Thursday, October 30, 2003

Zillions of Universes? Or Did Ours Get Lucky?

According to a controversial notion known as the anthropic principle, certain otherwise baffling features of the universe can only be understood by including ourselves in the equation. The universe must be suitable for life, otherwise we would not be here to wonder about it.

The features in question are mysterious numbers in the equations of physics and cosmology, denoting, say, the amount of matter in the universe or the number of dimensions, which don't seem predictable by any known theory — yet. They are like the knobs on God's control console, and they seem almost miraculously tuned to allow life.

A slight tweak one way or another from the present settings could cause all stars to collapse into black holes or atoms to evaporate, negating the possibility of biology.

If there were only one universe, theorists would have their hands full trying to explain why it is such a lucky one.

But supporters of the anthropic principle argue that there could be zillions of possible universes, many different possible settings ruled by chance. Their view has been bolstered in recent years by a theory of the Big Bang, known as inflation, which implies that our universe is only one bubble in an endless chain of them, and by string theory — the so-called theory of everything — whose equations seem to have an almost uncountable number of solutions, each representing a different possible universe.

Only a few of these will be conducive to life, the anthropic argument goes, but it is no more surprise to find ourselves in one of them than it is to find ourselves on the moist warm Earth rather than on Pluto.

In short we live where we can live, but those can be fighting words.

Scientists agree that the name "anthropic principle," is pretentious, but that's all they agree on. Some of them regard the idea as more philosophy than science. Others regard it as a betrayal of the Einsteinian dream of predicting everything about the universe.

Dr. David Gross regards it as a virus. "Once you get the bug you can't get rid of it," he complained at the conference.

Dr. Weinberg compared the situation to a person who is dealt a royal flush in a poker tournament. It may be chance, he said, but there is another explanation: "Namely, is the organizer of the tournament our friend?"

"But that leads to the argument about religion," he said to much laughter.

"Those who favor taking the anthropic principle seriously don't really like it," he said, "and those who argue against it recognize that it may be unavoidable."

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