Mathematics – Logic
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........65l&link_type=abstract
Thesis (PH.D.)--MASSACHUSETTS INSTITUTE OF TECHNOLOGY, 1993.Source: Dissertation Abstracts International, Volume: 54-06, Secti
Mathematics
Logic
Scientific paper
The standard cosmology is unable to explain the large-scale homogeneity and isotropy of the observed universe. In the standard model, our observable horizon contains many regions which were causally disconnected at earlier times. Consequently, the apparent smoothness of the observed universe is a mystery. Regions which could not have been in causal contact seem nonetheless to be identical in temperature and other such properties. In addition, the inclusion of grand unified theories into the standard cosmology gives rise to a cosmologically disastrous abundance of monopoles. Although the monopole problem has a very different source from the horizon problem, solutions to one are often intimately connected with solutions to the other. The horizon and monopole problems might be resolved if the universe grows old while it is still hot. We call this era of prolonged aging the MAD era. Extensions of Einstein gravity with a dynamical coupling strength G can provide such a MAD solution. Unlike an inflationary cosmology, there is no period of vacuum domination and possibly no entropy violation. If G is very small during an early hot era, then the expansion of the universe is slowed. Consequently, the universe cools slowly and is older at a given temperature than in a standard cosmology. An older universe has larger regions in causal contact which may become smooth without violating causality. Also, the large causal horizon can serve to dilute the monopole density. To complete the solution to these problems, the strength of G must grow quickly to reach the large value measured today. An actual mechanism which can drive the dynamical G from its proposed small early value to its large value observed today is still needed. We indicate directions to pursue to find a specific working model. In principle, while the strength of gravity grows the cosmic expansion accelerates. During this stage, density perturbations relevant for large-scale structure can possibly be produced. Inevitably, any perturbations would imprint a signature of an early MAD era on the cosmic background radiation. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).
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