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Strings can vibrate, but do they move?

  1. Jun 30, 2011 #1
    I am trying to find out if my general understanding of the strings in string theory is correct.

    The strings can vibrate along different nodes to create the particles. Do the strings themselves ever wander around as a whole string, or would they be considered to be locked in place like pieces of a grid?

    The way I picture it is that the strings, if they could be seen, would create a giant solid grid. A particle that is moving would jump from string to string as a vibrating wave, causing new strings to dance as it is seen to move, but those strings themselves are locked in the giant grid. All movement is not really movement, just vibration data being passed along the grid of strings. The grid of strings looks the same everywhere, even in a complete vacuum, but what would look different would just be the vibrations of the strings themselves creating matter and particles where it exists to the observer.

    Is this accurate, or are the strings themselves free to move around as well as vibrate?
  2. jcsd
  3. Jul 2, 2011 #2
    Did I ask a hard question? Hehe

    I figured after 95 views, one of those people would know the answer.
  4. Jul 2, 2011 #3


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    It’s cool to "think in pictures", but I guess it’s going to be hard in string theory since we are dealing with 11 dimensions (or something like that).

    I don’t know enough about string theory to give you a better answer, but why not check out these videos:


    Full playlist (6 parts): http://www.youtube.com/watch?v=E7FV9aaiwKQ&playnext=1&list=PLDBD5A9D4D1CE6869

    TED - Brian Greene on string theory
    Last edited by a moderator: Sep 25, 2014
  5. Jul 2, 2011 #4
    I have watched nearly every video on string theory; I find string theory and quantum mechanics extremely fascinating. I have listened to and watched quantum mechanics courses that are 40 hours long which help teach someone the general outlines of the theories. I am trying to develop my math skills enough in college right now so that I can begin speaking the language that physicists speak. Currently I have just begun. It's going to be years before I can derive most of the equations. Right now however, I am begging to know of this general picture of string theory that I asked about.

    To breakdown what I have gathered so far as my general understanding: Physicists were running into anomalies when looking at particles as point-particles, because of divergences and infinite soaring values when approaching the particles. Forces grew by 1/R when approaching the point particles. Strings satisfied those problems by providing a definite particle size, on the order of a Planck length. The strings may have a shape represented by the Calabi-Yau manifold, where 4 dimensions are more prominent so to speak, while the other 6 dimensions are curled up. Branches of the manifold vibrating at a specific frequency will supposedly create a specific type of particle. Music on the strings is what makes particles and mass and all of the known forces. Since the strings are a medium for this musical energy to exist upon, they need not move around themselves, only vibrate in place.

    I'm wondering if someone can confirm that last part, that the strings are the medium for the vibrations, and the strings do not actually move around, but stay in place and vibrate.

    I realize pictures are hard to paint without mathematics, but I wondered if this question is one which could be answered without the mathematics, just so I know if I am understanding the general theory at this point.

    One picture which led me to believe that what I am picturing in my mind is correct is this one I found while looking at Calabi-Yau manifold photos:

    [PLAIN]http://www.lpt.ens.fr/IMG/jpg/calabi-yau-grid-small.jpg [Broken]

    Notice the strings as part of a grid.

    Thanks for any interpretation on the subject.
    Last edited by a moderator: May 5, 2017
  6. Jul 2, 2011 #5
    Strings are free to move about as they please. They move like regular particles move in more familiar physics. Only, strings are allowed to move in 10 dimensions, so they can move around in 10 different ways.

    It is analogous to a guitar string, or something, that we are familiar with. It can move around just fine, and it can vibrate while doing so. You can play a guitar just fine while walking to the next room. The picture you posted represents the extra dimensions that string theory requires, not the strings themselves.
  7. Jul 3, 2011 #6
    So I had understood it wrong all along.

    Here is my following question. If the strings are free to move around, are there areas in space where a true vacuum exists, a place if you were to look at, not even strings could be found?

    If they can move, I would think the answer to that would be "yes". If that also becomes true, my curiosity goes further; how would forces permeate in an area of space without anything being there to carry the forces?

