Subject: Inflation!
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Posted on: 2013-02-26 17:05:00 UTC

(I just finished a 9-week astronomy course with Coursera, so...)

We observe from the cosmic microwave background ratiation ("the background temperature of the universe") that the energy levels in our bit of space - barring minor fluctuations like galaxy clusters and such - are remarkably uniform. Not completely uniform - there's fluctuations in the CMBR, which correspond in size to the expansion of the universe since the moment space became transparent.

[Quick explanation of this: If we imagine a bit of space one light-year across, which suddenly begins emitting randomised light across itself while expanding - and that one year later it has reached two light-years across - the light moving around in there will not have had time to cross the whole distance. Therefore, while in a small area of this space the temperature/light energy will have averaged out, there is no causal connection between the two sides of our 'bit of space' - they can't average with each other, so any imbalance when we set the light free remains present]

Unfortunately, the size of our observable universe (about 46 billion light-years, I think) is such that, were it to have been expanding steadily since the Big Bang, at the time space became transparent there wouldn't have been enough time for points on opposite sides of what we now see to have averaged out. Therefore, we ought to see wild imbalances in the CMBR, where very early fluctuations were preserved.

We don't. Therefore, it is hypothesised that very early in the universe's life, the whole thing expanded massively, meaning points which had already averaged out were suddenly too far away to have done so, were it not for this inflation.

But... it was proven last year that we (almost certainly) live in an infinite, flat universe. That means it was always infinite... just more compressed (that's how infinity works, I'm afraid). Which means that despite inflation, there are still (sigh) infinite reaches of space which did not have time to average out... and thus could have quite, quite different energy levels.

Of course, we do know that they're far beyond what we can see... which is quite a lot, really.

hS, astronomy!

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