# What happens if you go faster than light?

1. Mar 27, 2005

### mathlete

Let's say you are in water where light travels at a speed of $$\frac{c}{n_w}$$ where $$n_w = 1.5$$ and you travel faster than this speed - what happens? What do you see?

2. Mar 27, 2005

### whozum

The laws of the speed of light apply to any medium, not just vacuum. If the speed of light were 1m/s in a certain material, that speed would be unattainable in that same medium.

3. Mar 27, 2005

### ZapperZ

Staff Emeritus
Yes, it can. That's the whole principle behind the Cerenkov radiation - charged particles moving in a medium at a faster velocity than light in that medium. Huge detectors are used to detect neutrinos this way.

Zz.

4. Mar 27, 2005

### 1123581321

you will die, no seriously, you will. you will be of infinite weight and will require infinite energy to move, and will die. talk about letting yourself go. it is impossible to go faster than light, no matter what (unless you are a universe that just happens to be expanding, then, i read, it is possible. i don't know exactly how, but i will trust my reading skills

Fibonacci

5. Mar 27, 2005

### ZapperZ

Staff Emeritus
This is a faulty application of relativistic mass. Take a look at how it is applied with respect to ANOTHER observer. Pay attention to the fact that a person does NOT see his/her mass increasing since he/she is always in the same proper frame and does not observe his/her mass moving.

Zz.

6. Mar 27, 2005

### 1123581321

you didn't get that 'physics guru' for nothing, did you Zz.

Fibonacci

7. Mar 27, 2005

### chroot

Staff Emeritus
Fibonacci,

Please refrain from responding to question unless you are quite sure you are giving a correct answer.

- Warren

8. Mar 27, 2005

### whozum

Isn't that more of an exception than the rule?

9. Mar 27, 2005

### aek

offcourse it's an exception

10. Mar 27, 2005

### whozum

Then my answer to the OP is more or less correct. :D

11. Mar 27, 2005

### chroot

Staff Emeritus
No, it wasn't. It was completely wrong.

- Warren

12. Mar 27, 2005

### whozum

Care to explain why?

13. Mar 27, 2005

### chroot

Staff Emeritus
You said that objects cannot exceed the speed of light in a medium. That is completely false.

- Warren

14. Mar 27, 2005

### whozum

Wont argue with you. How do objects go faster than the speed of light in a medium?

15. Mar 28, 2005

### KingNothing

By covering a greater distance in the same amount of time. I suspect you are looking for a good reason why they 'can'. Well, there is simply nothing that prevents something (often an electron) from doing so. Laws of physics are generally written according to what restricts movement or any other characteristic. It's just the way we interpret them - if it's not restricted to move a certain way, then it can.

Cerenkov radiation does not need to be explained here - http://en.wikipedia.org/wiki/Cerenkov_effect
and scroll to "Physical Origins"

Last edited: Mar 28, 2005
16. Mar 28, 2005

### whozum

Isn't it restricted by the same reasons its restricted in vacuum?

17. Mar 28, 2005

### chroot

Staff Emeritus
whozum,

No. The speed of light in vacuum is a universal 'speed limit,' but the speed of light in an arbitrary medium is not.

- Warren

18. Mar 28, 2005

### hemmul

"in our world" there exists a universal speed limit c. From the Maxwell's equations we see that in vacuum light wave propagates with c. In the media this velocity is reduced due to existing wave impedance, but this doesn't mean that a universal constant is changed ;) just the EM wave propagates slower.

19. Mar 28, 2005

### ZapperZ

Staff Emeritus
I'm not sure what you mean by an "exception"? You said that NOTHING can travel faster than light in a particular medium with index of refraction greater than vacuum. I said no, this is not true. A neutrino, and the charged particle that it generates when it collides with other particles, CAN travel faster than light in a particular medium, such as water, ice, quartz plate, etc. This is how we detect neutrinos (see SuperKamiokande, MINOS, AMANDA, ICE CUBE, quartz plate in the linear accelerator that I work with, etc...).

This isn't an "exception" nor the rule. It is ALLOWED.

Zz.

20. Mar 28, 2005

### ZapperZ

Staff Emeritus
This is because in a dispersive media other than a vacuum, we define "speed of light" as being the GROUP VELOCITY. In a vacuum, the group velocity and the phase velocity are IDENTICAL. When light enters a medium, these two are dispersed (thus, the term dispersive medium) and they are no longer identical.

Again, it is instructive for many people learning this subject to ALWAYS go back and figure out how we define things, and how certain things are measured. This is especially true when we get to the really exotic things and properties, such as "stopping light" in a medium to 0 m/s. Why would that be any different than having light falls onto a black piece of paper? That's stopping it, isn't it?

To appreciate such things, one must learn the intrinsic properties of light and how we define/measure these properties.

Zz.