Re: My So-Called Universe

From: Damien Broderick (damienb@unimelb.edu.au)
Date: Thu Aug 21 2003 - 00:49:55 MDT


>Article in Slate, by Jim Holt:
>
>"One morning last April, the New York Times op-ed page ran a piece by
>the Australian physicist Paul Davies warning readers not to be so
>gullible as to believe there could be more than one universe.

I suspect this misrepresents Paul's views. Consider this quote from an
article in the Australian journal The Bulletin:

http://bulletin.ninemsn.com.au/bulletin/EdDesk.nsf/0/1605b5c0613ca233ca256b8
40019a3ea?OpenDocument

...How then do we reconcile the underlying time
symmetry of the laws of physics with a universe trapped on a
one-way journey to cosmic Armageddon?

The only way out is to take a critical look at what we mean by
"universe". As far out in space as our telescopes probe (about
10 billion light years), time's arrow points the same way as it
does on Earth. But what can be said about regions of space
that lie beyond? If the universe began, say, 13 billion years
ago, then light from galaxies more than 13 billion light years
away will not have reached us yet. This distance is not a true
edge of the universe, just an expanding horizon of visibility
that limits our cosmic gaze. If galaxies 100 billion light years
away possessed reversed arrows of time we wouldn't be able
to detect the fact for another 87 billion years.

Cosmologists are slowly coming around to the point of view
that what we normally term "the universe" might actually be
only a small part of a much vaster system, often called the
multiverse. The region of space we can see through our
telescopes would be just a "Hubble bubble" within an infinite
system of bubbles expanding or contracting regions of space
far beyond our cosmic horizon. A more radical possibility is
that these other bubbles might be completely disconnected
from our space, existing in parallel to our space and time. We
would never be able to detect them by direct means however
long we wait, although their existence might be inferred
indirectly.

If it were possible to take a god's-eye view of the multiverse,
there would be no overall arrow of time. Instead, some
universes would possess an arrow pointing forwards, others
backwards. The vast majority of universes would have no
definite arrow of time at all, but languish in a state of
perpetual disorder. Where a universe did have a strong
temporal directionality, beings within it would call the ordered
extremity "the beginning", but this designation would have no
absolute significance.

Why, then, do we humans find ourselves in one of those rare
universes with a definite arrow of time? The answer is easily
found. Only in universes with gravitational smoothness at one
extremity would stars and planets arise, and offer a
bio-friendly environment. Only in those universes that, by
chance, started out in a relatively ordered state would living
beings emerge to puzzle over the paradox of time's arrow and
write articles for publications such as The Bulletin.



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