How is heat caused by photons?

[brainstorm]

Well, of course. This is a question of whether two forces applied to a body are of the same magnitude or not. If they are, you will get recursive motion, otherwise you will not. This behavior does of course not depend on the forces applying to the body as long as the forces cause a restoring force at small displacements.

This is not clear. Maybe an example would help.

[/quote]I see no reason why they should be.[/quote]
It depends how independent their behavior is vis-a-vis each other and in what ways they are connected.

Well, I see it in the same way as a magnetic field, but I am not sure my concept of the magnetic field is the same as yours, so let me give a toy model. In this model the electromagnetic field is a property of empty space itself. If you consider a giant membrane spanning all space, you get the picture. Pull at some position of the membrane and let go and you will see a wave arising from that position and traveling across the membrane. Pull at another position and you see another wave traveling across the membrane. You can consider these waves as particle-like excitations of your membrane. If two of those waves meet somewhere on the membrane, the result in the meeting area will not only depend on the characteristics of these particle-like waves, but also on the characteristics of the membrane itself.

Well, you are implying that there is a membrane and it is universally present and that all matter-energy operates through manipulation of it. This is general-level theorizing, btw. The issue of these fields with reference to this thread is whether they are fundamental and whether it makes sense to discuss energy-transfer from photons to heat at the macro/collective/emergent level or in terms of interactions between elementary particles.

However, the difference between empty space and that membrane is that the membrane is made out of some material and you can in principle determine the membrane properties from its constituents. To the best of our knowledge empty space does not consist of anything else. Nevertheless, it is obviously able to transport energy in some forms, e.g. light, when you place it somewhere in empty space. So imho it is at best a multiplicity of geometric points, but not of something which has material form.

Empty space, imo, is a function of energy driving matter apart and that matter coalescing and entering into sustained orbits that prevents it from further coalescing. This is assuming that all matter-energy expanded from an original singular point where 3D space did not exist. Gravity fields thus clear out large parcels of empty space, but are other force-fields responsible for generating the gravity-fields? The big question is what forms matter and and why does it seem to exist as interacting particles that behave in certain ways?

Why do electrons emits photons and absorb them? How can an electron absorbing a photon transfer the energy in a way that results in heat (or electricity)? Etc. This was the OP topic and I think it can best be addressed with reference to the behavior of the individual particles involved, i.e. photons, electrons, and protons - and of course the forces that regulate their interactions.

 

[Cthugha]

This is not clear. Maybe an example would help.

An example? Imagine you have some object orbiting another object on a circular path, some planet and a sun for example. If there was no force acting on the planet, it would just move onward in a straight line. Accordingly, there must be a force acting on the planet. The absolute value of the speed does not change, so the force must be perpendicular to the motion of the planet and showing inward. It is obvious that gravitational interactions between the sun and the planet will be the origin of this force. Whether or not there will be stable orbits, depends on the speed of the planet and the attractive force between planet and sun. For certain combinations, there will be stable orbits. For other combinations, there will not be stable orbits.

In the beginning of QM people tried to do the same calculation for atoms. They considered the electron as orbiting around the nucleus with some speed and calculated the necessary inward force to keep it on track. However, due to the small scale and the charged electron and nucleus, the electromagnetic force replaces gravity as the attractive force. This classical approach leads to wrong results because electrons are not tiny balls and should radiate when orbiting something, but I hope you get the picture. If speed and attractive force match, there will be recursive motion. The origin of the force does not matter.

Well, you are implying that there is a membrane and it is universally present and that all matter-energy operates through manipulation of it. This is general-level theorizing, btw. The issue of these fields with reference to this thread is whether they are fundamental and whether it makes sense to discuss energy-transfer from photons to heat at the macro/collective/emergent level or in terms of interactions between elementary particles.

