From: LARRY KLAES (ljk4_at_msn.com)
Date: Tue Oct 28 2003 - 06:31:15 PST
Zillions of Universes? Or Did Ours Get Lucky?
October 28, 2003
By DENNIS OVERBYE
CLEVELAND - Cosmology used to be a heartless science, all
about dark matter lost in mind-bending abysses and
exploding stars. But whenever physicists and astronomers
gather, the subject that roils lunch, coffee breaks or
renegade cigarette breaks tends to be not dark matter or
the fate of the universe. Rather it is about the role and
meaning of life in the cosmos.
Cosmologists held an unusual debate on the question during
a recent conference, "The Future of Cosmology," at Case
Western Reserve University here.
According to a controversial notion known as the anthropic
principle, certain otherwise baffling features of the
universe can only be understood by including ourselves in
the equation. The universe must be suitable for life,
otherwise we would not be here to wonder about it.
The features in question are mysterious numbers in the
equations of physics and cosmology, denoting, say, the
amount of matter in the universe or the number of
dimensions, which don't seem predictable by any known
theory - yet. They are like the knobs on God's control
console, and they seem almost miraculously tuned to allow
life.
A slight tweak one way or another from the present settings
could cause all stars to collapse into black holes or atoms
to evaporate, negating the possibility of biology.
If there were only one universe, theorists would have their
hands full trying to explain why it is such a lucky one.
But supporters of the anthropic principle argue that there
could be zillions of possible universes, many different
possible settings ruled by chance. Their view has been
bolstered in recent years by a theory of the Big Bang,
known as inflation, which implies that our universe is only
one bubble in an endless chain of them, and by string
theory - the so-called theory of everything - whose
equations seem to have an almost uncountable number of
solutions, each representing a different possible universe.
Only a few of these will be conducive to life, the
anthropic argument goes, but it is no more surprise to find
ourselves in one of them than it is to find ourselves on
the moist warm Earth rather than on Pluto.
In short we live where we can live, but those can be
fighting words.
Scientists agree that the name "anthropic principle," is
pretentious, but that's all they agree on. Some of them
regard the idea as more philosophy than science. Others
regard it as a betrayal of the Einsteinian dream of
predicting everything about the universe.
Dr. David Gross regards it as a virus. "Once you get the
bug you can't get rid of it," he complained at the
conference.
Dr. Gross, director of the Kavli Institute for Theoretical
Physics in Santa Barbara, Calif., had agreed to lead a
panel discussion on the notorious principle. Often found
puffing on a cigar, he is not known to be shy about
expressing his opinion.
"I was chosen because I hate the anthropic principle," he said.
But playing a central role in defending the need for what
he called "anthropic reasoning" was Dr. Steven Weinberg, a
Nobel laureate from the University of Texas. Like Dr.
Gross, Dr. Weinberg is a particle physicist who is known
for being a hard-core reductionist in his approach to
science, but he evinces a gloomy streak in his writings and
his talks. He is still famous for writing in his 1977 book,
"The First Three Minutes," "The more the universe seems
comprehensible, the more it also seems pointless."
Dr. Weinberg is among the most prominent of theorists who
have reluctantly accepted, at least provisionally, the
anthropic principle as a kind of tragic necessity in order
to explain the gnarliest knob of all.
Called the cosmological constant, it is a number that
measures the amount of cosmic repulsion caused by the
energy in empty space. That empty space should be boiling
with such energy is predicted by quantum theory, and
astronomers in the last few years have discovered that some
cosmic repulsion seems to be accelerating the expansion of
the universe. But theoretical attempts to calculate this
constant, also known as lambda, result in numbers 1060
times as high as those astronomers have measured.
So despairing are physicists of understanding the
cosmological constant that Dr. Weinberg joked earlier at
the meeting that he would no longer read papers about it.
Back in 1989, before any cosmological constant had been
discovered, Dr. Weinberg used the anthropic principle to
set limits on the value of the constant. Suppose instead of
being fixed by theory, it was random from universe to
universe. In that case the value of the cosmological
constant in our universe may just be an "environmental
effect," he explained, and we shouldn't expect to be able
to predict it exactly any more than you can calculate how
much rain will fall in Seattle this Christmas.
