Friday Science: Hawking 10 (Unification)

It always feels good to finish a book. Here is the last review of Stephen Hawking's A Brief History of Time.

Chapter 1: Heliocentric
Chapter 2: Spacetime
Chapter 3: Expansion of the Universe
Chapter 4: Uncertainty Principle
Chapter 5: Elementary Particles and the Forces of Nature
Chapter 6: Black Holes
Chapter 7: Black Holes Ain't So Black
Chapter 8: The Origin and Fate of the Universe
Chapter 9: The Arrow of Time

Chapter 10: The Unification of Physics
As the title suggests, Hawking in this chapter is looking for a grand unification theory (GUT). He spends a little time on string theory, which is probably where he put his bet at one point. My sense is, however, that enthusiasm for string theory has waned these last few years as some of the particles it predicts have not been discovered during tests that should have produced some.

• The difficulty is to combine general relativity with quantum mechanics.
• He mentions old problem of renormalization. The math says "infinity," but we know what it should be from experiment. So you just substitute the experimental value and keep going.
• String theory: open string, closed string, two strings join. Two strings separate. Graviton's cross. Strings, strings, strings.
• String theory suggests there may be either ten or twenty-six dimensions. We don't see the others because they're two small.
• He goes into the anthropic principle again. Life can only exist when three dimensions predominate, so we're just lucky.
• It would take too much energy to find out what it would have been like near the big bang.
• Even a GUT would not predict everything about the future--uncertainty principle, some equations are just too hard to solve.

Here endeth Hawking.