# Question about the effect of c on light

1. Jul 5, 2009

### crapola77

hi i have a loose knowledge of physics and was wondering if anyone could help me with a question i have... IF one was able to travel the speed light, in the same orientation of a beam of light, would that light beam become matter from your frame of reference? or would it speed away from you at 186 million miles an hour?

2. Jul 5, 2009

### Naty1

That's the question Einstein asked himself at age 16.
At about age 26 he had the answer: The special theory of relativity: you cannot catch up with light. No matter how fast you move, light is still always observed at the same "c". It's one of the strangest classical phenomena, not at all intuitive, but has been experimentally verified with great accuracy.

3. Jul 5, 2009

### crapola77

got it, so lets say the sun collapses into a black hole in a couple minutes and i begin to fall into it with a flashlight, my flashlight still works?

4. Jul 5, 2009

### crapola77

or rather if i fall backwards into the blackhole at nearly the speed of light,or even the speed of light, my flashlight still sends a beam of light away from me at c?

5. Jul 5, 2009

### DaveC426913

Yes. No matter what fraction of the speed of light you achieve with respect to some external reference point, you will experience nothing untoward happen to your flashlight. Light will leave it at the speed of light.

6. Jul 5, 2009

### crapola77

ok, so if your external frame of reference by which you measure your speed to be c is lets say a star of a beam light, does the light which travels toward your eyes still travel toward you at the speed of light, despite the fact that you measure yourself traveling away from the light source at the speed of light

7. Jul 5, 2009

### DaveC426913

You cannot travel at the speed of light. You can only approach arbitrarily closely.

But yes, the beam of light will approach you at the speed of light.

8. Jul 5, 2009

### crapola77

ok ok but not considering that, because the fact that you can't subtract your velocity from light's at all seams to be the point, if you travel even 1mi an hr away from light it does not take the effect of allowing you to measure the speed of light going 1mi an hour less than it did when you were at rest. i assume its impossible to add you velocity with light's as well, which is to say if you travel at the speed of light towards a light source its light still travelstowards you at c

9. Jul 5, 2009

### Bob_for_short

In fact, in a transparent medium with n>1 the light travels with v<c, and there are particles faster than that (charged particles radiate the Cherenkov's radiation, neutral ones do not radiate).

10. Jul 5, 2009

### crapola77

whats n, sorry

11. Jul 5, 2009

### Bob_for_short

N is the medium refraction index. Used in the Snell equation, for example.

12. Jul 5, 2009

### DaveC426913

Whether you move away/toward the source of the light at 1 mile per hour or 669 million miles per hour, you will measure the speed of the light form the source at c.

The reason this is possible is that time passes differently in the two reference frames. At 99.9% of the speed of light, your frame of reference is basically slowed down by 99.9% (an over simplification) so that the light is still measured by you as c.