple molecules. As opposed to gas discharge, which forces an atom to emit all of its characteristic colors; florescence, phosphorescence, and laser emission all involve exploiting certain transitions so that only certain atomic colors are emitted. They can be considered special cases of gas discharge, as far as atomic color characterization is concerned. There are many other ways an object or material can emit or reflect visible light; such as through semiconductor electron-hole recombination (in LED's), Cherenkov radiation, chemical reactions, synchrotron radiation, or sonoluminescence; but all of these involve the interaction of many atoms or no atoms at all, and so are not pertinent to the current discussion. In summary: in the sense of traditional reflection, refraction, absorption, and thermal radiation, individual atoms are invisible. In the sense of Rayleigh scattering and gas discharge atoms do have a color. |
context: tag/atom/ question: Does an electron in an atom move at all? | First of all, I assume you meant to ask the question, "Does an electron in a stable (non-transitioning) atomic state experience any movement?" Obviously, an electron that is transitioning between states is moving from one state to the other. But for an electron that is just staying in one stable state in an atom, the question is more interesting. Does it move? The answer could be yes or no depending on how we define motion and what form of the electron we consider to be truly real. The problem is that an electron is not a solid little ball that we can watch zip around. An electron is a quantum object. As such, an electron is partially particle-like and partially wave-like, but is really something more complex that is neither a simple wave nor a simple particle. The electron is described by a probabilistic quantum wavefunction, which spreads out through space and vibrates, but in such a way that it still has certain discrete properties such as mass. When bound in a stable state in an atom, the electron wavefunction spreads out into a certain shape called an "orbital". The orbital does not contain the electron or describe the average location of a little hard electron orbiting around. Rather, the orbital is the electron. When bound in a stable state in an atom, an electron behaves mostly like an oscillating three-dimensional wave, i.e. the orbital vibrates. It's a bit like a vibrating guitar string. When you pluck a guitar string, you get the string shaking, which is what creates the sound. Scientifically, we would say that you have excited a standing wave in the string. The guitar string is not moving in the sense of shooting off to the other side of the room. In this sense, the guitar string is not moving at all, but remains clamped to the guitar. But the guitar string is moving in the sense that it is vibrating when you pluck it. If you pick one spot on the plucked string and look at it closely, it is definitely moving from one location in space to another, back and forth repeatedly. By pulling the string, you transferred chemical energy in your arm to elastic energy in the stretched string. When you let go, the elastic energy was converted to motional energy (kinetic energy) as the string snapped back and started vibrating. The total kinetic energy of the entire string averaged over time is zero, since the overall string is not going anywhere with respect to the guitar. But the kinetic energy of any small part of the string at a given moment is not zero. In this way, a plucked guitar string experiences local motion but not overall motion. An electron in an atomic orbital state acts somewhat like a plucked guitar string. It is spread out in a three-dimensional cloud-like wavefunction that vibrates. Whereas a guitar string vibrates up and down, an atomic electron wavefunction simply vibrates strong and weak. The frequency at which the electron wavefunction vibrates is directly proportional to the total energy of the electron. Electrons in higher-energy atomic states vibrate more quickly. Because an electron is a quantum object with wave-like properties, it must always be vibrating at some frequency. In order for an electron to stop vibrating and therefore have a frequency of zero, it must be destroyed. In an atom, this happens when an electron is sucked into the nucleus and takes part in a nuclear reaction known as electron capture. With all of this in mind, an electron in a stable atomic state does not move in the sense of a solid little ball zipping around in circles like how the planets orbit the sun, since the electron is spread out in a wave. Furthermore, an electron in a stable atomic state does not move in the sense of waving through space. The orbital electron does move in the sense of vibrating in time. But the truth is more complicated than this simple picture depicts. There are two things that describe the electron in quantum theory: the electron's quantum wavefunction, and the magnitude squared of the electron's quantum wavefunction. (The "magnitude squared" operation just means that you drop phase factors such as negative signs and then take the square. For instance, the magnitude squared of negative three is nine.) Interestingly, experiments can only directly measure the magnitude squared of the electron wavefunction, and yet we need the original wavefunction in order to predict the outcome of many experiments. For this reason, some people say that the magnitude squared of the wavefunction is the only real entity, whereas the original wavefunction itself is just a mathematical crutch that is needed because our theory is inelegant. Is the magnitude squared of the electron wavefuntion the real physical entity or is the original wavefunction the real physical entity? This question is really a philosophical one and not a physical one, so I will not pursue the question here. To scientists, the question, "What is actually real?" is unimportant. We are more concerned with making the equations match the experiments. So what does all this have to do with an electron in an atom? The point is that an atomic electron's raw wavefunction does vibrate, but the magnitude squared of the wavefunction does not vibrate. In fact, physicists call stable atomic electron states "stationary states" because the magnitude squared of the wavefunction is constant in time. If you consider the raw wavefunction to be the truly physical entity, then you have to say that an electron in an atom experiences motion in the form of a vibration. If you consider the magnitude squared of the wavefunction to be the truly physical entity, then you have to say that an electron in an atom experiences no vibration, and therefore no motion. I consider the first choice to make more sense. You can mathematically show that certain atomic electron states contain angular momentum (i.e. rotational momentum). It's hard to make sense of the claim that an atomic electron contains angular momentum and at the same claim that the electron is completely motionless in every sense of the word. For this reason, I prefer to view the raw wavefunction as the truly physical entity, and therefore an electron in an atom experiences motion in the form of vibrations. But, again, the question, "What is actually real?" is a philosophical one and is unimportant in science. The bottom line is that the raw wavefunction of an electron in a stable atomic state experiences vibrational motion. Whether you consider this motion real or not is up to you. |
context: tag/atom/ question: Does the human body contain minerals? | For the most part, the human body does not contain minerals. Scientifically speaking, a mineral is a naturally-occurring inorganic crystalline solid with a single chemical formula. Rocks are aggregates of minerals and organic materials. Except for in bones and teeth, the atoms and molecules making up a healthy body are not crystalline and are not solid. In this way, most of the molecules making up a human body fail to meet the definition of a mineral. Confusion often arises because many health professionals, nutritionists, and biologists misuse the word "mineral". When they say "mineral" in the context of human nutrition, they really mean "dietary element". Scientifically, the phrase "trace element" should really be used instead of "trace mineral" when talking about rare atoms required by the human body. The words "element" and "mineral" do not mean the same thing. A chemical "element" is a material containing only one kind of atom. In some cases, elements can form minerals, but they don't have to. For example, hydrogen is an element, but it is not a mineral because it is neither crystalline nor a solid. In contrast, quartz is indeed a mineral, but it is not an element because it contains more than one kind of atom. A gold nugget found in the ground is both an element (because it contains only gold atoms) and a mineral (because it has a natural crystalline solid structure). The small subset of materials in the world that contain only one kind of atom and have the atoms naturally bonded into a solid crystalline lattice are called "native element minerals". 1. Materials that are elements, but not minerals 2. Materials that are minerals, but not elements 3. Materials that are both minerals and elements (native element minerals): For example, table salt contains sodium atoms and chlorine atoms bound into a solid, ionic, cubic crystalline lattice. Naturally occurring salt is therefore a mineral. But as soon as you sprinkle salt on your tongue and begin to eat it, the salt dissolves in the water on your tongue. This means that the sodium and chlorine atoms break apart and float around in the water. You no longer have a mineral. You have elemental ions in solution. Your body then uses the dissolved elemental sodium ions to regulate fluid pressure levels and to send electrical signals along your nerves. In this way, you can eat minerals, but once you eat them, they aren't minerals anymore. Furthermore, you can get dietary elements from non-mineral sources. For example, you can get dietary sodium from milk, which is not a mineral. In fact, we get most of our dietary elements from non-mineral sources. The only mineral we really eat on a regular basis is table salt. The one exception in a healthy human is bone mineral, such as in bones and teeth. Bone mineral is indeed an inorganic, crystalline, solid with a single chemical formula and therefore qualifies as a genuine mineral. The mineral in your bones is called hydroxyapatite and has the chemical formula Ca5(PO4)3(OH). Our bodies build bone mineral on the spot, so we don't have to swallow hydroxyapatite crystals. But we do have to eat food with enough of the right kinds of atoms to build bone mineral. Looking at the chemical formula, we see that our bodies can't build bone mineral unless we supply it with enough calcium, phosphorus, oxygen, and hydrogen. A typical person has almost unlimited access to hydrogen and oxygen atoms through the water he drinks and the air he breaths. In contrast, a person can only get enough calcium and phosphorus to build healthy bones if he eats and drinks foods containing these elements. Minerals can also form in the human body as part of disease states such as in kidney stones. |
context: tag/atom/ question: How can an electron leap between atomic levels without passing through all the space in between? | An electron that is transitioning between two atomic states does not skip any intervening space. The idea of a quantum leap is highly misleading and commonly misunderstood. First of all, an electron is a quantum object. As such, it acts both as a wave and as a particle at the same time. When bound as part of an atom, an electron mostly acts like a wave. An atomic electron spreads out into cloud-like wave shapes called "orbitals". If you look closely at the various orbitals of an atom (for instance, the hydrogen atom), you see that they all overlap in space. Therefore, when an electron transitions from one atomic energy level to another energy level, it does not really go anywhere. It just changes shape. The orbital shapes with more fluctuations (with more highs, lows, and bends to its shape) contain more energy. In other words, when an electron transitions to a lower atomic energy level, its wave shape changes to have less kinks in it. But the electron does not "leap" anywhere. The wave behavior of an electron in an atom is very similar to the behavior of classical waves on a guitar string. When you pluck a guitar string, you excite standing waves in the string, which are what make the sound. A certain string can only experience certain types of standing waves because the string is clamped down on both ends. The types of waves allowed on a particular string are called its "harmonics". The harmonics of a string depend on the string's length, tension, and mass density. A particular guitar string (of a particular length, tension, and mass) can therefore only play a certain type of sound, which is a combination of its harmonics. If you are very careful about how you pluck the string, you can create a wave on the string which is mostly the lower, fundamental harmonic (which has very few kinks), or you can create a wave on the string which is mostly a higher harmonic (which has many kinks). It takes more energy and is therefore harder to strongly excite the higher harmonic in a guitar string. Furthermore, if you pluck the string properly so as to strongly excite a higher harmonic wave in the string, you can even coax the string to transition down to the lower-energy harmonic. The wave on the guitar string does not go anywhere when the string transitions from a higher-energy state to a lower-energy state. The wave just changes shape. In a similar way, the discrete set of electron orbitals possible in a certain atom are effectively the harmonics of the atom. The electron can transition to a higher harmonic wave shape by absorbing energy and kinking more, or transition to a lower harmonic wave shape by emitting energy and kinking less (relaxing). It should be clear at this point that an electron that transitions in an atom does not make any kind of leap from one location in space to another location in space. But you may still be worried that the electron makes a leap from one energy level to another, and therefore bypasses all the in-between energy states. Although we are talking about a leap on the energy scale, and not a leap in space, such a leap may still strike you as unnatural, as it should. The fact is that an electron transitioning in an atom does not actually discontinuously leap from one energy level to another energy level, but makes a smooth transition. You may wonder, "Doesn't quantum theory tell us that an electron in an atom can only exist at certain, discrete energy levels?" Actually, no. Quantum theory tells us that an electron with a stationary energy can only exist at certain, discrete energy levels. This distinction is very important. By "stationary energy" we mean that the electron's energy stays constant for a fairly long period of time. The orbitals of a particular atom are not the only allowed states that an electron can take on in the atom. They are the only stable states of the atom, meaning that when an electron settles down to a particular state in an atom, it must be in one of the orbital states. When an electron is in the process of transitioning between stable states, it is not itself stable and therefore has less restrictions on its energy. In fact, an electron that transitions does not even have a well-defined energy. Innate quantum uncertainty arises in the electron's energy because of its transition. The quicker an electron transitions, the more uncertain its energy. This "innate quantum uncertainty" is not some metaphysical mystery, but is better understood as the wave spreading out over many values. Just as the electron can spread out into a wave that extends over a region of space, it can also spread out into a wave that extends over a region along the energy scale. If you calculate the average energy (the "expectation value") of this transitioning electron's spread of energies, you find that the electron's average energy does not instantaneously jump from one energy level to another. Rather, it smoothly transitions on average from the one energy level to the other energy level over a period of time. There is really no "instantaneous quantum leap" at all. The electron does not leap in space, and it does not leap up the energy scale. In fact, the term "quantum leap" is almost universally shunned by scientists as it is highly misleading. If you want a better mental image, you can think of the electron as quickly, but smoothly sliding along the energy scale from one stable state to the next. Because a typical atomic electron transition is so fast (often on the order of nanoseconds), it can seem to be nearly instantaneous to the slow human senses, but fundamentally it is not. |
