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Brane + Brane = Big Bang => What About Time?

  1. May 17, 2004 #1
    I'm just trying to understand the idea that our universe may be the result of a collision between two branes. According to this, what we see around us is a 3D brane floating in a higher dimentional universe? When our brane collided with another brane, it trigerred the heating and expansion that be call "big bang". So does this mean that the time dimension was not affected by the big bang, and is not expanding along with our three spacial dimensions? Is this correct?
  2. jcsd
  3. Jun 8, 2004 #2
    I was away for a while, but now I'm back, and there is still no answer.. :frown:
  4. Jun 8, 2004 #3
    Hey alpha wolf, to be honest I don't really know the answer to your question but I read that the cyclic model is supposed to have cycled eternally therefore meaning that there was no beginning to it, i.e. time has always been flowing. However, I think that on Steinhardt's website (a major proponent of the cyclic model) Steinhardt proposes that there must have been something before these two branes came into existence but that he isn't really sure of what it is. Perhaps the event that created the two branes might have marked the beginning of time although I'm not sure. Anyways, I hope I have been of some help to you.

    By the way, is there any space for multiverses according to this cyclic model?
  5. Jun 9, 2004 #4
    I don't know what the cyclic model is, so I'm not sure whether it is the same thing I was refering to or some other idea... In any case, the cocept I was asking about certainly allows for such collisions to occur more than once and between many different pairs of branes, meaning there would be other universes out there, all which (including our own) are part of the overall multiverse..
  6. Jun 18, 2004 #5
    Once upon a time there was this philosopher guy who said "someting cannot come from nothing." In response to your question it would seem to me that time would be relative. Think of a black hole... to the obeserver on the outside of a black hole (haha.. just bare with me) the moment would come where the black hole did its stuff and then got to a point where all of the known laws of physics broke down.. it seems though that to the observer outside of this black hole (if that was possible--- let's just say the observer is a little electron guy that gets radiated from the black hole..or has the ability to observe this black hole from a seperate universe) the hole would eventually get so small and so dense that it would blow up! (This is where string theory says one brane has hit another brane) and would be the supposed beginning of our universe. Well relative to an object inside the black hole.. time would have stopped... all the known laws of physics would break down. However... we can use this example to think of time as being not just contained to our own universe (or membrane).. but also a part of the brane that collided with our brane. Whereas the laws of physics may have broken down on one side the laws of physics might remain intact on the other... I hope that helps.. -anton
  7. Jun 19, 2004 #6
    Whether or not time is part of our or the other membrane (or any other membrane for that matter), depends on two factors:
    1. The dimensionality (total number of dimensions) of each brane, Ni, (i being the brane's index).
    2. How many spacial dimensions each brane has, Si. Obvioulsy, Si can be either Ni or Ni-1.
    In any case, what's going on in the other brane has little relevance to what's going on in ours.

    The problem is this: if the higher-dimensional space(time) in which the branes are immersed doesn't have a time dimension, then there is no way to temporaly separate events outside of branes (or even inside any brane that doesn't contain its own time dimension). In that case, talking of a collision between branes is pointless, since a collision is a process, which requires time. On the other hand, if our brane doesn't contain its own time dimension, then GR's 4D description of our universe is not quite applicable. But, can you perhaps have both?

    As far as I can tell, there are three possible solutions to this:
    1. Our brane does not have its own time dimension, and GR is merely an excelent analogy to gravity's workings. I.e. it gives accurate results (within some limits), but provides the wrong mechanism (the wrong interpretation, if you will). This was the same situation with newton's gravitation, except newton's gravitation didn't provide any mechanism at all.
    2. All our brane's dimensions (including time) are shared with some of the dimensions of the higher-dimensional spacetime in which it is immersed. It's like if you draw something on a piece of paper, the drawing's two dimensions are actually two of our three spacial dimensions.
    3. I've heard that either M-theory or F-theory suggests that there are two temporal dimensions (don't remember which one). Perhaps one of these dimensions resides within our brane, and the other within the higher-dimensional spacetime.

    So which one is it then? Can we even tell at the current stage of string-theory development?
    Last edited: Jun 19, 2004
  8. Jun 20, 2004 #7
    Gravity spread out

    I can't imagine what a dimension that didn't contain time actually did. Well... it seems it wouldn't "do" anything--because to do means to move.. and to move means to have time. From the assumption that the higher dimesional space doesn't contain time seems to me to imply that it doesn't contain any matter with mass. For to have mass... one would assume the working of Gravity... and that would also imply movement.
    I just have this sense that speaking of a higher dimensional space that didn't consist of a time dimension would imply a void... and that doesn't sit well.. Granted this void in all ways could exist without affecting our brane.. it seems to follow that one could just ask... does it exist in the first place?

    I like to look at the struggle that even Einstein had... that is combining the forces of Gravity and Electromagnetism... while they both seem to act at the same rate... it appears that in our universe the electromagnetic force is much stronger than gravity... (in the classic example.. when you fall off of a building.. you don't go straight through the earth.. you get stopped by the EM force and go splat!) However gravity plays an important role (or as you say maybe only closely estimates) the movement of very large bodies. Couldn't it be that the apparent weakness of gravity is due to the fact that it isn't contained on our brane.. but is something that exists in the other branes as well??

    The idea of two seperate temporal dimensions at first seems cool.. But I actually can't even think of it... Wouldn't time be more of an exchange of perceptions... what would a second temporal dimension imply?

    I just feel that although we may not ever see parallel dimensions.. or seperate branes.. there is something attractive about FEELING them.
  9. Jun 20, 2004 #8
    Anton, I'm not quite sure you understood me correctly, so I will try to clarify. I know there must be a time dimension somewhere. It could be part of our brane, and it could be part of the higher-dimensional specetime in which that brane resides. It could also be part of both, but it doesn't have to be. For example, if our brane does not have its own time dimension, but the higher-dimensional spacetime does, it would be sufficient - as our brane moves through that external time dimension, everything in/on it would also be moving along that dimension.

    What I ultimitely want to know is whether our brane has its own time dimension or not (or kind of). There are three possibilities, which I have outlined in my previous post:
    1. (answer = no) Our brane doesn't have its own time dimension, but the higher-dimensional space-time does.
    2. (answer = kind of) Our brane has a time dimension, but it is the same dimension as that of the higher-dimensional space-time (i.e. they are overlapping).
    3. (answer = yes) Our brane does have its own time dimension, which is separate and complimentary to the time dimension of the higher-dimensional space-time.
    (Note that in all three cases I assume that the higher-dimensional spacetime does have a time dimension, because otherwise you cannot talk of a collision between branes to begin with).

    I want to know which of these is the case.

    Note: M-theory does in fact suggest that gravity is not constrained to our own brane, but that has nothing to do with my question.
    Last edited: Jun 20, 2004
  10. Jun 20, 2004 #9
    Wow dude

    Hey man... sorry to say... But I have no idea. That's some heavy stuff.
  11. Jun 21, 2004 #10
    Anyone else wants to try?

    My guess is that it's probably the 2nd case, but I'd like to know what M-theory has to say about this (if at all). Any M-theorist around here wants to give this a try?
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