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String Theory and 4 dimensions

  1. May 3, 2014 #1
    Anything that exists has to exist/interact with at least 4 dimensions, right? Stuff existing/interacting with other dimensions too (even if they can't be/haven't been observed) have to exist/interact with our 4D as well, right?
  2. jcsd
  3. May 3, 2014 #2
    That sounds like the kind of question one asks first before preceding to ask about the underlying question one is thinking about.

    For example, are you asking if the string must exist in all of the dimensions, or just some? And if just some, is it the higher dimensions that are optional with the lowest being required, or can a string exist in just the higher ones without the lower ones?

    Or, you might be asking about the geometry itself; what kind of geometry and dimensions are required for the string with respect to the Relativity concept of "no preexisting geometry"... as in, what does that mean with respect to the geometric dimensionality of the string? Do the Euclidean dimensions even apply at this level or are these a different kind of dimension?

    Or, you might be wondering about the existential dimensionality of the string with respect to the uncertainty principle. Much bigger things like protons are not thought to have a specific location prior to measurement... yet the ratio of the length of the string to the diameter of a proton is about the same as the ratio of your height (six feet?) to the distance between the Milky Way and Andromeda galaxies (2.5 million light years). That is, if you were the size of a string, the size of a proton would be like the distance to Andromeda. So strings are so small that attempting to locate a string, or even describing its parts and their relative positions while vibrating seems to suggest precision of location that uncertainty forbids.

    So, how are you thinking about this?
  4. May 11, 2014 #3

    Sir, please enlighten me on all the 3 scenarios.
  5. May 14, 2014 #4
    I was asking which scenario or something else might be the basis for your question because it is not clear what you are asking.

    Of the three things:

    The first is based on strings existing in many dimensions, so when you ask about 4 dimensions one needs to know if you mean the four "flat" dimensions only ("our 4d"), or if you are including some or all of the "curled" dimensions.
    Are you asking if four of the string dimensions are our flat 4d dimensions, or asking if the strings must be in all their dimensions?

    The second is subtle, but is based on a re-examination of what the dimensions might be... the four flat dimensions may suggest Euclidean geometry, but the remaining curled dimensions might suggest otherwise. Maybe 4d alone is different than 4d as a subspace of 10d or 26d?

    The third thing is about uncertainty and the supposed topologies and mechanics of the string (open/closed loops, "vibration", etc...). Atoms are small enough that the classical mechanics concepts don't seem to apply; strings are so much smaller that any sense of a string having attributes like length, tension, end points, vibration, etc... seems totally impossible. Yet, the strings are distinguished by their topologies and vibrations, which seems like assigning them hidden variables underneath the canonical quantum uncertainty.
    In other words, how is it that an electron prior to measurement has no position attribute, yet a string is given enough attributes to describe its shape (the relative positions of its topological structure) and mode of periodic displacement (the relative positions of the string excursion describing the vibration, the nodes, the harmonics), etc...?

    Anyway, just wonder from what basis you were presenting the question. If none of these apply, maybe you can clarify.
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