Connecting Quarks with the Cosmos Eleven Science Questions for the New Century (2003) / Chapter Skim
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7 Realizing the Opportunities
7 Realizing the Opportunities
Pages 132-172
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From page 132... ...
Other needed work is spelled out in the most recent astronomy decadal survey1 or has been recommended by the DOE/NSF High Energy Physics Advisory Panel or their Nuclear Science Advisory Committee. The committee's recommendations, which are presented at the end of this chapter, are meant to complement and supplement the programs in astronomy and physics already in place or recommended, to ensure that the great opportunities before us are realized.
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From page 133... ...
(Strong gravitational lensing produces multiple images of the lensed objects, while weak gravitational lensing simply distorts the image of the lensed object; see Figure 5.6.) The distribution of dark matter on large scales can be measured by studying motions of galaxies relative to the cosmic expansion.
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From page 134... ...
Direct detection of the gravitational radiation from inflation might be possible in the future with very-long-baseline, space-based laser interferometer gravitational-wave detectors. A promising shorter-term approach is to search for the signature of these gravitational waves in the polarized radiation from the CMB.
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From page 135... ...
Constellation-X, a high-resolution x-ray spectroscopic mission, will be able to probe the regions near the event horizons of black holes by measuring the red- and blueshifts of spectral lines emitted by gas accreting onto the black holes. LISA, a space-based laser interferometer gravitational-wave observatory, will be able to probe the space-time around black holes by detecting the gravitational radiation from merging massive black holes.
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From page 136... ...
Elements of this program will require a deep underground laboratory. Such an underground laboratory would perform experiments at the intersection of particle and nuclear physics.
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From page 137... ...
The existence and properties of this new phase of matter have important cosmological implications. Quark-gluon plasmas may also play a role in the interiors of neutron stars.
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From page 138... ...
. X-ray observations of neutron stars can shed light on how matter behaves at nuclear and higher densities, providing insights about the ohvsics of nuclear matter and nossiblv even of new states of matter.
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From page 139... ...
The predictions of QED have been tested with great precision in regimes accessible to laboratory study, such as in static magnetic fields as large as roughly 105 gauss. However, magnetic fields as large as 1 o42 gauss are commonly found on the surfaces of neutron stars (pulsars)
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From page 140... ...
The photons of the CMB come to us from a time when their creation and destruction effectively stopped because the universe had expanded to relatively low densities. The spectrum of the CMB differs from that of a blackbody by less than 1 part in 104, showing that the energy of CMB photons has not been perturbed since about 2 months after the big bang.
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From page 141... ...
The determination of the amount of ordinary matter, about ~ percent of the critical density, agrees with the determination based on the amount of deuterium produced during the first seconds and strengthens the case for a new form of dark matter dominating the mass in the universe. For the future, the Microwave Anisotropy Probe (MAP)
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From page 142... ...
This polarization anisotropy is expected to be most prominent at even finer angular scales than those for the temperature, requiring instruments with beams that are smaller than 0.1 degrees. In the fall of 2002, the first detection of the polarization of the anisotropy of the CMB by the DASI experiment was announced (see Figure 4.61; the amplitude and variation with angular scale was as expected.
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From page 143... ...
Based on what is known about polarization foregrounds and the existence of a false B-mode signal produced by gravitational lensing, a fully optimized experiment might well be able to detect gravitational waves from inflation, even if their effect on the CMB is three orders of magnitude smaller than that of density perturbations. Achieving this sensitivity would allow one to probe inflation models whose energy scale is 3 x 1045 GeV or larger, close to the energy where the forces are expected to be unified.
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From page 144... ...
It could be as "simple" as the energy associated with nature's quantum vacuum. Or, it is possible that our current description of a universe with dark matter and dark energy may just be a clumsy construction of epicycles that we are patching together to save what could be an obsolete theoretical framework.
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From page 145... ...
We know from the CMB that the universe is spatially flat and therefore that its total matter and energy density must sum to the critical density. On the other hand, all our measurements of the amount of normal and dark matter indicate that matter accounts for only one third of the critical energy density.
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From page 146... ...
New instruments, especially Constellation-X, which is planned for the end of the decade, should lead to further progress in the study of galaxy clusters. Pilot studies of the gravitational distortion of the images of distant galaxies by intervening mass concentrations (weak gravitational lensing)
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From page 147... ...
A wide-field space telescope could discover thousands of distant Type la supernovae and follow their light curves in the optical and near-infrared. Operating above the atmosphere ensures uniform sampling of light curves without regard to weather and helps to minimize systematic errors or corrections.
