Hi, I have a question which to many may seem quite stupid but it honestly has been perplexing me for a while now. I'm actually not sure if this is the correct place to post this but the question does seem to be based on the theory of relativity so here goes.(adsbygoogle = window.adsbygoogle || []).push({});

I think I'm correct in supposing that a photon i.e light moves at a constant speed in vacuum (approx 3 x 10^8 m/s) relative to all frames of reference. That is the speed of light will be measured to be the same by all observers in uniform motion regardless of their velocities.

Now 2 thoughts seem to arise in my mind from this.

First, if we consider the frame of reference of a photon. Now this photon moves at the speed of light relative to all reference frames. So, from the reference frame of the photon, all other frames of reference will seem to be moving relatively at the speed of light since it should be impossible for the photon itself to determine whether it is in moving or whether the other frame of reference is in motion.

So my question mainly is that from the point of view (or frame of reference, if you prefer) of the photon, do all other particles (in any arbitrary frame of reference) seem to be massless? The theory of relativity prevents any object with non zero rest mass from moving at the speed of light from any reference frame so if all other particles move at the speed of light relative to the photon, then to the photon they should appear to have zero rest mass.

The second question which may be an even sillier one is that in the frame of reference of one photon, what would the speed of other photons appear to be?

I really don't know if what I have proposed is correct or not? Could someone please tell me if there is an inconsistency in my logic? And please forgive me if there is something really fundamental which I am unaware of. I am new to relativity so it is very likely that I have missed out something. Thanks.

**Physics Forums - The Fusion of Science and Community**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Invariance of speed of light

Loading...

Similar Threads - Invariance speed light | Date |
---|---|

A How is the invariant speed of light enocded in SL(2,C)? | Dec 23, 2016 |

I On the invariant speed of light being the upper speed limit | Oct 30, 2016 |

I Does time dilation cause the speed of light to be invariant? | Feb 28, 2016 |

Invariance of the speed of light | Nov 12, 2014 |

The Principle of Invariant Light Speed | Sep 14, 2014 |

**Physics Forums - The Fusion of Science and Community**