March 2, 2009

I recently finished an astronomy course that re-ignited my interest in physics, and so I decided to learn about something that wasn’t taught in physics way back when I was in college – string theory. I went to The Teaching Company and ordered their course Superstring Theory: The DNA of Reality, by Professor James Gates. The course contains 24 half hour lectures on DVDs.

Einstein’s general theory of relativity does a pretty good job of explaining what we see on a macro astronomical scale. And quantum physics explains what we see and deduce in the smallest micro scales. But apparently these two theories are incompatible, at least mathematically. The proponents of string theory claim it unifies these two theories, finally achieving what Einstein spent the second half of his life trying to do.

One of the first things Professor Gates tells us is that string theory is a very complex mathematical construction, and that nothing in string theory has been proven in experimental physics. It’s just math and theory! He then makes the commitment to teach this course about string theory without resorting to complex math and equations. But if it’s all mathematics, what’s left to teach? Professor Gates intends that his various graphics and animations will make things clear to us non-mathematicians and non-physicists.

The course starts with an overview of the quantum world and the “denizens” that inhabit it. We learn about a lot of subatomic particles that are smaller than the more familiar electrons, neutrons, and protons in atoms – like quarks and leptons and photons and gravitons and many more. All the particles have corresponding anti-particles. And later in the course all the particles are paired with superpartners.

Until the superpartners came up, I enjoyed getting to know all these particles, most of which can be seen or deduced in lab experiments, so they seem real, even if rather small – around 10

^{-16}meters. But then we learn that the strings that underlie these particles (visualized as little vibrating loops or wiggly strings) are only 10

^{-33}or so meters. I would be okay with strings that are a few orders of magnitude smaller than quarks, but not 17 orders of magnitude. Surely there must be something in between!

The course now proceeds through a detailed history of the development of the initial string theory in 1968, and on to the first, second, and third string revolutions, where the older theories are updated with newer mathematics that solve various problems, which ultimately leads us to M-theory. (M could well stand for Magic.) And we learn many new names along the way – superstrings, supersymmetry, supergravity, and much, much more.

One of the unsettling facts about this sequence of string theories is that the mathematics only works well when it describes many more than the four dimensions in our universe (three in space and one time). Eventually we get down to ten dimensions. That was in 2005. I suspect string theory has evolved since then.

My major learning from this course is that string theory is extremely complicated. Professor Gates describes a few dozen particles, the contributions of a few dozen physicists with their few dozen theories, accompanied with zero lab-proven results. As he says repeatedly, this is mathematics, not physics. Physics requires both theory and experimental validation.

I now know a few more terms and a little about a few particles, but I’m a long way from understanding string theory. I believe that a lot more of this material will stick if I listen to the lectures a second time. But first I’m going to read a book that both Professor Gates and my daughter (a physics major) recommend to me, The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory, by Brian Greene. But it doesn’t look like an easy read either.

## 2 comments:

As I was reading this write-up, I found myself remembering a book I had read a few years ago. I remembered that it talked a lot about superstrings and the search for a unifying theory to merge relativity and quantum physics. Although it was written for the layman - sort of - it blew me away when it got into dimensions way past four.

So I went to my shelves to see what it was. I'm startled to see that it is Brian Greene's The Elegant Universe: Superstrings, Hideden Dimmensions, and the Quest for the Ultimate Theory. My copy is copyrighted in 1999. I wonder if that's the same version Kit plans to read.

I don't think I have the energy to re-read it and try to beat him to a post. but I will be interested to see what he thinks. I'd like to think that his Math/Physics background will get him through in better shape than my History/Economics background did for me.

I just bought

The Elegant Universefrom Amazon, and it is copyrighted 2003 and 1999. And that is why I didn't buy the book the first two times I thought about it. Things must have changed!The only addition in 2003 is a new preface, in which Greene says not much has changed, except the strings are perhaps a little bigger than we thought. I like that because as I said in the review, I think 10 to the -33 is too small!

(By the way, I tried to use the sup tag for the superscript, but couldn't. But I bet you could add sup and /sup tags to the two superscripts in the review.)

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