Review: The Grand Design

 The Grand Design came recommended by the Amazon Kindle direct mail ad, and it was available at the library so I checked it out and read it. It's an easy to read Physics primer that discusses the difficulty reconciling quantum mechanics and general relativity, and discusses what the evidence for the accuracy of these theories are.

What I enjoyed was how clearly written the descriptions of the weak Anthropic principle and the stronger versions of the Anthropic principles are. In particular, the authors go over how finely tuned the fundamental constants of nature are, and even go so far as to explain why the Universe had to have 3 dimensions instead of 4 or 6 or 10:

If one assumes that a few hundred million years in stable orbit are necessary for planetary life to evolve, the number of space dimensions is also fixed by our existence. That is because, according to the laws of gravity, it is only in three dimensions that stable elliptical orbits are possible. Circular orbits are possible in other dimensions, but those, as Newton feared, are unstable. In any but three dimensions even a small disturbance, such as that produced by the pull of the other planets, would send a planet off its circular orbit and cause it to spiral either into or away from the sun, so we would either burn up or freeze. Also, in more than three dimensions the gravitational force between two bodies would decrease more rapidly than it does in three dimensions. In three dimensions the gravitational force drops to ¼ of its value if one doubles the distance. In four dimensions it would drop to ⅛, in five dimensions it would drop to 1/16 and so on. As a result, in more than three dimensions the sun would not be able to exist in a stable state with its internal pressure balancing the pull of gravity. (kindle loc 1530)

Where the book fails is that it promotes M-theory as the one theory that would unify quantum theory with relativity, but doesn't go into why it's superior to all the other theories. One issue is that it's not a single theory, but a class of overlapping theories that can effectively have constants plugged in to satisfy the constraints of the universe we find ourselves in. The authors pretty much state that scientists have to give up on the idea of our laws of physics all deriving from one fundamental theory that fixes all the constants. That's quite disappointing for those who value elegance in their theories, but of couse, nothing says that our messy universe has to correspond to a model of a simple and elegant fundamental theory.