Dandy wrote:
What makes you so sure that the physical properties of the universe itself prevent anything travelling beyond the speed of light? Especially by the given background, that just last week it was in the news, that scientists succeeded in "beaming" (dematerialisation, transport, rematerialisation) single atoms over a short distance. But aside from that I was always wondering if it really should be impossible to exceed light speed.
Yes, it is. For anything material, and on average, that is; it is quite easy to demonstrate that shadows can easily move faster than light. Other people have slowed light to a near standstill, and then used quite clever tricks to temporarily transmit information across the 'slow light zone' faster than the reigning speed of light in that medium.
There is a way for matter to go faster than light on average, but it involves a cheat: think of the Cerenkov-effect, better known as the blue glow surrounding any bassin-based nuclear fission reactor. Electrons moving faster than the speed of light in water cause a shockwave very similar to an airplane exceeding the speed of sound. The excess energy is radiated away in the form of the blue glow. This also means that if tachyons (hypothetical faster-than-light particles) were real, and they move through space, they would produce (very visible) Cerenkov-like shockwaves, slowing down and down and down until their speed was infinitesimally higher than c.
All I know about black holes implies that exceeding light speed must be physically possible: If the gravitation of an black hole is really that big that even its own light can't escape from it, then it seems logical to me, that, if you're caught by the gravitation of this black hole, you will be accelerated in the direction of the centre of this gravity. As this gravity is that strong, that even light can't escape from it, it is logical that you will be accelerated so much , that you exceed light speed before reaching the surface of this black "hole".
Black holes are tricky buggers. For one thing, you shouldn't think of them in terms of ordinary objects, as this is the surest way of tying your brain in knots. Black holes do not attract light, they mearly bend space to such an enormous extent that what we think of as the normal straight travel path of a photon curves inward on itself, and becomes a circle. It still moves at c, but since its travel path is no longer pointing at us, we never see it either. The point where the curvature becomes (mathematically) infinite is known as the event horizon, and nothing bigger than an atom (and probably not even something this big) will ever get there. The rest is torn to pieces by huge gravitational tidal forces. I recall that for an outsider's point of view, it would even take an infinite time for that atom to actually reach the horizon.
There's tons more to be said about black holes (you can measure their density, which, believe it or not, becomes
less the more massive they are, to the point where they'd float in water or even air), but suffice to say that you will never exceed c anywhere during this final and very lethal trip of going to a black hole.