I was just aiming at electromagnetic fields in particular because these are easier to handle. This is a simplifying explanation after all and I do not claim to be able to give an exact explanation of a topic others need years of studying to understand in detail. If you insist on discussing interaction with matter, explanations starting from the level of individual elementary particles make even less sense because the underlying phenomena do not really depend on the exact kind of particles used and can already be demonstrated in classical mechanics:

If you take a mass and attach it to two springs attached to a wall, you get a pendulum with some certain resonance frequency. Now you can compare this to the case of two masses, each connected to a wall using springs and connected to each over via another spring. You will notice that in some cases, where both pendulums can exchange energy very efficiently, the coupled pendulums system will have different resonance frequencies than the single pendulums: The masses can both oscillate back and forth in phase or out of phase. The latter movement will have a higher resonance frequency. Whether this renormalization to new energy levels occurs depends on the interaction strength between the masses (depending on the spring stiffness), on the masses of the masses and on the resonance frequencies of the individual pendulums. This simple process is known as normal mode splitting or strong coupling. If you now increase the number of masses, you will get more resonance frequencies, accordingly. This is the basic process behind diverse machanisms like binding and antibinding orbitals in molecules, the formation of bands in solids for a large number of masses and the appearance of quasiparticles like polaritons if you couple different oscillators, for example a photon and an electronic transition. Although the exact numbers you have to enter for coupling strengths and the other constants depend on the individual particles used, this collective behavior showing up as a level splitting is pretty much independent of the kind of oscillator or different oscillators used. Therefore, I think it is more intuitive to consider this general feature of many-particle states as a many-body effect and insert the necessary parameters for some special case of interest.

The big question is what forms matter and and why does it seem to exist as interacting particles that behave in certain ways?

Most "why"-questions can be followed by further "why"-questions finally leading to the answer "beacause of the actual value the natural constants have". Then asking further "why"-questions mean that you will leave the realm of physics as it is not the task of physics to answer questions which cannot be tested empirically. "what forms matter?" is a question which can still be answered and is being worked on in the field of high energy particle physics and string theory, but I suppose a thorough answer will require some time spent on studying this field. I am a "solid-stater" and I do not feel competent enough to give a satisfying answer on that topic. But feel free to have a look at basic introductions at string theory. Just be warned that they are relying heavily on not-so-easy math.

Why do electrons emits photons and absorb them?

If I stay in the picture I gave above, then they do so because both can be considered oscillators and have some certain interaction strength. However, I have the feeling that will not satisfy you and you might want to know, why photons couple to charged particles...

How can an electron absorbing a photon transfer the energy in a way that results in heat (or electricity)? Etc. This was the OP topic and I think it can best be addressed with reference to the behavior of the individual particles involved, i.e. photons, electrons, and protons - and of course the forces that regulate their interactions.

In fact, absorption in the infrared, where you talk about heat are usually not governed by electrons, but are collective oscillations of the nuclei. However, the interaction of those with an infrared photon can occur, if there are enough coupled nuclei and enough energy level splittings that one of these energy levels matches the energy of the photon. However, it is in fact only the collective system of many nuclei, which can absorb the photon, not one nucleus on its own.

 

[jtbell]

you might want to know, why photons couple to charged particles...

Oh, we know that... it's because the universe obeys local U(1) gauge symmetry! Of course, that leads to the question, "why does the universe obey local U(1) gauge symmetry?"

 

[Cthugha]

That is exactly what I meant with the long chain of "why?"-questions finally leaving the realm of physics. My favorite answer to these final questions is always: "Because the flying spaghetti monster made it that way. Ramen."

 

[brainstorm]

In the beginning of QM people tried to do the same calculation for atoms. They considered the electron as orbiting around the nucleus with some speed and calculated the necessary inward force to keep it on track. However, due to the small scale and the charged electron and nucleus, the electromagnetic force replaces gravity as the attractive force. This classical approach leads to wrong results because electrons are not tiny balls and should radiate when orbiting something, but I hope you get the picture. If speed and attractive force match, there will be recursive motion. The origin of the force does not matter.

Yes, that is my point. And I don't see why it really matters what the shape of an electron orbit is, only whether its path is closed or open and whether it is a satellite or fulcrum. The fact that it is relative light and a satellite of the nucleus means that it can transmit energy without disturbing the inertia of the nucleus, which allows for the transmission of electricity without heat up to a certain point, no?

Whether this renormalization to new energy levels occurs depends on the interaction strength between the masses (depending on the spring stiffness), on the masses of the masses and on the resonance frequencies of the individual pendulums. This simple process is known as normal mode splitting or strong coupling. If you now increase the number of masses, you will get more resonance frequencies, accordingly. This is the basic process behind diverse machanisms like binding and antibinding orbitals in molecules, the formation of bands in solids for a large number of masses and the appearance of quasiparticles like polaritons if you couple different oscillators, for example a photon and an electronic transition. Although the exact numbers you have to enter for coupling strengths and the other constants depend on the individual particles used, this collective behavior showing up as a level splitting is pretty much independent of the kind of oscillator or different oscillators used. Therefore, I think it is more intuitive to consider this general feature of many-particle states as a many-body effect and insert the necessary parameters for some special case of interest.

