Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Braneworld Cosmology

  1. May 17, 2004 #1


    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    I personally dont follow braneworld cosmology, but there could be a thread about. It interests enough people here to have a discussion IMO

    A possible thread-starter is a recent post by sol2
    which has some beautiful images, or links thereto,
    tho not necessarily directly connected to braneworld theories
    and concludes with sol putting the question flat out: do you follow the theorizing about colliding braneworlds:

    in my case the answer is no but hopefully others do and will reply
  2. jcsd
  3. May 17, 2004 #2
    Thank you again Marcus I appreciate it.

    I know links make it difficult sometimes for threads, but to understand where I am coming from the imaging should help greatly and introduce new concepts here for consideration.

    From what I understood if we accept the eykroptic scenario we are making certain assumptions about the universe? How would we see string cosmology now become part of brane world?


    Can such a supersymmetrical states exist, and such clumping actions soon become realized as Andrey Kravtsov demonstrates here.


    Hopefully the picture can load?


    I appreciate any help here. I listed the "Moire effect and the heteordyne solution," as speculation, in seeing how such Branes could collide and then bounce.

    What is Brane world?
    Last edited: May 17, 2004
  4. May 17, 2004 #3
    Journey to the Tenth Dimension

    It is important to give this subject some perspective in generalizations, although there is deep mathemaical expressions that are beyond me. I will be supplying a few more links to help out here and hopefully there will be someone who is also interested that can help give some more perspective.

    It is good to see the Father of string theory speaking on this subject as well:)Gabriele Veneziano

    Type of possible space #2: The universe as we know it is merely a three-dimensional brane suspended in a four-dimensional bulk. Excellent question #2: What the hell is a brane? Attempted answer #2: Here is the Powerpoint version of everything you need to know about branes:

    · You live on a brane. · A brane is like a membrane. · Imagine the skin that forms on your soup when it gets cold. A brane is like that. · A brane is some sort of lower-dimensional thing (the 2-D skin) sitting in a higher-dimensional space (your 3-D soup). · Brane theory says our 3-D world is really just a brane. · Our brane sits in a 4-D space called the bulk. · Like so much congealed fat, we are prevented from escaping the brane and going into the higher-dimensional soup. · Only gravity is allowed to do that.

    This theory -- generally referred to as brane theory -- was devised in 1998, which is pretty recent by theoretical-physics standards (people have been noodling with various forms of string theory for about 30 years now). Three guys get the credit for coming up with it, one of whom -- Nima Arkani-Hamed -- was a 25-year-old fresh out of Berkeley with a Ph.D. He is now a professor in the physics department at Harvard. Smart guy. He and his cohorts Savas Dimopoulos and Gia Dvali had been working on a problem that had confounded big thinkers for, oh, a few decades, when they suddenly realized that all they had to do to get us out of it was to invent another dimension! Voilà!

  5. May 18, 2004 #4
    I have some questions about brane cosmology!
    The first is: usually brane world scenarios represent our unuiverse like a D-brane, and open strings are tied to the D-brane, and so can't scape of it, but gravitons are closed strings, are not tied and can scape. Now, how are the open strings tied to the D-brane? With glue? With a knot at each of the ends of the string? Sorry if it seems sarcastic, but I can't find an explanation of how they are tied
    The second question is: there are Calabi-Yau manifolds in Brane World cosmology? I know that there are CY-manifolds in other variants of string theory, they serve to keep compactified the extra dimensions, but I don't know if they exist in brane World cosmology
  6. May 18, 2004 #5


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    They end on the brane with "boundary conditions". Since the strings and branes are both mathematical objects in the string model, you don't need a physical epoxy to keep them attached, any more than you do to keep the legs of a triangle attached at the vertices.
  7. May 18, 2004 #6
    Pretend you lived on your computer screen and could only move on that two dimensional surface. The computer exists in three space dimensions but you can only move on a two dimensional subspace made by the screen, so the spacetime that you experience would look like three dimensions (two space plus time) rather than four.

    That's sort of the idea in a braneworld higher dimensional theory. Our observed four dimensional spacetime is like the computer screen, a subspace of some bigger space that we can't see because all matter and forces are constrained to move (mainly) on our subspace, or brane (as in membrane).The total space is called the bulk and the subspace or brane on which we would live is called the brane.

    Light is made of electromagnetic radiation, and in a braneworld model, the charges and the fields should propagate only on the brane. So there wouldn't be any way to probe the extra dimensions in the bulk by using light, even if the extra dimensions were large.

    Gravity is the force that determines the shape of spacetime. Therefore, at least in principle, gravity should propagate in all dimensions equally. That means we should be able to detect large extra dimensions by looking for suspicious behavior in the gravitational force.

  8. May 18, 2004 #7

    Our new ideas say nature has only one mass scale—the scale of the weak interactions. From this flows the idea that gravity is weak because the particle mediating the gravitational force, the graviton, lives far away from us in new extra spatial dimensions. The relative strength of the forces was formerly understood in terms of separation in energy space, but what we are now saying is the extreme weakness of gravity follows from its separation in new positional space having real extra dimensions.

    Our new picture is that the 3-D world is embedded in extra dimensions. Gauge forces and their particles are confined to this 3-D plane, but the graviton lives mostly outside this plane in the extra dimensions. That means the graviton exists mainly away from us, and hence its interaction with us, the force, is weak.

    What’s the size of this space? Note that gravity is very weak, which tells us the graviton spreads into extra space for interaction. To account for the observed weakness of gravity, the scale length of two new dimensions has to be about a millimeter, which is gigantic! For three or more dimensions the size becomes smaller than 1 mm.

    The basic notion underlying our work is to explain the observed separation in energy levels by separation in real space. This gives us a totally new perspective for addressing theoretical and experimental problems.

  9. May 19, 2004 #8
    Maybe another time and place for brane cosmlogy I guess.


    Once it is understand what GR means in a classical sense, one is able to take this view and incorporate it into the dscussion of cosmology as far as I could tell.

    Bringing the quantum ideas into the picture, and the amount of information in supersymmetrical points, helped in this sense in looking at the early universe.

    By including the understanding of the innnate ideas of curvature, and here we have talked about The Friedmann equation, the ideas around the Dirac matrices, and the questions of time. These all place a part in the topological features, as far as I could tell, in dynamics similar to the string and the winding of the factors considered in the KK Tower. Were relevant to how we see the dynamics of these branes arise from the string interpretations, now taken to a new perspective in brane world.

    One result of this was the leadng perspective of bubble technology and the geometrocdynamics of all these action combine into a dyamicl universe with galaxies and such, following these features of topological movements. Ina overall expanstory move we could have identified some of these action within the context of brane collisions and new universes froming.

    Why it then become important to me to consider orbital patterns for consideration. defintions and patterns of the fuzzy approach as evidence of the ideas and problems of gravity inclusion and what these were doing.

    Whatdoes energy reveal inthe undertsand ing of weak field measures versus strong and we retainthe ideas in gravitation. Starting to babble so will stop for now.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Braneworld Cosmology
  1. Cosmology for dummies (Replies: 23)

  2. Armchair cosmology (Replies: 2)

  3. New cosmology? (Replies: 2)

  4. Cosmological constant (Replies: 1)