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String and Relativity questions

  1. Apr 23, 2004 #1
    I’ve been a sideline follower of string theory ever since I seen Dr. Michio Kaku quite awhile back on Tech TV’s “Big Thinkers.” Recently I watched the three hour NOVA special “The Elegant Universe” hosted by Brian Greene. I have some issues with some of the ideas presented and I’m sure someone here can point me in the right direction.

    The way Einstein’s vision of gravity was presented with the warps in the fabric of space-time made no sense. The graphic depicted space-time as two dimensional, which would require an additional and unseen downward force on the orbiting body. Is there a three dimensional representation of Einstein’s space-time available on the internet?

    Have the ideas that 1) gravity is a side effect of the strong nuclear force (more mass = more proton/neutron bonds = gravity “bleeding off”) and that 2) week nuclear is the same as EM, already been studied and dismissed?

    Couldn’t time be something we made up? Why does it get its own dimension?

    How do comets that travel vast distances—pass by many “orbital” planets—still orbit the sun.

    Thank you in advance for your time,

  2. jcsd
  3. Apr 23, 2004 #2
    3D representation of spacetime on the Internet? Well, yes, if you agree that 2D space and 1 D time = 3D. But, if you mean 3D space, that would be a static representation, like a still photograph of a home run still high in the air. Of course the rubber-sheet representation shown on the TV and the Internet is a poor analogy. You are right to be dissatisified with it. The problem is that we cannot comprehend or represent the 3D and 1D nature of spacetime except by living "through" it.

    Is time something that we made up? I would say that it's just our living "through" spacetime. Time gets its own dimension because it really can't be treated like the space dimensions.

    Comets do eventually crash into the sun or the planets, or "melt" away. Just a matter of time.
  4. Apr 23, 2004 #3
    In the dimensions of space things can only be... add the dimension of time and they can move.

    All things (dimensions in space) happen in time.
    Last edited: Apr 23, 2004
  5. Apr 23, 2004 #4

    That's right as I far as I see it. Add the arrow of time to one of those directions


    It is difficult for people to understand how the nature of gravity is discerned from 3 dimenisons of space plus one of time....but in essence, your quote explains this? Maybe we can have a better explanation added here by someone?

    Not many understand the dynamical nature of reality from this perspective.

    There is a trail that must be followed through euclidean.

    Hope this historical helps

    The movement to the realization of a dynamical universe with the Friedman eqaution and the realization of the fifth postulate of Euclid, we have a new world to consider being introduced to Saccherri, Guass, Reinmann to name a few.

    In this, Minkowski and Lorentz information has to be considered as well. This is part and parcel fo the ideas behind a consistent geometrical determination seen in Kleins ordering of geometries.

    Of course I am open to corrections.
    Last edited: Apr 23, 2004
  6. Apr 23, 2004 #5
    I too am open to corrections :-)

    I wish I knew math and physics like some of you do... but I don't.

    I can only offer a very simple logic to the discussion.
  7. Apr 23, 2004 #6
    I'm still not sure why time gets its own dimension... The 3 visible space dimensions can operate independently, but they are dependent on the time dimension?

    Is the "strong nuclear" = gravity such a bad idea that no one commented?

    Thank you all for your replies,

  8. Apr 23, 2004 #7
    Spacetime is a phenomenological manifestation of the propagation of gravity. Because gravity universally couples with matter, it defines geometric and dynamic relations between physical objects. These relations manifest themselves as spacetime.

    Things are not "in" space (container space is an extremely troublesome view, philosophically and physically) nor do they move "through" time (this is effectively also a container view of time). They in a loose sense, "generate" spacetime.
  9. Apr 23, 2004 #8
    I found it to be an interesting idea, but I don't know enough physics to comment.

    But if there is a "duality" between the two forces, then it would be a further step to a nice ontological unification.

    I'd like to know what people with more knowledge into this have to say... Perhaps string theory has something to say about it.
  10. Apr 23, 2004 #9
    Are direction and distance the same? The spacial dimensions imply direction, but only with the dimension of time do they imply distance.
  11. Apr 23, 2004 #10
    How does dimension imply direction?