So what you're basically saying is that the electron orbits of atoms oscillate at different frequencies and the combinatory frequency patters cause the atom to be prone to bonding in certain ways with certain other atoms, like the synchonization of gears so that they will couple? Still, it sounds like if you were able to capture in slow-motion the moment when the bonding actually occurs, you would see a pattern of electrons meshing with and then interlocking with another such pattern. And yet even though the interaction is governed by the two patterns, the patterns themselves can only be explained by the different oscillation speeds of the different electrons in the system, which I assume in turn is due to the relationship between each electron and its nucleus, no?

Most "why"-questions can be followed by further "why"-questions finally leading to the answer "beacause of the actual value the natural constants have". Then asking further "why"-questions mean that you will leave the realm of physics as it is not the task of physics to answer questions which cannot be tested empirically. "what forms matter?" is a question which can still be answered and is being worked on in the field of high energy particle physics and string theory, but I suppose a thorough answer will require some time spent on studying this field. I am a "solid-stater" and I do not feel competent enough to give a satisfying answer on that topic. But feel free to have a look at basic introductions at string theory. Just be warned that they are relying heavily on not-so-easy math.

It was a peripheral question anyway. BTW, I don't think it is necessary to jump over all the hurdles of socialization into a field (such as string theory) to be able to get certain important concepts and arrive at meaningful knowledge. Sure, experts fantasize about being the only ones capable of understanding anything in their domain of knowledge because they have special comprehension access, but anyone in their own field of expertise can admit that there are simple ways of understanding things explained in very complex language (and math) by the experts. It may be very difficult to explain to people what is so relevant and nuanced about a particular idea, but in principle it can be communicated to lay people.

If I stay in the picture I gave above, then they do so because both can be considered oscillators and have some certain interaction strength. However, I have the feeling that will not satisfy you and you might want to know, why photons couple to charged particles...

So you're saying the reason a photon interacts with an electron is because their oscillation strength/frequency matches up? It's not just because they orbit fast enough that the electron doesn't have time to get by them? After all, if electrons aren't slow enough to have their speed and position measured simultaneously, then doesn't that mean that they blur by as fast as the light that's hitting them?

In fact, absorption in the infrared, where you talk about heat are usually not governed by electrons, but are collective oscillations of the nuclei. However, the interaction of those with an infrared photon can occur, if there are enough coupled nuclei and enough energy level splittings that one of these energy levels matches the energy of the photon. However, it is in fact only the collective system of many nuclei, which can absorb the photon, not one nucleus on its own.

So what would happen if that nucleus/atom was relatively isolated in a vacuum when the photon encountered it?

 

[Cthugha]

Yes, that is my point. And I don't see why it really matters what the shape of an electron orbit is, only whether its path is closed or open and whether it is a satellite or fulcrum. The fact that it is relative light and a satellite of the nucleus means that it can transmit energy without disturbing the inertia of the nucleus, which allows for the transmission of electricity without heat up to a certain point, no?

Unfortunately, this intuitive approach taken in the beginning of qm does not work. One of the basic results of classical electromagnetism is that any charged particle which is accelerated somehow must necessarily give off radiation in order to conserve energy. So, if the electron was orbiting the nucleus it would continuously lose energy that way and finally crash into the nucleus. And no, conductivity does not depend on what the single electron does to a single nucleus.

So what you're basically saying is that the electron orbits of atoms oscillate at different frequencies and the combinatory frequency patters cause the atom to be prone to bonding in certain ways with certain other atoms, like the synchonization of gears so that they will couple? Still, it sounds like if you were able to capture in slow-motion the moment when the bonding actually occurs, you would see a pattern of electrons meshing with and then interlocking with another such pattern. And yet even though the interaction is governed by the two patterns, the patterns themselves can only be explained by the different oscillation speeds of the different electrons in the system, which I assume in turn is due to the relationship between each electron and its nucleus, no?

