Restframe of Photon: Explained

  • Context: Graduate 
  • Thread starter Thread starter timmdeeg
  • Start date Start date
  • Tags Tags
    Frame Photon Rest
Click For Summary

Discussion Overview

The discussion centers on the concept of the rest frame of a photon within the context of relativity. Participants explore the implications of defining a rest frame for massless particles like photons, examining theoretical scenarios and the limitations of such concepts.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants assert that the concept of a rest frame for a photon does not exist, emphasizing that this is a fundamental aspect of relativity.
  • One participant proposes a scenario where a photon could hypothetically have a rest frame, but they clarify that this would be more science fiction than science.
  • Another participant discusses the implications of defining a rest frame in terms of momentum and energy, suggesting that a photon would vanish in its rest frame, leading to contradictions with observed phenomena.
  • There is speculation about the possibility of photons having a tiny mass, drawing parallels to neutrinos, which could imply a rest frame for such particles, but this remains a digression from the main topic.

Areas of Agreement / Disagreement

Participants generally agree that there is no valid rest frame for a photon, but there are competing views regarding hypothetical scenarios and the implications of massless particles.

Contextual Notes

Limitations include the speculative nature of hypothetical scenarios regarding photons and rest frames, as well as the unresolved implications of massless versus massive particles in this context.

timmdeeg
Gold Member
Messages
1,584
Reaction score
372
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?
 
Physics news on Phys.org
timmdeeg said:
Now consider a photon in its hypothetical restframe.

There isn't one. That's the whole point of the FAQ.
 
  • Like
Likes   Reactions: vanhees71
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,
 
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.
 
Last edited:
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.
 
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.
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
1K
  • · Replies 1 ·
Replies
1
Views
542
  • · Replies 26 ·
Replies
26
Views
2K
  • · Replies 19 ·
Replies
19
Views
4K
  • · Replies 19 ·
Replies
19
Views
3K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 17 ·
Replies
17
Views
4K
  • · Replies 25 ·
Replies
25
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 16 ·
Replies
16
Views
2K