# B Time Dilation and Length Contraction for Mediums

1. Dec 15, 2017

### Mohammed Ayaz Quadri

Hello I am new here and I am just Junior college student. So please use simpler terms. I need to know that does relativity work for mediums like air and water. I mean the equations of time dilation and length contraction, do they work for other mediums. If so shall I take C as the speed of light in vacuum or thr speed at that particular medium? Thank You.

2. Dec 15, 2017

### Staff: Mentor

Hi Mohammed, welcome to PF!

Relativity still works in a medium, and the c that you use is the speed of light in vacuum. The invariant speed is not changed inside a medium.

In fact, inside a medium, particles may exceed the speed of light in the medium as long as they do not exceed c.

3. Dec 15, 2017

### Ibix

To expand slightly on what Dale said, the quantity c in the Lorentz transforms and length contraction and time dilation formulae is an invariant quantity that is the same everywhere for everyone. It also happens to be the speed at which light travels in a vacuum. That's not actually a coincidence, but as far as relativity is concerned it's just an interesting fact.

So that means you always use c in the Lorentz transforms, not whatever the speed of light is in whatever medium you happen to be in.

4. Dec 15, 2017

### Mohammed Ayaz Quadri

Ty everyone. I didnt expected so quick answers. Can you help with this: I have heard that very few things found are traveling at a speed more that c. How far is this true? Ty

5. Dec 15, 2017

### Ibix

Nothing travels faster than c.

There was some brief confusion about neutrinos, but it turned out that there was a loose cable in the experiment's time recording apparatus. And there are purely hypothetical particles called tachyons, but they've never been detected. I should point out that I don't even know if there's a respectable theory that predicts tachyons, or if they're just science fiction. You do sometimes see them mentioned, though.

Edit: as Dale said, things can exceed the speed of light in a medium (look up Cerenkov radiation, which is a side-effect of this). But nothing exceeds c.

6. Dec 15, 2017

### phinds

NOTHING travels at more than c. Period.

EDIT: Ibix beat me to it.

7. Dec 15, 2017

### Ibix

My reply speed gets close to c.

8. Dec 15, 2017

### Orodruin

Staff Emeritus
You can increase it by dieting until you are massless! ;)

9. Dec 15, 2017

### phinds

And my brain is often in a vacuum, so together we've got it covered.

10. Dec 17, 2017

### Mohammed Ayaz Quadri

Ty. Everyone is very helpful here. Some interesting conversation going on, eh?