Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A non-expert question

  1. May 27, 2008 #1
    a non-expert question !!


    From what i understand , the number of spacetime dimensions needed by strings theory to be consistent arises due to the quantization of the classical action of the string , given that there shouldn't be tachyonic states in the mass spectrum of the theory . my question goes like this : why don't physicists look for a new quantization process that gives 4 dimensions , and looks like the known quantization when the string shrinks to a point particle , so that Q.M is modified for the sake of strings theory , but remains correct for our classical picture where particles are point like objects .

    in other words : strings theory modifies G.R by adding some corrections to einstein-hilbert action - right ??- that leave the action intact for large scales , but it doesn't seem to do the same when it comes to quantum mechanics !!! it certainly says a lot about QFT , but QM is a given in the formulation of strings theory !!!

    excuse my technical terms , i'm not an expert , i just have an interest in the subject .
  2. jcsd
  3. May 28, 2008 #2
    is it that my question isn't worthy of response or what :uhh:
  4. May 28, 2008 #3
    I am an amature and my opinion is of little consequence here, but I would suggest that your question is probably too broad to answer without writing a textbook. Try narrowing it down and be more specific.

    Also, this forum is jealously gaurded by persons who believe it should only be for discussion of papers published in peer-reviewed jounals. Your quesion sounds like you may be developing your own ideas.....a dangerous practice when all you are expected to do is to climb up on the shoulders of giants.

    Good luck.
  5. May 28, 2008 #4

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2015 Award

    I demand an answer! In under 10 hours! In the middle of the night!
  6. May 28, 2008 #5


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    That's certainly a very interesting idea. The problem is that it's just words (for now). There is clear way to generalize the quantization process. But I think it's an interesting idea...But without any specific idea about how to go about it, it's just speculation.
    I don't know whether anybody has ever made any attempt in that direction. And I don't know if anyone has ever spent some time thinking about it. It's the first time I hear the idea and it's interesting.

    You are right that string theory has the standard quantization approach as a starting point. It does not at all propose any modification of quantum mechanics. If you were to quantize classical strings in different way then the theory would no longer be called string theory but something else. Again, it' san interesting proposal but from the idea to an actual implementation involves a huge step and it's not clear at all how one would get started.
  7. May 28, 2008 #6


    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Don't worry starkind, mmzaj is on very safe ground. And it is a good thing that the mentors keep the bar raised because it encourages people to look in the literature for their ideas. It can be educational to do a search and find out where what you have thought up overlaps with some peer-review journal research---as often happens.

    In this case mmzaj have you looked here?
    This several times makes special mention of the D = 4 case.
    Like here: "Since any value of dimension can be used, and especially d=4, the applications could be more realistic..."

    I am not saying that Wikipedia is entirely reliable, or that the idea here is the same as yours. But there may be some overlap.

    Also you might look here:
    this article has further references to books and other source material

    It begins: "The non-critical string theory describes the relativistic string without enforcing the critical dimension. Although this allows the construction of a string theory in 4 spacetime dimensions, such a theory usually does not describe a Lorentz invariant background. Thus it is not a suitable theory of everything. However, there are recent developments which make possible Lorentz invariant quantization of string theory in 4-dimensional Minkowski space-time.

    There are several applications of the non-critical string..."

    I'm not well-informed about this but perhaps tossing out these links can be a little help to you.
    Last edited: May 28, 2008
  8. May 28, 2008 #7


    User Avatar
    Science Advisor

    Several years ago, some of the LQG theorists used their bizarro quantization process (nonseperable/huge hilbert space, Polymeyer states, etc) on the bosonic string.

    AFAIK thats the only case of using nonstandard quantization procedures w.r.t string theory perse.

    Suffice it to say, it wasn't well recieved, pretty much b/c it missed all the quantum anomalies of the system, which is bad.
  9. May 29, 2008 #8


    User Avatar
    Science Advisor

    Additional dimension in string theory are actually a GOOD thing, because otherwise string theory in 4 dimensions would be too simple, i.e., it could NOT accommodate specific interactions of the Standard Model of elementary particles. Perhaps it could be done with less than 10 dimensions, but certainly not with only 4 dimensions.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: A non-expert question