Connecting Quarks with the Cosmos Eleven Science Questions for the New Century (2003) / Chapter Skim
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4 How Did the Universe Get Going?
4 How Did the Universe Get Going?
Pages 60-77
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From page 60... ...
Today, the universe is filled with the cosmic background radiation, the residual heat from the big bang, which has been cooled by the expansion of the universe. This radiation fills space; there are roughly 400 microwave background photons in each cubic centimeter of space.
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From page 61... ...
. The fundamental set of observations that support the big bang model are the expansion of the universe; the existence of the cosmic microwave background (CRIB)
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From page 62... ...
satellite accurately measured the energy spectrum of this background and found that it agreed with the big bang model's prediction of a thermal spectrum to better than 1 part in 10,000. Although CMB observations are measuring the physical conditions 400,000 years after the big bang, it is possible to use the big bang model to extrapolate back to early times.
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From page 63... ...
These particles, products of the first microsecond of the big bang, may account for the bulk of the matter in the universe and may even be detectable in laboratory and astronomical searches (see Chapters 3 and 51. REFINING THE BIG BANG: THE INFLATIONARY PARADIGM Despite its successes in explaining the expansion of the universe, the abundance of light elements, and the properties of the CMB, the big bang model is incomplete.
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From page 64... ...
; new specialized detectors to search for dark matter particles; and in the coming years even more powerful probes. Taken together, observations of the effects of dark matter and dark energy and of the fluctuations in the remnant radiation from the big bang will soon allow percent-level determinations of several cosmological parametersthe expansion rate (Hubble constant)
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From page 65... ...
The nature of this dark energy and of dark matter remains a mystery and is the focus of Chapter 5. However, the absence of a precise identification of dark matter particles and the lack of a fundamental understanding of the nature of dark energy do not prevent calculations within the inflationary paradigm that connect the physics of the early universe to observations of the CMB and of galaxies and clusters today.
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From page 66... ...
The Heisenberg uncertainty principle prohibits precise knowledge of the energy density of the universe at the atomic scale, which leads to a fundamental source of lumpiness. Unfortunately, the tremendous mismatch between the subatomic length scales on which quantum fluctuations are important and the astrophysical scales associated with the structure in the universe renders this uncertainty principle possibility completely irrelevant in the standard big bang model.
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From page 67... ...
satellite as depicted orbiting Earth. CORE was launched in 1989 and made precision measurements of the COB radiation and discovered the 30 microkelvin variation in its intensity across the sky; image courtesy of NASA.
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From page 68... ...
Image courtesy of NASA, H
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From page 69... ...
The inflationary model makes detailed predictions for the statistical properties of the fluctuations on the cosmic background microwave sky. The predictions are consistent with the CMB fluctuations measured by the COBE satellite on large angular scales (see Figure 4.~)
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From page 70... ...
. Image courtesy of NASA.
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From page 71... ...
Included in this list are basic cosmological parameters, such as the size of the universe and the rate at which it is expanding, the average density of ordinary matter, the average density of dark matter particles, and the amount of dark energy, as well as basic parameters of inflation. The third test involves a detailed comparison of the two maps of the universe just discussed with other observations, including the distribution of dark matter revealed by gravitational lensing surveys (see Chapter 51.
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From page 72... ...
. Then, around the time of either the electroweak phase transition or the grand unification phase transition, a sequence of events called baryogenesis is believed to have occurred that was responsible for the origin of the slight imbalance between matter and antimatter.
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From page 73... ...
If they were violent enough, any of these phase transitions could have produced a cosmic background of gravitational waves the gravity-wave static that new instruments can detect. The characteristic wavelength of these emitted gravitational waves corresponds to the size of the visible universe when this phase transition occurred.
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From page 74... ...
They can also scatter and polarize light, producing both variations in the microwave temperature and a particular pattern in the polarization of the microwave radiation on large angular scales that carries the imprint of the gravitational wave perturbations. Since both density fluctuations and gravitational waves produce variations in the microwave background temperature, it is difficult to detect gravitational waves with temperature measurements alone.
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From page 75... ...
Image courtesy of the DASI Collaboration.
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From page 76... ...
A spaceborne laser interferometric detector could be sensitive to very-longwavelength gravitational waves. Although gravity-wave detectors have been designed to detect point sources of gravitational radiation, they might be able to observe the diffuse radiation from the inflationary era of the early universe predicted by some models, and they would certainly be sensitive to waves from phase transitions or other exotic epochs that have been hypothesized.
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From page 77... ...
Experiments that map the fluctuations of the microwave background on finer angular scales, together with weak gravitational lensing surveys, can measure the size and the rate of expansion of the universe, the density of ordinary and dark matter, and the basic parameters of inflation. Measurements of microwave background polarization fluctuations will be sensitive to primordial gravitational waves, possibly yielding clues to the physics that underlies inflation.
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