Jeremiah P. Ostriker
Princeton University

Development of Structures in the Universe:  Simulations Vs. the Real World


ABSTRACT

The study of cosmology, the origin, nature and future evolution of
structure in the universe, has been totally transformed in the last decade,
and computers have played a major role in the change.  New theories have
arisen from particle physics which make the subject, formerly almost a
branch of philosophy, into a quantitative science.  Initial,
semi-quantitative tests of these theories, either using data on galaxy
distributions in the local universe or the cosmic background radiation
fluctuations reaching us from the distant universe, indicate rough
agreement with the simplest predictions of the theories.  But now that
fully three- dimensional, time-dependent numerical simulations can be made
on modern, parallel architecture computers, we can examine (using good
physical modelling) the detailed quantitative predictions of the various
theories that have been proposed to see which, if any, can produce an
output consistent with the real world being revealed to us by the latest
ground- and space-based instruments.  Using these tools, we have been able
to reduce to a small number the currently viable options for the correct
cosmological theory.  All currently considered models, by construction,
match observations of the nearby universe.  Thus, tests, which will enable
us to eliminate options, will arise from observations of the universe at
moderate redshift z = (1 -> 5), using modern technology on rapidly
developing ground- and space-based instruments. At present, the most
acceptable model, passing all presently applied tests, is the low density
but flat Cold Dark Matter model with Omega_baryon = 0.04, Omega_CDM = 0.26, 
Omega_Lambda = 0.70.