Speed of a photon in one frame as viewed from another frame

  • #1

Summary:

What would be the speed of a photon in a beam of photons wrt another photon in the beam.

Main Question or Discussion Point

According to the 2nd postulate of Special Relativity, speed of light in vacuum is the same in all inertial reference frames.

If I take a beam of photons and see the other photons in the beam from a frame of reference of a single photon, do they look stationary or moving at the speed of light? Also, as the photon is itself moving with the doped how fast would the surrounding seem to move?
 

Answers and Replies

  • #2
Ibix
Science Advisor
Insights Author
6,641
5,408
As per the second postulate, the speed of light is the same in all inertial reference frames. Therefore an inertial reference frame in which light is at rest is a contradiction in terms. So there is no answer to your question - it is based on a faulty premise, namely that there is such a thing as the "frame of reference of a single photon".
 
  • Like
Likes Saptarshi Sarkar and vanhees71
  • #3
PeroK
Science Advisor
Homework Helper
Insights Author
Gold Member
13,780
6,268
Summary:: What would be the speed of a photon in a beam of photons wrt another photon in the beam.

According to the 2nd postulate of Special Relativity, speed of light in vacuum is the same in all inertial reference frames.

If I take a beam of photons and see the other photons in the beam from a frame of reference of a single photon, do they look stationary or moving at the speed of light? Also, as the photon is itself moving with the doped how fast would the surrounding seem to move?
There are no inertial frames moving at ##c## with respect to other inertial frames. In particular, there is no inertial frame moving along with a beam of photons.
 
  • Like
Likes Saptarshi Sarkar
  • #4
Mister T
Science Advisor
Gold Member
2,575
829
If I take a beam of photons and see the other photons in the beam from a frame of reference of a single photon,
Imagine chasing that photon in an effort to catch up to it. No matter how fast you chase after it, it will forever recede from you at speed ##c##.
 
  • Like
Likes Saptarshi Sarkar
  • #5
Nugatory
Mentor
12,855
5,503
Imagine chasing that photon in an effort to catch up to it. No matter how fast you chase after it, it will forever recede from you at speed ##c##.
And anyone watching you chase the flash of light, no matter their state of motion, will find that you are moving at less than ##c## while it is moving at ##c##.... so no surprise that you can’t catch it.

(Of course @Mister T knows this - the comment is for others reading this thread)
 
  • Like
Likes Saptarshi Sarkar

Related Threads on Speed of a photon in one frame as viewed from another frame

Replies
5
Views
1K
Replies
11
Views
2K
  • Last Post
Replies
13
Views
3K
  • Last Post
Replies
1
Views
16K
  • Last Post
2
Replies
45
Views
5K
  • Last Post
2
Replies
31
Views
14K
Replies
60
Views
7K
  • Last Post
Replies
16
Views
3K
Replies
29
Views
4K
Replies
3
Views
6K
Top