To: WSFAlist at keithlynch.net
Date: Tue, 29 Oct 2002 21:16:41 -0500
Subject: [WSFA] NYT: multiple universe speculation
From: ronkean at juno.com
Reply-To: WSFA members <WSFAlist at keithlynch.net>

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Subject: [WSFA] NYTimes.com Article: A New View of Our Universe: Only One of
Many

A New View of Our Universe: Only One of Many

October 29, 2002
By DENNIS OVERBYE

Astronomers have gazed out at the universe for centuries,
asking why it is the way it is. But lately a growing number
of them are dreaming of universes that never were and
asking, why not?

Why, they ask, do we live in 3 dimensions of space and not
2, 10 or 25? Why is a light ray so fast and a whisper so
slow? Why are atoms so tiny and stars so big? Why is the
universe so old? Does it have to be that way, or are there
places, other universes, where things are different?

Once upon a time (only a century ago), a few billion stars
and gas clouds smeared along the Milky Way were thought to
encompass all of existence, and the notion of understanding
it was daunting - and hubristic - enough. Now astronomers
know that galaxies are scattered like dust across the
cosmos. And understanding them might require recourse to an
even broader canvas, what they sometimes call a
"multiverse."

For some cosmologists, that means universes sprouting from
one another in an endless geometric progression, like
mushrooms upon mushrooms upon mushrooms, or baby universes
hatched inside black holes. Others imagine island universes
floating and even colliding in a fifth dimension.

For example, Dr. Max Tegmark, a University of Pennsylvania
cosmologist, has posited at least four different levels of
universes, ranging from the familiar (impossibly distant
zones of our own universe) to the strange (space-times in
which the fundamental laws of physics are different).

Dr. Martin Rees, a University of Cambridge cosmologist and
the Astronomer Royal, said contemplating these alternate
universes could help scientists distinguish which features
of our own universe are fundamental and necessary and which
are accidents of cosmic history. "It's all science, but
science for the 21st century, to seek the answers to these
questions," Dr. Rees said, adding that he is often accused
of believing in other universes.

"I don't believe," he said, "but I think it's part of
science to find out."

Some cosmologists now say the realm we call the observable
universe - roughly 14 billion light-years deep of galaxies
and stars - could be only a small patch of a vast bubble or
"pocket" in a much vaster ensemble bred endlessly in a
chain of big bangs.

The idea, they say, is a natural extension of the theory of
inflation, introduced by Dr. Alan Guth, now at the
Massachusetts Institute of Technology, in 1980. That theory
asserts that when the universe was less than a trillionth
of a trillionth of a second old it underwent a brief
hyperexplosive growth spurt fueled by an antigravitational
force embedded in space itself, a possibility suggested by
theories of modern particle physics.

Because inflation can grow a whole universe from about an
ounce of primordial stuff, Dr. Guth likes to refer to the
universe as "the ultimate free lunch." But Dr. Guth and
various other theorists - including Dr. Andrei Linde of
Stanford, Dr. Alexander Vilenkin of Tufts and Dr. Paul
Steinhardt of Princeton - have suggested that it may be an
endless one as well. Once inflation starts anywhere, it
will keep happening over and over again, they say, spawning
a chain of universes, bubbles within bubbles, in a scheme
that Dr. Linde called "eternal inflation."

"Once you've discovered it's easy to make a universe out of
an ounce of vacuum, why not make a bunch of them?" asked
Dr. Craig Hogan, a cosmologist at the University of
Washington.

In fact, Dr. Guth said, "Inflation pretty much forces the
idea of multiple universes upon us."

Moreover, there is no reason to expect that these universes
will be identical. Even within our own bubble, tiny random
nonuniformities in the primordial raw material would cause
the cosmos to look different from place to place. If the
universe is big enough, Dr. Tegmark and others say,
everything that can happen will happen, so that if we could
look out far enough we would eventually discover an exact
replica of ourselves.

Moreover, cosmologists say, the laws of physics themselves,
as experienced by creatures like ourselves, confined to
four dimensions and the energy scales of ordinary life,
could evolve differently in different bubble universes.

"Geography is a now a much more interesting subject than
you thought," Dr. John Barrow, a physicist at the
University of Cambridge, observed.

Inflation has gained much credit with cosmologists, despite
its strangeness, Dr. Guth noted, because it plays a vital
role in calculations of the Big Bang that have been
vindicated by the detection of the radio waves it produced.
The prediction of other universes must therefore be taken
seriously, he said.

