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Ch. 5 - The Theory of Everything

Please use this thread for discussing Ch. 5 - The Theory of Everything.

I think this chapter is where the layman such as myself starts to get lost. On p. 107 he talks about renormalization, subtracting infinities, blah blah blah. By the end of the chapter, he is talking about different versions of string theory making up M-theory with eleven dimensions that has 10^500 solutions, and somehow this is supposed to correspond to 10^500 universes.

I should point out that I'm not saying that a very complex theory that is inaccessible to the layman can't be true (or a good model at least), but I'm critical of the book because he doesn't seem to making much of an effort to make the case for it, and we are left wondering why he is so enthusiastic and satisfied with this theory. Not to mention, as I've said before, whether his interpretation of all this mathematics is just poetic license. (I pulled a quote on this that I will post for the next chapter's thread)

I agree with your criticism.

Another book I'm reading, The Cosmic Landscape by Leonard Susskind, helped me some here. Susskind also mentions the 10^500 solutions. I think the point is that each solution represents a different configuration of physical constants defining another set of "laws of physics", each with its own set of elementary particles with different masses and forces and interactions.

You know how polynomial equations can have multiple solutions? For example, x^2 - 1 = 0 has a root at 1 and a second at -1. That's my analogy for the multiple M-theory solutions.

Susskind talks about the mathematical construct of M-theory as a "landscape", saying that solutions represent low energy states or "valleys" in the landscape. It just so happens that the valley where our universe sits allows for the physical laws that we experience. In other valleys, the laws are different. If you cross a pass into a valley where the physics doesn't allow for atoms, you'll suddenly disintegrate.

As Leonard describes it, M-theory was supposed to be the "final answer" that would explain once and for all why our universe is the way it is -- why the proton is 1836 times as massive as the electron and how gravity and quantum mechanics fit together, etc -- and it would make it all look inevitable. M-theory was supposed to explain why the universe couldn't be any other way. Instead, it says, "Here are 10^500 different ways it could be. You just happen to be in the one that won the lottery and turned out to be stable enough for complex life to evolve."

I hope my talking about The Cosmic Landscape in the discussion of The Grand Design isn't giving anyone heartburn. The Cosmic Landscape has done a better job of helping me understand the issues and how the science evolved.

tbarron, I'm interested in any source that helps make sense of this stuff. Although I'm inclined to do some more reading on quantum theory in general before tackling some of the speculation on string theory and M-theory for example.

Because I received my physics Ph.D. from Stanford, I knew Lenny Susskind, author of The Cosmic Landscape, and attended a class of his. I was impressed with how clear that book was, especially since it was so difficult to follow his technical discourse as a grad student.

String theory is so complicated that most physicists don't understand it unless they specialize in that area. It's a big leap in complexity compared to quantum mechanics, which every physics undergrad takes a few courses in and understands at some level.

Since books for laymen can't explain the gory mathematical background, they consist of analogies and vague ideas. No matter how good the author is, there are limits to how much substance can be conveyed.