Big bang/Talk

"distant galaxies can actually move apart faster than the speed of light"

I admit that I am not a physicist, but this really surprises me. Is this actually true?

Yes - nothing can travel "through" space faster than the speed of light. However if the space itself is expanding then two objects which are at rest (relative to their local environment) can move away from each other at speeds greatly in excess of the speed of light. To conceptualise this - imagine a balloon with dots drawn all over it. Blow up the balloon. Now none of the dots have moved relative to the balloon itself, yet they are now further apart from each other. Read Lawrence Krauss's book "The Physics of Star Trek" - he explains this beautifully (exploitation of this was the justification for how the warp drive worked) - MMGB

In the [observable universe]? (that sphere around us of radius n light years, where n is the age of the universe in years) I do not think it is possible for two objects to recedes faster than the speed of light. Due to the initial inflation the universe is much larger than the observable universe and perhaps the example here is the relative motions of galaxies that are farther apart than n light years and so are not mutually observable -- however such objects can never be seen from each other and in generaal it is impossible for either to have any influence on the other ever (I think). --Eob

No, objects in the observable universe can be receding faster than the speed of light. It works because what we see lies in the distant past - just because the objects are too far away for light to reach us now, doesn't mean they were when the light was emitted.

I see. But what does "now" mean? Under relativity there is no concept of simultaneity.

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Again I have to prefix this with "I am not a physicist and I don't play one on TV", but...even with the "balloon" analogy, I am having a hard time believing that it is possible for the dots on the balloon to move apart faster than the speed of light under the constraints of relativity. The fact that they are locally "at rest" doesn't really mean anything anyway, does it? After all, in Einsteinian space-time there is no absolute sense in which anything is at rest anyway.

I am not saying that it is wrong that galaxies can move apart faster than the speed of light--but it is completely alien to my (admittedly limited) understanding of relativistic physics. Egern

I'm not sure of the which is right, but perhaps this issue is being conflated with the apparent superluminal velocity of distant galaxies? [1] -- DrBob

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Replaced the following

Although the Big Bang Theory is widely accepted, it probably will never be proved; consequently, it leaves a number of tough, unanswered questions.

with

The Big Bang Theory is now the accepted scientific view of the origin of the Universe.

because it gave the wrong impression -- no scientific theory is ever fully "proved". Statements like this just gives fodder to the creationists and their ilk. (Woops, stepping a little outside NPOV there). Perhaps the original author could elaborate on the "number of tough, unanswered questions" -- Eob