[bezoar]

The speed of light was the speed at which my ex boyfriend drove his car.

[OmnipotentOne]

SO the speed of light is 670million mph, and that is a fixed speed, so unless we somhow go faster that speed will alwasy be fixed.

[qpan]

I thought the speed of light was 299 792 458 m / s ?

Also, no matter how fast or slow you go, the speed of light still remains constant (it is impossible to catch up with a photon).
If you travel "faster" than light, what actually happens is time majorly dilates to compensate for the fact that you observe light to be travelling at 299 792 458 m / s (so you effectively travel back in time, if it is possible and assuming you could actually travel "faster" than light).
A simple thought experiment to prove this:
Due to relativity, we are entitled to say that we are, at this instant travelling faster than light in some reference frame (and everything around us is also travelling faster than the speed of light at a similar speed to us). Now as we are theoretically travelling "faster" than light relative to a point in space,  we can measure the speed of light in a vacuum, and it is 299 792 458 m / s, as proved by numerous scientists. We are perfectly entitled to do this as there is no such thing as absolute speed -  and this simple experiment shows that the speed of light is the same for everyone, even if they are travelling "faster" than the speed of light relative to some point in space. In our experiment, the reference point would have to actually be a moving point in space travelling faster than the speed of light away from us. We would be travelling backwards in time relative to this point, but as our surroundings are travelling at similar speeds to us, we are NOT travelling backwards in time relative to our surroundings.

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

[Ylide]

Just to clarify:

The speed of light is fixed in it's medium.  It's very important to note the distinction.  The speed of light in a vacuum is 2.9979x10^8 m/s only in a vacuum.  It is slower in most other media (gases like atmospheres, liquids, clear solids) and faster in a select few.  (can't remember what media they used to get light going faster than c)

Either way, no matter what the medium, you're still not going to, as gpan put it, catch up with a photon.

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[qpan]

I think they used caesium vapor to get light to travel faster than the speed of light in a vacuum.

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

[Ylide]

yea, that sounds right...I knew it was some metal vapor, but I couldn't recall which.  



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[C-guy]

quote:Either way, no matter what the medium, you're still not going to, as gpan put it, catch up with a photon.

I disagree. Certain radioactive materials emit particles going faster than the speed of light in water or air. This is what causes the Cerenkov effect.


Moving at the speed of light.

[chris]

Hi C-guy.

Can you please explain what the cerenkov effect is ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx

[C-guy]

This is the best site I could find in ten minutes.

http://nova.nuc.umr.edu/~ans/cerenkov.html [nofollow]

Moving at the speed of light.

[qpan]

quote:Originally posted by C-guy

quote:Either way, no matter what the medium, you're still not going to, as gpan put it, catch up with a photon.

I disagree. Certain radioactive materials emit particles going faster than the speed of light in water or air. This is what causes the Cerenkov effect.


Moving at the speed of light.

In a vacuum, nothing can catch up with a photon (as even if you were travelling faster than the speed of light relative to a point, relative to you the speed of light in a vacuum would remain constant- time itself would instead, warp).
Would anything actually be able to catch up with a photon in another medium though?


"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

[tweener]

Good question.  I don't understand the quantum mechanical explanation of why the speed of light in a material is slower than that in a vacuum.  If the beta particles in a nuclear reactor are emitted with a speed greater than that of light in water (but slower than in a vacuum), they might be able to catch a photon in the water.  Maybe.

After reading the link about Cherenkov radiation, I still don't understand how the beta particles interact with the water molecules.  The rotational energy of a water molecule causes radiation at 22 Ghz 30somthing GHz and a few other lines a little higher.  These frequencies are substantially below infrared and would not cause "blue" light.  I'm not saying it doesn't happen, I just don't understand the process.  A few minutes with Google would probably help a lot, but I'm too lazy.

----
John - The Eternal Pessimist.

[Ylide]

John:  A beta particle is basically a high energy electron.  When it collides with a water molecule, it will impart some energy to it.  This can cause an electron in one of the atoms in the water molecule to jump an energy level or two.  When it drops back down to its normal level, it will emit light of a certain energy.  Without doing the calculations, I'm guessing that energy corresponds to the frequency of blue light.  Find me the average energy of a beta particle and I'll do the calculations and settle the matter.

I'm guessing that any medium that would slow light to below 'c' would slow any other particle's travel speed as well.  If the photon is faster than 'c' in that medium, it would be just as hard to catch.  



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