    I think distance does not need time. We can talk about distance as a purely spatial quality, with having to discuss how it changes in time. Of course, that indicates that velocity requires time. But that's more of a mathematical point of view.

    Physically, I don't think there's much sense in talking about space independent of time, as general relativity seems to show.
  12. Apr 24, 2004 #11
    Isn't spacial dimension... up and down, left and right and back and forth?

    That seems like direction without speaking to distance.

    To move in any of those directions for any distance speaks of time.
  13. Apr 24, 2004 #12
    You're right, moving in a direction speaks of time. However, we can talk about the distance between objects without having to talk about moving between them. For instance, if I take the numbers 2 and 5, I can say the distance between the two is 3. There is no notion of time involved here.

    But physically, I think we necessarily have to speak of time when speaking of space, since there is no mutual independence.
  14. Apr 24, 2004 #13
    Is it possible that the distance between numbers is metaphorical... and that the universe itself is metaphorical? Something like that.
  15. Apr 24, 2004 #14
    No, I don't think that the distance between numbers is metaphorical. We can construct propositions which explicitly "talk about" the distance between numbers. That's not metaphor.

    We can talk about the distance between numbers being metaphorical in that we can conceive of such distance being isomorphic to the distance between two physical objects. There is a formal analogy between the two. However, since the amount of distance between two physical objects is itself an abstract idea, we can only talk about it sensibly by mathematics. I think that pretty much gets us back to square one.

    Whether the universe is itself metaphorical... I'm not sure. I think it is clearly obvious that there are certain things which are metaphorical (such as music), but I'm not sure about the universe as a whole.
  16. Apr 24, 2004 #15
    Any analogy to do with general relativity is going to be very oversimplified. 4 dimensional space/time is a very different concept to the 3 dimensions of space and one of time that we know and love. Within relativity, (special and general) time is treated on completely equal footing to the other spacial dimentions - in fact it is usually multiplied by the speed of light to give it the same dimensions as distance. It is a very mathematical subject (even Einstein felt it was "invaided" by mathematicians to such a degree that he could no longer follow it) and I imagine it is very difficult for popular science to simplify - there is a reason why its proper study is left till the final year of university.

    I'm not sure what your strong nuclear force question means. I have never heard of gravity bleeding off the strong force - which is very short range and only acts over distance the size of the nucleus. Was this idea on the elegant universe program? If so which chapter?

    The electroweak unification was performed by Glashow, Weinberg and Salam independantly in the 1960s and treats the EM and Weak interactions as different manifestations of a unified force. It starts with 4 massless bosons which mix to give the physical particles that mediate the two forces (the Weak bosons W+,W-,Z0 and the EM photon). This theory started an idea you may have heard of before - the Higgs Mechanism - which was required to explain how the Weak bosons aquired mass. It underpins much of the standard model but is somewhat ad hoc which is unsurprising since the standard model is most likely incomplete. Nevertheless its results agreed perfectly with experiment.
  17. Apr 24, 2004 #16
    I was hopeful that someone here knew of a better graphic that what they showed in the program... The sun was sitting on a trampoline.

    With the stong nuclear force question... It wasn't in the program. I just wondered if anyone looked into the possibility that it could be the same as or the source of gravity.
  18. Apr 24, 2004 #17


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    Many links on this page, one of them must be what you're looking for.
  19. Apr 25, 2004 #18


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    There are basic problems about identifying gravity with any of the quantum forces known. The carriers of the weak and stong forces are what is called vector bosons, which means the number of degrees of freedom in their internal symmetry is four. The graviton on the other hand willl have to be a symmetric rank two tensor particle, with ten internal degrees of freedom. This latter fact is due to the fact that it has to have low energy behavior that mimics general relativity, a theory that, like quantum mechanics, has never failed a test that was put to it.
  20. Apr 26, 2004 #19
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