Tracing the Big Bang
Cambridge, Mass. — HORATIO Alger tales still abound. They just occur in places one wouldn't think of looking. Take theoretical astrophysics, for example. On the morning of Dec. 6, 1979, Alan Guth woke up a mere post-doctoral student with the same worries -- especially job-related ones -- as any other young expert in this hotly competitive field.
But later that day, inspiration came. By evening he had scribbled a set of equations into a notebook that helped explain the birth of the cosmos. It set the world of cosmology on its collective ear.
Soon, Dr. Guth was famous, feted at dinners, in demand as a lecturer, and showered with employment invitations. Then came a faculty position at the Massachusetts Institute of Technology and, not long after that, tenure.
Today, ensconced in a position of security and prestige that would be remarkable for someone 10 years his senior, Guth is lounging in a chair at his MIT office, reflecting on the past: ``I was lucky,'' he says.
However it happened, Guth managed to extend the laws of modern particle physics and gravity theory in ways that had occurred to no one before him.
In the process, he addressed some of the weightiest concerns that cosmologists, having only a sketchy notion of the universe's beginnings, ponder today.
His theory suggested how the Big Bang might have started. It explained how the primordial chaos of the universe yielded to the celestial hierarchy of galaxies and clusters of galaxies.
Above all, it attempted to explain the origin of all the matter and energy in the universe.
And future versions of the theory have become a foundation of modern cosmology.
It is called the inflationary scenario. Guth's theory says that the universe exploded into existence at a far faster rate than had been predicted by the Big Bang theories. During a flicker of time just after the first speck of the cosmos popped into existence, the universe began doubling and doubling again in size, about 100 times.
The inflationary era didn't take long -- the flash of a strobe light would represent a larger chunk of the universe's 15 billion-year life span than the inflationary period did in history's first second. But it stabilized a universe teetering between uncontrolled expansion and utter collapse.
Ultimately, it laid the goundwork for the evolution of atoms, stars, and life.
``It is another pedestal in cosmology,'' Heinz Pagel, a theoretical physicist at Rockefeller University and president of the New York Academy of Sciences, says of Guth's theory. ``It doesn't answer all the questions, but the inflation model is extraordinarily attractive because it answers so many of the questions raised by the Big Bang.''
Through continuous minute refinements, as well as constant theoretical arguments bandied about in scientific journals around the globe, the inflationary scenario has emerged as the leaping point for the next advances in understanding of the universe's origins. As such, it is the latest in a succession of intellectual footsteps toward what scientists hope will be an answer to cosmology's most basic question: Why is the universe the way it is?
To that end, cosmology's main tool hasn't changed in 68 years. It is Albert Einstein's theory of general relativity -- an attempt to explain gravity in terms of geometry.
The theory claims that space warps or curves under the pressure of matter just as a mattress sags under the weight of a sleeper.
Thus relativity reduces the flight of a tennis ball or the motion of the planets to a four-dimensional web of space and time.
Since the time it was published, scientists have been trying to use relativity to explain the cosmos.
``The field of cosmology is basically concerned with finding solutions to Einstein's equations,'' says University of Chicago physicist Edward Kolb, who heads a cosmology team at the nearby Fermi National Accelerator Laboratory.
From the beginning, however, the results were mixed. The first to apply relativity theory to the structure of the universe was Einstein himself. But when he did so, his equations told him that the universe either had to be expanding or contracting -- something that the eminent physicist, who had his own idea about how the cosmos should be, was not prepared to accept.
So he fiddled with his equations until they confirmed his hunch that the universe was static and infinite.
A few years later, after astronomer Edwin Hubble discovered that the universe was in fact expanding, Einstein called this mathematical jiggery-pokery ``my greatest blunder.''
Hubble found that the galaxies were apparantly receding from the Mt. Wilson observatory telescope, where he made his observations, at a clip of several thousand miles per second. Like raisins in a loaf of rising dough, they also seemed to pick up speed as they moved farther out into the universe's edge.
To many scientists, the conclusions seemed obvious. The galaxies had to be fleeing from somewhere. Run the cosmic motion picture backwards, and you'd see them all rush into a unimaginably dense and hot clump -- the precursor of a Big Bang. The implications were revolutionary: The notion of a stable, eternally unchanging and perhaps infinitely old universe was about to be replaced by the notion of an evolving universe of finite age.
