posted
Well, Omega, is this about right or am I putting words in your mouth?
Yes.
What would it take to actually slow light down? An increase in the mass of the universe?
Well, the speed of light is one of those fundamental constants of the universe. Why it would change would depend on why it's a fundamental constant to begin with, which is more of a philosophy question.
-------------------- "This is why you people think I'm so unknowable. You don't listen!" - God, "God, the Devil and Bob"
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And doesn't light travel at differing speeds according to the conditions present and whatnot?
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Cartman
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posted
What you're thinking of is the refractive index of various transparent media (glass, water, etc). Relativity concerns the speed of light in vacuum, which is an absolute limit. Gravity has no influence on the rate of propagation, it only affects the direction light travels in.
Light can be slowed artificially by something called a Bose-Einstein condensate -- basically a bunch of particles cooled to a temperature near absolute zero, causing them to spread out and overlap (one of those weird quantum effects governed by Heisenberg's uncertainty principle).
[ August 12, 2002, 07:33: Message edited by: Colorful Cartman ]
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posted
Well, that's obviously what I meant. I just didn't want to bore everyone.
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Cartman
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quote:Originally posted by Colorful Cartman: What you're thinking of is the refractive index of various transparent media (glass, water, etc). Relativity concerns the speed of light in vacuum, which is an absolute limit. Gravity has no influence on the rate of propagation, it only affects the direction light travels in.
Out of curiosity, what happens to light travelling at right angles to said gravity source? i.e. If gravity can only affect the direction of light, shouldn't we be able to see black holes? But obviously we can't....so what gives?
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Cartman
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True, we can't see black holes directly, but we can detect their presence by observing how light behaves in their vicinity. Gravity is, in essence, a manifestation of the curvature of the fabric of spacetime -- matter bends the universe around itself, creating pits in the proverbial rubber sheet. General relativity describes this phenomenon better than I can, so I'll shut up before I venture too far into the realm of fuzzy logic. Anyhoo...
Near a black hole, the spacetime distortion is extremely severe and causes black holes to have, erh, weird properties. In particular, a black hole has something called an "event horizon". This is a spherical surface that marks the boundary of the black hole. Think of it as the radius of Doom(TM).
Suppose you're standing on the surface of a planet. You throw a rock straight up into the air. Assuming you don't throw it too hard, it will rise for a while, but eventually the acceleration due to the planet's gravity will make it start to fall down again. If you threw the rock hard enough, however, you could make it escape the planet's gravity entirely. It would keep on rising forever. The speed with which you need to throw the rock in order that it just barely escapes the planet's gravity is called the "escape velocity." As you would expect, the escape velocity depends on the mass of the planet: if the planet is extremely massive, then its gravity is very strong, and the escape velocity is high. A lighter planet would have a smaller escape velocity. The escape velocity also depends on how far you are from the planet's center: the closer you are, the higher the escape velocity.
Now, imagine an object with such an enormous concentration of mass in such a small radius that its escape velocity was greater than the speed of light. Since nothing can go faster than light, nothing could escape that object's gravitational field -- including light itself.
So you see, black holes are mostly harmless. Just don't get too close.
"Out of curiosity, what happens to light travelling at right angles to said gravity source?"
What in the world is that supposed to mean? The gravitational force propagates out from an object in all directions. How can you move at a right angle to that? It would be like saying you were moving at a right angle to a light bulb.
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posted
Tangent to the curvature of the gravitational field, perhaps?
-------------------- "This is why you people think I'm so unknowable. You don't listen!" - God, "God, the Devil and Bob"
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posted
BTW: The question might make more sense if it were phrased: Hey! Do gravitons propagate in a straight line?
I think, anyway. It's the only thing that makes sense.
If I'm right: Gravitons propagate (supposedly) in a wave/particle form, simultaneously. Thus, if you were in a really fast and tiny spaceship that could predict the peculiarites and picadillos of quirky graviton movement, you could move perpendicular to them. IF you could perform quantum tunneling, which is nothing like what is shown on Star trek: voyager.
That's if gravitons exist. I don't want to sound like a quack, but I don't think they do. Physicists don't have any physical proof for them, after all, even though they've been predicted by QM. We've managed to find smaller shit that hasn't even been predicted, but though they've actually been LOOKING for gravitons, they've never found one. Nor have they even found a TRACE of one.
I know logically that this doesn't mean they'll never find one, but...I think the theory of gravity needs some tuning up.
But, I don't think super-strings exist either. I'm weird.
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posted
TP: Even if the gravitons came out in straight lines, they'd be emitted in all directions. The only way to move at right angles to them would be to orbit the body in a circle...
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You know, all I was asking was what happens to light is moving directly away from the black hole, but still within the event horizon. i.e. light rays moving along the normal line, if you can visualise a black hole as a two dimensional circle (not the tangent line, the normal line)
If gravity can only affect the direction, but not the speed of light, then what does light travelling on the normal line do? Does it just pick a completely random direction to turn in order to stay within the event horizon? That seems a bit odd.
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