context: tag/atom/ question: How can radioactive decay just happen with nothing triggering it? | Although a radioactive decay event seems spontaneous and is unpredictable, it is indeed triggered by a physical agent. That physical agent is a vacuum fluctuation. Due to the quantum nature of the universe, a vacuum always contains vacuum fluctuations. Vacuum fluctuations are also called vacuum energy and zero-point energy. You can think of vacuum fluctuations as a sea of particles and antiparticles briefly popping into and out of existence. These particles originate from the vacuum itself due to intrinsic quantum uncertainty. Vacuum fluctuations are very short-lived (short-lived enough that they do not violate any conservation laws, within the level of quantum uncertainty). However, vacuum fluctuations are physically real and cause real effects. For instance, vacuum fluctuations tend to weaken, or screen, electromagnetic fields. Vacuum fluctuations also give rise to the Casimir effect as well as the Lamb shift in hydrogen energy levels. Every spontaneous quantum transition is actually triggered by a vacuum fluctuation. Lasers crucially depend on vacuum fluctuations. The light emitted from a laser is generated by a chain reaction of coherent photon emissions. This chain reaction is triggered at the beginning by a vacuum fluctuation. When an electron is put in an excited atomic state and left alone, it will eventually, naturally transition back down to its original state. When exactly this happens seems spontaneous, but it is actually triggered by a vacuum fluctuation. Similarly, vacuum fluctuations are what trigger a radioactive decay event. As part of the background quantum fluctuations that are intrinsic to the vacuum, a particle pops into existence just long enough to collide with the nucleus and trigger radioactive decay. The exact moment that radioactive decay happens is random and unpredictable because vacuum fluctuations are random and unpredictable. All of this just leads to the question, what triggers vacuum fluctuations? The answer is that nothing triggers vacuum fluctuations. They are constantly happening due to the quantum nature of the universe. Vacuum fluctuations are a well-established principle of mainstream physics. Note that there are a lot of incorrect, unscientific notions online about vacuum energy. Even though vacuum energy is real, it cannot be harnessed as a free source of energy. Quantum physics is strange, but it still must obey the physical conservation laws of the universe, including the law of conservation of energy. A vacuum fluctuation cannot permanently give its energy to another object. That would violate the law of conservation of energy. In fact, conservation of energy is what prevents a vacuum fluctuation from continuing to exist beyond its short life. However, if conditions are right, a vacuum fluctuation can be given enough energy from another object for it to be promoted to a stable particle that continues to exist. For instance, in an effect called spontaneous emission, an electron transitions spontaneously from an excited quantum state to a lower quantum state and emits a bit of light called a photon in the process. It looks like the photon is just created out of nowhere. However, the more accurate description is that a photon vacuum fluctuation collides with the electron, triggering the electron to transition. In the process, the electron gives some of its energy to the vacuum fluctuation, thereby promoting it to a regular photon that can continue to exist forever. |
context: tag/atom/ question: How does dissolving a salt molecule in water make its atoms ionize? | Dissolving a salt molecule in water does not make its atoms ionize. The atoms in solid salts are already ionized long before touching water. Electrons in an atom can only take on specific wave states, and only one electron can occupy one wave state at a time. As a result, electrons in an atom take different states, starting from the lowest energy state and going upwards in energy until the electrons have all found distinct states. For various reasons that are not worth mentioning here, electron states in atoms tend to form various groups, with the states in the same group having very similar energies and states. Chemists call these groups of electron states "shells", even though they have nothing to do with literal shells. The interesting thing is that an atom with completely filled shells is very stable (all the available states in each group are occupied by electrons). On the other hand, an atom with its outermost shell only partially filled has a strong tendency to steal, lose, or share electrons from other atoms in order to fill its outermost shell and become stable. Such atoms are therefore chemically reactive. A well-known salt is sodium chloride (table salt), so let's use it as an example. A single neutral sodium atom has eleven electrons. Ten of these electrons fill states such that they form complete shells. The eleventh electron of sodium, however, is alone in the outermost, partially filled shell. Electrons are bound in atoms because their negative electric charge experiences electric attraction to the positive charge of the atom's nucleus. But for sodium, the negatively-charged electrons in the inner, completed shells do a good job of blocking, or screening, the attractive force of the nucleus on the eleventh electron. As a result, the eleventh electron of sodium is loosely bound to the atom and is ripe for being stolen by a more powerful atom. In contrast, chlorine (17 electrons) has all of its shells filled with electrons except for its outermost shell which is one electron short of being complete. There is a very strong attraction by the chlorine atom on an outside electron which is needed to complete its shell. Sodium and chlorine are therefore a perfect match. Sodium has one electron it is not holding onto very strongly, and chlorine is looking for one more electron to steal to fill its shell. As a result, a pure sample of sodium reacts strongly with a pure sample of chlorine and the end product is table salt. Each chlorine atom steals an electron from the sodium atom. Each sodium atom now has 11 positive protons and 10 negative electrons, for a net charge of +1. Each chlorine atom now has 17 positive protons and 18 negative electrons for a net charge of -1. The atoms have therefore been ionized by the reaction that forms solid table salt, all without the presence of water. Both the sodium and the chlorine ions now have completely filled shells and are therefore stable. This is a good example of an atom that naturally has an unequal number of electron and protons. The net positive sodium ion is now attracted to the net negative chlorine ion and this attraction forms what we call an "ionic bond". But, in reality, we don't have just one sodium ion sticking to ion chlorine ion. Instead, a lattice of many sodium ions ionically bonds to a lattice of chlorine ions, and we end up with a crystalline solid. Each sodium ion in the crystalline lattice of table salt is bound to the 6 nearest chlorine ions, and the same goes for each chlorine ion. The atoms in table salt are therefore already in the ionized state. Adding water does not ionize the atoms in salt, because they are already ionized. Instead, the water molecules stick to the already formed ions in the salt. The textbook titled Cell and Molecular Biology: Concepts and Experiments by Gerald Karp states, "A crystal of table salt is held together by an electrostatic attraction between positively charged Na+ and negatively charged Cl– ions. This type of attraction between fully charged components is called an ionic bond (or a salt bridge). Ionic bonds within a salt crystal may be quite strong. However, if a crystal of salt is dissolved in water, each of the individual ions becomes surrounded by water molecules, which inhibit oppositely charged ions from approaching one another closely enough to form ionic bonds." Each water molecule has a permanent dipole, meaning that one end is always slightly positively charged and the other end is always slightly negatively charged. The charged ends of the water molecules are so strongly attracted to the charged ions in the salt crystal that the water destroys the solid lattice structure of the salt and each sodium and chlorine ion becomes surrounded by a layer of sticky water molecules. In chemistry, we say the salt has been dissolved by the water. It's like a rock band exiting the limousine into a crowd of fans and becoming separated as each band member gets surrounded by his own circle of fans. If the atoms in solid salt were not ionized to begin with, the water would not do such a good job dissolving the salt. |
context: tag/atom/ question: If I hammered and flattened a penny enough, could I cover the entire earth with it? | No. If you spread out the atoms from a single penny over the entire surface of the earth, you would no longer have a single piece of solid material since the atoms would be too far apart to bond to each other. Let's do some careful calculations to show this result. A modern United States penny has a mass of 2.500 grams according to the US Mint. Since a penny is composed of 97.50% zinc and 2.50% copper, it therefore contains 2.4375 grams of zinc and 0.0625 grams of copper. At a molar mass of 65.380 grams per mole for zinc and 63.546 grams per mole for copper, a penny therefore contains 0.037282 moles of zinc and 0.00098354 moles of copper. Since a mole of atoms contains 6.0221 x 1023 atoms, there are 2.2452 x 1022 zinc atoms and 5.9230 x 1020 copper atoms in a penny, for a total of 2.3044 x 1022 atoms in a penny. The earth has a surface area of 510,072,000 square kilometers, or 5.10072 x 1032 square nanometers. The surface area of the earth really depends on what you include in your definition of surface. For instance, if we wish to cover the area of every leaf on every tree and shrub with atoms from the penny, then this will change our answer. Surprisingly, it will not change our answer very much. Most of the earth is covered in relativity flat oceans, sandy deserts, snow fields, barren rocks, and meadows. Trees, shrubs, buildings, and other irregularly-shaped objects only cover a very small percentage of the earth (trees and buildings seem common to most of us humans because most of us live near crowded concentrations of trees and/or buildings). At any rate, we must pick some definition of earth's surface area to make any calculations. The number cited above does not include the surface area of tree leaves and other small irregularities. In the context of trying to cover the earth with a flattened penny, you can think of this definition of surface area as us lowering a sheet of zinc so that it drapes along the tops of the trees, but does not wrap around any of the leaves or branches of the trees. The thinnest we could ever hammer a sheet of material is one atom thick. We therefore assume that we are creating a one-atom-thick planar sheet of material. Using the above value for earth's surface area, we divide it by the number of atoms in a penny to find how much area each atom will occupy when the atoms are spread evenly across earth's surface. We get the value of 2.21347 x 1010 square nanometers per atom, or 0.0000343 square inches per atom. This may seem like a small area, but it is huge compared to the types of areas spanned by simple molecules. From here on out we will assume that all of the atoms in the penny are zinc atoms. This is a good assumption because almost all of the atoms in the penny are zinc atoms (97.5%). Also, in terms of atomic size and bonding distance, zinc and copper are nearly identical. When allowed to bond into a solid piece of material, zinc atoms arrange themselves into stacks of planar hexagonal grids. Therefore, in creating our one-atom thick sheet of zinc, we will arrange our zinc atoms along a planar hexagonal grid. If the penny's atoms are spread out uniformly on a hexagonal grid covering earth's surface, then each atom will have to be 159,870 nanometers away from its next nearest atoms in order to cover the entire earth (for a hexagonal grid of objects, the distance between nearest-neighbor objects is 1.0746 times the square root of the area that each object has to itself). In other words, taking the atoms of a single penny and spreading them out over the entire earth in a hexagonal arrangement will cause each atom to be about 0.16 millimeters away from its neighboring atoms. In order to form a solid chunk of material, atoms have to be close enough to form stable bonds. In regular pieces of zinc metal, stable chemical bonds are formed when each zinc atom is a distance of 0.26649 nanometers away from its next nearest zinc atoms. Therefore, the atoms of our smashed penny will be almost exactly 600,000 times too far apart to maintain stable bonds and constitute a solid piece of metal. With this kind of separation, we don't have a solid penny at all. We have a very dilute zinc gas spread over the earth. These widely separated atoms would blow around, dissolve into the ocean, mix with the clouds, and react with other atoms, so that we no longer have any type of distinct object that we would say is covering the earth. For this reason, you cannot hammer and flatten a penny until it covers the entire. The earth is simply too big and a penny has simply too few atoms to accomplish this task. Even if we break each zinc atom into 30 hydrogen atoms (ignoring all the messy details of the nuclear reactions involved), the atoms are still about a hundred thousand times too far apart to form stable chemical bonds. Besides, hydrogen atoms don't bond to form a solid chunk of material under normal conditions. These thoughts lead to another question: How much area can a smashed penny cover and still remain a solid chunk of material? To calculate this, we again realize that the thinnest a material can get is one atom thick. Also, the distance that zinc atoms need to be from each other and still stay bonded as a solid is 0.26649 nanometers, as already mentioned. This means that as part of a hexagonal planar arrangement of atoms, each zinc atom needs to occupy 0.0615 square nanometers of area. Multiply this number by the 2.3044 x 1022 atoms in a penny and we get a total area of 1417 square meters, which is about a quarter of the size of an American football field. In other words, if you had a special machine that carefully hammered a penny until it was everywhere just an atom thick, it would only cover a quarter of a football field. Keep in mind that at this thickness, you would be hard pressed to even see the penny and you would rip the penny when walking on it without feeling any resistance (think of walking on aluminum foil, but much, much thinner). To cover the entire earth's surface with one-atom-thick smashed pennies, you would need at least 360 billion pennies. |