Well, they are not really orbiting as I mentioned above, but anyway: No, the electron resonances are not necessarily at different frequencies. Strong coupling works even better when they are at the same frequency. However, the combined system of two coupled resonances will have two different resonance frequencies. That is a rather general feature. It does not matter, whether you couple two springs that way or form molecules or couple light to excitons or whatever. Basically this whole approach can be applied to any strong coupling resonances (as long as they are similar to spring pendulums insofar as there is a restoring force). Of course the exact numbers where the final modes will lie are a result of the initial modes and the coupling strengths, but the general mechanism does not depend on that.

And once you have this broadening into bands of energy levels for many oscillators, conductivity becomes easy to explain. Usually the lowest of these bands will be filled and the next highest will be empty. To get conduction, you need to excite states with a well defined electron momentum, so you need to populate the next highest band (as every state of the lower bands is already populated the necessary states are not available there). Now the energy difference between the bands (analogous to the splitting of frequencies explained before) matters. If the energy is large, it costs a lot of energy to promote an electron to the higher band. This energy is not there and the material will not be a conductor. If there is no splitting, this excitation can happen easily and you will get a conductor. If you have a small splitting, the tempereture of your material might be high enough to promote electrons to higher bands. You get a semiconductor.

To get a basic understanding of these concepts, it is really not necessary to understand the exact nature and strengths of the forces involved. Those will only determine the exact energies where the resulting bands will lie. However, the occurrence of such bands is just a consequency of the large numbers of particles occurring. There is no analog to these band in single atoms and therefore one should not start from single atoms to explain conductivity.

I mean, if these properties were already imprinted in the single atoms, why would graphite and diamond - both pure carbon - have so very different properties in terms of heat conductivity, for example?

So you're saying the reason a photon interacts with an electron is because their oscillation strength/frequency matches up? It's not just because they orbit fast enough that the electron doesn't have time to get by them? After all, if electrons aren't slow enough to have their speed and position measured simultaneously, then doesn't that mean that they blur by as fast as the light that's hitting them?

Here I do absolutely not get what you mean. Orbiting photons? Electrons not slow enough to have speed and position measured simultaneously? Blurring electrons? You seem to have some strange misconceptions about photons and uncertainty

So what would happen if that nucleus/atom was relatively isolated in a vacuum when the photon encountered it?

You would get some discrete resonances. Only photons of well defined energies will interact with the atom.

 

[brainstorm]

Unfortunately, this intuitive approach taken in the beginning of qm does not work. One of the basic results of classical electromagnetism is that any charged particle which is accelerated somehow must necessarily give off radiation in order to conserve energy. So, if the electron was orbiting the nucleus it would continuously lose energy that way and finally crash into the nucleus. And no, conductivity does not depend on what the single electron does to a single nucleus.



Well, they are not really orbiting as I mentioned above, but anyway: No, the electron resonances are not necessarily at different frequencies. Strong coupling works even better when they are at the same frequency. However, the combined system of two coupled resonances will have two different resonance frequencies. That is a rather general feature. It does not matter, whether you couple two springs that way or form molecules or couple light to excitons or whatever. Basically this whole approach can be applied to any strong coupling resonances (as long as they are similar to spring pendulums insofar as there is a restoring force). Of course the exact numbers where the final modes will lie are a result of the initial modes and the coupling strengths, but the general mechanism does not depend on that.

And once you have this broadening into bands of energy levels for many oscillators, conductivity becomes easy to explain. Usually the lowest of these bands will be filled and the next highest will be empty. To get conduction, you need to excite states with a well defined electron momentum, so you need to populate the next highest band (as every state of the lower bands is already populated the necessary states are not available there). Now the energy difference between the bands (analogous to the splitting of frequencies explained before) matters. If the energy is large, it costs a lot of energy to promote an electron to the higher band. This energy is not there and the material will not be a conductor. If there is no splitting, this excitation can happen easily and you will get a conductor. If you have a small splitting, the tempereture of your material might be high enough to promote electrons to higher bands. You get a semiconductor.

To get a basic understanding of these concepts, it is really not necessary to understand the exact nature and strengths of the forces involved. Those will only determine the exact energies where the resulting bands will lie. However, the occurrence of such bands is just a consequency of the large numbers of particles occurring. There is no analog to these band in single atoms and therefore one should not start from single atoms to explain conductivity.

