The New York Times
May 22, 2001
<http://www.nytimes.com/2001/05/22/science/22BANG.html>
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Before the Big Bang, There Was . . . What?
By DENNIS OVERBYE
What was God doing before he created the world? The philosopher and writer
(and later saint) Augustine posed the question in his "Confessions" in the
fourth century, and then came up with a strikingly modern answer: before
God created the world there was no time and thus no "before." To paraphrase
Gertrude Stein, there was no "then" then.
Until recently no one could attend a lecture on astronomy and ask the
modern version of Augustine's question � what happened before the Big Bang?
� without receiving the same frustrating answer, courtesy of Albert
Einstein's general theory of relativity, which describes how matter and
energy bend space and time.
If we imagine the universe shrinking backward, like a film in reverse, the
density of matter and energy rises toward infinity as we approach the
moment of origin. Smoke pours from the computer, and space and time
themselves dissolve into a quantum "foam." "Our rulers and our clocks
break," explained Dr. Andrei Linde, a cosmologist at Stanford University.
"To ask what is before this moment is a self-contradiction."
But lately, emboldened by progress in new theories that seek to unite
Einstein's lordly realm with the unruly quantum rules that govern subatomic
physics � so-called quantum gravity � Dr. Linde and his colleagues have
begun to edge their speculations closer and closer to the ultimate moment
and, in some cases, beyond it.
Some theorists suggest that the Big Bang was not so much a birth as a
transition, a "quantum leap" from some formless era of imaginary time, or
from nothing at all. Still others are exploring models in which cosmic
history begins with a collision with a universe from another dimension.
All this theorizing has received a further boost of sorts from recent
reports of ripples in a diffuse radio glow in the sky, thought to be the
remains of the Big Bang fireball itself. These ripples are consistent with
a popular theory, known as inflation, that the universe briefly speeded its
expansion under the influence of a violent antigravitational force, when it
was only a fraction of a fraction of a nanosecond old. Those ripples thus
provide a useful check on theorists' imaginations. Any theory of cosmic
origins that does not explain this phenomenon, cosmologists agree, stands
little chance of being right.
Fortunately or unfortunately, that still leaves room for a lot of
possibilities.
"If inflation is the dynamite behind the Big Bang, we're still looking for
the match," said Dr. Michael Turner, a cosmologist at the University of
Chicago. The only thing that all the experts agree on is that no idea works
� yet. Dr. Turner likened cosmologists to jazz musicians collecting themes
that sound good for a work in progress: "You hear something and you say, oh
yeah, we want that in the final piece."
One answer to the question of what happened before the Big Bang is that it
does not matter because it does not affect the state of our universe today.
According to a theory known as eternal inflation, put forward by Dr. Linde
in 1986, what we know as the Big Bang was only one out of many in a chain
reaction of big bangs by which the universe endlessly reproduces and
reinvents itself. "Any particular part of the universe may die, and
probably will die," Dr. Linde said, "but the universe as a whole is immortal."
Dr. Linde's theory is a modification of the inflation theory that was
proposed in 1980 by Dr. Alan Guth, a physicist. He considered what would
happen if, as the universe was cooling during its first violently hot
moments, an energy field known as the Higgs field, which interacts with
particles to give them their masses, was somehow, briefly, unable to
release its energy.
Space, he concluded, would be suffused with a sort of latent energy that
would violently push the universe apart. In an eyeblink the universe would
double some 60 times over, until the Higgs field released its energy and
filled the outrushing universe with hot particles. Cosmic history would
then ensue.
Cosmologists like inflation because such a huge outrush would have smoothed
any gross irregularities from the primordial cosmos, leaving it homogeneous
and geometrically flat. Moreover, it allows the whole cosmos to grow from
next to nothing, which caused Dr. Guth to dub the universe "the ultimate
free lunch."
Subsequent calculations ruled out the Higgs field as the inflating agent,
but there are other inflation candidates that would have the same effect.
