The Elegant Universe

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This past Shabbos was a quiet one, and I mostly just caught up on some reading. Most notably, I went back and read the end-notes for The Elegant Universe by Brian Greene. I'd finished the main text earlier this week, but I wanted to collect all the end-notes to see if anything terribly interesting was hidden within. The book was quite enjoyable. As its subtitle suggests, it is about "Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory." This was particularly interesting to me since until reading this book I didn't know much about string theory other than that it is a cutting edge branch of physics that, though still in its infancy, promises to heal the pernicious rift that divides relativity theory and quantum mechanics and provide us with a unified view of the rules that govern the universe's most fundamental machinery.

It starts by explaining the most salient concepts of both quantum mechanics and Einstein's special and general theories of relativity. It then goes on to illustrate how relativity and quantum mechanics are incompatible with each other and why this might bug us so much. The second two thirds of the book is devoted to a gloss of the various aspects of string theory: a history of its development, an explanation of how it reconciles quantum mechanics with relativity, a high-level tour through the concepts of string theory and their remarkable consequences, a discussion of how this controversial and unconfirmed theory might one day be verified, and a view of the severe mathematical obstacles physicists must overcome in order to extract useful predictions from string theory.

Oddly enough, my favorite part of the book was the introductory parts that dealt with relativity and quantum mechanics. Since both of these branches of physics have been extremely well developed and confirmed with astounding accuracy in the past century, I've had plenty of exposure to these theories both through my formal education and my independent recreational exploration. So this familiar material should have been old hat to me. But Brian Greene surprised me by providing expositions that gave me fresh insights into these pillars of modern physics.

My favorite little gem was his explanation of the Heisenberg uncertainty principle, which made the principle make sense for me in a way that it never did before. It's so simple: since every method of measurement boils down to poking something with one or more particles, the only way you can measure position without disturbing velocity is to poke very, very lightly. But the only way to poke so very lightly is to use probing particles of very low frequency (since lower frequency means lower energy). But since low frequency means large wavelength, the gentleness of your poking has come at the cost of precision in measuring position, since you've only narrowed the position down to the large space covered by that long wavelength. You can only measure position precisely by using particles with short wavelength, whose high energy completely screws up your velocity measurement. So you're stuck having to choose one or the other.

I was also especially charmed by a surprising perspective on special relativity that the text helped me discover: everything in the universe is travelling at the speed of light and is forever fixed in this speed, not just photons and other such massless particles. We're just used to thinking otherwise because the massy objects of our everyday experience have most of this speed directed in the dimension of time; all of it, in fact, when an object is stationary in space. Whenever we get our bodies moving through the familiar three dimensions of space, we aren't really changing our speed through spacetime at all: we're just stealing some speed away from the direction of time (thus slowing down our clocks whenever we move), just like turning your moving automobile from facing north to facing north-east only converts part of its north-south motion into east-west motion without changing the overall speed. Thinking about the universe in such delightfully unconventional ways is what I really love about modern physics.

The stringy majority of the book was also good, but wasn't nearly as satisfying since those ideas were explained with a lot less completeness and a lot more vagueness. Of course, this fact is inevitable for at least two reasons. First, string theory is far from completely understood by the very scientists developing it (that's what it means to be cutting-edge), so the author certainly can't give you answers which nobody has yet. Second of all, the mathematics behind the parts of string theory that are well-understood are far too complicated to be explained without bloating up the text to gargantuan proportions and completely losing the audience of the layperson in the process. Thus, I can completely forgive this book for sacrificing precision in the name of comprehensibility. The Elegant Universe serves quite effectively in the role of introducing non-physicists to this fascinating frontier of science, and if it's whetted my appetite for a more detailed exploration of the finer details and mathematics, then that can only be counted in its favor.