``It's hard to underestimate the import of that idea,'' says Harvard science historian Owen Gingerich. ``It revitalized cosmology. It raised all sorts of new questions and really marked the start of experimental cosmology.''
It also meant that the theoretical tools of Einstein, as well as the telescopes used by Hubble, were alone inadequate to explain the cosmos.
``Relativity can, for instance, explain that the universe had once been clumped into a dense fireball,'' says MIT's Guth. ``But it can never explain how matter actually behaved.''
So from that point, other kinds of science have been mobilized.
For instance, the Big Bang theory finally attained consensus status in the scientific community after a serendipitous discovery by two researchers at Bell Labs of a feeble hiss from microwave particles saturating the universe.
It turned out to be the echo of the Big Bang. Its discoverers, Arno Penzias and Robert Wilson, won the Nobel Prize.
Their discovery posed questions of its own.
For all the Big Bang's supposed violence, it apparently carried out its mission with harrowing precision. The explosive momentum pushing the universe outward and the gravitational pull drawing everything together had to be balanced almost perfectly.
If the outward push had dominated, then the universe would have thinned out before it had time to clump into galaxies, stars, and planets. If, on the other hand, the gravity's inward pull had dominated, the nascent universe would have been smothered by the Big Crunch.
So how could the universe be so perfectly balanced that, after perhaps 15 billion years, scientists still are not sure which impulse will dominate? The Big Bang model doesn't say.
Another problem concerned the smoothness -- scientists call it the homogeneity -- of the universe. Take a large chunk of one part of the universe and compare it with a big chunk of the other, and you might be hard pressed to tell the difference. Once again, the Big Bang theory does not explain why this is. It just says that it is so.
Another problem that the Big Bang doesn't address is the so-called flatness of the universe. Einstein predicted that space is curved: If you could see to the ``edge'' of the universe, you would end up looking at the back of your head.
Yet no matter how powerful telescopes have become, ``we just haven't been able to `see' the curvature of space,'' says University of Chicago physicist Michael Turner. ``Either curvature is on a very grand scale, or something is wrong with the theory.''
It is still beyond the ken of science to explain exactly how all the universe started out. But such concerns, Guth says, ``are really irrelevant. The predictions of inflation aren't affected by whatever assumptions one makes before inflation begins.''
All that is needed is a primordial cosmic foam -- bubbling, inchoate, ballooning in one place, shriveling in another, frigid here, searing there. Matter may not have existed at this time. Instead, only tremendous amounts of compacted energy may have existed. Physicists say that here our entire concept of time and space breaks down.
Shortly after this period physics as we know it begins. About 1 million trillion trillion trillion trillionths of a second after the universe is thought to have begun, science hits a barrier known as the Planck time. No physical theory is equipped to explain the events that happened prior to this point. In fact, since time as we know it may not have existed before this point, there may have instead been an infinite stretch of time. The Planck time comes only by extending the laws of known physics back to infinite temperatures at zero time.
In any event, very shortly after the Planck time, at least one infinitesimal bubble began to expand and cool. Instead of shrinking back into place like the other bubbles, however, it continued to expand and cool until its temperature lowered to a critical point -- about 1 billion billion billion degrees Fahrenheit. The terrificly concentrated cosmic energy began to exist in a state scientists call a false vacuum.
At that point there was no return. The universe as we know it was on the way.
It may be hard to see the resemblance between the fiery concatenation of forces back then and the apparent harmony of the cosmos today, but it was at this moment that the physical laws that shape today's world are thought to have taken shape. Particles like electrons, quarks, and neutrinos began to get heavier and alter the way they interacted with one another.
Physicists use terms like ``phase transition'' and ``symmetry breaking'' to describe this moment. At this point a kind of crystallization took place, like water freezing into ice.
Quarks fused themselves into protons, while the electrons and neutrinos remained free as they are today. The various energy fields became rigid, and space began to acquire a type of structure.
At the same time, this ``crystallization'' produced a tremendous amount of pressure in the bubble, causing it to inflate like a balloon. Of course, this expansion was on a much grander scale: The inflation scenario holds that the entire observable universe sprang from a space a trillionth the size of a proton.