context: tag/atom/ question: What is the shape of an electron? | Depending on how you define "shape", an electron either has no shape, or an electron can take on various wave shapes. The shape of an electron is never statically round like an orange. The reason for this is that an electron is not a solid little ball, despite being so often portrayed this way in the popular media and in elementary-level science texts. Rather, electrons are quantum objects. Along with all other quantum objects, an electron is partly a wave and partly a particle. To be more accurate, an electron is neither literally a traditional wave nor a traditional particle, but is instead a quantized fluctuating probability wavefunction. This wavefunction looks in certain ways like a wave and in other ways like a particle. An electron looks like a particle when it interacts with other objects in certain ways (such as in high-speed collisions). When an electron looks more like a particle it has no shape, according to the Standard Model. In this context, physicists call an electron a "point particle," meaning that it interacts as if it is entirely located at a single point in space and does not spread out to fill a three-dimensional volume. If you find the concept of a fixed amount of mass being contained in the infinitely small volume of a single point illogical, then you should. But you have to realize that the electron is not literally a solid ball. This means that the electron's mass is not literally squeezed into an infinitely small volume. Rather, in certain cases where the electron looks somewhat like a particle, it interacts as if it were completely located at a single point. Therefore, in the sense of particle-like interactions, an electron has no shape. Note that an electron is a fundamental particle; it is not made out of anything else (according to our current experiments and theories). All fundamental particles interact as shapeless points when acting like particles. But not all quantum objects are fundamental, and therefore not all quantum objects are point particles. The proton, for instance, is not fundamental, but is instead composed of three quarks. The existence of particles inside a proton means that a proton must spread out to fill a certain space and have a certain shape. A proton is not a point particle, but is in fact a sphere with a radius of 8.8 × 10-16 meters. (Note that as a quantum object, a proton is not a solid sphere with a hard surface, but is really a quantized wave function that interacts in particle-like collisions as if it were a cloud-like sphere.) If the electron was composed of other particles, it could indeed have a shape when interacting like a particle. But it doesn't. The electron is a point particle. When an electron is behaving more like a wave, it can have all sorts of shapes, as long as its shape obeys the electron wave equation. An electron's wave equation, and therefore its shape, is a function of its energy and the shape of the potential well trapping it. For instance, when an electron is bound in a simple hydrogen atom, an electron can take on the familiar orbitals taught in elementary physics and chemistry classes, such as the shape shown on the right. In fact, the word "orbital" in this context really just means "the shape of an electron when acting as a wave bound in an atom". Each atomic orbital is not some mathematical average of where the electron has been, or some average forecast of where the electron may be. Each orbital is the electron, spread out in the quantum wavefunction state. In the sense of its wave-like state, an electron in a hydrogen atom can have the shape of layered spheres (the "s" states), layered dumbbells (the "p" states), layered four-leaf clovers (the "d" states), and other shapes at higher energies. In other atoms and molecules, an electron can take on even more complex shapes. An electron can also be trapped by other objects besides atoms. For instance, electrons trapped in the potential wells of a quantum cascade laser take on shapes that look more like traditional waves. An example of electron wavefunction shapes in a quantum cascade laser is shown on the right. Note that when scientists or journalists say "the shape of an electron is round," they are not talking about the literal shape. They are talking about the electric field distribution created by a free electron, which is entirely different from the actual shape. |
context: tag/atom/ question: What is the strongest magnetic field possible? Is there a limit? | There is no firmly-established fundamental limit on magnetic field strength, although exotic things start to happen at very high magnetic field strengths. A magnetic field exerts a sideways force on a moving electric charge, causing it to turn sideways. As long as the magnetic field is on, this turning continues, causing the electric charge to travel in spirals. Once traveling in spirals, an electric charge acts like a small, oriented, permanent magnet and is therefore repelled from regions of high magnetic field gradient. Therefore, electric charges tend to spiral around magnetic field lines and be pushed away from regions where magnetic field lines bunch up. These two effects cause electric charges to get trapped along magnetic field lines that are strong enough. Examples of this effect include ions trapped in earth's ionosphere, radiation trapped in earth's radiation belts, hot plasma looping over the sun's surface in solar prominences, and plasmas contained in the laboratory using magnetic traps. The stronger the magnetic field gets, the more violently an electric charge is pushed sideways by the magnetic field, the faster and tighter it therefore spirals around in circles, and the stronger it gets pushed away from regions of high magnetic field gradient. Interestingly, all normal objects are made out of atoms, and all atoms are made out of electric charges: electrons and protons. Therefore, strong enough magnetic fields have the ability to deform and even break objects. When a magnetic field gets stronger than about 500,000 Gauss, objects get ripped to pieces by the intense forces. For this reason, scientists cannot build a machine that creates a magnetic field stronger than 500,000 Gauss and survives longer than a fraction of a second. Strong enough magnetic fields therefore destroy objects as we know them. Note that the magnetic fields used in medical MRI scanners are much weaker than 500,000 Gauss and are perfectly safe when used properly. While the destructive nature of strong magnetic fields places a practical limit on how strong of a field earthlings can create, it does not place a fundamental limit. Magnetic fields that surpass about a billion Gauss are so strong that they compress atoms to tiny needles, destroying the ordinary chemical bonds that bind atoms into molecules, and making chemistry as we know it impossible. Each atom is compressed into a needle shape because the electrons that fill most of the atom are forced by the magnetic field to spin in tiny circles. While such extremely strong magnetic fields are not possible on earth, they do exist in highly-magnetized stars called magnetars. A magnetar is a type of neutron star left over from a supernova. The intense magnetic field of a magnetar is created by superconducting currents of protons inside the neutron star, which were established by the manner in which the matter collapsed to form a neutron star. In a review paper presented at the Fifth Huntsville Gamma-Ray Burst Symposium, Robert C. Duncan summarized many of the theoretically-predicted exotic effects of magnetic fields that are even stronger: "In particular, I describe how ultra-strong fields At the most extreme end, a magnetic field that is strong enough could form a black hole. General Relativity tells us that both energy and mass bend spacetime. Therefore, if you get enough energy in one region, then you bend spacetime enough to form a black hole. The black hole does not destroy the magnetic field, it just confines it. Even stronger magnetic fields create larger black holes. It is currently not known whether this is actually possible, as there may be unknown mechanisms that limit a magnetic field from ever getting this strong. Certain unconfirmed extensions of current theories state that there is a fundamental limit to the strength of a magnetic field. For instance, if a magnetic field gets too strong, it may create magnetic monopoles out of the vacuum, which would weaken the magnetic field and prevent it from getting any stronger. However, since there is currently no evidence that magnetic monopoles actually exist, this purported limit is likely not real. We may someday discover a fundamental limit to the magnetic field strength, but there is currently no experimental evidence or well-established theoretical prediction that a limit exists. |
context: tag/atom/ question: What makes radioactive atoms get old so quickly and decay? | Atoms don't age. Atoms radioactively decay when a lower-energy nuclear configuration exists to which they can transition. The actual decay event of an individual atom happens randomly and is not the result of the atom getting old or changing through time. The phrases "getting old" or "aging" are rather vague and could refer to a lot of things. For biological organisms and mechanical devices, "aging" usually refers to the progression of complex internal processes. A single atom does not have any internal biological or mechanical systems, and therefore does not age in this way. There is no clock inside an atom telling it that it is now a minute older. For other objects, "aging" refers to the wearing down or corrosion of the object because of repeated use or exposure to the environment. Atoms are too simple to wear down, corrode, or steadily change. No matter what reasonable definition we use for the word "aging", individual atoms don't do it. Note that aging is different from experiencing time. Everything, including atoms, experiences time. An atom can sit at on my desk on Tuesday and then fall off and sit on the carpet on Wednesday, because it experiences time. However, an isolated atom does not deterministically change from one day to the next. (An atom's electrons and nucleons can be excited, but these excited particles quickly relax back down to the ground state. Therefore, excitations do not fundamentally change the atom. Also, an atom's nucleus can change via nuclear reactions, but these changes are random rather than the result of aging.) If atoms don't age, how do radioactive atoms know when to decay? How can we possibly say that a radioactive isotope has a lifetime if it does not age? The answer is that radioactive atoms don't know when to decay. In fact, an individual radioactive atom does not decay at a particular, predictable time. It's not like an atom has an internal clock ticking away telling it when it's time to fall apart. Rather, an atom decays at a random time, completely independent of how long it has been in existence. Radioactive decay is governed by random, statistical effects and not by internal deterministic machinery. A particular radioactive atom can and will decay at any time. The "lifetime" of a radioactive isotope is not a description of how long a single atom will survive before decaying. Rather, it is a description of the average amount of time it takes for a significant portion of a group of radioactive atoms to decay. A characteristic lifetime does not come about by the progression of internal machinery, but by the statistical behavior of a large group of atoms governed by probability. An analogy may be helpful. A standard six-sided die will show a single number between "1" and "6" when rolled. Let us agree that when we roll a "6", we smash the die to pieces and the game is over for that particular die. We begin rolling the die and get a "3", and then a "1" and then a "5". Next we roll a "6" and destroy the die as agreed upon. Since the die was destroyed after four rolls, we say that this particular die had an individual lifetime of four rolls. Now we get a new die and repeat the game. For this die, we roll a "2", then a "1", then "4", "3", "1", "5", and then finally a "6". This die therefore had an individual lifetime of seven rolls. When we repeat this game for many dice, we discover that the individual lifetime of a particular die can be anything from one roll to hundreds of rolls. However, if we average over thousands of individual lifetimes, we find that the dice consistently have an average lifetime of about six rolls. Since an individual die has no internal machinery telling it to show a "6" after a certain number of rolls, the individual lifetime of a die is completely random. However, since the random events are governed by probabilities, we can experimentally find a fixed characteristic average lifetime of a group of dice by averaging over a large ensemble of dice. We can also mathematically find the average lifetime by calculating probabilities. For the die, there are six possible outcomes to a single roll, each with equal probability of occurring. Therefore, the probability of rolling a "6" and destroying the die is 1 out of 6 for every roll. For this reason, we expect it to take six rolls on average to roll a 6 and destroy the die, which is just what we found experimentally. The dice do not have a predictable average lifetime because they age, but because they experience probabilistic events. In the same way, atoms do not age and yet we can identify a meaningful decay lifetime because of the probabilities. |
context: tag/atom/ question: Why do atoms always contain the same number of electrons and protons? | Atoms do not always contain the same number of electrons and protons, although this state is common. When an atom has an equal number of electrons and protons, it has an equal number of negative electric charges (the electrons) and positive electric charges (the protons). The total electric charge of the atom is therefore zero and the atom is said to be neutral. In contrast, when an atom loses or gains an electron (or the rarer case of losing or gaining a proton, which requires a nuclear reaction), the total charges add up to something other than zero. The atom is then said to be electrically charged, or "ionized". There is a major difference between the neutral state and the ionized state. In the neutral state, an atom has little electromagnetic attraction to other atoms. Note that the electric field of a neutral atom is weak, but is not exactly zero because the atom is not a point particle. If another atom gets close enough to the atom, they may begin to share electrons. Chemically, we say that the atoms have formed bonds. In contrast to neutral atoms, the field due to an ionized atom is strong, even at larger distances. The strong electric field of ions makes them strongly attracted to other atoms and molecules, to the point of being highly chemically reactive. Ionized atoms can be free radicals, which are atoms with a dangling bond that are highly reactive. In the human body, free radicals can react with DNA, leading to mutations and possibly cancer. Atoms become ionized when light with enough energy knocks off some of their electrons. Only light waves at the frequencies of X-rays and gamma rays have enough energy to ionize atoms and therefore lead to cancer. The cancer-causing power of only certain frequencies is why you can use your cell phone as much as you want, but you can only get an X-ray image taken on rare occasions. Free radicals occur naturally in your body. They only become dangerous when there are more free radicals than your body can handle. But not all ions in the body are bad. Because of the charged nature of ions, the human body makes use of them to pass electric signals through nerves. The body also uses ions to control fluid levels and blood pressure. The most-used ions in the human body are sodium, potassium, calcium, magnesium and chloride. Ions are also created whenever you electrostatically charge an object, such as when you rub a balloon on your hair. For this reason, your clothes dryer machine can be thought of as an ion maker. As clothes rub together in the machine, electrons get knocked from one atom to another. The result is the all-too familiar static cling. Electricity and strong electric fields do a good job of creating ions (think lightning). The neutral state of an atom is typically the most stable configuration (unless molecular bonds and the chemical environment complicates the picture), so ions tend to discharge and return to their neutral state over time. The reason for this is that, as an ion, the atom has a strong electric field that attracts the needed electron or the needed atom to take its extra electron. But once the atom becomes neutral, it has an equal number of electrons and protons, it does not have a very strong field, and therefore has little possibility of changing. |
context: tag/atom/ question: Why don't atoms collapse if they are mostly empty space? | Atoms are not mostly empty space because there is no such thing as purely empty space. Rather, space is filled with a wide variety of particles and fields. Sucking all the particles and fields out of a certain volume won't make the space completely empty because new particles will still flash into existence due to vacuum energy. Additionally, the Higgs field can't be removed. Even if we ignore every kind of field and particle except electrons, protons and neutrons, we find that atoms are still not empty. Atoms are filled with electrons. It's true that a large percentage of the atom's mass is concentrated in its tiny nucleus, but that does not imply that the rest of the atom is empty. Rather, it implies that the rest of the atom has relatively low density. The misconception of an empty atom is taught by incorrect elementary-level science books and is based on the false picture of electrons as balls. In this view, the atom consists of electron balls whizzing around the atomic nucleus which is itself a ball. In this picture, the space between the electrons and the nucleus is therefore empty space. While this picture (the Bohr model) is simple to imagine, it was shown to be wrong almost a century ago. Electrons (as well as all particles) are partially particle-like and partially wave-like, depending on the situation. When bound in atoms in an undisturbed state, electrons act like waves. These waves are three-dimensional probability density waves that spread out to fill the entire atom. The electrons do not spread out uniformly, but rather follow specific distribution patterns called "orbitals". The shape of the orbitals underpin all chemical reactions. As an example of some orbitals, the single-electron density distribution is shown on the right for hydrogen in the first few lowest states. The lighter points indicate regions where the electron has a higher density. Note that each image represents a single electron. The different light spots and bands in a single image are all part of a single electron's wave state. Because bound electrons spread out into fuzzy density waves, there is no definite "edge" to an atom. The electron actually spreads out to fill all space, although far away from the atom it is thin enough to be negligible. Interestingly, electrons in the atom even spread out so as to overlap with the nucleus itself. This electron-nucleus overlap makes possible the effect of electron capture, where a proton in the nucleus can react with an electron and turn into a neutron. If atoms were mostly empty space, we could remove this space and shrink atoms. In reality, atoms do not contain any empty space. Rather, they are filled completely with spread-out electrons, making the shrinking of atoms impossible. |
