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Different universes?

  1. Nov 2, 2005 #1
    i don't know much about strings and branes, but i'm under the impression with branes there could be other universes completed independent of the one we live in created by the big bang... right?

    my question is, do these other universes have the same fundamental forces that we have, and if they do, do they apply themselves in the same way? or could they have completely new fundamental forces?

    is this a dumb question?
  2. jcsd
  3. Nov 2, 2005 #2
    You can get extra universes in any brand of theory. We humans have fertile imaginations. And to judge brane world scenarios, I would look more to the sociology of science than the strength of the ideas. String theory needs to look as if it has promising predictions within reach of experimental test.
  4. Nov 2, 2005 #3


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    I cannot tell you about string theory, but as far as I know still within standard physics the universe could had performed a (or some) phase transition(s) leading to different domains with different vacua and different masses of particles that carry forces for low energies. However, I am not sure whether this means that there would be different interactions or just the same but with different behaviour. It would be interesting to know what string theory predicts.
    Last edited: Nov 2, 2005
  5. Nov 2, 2005 #4

    Hans de Vries

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    If you would follow Leonard Susskind, One of the first string-theorist,
    going back to the early Gabrielle Veneziano days, then about everything is
    possible. The hypthesis of Eternal Inflation contains countless numbers
    of universes (~10500), all with different laws of physics.

    Susskind's public lecture on this for a wider audience is here :


    However, to say that string theory predicts this? Isn't it more a lack
    of prediction which allows all this... Younger string theorist generally
    don't agree with this Landscape model, probably because they haven't
    yet given up on making predictions with string theory :^)

    Regards, Hans
  6. Nov 2, 2005 #5
    Seriously for a moment, a swamp of possibilities is an embarrassment for some ontologies but a necessity for others.

    The real question becomes whether there are indeed an infinity of actual universes, or whether there is only a single "realm" of infinite potential and then a single (or a very few) actual universes that can self-organise out of this swamp. Describing this in open systems terms, it would be a draining of the swamp! Only certain (dimensional) structures could dissipate the potential contained in the swamp.

    In this view, the swamp is a vagueness, a chaos of dimensional potential. Then the symmetries we find at the root of mathematical structure act as a filter on this swamp, selecting for what can stably exist.

    For instance, we know that mathematical structure in number theory diminishes rapidly as we go from 1 to 2, 4 and 8 dimensions. Like a fading echo.

    So string theory would be charting the hierarchical path from vague potential to crisp existence. Things get folded up progressively until they become the highly constrained 3+1 dimensional structure that can't fold up any more. Reversing the story (in anthropic fashion), the weak structure found out at monster-dimensions, or 24 then 11 dimensions, becomes an increasingly strong and clear signal as dimensionality shrinks down to the "ideal" of a zero-d point.

    This kind of view should please the many mathematical Platonists once they recall that Plato eventually needed a chora to ground his platonic realm of forms. The forms are the crisp harmonic structures that "have to be" because they are the patterns, the topological regularities, that emerge when everything tries to fold itself up in every possible way. But the chora is the vague potential - the swampy ur substance - that is the necessary generative ground.

    One day swamps will be celebrated and their character properly modelled! A universe may even be seen as serving the purpose of an expanded second law - the draining of swamps.:approve:

    Cheers - John McCrone.
  7. Nov 8, 2005 #6
    There are no dumb questions, only those not asked.

    However, I would like to throw the fact into the discussion that starting from string theory, the other universes are not completely independent, as they all have the same underlying (potentially) fundamental theory. I guess, what you mean with 'fundamental forces' are then the low-energy effects (that we call the Standard Model)? These I would think could be different - now you might ask, how different can they be in order to allow intelligent life to exist, and there it is...

    Take Care,

  8. Nov 9, 2005 #7


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    I guess he meant that they are not interacting, in the sense that everything that happens in one of that universes will never have an influence on the others. This is also the way I would understand the term “dependent”: A depends on B, if A is in some causal relation to B, or is somehow affected by B. The universes would be independent if the dynamics of one universe is independent of the events that occurr in all other unverses.

    In the cosmology based on the standard big-bang picture this is not the case. The different domains that may result from phase transitions are located in the same spacetime and may interact. I think that basically the universes can interact if there is some spacetime (four or more dimensional) that connects them. I guess something similar occurs in string theory.

