# If speed of light isn't a constant

1. Jan 6, 2009

### sganesh88

If speed of light varies with the reference frame, as the michelson-morley experiment wanted to show, what influence would it have on the modern physical laws? How would the universe look like from a physicist's point of view then?

P.S: If this question had already been asked and discussed in detail, could some knowledgeable folks guide me there? The search tool in physicsforums isn't that good, i feel.

2. Jan 6, 2009

### tiny-tim

Hi sganesh88!

It would leave the transformation laws (between the coordinates of one inertial observer and another) of the electromagnetic field unexplained …

they were correctly determined in the nineteenth century, and they were inconsistent with Newtonian space-time.

3. Jan 6, 2009

### Naty1

You would not be here...atoms would not form....no life...no matter except maybe subatomic particles....

4. Jan 7, 2009

### sganesh88

Can you elaborate? What does speed of light have to do with atom formation?

5. Jan 7, 2009

### Naty1

Light is electromagnetic radiation. If it's speed varied electromagnetic fields would pulse with as velocity changed...electrons would not know where they were supposed to be....

For other insights try Wikipedia:
http://en.wikipedia.org/wiki/Variable_speed_of_light
These are views different from the likely intent of your question...but raise all sorts of insights as well as further questions.

Last edited: Jan 7, 2009
6. Jan 7, 2009

### jambaugh

Remember that the speed of light we measure is a ratio of a distance traveled and a time duration. If one person claims this ratio varies then another can claim that, No it is distances and/or time which is being stretched and/or bent. So imagine a theory which allows the bending of space-time geometry and it already incorporates the variation of the measured values of the speed of light with respect to stretchable measuring rods and variable clocks because it is all relative as to whether you say your measuring rod stretched or light slowed down.

[edit: I forgot to mention that Einstein's General Relativity is such a theory and so it recasts varying speed of light as gravitational bending of space-time. You could also do the reverse and model the bending of light via gravity as refraction due to varying speed of light. I'm not sure how far this can be pushed. But as I recall you can view the varying metric of GR as a tensor expressing varying light speeds in various directions, in short view part of $g_{\mu\nu}$ an index of refraction tensor. This is all "off the cuff" and I'll think about it some more and post corrections later.]

The only other issue is whether you can define distances or time intervals independently of light i.e. by considering scales of fundamental non-photonic processes like nuclear decay electron mass, etc. Again there is a relativity here. Is light slowing down or is the charge/mass ratio of the electron changing thereby affecting the lengths of physical measuring rods?

It is the current convention to hold the speed of light in a vacuum as a numerical constant and use that constant to define lengths in terms of durations. We may then speculate as to whether, with this convention, the other fundamental constants vary over time and space.

Last edited: Jan 7, 2009
7. Jan 7, 2009

### jambaugh

Followup: Here's a paper treating weak-field gravity as if a refractive medium."http://arxiv.org/abs/gr-qc/0411034" [Broken]

Recall that the index of refraction is 1/speed of light in the medium. And the refractive-index tensor is used for an anisotropic medium (speed of light is different in different directions).

Last edited by a moderator: Apr 24, 2017 at 10:03 AM