Gravitation, Cosmology, and Cosmic-Ray Physics (1986) / Chapter Skim
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12. Highlights
12. Highlights
Pages 90-100
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From page 90... ...
. The baryon density at T~ 109 K can be computed from the present baryon density and the present temperature of the background radiation; and the expansion rate can be calculated for isotropic, homogeneous cosmological models provided that the number of species of light particles is known.
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From page 91... ...
1 shows the predicted primordial abundances of several light nucleic as functions of the present baryon density- a poorly known cosmological parameter. The observed abundances are shown by shaded rectangles, with 7Li being a recent addition.
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From page 92... ...
The classical methods to study the geometry of space-time use visible galaxies and radio sources as coordinate measures. Usually, source intensity is used as a measure of distance, but this requires a knowledge of time dependence of the source luminosity and spectrum.
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From page 93... ...
MICROWAVE BACKGROUND SPEC T R U M _ 10 14 _ :r ~n ~ 10 46 cot cot |
From page 94... ...
The inferred velocity of our galaxy is surprisingly large and suggests that we are being perturbed by local mass concentrations such as the Virgo cluster of galaxies and its surroundings. Failure to observe a quadrupole anisotropy with an amplitude larger than 10-4 K provides an important constraint on homogeneous but anisotropic cosmological models.
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From page 95... ...
There is considerable theoretical and observational activity devoted to tracing the evolution of this structure back to its origins. Evidence exists that radio sources, quasars, and perhaps also galaxies have changed appreciably between the epoch z ~ 3 and the present.
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From page 96... ...
1? ~ ~ ~ l l ll 1 0' 301 1 ° 3° ,,, , I 1 1, 1 0 ° 30° 90° 180° Angular scale 10 1.0 0.1< .01 FIGURE 12.3 Current results of searches for anisotropy in the cosmic microwave background radiation.
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From page 97... ...
Since the dark-matter candidates mentioned so far are made from baryons, the nucleosynthesis constraint on baryon mass density has strong implications here. Stars, "Jupiters," and even black holes born after big-bang nucleosynthesis are included in the baryon density constraint noted in Figure 12.1- a density far short of that needed to close the universe.
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From page 98... ...
~ Some proposed particles have natural clustering scales that can be compared to observed structure, but it is still controversial which clustering lengths give the best fit to the phenomena. COSMOLOGY AND GRAND UNIFICATION A recent dramatic development in theoretical physics was the realization that the early universe is a useful laboratory for the testing of particle physics; conversely, new ideas in particle physics can be applied to some fundamental cosmological questions.
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From page 99... ...
The idea is that if scalar fields exist, their vacuum expectation value could provide a contribution to the mass density that remains constant in time, like the effect of the cosmological constant first introduced by Einstein. During the time following the GUT era when vacuum expectation energy dominates, the universe expands much faster than in the usual big-bang models, and this exponential expansion drastically dilutes the density of monopoles.
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From page 100... ...
has the current mass-energy density in the universe exactly equal to Pc, the critical closure density. At present, the study of the inflationary class of big-bang models is one of the most exciting areas within the rapidly growing union of theoretical particle physics and cosmology.
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