Excerpt from A Short History of Nearly Everything by Bill Bryson, plus links to reviews, author biography & more

What is extraordinary from our point of view is how well it turned out for us. If the universe had formed just a tiny bit differently--if gravity were fractionally stronger or weaker, if the expansion had proceeded just a little more slowly or swiftly--then there might never have been stable elements to make you and me and the ground we stand on. Had gravity been a trifle stronger, the universe itself might have collapsed like a badly erected tent, without precisely the right values to give it the right dimensions and density and component parts. Had it been weaker, however, nothing would have coalesced. The universe would have remained forever a dull, scattered void.

This is one reason that some experts believe there may have been many other big bangs, perhaps trillions and trillions of them, spread through the mighty span of eternity, and that the reason we exist in this particular one is that this is one we could exist in. As Edward P. Tryon of Columbia University once put it: "In answer to the question of why it happened, I offer the modest proposal that our Universe is simply one of those things which happen from time to time." To which adds Guth: "Although the creation of a universe might be very unlikely, Tryon emphasized that no one had counted the failed attempts."

Martin Rees, Britain's astronomer royal, believes that there are many universes, possibly an infinite number, each with different attributes, in different combinations, and that we simply live in one that combines things in the way that allows us to exist. He makes an analogy with a very large clothing store: "If there is a large stock of clothing, you're not surprised to find a suit that fits. If there are many universes, each governed by a differing set of numbers, there will be one where there is a particular set of numbers suitable to life. We are in that one."

Rees maintains that six numbers in particular govern our universe, and that if any of these values were changed even very slightly things could not be as they are. For example, for the universe to exist as it does requires that hydrogen be converted to helium in a precise but comparatively stately manner--specifically, in a way that converts seven one-thousandths of its mass to energy. Lower that value very slightly--from 0.007 percent to 0.006 percent, say--and no transformation could take place: the universe would consist of hydrogen and nothing else. Raise the value very slightly--to 0.008 percent--and bonding would be so wildly prolific that the hydrogen would long since have been exhausted. In either case, with the slightest tweaking of the numbers the universe as we know and need it would not be here.

Excerpted from A Short History of Nearly Everything by Bill Bryson Copyright© 2003 by Bill Bryson. Excerpted by permission of Broadway, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.