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The ``hot'' in the hot big-bang cosmology makes fundamental physics an inseparable part of the standard cosmology. The time - temperature relation, kBT ~ 1 MeV (t/sec )-1/2, implies that the physics of higher energies and shorter times is required to understand the Universe at earlier times: atomic physics at t 1013 sec, nuclear physics at t ~ 1 sec, and elementary-particle physics at t < 10-5 sec. The standard cosmology model itself is based upon Einstein's general relativity, which embodies our deepest and most accurate understanding of gravity.

The standard model of particle physics, which is a mathematical description of the strong, weak and electromagnetic interactions based upon the SU(3) circle_cross SU(2) circle_cross U(1) gauge theory, accounts for all known physics up to energies of about 300 GeV (Gaillard et al. 1999). It provides the input microphysics for the standard cosmology necessary to discuss events as early as 10-11 sec. It also provides a firm foundation for speculations about the Universe at even earlier times.

A key feature of the standard model of particle physics is asymptotic freedom: at high energies and short distances, the interactions between the fundamental constituents of matter - quarks and leptons - are perturbatively weak. This justifies approximating the early Universe as hot gas of noninteracting particles (dilute gas approximation) and opens the door to sensibly speculating about times as early as 10-43 sec, when the framework of general relativity becomes suspect, since quantum corrections to this classical description are expected to become important.

The importance of asymptotic freedom for early-Universe cosmology cannot be overstated. A little more than twenty-five years ago, before the advent of quarks and leptons and asymptotic freedom, cosmology hit a brick wall at 10-5 sec because extrapolation to early times was nonsensical. The problem was twofold: the finite size of nucleons and related particles and the exponential rise in the number of ``elementary particles'' with mass. At around 10-5 sec, nucleons would be overlapping, and with no understanding of the strong forces between them, together with the the exponentially rising spectrum of particles, thermodynamics became ill-defined at higher temperatures.

The standard model of particle physics has provided particle physicists with a reasonable foundation for speculating about physics at even shorter distances and higher energies. Their speculations have significant cosmological implications, and - conversely - cosmology holds the promise to test some of their speculations. The most promising particle physics ideas (see e.g., Schwarz & Seiberg 1999) and their cosmological implications are:

Advances in fundamental physics have been crucial to advancing cosmology: e.g., general relativity led to the first self-consistent cosmological models; from nuclear physics came big-bang nucleosynthesis; and so on. The connection between fundamental physics and cosmology seems even stronger today and makes realistic the hope that much more of the evolution of the Universe will be explained by fundamental theory, rather than ad hoc theory that dominated cosmology before the 1980s. Indeed, the most promising paradigm for extending the standard cosmology, inflation + cold dark matter, is deeply rooted in elementary particle physics.

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