The fabric of the cosmos

I have read a number of lay (read - not for physicists but not for your average college drop-out either) physics books over the years, mostly having to do with quantum mechainics and the nature of physical reality or relavity. Prior to "Fabric", I think my favorite was John Gribbin's "In Search of Schroedinger's Cat". I thought I had a pretty good grasp of the essentials of quantum mechanics for a layman, and learned relatively little that was really new from most of the others. But I found a lot of new material in"Fabric". The way the quantum measurement problem was dealt with or resolved was great - new to me. The discussion of entanglement, and why everything is in fact *not* connected to everything else was also new to me, and well done. There is a ton of new physics from the late 1990s that is reviewed here. This book contains everything a newcomer to quantum mechanics needs, but also has tons to offer folks who have read on this subject before. And that alone is is quite an accomplishment,. more than worth the price of admission.

But, at least for me, the most ennjoyable sections of the book were the ones middle that dealt with relativity, both general and special, how they relate to older and current cosomological models, and unification with quantum mechanics. I thought I sort of understood relativity (again, at an educated layman's level), but I learned a ton from this book (gravity depends not only on mass and energy but also pressure!!). The early foundations of relativity and the relation to Mach were great. The relation of Einstein to modern cosmology, Higg's fields, the big bang, inflaton theory, repulsive gravity, the universe expanding at a rate potentially faster than the speed of light (with no contradiction to relativity!!) - these were all new to me, and explained very well.

One could quibble with the style a little. The constant use of analogies and examples starring the Simpson's or Mulder and Scully might turn some people off. I didn't mind then, but I didn't love them either. The book is very long - perhaps too long, and there is a fair amount of recapitulation. This recapping bothered me in the beginning until I realized (about three quarters fof the way through the book) that there was so much new stuff here that I was going to have to read the book again, pretty soon.

There is a tremendous amount of material here, all of it interesting, very up-to-date,and all of it well presented. If you are at all interested in modern physics, and the nature of the universe, this book is a great read.

There is one important subject that the author discusses that I would like to comment on. In chapter 5 and elsewhere the author compares spacetime to a frozen river and to a loaf of bread. The author seems to be saying that spacetime is a four dimensional block, perhaps with a frozen part and part with a dynamic part. The frozen river analogy suggests something solid but continuous. The author says, also, that spacetime incorporates past events and future events.

I think that spacetime is more complicated. Spacetime must, in my humble view, include only active space. That is, spacetime must include only space where something is happening, or, where motion is taking place. We know that time itself is dependent on motion, and is really an expression of motion. We know that we have never observed through a telescope spacetime that is not dynamic, or where motion is not taking place. And we know that we have never observed the future by looking through a telescope, despite the fact that Earth with the Sun and galaxy is moving at approximately 600 km/s (1.3 million miles per hour) relevant to the local cosmic flow. Motion relevant to the cosmic flow should, in theory, allow a view of future spacetime at distant locations. This is what the author says is the case when he slices the spacetime loaf at angles.

One conceptual difficulty with the frozen river analogy is that, by including past and future space-time, there is the suggestion of a "creation" event for the whole of space-time, not just a birth of spacetime. For example, if future spacetime exists, then all of future spacetime exists at once, and must have been created all at once. The frozen river analogy also implies a frozen part, that is, a part that once was in motion but is now a frozen and unmoving record. But observation does not support this. While past spacetime must be frozen, future space time must by dynamic and moving, with a boundary between the frozen and moving part. The boundary would be moving as more frozen history gets incorporated.

A better way to look at spacetime, in my view, is to think of it as a four dimensional space that includes all of active space, and includes only active space.