2005 : WHAT DO YOU BELIEVE IS TRUE EVEN THOUGH YOU CANNOT PROVE IT?

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Professor of Physics and Director of the Institute of Cosmology at Tufts University
Physicist; Institute of Cosmology, Tufts University

There are good reasons to believe that the universe is infinite. 

If so, it contains an infinite number of regions of the same size as our observable region (which is 80 billion light years across). It follows from quantum mechanics that the number of distinct histories that could occur in any of these finite regions in a finite time (since the big bang) is finite. By history I mean not just the history of the civilization, but everything that happens, down to the atomic level. The number of possible histories is fantastically large (it has been estimated as 10 to the power 10 to the power 150), but the important point is that it is finite.

Thus, we have an infinite number of regions like ours and only a finite number of histories that can play out in them. It follows that every possible history will occur in an infinite number of regions. In particular, there should be an infinite number of regions with histories identical to ours. So, if you are not satisfied with the result of the presidential elections, don't despair: you candidate has won on an infinite number of earths.

This picture of the universe robs our civilization of any claim for uniqueness: countless identical civilizations are scattered in the infinite expanse of the cosmos. I find this rather depressing, but it is probably true.

Another thing that I believe to be true, but cannot prove, is that our part of the universe will eventually stop expanding and will recollapse to a big crunch. But this will happen no sooner than 20 billion years from now, and probably much later.