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

What does a temporally infinite universe imply?

  1. Mar 25, 2015 #1
    In their admirably bold Dec. 2014 paper "Cosmology from quantum potential", Ali and Das claim that a reformulation of General Relativity, using Bohmian quantal trajectories in place of geodesics, tentatively confirms that the universe is of infinite age and had no beginning.

    I'm grateful to them for it. Particularly since Special Relativity shows space and time to be integral with each other, or at least "globally inseparable", I've never understood why the Copernican Principle rarely seems to be really considered as applying to time: I could never understand why any event in spacetime would have been so "special" as to mark spacetime's own start.

    It seems to me that a universe without a beginning implies either a spatially closed universe or a bouncing one. Because a spatially closed universe would, even if expanding or contracting forever within a larger region that (in our times) admits nonzero values for much of the physical space in its fields only hypothetically, always occupy only a widening or shrinking section of it of it (whose specialness might nevertheless only equate to the opposing specialness of those regions either "not yet" or "already" destined for its future or past expanse), in spite of its potential for occupying other sections of those regions (one or another of which would, at one or more given times, remain TOTALLY empty). The condensate envisaged by Ali and Das, consisting partly of gravitons each having a tiny mass and partly of a portion of their potential field, would fill the spacetime of all events perceived by any observers as either taking place or having occurred already.

    Because Guth had said that an inflating universe might have a considerable prehistory, I'm hoping to get some informed opinions as to whether it could be embedded (using that term loosely) in Ali and Das' field of gravitons. At the level of popularizations where ignorance of most physics and mathematics have left me, I've always had difficulty understanding how gravity (which Guth considers, in both its attractive and its repulsive forms, as negative energy) could be the source of positive energy and matter, unless its inflation would occur in just such a setting of positive and potential energy as Ali and Das propose.

    I'm assuming that inflation could result either from a false vacuum "quantum tunneling" into a region (perhaps formed by some combination of attractive gravitation and random collisions) of extreme energy density and subsequently turning its gravitation into the repulsive version by the negative pressure of its cooling, or by the quantum mechanism likened by Rovelli (in his Mar. 2014 paper "Planck Stars") to the 'force' which keeps electrons from falling into the nuclei of hydrogen atoms, as a result of their attraction to protons, when their wavelengths are not exact factors of the atomic radii. (I know that the paper by Ali and Das was based on a quantum reformulation of the Raychaudhuri equation, but I don't imagine that this would imply any particular "take" on the nature of inflation, which as influential a quantum physicist as Bojowald feels to be important in the observed distribution of matter.)

    More specifically, what I'm hoping to find out is whether its friction or pressure with the tiny mass of the hypothesized gravitons would slow the expansion (resulting from either or both of the mechanisms I've mentioned) of any region also filled with them sufficiently to either prevent it from becoming exponential or prevent it from subsequently continuing eternally. (It's my impression that such friction or pressure is what ends inflation in the local "bubbles", "pockets", or "islands" that include the one containing our observable region, but I'm not asking about that.)
     
  2. jcsd
  3. Mar 25, 2015 #2

    jedishrfu

    Staff: Mentor

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook