October 18, 2004

When theories collide... The theoretical physics community is having a disagreement. That, of course, is not unusual. What is interesting is that they're doing it in blogspace, so we get to cheer them on, take sides, and make abusive gestures as appropriate. The problem is String Theory. Specifically, a rather complex thing known as the String theory landscape.

It seems that there are around 10^500 possible string theories. Each of them describes a different universe. The Universe we observe seems to be rather strange. Is it because we're here to observe it? Is that a cop-out? Does string theory predict nothing? Or everything? Anyway, Grab your popcorn and tune in.

posted by Chaz 20 years ago
  • Ah, excellent post.
  • Very, very, very, very interesting to me Chaz (as a Physics major), thank you for the post. I haven't really dealt much with string theory, but one comment I can make is that the Anthropic principle does make a bit of sense (I don't ascribe to any view on string theory, yet) in a quantum sense. One of the basic tenants of quantum mechanics is that a system can exist in a number of states (take Schrodinger's cat, who was both alive and dead) until the system is viewed when it takes one very real state (whoops! Cat's dead.) That could be why humans have such an impact on the universe, merely because we are watching it, not because god made it special which I saw as a comment on one of the blogs.
  • loto: The latest issue (September/October) of the Skeptical Enquirer has an article by Mark Perakh entitled "The Anthropic Principle and the Big Bang: Natural or Supernatural? A Simple Probabilistic Answer". There is an early version of this article on his website. Interesting reading -- especially since it never even occured to me that the Anthropic Principle could be interpreted by some as support for a intellegent design or special creation scenario. There also seems to be some buzz that the Copenhagan and Many Worlds interpretations of QM may have been falsified recently. AFAIK, the experiment hasn't been duplicated yet. The experiment doesn't falsify the Transactional Model, though.
  • I had a quantum tenant once. You could never tell if he was in or out. But seriously, loto, your sketch of Schrödinger's cat gedankenexperiment betrays common misconceptions. First of all, remember that it is intended to illustrate a sort of deficiency of QM when translating from micro- to macroscopic scales. Second, it is not that the cat is both dead and alive, but rather that it is in a mixture of states. The interpretations of this statement are a bit philosophical. The Copenhagen interpretation says that the mixture transitions to a single state when an observation is made. (But what is an observation? you ask. Good question. Some people define it based on interactions between particles and detectors, but such definition are not only arbitrary, but also highlight an important incompleteness of the Copenhagen interpretation.) By the way, the observation doesn't require humans. The Many-Worlds interpretation says that the dead-cat and alive-cat states are both persistent, but decohered. When the cat is observed, the observer-states and cat-states are entangled, but each possibility is independently (and non-interactingly) present— parallel universes if you will This interpretation is popular among Sci-Fi authors. (Take these statements with plenty of salt. It is hard to be precise without a fair bit of algebra.)
  • Is it that obvious that I don't start quantum physics till next semester? *grins*
  • I find the tone of the comments (particularly to Peter Woit's blog entry) almost as much fun as the content. Theoretical physicists at the highest levels seem to have a high level of arrogance, and no tolerance for stupidity. Because they are pretty clever people, "stupid" in this context seems to mean "unlikely to win a Nobel". Some of the comments are rather direct. It's interesting to speculate whether the arrogance comes from brilliance, or if it is a prerequisite for taking the Universe to bits with your mind. Maybe both. I'm thoroughly enjoying the spectacle of really bright people accusing each other of being unable to grasp the facts. Anyway, just to put a dog in the fight, I think the Anthropic Principle is a completely irrelevant concept. It doesn't matter whether it's true or not. The Universe seems to exist, and my (arrogant) desire is to see it fully described. A theory that has failed to make a concrete prediction in it's 30-year history seems to have some 'splaining to do. PS - tensor - neat nick for this topic.
  • Whoa, dude...wait a minute...you've got some string and a cat...I do that all the time at home! Man, and that physics stuff is supposed to be so hard.
  • I'm curious, since there are a lot of physics monkeys in this thread. Have you seen What The Bleep Do We Know and if so, what did you think of it? I don't want to spoil it by spouting my opinion of it but I'm curious what people closer to physics than I thought.
  • I remain astonished that anyone takes either the strong or weak anthropic principles seriously. The strong version is absurd. The weak version is trivial. One lesson here is that, in general, physicists make piss-poor philosophers. Of course, many philosophers are piss-poor philosophers, so there ya go.
  • shawnj: I saw What The Bleep Do We Know recently. My opinion of the movie is that it is pseudoscience. Extremely bad.
  • Ditto to Nomen Nescio comment regarding it as science: extremely bad pseudoscience. As a movie? It's even worse.