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

Although everyone calls it the Big Bang, many books caution us not to think of it as an explosion in the conventional sense. It was, rather, a vast, sudden expansion on a whopping scale. So what caused it?

One notion is that perhaps the singularity was the relic of an earlier, collapsed universe--that we're just one of an eternal cycle of expanding and collapsing universes, like the bladder on an oxygen machine. Others attribute the Big Bang to what they call "a false vacuum" or "a scalar field" or "vacuum energy"--some quality or thing, at any rate, that introduced a measure of instability into the nothingness that was. It seems impossible that you could get something from nothing, but the fact that once there was nothing and now there is a universe is evident proof that you can. It may be that our universe is merely part of many larger universes, some in different dimensions, and that Big Bangs are going on all the time all over the place. Or it may be that space and time had some other forms altogether before the Big Bang--forms too alien for us to imagine--and that the Big Bang represents some sort of transition phase, where the universe went from a form we can't understand to one we almost can. "These are very close to religious questions," Dr. Andrei Linde, a cosmologist at Stanford, told the New York Times in 2001.

The Big Bang theory isn't about the bang itself but about what happened after the bang. Not long after, mind you. By doing a lot of math and watching carefully what goes on in particle accelerators, scientists believe they can look back to 10-43 seconds after the moment of creation, when the universe was still so small that you would have needed a microscope to find it. We mustn't swoon over every extraordinary number that comes before us, but it is perhaps worth latching on to one from time to time just to be reminded of their ungraspable and amazing breadth. Thus 10-43 is 0.0000000000000000000000000000000000000000001, or one 10 million trillion trillion trillionths of a second.

Most of what we know, or believe we know, about the early moments of the universe is thanks to an idea called inflation theory first propounded in 1979 by a junior particle physicist, then at Stanford, now at MIT, named Alan Guth. He was thirty-two years old and, by his own admission, had never done anything much before. He would probably never have had his great theory except that he happened to attend a lecture on the Big Bang given by none other than Robert Dicke. The lecture inspired Guth to take an interest in cosmology, and in particular in the birth of the universe.

The eventual result was the inflation theory, which holds that a fraction of a moment after the dawn of creation, the universe underwent a sudden dramatic expansion. It inflated--in effect ran away with itself, doubling in size every 10-34 seconds. The whole episode may have lasted no more than 10-30 seconds--that's one million million million million millionths of a second--but it changed the universe from something you could hold in your hand to something at least 10,000,000,000,000,000,000,000,000 times bigger. Inflation theory explains the ripples and eddies that make our universe possible. Without it, there would be no clumps of matter and thus no stars, just drifting gas and everlasting darkness.

According to Guth's theory, at one ten-millionth of a trillionth of a trillionth of a trillionth of a second, gravity emerged. After another ludicrously brief interval it was joined by electromagnetism and the strong and weak nuclear forces--the stuff of physics. These were joined an instant later by swarms of elementary particles--the stuff of stuff. From nothing at all, suddenly there were swarms of photons, protons, electrons, neutrons, and much else--between 1079 and 1089 of each, according to the standard Big Bang theory.

Such quantities are of course ungraspable. It is enough to know that in a single cracking instant we were endowed with a universe that was vast--at least a hundred billion light-years across, according to the theory, but possibly any size up to infinite--and perfectly arrayed for the creation of stars, galaxies, and other complex systems.

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.