context: tag/atom/ question: Why don't electrons in the atom enter the nucleus? | Electrons in the atom do enter the nucleus. In fact, electrons in the s states tend to peak at the nucleus. Electrons are not little balls that can fall into the nucleus under electrostatic attraction. Rather, electrons are quantized wavefunctions that spread out in space and can sometimes act like particles in limited ways. An electron in an atom spreads out according to its energy. The states with more energy are more spread out. All electron states overlap with the nucleus, so the concept of an electron "falling into" or "entering" the nucleus does not really make sense. Electrons are always partially in the nucleus. If the question was supposed to ask, "Why don't electrons in the atom get localized in the nucleus?" then the answer is still "they do". Electrons can get localized in the nucleus, but it takes an interaction to make it happen. The process is known as "electron capture" and it is an important mode of radioactive decay. In electron capture, an atomic electron is absorbed by a proton in the nucleus, turning the proton into a neutron. The electron starts as a regular atomic electron, with its wavefunction spreading through the atom and overlapping with the nucleus. In time, the electron reacts with the proton via its overlapping portion, collapses to a point in the nucleus, and disappears as it becomes part of the new neutron. Because the atom now has one less proton, electron capture is a type of radioactive decay that turns one element into another element. If the question was supposed to ask, "Why is it rare for electrons to get localized in the nucleus?" then the answer is: it takes an interaction in the nucleus to completely localize an electron there, and there is often nothing for the electron to interact with. An electron will only react with a proton in the nucleus via electron capture if there are too many protons in the nucleus. When there are too many protons, some of the outer protons are loosely bound and more free to react with the electron. But most atoms do not have too many protons, so there is nothing for the electron to interact with. As a result, each electron in a stable atom remains in its spread-out wavefunction shape. Each electron continues to flow in, out, and around the nucleus without finding anything in the nucleus to interact with that would collapse it down inside the nucleus. It's a good thing too, because if electron capture was more common, matter would not be stable but would collapse down to a handful of nuclei. |
context: tag/atom/ question: Why don't metals burn? | Metals do burn. In fact, most metals release a lot of heat when they burn and are hard to put out. For example, thermite is used to weld train rails together. The fuel in thermite is the metal aluminum. When thermite burns, the aluminum atoms bond with oxygen atoms to form aluminum oxide, releasing a lot of heat and light in the process. As another example, hand-held sparklers use aluminum, magnesium, or iron as the fuel. The flame of a sparkler looks different from the flame of a wood fire because metal tends to burn hotter, quicker, and more completely than wood. This is what gives a lit sparkler its distinctive sparkling flame. In fact, most fireworks contain metal fuels. As another example, old flash tubes used in photography were nothing more than burning bits of magnesium in a glass bulb. Also, the space shuttle's solid rocket boosters used aluminum as the fuel. Some metals, such as sodium, burn so well that we don't make everyday objects out of them. Any boy scout who has started a fire using steel wool can attest to the fact that metals burn. Still, you may wonder why holding up a lit match to aluminum foil does not make it burn. Similarly, placing a metal pan on a kitchen flame does not make the pan burst into flames. In everyday situations, metal objects don't seem to burn so much. How can this be possible if metals actually do burn? There are three main factors involved. First, if you have a solid chunk of metal, it is hard to get oxygen atoms close enough to the majority of the metal atoms to react. In order to burn the metal, each metal atom has to get close enough to an oxygen atom to bond to it. For large chunks of metal; like spoons, pots, and chairs; most of the atoms are simply too deeply buried to have any access to oxygen molecules. Furthermore, metals don't vaporize easily. When you burn a chunk of wood or a wax candle, the fuel particles readily vaporize, meaning that with just a little heat, they shoot out into the air where they have better access to oxygen atoms. In contrast, solid metals tend to have their atoms very tightly bound together, meaning that it is much harder to use heat to vaporize the metal. Also, organic materials like wood or cloth contain a lot of their own oxygen, whereas raw metals don't. This is one reason why it is much harder to burn a metal spoon than a wooden spoon, even though they both consist of large chunks of material. With this fact in mind, all we have to do is manually break apart the metal atoms in order to get them to burn better. In practice, this means grinding the metal down to a fine powder. When used as a fuel in commercial products and industrial processes, metals usually come in the form of a powder. Although, even if you have ground a metal block down to a powder, it still won't burn as efficiently as it could if you just use the oxygen in the ambient air. The problem is that air does not actually contain that much oxygen. Air is mostly nitrogen. The best approach is to mix oxygen directly into the powder. Raw oxygen won't work so well because it is a gas at room temperature and will float away. Instead, solid compounds containing loosely bound oxygen atoms can be mixed into the metal powder. In this way, the oxygen atoms can stably sit right next to the metal atoms, ready to react. This approach is the most efficient way to get metals to burn well. For example, thermite is just aluminum powder (the fuel) mixed in with iron oxide (the oxygen source). The second reason that everyday metal objects don't burn so well is that metals generally have a higher ignition temperature. Because the atoms in a typical metal are so tightly bound to each other, it takes more energy to break them apart and free them up, even if the oxygen atoms are sitting right next to them. Candle flames, match flames, campfires, and kitchen stove flames simply don't get hot enough to ignite most metals, even if the metal is in the ideal powder form. Chemical reactions that produce higher temperatures must be used to ignite most metals. For example, the combustion of magnesium strips can be used to ignite thermite. The last reason that everyday metal objects don't burn so well is that metals tend to be excellent thermal conductors. This means that if a spot on a metal object starts to build up some heat, the heat very quickly flows through the metal to cooler parts of the object. This makes it hard to build up enough heat in one spot to reach the ignition temperature. Even if you have a flame torch running at a high enough temperature, it is difficult to use the torch to ignite a chunk of metal because the heat keeps flowing away through the metal. In summary, because most atoms in a solid chunk of metal don't have access to oxygen atoms, because metals have a high ignition temperature, and because metals are good thermal conductors, they don't burn very well in everyday situations. The ideal way to get a metal to burn is to grind it into a powder, mix in an oxidizer, contain it so heat can't escape, and then apply a high temperature ignition device. |
context: tag/black-hole/ question: Are there different types of black holes? | Yes, there are different types of black holes. The most straightforward way to classify black holes is according to their mass. You may think that because a black hole is in essence just a clump of matter that is dense enough to trap light, black holes of all masses should exist. In other words, black holes should exist along a continuous range of masses. However, that is not what we find in practice. The only types of black holes that have been firmly established to exist are stellar-mass black holes and supermassive black holes. Stellar-mass black holes are formed from the gravitational collapse of a single star or from the merger of two neutron stars. Therefore, stellar-mass black holes have masses similar to the masses of stars. More specifically, stellar-mass black holes have masses ranging from about 3 times the mass of our sun to about 50 times the mass of our sun. In contrast, supermassive black holes have a mass greater than about 50,000 times the mass of our sun and are typically millions to billions times the mass of our sun. Supermassive black holes are far too large to have formed from the gravitational collapse of a single star. However, scientists do not currently know how supermassive black holes form. Supermassive black holes are always found at the center of a galaxy and almost all galaxies have a supermassive black hole at its center. This seems to suggest that each supermassive black hole is formed as part of the formation of its galaxy. Interestingly, there seems to be zero or very few black holes with a mass between that of stellar black holes and supermassive black holes. The range between about 50 times the mass of our sun to about 50,000 times the mass of our sun seems like a huge range over which black holes typically do not exist. Any black hole with a mass in this range is called an intermediate black hole. A few decades ago, intermediate black holes were thought to not exist at all. However, recent observations seem to suggest that intermediate black holes may exist but are very rare. There may be many reasons why intermediate black holes are very rare, but one reason is likely the most important. This reason is that there are not any common physical mechanisms in the universe that can collapse matter down to a black hole of intermediate size. Most stars are too small to collapse down to intermediate black holes and whatever galactic mechanism produces supermassive black holes seems to involve masses that are too large to produce intermediate black holes. This is an ongoing area of research. Also interestingly, there seems to be no black holes that have a mass smaller than that of the stars (which spans a huge range from the mass of planets down to masses smaller than that of electrons). Termed mini black holes or micro black holes, the laws of physics as currently understood seem to suggest that it is indeed physically possible for them to exist. However, scientists cannot find any evidence of mini black holes existing. Perhaps mini black holes can exist but there is no natural physical mechanism that can produce them. Or perhaps mini black holes cannot exist for fundamental physical reasons. If mini black holes did exist, it is likely that they would quickly evaporate away to nothing through Hawking radiation. This is also an ongoing area of research. These concepts are summarized in the table below, where the numbers shown are approximate and the values for mass are that value times the mass of our sun. Another way to classify black holes is according to physical structure. The point-of-no-return nature of black holes means that most of the information that enters a black hole is destroyed or permanently locked away from the rest of the universe. For instance, there are no such things as rocky black holes or gaseous black holes like there are rocky planets and gaseous planets. All the rocks, gases, and dust particles that fall into a black hole get crushed down to a featureless speck of mass or ring of mass. Similarly, there are no such things as hot black holes or cold black holes. Also, there is no difference between a black hole formed from regular matter and a black hole formed from antimatter (although I should note here that there are not actually clumps of antimatter in our universe that are large enough to form black holes). The very nature of a black hole leads it to collapse all of its mass and energy down to an indistinguishable clump and to smooth out all irregularities and asymmetries. Because everything becomes indistinguishable within a black hole, the word "mass" in this context actually refers to mass and energy. However, a black hole does indeed retain a few properties that are externally measurable: its overall mass, its overall electric charge, and its overall spinning rate. Note that a few other properties of a black hole such as radius and magnetic moment are externally measurable, at least in principle, but these are not independent parameters. In other words, they are directly dependent, and arise from, the black hole's mass, charge, and spin. These three properties are the only independent, externally-observable black hole properties. If two isolated black holes had the same mass, charge, and spin, they would be indistinguishable.
The reason that the total mass, total charge, and total spin of a black hole are measurable from outside of the black hole despite being internal properties is that they obey universal conservation laws. Another way of saying this is that these properties are connected to fundamental symmetries in spacetime and therefore affect spacetime curvature.
We can therefore classify black holes according to mass, charge, and spin. I have already described classifying black holes by mass. If we just focus on charge and spin, we can make the following classification categories: black holes that are not spinning and have no net electric charge (Schwarzschild black holes), black holes that are spinning and have no net electric charge (Kerr black holes), black holes that are not spinning and do have a net electric charge (Reissner-Nordstrom black holes), and black holes that are spinning and do have a net electric charge (Kerr-Newman black holes). In our universe, black holes are almost always spinning (because they form from spinning bodies of matter) and almost always have zero net electric charge (because of the tendency of electric charge to attract opposite types of electric charge and self-neutralize). Therefore, Kerr black holes are by far the most common. These concepts are summarized in the table below.
Combining all of the concepts in this article, we see that the most common black holes in our universe are spinning, uncharged stellar-mass black holes and spinning, uncharged supermassive black holes.
Black Hole TypeNameHow Common
non-spinning, unchargedSchwarzschild Black Holerare
spinning, uncharged Kerr Black Holecommon
non-spinning, chargedReissner-Nordstrom Black Holerare
spinning, chargedKerr-Newman Black Holerare
Topics:
black hole, charge, energy, gravity, mass, spin
The reason that the total mass, total charge, and total spin of a black hole are measurable from outside of the black hole despite being internal properties is that they obey universal conservation laws. Another way of saying this is that these properties are connected to fundamental symmetries in spacetime and therefore affect spacetime curvature.
We can therefore classify black holes according to mass, charge, and spin. I have already described classifying black holes by mass. If we just focus on charge and spin, we can make the following classification categories: black holes that are not spinning and have no net electric charge (Schwarzschild black holes), black holes that are spinning and have no net electric charge (Kerr black holes), black holes that are not spinning and do have a net electric charge (Reissner-Nordstrom black holes), and black holes that are spinning and do have a net electric charge (Kerr-Newman black holes). In our universe, black holes are almost always spinning (because they form from spinning bodies of matter) and almost always have zero net electric charge (because of the tendency of electric charge to attract opposite types of electric charge and self-neutralize). Therefore, Kerr black holes are by far the most common. These concepts are summarized in the table below.
Combining all of the concepts in this article, we see that the most common black holes in our universe are spinning, uncharged stellar-mass black holes and spinning, uncharged supermassive black holes.
