I am puzzled with the following explanation of Max Tegmark:(adsbygoogle = window.adsbygoogle || []).push({});

http://space.mit.edu/home/tegmark/multiverse.html

Check bold Can a finite universe grow infinite?

From Mark Tranchant, mtranch2@ford.com, Tue Apr 15 03:41:08 2003

Q: Your Level I calculations rely on two assumptions:

A Big Bang approximately 14 billion years ago

Infinite space to play with

How do you reconcile these two - how do we get from a tiny expanding sphere to infinite space in finite time? Incidentally, congratulations for writing the first article I've read to use a number larger than a googolplex...

A: If space started out finite (curved up like a hypersphere, say), then it always remains finite. Conversely, if it is infinite now, it was infinite from the very beginning. For more details on this, check out Ned Wright's cosmology FAQ.A interesting exception to this is inflation (see next question), which can create something infinite out of something finite.

How can you make an infinite universe in a finite bubble?

From David Coule, David.Coule@port.ac.uk, November 29, 2003 19:39:41

Q: In the Level I case, where does it say that a spatially infinite universe is a prediction of inflation? There is suposedly a geodesic incompletness theorem of Borde, Guth and Vilenkin, gr-qc/0110012, that shows that only a finite time worth of inflation could have happened.So if the initial patch is finite there is still at present only a finite volume created. Garriga and Vilekin's philosophical mussings contradicts this result!

A:The trick is that you generically obtain an infinite universe even after a finite abount of inflation. The subtle trick involves the t=constant spatial hypersurvaces perceived by observers curving upwards in spacetime towards the infinite future time direction. Loosely speaking, the infinite future time direction gets warped into an infinitete space.Please see Garriga & Vilenkin 2001, Phys. Rev. D 64, 043511 and references therein for details.

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# Infinite Universe from finite bubble

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