Martin Rees on the multiverse

From: Hal Finney <>
Date: Tue, 15 Apr 2003 15:21:44 -0700

I was reading a 2001 paper by Martin Rees, Britain's Astronomer Royal,
where he offers some support for the multiverse concept. This is from, sections 7.2 and following.

First he addresses the issue that the multiverse is unscientific because
it is unobservable. He offers a "slippery slope" argument in terms of
four examples of increasing "horizons":

   (i) Galaxies beyond range of present-day telescopes

   (ii) Galaxies unobservable - even in principle - until a remote cosmic

   (iii) Galaxies that emerged from `our' big bang, but are unobservable
         in principle, ever

   (iv) Galaxies in disjoint universes

The idea is that everyone would agree that (i) is real, almost everyone
(ii), many people (iii), and so maybe we should not be so negative about

He goes on in the next section to describe a Bayesian-flavored test
of the multiverse model. We know that the cosmological constant
"omega" has to be below a certain threshold to allow galaxies to form.
So based on a multiverse concept plus the anthropic principle, we expect
omega to be somewhat smaller than this. But we don't expect it to be too
much smaller. An observation of a super-small omega, much smaller than
the multiverse model can explain, is evidence against the multiverse.
And likewise for other cosmological and physical parameters.

Hal Finney
Received on Tue Apr 15 2003 - 18:24:46 PDT

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