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The cyclic model

  1. Jan 4, 2004 #1
    The cyclic model was introduced in this paper:
    "A cyclic model of the universe"
    and is a idea of Steinhardt and Turok. (Some might some day recognize the great quantities of ideas that Steinhardt has introduced in the last 30 years).
    The model proposes an universe with no beginning, existing since infinite time. We inhabit in a brane, and there's another brane that is a "mirror image" of our brane, and this two branes periodically collide, the Big Bang is produced, then they separate, and turn to collide and so on. Very simple. No metaphysics questions about the beginning.Is postulated that one brane has positive tension and the other negative tension. Now, what this means? I can't make head and tails of what means negative tension.
    And, what means that the other brane is a mirror image of our brane? Does it mean that there's another Physicsforums,another new year's day, another Eiffel tower, in the other brane?
    Last edited: Jan 4, 2004
  2. jcsd
  3. Jan 5, 2004 #2
    If there is no beginning, then doesn't that just beg the question as to where the universe came from?
  4. Jan 5, 2004 #3
    Re: Re: The cyclic model

    I consent. It used to be a tradition to disregard these sort of questions as being "meaningless", and without a clear intuition in mind (without referring, as a last resort, to the antropic principle), but with the advent of string theory and loop quantum gravity, the question comes up as a natural inquiry in the theory.

    The Cyclic Model merely remediates some shortcomings the original models had many years ago, and by doing so, fits in pretty damn close to the current observed accelerated universe. Suffice to say though, it borrows heavily from a more contemporary, and while we're at it, attractive proposal, "Ekpyrotic Universe" and the various "Pre-big Bang" scenarios before and after it (not to mention the quite recent "Branegas Cosmology" picture).

    Finding a "background independent" (non-perturbative) regime of M-Theory (which constitutes the myriad of string theories out there through all sorts of dualities) would go a long way towards preempting the prevailing notion of these nonsensical, orthic questions and firmly rely the results to the rest of the world.

    Hopefully, splicing LQG & String Theory in one way or another, may be just what the doctor ordered for solving this perpetual enigma.

    At the end of the day, it all boils down to "elegancy" and the Cyclic proposition, does nothing to mitigate the extremely limited, in essence, and if i may add, mundane collage of the universe it presents us with.
    Last edited: Jan 5, 2004
  5. Jan 5, 2004 #4
    The cyclic model says that the two three dimensional branes have been colliding and separating from an infinite past. I like the idea, cause I'm lately having preferences for cosmologies without beginning, my favourite is LQC, but like alexsok said, the cyclic model is a derivation of the ekpyrotic universe, and is really a sound proposal. (If you like scenarios of this kind, read about the "pyrotechnic universe", an idea of Andrei Linde, that is also a derivation of the ekpyrotic universe)
    What the cyclic model proposes is that, after the two branes collide, they separate and expand for at least a trillion (1012) of years, then the branes contract, turn to collide, and the cycle begins another time. There's no period of inflation in our brane in the cyclic model, but the dynamics of contraction/expansion are driven by the same scalar field, a kind of quintessence acting like a dark energy driving the expansion and the contraction. But this is practically all my knowledge about the cyclic model, I have to read more about it
    Last edited: Jan 5, 2004
  6. Jan 6, 2004 #5
    Let the question begging begin: Then where did the two branes come from?
  7. Jan 6, 2004 #6
    The branes have existed forever. They have been colliding and separating forever, the problem is that I don't understand very much the mechanism attraction/repulsion between them, seems that exist some interbrane force driven by some kind of potential. Branes existing forever is not more absurd that the idea postulated by standard big Bang (appearance of spacetime at time zero)
  8. Jan 6, 2004 #7
    The gist of your inquiry is basically the same as the naive questioning we grappled with so fiercely, attempting ferociously to find an applicable and reciprocal principle, according to which, our universe is governed, consentaneous with the Big Bang cosmology and etymologizing of it's inevitable origin. No my friends, no such principle sought, would be discovered, if we keep walloping our heads at a stalwart wall!

    Despite what some people would say, this is PRECISELY the issue at hand here! Allow me to provide a living example. NASA's latest probe to Mars, Spirit, has lifted the curtain a bit, and cushioned itself of the imprecations from the not too fruitful future, but the clock is ticking, and chances abreast it! It wouldn't surprise me one bit, if the entire mission turns out to be a big chit-chat, and no traces of life whatsoever come floating over the air. The reason is extremely explicable: we might not "operate" according to the right mechanism we should if we're to delineate any life on Mars! We all are unimaginably accustomed to the life conditions on Earth, and thus, function according to common axioms and postulates, familiar to us! Perhaps life on Mars are manuevered by entirely different mechanics, unknown to us, and we all excogorate and persist in keeping our faith at something we do not comprehend at all!

    We are "Earth-centric" mate, but can you say that we're ignorant and exceedingly nascient? Sure you can! Delving into this matter is worthwhile, and unless the tentative answers we're provisioned with are copasetic to our soul and spirit, we ought to aspire for the ultimate question: where did the physical laws come from? In case a complementary solution to this problem is not procured over the next centuries, all we'd be left is a mere "description" of the world we're living in, obviously, a few notches up from the prior, but nearly identical, elucidation. Just my 2 cents.

    This paper is dated to the 23rd of December, and seems to be a nice idea...


    Last edited: Jan 6, 2004
  9. Jan 8, 2004 #8
    So, it seems that negative tension branes are not exclusive of the cyclic model. For example, the Randall-Sundrum I model (RS1), that was proposed in this paper:
    "A large mass hierarchy from a small extra dimension"
    is a brane-world model consisting of two 3-branes embedded in a five-dimensional Anti-de Sitter space. Our brane is called the TeV brane, and the other is called the Planck brane. Is postulated that our 3-brane has negative tension
    A formula for the tension of a D-brane is given in the first page of this paper
    "A note on brane tension and M-theory"
    so, maybe you just have to plug the variables in the formula, and if the result is negative, then that is a negative tension D-brane
    Last edited: Jan 8, 2004
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