Try this one....

[chainfire]

(I was told this ages ago, and the answer - but I can't remember what it was, so lets see if you will get it)
You have a very long cord. You twist it around at a speed close to, but not reaching the speed of light. The end of the cord will be going faster that the speed at the centre (think of a whip - the end moves faster than the speed of sound). But nothing can go faster than the speed of light! How is it possible that the end of the cord is going faster than the centre (- "close to the speed of light") ?
I'm sorry if this question is a bit confusing, i'll try to clear up any queries, but I just remember being asked this question, so I might have wrote something wrong.

[fo3nix]

It won't be going faster than the speed of light, it'll just be going faster than the centre.

[bonsaimaster]

this was on QI and they said that when a whip is cracked the leather curls up more and more the at the end it creates a mini sonic boom and thats it going to the speed of sound (the question he asked was wat was the first thing to reach the speed of light (they said stuff like a plane that was alan davis!))

[chainfire]

tonyted: I was told that the end was moving faster than the speed of sound, but I may be wrong

Fo3nix: What about if the centre was going just a fraction less than the speed of light, therefore, the end should be going the same speed/faster than the speed of light

[fo3nix]

no, that's the "old" way of thinking about it, before Einstein.

if the centre is moving at 0.99c (99% the speed of light), then the outside could be moving at 0.999c.

[chainfire]

Ok, thank you for that.

[fo3nix]

It's confusing and illogical, but that's the way it is.

[chainfire]

I know. Sometimes you just have to accept something, whether or not it makes sense.

[fo3nix]

It has been proven. You can take particles and speed them up and they'll go faster and faster and faster, all the time getting closer to the speed of light. But they'll never quite reach it.

[chainfire]

just wondering, how can light reach that speed, but nothing else can? Also, I think I read somewhere that just after the big bang, matter moved faster than the speed of light: basic link (quickly googled): http://www.astronomycafe.net/qadir/q2554.html

[fo3nix]

GR doesn't explain things too well at that level. It fails when things get very heavy and very small.

As for light, well it's unique in that it doesn't "reach" it, it's always at that speed.

[stevie21]

And light has zero mass so doesn't get "heavier" at that speed?
Also, I've heard the same about the whip crack being a tiny sonic boom.

[fo3nix]

yea, the whip crack is a tiny sonic boom. but this speed is nowhere near the speed of light, so doesn't need any special relativity.

photons, the particles that make up the electromagnetic spectrum are, as you say, massless. only a massless particle can travel at the speed of light, and it'll always do so. any particles with mass (even very small mass) can get closer and closer to the speed of light, but will never quite reach it.

there are theoretical particles called tachyons that travel at speeds greater than the speed of light, but again can never quite reach the speed of light. but to them this means they can't quites slow down enough. however, these are very theoretical. it's just something allowed by some equations, but that's no real indication that they might exist.

[chainfire]

i'm guessing that all waves in the electromagnectic spectrum travels at the speed of light (in a vacuum), e.g. UV, Infrared, Radio, etc. Does anything else, apart from these waves travel at that spped.

[chainfire]

i'm guessing that all waves in the electromagnectic spectrum travels at the speed of light (in a vacuum), e.g. UV, Infrared, Radio, etc. Does anything else, apart from these waves travel at that speed.

[Zevon]

Theoretically gravitons travel instantaneously as gravity is instantly felt by two masses if one is suddenly brought into existence or destroyed, can be tested with matter/anti-matter annihilation.
Neutrinos are also massless but do not travel at light speed.

[fo3nix]

chainfire: yea, you're right. there's no difference between radio waves, x-rays, light, etc. apart from the frequency of the wave.

zevon: the graviton does not theoretically travel instantaneously. this was Newton's idea, but Einstein modified it to travel at the speed of light.

neutrinos are perhaps massless, perhaps not. there's not definite score with them yet. recent experiements like the super-K have shown them to be not massless.