05/29/91
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STANFORD -- When cosmologist Andrei Linde departed for Moscow on May 28 to speak at a congress of physicists honoring the late Andrei Sakharov, he carried a videotape of the universe in his briefcase.
It's a computer simulation of the first fractions of a second after the universe began. For Linde, a professor of physics at Stanford on leave from Lebedev Physical Institute in Moscow, it represents a first chance to use a large computer to model his ideas. Like many theoretical physicists -- especially from the Soviet Union -- he usually works by observation, mathematical calculation and intuition.
The simulation also represents the fruits of a collaboration between the 43-year-old theoretician and a bright, computer-savvy teenager -- his son Dmitri, 15.
After 10 days of intense programming, with calculations that used up five megabytes of computer memory for each frame of the simulation, Dmitri caught the excitement of speculation about the beginnings of matter and time. He told his mother: "It is too beautiful to be false."
The universe of their model behaves far differently from the slowly expanding bubble of space and time that most believe emerged from the Big Bang.
For one thing, there's more than one bubble. And some bubbles expand less like a balloon than like a cherry bomb. They undulate like waves across a field of color, then explode in starbursts of red, blue, gold and silver.
Andrei Linde is one of the originators of the inflationary universe scenario, which many cosmologists accept as a likely explanation of how the universe formed. The May 27-31 Sakharov Congress will be the first time that his fellow physicists have seen a three-dimensional, animated computer simulation of what the exponentially expanding universe must look like.
The image is a way for him to demonstrate some recent developments in inflationary cosmology, which could change scientists' understanding of the structure of the universe.
Most intriguing is the idea that the universe, which looks like one big ball from a local perspective, could be seen from outside as a multi-faceted collection of many connected universes, eternally reproducing themselves.
The inflationary scenario suggests that, just after the universe was created, it expanded to an unimaginably large size, then converted its energy to heat and matter. Linde uses his simulation to point out that this expansion may not be the same as the Big Bang that has been thought to have begun the story. In fact, inflation could have occurred no matter how the universe originated -- even if there was no Big Bang at all.
By his calculations, there also may be no Big Crunch, no end to the universe as a whole. New segments --"mini-universes" as large or larger than our own -- may be evolving all the time. Others may be slowly subsiding into the foam of space and time.
"I do not know if the universe had a beginning," Linde says, "but I know it will have no end."
The domain that can be seen with telescopes and deduced from experiments with particle physics may be only one slowly expanding sphere among infinite numbers of spheres. Some of the laws of physics that seem immutable in this universe -- even the dimensions of space and time -- may be entirely different in other spheres.
This concept, sometimes called the chaotic, self-reproducing universe scenario, is Linde's particular contribution to inflationary theory.
Linde is the author of more than 100 papers and two books on particle physics, phase transitions and cosmology. His wife, Renata Kallosh, is also a professor of physics at Stanford on leave from Lebedev Physical Institute; she is an expert on quantum field theory and superstring theory. In addition to Dmitri, they have a younger son, Alex, 13.
To make a model of his universe, Linde has used computers lent by several companies with friendly ties to Stanford, including Sun Microsystems and NeXT Inc. For his animated simulation, he used a powerful workstation lent by Silicon Graphics Co. of Mountain View. The computer has 64 megabytes of random access memory, plus built-in color graphics and animation capabilities.
The firm could only lend the workstation for a short time; Linde had a little more than a week to learn to represent his calculations in graphic color. He enlisted Dmitri -- in his father's words, "a computer addict" -- for some intense father-son teamwork. A junior at Gunn High School in nearby Palo Alto, he had already taught himself the program Mathematica, which his father uses for some calculations.
The simulation begins with depiction of a flat region smaller than the size of an atom, with an extremely great energy density. The action of gravity on such a region theoretically would cause it to expand to a size much larger than the part of the universe we can observe.
Each frame shows perturbations -- waves and peaks in gold and green -- as the region doubles and quadruples again and again in size. Symmetries break; some parts of the universe expand slowly, like the slowly receding galaxies we can see from Earth. Other domains appear to explode like fireworks.
Linde, who once studied to be a painter, often has used diagrams and drawings to represent his ideas. Seeing them in three- dimensional color, he says, "I did not expect that you could depict it all in such an emotionally beautiful form."
He recently received a grant from the office of the Dean of Research at Stanford to enable him to purchase a computer of his own for research. He expects to use it for further studies in astrophysics and cosmology. But having used computers primarily as word processors throughout his career, he sees limits to their use in the field of theoretical physics.
"If you use a computer as a substitute for your brain, then perhaps it is bad, since your brain becomes paralyzed," he says. "But if you use it just to make your hands longer, that is all right."
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