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Letters to Nature
Nature 302, 505 - 506 (07 April 1983); doi:10.1038/302505a0

The impossibility of a bouncing universe

Alan H. Guth* & Marc Sher

*Center for Theoretical Physics, Laboratory for Nuclear Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
Department of Physics, University of California, Irvine, California 92717, USA

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.



1. Petrosian, V. Nature 298, 805 (1982). | ISI |
2. Sher, M. Phys. Rev. D22, 2989 (1980). | Article | ISI | ChemPort |
3. Weinberg, S. Gravitation and Cosmology (Wiley, New York, 1972).
4. Huang, K. Statistical Mechanics Chs 8, 9 (Wiley, New York, 1963).

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