The discussion centers on the absorption and re-emission of photons, particularly in the context of atomic physics and solar plasma. When a photon is absorbed by an atom, it is destroyed, transferring its energy to an electron, which may then emit a photon of lower energy as it returns to a stable state. This process is influenced by the ionization state of the plasma, with nearly all light nuclei being ionized in the Sun's core. The conversation also touches on the fundamental mechanisms of energy transfer and the nature of photons and electrons in quantum physics.
PREREQUISITESPhysicists, astrophysicists, and students of quantum mechanics seeking to deepen their understanding of photon behavior and energy transfer in atomic and plasma contexts.
Nope. Energy is constant for a given photon. You just wrote down the equation. Both h and f are constants (h is universal constant, f is constant for a given photon) so E must also be constant. Keep in mind that frequency tells you how many cycles are there per second and so it does not change during the cycles.John Huang said:A photon of frequency f has energy of E=hf and the energy of that photon has highest energy at crests and lowest energy at troughs in each of all cycles.
Darwin123 said:Since photons have zero rest mass, one can only talk about the kinetic energy in the final state.
QED stands for "quantum electrodynamics". The electromagnetic interaction between particles is the only thing analyzed in QED. QED includes all sorts of methods for determining how and when photons are generated.
SR uses modified versions of the same force laws between particles as in Newtonian physics. GR has field equations which again show how particles interact. All combinations of quantum mechanics and relativity relate to how photons and other particles are created.
Maybe you are talking about a different type of "how" than most of us are thinking. Perhaps you can explain what type of "how" and "control" that you are talking about.
Dead Boss said:Nope. Energy is constant for a given photon. You just wrote down the equation. Both h and f are constants (h is universal constant, f is constant for a given photon) so E must also be constant. Keep in mind that frequency tells you how many cycles are there per second and so it does not change during the cycles.
John Huang said:Yes, all QED, SR & GR relate to how photons and other particles are created. But, no detail like which part of a photon is created first and which part is created later. They just talk about under what situation a photon of certain energy will be created.
Let me use your statement "Since photons have zero rest mass, one can only talk about the kinetic energy in the final state." to ask you one of the detail characters of a photon. If all a photon has is kinetic energy then which structure a photon uses it to control the speed to run between the fastest and the lowest speed in each cycle? I like to know that knid of detail. A newborn photon may show that character differently at the beginning of the birth.
John Huang said:Thanks for your input. How do you explain the stationary wave in a microwave which heat up certain spots of a chocolate quicker?
No, SR and GR do not do that.John Huang said:Yes, all QED, SR & GR relate to how photons and other particles are created.
A photon is an elementary particle, it has no smaller parts (at least according to all measurements done so far).But, no detail like which part of a photon is created first and which part is created later.
A theory which describes all our observations. The ultimate goal of physics (if there would be nothing else but electromagnetism). What else do you want?They just talk about under what situation a photon of certain energy will be created.
There are no cycles. Just forget that. It is wrong.If all a photon has is kinetic energy then which structure a photon uses it to control the speed to run between the fastest and the lowest speed in each cycle?
Is this perhaps a machine translation error? A photon does not have organs (organs are body parts like the heart and liver) and does not breathe (breathe means to inhale and exhale air) nor does it have any structure (it is a fundamental particle). Surely you did not intend to say any of that.John Huang said:I believe a complicated object with a breathing organ like a photon must have a structure. What do you think?
Here, energy means both kinetic energy and the energy associated with rest mass. Most particles have a nonzero rest mass. Photons have a zero rest mass, but they have a positive kinetic energy.John Huang said:If the linier momentum and the angular momentum are the only concern related to that kind of energy used to create a photon then do you mean the energy is a kinetic energy?
I am a physicist, not a veterinarian!John Huang said:I mean, how two particles work together to control the speed of the newborn photon to be exactly c?
DaleSpam said:Is this perhaps a machine translation error? A photon does not have organs (organs are body parts like the heart and liver) and does not breathe (breathe means to inhale and exhale air) nor does it have any structure (it is a fundamental particle). Surely you did not intend to say any of that.
No, as several other people have already told you, its energy is constant. You need to forget this incorrect idea that its energy cycles up and down.John Huang said:Thanks for listening. About breathing, the electic/magnetic field moves with a photon (or is carried by a photon) is like a sine wave, not a constant amount, don't you think it is like the photon is breathing energy?
