Excerpt from The Fabric of the Cosmos by Brian Greene, plus links to reviews, author biography & more

But while formulating his laws of motion, Newton encountered a critical stumbling block, one that is of particular importance to our story (Chapter 2). Everyone knew that things could move, but what about the arena within which the motion took place? Well, that's space, we'd all answer. But, Newton would reply, what is space? Is space a real physical entity or is it an abstract idea born of the human struggle to comprehend the cosmos? Newton realized that this key question had to be answered, because without taking a stand on the meaning of space and time, his equations describing motion would prove meaningless. Understanding requires context; insight must be anchored.

And so, with a few brief sentences in his Principia Mathematica, Newton articulated a conception of space and time, declaring them absolute and immutable entities that provided the universe with a rigid, unchangeable arena. According to Newton, space and time supplied an invisible scaffolding that gave the universe shape and structure. Not everyone agreed. Some argued persuasively that it made little sense to ascribe existence to something you can't feel, grasp, or affect. But the explanatory and predictive power of Newton's equations quieted the critics. For the next two hundred years, his absolute conception of space and time was dogma.

Excerpted from The Fabric of the Cosmos by Brian Greene Copyright© 2004 by Brian Greene. Excerpted by permission of Knopf, 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.