More important, from the pre- Big-Bang perspective, Dr. Linde concluded,
one inflationary bubble would sprout another, which in turn would sprout
even more. In effect each bubble would be a new big bang, a new universe
with different characteristics and perhaps even different dimensions. Our
universe would merely be one of them.
"If it starts, this process can keep happening forever," Dr. Linde
explained. "It can happen now, in some part of the universe."
The greater universe envisioned by eternal inflation is so unimaginably
large, chaotic and diverse that the question of a beginning to the whole
shebang becomes almost irrelevant. For cosmologists like Dr. Guth and Dr.
Linde, that is in fact the theory's lure.
"Chaotic inflation allows us to explain our world without making such
assumptions as the simultaneous creation of the whole universe from
nothing," Dr. Linde said in an e-mail message.
Questions for Eternity
Trying to Imagine the Nothingness
Nevertheless, most cosmologists, including Dr. Guth and Dr. Linde, agree
that the universe ultimately must come from somewhere, and that nothing is
the leading candidate.
As a result, another tune that cosmologists like to hum is quantum theory.
According to Heisenberg's uncertainty principle, one of the pillars of this
paradoxical world, empty space can never be considered really empty;
subatomic particles can flit in and out of existence on energy borrowed
from energy fields. Crazy as it sounds, the effects of these quantum
fluctuations have been observed in atoms, and similar fluctuations during
the inflation are thought to have produced the seeds around which today's
galaxies were formed.
Could the whole universe likewise be the result of a quantum fluctuation in
some sort of primordial or eternal nothingness? Perhaps, as Dr. Turner put
it, "Nothing is unstable."
The philosophical problems that plague ordinary quantum mechanics are
amplified in so-called quantum cosmology. For example, as Dr. Linde points
out, there is a chicken- and-egg problem. Which came first: the universe,
or the law governing it? Or, as he asks, "If there was no law, how did the
universe appear?"
One of the earliest attempts to imagine the nothingness that is the source
of everything came in 1965 when Dr. John Wheeler and Dr. Bryce DeWitt, now
at the University of Texas, wrote down an equation that combined general
relativity and quantum theory. Physicists have been arguing about it ever
since.
The Wheeler-DeWitt equation seems to live in what physicists have dubbed
"superspace," a sort of mathematical ensemble of all possible universes,
ones that live only five minutes before collapsing into black holes and
ones full of red stars that live forever, ones full of life and ones that
are empty deserts, ones in which the constants of nature and perhaps even
the number of dimensions are different from our own.
In ordinary quantum mechanics, an electron can be thought of as spread out
over all of space until it is measured and observed to be at some specific
location. Likewise, our own universe is similarly spread out over all of
superspace until it is somehow observed to have a particular set of
qualities and laws. That raises another of the big questions. Since nobody
can step outside the universe, who is doing the observing?
Dr. Wheeler has suggested that one answer to that question may be simply
us, acting through quantum- mechanical acts of observation, a process he
calls "genesis by observership."
"The past is theory," he once wrote. "It has no existence except in the
records of the present. We are participators, at the microscopic level, in
making that past, as well as the present and the future." In effect, Dr.
Wheeler's answer to Augustine is that we are collectively God and that we
are always creating the universe.
Another option, favored by many cosmologists, is the so-called many worlds
interpretation, which says that all of these possible universes actually do
exist. We just happen to inhabit one whose attributes are friendly to our
existence.
The End of Time
Just Another Card in the Big Deck
Yet another puzzle about the Wheeler-DeWitt equation is that it makes no
mention of time. In superspace everything happens at once and forever,
leading some physicists to question the role of time in the fundamental
laws of nature. In his book "The End of Time," published to coincide with
the millennium, Dr. Julian Barbour, an independent physicist and Einstein
scholar in England, argues that the universe consists of a stack of
moments, like the cards in a deck, that can be shuffled and reshuffled
arbitrarily to give the illusion of time and history.
The Big Bang is just another card in this deck, along with every other
moment, forever part of the universe. "Immortality is here," he writes in
his book. "Our task is to recognize it."
