Is this a postulate? I get the expansion of the universe, the addition of discrete bits of space time between me and a distant galaxy, until very distant parts of the universe are moving relative to me, faster than the speed of light. But the other sure seems like (giant steaming load of convenience) I think I get reasons why, because they don't have any other way to explain the size of the universe and so on. Just seems it would be much easier to say the universe is eternal and cyclical in nature, and call it a day!
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There are rules about things moving through space faster than light - there is no rule about space expanding faster than light.
As long as it can't be used to transfer information then there is no problem with relativity.
Martin Beckett
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The recession rates of cosmologically distant objects are not relative velocities, so there's no reason to compare them to the speed of light.
They can be defined as follows. Conceptually, imagine a chain of galaxies that leads to some target galaxy. Each galaxy along the chain has some small velocity relative to the galaxy before it. If you add all of those relative velocities together, that should give you the velocity of the target galaxy, right? However, velocities in relativity add in a special way; see the relativistic velocity addition formula. The cosmological recession rate is computed by instead just adding the relative velocities naively, without properly using relativistic velocity addition. That's why we should not be concerned that it can exceed the speed of light.
It's also worth noting that the relative velocity between cosmologically distant objects doesn't even have a unique meaning. You can just as well say that it is very high or that it is zero.
(Some text was adapted from one of my other answers.)
Sten
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