Black Hole TypeNameHow Common
non-spinning, unchargedSchwarzschild Black Holerare
spinning, uncharged Kerr Black Holecommon
non-spinning, chargedReissner-Nordstrom Black Holerare
spinning, chargedKerr-Newman Black Holerare
Topics:
black hole, charge, energy, gravity, mass, spin
The reason that the total mass, total charge, and total spin of a black hole are measurable from outside of the black hole despite being internal properties is that they obey universal conservation laws. Another way of saying this is that these properties are connected to fundamental symmetries in spacetime and therefore affect spacetime curvature. We can therefore classify black holes according to mass, charge, and spin. I have already described classifying black holes by mass. If we just focus on charge and spin, we can make the following classification categories: black holes that are not spinning and have no net electric charge (Schwarzschild black holes), black holes that are spinning and have no net electric charge (Kerr black holes), black holes that are not spinning and do have a net electric charge (Reissner-Nordstrom black holes), and black holes that are spinning and do have a net electric charge (Kerr-Newman black holes). In our universe, black holes are almost always spinning (because they form from spinning bodies of matter) and almost always have zero net electric charge (because of the tendency of electric charge to attract opposite types of electric charge and self-neutralize). Therefore, Kerr black holes are by far the most common. These concepts are summarized in the table below. Combining all of the concepts in this article, we see that the most common black holes in our universe are spinning, uncharged stellar-mass black holes and spinning, uncharged supermassive black holes. |
context: tag/black-hole/ question: Can you go fast enough to get enough mass to become a black hole? | Traveling at high speed does not affect your mass, even in Einstein's theory of Special Relativity. For some reason, pre-college teachers, popular science books, and older physics textbooks claim that objects gain mass when they are traveling at higher speeds. This claim is wrong. If you define something called "relativistic mass" that is completely different from regular mass, then this claim could be made to look true. But doing so is very confusing and misleading. Today's physicists no longer treat the motion energy of an object as "relativistic mass" because doing so is misleading. When an object gains speeds, the entity that it gains is called "kinetic energy", even in Special Relativity. The total energy of a moving object is therefore its rest energy plus its kinetic energy. The rest energy of an object is contained in its mass. The relativistic total energy of a moving object is: E = mc2/(1-v2/c2)1/2 In this equation, m is the mass of the object (which does not change no matter how fast the object is moving), c is the speed of light, and v is the speed of the object. If the object is not moving, v = 0, then there is no kinetic energy and the total energy just equals the rest energy. Plugging v = 0 into the equation above, we end up with the famous equation E = mc2. The rest energy of an object is therefore mc2, telling us that the rest energy is contained completely in the form of mass. The kinetic energy EK is therefore the total energy minus the rest energy: EK = E – mc2 EK = mc2(1/(1-v2/c2)1/2 – 1) This equation shows us that as the speed increases, the kinetic energy increases, but the mass never changes. In the limit that the speed of the object v approaches the speed of light in vacuum c, the kinetic energy becomes infinite. The law of conservation of energy tells us that to get an object traveling with infinite kinetic energy, we have to give it infinite energy. This act is clearly impossible as there is only a finite amount of energy in the observable universe. This facts means that objects with mass can never travel exactly at the speed of light in vacuum, as that state would require infinite energy. But objects can get very close to the speed of light. Mass is the property of an object that describes two things: When an object is traveling at a high speed, its resistance to acceleration does not change and its ability to experience gravity does not change. The mass of an object therefore does not change when it travels at high speed. This fact is predicted by Einstein's theories and verified by experiment. An object can never be turned into a black hole, or even be made slightly overweight by speeding it up. |
context: tag/black-hole/ question: Does every black hole contain a singularity? | In the real universe, no black holes contain singularities. In general, singularities are the non-physical mathematical result of a flawed physical theory. When scientists talk about black hole singularities, they are talking about the errors that appear in our current theories and not about objects that actually exist. When scientists and non-scientists talk about singularities as if they really exist, they are simply displaying their ignorance. A singularity is a point in space where there is a mass with infinite density. This would lead to a spacetime with an infinite curvature. Singularities are predicted to exist in black holes by Einstein's theory of general relativity, which is a theory that has done remarkably well at matching experimental results. The problem is that infinities never exist in the real world. Whenever an infinity pops out of a theory, it is simply a sign that your theory is too simple to handle extreme cases. For example, consider the simplest physical model that accurately describes how waves travel on a guitar string. If you drive such a string at its resonant frequency, the simplest model predicts that the vibration of the string will increase exponentially with time, even if you are driving it gently. The string actually does this... up to a point. The problem is that the exponential function quickly approaches infinity. The model therefore predicts that a guitar string driven at its resonant frequency will, in time, vibrate passed the moon, passed the stars, out to infinity, and then back. Does the string actually vibrate infinitely just because the model says so? Of course not. The string snaps long before vibrating out to the moon. The appearance of the infinity in the model therefore indicates that the model has reached its limitations. The simple model of waves on a string is correct as long as the vibrations are small. To avoid the infinity in the equations, you need to build a better theory. For vibrating guitar strings, all you have to do is add to the model a description of when guitar strings snap. As another example, consider a thin glass drinking goblet. If a singer sings a note at the right pitch, the goblet begins to shake more and more. The simplest model would predict that, in time, the goblet will be shaking infinitely. In real life, this does not happen. Instead, the singing causes the goblet to shatter to pieces when the shaking becomes too violent. Every scientific theory has its limitations. Within its realm of validity, a good theory matches experimental results very well. But go beyond the limitations of a theory, and it starts giving predictions that are inaccurate or even just nonsense. Physicists hope to one day develop a theory of everything that has no limitations and is accurate in all situations. But we do not have that yet. Currently, the best physics theories are quantum field theory and Einstein's general relativity. Quantum field theory very accurately describes the physics from the size of humans down to the smallest particle. At the same time, quantum field theory fails on the planetary and astronomical scales, and, in fact, says nothing at all about gravity. In contrast, general relativity accurately predicts gravitational effects and other effects on the astronomical scale, but says nothing about atoms, electromagnetism, or anything on the small scale. Using general relativity to predict an electron's orbit around an atomic nucleus will give you embarrassingly bad results, and using quantum field theory to predict earth's orbit around the sun will likewise give you bad results. But as long as scientists and engineers use the right theory in the right setting, they mostly get the right answers in their research, calculations, and predictions. The good thing is that general relativity does not overlap much with quantum field theory. For most astronomical-scale and gravitational calculations, you can get away with using just general relativity and ignoring quantum field theory. Similarly, for small-scale and electromagnetic calculations you can get away with using quantum field theory and ignoring general relativity. For example, you use just quantum field theory to describe what the atoms in the sun are doing, but use just general relativity to describe what the sun is doing as a whole. Many efforts are underway to consistently unite quantum field theory and general relativity into one complete theory, but none of these efforts have been fully solidified or confirmed by experiments. Until a successful theory of everything comes along, physicists can mostly get by with using both general relativity and relativistic quantum theory in a patchwork manner. This approach mostly works because the realms of validity of both theories do not overlap much. But this approach breaks down when you have an astronomical object collapsed down to quantum sizes, which is exactly what a black hole is. A black hole forms when a massive star runs out of the fuel needed to balance out gravity, and collapses under its own gravity to a very small size. General relativity predicts that the star collapses to an infinitely small point with infinite density. But, as should now be clear, such a beast does not really exist in the real world. The appearance of a black hole singularity in general relativity simply indicates that general relativity is inaccurate at very small sizes, which we already knew. You need quantum field theory to describe objects of small sizes. But, quantum field theory does not include gravitational effects, which is the main feature of a black hole. This fact means that we will not known exactly what is going on in a black hole until scientists can successfully create a new theory that accurately describes small sizes and strong gravitational effects at the same time. Whatever the new theory ends up telling us, it will most certainly not say that there are singularities in black holes. If it did, that outcome would simply indicate that the new theory is just as bad as the old theory. In fact, one of the requirements for the future theory of everything is that it not predict singularities in black holes. In this sense, the interiors of black holes are the final frontier for theoretical physics. Just about everything else in the universe can be accurately described (at least in principle) using our current theories. |
context: tag/black-hole/ question: How can there be anything left in the universe? Don't black holes suck everything in? | Black holes don't suck everything in. Black holes have gravity in the same ways stars have gravity. For this reason, planets orbit safely around black holes in the same way they orbit around our sun. The only difference between a black hole and a star is that the black hole has a small enough radius that light inside this radius cannot escape. There is a gigantic black hole at the center of our galaxy, and yet we are not in any danger of being sucked into it. Our entire galaxy orbits safely around the black hole at its center, as described in the book "The Galactic Supermassive Black Hole" by Fulvio Melia. It is true that if anything gets too close to a black hole, it will "hit it" and fall in, but this is generally no different from an earth satellite crashing into the ocean after years of slowing down due to friction |
context: tag/black-hole/ question: How does a black hole give off light? | A black hole itself does not give off any light. That is why it is called black. However, matter that is near a black hole can give off light in response to the black hole's gravity.
A black hole is a region of space where gravity is so strong that nothing can escape, not even light. It might be surprising to you to hear that gravity can affect light even though light has no mass. If gravity obeyed Newton's law of universal gravitation, then gravity would indeed have no effect on light. However, gravity obeys a more modern set of laws known as Einstein's general theory of relativity. According to general relativity, gravity is actually caused by a curving of space and time. Since light travels in a straight line through straight spacetime, the curving of spacetime causes light to follow a curved path. The gravitational curvature of light's path is a weak enough effect that we don't notice it much on earth. However, when gravity is very strong, the bending of light's path becomes significant. A black hole is a region where spacetime is so curved that every possible path which light could take eventually curves and leads back inside the black hole. As a result, once a ray of light enters a black hole, it can never exit. For this reason, a black hole is truly black and never emits light.
However, this restriction only applies to points inside the black hole. Light that is near a black hole, but not actually inside it, can certainly escape away to the rest of the universe. This effect is in fact what enables us to indirectly "see" black holes. For instance, there is a supermassive black hole at the center of our galaxy. If you point a high-power telescope exactly at the center of our galaxy and zoom way in, you don't see anything. A black hole by itself is truly black. However, the black hole's gravity is so strong that it causes several nearby stars to orbit the black hole. Since these stars are actually outside of the black hole, the light from these stars can reach earth just fine. When scientists pointed a high-power telescope at the center of our galaxy for several years, what they saw was several bright stars orbiting around the same blank spot. This result indicated that the spot is the location of a supermassive black hole.
As another example, a large cloud of gas and dust can fall towards a black hole. In the absence of friction, the black hole's gravity would simply cause the gas particles to orbit the black hole rather than fall in, similar to how stars orbit a black hole (i.e. black holes don't suck). However, the gas particles constantly smash into each other, thereby converting some of their kinetic energy into heat. With the loss of kinetic energy, the gas particles fall closer to the black hole. In this way, friction causes a large gas cloud to swirl toward a black hole and heat up along the way. Eventually, the cloud of gas falls into the black hole and becomes part of it. However, before the gas actually enters the black hole, it heats up enough to begin glowing, just like how a toaster element glows when it heats up. The light that is emitted consists mostly of x-rays but can also include visible light. Since this light is emitted by the gas before the gas enters the black hole, the light can escape away to the rest of the universe. In this way, light can be emitted from a glowing gas cloud just outside of a black hole even though the black hole itself emits no light. Therefore, we can indirectly "see" a black hole by seeing the glowing gas cloud that surrounds it. This gas cloud is called an accretion disk. When atoms of gas become hot enough, the atoms' electrons are ripped off, causing the atoms to become ions. A cloud of gas that is mostly ionized is called a plasma.
The situation gets even more interesting. As the plasma cloud gets pulled ever closer to the black hole, the plasma gets moving faster and faster. At the same time, there is less and less room for all of this plasma. As a result of this high speed and this crowding effect, some of the plasma ricochets far away from the black hole. In this way, two giant jets of glowing plasma are formed, which are called astrophysical jets. The jets shoot plasma far away from the black hole, never to return. Again, this is possible because the plasma in the jets was never actually inside the black hole. When such jets are created by supermassive black holes, they can stretch out for hundreds of thousands of light years. For instance, the image below shows a photograph of galaxy M87 captured by the Hubble Space Telescope. The bright yellow spot in the upper left of the image is the central region of the galaxy and the violet line is the glowing astrophysical jet created by the supermassive black hole at the center of the galaxy. In summary, a black hole itself cannot emit light, but it's intense gravity can create accretion disks and astrophysical jets outside the black hole which emit light.
Photograph captured by the Hubble Space Telescope. The violet line is light emitted by a giant plasma jet created by a supermassive black hole located at the center of galaxy M87. Public Domain Image,
source: NASA.