Dr. Carlo Rovelli, a quantum gravity theorist at the University of
Pittsburgh, pointed out that the Wheeler- DeWitt equation doesn't mention
space either, suggesting that both space and time might turn out to be
artifacts of something deeper. "If we take general relativity seriously,"
he said, "we have to learn to do physics without time, without space, in
the fundamental theory."
While admitting that they cannot answer these philosophical questions, some
theorists have committed pen to paper in attempts to imagine quantum
creation mathematical rigor.
Dr. Alexander Vilenkin, a physicist at Tufts University in Somerville,
Mass., has likened the universe to a bubble in a pot of boiling water. As
in water, only bubbles of a certain size will survive and expand, smaller
ones collapse. So, in being created, the universe must leap from no size at
all � zero radius, "no space and no time" � to a radius large enough for
inflation to take over without passing through the in-between sizes, a
quantum-mechanical process called "tunneling."
Dr. Stephen Hawking, the Cambridge University cosmologist and best-selling
author, would eliminate this quantum leap altogether. For the last 20 years
he and a series of collaborators have been working on what he calls a "no
boundary proposal." The boundary of the universe is that it has no
boundary, Dr. Hawking likes to say.
One of the keys to Dr. Hawking's approach is to replace time in his
equations with a mathematical conceit called imaginary time; this technique
is commonly used in calculations regarding black holes and in certain
fields of particle physics, but its application to cosmology is controversial.
The universe, up to and including its origin, is then represented by a
single conical-shaped mathematical object, known as an instanton, that has
four spatial dimensions (shaped roughly like a squashed sphere) at the Big
Bang end and then shifts into real time and proceeds to inflate. "Actually
it sort of bursts and makes an infinite universe," said Dr. Neil Turok,
also from Cambridge University. "Everything for all future time is
determined, everything is implicit in the instanton."
Unfortunately the physical meaning of imaginary time is not clear. Beyond
that, the approach produces a universe that is far less dense than the real
one.
The Faith of Strings
Theorists Bring on the 'Brane' Worlds
But any real progress in discerning the details of the leap from eternity
into time, cosmologists say, must wait for the formulation of a unified
theory of quantum gravity that succeeds in marrying Einstein's general
relativity to quantum mechanics � two views of the world, one describing a
continuous curved space-time, the other a discontinuous random one � that
have been philosophically and mathematically at war for almost a century.
Such a theory would be able to deal with the universe during the cauldron
of the Big Bang itself, when even space and time, theorists say, have to
pay their dues to the uncertainty principle and become fuzzy and discontinuous.
In the last few years, many physicists have pinned their hopes for quantum
gravity on string theory, an ongoing mathematically labyrinthean effort to
portray nature as comprising tiny wiggly strings or membranes vibrating in
10 or 11 dimensions.
In principle, string theory can explain all the known (and unknown) forces
of nature. In practice, string theorists admit that even their equations
are still only approximations, and physicists outside the fold complain
that the effects of "stringy physics" happen at such high energies that
there is no hope of testing them in today's particle accelerators. So
theorists have been venturing into cosmology, partly in the hopes of
discovering some effect that can be observed.
The Big Bang is an obvious target. A world made of little loops has a
minimum size. It cannot shrink beyond the size of the string loops
themselves, Dr. Robert Brandenberger, now at Brown, and Dr. Cumrun Vafa,
now at Harvard, deduced in 1989. When they used their string equations to
imagine space shrinking smaller than a certain size, Dr. Brandenberger
said, the universe acted instead as if it were getting larger. "It looks
like it is bouncing from a collapsing phase."
In this view, the Big Bang is more like a transformation, like the melting
of ice to become water, than a birth, explained Dr. Linde, calling it "an
interesting idea that should be pursued." Perhaps, he mused, there could be
a different form of space and time before the Big Bang. "Maybe the universe
is immortal," he said. "Maybe it just changes phase. Is it nothing? Is it a
phase transition? These are very close to religious questions."
Work by Dr. Brandenberger and Dr. Vafa also explains how it is that we only
see 3 of the 9 or 10 spatial dimensions the theory calls for. Early in time
the strings, they showed, could wrap around space and strangle most of the
spatial dimensions, keeping them from growing.