I mean, if these properties were already imprinted in the single atoms, why would graphite and diamond - both pure carbon - have so very different properties in terms of heat conductivity, for example?



Here I do absolutely not get what you mean. Orbiting photons? Electrons not slow enough to have speed and position measured simultaneously? Blurring electrons? You seem to have some strange misconceptions about photons and uncertainty



You would get some discrete resonances. Only photons of well defined energies will interact with the atom.

I typed a long response to your post and it got lost when I submitted it. I'm kind of discouraged to try to type it again. I believe I'm getting the oscillation frequency pattern-effects you're talking about but I still think you're unnecessarily avoiding including behavior of the individual oscillators in the model. Also, I don't see how "oscillation" is a different model from a planetary model such as Bohr's since planets are oscillators as well. I also pointed out in the post that I think it is possible for electrons to consistently lose energy through radiation and regain momentum from collisions. I think this would serve as a general mechanism for transferring heat from a system into radiation. Considering that all matter radiates black-body emissions, why wouldn't the cause of this be consistent evaporation of electron momentum into radiation?

 

[Cthugha]

Also, I don't see how "oscillation" is a different model from a planetary model such as Bohr's since planets are oscillators as well.

Not really. If you apply such a harmonic oscillator model, you have some energy oscillating back and forth between two types. You have kinetic energy and the energy for deforming the spring in a spring pendulum, you have photons and electronic transitions for Rabi oscillations or you have potential and kinetic energy for a string pendulum. In the ideal circular orbit case, a planet is just orbiting its sun at some equilibrium position. No energy is changing from one type to the other.

I also pointed out in the post that I think it is possible for electrons to consistently lose energy through radiation and regain momentum from collisions. I think this would serve as a general mechanism for transferring heat from a system into radiation.

Electrons are almost not involved at all in processes concerning heat. Most of the heat is "stored" in collective motion of the nuclei.

Considering that all matter radiates black-body emissions, why wouldn't the cause of this be consistent evaporation of electron momentum into radiation?

This applies only to matter to which a temperature can be assigned. This is a statistical concept that is only sensible for large numbers of particles. A single atom for example will not emit black-body emission.

 

[brainstorm]

Not really. If you apply such a harmonic oscillator model, you have some energy oscillating back and forth between two types. You have kinetic energy and the energy for deforming the spring in a spring pendulum, you have photons and electronic transitions for Rabi oscillations or you have potential and kinetic energy for a string pendulum. In the ideal circular orbit case, a planet is just orbiting its sun at some equilibrium position. No energy is changing from one type to the other.

So the term, "oscillator," refers to back-and-forth translation between two types of energy? So an electron orbit rising and falling with photon absorption/emissions is an oscillator but the same electron in an undisturbed consistent orbit would not be? So the oscillations you described that transmit electric current? What two states do the electrons oscillate between in that case?

Electrons are almost not involved at all in processes concerning heat. Most of the heat is "stored" in collective motion of the nuclei.

How would energy transfer between two nuclei except through contact between the electrons, since the protons are so far isolated from each other by the electrons?

This applies only to matter to which a temperature can be assigned. This is a statistical concept that is only sensible for large numbers of particles. A single atom for example will not emit black-body emission.

So electrons/atoms only emit radiation at certain moments and at other moments they emit absolutely none? I used to think that until someone who claimed to be a physicist told me that atoms are always emitting some level of radiation and that was called black-body radiation. I read about black-body radiation, and Max Planck's finding that radiation is absorbed and emitted in discreet "packets" determined by frequency and that it is not possible to radiate energy in partial amounts of such "packets." So what you're saying is that only certain atoms within a substance are actually emitting radiation at any given moment and the others are not? Does this mean that energy has to build up to a certain level in an atom before it will trigger a photon-emission? That is what I used to think before this person told me electrons are always emitting some level of radiation.

According to the planetary logic of the atom, the photon gets emitted when the electron "jumps" a level and then falls back to its original level. So if those levels are discreet, which makes sense considering that the radiation travels in discreet packets, then it would make sense that there would be a period of energy build-up before triggering the photon emission, much like a capacitor builds up so much charge before releasing it. So please confirm to me, then, that atoms do not emit radiation except intermittently according to their energy level.