Topics:
black hole, light, relativity, spacetime
A black hole is a region of space where gravity is so strong that nothing can escape, not even light. It might be surprising to you to hear that gravity can affect light even though light has no mass. If gravity obeyed Newton's law of universal gravitation, then gravity would indeed have no effect on light. However, gravity obeys a more modern set of laws known as Einstein's general theory of relativity. According to general relativity, gravity is actually caused by a curving of space and time. Since light travels in a straight line through straight spacetime, the curving of spacetime causes light to follow a curved path. The gravitational curvature of light's path is a weak enough effect that we don't notice it much on earth. However, when gravity is very strong, the bending of light's path becomes significant. A black hole is a region where spacetime is so curved that every possible path which light could take eventually curves and leads back inside the black hole. As a result, once a ray of light enters a black hole, it can never exit. For this reason, a black hole is truly black and never emits light. However, this restriction only applies to points inside the black hole. Light that is near a black hole, but not actually inside it, can certainly escape away to the rest of the universe. This effect is in fact what enables us to indirectly "see" black holes. For instance, there is a supermassive black hole at the center of our galaxy. If you point a high-power telescope exactly at the center of our galaxy and zoom way in, you don't see anything. A black hole by itself is truly black. However, the black hole's gravity is so strong that it causes several nearby stars to orbit the black hole. Since these stars are actually outside of the black hole, the light from these stars can reach earth just fine. When scientists pointed a high-power telescope at the center of our galaxy for several years, what they saw was several bright stars orbiting around the same blank spot. This result indicated that the spot is the location of a supermassive black hole. As another example, a large cloud of gas and dust can fall towards a black hole. In the absence of friction, the black hole's gravity would simply cause the gas particles to orbit the black hole rather than fall in, similar to how stars orbit a black hole (i.e. black holes don't suck). However, the gas particles constantly smash into each other, thereby converting some of their kinetic energy into heat. With the loss of kinetic energy, the gas particles fall closer to the black hole. In this way, friction causes a large gas cloud to swirl toward a black hole and heat up along the way. Eventually, the cloud of gas falls into the black hole and becomes part of it. However, before the gas actually enters the black hole, it heats up enough to begin glowing, just like how a toaster element glows when it heats up. The light that is emitted consists mostly of x-rays but can also include visible light. Since this light is emitted by the gas before the gas enters the black hole, the light can escape away to the rest of the universe. In this way, light can be emitted from a glowing gas cloud just outside of a black hole even though the black hole itself emits no light. Therefore, we can indirectly "see" a black hole by seeing the glowing gas cloud that surrounds it. This gas cloud is called an accretion disk. When atoms of gas become hot enough, the atoms' electrons are ripped off, causing the atoms to become ions. A cloud of gas that is mostly ionized is called a plasma. The situation gets even more interesting. As the plasma cloud gets pulled ever closer to the black hole, the plasma gets moving faster and faster. At the same time, there is less and less room for all of this plasma. As a result of this high speed and this crowding effect, some of the plasma ricochets far away from the black hole. In this way, two giant jets of glowing plasma are formed, which are called astrophysical jets. The jets shoot plasma far away from the black hole, never to return. Again, this is possible because the plasma in the jets was never actually inside the black hole. When such jets are created by supermassive black holes, they can stretch out for hundreds of thousands of light years. For instance, the image below shows a photograph of galaxy M87 captured by the Hubble Space Telescope. The bright yellow spot in the upper left of the image is the central region of the galaxy and the violet line is the glowing astrophysical jet created by the supermassive black hole at the center of the galaxy. In summary, a black hole itself cannot emit light, but it's intense gravity can create accretion disks and astrophysical jets outside the black hole which emit light. |
context: tag/black-hole/ question: How does a supernova completely destroy a star? | A supernova does not completely destroy a star. Supernovae are the most violent explosions in the universe. But they do not explode like a bomb explodes, blowing away every bit of the original bomb. Rather, when a star explodes into a supernova, its core survives. The reason for this is that the explosion is caused by a gravitational rebound effect and not by a chemical reaction, as explained by NASA. It is true that within most stars there are violent hydrogen fusion reactions churning away, but these do not cause the supernova. Stars are so large that the gravitational forces holding them together are strong enough to keep the nuclear reactions from blowing them apart. It is the gravitational rebound that blows apart a star in a supernova. Consider the typical momentum transfer exhibit found in many science museums, as depicted in the animation on the right. Rubber balls of different sizes are held at different heights. The balls are then let go at the same moment. Gravity pulls them all down and they all fall towards the ground. In the next few moments, the bottom ball hits the ground and bounces back, and then the balls start colliding. Momentum equals mass times velocity. This means that a heavy object going slow has as much momentum as a light object going fast. When two objects collide, they transfer some momentum. When a heavy slow object collides with a light object, it can give it a very high velocity because of the conservation of momentum. As this animation shows, by arranging the rubber balls from heaviest on the bottom to lightest on the top, momentum is transferred to ever lighter objects, meaning ever higher speeds. As a result, even though gravity is pulling all the balls downwards, the upper balls rebound at incredible speeds. This is all in keeping with the law of conservation of momentum. The lower balls are too heavy and too slow to fly off. They remain behind as the surviving core of the original system. On the other hand, the upper balls are blown away (in a science museum exhibit, they are captured at the top of the apparatus so that the demonstration can be rerun). This explosion of rubber balls occurs without any significant chemical or nuclear reactions taking place. This explosion is simply due to gravity and momentum transfer, i.e. a gravitational rebound. If you look closely at the animation, you see that the rebound takes the form of an outward shock wave that gains in intensity as it spreads. A supernova is the same kind of explosion as this rubber-balls demonstration. An aging star is composed of denser layers down towards the center, and thinner layers near the surface. The star's nuclear reactions typically balance out the force of gravity. But when the star runs out of fuel, the nuclear reactions slow down. This means that gravity is no longer balanced. Gravity begins collapsing the star. After the core of a collapsing star reaches a critical density, its pressure becomes strong enough to hold back the collapse. But, like the rubber balls, the star has been falling inwards and now bounces back. The outer layers are blown off into space in a giant explosion, spreading fertile dust clouds through-out the universe . But because of the momentum transfer, the star's core survives. The collapsing event has so intensely squeezed the star's core, that it transforms into something exotic. If the star started out with between 5 and 12 times the mass of our sun, the core becomes a big ball of neutrons called a neutron star. If the star started out with more than 12 times the mass of our sun, the core becomes a black hole. You may be tempted to argue that when a star explodes so that all that remains is a black hole, there is nothing left and the star has therefore been completely destroyed. But a black hole is not nothing. Black holes have mass, charge, angular momentum, and exert gravity. A black hole is just a star that is dense enough, and therefore has strong enough gravity, to keep light from escaping. The black hole created by a supernova is the leftover core of the star that exploded. Not all stars experience a supernova. Stars that have less than 5 times the mass of our sun are too light to experience this violent transformation. They simply don't have enough gravity to collapse and rebound so violently. Instead, when lighter stars run out of nuclear fuel, they go through a series of stages and then settle down as long-lived white dwarfs. Whether stars end up as neutron stars, black holes, or white dwarfs, they never go completely away. |
context: tag/black-hole/ question: Is a black hole a 2D or a 3D object? | A black hole is actually a four-dimensional object. A black hole extends across all four physical dimensions of the universe. The four dimensions that form the background framework of the universe consist of three spatial dimensions and one time dimension. These four dimensions are inseparably connected into one unified framework called spacetime. While it may sound exotic to say that a black hole is a four-dimensional object, the mundane truth is that all physical objects are four-dimensional objects*. For instance, a desk extends a few feet in the x direction (we call this its width), extends a few feet in the y direction (we call this its length), extends a few feet in the z direction (we call this its height), and extends a few years in the t direction (we call this its lifetime). A desk is therefore spread out across many points in each of the three spatial dimensions and across many points in time. The size of the desk in the time dimension extends from the moment that it was built to the present moment and will continue to extend through time until the moment it is destroyed. In this way, the desk is a physical four-dimensional object that fills a four-dimensional volume. The same is true of chairs, apples, kites, asteroids, stars, and all other physical objects. Calling the time dimension the fourth dimension is more than just a clever use of words. There are profound physical effects that force us to consider time as a dimension attached to the three spatial dimensions. An object that in one reference frame is observed to have a large extent in the length dimension and a small extent in the time dimension will, in another reference frame, be observed to have a small extent in the length dimension and a large extent in the time dimension. In other words, because of relativistic effects such as length contraction and time dilation, how an object fills out its four-dimensional volume depends on the reference frame. Therefore, the time component of spacetime cannot be ignored. While a black hole is similar to a chair or a tree in that it exists extended across the four physical dimensions of the universe, a black hole is uniquely different for another reason. A black hole consists of spacetime that is so warped that nothing can escape, not even light. In fact, the spacetime of a black hole is so warped that, to a distant observer, spacetime itself is observed to cease to exist at the black hole's event horizon (which can roughly be thought of as the surface of the black hole). To a distant observer, a black hole is literally a hole in the spacetime framework; there is no "inside" of a black hole. All of the black hole's mass and trapped light is observed from far away (if it could be observed) to exist at its event horizon. To a distant observer, nothing exists inside a black hole, not even space or time. If this concept does not sit right with you, then you can think of it as an apparent effect arising from being in a reference frame that is observing the black hole from far away. To an observer very close to the event horizon of a black hole or even inside the event horizon, spacetime does not end at the event horizon and there is indeed an inside to a black hole. The views of both observers are correct, without there being a contradiction, because of the relativistic nature of spacetime. If a black hole is a four-dimensional object, then what is its shape? A black hole that is not rotating is spherical in shape (i.e., its event horizon is spherical) and extends linearly through the time dimension. You can roughly think of a black hole as a star that traps all of its light, and therefore it seems natural that a black hole is spherical. Furthermore, a black hole that is rotating is very close to being spherical in shape but is slightly flattened along its rotational axis. This shape is called an oblate spheroid. A rotating black hole also extends linearly though the time dimension. Interestingly, all real black holes are rotating because they form from giant rotating clouds of matter. However, black holes that are rotating very slowly can be approximated to be not rotating. Note that if a black hole is changing (e.g., matter is falling non-uniformly into the black hole), then things get more complicated and its shape is not exactly spherical, but these basic ideas still apply to a good approximation. In summary, a black hole is a four-dimensional object with a spherical or nearly spherical shape that extends linearly through time. *Note that fundamental particles such as electrons act in certain ways like point particles, meaning that they act like they have exactly zero width, zero length, zero height, and extend across many points in time. You could therefore argue that fundamental particles are physical one-dimensional objects. However, fundamental particles are quantum particles and therefore simple concepts such as size and volume do not have direct, literal, physical meaning. An electron (when acting perfectly as a particle) indeed does not have a fixed, definite, non-zero physical radius. In fact, in many experiments, an electron acts externally as if it had a radius of exactly zero. However, an electron also has a finite mass and does not have an infinite mass density, which implies that it cannot have a fixed radius of exactly zero. Furthermore, if all the mass of an electron were truly packed into an infinitely small volume, it would become a black hole, which it does not. This apparent contradiction is resolved by the fact that fundamental quantum particles simply do not have a definite radius at all. Quantum particles are not definite, hard, fixed balls of matter and/or energy. Rather, quantum particles are fluctuating, ambiguous, smeared-out probability clouds of matter and/or energy. Fundamental particles do not have zero radius in a fixed, definite, classical sense and therefore are ultimately four-dimensional objects. |
context: tag/black-hole/ question: Where is the center of the universe? | According to all current observations, there is no center to the universe. For a center point to exist, that point would have to somehow be special with respect to the universe as a whole. Let us think about all the different types of effects that could create a center. First, if an object is rotating, you can define a center of rotation. The center of rotation is the one spot on a rotating object that is stationary. For the earth, the center of rotation is the axis connecting the North and South pole. For a basketball player spinning a basketball on his finger, the center of rotation is the point where the ball touches his finger. The center of rotation for a wheel on an axle is the center of the axle. Observations of the universe have not found any rotation at all to the universe as a whole. With no rotation, there is no center of rotation. Next, you can define a center of mass. If an object is finite, the center of mass is just the point that, on average, has an equal amount of mass surrounding it in all directions. The situation gets more complicated for an infinite object. If an object is infinite and uniform, you simply cannot define a center of mass because all points are identical. On the other hand, if an object is infinite but not uniform (for instance it has a single knot of high density at one point), you can define the center of mass of the entire object as the center of mass of the non-uniformity. For instance, consider a cloud in the sky. Certain kinds of clouds don't have a well-defined boundary, but instead just stretch out in all directions, getting thinner and thinner. Even though the cloud stretches out effectively to infinity, the high density region of the cloud exists in a limited volume, so you can find a center of mass through a limiting procedure. Observations currently indicate that the universe is infinite in size. Although planets and stars do represent non-uniformities in the spacetime structure, on the universal scale, such uniformities are randomly dispersed. On average, therefore, the universe is uniform. Being infinite and uniform, there is no way to define a center of mass for the universe. Another possibility is a center of charge. Similar to the center of mass, this would be a point in an object where the amount of electric charge is on average the same in all directions surrounding it. The center of charge for a uniformly charged sphere would just be the center of the sphere. Similar to the mass distribution, the charge distribution of the universe is infinite and uniform on average so that there is no center of charge. Next, there could be a center of curvature. Like a salad bowl, there could be a central point to the universe from which all other points curve away from. But current observations have found the universe to be flat and not curved at all. Yet another possibility is a center of expansion. If you bolt a rubber sheet to the ground and then have people pull on all sides, the place where the sheet is bolted becomes the center of expansion. The center of expansion is the point in space from which all other points are moving away. A wealth of astronomical observations has revealed that the universe is indeed expanding. These observations are the foundation for the concept that a Big Bang started the universe. Because the universe is expanding, if you run time backwards, there had to be a time when the universe was all compacted to one point. Since the universe is expanding, you would think there is a center of expansion. But observations have revealed this not to be the case. The universe is expanding equally in all directions. All points in space are getting uniformly distant from all other points at the same time. This may be hard to visualize, but the key concept is that objects in the universe aren't really flying away from each other on the universal scale. Instead, the objects are relativity fixed in space, and space itself is expanding. You might be tempted to say that the location of the Big Bang is the center of the universe. But because space itself was created by the Big Bang, the location of the Big Bang was everywhere in the universe and not at a single point. The major aftereffect of the Big Bang was a flash of light known as the Cosmic Background Radiation. If the Big Bang happened at one location in space, we would only see this flash of light coming from one spot in the sky (we can see a flash that happened so long ago because light takes time to travel through space and the universal scale is so big). Instead, we see the flash as coming equally from all points in space. Furthermore, once the motion of the earth is accounted for, the flash of light is equally strong in all directions on average. This indicates that there is no center of expansion. Another way to define a center would be to identify some object or feature that exists only at one spot, such as a supermassive black hole or super-large nebula. But observations indicate that all types of objects are randomly peppered through the universe. No matter how we try to define and identify it, the universe simply has no center. The universe is infinite and non-rotating. Averaged over the universal scale, the universe is uniform. |
