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Physics M-theory

  1. Dec 17, 2007 #1
    1. The problem statement, all variables and given/known data
    why they created m-theory?? or why did they find m-theory and how does it help us..
  2. jcsd
  3. Jan 25, 2008 #2
    This might help answer some of your question about M-theory:

    Horizons - Parallel Universes - Part 1
    Part 2
    Part 3
    Part 4
    Part 5
    Part 6

    What I'm curious about is: if M-theory is correct, could gravity "leaking" from other membrane universe to ours account for what we think of as dark matter?

    If other universes' gravity can make itself felt in our universe, maybe galaxies and clusters in the "nearer" universes can have an effect on ours, since, presumably, the galaxies in the clusters of nearby universes would be in aproximately the same "locations".
  4. Jan 25, 2008 #3
    A pretty good video you could look at is "The Elegant Universe". I found it interesting
  5. Jan 25, 2008 #4


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  6. Jan 26, 2008 #5


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    If I'm not mistaken, when I read Hawking's book "The Universe in a Nutshell" some years back, this is what he suggested, i.e., the bulk of dark matter may be due to the effects of high frequency gravitational waves from another universe that may, unlike light waves, be able to penetrate the miniscule dimensions of the higher order dimensions (expounded by M-Theory) of our space-time universe. I don't know what current thinking says, though.
  7. Jan 28, 2008 #6
    If M-theory is correct, and there are indeed an infinite number of parallel universes making up what cosmologists call the "Bulk", then there must be an infinite number of civilizations occupying the Bulk, as well as an infinite number of lifeless universes. If Lisa Randall is correct, and gravity can propogate from membrane to membrane through the Bulk, then it may be possible to use gravity waves to communicate with other Bulk civilizations, lifeforms on other membranes.

    If strong enough gravity waves can be generated, and then varied enough to impart information to the waves, then beings in other mambranes might be able to detect those waves and decipher them to glean messages from them.

    To generate such waves, a civilization might bring 2 neutron stars or black holes into a stable binary orbit, which would generate continuous gravity waves, which could act as a carrier wave. This carrier wave could then be disrupted in a predictable manner by orbiting a third neutron star or black hole around the original binary pair. The orbit of the third would have to be variable so as to be able to add information to the carrier wave.

    It may be that a multi-dimensional chat room is already under way, and has been for eternity past!

    I'm curious, does M-theory add credibility to the many-worlds interpretation of quantum mechanics?

    And what about quantum computing? Would its success seem to indicate that these parallel universes are really existent?
    Last edited: Jan 28, 2008
  8. Jan 28, 2008 #7
    Thanks, PhanthomJay! I have yet to read that particular work, but I intend to get to it soon. I'm interested to see what Hawking thinks about it.
  9. Jan 28, 2008 #8
    The "parallel worlds" of MWI quantum mechanics have no relationship to the "braneworlds" in M-theory, I am quite sure.

    Also quantum computing does not favor any one interpretation of quantum mechanics over any other. Quantum computing is just the same quantum mechanics from fifty years ago, just it is now being applied in an unusual way. It's subject to, and therefore unable to tell us very much new about, the same interpretational puzzles that the quantum mechanics of fifty years ago was.

    The communication-via-gravity-waves idea is definitely interesting though...
  10. Jan 28, 2008 #9
    OK, I was curious about that aspect of the idea of parallel worlds.

    I thought that the atoms in a quantum computer make use of other dimensions to arrive at their solutions, but if they're not making use of the same dimensions proposed in M-theory, then what dimensions do they make use of?

    Thanks, I wonder if this idea could be used to gain evidence for the theory. If we could build something that can detect communications via gravity waves from other-dimensional universes, then that should go a long way towards bolstering the theory.
  11. Jan 28, 2008 #10
    This is not strictly correct. The atoms in a quantum computer make use of the quantum wavefunction-- they make use of the "information" that can be stored in the quantum wavefunction, and they make use of the way that states of the quantum wavefunction can interfere and be entangled, and in particular they make use of the fact that quantum probabilities are complex numbers.

    Now, as far as I understand things, if you believe in the many worlds interpretation, then the wavefunction is just a description of the behavior of all the parallel worlds. So IF you have already accepted the many worlds interpretation, then saying "the atoms in a quantum computer make use of a quantum wavefunction" is actually the same thing as saying "the atoms in a quantum computer make use of parallel worlds". But the quantum computer behaves the same even if you do not accept the many worlds interpretation.

    Something you may have heard, because people in the news and such say this a lot, is that a quantum computer "tries every single possible solution to a problem simultaneously, and picks out the one which is right". *THIS IS NOT CORRECT*. It is just plain wrong, or to the extent it's right it's only true as a metaphor about probabilistic computing.

    If this stuff really interests you may want to read Scott Aaronson's quantum computing course notes. (It's kind of long so if you're not into it you might want to jump right to the part where he starts talking about quantum stuff-- although if you do that you won't know why probability is important to quantum computers...)

    Well again I'm not the best person to ask about MWI, but one thing to remember is that the "parallel worlds" of MWI are *NOT* the same thing as "dimensions". Science fiction likes to describe alternate realities as "parallel dimensions" but this is just a trick of language. I have never that I've noticed heard an actual physicist use the word "dimension" to describe an MWI world.
  12. Jan 29, 2008 #11
    Thanks, Coin, that helps a lot! I'll look at that link when I have time, it looks really fascinating.
  13. Feb 1, 2008 #12
    Mseems to be another step in the process of dethroning humanity from the center of importance in the scheme of existence. With only 4D space/time, we could at least console ourselves with the thought that our intelligence and civilization might put us in the running for most importance, but with multiple infinite universes, we are only one of an infinite number of intelligent civilzations in the bulk.
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