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Elegant Universe Airs Tonight on PBS
fatarfy writes "USA Today among others has an article discussing tonight's presentation of Brian Greene's Elegant Universe, which discusses String Theory. It airs on PBS. From the article: 'The two segments of the show turn their spotlights on a crisis in physics, one invisible to the general public but increasingly embarrassing to the discipline. Simply put, Einstein's unbelievably accurate explanation of gravity, known as general relativity, is completely out of whack with the equally accurate explanation of electromagnetism, radioactivity and atomic forces known as quantum mechanics. The theories are mankind's most fundamental views of verifiable reality, and the disagreement means that something important about the universe eludes our understanding.' Sounds like it's worth watching."
I don't know about you, but I have no problem perceiving four dimensions (the fourth being time). Still a very valid point that we shouldn't limit ourselves to an arbitrary value based on perceptions though :)
Surely we can agree that the gap between quantum and relativity needs to be filled, but going off on a whole set of random assumptions based on what needs to be true to solve a little math issue might not be the best approach. Then again, look what it did for Einstein... Of course the difference there was that his predictions were actually observed...
The thing I find funny about critics of string theory is their objection to the idea that there can be multiple dimensions beyond the three dimensions people can perceive.
Who fits that description, though? I know lots and lots of theorists in elementary particles and fields who are critics of string theory, but not for that reason. Indeed, it'd be odd if so, since mainstream particle theorists have been building models incorporating additional "dimensions" since the 1950s (e.g. isospin models in particle and nuclear physics).
The real criticism of string theory is much more fundamental. In order to be taken seriously -- indeed, to even be considered scientific -- a physical theory should be falsifiable. There should be some experiment I can do or observation I can make where, if it doesn't come out the way the theory says, then the theory is wrong. But since string theory describes the nature of things at energies around the Planck scale -- 19 orders of magnitude greater than the mass of the proton, or 16 orders of magnitude higher than the best particle accelerators we've built -- how do you test the theory? String theorists say that they simply haven't been clever enough yet to figure out how to make unique predictions at potentially experimentally accessible energies, but that they will be; and maybe they're right. I hope they're right, because string theory is beautiful in a lot of ways (at one point, I wanted to do string theory). But they've been saying that for 20 years now, since Green (no relation), Schwarz and Witten's stuff.
The TV show is based on a book of the same title, which I've read. I don't think it's the best introduction to the subject of quantum gravity, because it's all predicated on string theory, which is only one possible candidate for a theory of quantum gravity. Actually string theory has made essentially no progress in the last 20 years. You still can't calculate anything with it, it still doesn't make testable predictions, and there are still too many different versions of string theory, with no way to tell which (if any) is correct.
A much better book is Lee Smolen's Three Roads to Quantum Gravity. What I like about it is that it focuses on basic principles of what a theory of quantum gravity must be like, rather than just describing all the (probably incorrect) details of one (probably incorrect) theory. Before reading Smolen's book, I'd also recommend starting off with QED: The Strange Theory of Light and Matter by Feynman, which describes the relatively well understood unification of quantum mechanics with special relativity (as opposed to general relativity).
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