    On the other hand and in light of that definition of dependence, one could say that one universe depends on the fundamental laws of physics which govern its dynamics. These laws may be the same for all other universes. However, I assume that fundamental physical laws do not depend on the dynamics of one universe. I mean, the universe is clearly affected by that fundamental physical laws, but the fundamental physical laws are not affected by him. Does it make sense to speculate with the possibility that the fundamental physical laws could be subject of some dynamics being affected by something?
    Last edited: Nov 9, 2005
  9. Nov 9, 2005 #8
    Swamps, or more properly, wetlands, are a vital part of our ecology. They filter and clean the water that flows into them, and act as nurseries to countless species which are members of the web of life. The draining of swamps is an unsound practice which damages the water table and puts holes in the infrastructure which supports all of us. Streams, rivers, and ultimately the ocean suffer from the effects of draining swamps. Run-off then goes directly to the sea, carrying soil and pollutants with it. I have swamps on my property, and I find it wise to honor and protect them. In return, they give me hours of peaceful meditation and an abundance of wildlife to observe.

    I don't know if the swamp of ideas now engulfing string theory is a fertile wetland promoting new and better theories, or just a cesspool of wasted constructions waiting for bacterial degradation to primary elements. I do know that students of biological ecology will find the high-energy physicists reference to swamps as a derogatory device infantile and uneducated.

    Life on this planet needs swamps and biological diversity. I don't know if life on this planet needs string theorists, or high-energy physics in general. It is possible that it does, or will, have a need for such things. I do know that people who throw mud at others end up getting a lot of it on themselves.

    I think we should get rid of the swamp metaphore, but not of the swamp itself. What are we really trying to talk about? Can't we be more descriptive, and use real terms instead of a handwaving metaphore? It has been reported that some of the different forms of String theory are mathematically identical through S- and T-dualities , only applied to differing local conditions. One form applies to cosmological scales, another form to the Calabi-Yau manifolds at the Planck scale. It seems possible that all the forms of string theory may eventually be unified under the as-yet undiscovered M-theory. What use does it serve to try to stomp on researchers who think they see a way towards such a unification?

  10. Nov 9, 2005 #9


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    Splendid post, Richard! One of the most irritating thing about particle physicists is the impulse to be "cute", caught from Gell-Mann (author of "strange" and "quark"). Most of them are not as well-educated as Gell-Mann and their cuteness is often ham-handed as you note in this case.
  11. Nov 9, 2005 #10
    "I think we should get rid of the swamp metaphore, but not of the swamp itself. What are we really trying to talk about? Can't we be more descriptive, and use real terms instead of a handwaving metaphore?"

    Hard to tell if any of your grumbling was directed at me. But I certainly live on a drained swamp (that is Christchurch). And I trained in ecology, so that is why I have a systems perspective on all things.

    You perhaps missed the essential point. The second law of thermodynamics and the scope it gives for self-organised dissipative structures is a major constraint on cosmological speculation. And it may even be directly applicable to the maths that string theory is working upon.

    If you prefer it, the proper technical term for the swamp from a organicist's point of view would be vagueness.
  12. Nov 9, 2005 #11
    Hi mccrone

    No offense meant. I just felt protective of my swamp, is all. Lots of swamps hereabouts have been drained for farm fields, runways, shopping center parking lots, and other developments which make me feel grumpy. IIRC the swamp metaphore was used by Vafra to disparage anything that lies outside the stringy landscape.

    Anyway what you say is interesting. What constraints do you see on cosmology based on entropy? I have a hunch that there may actually be a limit on disorder, based on the speculation that virtual particals from Unruh and Hawking style radiation may actually appear at random places and times, but still with enough density to cause a minimum amount of order to persist even in the heat-death model.

    My hunch is that new particals are generated by the expansion process, so that not everything has to have been present at the big bang, and also so that no matter how long expansion continues, there will always be some level of order in any universe. It is just a humble thought and I have no supporting links to offer.

    Anyway, as always, I wish you well. Thanks for being here.

  13. Nov 9, 2005 #12
    Seeing the Universe as a dissipative structure suggests far more radical thoughts than that!

    But you should check out Lineweaver - http://www.mso.anu.edu.au/~charley/papers/LineweaverChap_6.pdf

    The heat death would indeed be asymptotic as the event horizon - in black body fashion - would still be radiating photons of a wavelength of the then current visible universe!

    Also see Swenson -

    These are the shallow end of the pool but useful starters.

    And when it comes to the entropy question, the disorderly wanderings of mass particles is pretty much an afterthought. It is how you properly account for the expansion of the void that is the burning question

    Note how Lineweaver takes the standard party line that the vacuum is a nothing and so it can be created freely. But a void is a coherent (orderly!) expanse of (always expanding!) dimensionality.