context: tag/black-hole/ question: Why does everything in our galaxy orbit the supermassive black hole at the center? | Strictly speaking, everything in our galaxy does not orbit the supermassive black hole at the center. Everything in the galaxy orbits the center of mass of the galaxy. The supermassive black hole just happens to be at the center. If the black hole at the center were removed, the galactic orbits of almost all objects in the galaxy would not change (except for the few stars that are very close to the black hole). Our galaxy contains a lot of mass, which includes stars, gas, planets, and dark matter. The black hole in the center is only about one millionth of the total mass of our galaxy. Because mass causes gravity, and gravity causes orbits, the galactic orbital paths of all objects in the galaxy are caused by the total mass of the galaxy and not the mass of the black hole at the center. Consider this analogy. Three girls form a circle and all lock their hands at the center of the circle. These girls now run quickly and steadily around their circle so that they can feel the strain in their arms. Even though they can feel the centrifugal force pushing them outwards, they do not fly off because their linked arms pull inward. The girls are all, in a sense, in orbit around their combined center of mass. They are not orbiting the gold ring on the finger of one of the girls, which happens to be at the center of their circle. If she took off her ring, their motion would not change much. The girls are like the objects in our galaxy, their linked arms are like the gravitational force linking everything together, and the gold ring is like the black hole. Every object in the galaxy is in orbit around the center of the combined mass of the galaxy. The center of mass is often called the "barycenter". In general, small bodies do not orbit large bodies. Instead, large and small bodies together orbit their combined center of mass. The textbook "Orbital Mechanics" by Tom Logsdon notes, "Newton also modified Kepler's first law by noting that if both of the two bodies in question have appreciable mass, the smaller body will not orbit about the center of the larger body. Instead, both of them will orbit around their common barycenter. A similar phenomenon can be observed at a football game. When a majorette tosses her baton into the air, it does not rotate around the heavy end. Instead, the entire baton rotates about its center of mass." |
context: tag/brain/ question: Do blind people dream in visual images? | Yes, blind people do indeed dream in visual images. For people who were born with eyesight and then later went blind, it is not surprising that they experience visual sensations while dreaming. Dreams are drawn from memories that are stored in the brain as well as from brain circuitry that is developed while experiencing the outside world. Therefore, even though a person who lost his vision may be currently blind, his brain is still able to draw on the visual memories and on the related brain circuits that were formed before he went blind. For this reason, he can dream in visual images. What is more surprising is the discovery that people who were born blind also dream in visual images. The human experience of vision involves three steps: (1) the transformation of a pattern of light to electrical impulses in the eyes, (2) the transmission of these electrical impulses from the eyes to the brain along the optic nerves, and (3) the decoding and assembly of these electrical impulses into visual sensations experienced in the brain. If any one of these three steps is significantly impaired, blindness results. In the vast majority of cases, blindness results from problems in the eyes and in the optic nerves, and not in the brain. In the few cases where blindness results from problems in the brain, the person usually regains some amount of vision due to brain plasticity (i.e. the ability of the brain to rewire itself). Therefore, people who have been blind since birth still technically have the ability to experience visual sensations in the brain. They just have nothing sending electrical impulses with visual information to the brain. In other words, they are still capable of having visual experiences. It's just that these experiences cannot originate from the outside world. Dreams are an interesting area because dreams do not directly originate from the outside world. Therefore, from a plausibility standpoint, it is possible for people who have been blind since birth to dream in visual images. However, just because blind people have the neural capacity to experience visual sensations does not automatically mean that they actually do. Scientists had to carry out research studies in order to determine if people who have been blind since birth actually do dream in visual images. At this point, you may be wondering, "Why don't we just ask the people who have been blind since birth if they dream in visual images?" The problem is that when you ask such people this question, they will always answer no. They are not necessarily answering no because they actually do not have visual dreams. They are saying no because they do not know what visual images are. A girl with eyesight visually recognizes an apple because at some point in the past she saw the apple and ate it, and therefore is able to connect the image of an apple with the taste, smell, shape, and touch of an apple. She is also able to connect the image with the word "apple." In other words, the visual image of an apple becomes a trigger for all the memories and experiences she has previously had with apples. If a girl has never personally experienced the visual image of an actual apple, then the experience of seeing an image of an apple in a dream for the first time has no connection to anything in the real world. She would not realize that she is seeing an apple. As an analogy, suppose you have never tasted salt. No matter how much people describe salt to you, you do not know what the experience is really like until you experience it personally. Suppose you were all alone your whole life, cut off from all people and all of society, and you came across a bag of very salty potato chips for the first time. When you eat the chips, you would experience the taste of salt for the first time, but you would have no way to describe it, because you would have no other previous experiences or connections with it. Similarly, people who have been blind since birth have no experience of connecting visual sensations with external objects in the real world, or relating them to what sighted people describe as vision. Therefore, asking them about it is not useful. Instead, scientists have performed brain scans of people who have been blind since birth while they are sleeping. What scientists have found is that these people have the same type of vision-related electrical activity in the brain during sleep as people with normal eyesight. Furthermore, people who have been blind since birth move their eyes while asleep in a way that is coordinated with the vision-related electrical activity in the brain, just like people with normal eyesight. Therefore, it is highly likely that people who have been blind since birth do indeed experience visual sensations while sleeping. They just don't know how to describe the sensations or even conceptually connect in any way these sensations with what sighted people describe as vision. With that said, the brain scans during sleep of people who have been blind since birth are not identical to those of sighted people. While people who have been blind since birth do indeed dream in visual images, they do it less often and less intensely than sighted people. Instead, they dream more often and more intensely in sounds, smells, and touch sensations. We should keep in mind that a person who has been blind since birth has never had the experience of seeing images originating from the external world and therefore has never formed visual memories connected to the external world. The visual components of their dreams therefore cannot be formed from visual memories or the associated circuitry. Rather, the visual sensations must arise from the electrical fluctuations that originate within the brain. What this means is that people who have been blind since birth probably do not experience detailed visual images of actual objects such as apples or chairs while dreaming. Rather, they probably see spots or blobs of color floating around or flashing. The spots may even correlate meaningfully to the other senses. For instance, a dream of a police car siren sound traveling from the left to the right may be accompanied by the visual sensation of a spot of color traveling from the left to the right at the same speed. In summary, the current evidence suggests that people who have been blind since birth do indeed dream in images, but we do not know exactly what they see. On a related note, brain scans have found that all humans dream in visual images before they are born. Because the womb is in total darkness, and therefore none of us experienced actual vision before we were born, this means that we all experienced visual dreams before birth despite having no visual memories to draw from. Therefore, the visual dream experiences of a fetus are similar to those of an adult who has been blind since birth. |
context: tag/brain/ question: Do scientists have a hard time understanding art? | Actually, scientists tend to be more art-minded than your average person. Science is a highly creative process, and so it tends to attract people who innately understand art, appreciate art, and create art. The old notion goes that one half of the brain is highly creative and the other half of the brain is highly technical/mathematical. According to this old notion, each person has a dominant half, resulting in only two types of people in the world: creative people who can't do math, and technical people who can't make art. First of all, this old notion is simply wrong. The brain is very complex. Creativity and technical ability, along with hundreds of other traits, emerge from a complicated interaction of neurons that involves the whole brain. A study performed by Harnam Singh found that "Notably, the MG [Mathematically Gifted] showed no reliable left-right differences when processing global or local information on unilateral trials." This study found that mathematical ability is more a function of how well the two halves of the brain communicate and work together and not a function of which half dominates. Furthermore, there are creative technical people and non-creative, non-technical people, so the two traits are not mutually exclusive. Also, there are billions of different kinds of people in the world, each with his or her unique blend of traits. Even if half of the brain was solely creative and the other half was solely technical, real science requires both, so scientists would have both halves equally dominant. It is true that science uses mathematics and technical recipes. But those are just the language of science. The meat of science is highly creative: forming hypothesis, building new tools, crafting new models, designing new experiments, interpreting results, and making conceptual connections. The only part of science that is not very creative (running the experiment once everything is designed and setup) is not even done typically by scientists these days. The actual running of an experiment is typically carried out by machines or lab technicians. Forming a hypothesis involves creating an idea about how the world works that may or may not be true. There are no technical recipes for making original hypotheses. When students read biographies of great scientists, they often puzzle, "how did he come up with this idea in the first place?" Often, the only answer is, "He was creative." Some of the best scientists have the craziest ideas for a new model or a new experiment. Most of these ideas don't work out, but some do. Building new scientific tools; such as microscopes, telescopes, particle accelerators, and particle detectors; is an important form of science. People who use established science to build ever better tools are engineers. People who use new science in order to build better tools are scientists. There is not one right way to build a better tool. It requires a lot of creativity to think up ways to apply some new science in order to create a better tool. Similarly, new models, new theories, and new experiments have to thought up by a creative person before they can be tested, applied, and tweaked. When a given experiment spits out a set of resulting numbers, it takes creativity to make connections and interpret the numbers. Scientists are very much like artists: they create new ideas, apply them, and see if they work. For science, an idea "works" if it predicts the behavior of the physical universe. For art, an idea "works" if it pleases the senses and/or successfully conveys a meaningful concept, emotion, or impression. Just as there is not one right way to paint a tree, there is not one right way to make a telescope. (Although, there are more wrong ways to make a telescope than there are wrong ways of painting a tree. In this sense, art is more forgiving than science.) If you have a picture in your mind of a person non-creatively carrying out a predefined list of technical steps, you have not pictured a scientist. You have pictured an assembly-line worker, a repairman, or an accountant. Because science is a highly creative process, scientists tend to be painters, singers, sculptors, composers, illustrators, poets, or novelists in their free time. Einstein played the violin. Max Plank was a good pianist, but gave up a promising career at the conservatory to study physics and become one of the founders of quantum theory. Feynman was secretly a published artist and not-so-secretly an avid drummer. A study by R. S. Root-Bernstein found that the success of a budding scientist is strongly correlated with the degree to which he enjoys musical and artistic hobbies. |
context: tag/brain/ question: How bad of an alcoholic do you have to be to have your brain affected? | One drink of alcohol is enough to affect your brain, whether you are an alcoholic or a casual social drinker. Alcohol is a psychoactive drug that interferes directly with the normal functioning of many parts of the brain. Fortunately, much of the effect caused by alcohol consumption can be repaired by the body when the person stops drinking. But ongoing alcohol consumption at heavy levels can cause damage so severe that the body cannot repair it and the damage becomes permanent. The National Institute of Health states, "Difficulty walking, blurred vision, slurred speech, slowed reaction times, impaired memory: Clearly, alcohol affects the brain. Some of these impairments are detectable after only one or two drinks and quickly resolve when drinking stops. On the other hand, a person who drinks heavily over a long period of time may have brain deficits that persist well after he or she achieves sobriety...Alcohol can produce detectable impairments in memory after only a few drinks and, as the amount of alcohol increases, so does the degree of impairment. Large quantities of alcohol, especially when consumed quickly and on an empty stomach, can produce a blackout, or an interval of time for which the intoxicated person cannot recall key details of events, or even entire events." Drinking alcohol (ethanol) is a two-carbon alcohol with the molecular formula CH3-CH2-OH. The hydroxyl group on the end (-OH) is able to participate in hydrogen bonding and accounts for much of its physical properties. |
context: tag/brain/ question: How can we unlock the 90% of our brain that we never use? | Healthy humans use all of their brain. There is no part of the brain that goes unused. Certain tasks work certain parts of the brain more, but they all play important roles, as explained by neurobiologist Dr. Eric Chudler. Brain maps, as found in modern anatomy books, indicate that each part of the brain has a specific function essential to a healthy human. If there were a part of your brain that really went unused, then you could safely damage that part in an accident with no ill effects. But decades of medical records show that damage to any part of the brain has severe effects. If 90% of the brain were not used, then 90% of the brain tumors would cause no problem. Imagine brain doctors telling 90% of their cancer patients, "I have good news and bad news. Bad news: you have a brain tumor. Good news: it's in the part of the brain that you will never use." The thought is absurd. If the 10% myth is instead supposed to mean that humans only use 10% of their brain in a given moment, it is still false. The brain is not a collection of independent machines that are turned on or off depending on whether you are reading or singing. Rather, brain functions emerge as a complex interplay of many parts of the brain. Physiologically, nerves are like muscles in that they degenerate when unused. If 90% of the brain went completely unused, then that portion would degenerate significantly. But brain scans of a healthy person reveals all parts to be intact. This myth was propagated by authors trying to sell books on mystical ways to unlock your hidden potential, claiming that unused brain power could be tapped using the methods in their books. The greatest danger to your brain is not the possibility that a large portion is going on unused. Rather, the greatest dangers are stroke, Alzheimer's disease, and tumors. The best ways to protect yourself from such risks include eating healthy, exercising, and getting enough rest. Do you really want to use your brain to its full potential? Then put down your unlocking-hidden-brain-potential book and go on a run. |
