From: Spudboy100@aol.com
Date: Wed Aug 14 2002 - 22:45:17 MDT
http://www.nature.com/nsu/020812/020812-2.html
Is physics watching over us?
Our Universe is so unlikely that we must be missing something.
13 August 2002
In an argument that would have gratified the ancient Greeks, physicists have
claimed that the prevailing theoretical view of the Universe is logically
flawed. Arranging the cosmos as we think it is arranged, say the team, would
have required a miracle1.
An ever-more-rapidly expanding Universe is destined to repeat itself, say
Leonard Susskind of Stanford University, California, and his colleagues. But
the chances that such re-runs would produce worlds like ours are
infinitesimal.
So either space is not accelerating for the reasons we think it is, or we
have yet to discover some principle of physics, the researchers conclude.
Like a guardian angel, this principle would pick out those few initial states
that lead to a Universe like ours, and then guide cosmic evolution so that it
really does unfold this way.
The incomprehensibility of our situation even drives Susskind's team to
ponder whether an "unknown agent intervened in the evolution [of the
Universe] for reasons of its own". But creationists should not rejoice: even
a god such as this can't explain how things got so strange.
The problem stems from the observation in 1998 that the Universe's expansion
seems to be speeding up. The most popular explanation for this is that there
is a cosmological constant - a repulsive force that opposes gravity.
As things stand, other galaxies will eventually disappear as they zoom away
from us faster than the speed of light. Then nothing that happens in those
parts of the cosmos can affect us. Our world - and everywhere else - will be
isolated behind a boundary called a de Sitter horizon.
This view holds that the Universe will fragment into a foam of bubbles
separated by de Sitter horizons: a de Sitter space. Each bubble would
eventually settle into a bland, lifeless uniformity. And that would be the
end of history.
Here we go again
Or would it? Thermodynamics says otherwise, reckon Susskind and his
colleagues. Wait long enough, and everything that can happen, will. There is
nothing to stop a drop of ink dispersed in a glass of water from gathering
its molecules back into a single drop. It's incredibly unlikely but, with
infinite patience, we'll see it happen.
In the same way, a Universe driven to become a de Sitter space by a
cosmological constant will, after an absurdly long time, return to something
like its original condition, the researchers say. A new cosmic history will
then unfold, including the reappearance of life. But the chances that such a
cosmic recurrence will produce a Universe like ours are extremely slim.
Cosmologists have a rejoinder to this kind of argument, called the anthropic
principle. This says that, no matter how unlikely the Universe seems, the
very fact that we are here to ask such questions resolves the paradox. If
things were otherwise, life wouldn't exist and the question would never
arise.
But Susskind's team show that the anthropic principle won't help, because a
vast number of Universes would permit life and yet look quite different from
this one. All of these habitable Universes would result from 'miraculous'
statistical events. But there are so many of them that they would vastly
overwhelm a cosmos like ours.
Even if 'something' had set the peculiar initial conditions of our Universe,
this would only apply for its first run. Subsequent recurrences would produce
a quite different Universe.
In that case, we'd have to conclude that we are in the first unfolding of
this carefully crafted Universe. This all seems too much like special
pleading, the researchers say.
So either there is no cosmological constant after all - in which case, why is
the Universe accelerating? - or we're missing something fundamental.
References
Dyson, L., Kleban, M. & Susskind, L. Disturbing implications of a
cosmological constant. Preprint <http://xxx.lanl.gov/abs/hep-th/0208013>,
(2002).
© Nature News Service / Macmillan Magazines Ltd 2002
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