Wednesday, October 5, 2011
Congratulations to the physics Nobel laureates for being recognised for their discovery that the rate of expansion of the universe is increasing!
I was thinking, is there any way that we could have predicted that we would observe the rate the universe was expanding was accelerating, given only the fact that we are here to observe it? Or, given only the fact that we are here, plus a few common-sense assumptions?
So in principle, we could have found the universe was growing, shrinking, or staying the same size.
If it was staying the same size, it seems a bit much to think of it being created ex nihilo at some finite size, so either it would have to be infinite in space and time, or it would have to have started out long enough ago that it had time to grow to a particular size and lose all trace of ever having been growing. And by the principle of uniformitarianism – which is to say that our position is nowhere special – if we saw that it wasn't growing, we would have to assume that it stopped growing a looooong time ago. I think, given all that time, it makes sense that life would have started long ago, and spread throughout the universe, and changed things to suit itself, so that primitive life 'red in tooth and claw' like we have here would never have gotten started, and chances are we would not be here to observe the universe being the same size.
If the universe was shrinking, it would make sense that it was shrinking toward a 'Big Crunch' of some size. Now, we know all sorts of quantities that are conserved in the universe, and also that singularities are not really singularities, but emit radiation. So it would make sense from those observations that the Big Crunch would not be the end of the universe, but would be followed by a Big Bang, and that we were living in an oscillating universe that had most likely- uniformitarianism again- been through very many Big Crunches, and was really really old. And, it makes sense that in one of its previous cycles life would have gotten clever enough to pass information on to a future universe, information that would have given life a leg up early, so it spread throughout the universe, and changed things to suit itself, so that primitive life like us, etc. etc., and we wouldn't be here to observe the universe shrinking in this cycle.
So, chances are the universe has to be expanding for us to observe it.
If it is expanding and deccelerating, we don't have any good reason to expect it to stop deccelerating – which means eventually we would expect it to be shrinking instead of expanding – which gets us back to that oscillating universe we aren't around to see.
So I would suggest, given the uniformitarian idea that we aren't at any uniquely special time in the life of our universe, the optimistic idea that the conservation laws we see have broad validity, and the other optimistic idea that sentient beings are damnably clever and can figure out how to do all kinds of neat stuff, a universe that we are here to observe is most likely to be a universe that is expanding at an accelerating rate. IMHO.
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