In the last few years, however, string theorists have been galvanized by
the discovery that their theory allows for membranes of various dimensions
("branes" in string jargon) as well as strings. Moreover they have begun to
explore the possibility that at least one of the extra dimensions could be
as large as a millimeter, which is gigantic in string physics. In this new
cosmology, our world is a three-dimensional island, or brane floating in a
five- dimensional space, like a leaf in a fish tank. Other branes might be
floating nearby. Particles like quarks and electrons and forces like
electromagnetism are stuck to the brane, but gravity is not, and thus the
brane worlds can exert gravitational pulls on each other.
"A fraction of a millimeter from you is another universe," said Dr. Linde.
"It might be there. It might be the determining factor of the universe in
which you live."
Worlds in Collision
A New Possibility Is Introduced
That other universe could bring about creation itself, according to several
recent theories. One of them, called branefall, was developed in 1998 by
Dr. Georgi Dvali of New York University and Dr. Henry Tye, from Cornell. In
it the universe emerges from its state of quantum formlessness as a tangle
of strings and cold empty membranes stuck together. If, however, there is a
gap between the branes at some point, the physicists said, they will begin
to fall together.
Each brane, Dr. Dvali said, will experience the looming gravitational field
of the other as an energy field in its own three-dimensional space and will
begin to inflate rapidly, doubling its size more than a thousand times in
the period it takes for the branes to fall together. "If there is at least
one region where the branes are parallel, those regions will start an
enormous expansion while other regions will collapse and shrink," Dr. Dvali
said.
When the branes finally collide, their energy is released and the universe
heats up, filling with matter and heat, as in the standard Big Bang.
This spring four physicists proposed a different kind of brane clash that
they say could do away with inflation, the polestar of Big Bang theorizing
for 20 years, altogether. Dr. Paul Steinhardt, one of the fathers of
inflation, and his student Justin Khoury, both of Princeton, Dr. Burt Ovrut
of Penn State and Dr. Turok call it the ekpyrotic universe, after the Greek
word "ekpyrosis," which denotes the fiery death and rebirth of the world in
Stoic philosophy.
The ekpyrotic process begins far in the indefinite past with a pair of flat
empty branes sitting parallel to each other in a warped five-dimensional
space � a situation they say that represents the simplest solution of
Einstein's equations in an advanced version of string theory. The authors
count it as a point in their favor that they have not assumed any extra
effects that do not already exist in that theory. "Hence we are proposing a
potentially realistic model of cosmology," they wrote in their paper.
The two branes, which form the walls of the fifth dimension, could have
popped out of nothingness as a quantum fluctuation in the even more distant
past and then drifted apart.
At some point, perhaps when the branes had reached a critical distance
apart, the story goes, a third brane could have peeled off the other brane
and begun falling toward ours. During its long journey, quantum
fluctuations would ripple the drifting brane's surface, and those would
imprint the seeds of future galaxies all across our own brane at the moment
of collision. Dr. Steinhardt offered the theory at an astronomical
conference in Baltimore in April.
In the subsequent weeks the ekpyrotic universe has been much discussed.
Some cosmologists, particularly Dr. Linde, have argued that in requiring
perfectly flat and parallel branes the ekpyrotic universe required too much
fine-tuning.
In a critique Dr. Linde and his co- authors suggested a modification they
called the "pyrotechnic universe."
Dr. Steinhardt admitted that the ekpyrotic model started from a very
specific condition, but that it was a logical one. The point, he said, was
to see if the universe could begin in a long-lived quasi-stable state
"starkly different from inflation." The answer was yes. His co-author, Dr.
Turok, pointed out, moreover, that inflation also requires fine-tuning to
produce the modern universe, and physicists still don't know what field
actually produces it.
"Until we have solved quantum gravity and connected string theory to
particle physics none of us can claim victory," Dr. Turok said.
In the meantime, Augustine sleeps peacefully.
Copyright 2001 The New York Times Company
