[Capuchin]

Oh no, normal light will have a phase velocity faster than the speed of light if you have a material with a refractive index less than 1.

This means that the front edge of the group of photons moves faster than the speed of light, however, it's impossible to transfer information this way (at the moment) because the information is spread out over the whole group (this is the group velocity) (so you have to wait for the end of the group to arrive, which arrives at the speed of light). So it doesn't break any rules.

Particle accelerators routinely accelerate particles to something like 0.99c.

Tachyons might actually be the one thing that can move faster than the speed of light. These are theoretical particles that have not yet been observed. The theory is that while you cannot accelerate something beyond the speed of light, If something was created with a superluminal speed, then it could happily exist in that state forever. This is of course contraversial and nobody knows if they exist or not.

Edit: Yes curlyben, tachyons, but they might not even be real :)

[nindzha]

Is it true that if u circle around earth at some speed, u are younger than u would be at earth. I think its called a twin pharadox. Can someone explain in plain english.
Thanks.

[worthbeads]

What about black holes? In theory, you could say light, when being sucked into black holes, eventually reaches a speed of zero, so therefor, You could go the speed of some light right now. But there's probably some counter example you could give to prove me wrong. I really have no idea about what I am talking about.

[worthbeads]

Let me clarify and add at the same time. Is it possible to go as fast, or if not faster than light if:

1. light passing a black hole (not going directly at it) could be bent, eventually slowing the speed of light, making you faster than some light?

2. you yourself were sucked into a black hole (even though you would end up in quintillions of pieces)?

[Capuchin]

A black hole is no different than any other massive object in space, it is just so dense that there is a point called the event horizon, past this point we have no idea what happens. Physics may be totally collapsed. The gravity isn't any stronger or greater than any other object of that mass, it's just small enough that the event horizon is OUTSIDE the object.

We are talking about moving faster than the speed of light in a vacuum. There are materials we have on earth that can slow light to a few mm/s, I can easily run faster than that, would you say I can run faster than the speed of light?

[Lord_Darkclaw]

I'm curious as to why light travels at the speed it does - I've had a quick look on Google but the answer seems to be "it just does". :confused:

There must have been a point in time before the speed of light was set, which makes me wonder if the mechanism that set the speed of light could be reproduced... could it be used to change the properties of light? Trippy thought. :)

[Capuchin]

Massless particles always move at the speed of light :)

(Tachyons move faster than the speed of light, because they have imaginary mass)

[Capuchin]

I don't think it's right to say that light decelerates to 0 within the event horizon, worthbeads, you're treating it like a normal particle.
It merely follows the curve of spacetime, which is curved in such a way that light cannot navigate a path to a point outside the event horizon.

Another consequence of quantum mechanics is that light can move faster than the speed of light over very short distances, it only moves at the speed of light on average.

It may also be possible to make a photon move faster than the speed of light between Casimir plates. Thse are plates that are brought together such that there is less than an atomic diameter between them. The vacuum between these plates is perfect, and may even not contain Zero-point energy. If there is no Zero point energy, the vacuum will be "more perfect than a perfect vacuum", and so light will be able to move faster through it. However it is not possible to measure experimentally at the current time, and so is theoretical.

[NeedKarma]

How timely
http://science.slashdot.org/science/.../0210240.shtml

[Capuchin]

That looks like what I stated before - the phase velocity is faster than the speed of light, but the group velocity is not, so you cannot transfer information this way.

But, like that article says, I'd like to see the paper first :)

[worthbeads]

I have an interesting question. Assume you are in a room covered in mirrors (all walls, floor, ceiling). You yourself are covered in a material that is 100% reflective (the mirrors are also 100% reflective). In the perfectly reflective room, you strike a match. Assuming your body, the match, and the mirrors do not absorb light and only reflect it, would the room stay lit long after the match went out? Would there be a limit on how bright it would be inside the room?

[Capuchin]

Your eyes would absorb photons in order to see them, so, do you want to go into "if you light a match in a perfectly mirrored room, but nobody is there to see it, is it lit up"? :P

Also, any gas in the room would also attenuate the light fairly quickly.

[worthbeads]

I have an interesting question. Assume you are in a room covered in mirrors (all walls, floor, ceiling). You yourself are covered in a material that is 100% reflective (the mirrors are also 100% reflective). In the perfectly reflective room, you strike a match. Assuming your body, the match, and the mirrors do not absorb light and only reflect it, would the room stay lit long after the match went out? Would there be a limit on how bright it would be inside the room?

I am aware eyes absorb light. Just assume no person is in the room.

[Capuchin]

Okay well the atmosphere in the room absorbs it then, if you had perfect vacuum, then the brightness in the room would be proportional to the amount of time you left the match lit for as long as forever.

[worthbeads]

Would it keep getting brighter and brighter, with no limit?

[Capuchin]

Until the fire runs out of fuel.

[johnzule]

Pardon if this is old news...

blsb.html

Social Ecology Eclectic : Light exceeds its own speed limit, or does it?

[Capuchin]

Yes, I did mention this earlier in the thread. There is no evidence that information can be transferred faster than light using this method.