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The Question

(Submitted August 05, 2010)

I have heard that WMAP proved that the universe is spatially flat with a very high accuracy. And I know from Freidmann models that the flat universe is spatially infinite. So my question is, can we say that WMAP proved the spatial infinity of the universe? And does this contradict with the fact that the universe is temporally finite; it's age is 13.7 billion years old?

The Answer

No. WMAP showed that inflation must have happened, so the part of the Universe that we can see was driven to flatness by the rapid expansion. There could be much more of the Universe out there beyond what we can see, but we cannot know anything about it because it is not causally connected to us (basically it is too far away). The finite age of the Universe is just our measurement of how much time has elapsed since the start of inflation and the Big Bang and has nothing to do with whether or not the Universe is spatially infinite. It does determine how much of the Universe we can see.

Jay and Jeff
for Ask an Astrophysicist

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