May 22, 2001, Tuesday

SCIENCE DESK

Before the Big Bang, There Was . . . What?

By DENNIS OVERBYE (NYT) 3457 words

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.

Correction: May 23, 2001, Wednesday An article in Science Times yesterday about ideas on the origin of the universe misstated the affiliation of Dr. Burt Ovrut, a scientist who speculated that the Big Bang was ignited by a clash of island universes. He is at the University of Pennsylvania, not Penn State.

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