    You can again do away with the entropy questions this raises by predicting a convenient recollapse (though the information paradoxes thus created are familiar). Or you can suggest from first principles that a universe cannot recollapse but must forever strive to fulfill its thermodynamic destiny of expanding from a hot point to a cold void (and thus draining the swamp of vagueness of its potential for crisp order...and crisp disorder).

    Cheers - John McCrone.
  14. Nov 10, 2005 #13
    Thanks! I am grateful for the links and for the instruction. Happens I am preoccupied for the next several days, perhaps until next Wednesday, but I will download and try to understand the gist of the links.

    Cheers, indeed!

    Be well,

  15. Nov 10, 2005 #14
    I have a preference for Smolin's cosmology where new universes are born from black holes, and this has been going on for so long, like forever, that all persent universes are of the type that maximazes the number of its black holes, aND THEREFORE, i THINK, THEY ALL HAVE THE SAME FUNDAMENTAL LAWS.

    Sorry about the caps. Anyway, regarding the entropy question: At the center of a black hole capable of universe birth, is a singularity- actually a ellipsodial membrane containing, I think, the unified field, in which entropy is renormalized. So every universe starts anew, but is fundamentally the same.

    In this cosmology, universe recollapse is not necessary>
  16. Nov 10, 2005 #15
    going back to the swamp analogy...

    could string theory be represented by new orleans holding back the tide with crude and obsolete levies, draining of swamps and building of tightly controlled (oil)lines carrying energy that once breached, poison the environment for the settllers ???

    ...and with regard to multiverse or megaverse, which is your preferred option ???
  17. Nov 11, 2005 #16
    Hi all

    I read through the Lineweaver link briefly and found it interesting. I have a few questions about the graphs. One graph representing cosmogeny is pleasently reminiscent of a lotus mandala! However it shows our past light-cone like a bud at the center bottom, and receding (red-shifted) galaxies spreading outward outside of the light cone. I have a problem with this representation, since we cannot observe anything outside of our light cone. I'll have to look at it again when I have more time.

    Then there is another figure in which the entropy lines for cosmogeny are traced. The formation of baryons, nucleons, atoms, and stars are represented, as I recall. At the bottom right our sun is given its own line, which shows an entropy differential between the sun (hot) and earth (cold). However I had trouble reconciling the meaning of the spike in entropy with the time line shown at the bottom of the graph.

    Anyway, thanks mccrone, for the links. The second link seems to be an advert for a book I can't afford to buy, but it does look interesting.

    be well,

  18. Nov 11, 2005 #17
  19. Nov 12, 2005 #18


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    In a static universe the lightcone is a cone. However, this is not the case in an expanding universe as you can see in Lineweaver´s paper. In an expanding universe the section of that cone does increase more slowly than in a static universe as you go backwards in time. This is obvious because going backwards in time space was more contracted than in a static universe. Further on, still going backwards in time, one reaches a time at which the expansion of space was very strong (the Hubble parameter tends to infinity when t -> 0), the lightcone "bends" and its section starts decreasing until it becomes zero at t = 0.

    The particle horizon is the region that delimites our observable universe. We are not observing things at the particle horizon as they are now, but as they were in past. Note that in a static universe, the particle horizon now would be of the same size than the section of the lightcone at t = 0. A photon sent at t = 0 in a static universe at a distance D from us would reach us today and then, we would therefore say that our particle horizon is located at a distance D from us. In an expanding universe things are different and very interesting, because everything that is located at our particle horizon now, was at zero distance from us (our comoving position) at t = 0 (size of the lightcone at t = 0).

    To imagine the shape of the lightcone consider a photon which is sent at t = 0 to us (or an instant after t = 0 from a very near position to our comoving position). The expansion of space is very strong, the photon is carried away from us by the expansion and is not able to reach us. A (cosmological) time later, when expasion slows down, the photon will be able to "win" against it and will start approaching us and will reach us at present. To imagine the particle horizon you should consider the present location of that point from which the photon was emitted at t = 0. Obviously it will be very far away now.
  20. Nov 13, 2005 #19


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    At least they have different standard model parameters, and may be also other fundamental laws. You can read in Smolin's Scientific alternatives to the anthropic principle:
    This, as some kind of mutation, is a prerequisite for Smolin's natural selection to work.
  21. Jan 17, 2010 #20
    Isn't that how Eistein discovered possibility of time being curved?
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