# Light speed

1. Aug 9, 2004

### Tree Penguin

Is the top speed of light emitted by something the velocity of the light emitter + lightspeed or just lightspeed?

Last edited: Aug 9, 2004
2. Aug 9, 2004

### Staff: Mentor

The speed of light is always C. The speed of the emitter is irrelevant.

3. Aug 9, 2004

### Staff: Mentor

speed of light is source independent

The speed of the light emitter does not add to the speed of the light itself. The speed of light is a constant independent of the speed of the source or the detector.

4. Aug 9, 2004

### Gonzolo

That's why we need special relativity.

5. Aug 10, 2004

### Tree Penguin

Can yuo explain that to me (i am a physics noob)?

I read about galaxies moving away from us at near lightspeed, is the lightspeed relative to the galaxy's own velocity (as if it where stuck in one place). I guess so as i understood all movement was relative. (might that be special relativity?)

Tell me and correct me if i said anything stupid. Thanks :).

6. Aug 10, 2004

### kuenmao

Special relativity states that the speed of light in vacuum is a constant "c" to any observer. So, the "lightspeed" is relative to everyone.
You'll need to learn special relativity to understand the idea :)

7. Aug 10, 2004

### Prometheus

Notice the last 3 words. The speed of light is constant, within the perception of any given observer.

Were there differences in the rate of motion through space of light emitted from various sources, the perception of any observer would be that the light moves at the same speed as all other light, due to the compensation factor of the perception of motion through time. The speed of light is constant in space-time.

8. Aug 10, 2004

### Tree Penguin

I think i will have to look up general relativity. For some reason something clicked inside my brain but it's still not entirely clear to me.

Thanks!

9. Aug 10, 2004

### Staff: Mentor

You are welcome to discuss your personal theories and opinions in Theory Development, but not here in the main forums. You already have a thread going on this very topic: https://www.physicsforums.com/showthread.php?t=31953

10. Aug 10, 2004