Anthropic principle does not require multiverse

Posted in Uncategorized by sarkology on May 22, 2010

The probability of that we find ourselves in a universe/region that is hospitable to life, is 1. In other words, p(universe hospitable|we exist) = 1.

I may have heard this wrong, but it seems some people are proposing that if we posit a multiverse or parallel universes, it is not surprising that the universe is the way we happen to find it to be. Out of so many universes, we would naturally find ourselves to inhabit one that is hospitable to life.

I don’t see how this is necessary or helpful at all.

First. It is not necessary because we could have simply not have existed. This is contrary to evidence of course, since we clearly do happen to exist. But if we did not exist, then there would be nothing to explain.

Second. It is not helpful because, by the anthropic principle, postulating the multiverse does not increase our prior probability of existence. Let “we find ourselves in a hospitable universe” be H, and “we exist” to be E. Then the anthropic principle says p(H|E)=1. So, p(H)*p(E|H)/p(E)=1 or p(E)=p(H)*p(E|H). Postulating the multiverse says nothing about p(E|H). On the other hand, not postulating the multiverse would allow us to increase p(H) (to 1) and so p(E) to p(E|H). Taking this universe as a brute fact maximizes our prior probability of existence.

Am I missing something here?


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