Letter | Published:

The impossibility of a bouncing universe

Naturevolume 302pages505506 (1983) | Download Citation



Petrosian1 has recently discussed the possibility that the restoration of symmetry at grand unification in a closed contracting Robertson–Walker universe could slow down and halt the contraction, causing the universe to bounce. He then went on to discuss the possibility that our universe has undergone a series of such bounces. We disagree with this analysis. One of us (M.S.) has already shown2 that if a contracting universe is dominated by radiation, then a bounce is impossible. We will show here two further results: (1) entropy considerations imply that the quantity S (defined in ref. 1 and below), which must decrease by 1075 to allow the present Universe to bounce, can in fact decrease by no more than a factor of 2; (2) if the true vacuum state has zero energy density, then a universe which is contracting in its low temperature phase can never complete a phase transition soon enough to cause a bounce.

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  1. 1

    Petrosian, V. Nature 298, 805 (1982).

  2. 2

    Sher, M. Phys. Rev. D22, 2989 (1980).

  3. 3

    Weinberg, S. Gravitation and Cosmology (Wiley, New York, 1972).

  4. 4

    Huang, K. Statistical Mechanics Chs 8, 9 (Wiley, New York, 1963).

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  1. Center for Theoretical Physics, Laboratory for Nuclear Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139, USA

    • Alan H. Guth
  2. Department of Physics, University of California, Irvine, California, 92717, USA

    • Marc Sher


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