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Cosmology A Research Briefing (1995) / Chapter Skim
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IV. THE DISTANT UNIVERSE
Pages 25-32

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From page 25...
... In tile future, a main goal will be to image distant galaxies at tile highest possible angular resolution, both with the HST and with groundbased techniques. The development of adaptive optics technology, which sharpens the view of grounci-based telescopes, and its application to distant galaxy research will open a powerful new channel of information about the distant universe.
From page 26...
... These absorption studies have shown that the absorbing gas occurs in lumps, and that there is little neutral hydrogen in a smoothly distributed intergalactic medium. One explanation of this lack of neutral hydrogen is that, at some point, the entire universe was reionized heated so hot that hydrogen atoms were broken up into their constituent protons and electrons.
From page 27...
... Finally, the presence of a population of massive objects, such as galaxies, screening a population of background sources, such as quasars, produces tensing effects detectable through statistical analysis of the ellipticities of the tensed images. Gravitational lenses provide a unique opportunity to infer the properties of the spacetime in which they are embedded, the mass distribution of the lens, and the detailed properties of the background source.
From page 28...
... Current limits appear to preclude models in which the A term dominates the universe; improved constraints will be possible with improved imaging using the newly completed Very Long Baseline Array (V1:,BA) , the HST, and ground-based optical telescopes equipped with adaptive optics systems.
From page 29...
... Recent theoretical analysis describes how this method can provicle a solid measurement of the matter-clustering amplitude of the foreground mass distribution. Elongated images are more likely to occur near large concentrations of matter, such as clusters of galaxies, where several spectacular examples have already been observed (see Figure 7~.
From page 30...
... Moreover, energies in the Big Bang reached up to 10~4 times higher than any conceivable terrestrial accelerator, and these energies probe realms that are inaccessible to our laboratory experiments. For this reason the Big Bang is sometimes called the "poor man's particle accelerator." Tile aim of early-universe cosmology is to trace the successive transitions of forces and particles from the earliest, fiercely hot moments of the Big Bang to the epoch of atom formation at 4,000 K (see section II on the cosmic microwave background radiation)
From page 31...
... One example is the abundance of 31 primordial helium and deuterium, discussed in more detail below. Primordial Nucleosynthesis and Dark Matter Along with the Hubble expansion and the cosmic microwave background radiation, one of the pillars of the Big Bang theory is its successful prediction of the abundances of the light elements deuterium, helium, and lithium.
From page 32...
... is not symmetric at the low temperatures of the present universe. As time progressed, the temperature decreased, and the vacuum underwent a phase transition from a symmetric state of higher energy.


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