That explained the uniformity of the universe -- in such a small space it would have been impossible for some parts to have been hotter or colder than others. It also explained the universe's ``lumpiness.'' The cosmic ectoplasm in the inflationary scenario undergoes the proper amount of buckling and contortion during the period of phase transition to create eventually the clumps that, one day, led to galaxies and clusters of galaxies.
It also explains the flatness problem. Space flattens out during inflation just as the surface of an expanding balloon flattens out. The more the region inflates, the smoother it gets.
The inflationary period had another result has well.
When water cools, it radiates a certain amount of latent heat. So too, did the cooling bubble of the universe. But here the heat generated a firestorm of electrons, photons, quarks, and neutrinos. Matter may have ``dropped out'' of the universe the way raindrops congeal from a storm cloud.
In the midst of this fury any matter that may have been in the bubble to begin with would have been overwhelmed. It is even possible, Guth says, that no previous matter existed. If that is so, then ``the universe may be the ultimate free lunch,'' he says.
Guth originally assumed that the inflationary period ended suddenly. ``It was a big mistake,'' he recalls: The Guth universe looked patchy and not at all like the one we know.
A corrected version, introduced in 1982 by A. D. Linde of the Lebedev Physical Institute in Moscow and, independently, by Andreas Albrecht and Paul J. Steinhardt of the University of Pennsylvania, solved the problem. And from this adjustment, the fine-tuning process greeting any scientific theory continues.
With the end of the inflationary period begins the era of standard cosmology and the more leisurely expansion rates dictated by the Big Bang take over.
But Guth's theory also puts out the idea that the bubble that became our bubble might have been imbedded in a foam of such bubbles. Some might have similarly expanded. Thus, the 10 billion-light-year expanse visible to our telescopes might be just a smaller part of a larger universe.
``We really don't know,'' Guth says. All of this is, of course, pure hypothesis. Inflation is based on one of a number of grand unified theories (GUTs) that try to link three of the four fundamental forces of nature: electromagnetism, which lights bulbs and makes clothes cling; the strong force, which binds the atom's nucleus; and the weak force, which controls certain types of radioactive decay. The goal of these theories is to help scientists understand the nature of the universe during the so-called ``Grand Unified Era'' that popped in and out of existence right after the Planck Time.
Gravity, the fourth force, has so far eluded science's most valiant attempts to link it with the other three forces into ``superunification.'' Presumably, it was this grand superforce that reigned supreme before the Planck barrier.
Inflation has found many champions because its basic concept is so straightforward and compelling. Many scientists say it makes the universe as we know it almost seem inevitable.
``There may be lots of small adjustments,'' says Dr. Pagel. ``But until something more convincing comes around, it is the best we have.'' Chart: How cosmologists view the creation of the universe: 1. The Big Bang. From a space one-trillionth the size of a proton, and under unimaginably high temperature, the Big Bang occurs. Prior to this explosion, there may have been no matter, only highly dense energy. 2. plus 10-43 of a second. Planck time. The universe is 10-28 of a centimeter in diameter. Physics as we know it begins. Gravity separates from the single unified force thought to have existed at the time of the Big Bang, leaving the electronuclear (grand unified) force. 3. plus 10-35 of a second. The universe is cooling and begins to inflate exponentially. The universe grows from 10-24 of a centimeter in diameter to the size of a softbal. The strong force, which binds particles within atomic nuclei, and the electroweak force, separate from the grand unified force. Energy begins to form matter - electrons and quarks - as well as antimatter. 4. plus 10 -11 of a second. The electroweak force divides into electromagnetic and weak forces, the latter controlling some forms of radioactive decay. By 10-6 seconds, the universe is the size of our solar system. Quarks form neutrons and protons. Matter and antimatter destroy each other, but enough matter remains to form the universe as we know it. 5. plus 10- 5 years. Stable atoms form from electrons and atomic nuclei (which began forming at Big Bang plus 3 minutes). Matter begins to emit radiation and light is able to travel through space. The universe is now about 10 -3 of its current size, thought to be about 40 billion light years across. 6. plus 10-8 to 10-9 years. At 10- 8 years, protogalaxies begin to form out of the sea of hydrogen and helium that pervades the universe. The universe is slightly more than 1/10 its current size. By 10-9 years the universe is nearly its current size. Galaxies and quasars form. But it will take another 15 billion years for our sun to form.