Photon states should not evolve?

[Tio Barnabe]

Since proper time for photons doesn't change, i.e. in their reference frame time doesn't change, then it should be that photons don't change their quantum mechanical state, or the equivalent in Maxwell's theory.

One could say, well they don't experience time, but we do. Okay, but since their reference frame is inertial, as well as ours (if we properly choose so), so the laws of nature should be the same in their reference frame as well as in our reference frame. Therefore, if they don't experience time and thus, in their reference frame their state never evolve, so we should observe the same thing. Why is it not so? May be because Rules of General Relativity applies only for "objects" traveling at a speed less than that of light?

 

[Dale]

Since proper time for photons doesn't change, i.e. in their reference frame

There is no such thing as the reference frame of a photon.

since their reference frame is inertial, as well as ours

It is not.

 

[Tio Barnabe]

There is no such thing as the reference frame of a photon.

So should I have said "point of view" of a photon instead?

 

[Tio Barnabe]

Let's not get stuck in the technical details. I think everyone reading my opening post understands what I am asking.

 

[Dale]

So should I have said "point of view" of a photon instead?

In relativity "point of view" is a colloquialism for "reference frame". Either way, it is the same thing, and a photon doesn't have one

 

[Dale]

Let's not get stuck in the tecnical details.

You are asking a technical question. The technical details are essential.

Your question is based on a faulty assumption. So the proper answer to the question is to point out the inconsistency

 

[Tio Barnabe]

You are asking a technical question. The technical details are essential.

Your question is based on a faulty assumption. So the proper answer to the question is to point out the inconsistency

Then focus on the main point of my question, please.

 

[Ibix]

Talking of the reference frame of a photon is contradicting yourself. You'll never get a sensible answer from that starting point, so it's not surprising that you are struggling trying to make sense of the consequence of your initial mistake. The solution is to start somewhere else in your reasoning.

 

[Tio Barnabe]

Okay. So should we always analyse a photon from a reference frame where time evolves?

 

[Ibix]

Okay. So should we always analyse a photon from a reference frame where time evolves?

There is no reference frame in which "time stands still", so you don't really have an option. Your initial mistake was in trying to define one.

 

[jerromyjon]

Since proper time for photons doesn't change

Photons only move at c in a vacuum...

 

[Ibix]

Photons only move at c in a vacuum...

Please don't get into photons in a medium in this thread. You need quantum field theory to do it justice and naive assumptions about "photons slowing down" are pretty much wrong, in my limited understanding.

 

[martinbn]

Let's not get stuck in the technical details. I think everyone reading my opening post understands what I am asking.

I don't. I find it very unclear and confused.

 

[jerromyjon]

Please don't get into photons in a medium in this thread.

I wasn't trying to, I was just pointing out a fact that "the point of view of a photon" only makes some kind of sense when that is all there is in empty space.

naive assumptions about "photons slowing down" are pretty much wrong, in my limited understanding.

I'd bet you know much more than me about it, but I do agree photons "slowing down" is just a pop-science attention grabber.

 

[Dale]

Okay. So should we always analyse a photon from a reference frame where time evolves?

As @Ibix mentioned, there are no other kinds of reference frames!

Then focus on the main point of my question, please.

I did. The main part of your question is based on a faulty premise. The question is simply wrong and cannot be answered

 

[Tio Barnabe]

Is it also wrong to say that photons don't experience time?

 

[jtbell]

What does it mean for a photon to "experience" something?

 

[jerromyjon]

Is it also wrong to say that photons don't experience time?

Photons don't lose energy with time. The cosmic microwave background has been traveling for over 13 billion years and the frequency has been redshifted by expansion of space but it is still coming at us since the recombination epoch.

 

[Tio Barnabe]

Photons don't lose energy with time

This statement seems to contradict this one

the frequency has been redshifted by expansion of space

What does it mean for a photon to "experience" something?

I mean in the sense that things like energy, position, etc evolve with time.

 

[phinds]

I wasn't trying to, I was just pointing out a fact that "the point of view of a photon" only makes some kind of sense when that is all there is in empty space.

No, "the point of view of a photon" NEVER makes sense.

 

[phinds]

I mean in the sense that things like energy, position, etc evolve with time.

Which is something WE observe. The photon does not "observe" or "experience" anything.

 

[Dale]

Is it also wrong to say that photons don't experience time?

Without anthropomorphising, photons are governed by the laws of QED, which do include the way a photon's state evolves over time. Whether that implies they "experience" time is more a question of semantics than physics

 

[Carrock]

In special relativity, you can make the the frequency or momentum etc of a photon any arbitrary finite value you want, by choosing an appropriate reference inertial frame from which to measure it.

Similarly, in GR, any apparent bending, doppler shift etc is a result of curved space etc and using a non-local reference frame to calculate the apparently changing state of the photon.It would be possible, by using suitable different local inertial frames near different points on the photon's path, to calculate the photon's state to be unchanging.

i.e. by using 'correct' inertial frames, photons' state can be calculated to never evolve.

It's perhaps worth mentioning that the changing state of moving neutrinos is regarded as strong evidence they have mass.

 

[jerromyjon]

Photons don't lose energy with time.

This statement seems to contradict this one

the frequency has been redshifted by expansion of space

I thought the same thing when I was thinking of what to type, but when you look at comparatively short distances and humanly observable time frames any loss of energy would be irrelevant and minuscule. The fact that they do lose energy to expansion should give you the clue that photon states HAVE to evolve to account for this.

 

[Carrock]

The fact that they do lose energy to expansion should give you the clue that photon states HAVE to evolve to account for this.

You're assuming the energy of a photon must be defined by a comoving inertial frame.
Unless you can justify that, then you can choose a local frame where the photon has not lost energy or evolved.

 

[jerromyjon]

You're assuming the energy of a photon must be defined by a comoving inertial frame.

Yes, I'm specifying that. Many things affect the wavelength of photons, time is not one of them.

 

[zonde]

Since proper time for photons doesn't change, i.e. in their reference frame time doesn't change, then it should be that photons don't change their quantum mechanical state, or the equivalent in Maxwell's theory.

Photons change their quantum mechanical state in Schrödinger picture. But you can adopt Heisenberg picture for photons and leave Schrödinger picture for massive particles. This should resolve your question.

 

[rrogers]

In relativity "point of view" is a colloquialism for "reference frame". Either way, it is the same thing, and a photon doesn't have one

I don't know what "reference frame" means but in GR, coordinate systems using null geodesics are used for certain purposes. Photons, in GR, have "direction" and an associated foliation.

 

[Dale]

I don't know what "reference frame" means but in GR, coordinate systems using null geodesics are used for certain purposes. Photons, in GR, have "direction" and an associated foliation.

Although often we use the term "reference frame" to mean "coordinate system", this is one case where the difference becomes important. The technical term for a reference frame is a tetrad. It consists of a set of four vector fields covering some section of spacetime. Three of the vector fields are spacelike and one is timelike and they are orthonormal. So even though you can define coordinate systems with null basis vectors, the basis vectors of those coordinates do not form a tetrad or reference frame

 

[martinbn]

Technically they (the null vectors) do form a tetrad, but not a reference frame.