String Theory: Valid?

topic posted Thu, October 26, 2006 - 6:03 PM by  Jenna
I have long since been a fan of Brian Greene's and have always thought String Theory to be a valid theory. But lately there has been much controversy over whether it can be considered a theory or not. I has yet to be successfully tested yet there are equations behind it. What do you think? Is it a valid theory or just a hypothosis?
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    Re: String Theory: Valid?

    Thu, October 26, 2006 - 7:15 PM
    String theory elegantly explains or rather provides alternate equations for things we already know. To be proven as a valid theory it needs to be able to predict something we do not know that can be verified.

    Still, there is just too many standard well known equations that fall out of it for there not to be something to it other than a clever math trick. But that's just my opinion.
    • Re: String Theory: Valid?

      Thu, October 26, 2006 - 7:36 PM
      Last I heard, string theory has yet to predict anything. Implying it can't even predict what we know, but that may just be my understanding of other people's comments as I haven't studied it myself.

      I suspect that the extra dimensions are really just functions of the known 4 dimensions. If so, then I think there is something workable there.
      • Re: String Theory: Valid?

        Fri, October 27, 2006 - 1:12 AM
        From what I understand, string theory has a lot of problems. I believe to say that standard equations that we know "fall out" of string theory naturally is a misrepresentation. In its current state, I think it takes a lot of unseemly hacking to get those results. I am also not aware of any testable predictions, and, in fact, have heard more than once (directly from the horse's mouth, as it were, in one case, namely from someone who had done his Ph.D. in string theory) that string theory is unlikely to produce any predictions that will be testable with technology available in our lifetimes. Kind of turned me off from pursuing it further (at least, professionally). Hypno, if you can point to a source that says otherwise, I would like to see it.

        I have some understanding of the problems with string theory which I have picked up in various places, but I can't do them justice*. I can suggest a few books (one of which I am currently reading, one of which I where have skimmed bits, and one of which I poked through earlier today, coincidentally). In reverse order (which I think would be the order to most directly address your question, Jenna) they are "The Trouble with Physics" and "Three Roads to Quantum Gravity", both by Lee Smolin, and "Warped Passages" by Lisa Randall, a physics professor at Harvard. In fact, I recommend reading Randall's book in general. I think people that have been following some of the other threads on this board might find her perspective on modeling and scale in physics valuable. These are all books written for the layman.

        And, no, the extra dimensions are not "just functions of the known 4". Troy, with all you've written about other people studying before they spin a tale, I'm a bit surprised you would say this.

        *I can't resist throwing out one tidbit. I went to a talk once where the thing that stood out in my mind was when the speaker said that the metric in string theory might not even be expressable in closed form. Sorry, I can't easily explain what that means, but trust me, it's nasty. That was a long time ago, though.
        • Re: String Theory: Valid?

          Fri, October 27, 2006 - 8:30 AM

          "And, no, the extra dimensions are not "just functions of the known 4". Troy, with all you've written about other people studying before they spin a tale, I'm a bit surprised you would say this. "

          There was a reason I said "suspect" and what I said was not said blindly. I've some idea on why the extra dimensions are there but I also know that a sufficiently complex unknown function (particularly of several variables) is extremely difficult to distinguish from a free variable. I never liked the argument that the "extra" dimensions had to be wrapped up tightly. If the "dimensions" were actually functions, then I would be much more comfortable with them having to be tightly wrapped-up. All of this is a hypothesis that could easily be wrong.
        • Re: String Theory: Valid?

          Fri, October 27, 2006 - 2:35 PM
          This is a direct link to an article written by Brian Greene, one of the leaders in the "fight for string theory".

          I think it explains alot... good reading too!
          • Re: String Theory: Valid?

            Fri, October 27, 2006 - 3:33 PM
            To quote the article:

            "But to suggest dropping research on the most promising approach to unification because the work has failed to meet an arbitrary timetable for complete success is, well, silly."

            String theory is the most promising thing around because like mistletoe it has grown around the tree (of physics) and virtually choked it to death. Will any of the current theories ever bare edible fruit? Who knows, personally I doubt it.
            • Re: String Theory: Valid?

              Sun, October 29, 2006 - 11:56 AM
              It is truly hard to say at this point but I do think string theory and other such theories have got their chances but it just takes time and patience.
          • Re: String Theory: Valid?

            Fri, October 27, 2006 - 5:13 PM
            Jenna, thanks for the pointer. Maybe I shouldn't post late at night. :) What I wrote may have given the impression that I think string theory is junk. I have misgivings about it, but there certainly seem to be a number of positive aspects to it, too. I'm certainly pleased at the thought that we might see some interesting new experimental results in the next decade. I was more or less trying to say that, from what I understand, string theory has a long way to go before it can be accepted as valid. More to the point, I thought those books might be of interest. The authors certainly understand string theory far better than I do.

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