Lucky Numbers
Adjusting the Dials of Nature's Console

The prospect of
this plethora of universes has brought new attention to a
philosophical debate that has lurked on the edges of
science for the last few decades, a debate over the role of
life in the universe and whether its physical laws are
unique - or, as Einstein once put it, "whether God had any
choice."

Sprinkled through the Standard Model, the suite of
equations that describe all natural phenomena, are various
mysterious constants, like the speed of light or the masses
of the elementary particles, whose value is not specified
by any theory now known.

In effect, the knobs on nature's console have been set to
these numbers. Scientists can imagine twiddling them, but
it turns out that nature is surprisingly finicky, they say,
and only a narrow range of settings is suitable for the
evolution of complexity or Life as We Know It.

For example, much of the carbon and oxygen needed for life
is produced by the fusion of helium atoms in stars called
red giants.

But a change of only half a percent in the strength of the
so-called strong force that governs nuclear structure would
be enough to prevent those reactions from occurring,
according to recent work by Dr. Heinz Oberhummer of Vienna
University of Technology. The result would be a dearth of
the raw materials of biology, he said.

Similarly, a number known as the fine structure constant
characterizes the strength of electromagnetic forces. If it
were a little larger, astronomers say, stars could not
burn, and if it were only a little smaller, molecules would
never form.

So is this a lucky universe, or what?

In 1974, Dr. Brandon Carter, a theoretical physicist then
at Cambridge, now at the Paris Observatory in Meudon,
pointed out that these coincidences were not just luck, but
were rather necessary preconditions for us to be looking at
the universe.

After all, we are hardly likely to discover laws that are
incompatible with our own existence.

That insight is the basis of what Dr. Carter called the
anthropic principle, an idea that means many things to many
scientists. Expressed most emphatically, it declares that
the universe is somehow designed for life. Or as the
physicist Freeman Dyson once put it, "The universe in some
sense must have known that we were coming."

This notion horrifies some physicists, who feel it is their
mission to find a mathematical explanation of nature that
leaves nothing to chance or "the whim of the Creator," in
Einstein's phrase.

"It touches on philosophical issues that scientists
oftentimes skirt," said Dr. John Schwarz, a physicist and
string theorist at the California Institute of Technology.
"There should be mathematical ways of understanding how
nature works."

Dr. Steven Weinberg, the University of Texas physicist and
Nobel laureate, referred to this so-called "strong" version
of the anthropic principle as "little more than mystical
mumbo jumbo" in a recent article in The New York Review of
Books.

Sorting Universes
Finding a Home for the 'A-Word'

Nevertheless, the
"A-word" is popping up more and more lately, at conferences
and in the scientific literature, often to the groans of
particle physicists. The reason is the multiverse.

"It is possible that as theoretical physics develops, that
it will present us with multiple universes," Dr. Weinberg
said.

If different laws or physical constants prevail in other
bubble universes, the conditions may not allow the
existence of life or intelligence, he explained.

In that case the anthropic principle loses its mysticism
and simply becomes a prescription for deciding which
bubbles are capable of supporting life.

But many string theorists still resent the principle as an
abridgment on their ambitions. The result has been a
spirited debate about what physicists can expect from their
theories.

"They have the pious hope that string theory will uniquely
determine all the constants of nature," said Dr. Barrow,
who wrote the 1984 book "The Cosmological Anthropic
Principle" with Dr. Frank Tipler, a Tulane University
physicist. The book argued that once life emerges in the
universe it will never die.

In a recent paper titled "The Beginning of the End of the
Anthropic Principle," three physicists - Dr. Gordon Kane of
the University of Michigan, and Dr. Malcolm Perry and Dr.
Anna Zytkow, both of Cambridge - argued that a unified
theory of physics, as string theory purports to be, when
finally formulated, would specify most of the constants of
nature or specify relationships between them, leaving
little room for anthropic arguments.

"The anthropic principle isn't as anthropic as people
wanted," Dr. Kane said in an interview.

But in a rejoinder titled "Why the Universe Is Just So,"
Dr. Hogan of Washington argued that physics was replete
with messy processes like quantum effects, which leave some
aspects of reality and the laws of physics to chance.
According to string theory, he pointed out, the laws of
physics that we mortals experience are low-energy,
4-dimensional shadows, of sorts, of a 10- or 11-dimensional
universe. As a result, the so-called "fundamental
constants" could look different in different bubbles.

