-uht!'s Reviews > Three Roads To Quantum Gravity

Three Roads To Quantum Gravity by Lee Smolin
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's review
Oct 01, 07

bookshelves: science

This is one of the small list of books that has forever changed my paradigm. Unlike the other ones, I was aware of the paradigm change as it was happening and I could not put this book down.

"...the first principle of cosmology must be 'There is nothing outside the universe' . . . This first principle means that we take the universe to be, by definition, a closed system. It means that the explanation for anything in the universe can involve only other things that also exist in the universe . . . If something has a position, that position can be defined only with respect to the other things in the universe. If it has a motion, that motion can be discerned only by looking for changes in its position with respect to other things in the universe."

Space is, therefore, a network of relationships.

Secondly, any observer within the closed system is observing a system of which she is a part. The act of observation changes the closed system, which is the founding principle of quantum mechanics. This is the most simple and profound explanation I've ever heard of this phenomenon.

Further, space is a set of processes, not things. These processes are "transfer[s] of information." Smolin believes that space is discrete, i.e. that it is made up of elementary parts, which he calls "elementary events." The Planck scale is the measure of these events. Space being discrete means that this region of 'space' represents a finite number of events and that a finite amount of information is contained in it. By information, he means that a finite number of yes/no questions may be answered about that elementary unit.

Further, the presence of matter, changes the PRIORITY of causes in this event-driven model of space. I've typically heard this referred to as the shape of space-time, but Smolin, having redefined space as a network of relationships (and I think "changing, contiguous relationships" is implied, due to the nature of life), shows that matter simply rearranges the relationships.

I love this view of space and it fits everything I have studied about everything. In particular, it reminds me of Bertrand Russell's epistemology. At first Russell seemed to be saying that we could only *know* relationships, but he then radically redefines "me" as a set of changing relationships. Smolin takes this one step further, redefining all that exists as a network of relationships affected by the observer.

A couple more unrelated but cool observations:

"It is commonly assumed that anything that is observer-dependent is subjective, meaning that it is not quite real. But . . . in a universe defined by [the theory of relativity], something may be both objectively tru and at the same time knowable only by some observers and not others."

"So, in the end, the most improbable and hence the most puzzling aspect of space is its very existence. The simple fact that we live in an apparently smooth and regular three-dimensional world represents one of the greatest challenges to the developing quantum theory of gravity. If you look around at the world seeking mystery, you may reflect that one of the biggest mysteries is that we live in a world in which it is possible to look around, and see as far as we like. . . the greatest gift the quantum theory of gravity could give the world would be a renewed appreciation of the miracle that the world exists at all, together with a renewed faith that at least some small aspect of this mystery may be comprehended."

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