• E-mail
• Print
• Comment
• Font Size
• Digg
• del.icio.us
• Discuss article

Theory of anything? Or maybe everything Too many answers to a cosmic question

Posted on: Monday, 8 September 2003, 06:00 CDT

Call it the theory of anything. Einstein once wondered aloud whether God had any choice in creating the universe. It was his fondest hope that the answer was no. He and subsequent generations of physicists have hoped that at the end of their labors there would be one answer a so-called Theory of Everything that would explain why the details of the world are the way they are and cannot be any other way: why there was a Big Bang, the number of dimensions of space-time, the masses of elementary particles. For 20 years, physicists have lodged those hopes in string theory, a mathematically labyrinthian effort to portray nature as made up of tiny wriggling strings and membranes, rather than pointlike particles or waves. Once called a piece of 21st-century physics that had fallen into the 20th century by accident, string theory has become one of the hippest topics in science, celebrated in books like the recent best seller The Elegant Universe, by the Columbia theorist Brian Greene, and the subject of a miniseries on Nova on public television this autumn. In principle, strings can unite all the forces of nature, including gravity, in a single mathematical framework. But the stringiness of nature manifests itself only at energies and temperatures that can be generated in a particle accelerator the size of a small galaxy. As a result, physicists have been left at the mercy of their mathematical imaginations or sifting cosmological data for hints of a clue from God's own particle accelerator, the Big Bang. The hope was that when all was said and done, there would be only one solution to the theory's tangled equations, one answer corresponding to only one possible universe. But recent progress in string theory paradoxically seems to leave physics further than ever from that dream of a unique answer. In a series of conceptual and technical breakthroughs, a group of theorists at Stanford University in California showed this year that string theory could describe a universe whose expansion was accelerating something that many experts thought impossible. That was no small accomplishment, because cosmologists now theorize that some puzzling and so far unidentified dark energy is wrenching space apart ever more violently. This energy seems to make up 70 percent of the cosmos, according to astronomical observations. The new calculations suggest that this dark energy cannot last forever, that it will disappear sometime in the far future, according to the researchers, Shamit Kachru, Renata Kallosh and Andrei Linde, all of Stanford, and Sandip Trivedi of the Tata Institute of Fundamental Research in Bombay. But the same calculations confirmed that string theory could have an infinite number of solutions, each representing a different universe with slightly different laws of physics. The detailed characteristics of any particular one of these universes the laws that describe the basic forces and particles might be decided by chance. As a result, string theorists and cosmologists are confronted with what Leonard Susskind of Stanford has called the cosmic landscape, a sort of metarealm of space-time. Contrary to Einstein's hopes, it may be that neither God nor physics chooses among these possibilities, Susskind contends. Rather it could be life. Only a fraction of the universes in this metarealm would have the lucky blend of properties suitable for life, Susskind explained. It should be no surprise that we find ourselves in one of these.

We live where we can live, he said. Susskind conceded that many colleagues who harbor the Einsteinian dream of predicting everything are appalled by that notion that God plays dice with the laws of physics. Among them is David Gross, director of the Kavli Institute of Theoretical Physics in Santa Barbara, California, who said, I'm a total Einsteinian with respect to the ultimate goal of science.

Physicists should be able to predict all the parameters of nature, Gross said, adding, They're not adjustable.

But Max Tegmark, a cosmologist at the University of Pennsylvania, said, I think this grand dream is basically dying.

Michael Douglas of Rutgers and the Institute of Advanced Scientific Studies, near Paris, called the plethora of string universes the Alice's Restaurant problem.

You can get anything you want at Alice's Restaurant, he said. Is this a theory of something, very many things or nothing? That's what we're trying to establish.

Rather than sifting myriad solutions for the one that fits our universe, Douglas has developed statistical methods to analyze the set of string solutions as a whole to find patterns that will not show up when the solutions are examined one by one. The results could help ascertain which features of this zoo of possibilities are more common and which are more rare, and how many solutions really are too many.

My own philosophy, Douglas said in an interview, is that we should do our best to listen to what string theory is trying to tell us. It is smarter than we are.

Kachru suggested that it might be wishful thinking to expect that a smoking gun confirmation of string theory could be found from comparing it to today's universe. The full glories of string theory, he said, manifest themselves only at energies trillions of times what earthbound particle accelerators can produce. Perhaps, he said, theorists should be looking for the smoking gun in the Big Bang. Asked what the smoking-gun question might be, Kachru laughed and said, If I knew, I would be working in that field.

More News in this Category