You have to be very careful talking about photons in laser beams. The photons in a laser beam are in what is called a coherent state, which has some strange properties. For one, there is an uncertainty relationship about the number of photons, meaning that a laser beam does not have a definite number of photons.John Huang said:About organ, since a photon in a laser beam can aim at a precise point so that its energy is stored at the center kernel and it also has polarization so that a photon has extended part to handle polarization.
That is an interesting question. I suppose that you could come up with one or more shape operators and use those to measure the shape of a photon. It would be a lot of effort, and I don't think that anyone has bothered, but I don't know why it couldn't be done.John Huang said:A fundamental particle still has a shape, isn't it? That is what I like to know.
DaleSpam said:No, as several other people have already told you, its energy is constant. You need to forget this incorrect idea that its energy cycles up and down.
The field of a photon is not a classical field from Maxwell's equations with an associated classical energy density. It is a quantum field (aka wavefunction) which represents the probability of detecting the photon there. Wherever you detect it, it will have its full given amount of energy.
That isn't even close to an accurate description of how a photon moves. A better description would be that a photon moves along all possible paths at all different speeds simultaneously. Each of these possible paths interferes with all of the others in a specific way to establish the probability of detecting the photon at a given time and place.John Huang said:You see, if a photon moves along a STRAIGHT line at a CONSTANT speed
It might indeed be easier, but unfortunately we are stuck with a not-so-easy universe. What you suggest is contradicted by experiment, and the more complicated idea is confirmed by experiment.John Huang said:To me, all of three possible energies and the fourth option of possibility are not easy to understand. That is why I think, it will be a little bit easier if a photon will never die.
If a car moves along a straight line at constant speed with a given energy, do you expect a uniform distribution for its position on the line (if you measure it)? I don't.John Huang said:You see, if a photon moves along a STRAIGHT line at a CONSTANT speed with a GIVEN energy, then logically speaking, you will expect an EVENLY distributed possibility EVERYWHERE on the line to find that photon. Isn't it?
Photons have a circular polarization, they do not have those concepts.How can the nature assign the CREST and TROUGH sections of that line to have high possibility under the idea of QFT?
No.I don't know what kind of energy is carried by a photon. To make a photon both wave and particle, a photon may have different mass, electric field, speed or possibility per cycle.
DaleSpam said:That isn't even close to an accurate description of how a photon moves. A better description would be that a photon moves along all possible paths at all different speeds simultaneously. Each of these possible paths interferes with all of the others in a specific way to establish the probability of detecting the photon at a given time and place.
DaleSpam said:It might indeed be easier, but unfortunately we are stuck with a not-so-easy universe. What you suggest is contradicted by experiment, and the more complicated idea is confirmed by experiment.
The result of the interference of all possible parts is usually something close to a straight line, this can be calculated.John Huang said:Yes, "Each of these possible paths interferes with all of the others in a specific way" and a photon always appeare (ALMOST 100% as we are able to measure) with a constant speed along a straight line in VACUUM.
No. There is no need to accelerate anything.If the experiment must CREATE a photon, physicists will face another problem. What kind of force should be used to accelerate a photon to run from 0 to c and how long does it take? If a photon will not die, it will be easier with the exchange of momentum.
Hey,what about the plane polarized?Photons have a circular polarization, they do not have those concepts.
which path,can you follow photon?Yes, "Each of these possible paths interferes with all of the others in a specific way" and a photon always appeare (ALMOST 100% as we are able to measure) with a constant speed along a straight line in VACUUM.
Damn it!If the experiment must CREATE a photon, physicists will face another problem. What kind of force should be used to accelerate a photon to run from 0 to c and how long does it take? If a photon will not die, it will be easier with the exchange of momentum.
As an expectation value for the speed of a large number of photons, sure. However, the question you posed was not about speed but about how the probability amplitude varies, and the interference I mentioned is how.John Huang said:Yes, "Each of these possible paths interferes with all of the others in a specific way" and a photon always appeare (ALMOST 100% as we are able to measure) with a constant speed along a straight line in VACUUM.
The expectation of the speed never runs at 0 and always runs at c, so there is no photon acceleration. Furthermore, the expectation of the momentum, like the energy, is always constant.John Huang said:If the experiment must CREATE a photon, physicists will face another problem. What kind of force should be used to accelerate a photon to run from 0 to c and how long does it take?
Again, nature doesn't care about what is easier for you to understand, so it is completely useless to talk about it.John Huang said:If a photon will not die, it will be easier with the exchange of momentum.