context: tag/brain/ question: How do I turn on more parts of my brain and get smarter? | Turning on more parts of your brain does not make you smarter. The brain does not really work that way. An example of a brain experiencing high activation is a seizure. During a seizure, a person has severely decreased functioning and mental capability. A person having a seizure can't talk, can't walk, and can't do math problems. This extreme example should make clear that "turning on more of the brain" does not equal "smarter". The brain contains a complex network of neurons that includes many feedback loops. Thoughts, memories, and calculations in the brain are emergent phenomena that arise out of the interplay of many neurons. A new idea is not stored in a single neuron. Rather, an idea is stored in the way many neurons are connected together. More specifically, an idea is stored in the way a brain signal travels through these connections in a cascading, looping, non-linear fashion. The analogy that the brain works like a computer is completely wrong. Standard microchip computers are deterministic, linear, and have localized processing operations. This type of processing is excellent for doing long mathematical calculations and carrying out deterministic actions such as displaying photos or editing text documents. However, this type of processing is terrible at generating creativity, recognizing patterns in complex systems, attaching value to information, extrapolating complex trends, learning new skills, and generalizing data into a small set of principles. In contrast to computers, the brain is non-deterministic, asynchronous, non-linear, and has delocalized processing operations. In this way, the brain is really the opposite of a traditional microchip computer; it is good at generating creativity, recognizing patterns, evaluating information, extrapolating trends, learning new skills, and generalizing data; but it is bad at doing long numerical calculations. Since a computer is linear and deterministic, you can make it more powerful simply by installing more processor cores and more RAM. In contrast, the brain is non-linear and non-deterministic, so turning on more neurons at once won't make the brain smarter. These comments lead to the question, "How does a person get smart?" My response is, "What do you mean by smart?" I do not give this response to be evasive. My response gets at the core of how a brain works. Strictly speaking, your brain is always getting smart in some way, whether you are working at it or not (assuming your brain is generally healthy). Your brain is always processing the external world, finding patterns, forming memories, and learning information. From a neurological perspective, skipping your math homework and watching cartoons instead does not make your brain any less smart. It just makes your brain good at reciting cartoon theme songs instead of being good at solving math problems. If your job is to recite cartoon theme songs on stage, then watching cartoons will make you smarter than completing your math homework will. With this in mind, "smart" does not really mean using your brain more. Assuming you are generally healthy, you always use the optimal amount of brain power whether you try to or not. "Smart" means using your brain to learn the information and skills that are important to you. The fields of mathematics, science, language, and history all contain facts, concepts, and skills that pertain to the real world. These concepts and skills either exist in the real world, are applicable to the real word, or are useful in carrying out professions in the real world. For these reasons, the learning of concepts and skills in mathematics, science, language, and history has become culturally associated with being smart. But a person who drops out of school and spends all of his time enjoying video games, television, movies, and fantasy books is still smart in the neurological sense of learning things and filling his brain with information. He is just smart in areas that are mostly useless, non-productive, and non-employable. Note that making a video game is entirely different from playing a video game. Memorizing where all the treasures are hidden in your favorite video game does not make you more able to get a job designing games. It takes mathematics, language, art, and programming skills to build virtual worlds. That is what I mean when I say that the knowledge and skills gained by playing video games are mostly useless, non-productive, and non-employable. In short, the way to get smart is to decide what field is important to you, and then spend a lot of time working and learning in that field. If you want to get good at math, do math problems again and again. Furthermore, you have to put in the work to make sure you learn to do the math problems correctly. If you want to get good at playing the violin, practice every day. There is no magical way to learn a subject without putting in the hard work and time. With that said, there are more effective ways of learning a subject than others. As mentioned previously, the human brain is constructed so that it is good at recognizing and learning patterns. Therefore, you will learn a subject more quickly if you first learn the rules, and then connect the information into patterns using the rules as you go. For instance, learning how to read by going through a list of 5000 of the most common words and simply memorizing the sound of each word is slow and tedious. In contrast, mastering a few dozen phonics rules is much more effective. As another example, memorizing a list of battle names and dates in a particular war is less productive. In contrast, it is more effective to first learn about war heroes, weapons technology, basic geography, and the war strategies that were used; and then connect the names and dates of the battles to these concepts. Creating maps, charts, timelines, and biographies is far more effective for learning history than memorizing unconnected list of facts because the human brain is optimized for seeing and learning patterns. |
context: tag/brain/ question: How do nerves control every organ and function in the body? | Nerves do not control every tissue and function in the human body, although they do play a large role. There are three main ways that bodily organs and functions are controlled: Nerves carry orders from the brain and spinal cord in the form of electrical signals. Nerves also help sense the state of tissues and relay this information back to the brain and spinal cord, enabling us to experience pain, pleasure, temperature, vision, hearing, and other senses. The body uses electrical signals sent along nerves to control many functions because electrical signals can travel very quickly. At the end of each nerve's axon terminals the electrical signals are converted to chemical signals which then trigger the appropriate response in the target tissue. However, the control exerted by the nervous system inevitably resides in the brain and spinal cord, an not in the nerves, which just pass along the signals. Most signals get processed in the brain, but high-risk signals are processed and responded to by the spinal cord before reaching the brain in the effect we call "reflexes". Although the central nervous system plays a large role in controlling the body, it is not the only system that exerts control. The endocrine system is a series of endocrine glands throughout the body that excrete certain chemical signals called hormones into the blood stream. The circulating blood then takes the hormones throughout the entire body where different tissues respond in characteristic ways to the hormones. The response of an organ or system to a hormone depends on how much of that hormone is present in the blood. In this way, endocrine glands can exert control over different organs and functions of the body by varying how much hormone they emit. In contrast to the central nervous system, the pathway of control for the endocrine system is purely chemical and not electrical. For example, the thyroid gland in the neck controls how quickly the body uses energy by secreting varying levels of thyroid hormone. Too much thyroid hormone, and you become restless, jittery, and unable to sleep. Too little thyroid hormone and you become sleepy, lethargic, and enable to think straight. A healthy body constantly monitors the activity level and adjusts the thyroid hormone levels as needed. Other examples of endocrine glands are the adrenal glands, which prepare the body for facing an emergency, and the reproductive glands, which control body mass and reproduction. Hormones in the body control functions as diverse as libido, fertility, menstruation, ovulation, pregnancy, child birth, lactation, sleep, blood volume, blood pressure, blood sugar, the immune system, vertical growth in children, muscle mass, wound healing, mineral levels, appetite, and digestion. Ultimately, much of the endocrine system is subservient to the brain via the hypothalamus, but the endocrine system does operate somewhat independently using feedback loops. Lastly, organs and functions in the body are controlled through local self-regulation. Rather than depend on the brain to dictate every single minute task, organs and cells can accomplish a lot on their own so that the brain is freed up for more important tasks. An organ can communicate regulatory signals through its interior using localized chemical signals such as paracrine hormone signalling. Typically, such hormones do not enter the blood stream, but are transported locally by simply flowing in the space between cells. This approach works because paracrine hormones are only meant to operate on nearby cells. For example, the clotting of blood and healing of wounds are controlled locally through an exchange of paracrine hormones. The organ with the highest degree of self-regulation is probably the liver. The liver hums along nicely, performing hundreds of functions at once without much direction from the rest of the body. An organ can also communicate through its interior electrochemically. For instance, the heart does not beat because a nerve is telling it to. The heart beats on its own through a cyclic wave of electrical impulses. While it is true that the brain can tell the heart to speed up or slow down, the actual beating of the heart is controlled locally. Also, each cell of the body has some degree of self-regulation internal to the cell itself. Some cells exert more internal control than others. For instance, white blood cells hunt down and destroy germs in a very independent fashion, as if they were autonomous organisms. Active white blood cells do not wait for the brain or a hormone to tell them to do their job. Sperm cells are so autonomous that they can continue to survive and function properly even after completely leaving the male's body. In reality, the central nervous system, the endocrine system, and the local regulation systems are not independent, but exert control over each other in a complicated manner. |
context: tag/brain/ question: How does ice cream in your stomach cause a headache? | An ice cream headache has nothing to do with your stomach, but is rather the result of the roof of your mouth (your palate) getting cold too quickly. In fact, you can get an ice cream headache before even swallowing the ice cream. Ice cream headaches occur whenever you eat or drink something cold too rapidly, and they last about 20 seconds. Eating cold food slowly can give your palate time to cool down normally and adjust to the low temperatures without causing a headache. According to the Mayo Clinic, the exact mechanism at work in ice cream headaches is not currently known, but it is believed that the headache is a case of referred pain. When the roof of your mouth gets cold too quickly, the pain signal sensed in your mouth is passed on to the trigeminal nerve, which then passes it on to the brain where it is processed and experienced. The trigeminal nerve senses pain from the entire face and forehead, so when it gets overloaded, pain from your mouth seems to be coming from your forehead. Ice cream headaches can be avoided by eating cold foods slowly, letting the cold food warm up before eating it, or by swishing a bit of the cold food around in your mouth before consuming the rest in order to help your palate adapt. If they do occur, these headaches can be alleviated by pressing your warm tongue against the roof of your mouth to warm it up, or by drinking a warm beverage. |
context: tag/brain/ question: How long can you use a cell phone before getting a brain tumor? | Cell phones do not cause cancer, no matter how long they are used, because they communicate using radio waves. Radio waves simply don't have enough energy per photon to ionize atoms. The World Health Organization states, "Only the high frequency portion of the electromagnetic spectrum, which includes X rays and gamma rays, is ionizing". Cancer occurs when the DNA in a cell is altered so that the cell grows in an uncontrolled way. DNA can be altered in many ways, but when it comes to cancer due to radiation exposure, an electron must be knocked off a molecule by a bit of radiation. The smallest possible bit of electromagnetic radiation is known as a photon. Electrons are bound to molecules, so it takes a certain minimum energy to knock off the electron. Light with frequencies above ultraviolet (x-rays and gamma rays) are known as ionizing radiation because each photon has enough energy to knock an electron off a molecule. Photons of light with frequencies at and below ultraviolet (radio waves, microwaves, infrared, red, orange, yellow, blue, violet) are non-ionizing. They simply don't have enough energy to remove an electron and cause cancer. Increasing the strength of a radio wave will not help it knock off electrons. Increasing the strength of a radio wave simply introduces more photons into the beam. But each radio photon still has the same energy it always does, which is not enough to ionize. When non-ionizing waves flow past a molecule, they shake up the electrons a bit but don't knock them off. This electron shaking leads to heating. A microwave oven heats up your food in the same way a campfire heats up your skin and in the same way a radio wave ever-so-slightly heats up your body. None of them causes cancer, no matter how long you sit there. You may get burned by sticking your hand in the fire or grabbing a hot dish right out of the microwave, but you won't get a tumor. If a radio wave did cause cancer, then candlelight would cause far more cancer, because visible light has far more energy per photon. In terms of radiation, a candle emits far more energy than a cell phone, and they are both harmless. Infrared waves have more energy per photon than radio waves, and everything with a non-zero temperature emits infrared waves. This means that the infrared waves coming from your chair, your pencil, and your clothes would give you cancer long before radio waves from your cell phone would, but they don't. The world is swamped with natural radio waves and infrared waves. Just ask any infrared camera designer what his main obstacle is in designing a camera and he will tell you his greatest challenge is separating the meaningful waves from all the background waves in the air. Anybody who has struggled with an old-fashioned analog TV antenna in an attempt to get a clear picture can tell you that the natural radio waves in the air can be quite overwhelming compared to the man-made ones. People who are worried about being bombarded with radio waves in our increasingly wireless world must realize that the sun and the rocks have been bombarding mankind with infrared and radio waves long before radio broadcast stations and WIFI routers came along. There are electromagnetic waves with high enough frequency to damage molecules: x-rays and gamma rays. That's why if you get too many x-ray scans taken you will get cancer. In addition, alpha, beta and neutron radiation can cause cancer, but they are only created by nuclear reactions, and not by cell phones. Any machine that produces x-rays is known to be dangerous and is heavily regulated in order to ensure safe use. |
context: tag/brain/ question: What part of the brain is hurt when you get headaches? | Most headaches have nothing to do with the brain being damaged or strained. There is more to your head than your brain. Surrounding your brain are meninges, bones, muscles, skin layers, lymph nodes, blood vessels, the eyes, ears, mouth, nose and cavities called sinuses. Most headaches are caused by strain or pressure buildup in these other areas and not in your brain. Brain tumors and strokes can cause headaches, but they usually cause other more serious symptoms such as unconsciousness, seizures, paralysis, and vision loss. For people with tumors or strokes, headaches are typically the least of their concerns. And even when a brain tumor does cause a headache, it does so indirectly by applying pressure to the skull and other parts of the head. In fact, the brain itself lacks pain receptors, so it is literally impossible to have pain in your brain. Surgeons can perform operations on the brain without numbing it for this reason. The brain is the place where we process and experience bodily sensations, so all pain ends up getting experienced in the brain. But all pain originates outside the brain. Sometimes a headache seems to be coming from deep within your head, but that is just a psychological/physiological trick where intense pain seems to spread out and come from other places than where it is really occurring. There are hundreds of types of headaches, all with different causes. For generally healthy people, the most common sources of headache are tension and head colds. |
context: tag/brain/ question: Why are human brains the biggest? | The brains of humans are not the biggest compared to all other animals. The average human brain has a mass of about 1 kg. In contrast, the brain of a sperm whale has a mass of 8 kg and that of an elephant has a mass of 5 kg. You may be tempted to think that bigger brains means smarter and that because humans are the smartest animals, we must have the biggest brains. But biology does not work that way. When an animal has a larger overall size, all of its organs must be generally bigger just to keep it alive. A sperm whale weighs 35 to 45 metric tons and stretches about 15 meters long. With so much biological tissue to take care of, the sperm whale needs a giant heart to keep blood pumping to all this tissue, giant lungs to provide oxygen to all this tissue, and a giant brain to coordinate it all. The sperm whale needs a giant brain not because it is intelligent, but because it has so much low-level functions to carry out with such a huge body. Intelligence is instead more strongly linked to the brain size relative to the body size. If a large brain is housed in a small body, there is less low-level signal processing and control that the brain has to carry out. As a result, the brain can be freed up for more higher-order thinking. But even this picture is over-simplified. Intelligence seems to depend on many things: absolute brain size, relative brain size, connectivity, energy expenditure, etc. But as a rough model, relative brain size is indeed correlated to intelligence within main groups of organisms. While humans do not have the biggest brains overall, we do have the biggest brains relative to our body size among the mammals. |
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