# Is it possible that the speed of light has changed since the beginning of the universe? [duplicate]

Is there any research or publication in Modern Physics that considers the possibility that the speed of light has changed since the Big Bang, and not remained constant (as what we know it today)?

By changed, I mean either gradually or abruptly, though I guess that the former makes more sense.

Now, I am guessing that the answer to this question might be more of "a matter of terminology".

For example:

We can say that the speed of light hasn't changed in the perspective of everyone who is within the given space, but since this space by itself has expanded, anyone theoretically "outside it" will "see" that light is in fact covering a larger distance per time unit (larger than what it used to when the given space was smaller)... Or we can say that it has slowed significantly, while the universe itself hasn't expanded at all.

On the other hand, I might be speaking nonsense here, so I'd be happy if one of you out there (or here) could enlighten me on this...

## marked as duplicate by John Rennie, Jon Custer, Qmechanic♦Nov 21 '17 at 18:04

• Possible duplicate of Has the speed of light changed over time? – user121330 Nov 21 '17 at 17:12
• – John Rennie Nov 21 '17 at 17:15
• I don't think "a change in the speed of light" has a physical meaning. A change relative to what? Say, relative to the size of the Earth orbit. However, the size of the orbit depends on the mass and the mass depends on the energy as in $E=Mc^2$, so a change in the speed of light would also change the size of the orbit. The speed of light simply is a convention of how we measure things, but ultimately it a 1:1 symmetry relation between space and time: $c=1$ as in 1 light second per second where 1 meter is defined as 1/299,792,456th part of 1 light second. – safesphere Nov 21 '17 at 18:20
• I personally found several papers on cosmology where changing c is discussed. At least they were from professionals. If I recover my pdf I will post the refs here. – Alchimista Nov 21 '17 at 19:11