Dr. Hogan admitted that this undermined some of the
traditional aspirations of physics, writing, "at least some
properties of the world might not have an elegant
mathematical explanation, and we can try to guess which
ones these are."

Even string theorists like Dr. Kane admit that, in the
absence of a final form of the theory, they have no idea
how many solutions there may be - one, many or even an
infinite number - to the "final" string equations. Each one
would correspond to a different condition of space-time,
with a different set of physical constants.

"Any set that allows life to happen will have life," he
said.

Dark Energies
When the Numbers Just Don't Add Up

But even some of the most hard-core physicists, including
Dr. Weinberg, suggest they may have to resort to the
anthropic principle to explain one of the deepest mysteries
looming like a headache over science: the discovery that
the expansion of the universe seems to be speeding up,
perhaps in a kind of low-energy reprise of an inflation
episode 14 billion years ago.

Cosmologists suspect a repulsion or antigravity associated
with space itself is propelling this motion. This force,
known as the cosmological constant, was first proposed by
Einstein back in 1917, and has been a problem ever since -
"a veritable crisis," Dr. Weinberg has called it.

According to astronomical observations, otherwise
undetectable energy - "dark energy" - accounts for about
two-thirds of the mass-energy of the universe today,
outweighing matter by two to one. But according to modern
quantum physics, empty space should be seething with energy
that would outweigh matter in the universe by far, far
more, by a factor of at least 1060. This mismatch has been
called the worst discrepancy in the history of physics.

But that mismatch is crucial for life, as Dr. Weinberg
first pointed out in 1987. At the time there was no
evidence for a cosmological constant and many physicists
presumed that its magnitude was in fact zero.

In his paper, Dr. Weinberg used so-called anthropic
reasoning to pin the value of any cosmological constant to
between about one-tenth and a few times the density of
matter in the universe. If it were any larger, he said, the
universe would blow apart before galaxies had a chance to
form, leaving no cradle for the stellar evolution of
elements necessary for life or other complicated
structures.

The measured value of the constant is about what would be
expected from anthropic arguments, Dr. Weinberg said,
adding that nobody knows enough about physics yet to tell
whether there are other universes with other constants. He
called the anthropic principle "a sensible approach" to the
cosmological constant problem.

"We may wind up using the anthropic principle to satisfy
our sense of wonder about about why things are the way they
are," Dr. Weinberg said.

Beyond the Dark
Searching for Proof From Better Theories

For Dr. Rees,
the Astronomer Royal, it is not necessary to observe other
universes to gain some confidence that they may exist. One
thing that will help, he explained, is a more precise
theory of how the cosmological constant may vary and how it
will affect life in the universe. We should live in a
statistically typical example of the range of universes
compatible with life, he explained. For example, if the
cosmological constant was, say, 10 percent of the maximum
value consistent with life, that would be acceptable, he
said.

"If it was a millionth, that would raise eyebrows."

Another confidence builder would be more support for the
theory of inflation, either in the form of evidence from
particle physics theory or measurements of the cosmic Big
Bang radiation that gave a more detailed model of what
theoretically happened during that first trillionth of a
trillionth of a second.

"If we had a theory then we would know whether there were
many big bangs or one, and then we would know if the
features we see are fixed laws of the universe or bylaws
for which we can never have an explanation," Dr. Rees said.

In a talk last month at a cosmology conference in Chicago,
Dr. Joseph Polchinski, from the Institute for Theoretical
Physics at the University of California in Santa Barbara,
speculated that the there could be 1060 different solutions
to the basic string equations, thus making it more likely
that at least one universe would have a friendly
cosmological constant.

Reminded that he had once joked about retiring if a
cosmological constant was discovered, on the ground that
the dreaded anthropic principle would be the only
explanation, he was at first at a loss for words.

Later he said he hoped the range of solutions and possible
universes permitted by string theory could be narrowed by
astronomical observations and new theoretical techniques to
the point where the anthropic principle could be counted
out as an explanation.

"Life is still good," he said.

But Dr. Hogan said that multiple universes would have to be
taken seriously if they came out of equations that science
had faith in.

"You have to be open-minded," he said. "You can't impose
conditions."

"It's the most scientific attitude," he
added.

http://www.nytimes.com/2002/10/29/science/space/29COSM.html?ex=1036857308
&ei=1&en=21a4cfba57aae106

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