    That is one of the questions which had made me think of the string world originally as a solid grid with strings everywhere.
  8. Jul 3, 2011 #7
    i know next to nothing on string theory but aren't each of the strings the planck length (10^-5 the diameter of a proton)? given a GUT based on string theory would have everything "quantumed", that distance of vacuum would not really exist in terms of forces acting on it because it must all be conserved. a really poor example is a piano, you can play note C and C sharp but you wouldn't try to play a note in between even if you see a gap in between the keys of the piano. this (i think) is how a discrete, quantum universe works.

    i hope you understand this - cause i don't lol
  9. Jul 3, 2011 #8


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    Yes, they are.

    Quantizing a string shows that there are infinitly many modes describing different vibrations (just like the vibrations of a guitar string). In addition there "zero modes" describing the displacement of a string as a whole w/o any vibration (or any "deformation"). This is standard string theory and can be found in any introductory book.
  10. Jul 4, 2011 #9


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    Why would they be locked? Look at the solution of the embedding coordinates X in the bosonic case:

    X^{\mu}(\tau, \sigma) = x_0^{\mu} + \sqrt{2\alpha'}\alpha_0^{\mu}\tau + \ldots

    The dots are the oscillator terms; if they're all zero, one recovers the motion of a point particle moving in flat spacetime. For tau=0 the position of the center of mass is x_0.
  11. Jul 4, 2011 #10


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    I see that you know more about strings than I do :blushing:, therefore, see this as only 'philosophical speculations' of my own.

    I think I see what you’re after... you think of the vacuum as a grid of strings, right? Almost like a 'sheet', and when you move one end of the sheet you will 'propagate' the known forces through vibrations/waves in this 'sheet', right?

    Now, I’m just guessing, but in the 'normal' QM case the forces is due to exchange of particles, i.e. the Bosons in the Standard Model:

    And I think that the 'only' thing String Theory does, is breaking these bosons in 'finer parts' – i.e. strings that vibrate 'internally'...

    Thus, you will have a lot of 'packages' of strings 'running' back and forth to make up the four known fundamental interactions/forces.

    Now, I suspect all the real experts out there will run me over completely...

    * running away * :smile:
  12. Jul 4, 2011 #11
    just to add, now that i understand more, in bosonic string theory and superstring theories, the strings are able to move. they oscillate to give their properties but can also move creating a 2-dimensional structure called a worldsheet. Closed strings can move freely in vacuum but open strings are only able to move if connected on one end to a membranne surface known as a D-brane

    hope this answers your question - and is correct?
  13. Jul 4, 2011 #12


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    Ah! Of course you’re right mibaokula, and AFAIK it’s only gravity that is a closed string, right?
  14. Jul 4, 2011 #13
    Yeah I think so. But only in type I superstring theory I believe. Type I superstring theory is the only super stringtheory out of
  15. Jul 4, 2011 #14
    The big five that have closed strings. The other for only have open strings (boson string theory might have closed strings)

    Anyways, the theoretical physicists believe that gravity appears weak because of the fact that is a closed string not restricted to our membrane.

    Sorry for the cut-off. I accidentally posted the message prematurely.
  16. Jul 4, 2011 #15


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    Okay, thanks!
  17. Jul 4, 2011 #16
    I think rather than say that fundamental particles are split into packets of string, string theory says that each fundamental particle IS a string. I'm not sure but i think true vacuums still exist between these strings
  18. Jul 4, 2011 #17
    In some forms of string theory there are multidimensional "branes" which the strings can act on. they are normally called d branes.
  19. Jul 5, 2011 #18
    If strings can wander in hidden extra dimensions so in a high energy experiments can one see particles disappear suddenly and reappear or vanish for very long periods ? Also if electromagnetic radiation is confined to 3 dimensional space so no photonic string can dissappear but does other particles like electrons cross to hyperdimensional space? The electron field is coupled to maxwell's field so this can't happen right?
    Last edited: Jul 5, 2011
  20. Jul 5, 2011 #19


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    Of course, you’re right again. Sorry for fuzzy expressions...

    If I would try to save my a*s, I could say that the 'packet' is what we 'see' from the 'perspective' of the Standard Model, but I skip that – it would probably only cause even more confusion... :blushing:

    Where are the hardcore string experts?
  21. Jul 5, 2011 #20


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    More speculations on my behalf; I think that in the LHC they are anticipating the possibility of detecting supersymmetry (SUSY) and large extra dimensions (by detecting 'losses' in the measurement).

    But so far, the LHC appear not to support large extra dimensions, I think...
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