Restframe of Photon: Explained

In summary, the concept of the rest frame of a photon doesn't make sense because there is no frame in which a photon can have an arbitrary velocity.
  • #1
timmdeeg
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D H said:
I've read that in relativity the concept of the rest frame of a photon doesn't make sense. Why is that?
Consider a mass in its restframe relative to which another mass can have an arbitrary velocity ##v < c##.

Now consider a photon in its hypothetical restframe. Can a mass have an arbitrary velocity ##v < c## relative to the photon?
 
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  • #2
timmdeeg said:
Now consider a photon in its hypothetical restframe.

There isn't one. That's the whole point of the FAQ.
 
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  • #3
timmdeeg said:
Now consider a photon in its hypothetical restframe.
There is no rest frame for a photon, hypothetical or otherwise.

It is possible to conjecture a scenario where photons have rest frames, but such a conjecture would be science fiction, not science. And it definitely would not be an allowed topic for discussion on PF. Thank goodness,
 
  • #4
I think of another scenario to deny rest frame of a photon. The rest frame is defined as momentum of system, say a photon, is zero there. By the relation E=pc energy is also zero. A photon vanishes in its rest frame. When we move against this photon vacuum at the rest frame, photon would get momentum and energy, and revive. But we have not observed such generated photons from vacuum by Lorentz transformation.

As a digression of the question a photon may be not massless perfectly but has a tiny tiny mass following the line as once thought massless neutrionos are now believed to have mass. Neutrino and photon with mass have rest frame. Even in this digression massless particle, if it exists, has no rest frame.
 
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  • #5
PeterDonis said:
There isn't one. That's the whole point of the FAQ.
Sure. To recognize this by himself I was hoping the question "Can a mass have an arbitrary velocity ##v < c ## relative to the photon? " should be helpful.
 
  • #6
timmdeeg said:
To recognize this by himself I was hoping the question "Can a mass have an arbitrary velocity v<cv < c relative to the photon? " should be helpful.

But you posted in the original FAQ thread, not the thread where I moved his post. So I thought you were responding to the original FAQ.
 

1. What is the restframe of a photon?

The restframe of a photon is the frame of reference in which the photon appears to be at rest. This means that in this frame, the photon's energy and momentum are both equal to zero.

2. Why is the restframe of a photon important?

The restframe of a photon is important because it allows us to understand the nature of light and its behavior. It also helps us to make accurate measurements and predictions in the study of physics and cosmology.

3. How is the restframe of a photon determined?

The restframe of a photon is determined by measuring its energy and momentum in different frames of reference and finding the frame in which they both equal zero. This can be done using the principles of special relativity.

4. Does the restframe of a photon change?

No, the restframe of a photon does not change. It is a fundamental property of the photon and is independent of the observer's frame of reference.

5. How does the concept of the restframe of a photon relate to the speed of light?

The speed of light is constant in all frames of reference, including the restframe of a photon. This is a fundamental principle of special relativity and is essential in understanding the behavior of light.

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