In his paper, Dr. Weinberg argued that lambda in our
universe could not be too big or the repulsive force would
have prevented the formation of galaxies, stars and us.
Since we are here, the constant should be small.
The recently discovered "dark energy" causing the cosmic
acceleration fits comfortably inside Dr. Weinberg's limits,
vindicating in a way the anthropic approach.
In his talk, Dr. Weinberg described the anthropic principle
as "the sort of historical realization scientists have been
forced to make from time to time."
"Our hope was to explain everything," he said. "Part of
progress is we learn what we can explain on fundamental
grounds and what we cannot."
Other panelists, including Dr. Alex Vilenkin, a physicist
from Tufts University, suggested that the anthropic
reasoning was a logical attempt to apply probabilities to
cosmology, using all the data, including the fact of our
own existence. Dr. John Peacock, a cosmologist at the
University of Edinburgh, argued that the anthropic
principle was not a retreat from physics, but an advance.
The existence of an ensemble of universes with different
properties, he explained, implies a mechanism to produce
variation, a kind of cosmic genetic code, the way that
evolution implies the existence of genes.
"You gain new physics," Dr. Peacock said.
But when his
own turn came, Dr. Gross questioned whether the rules of
the anthropic game were precise enough. What were the
parameters that could vary from universe to universe? How
many could vary at once? What was the probability
distribution of their values, and what was necessary for
"life"?
Anthropic calculations are inherently vague and imprecise,
he said. As a result, the principle could not be disproved.
But he was only getting warmed up. His real objection, he
said, was "totally emotional."
Ascribing the parameters of physics to mere chance or
vagaries of cosmic weather is defeatist, discouraging
people from undertaking the difficult calculations that
would actually explain why things are they way they are.
Moreover, it is also dangerous, he declared to ringing
applause.
"It smells of religion and intelligent design," he said,
referring to a variety of creationism that argues that the
universe is too complex to have evolved by chance.
Dr. Lawrence Krauss, the astrophysicist from Case Western
who had organized the conference and recruited the panel,
characterized the anthropic principle as "a way of killing
time" when physicists didn't have a better idea. Dr.
Krauss, who has battled creationists over biology
instruction in the public schools in Ohio, said he had
encountered anthropic arguments as an argument for
fine-tuning, the idea that God had fixed the universe just
for us.
Dr. Weinberg replied that the anthropic principle was not
really a part of science, but rather "a guess about the
future shape of science."
"If we didn't have things in our universe that seem
peculiar, like the value of the cosmological constant, we
wouldn't worry about it," he said.
Dr. Weinberg compared the situation to a person who is
dealt a royal flush in a poker tournament. It may be
chance, he said, but there is another explanation: "Namely,
is the organizer of the tournament our friend?"
"But that leads to the argument about religion," he said to
much laughter.
In fact, Dr. Weinberg said, the anthropic principle was "a
nice nontheistic explanation of why things are as nice as
they are."
By then the audience was squirming to get in on the action.
Hands were waving as Dr. Gross called the session to an
end. "Clearly there is a diversity of opinion," he intoned.
"Some people find the small value of cosmological constant
so bizarre that only the anthropic principle will pick it out."
Nobody who adheres to the anthropic principle, he said,
would hold on if there were "an honest old-fashioned
calculation," that explained the cosmological constant.
Given the floor for the last word, Dr. Weinberg agreed that
it was too soon to give up hope for such a breakthrough.
"I'm prepared to go on hoping that one will be found," he
said. "But after the passage of time one begins to
entertain other possibilities, and the anthropic
explanation is another possibility."
Applying that mode of reasoning, he said, could help make
the cosmological constant less peculiar,
"But we don't know if that's the help that we really
deserve to get," he concluded.
And it was time for lunch.
Dr. Gross reported later that younger physicists had thanked him for his stand.
Dr. Weinberg said the panel had generated more fuss than
the subject deserved.
"Those who favor taking the anthropic principle seriously
don't really like it," he said, "and those who argue
against it recognize that it may be unavoidable."
http://www.nytimes.com/2003/10/28/science/space/28COSM.html?ex=1068351363&ei=1&en=6ff7078e62cbd6e1
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