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From page 148... ...
. However, when it comes to addressing three of the questions What is dark matter?
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From page 149... ...
. Existing underground labs are WIPP, Homestake, and Soudan in the United States; Kamioka in Japan; Boulby, Gran Sasso, Baksan, and Frejus in Europe; and Sudbury in Canada.
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From page 150... ...
The establ ishment of appropriate i Infrastructure to assemble and operate SNO at this depth accounted for a substantial part of the cost and the construction time. The Laboratori Nazionali del Gran Sasso, in Italy, and a facility in the Baksan valley in Russia are two general-purpose national underground laboratory facilities (see Figure 7.11.
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From page 151... ...
Massive neutrinos contribute about as much to the universe's matter budget as do stars, but they are unlikely to constitute the bulk of the dark matter. The lightest supersymmetric particle (neutralino)
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From page 152... ...
In many cases, with present knowledge and available technologies, our questions on dark matter, neutrino mass, and proton stability are ripe for major experimental breakthroughs. Such experiments must be in locations well isolated from cosmic rays.
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From page 153... ...
Astrophysicists are now recognizing that the strong gravitational fields and extreme densities and temperatures found in objects like black holes, neutron stars, and gammaray bursts allow us to test established laws of physics in new and unfamiliar regimes. A key scientific component of NASA's Beyond Einstein initiative is the use of space-based observatories to probe physics in extreme regimes not accessible on Earth.
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From page 154... ...
Constellation-X will also measure continuum flares and subsequent changes in line emission, providing data on the effect of gravity on time near a black hole and thereby testing the validity of general relativity in the strong gravity I i mitt Additional tests of general relativity can be made by observing quasiperiodic oscillations (QPOs) of the x-ray flux emitted by matter falling onto neutron stars or black holes in galactic binaries.
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From page 155... ...
In addition, it can measure the evolution of the gravity wave signal emitted as neutron stars or white dwarfs spiral into the supermassive black holes in the nuclei of galaxies. The details of the wave shapes are sensitive to general relativistic effects, so can be used to probe gravity in the strong field limit.
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From page 156... ...
For example, a space-based x-ray interferometer could directly image gas orbiting a black hole, tracing the gravitational field down to the event horizon. A sensitive x-ray polarimeter could probe QED in magnetic fields exceeding 1044 gauss, well above the QED critical field, where quantum effects become important.
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From page 157... ...
Acceleration of particles to high energy is a characteristic feature of many energetic astrophysical sources, from solar flares and interplanetary shocks to galactic supernova explosions and distant active galaxies powered by accretion onto massive black holes. The signature of cosmic accelerators is that the accelerated electrons, protons, and heavier ions have a distribution of energies that extends far beyond the thermal distribution of particles in the source.
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From page 158... ...
Possible sites for cosmic accelerators include highly ~ - -- ~ - - - - O - - 0' - -magnetized neutron stars, million-solar-mass black holes accreting matter at the centers of active galaxies, and jets from gamma-ray burst sources, possibly involving stellar-mass black holes. A problem for all these hypothetical mechanisms is that all calculations find it difficult to achieve per
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From page 159... ...
Even more exotic is the suggestion of a violation of Lorentz invariance at very high energy in such a way that the energy-loss mechanism in the microwave background is not effective, but this still leaves open the question of how such high energy was achieved in the first place. The problem of the origin of the highest-energy cosmic rays has been the focus of a series of increasingly large air shower experiments of two types.
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From page 160... ...
National Research Council, Frontiers in High Energy Density Physics: The X-Games of Contemporary Science, Washington, D.C., National Academies Press, 2003.
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From page 161... ...
In addition, several experimental facilities have been constructed in which it is possible to squeeze plasma to tiny volumes and large pressures and to study how they behave. In particular, it should be possible to study turbulence and magnetic reconnection, which take place when magnetic field lines exchange partners.
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From page 162... ...
Examples include laboratory experiments to test gravitational interactions, theoretical work and computer simulations to understand complex astrophysical phenomena, and small-scale detector development for future experiments. These examples are not intended to be exhaustive but to illustrate the need for a balanced program of research on the physics of the universe that provides opportunities for efforts that address the scientific questions but that do not necessarily fit within major program themes and their related large projects.
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From page 163... ...
Theoretical and computational work will play integral roles in addressing several of the scientific questions. To test whether Einstein had the last word on black holes will require analytically and numerically generated gravitational waveforms from black hole mergers that can be compared with gravitational-wave data.
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From page 164... ...
They range from understanding the birth and destiny of the universe to testing Einstein's theory of gravity in black holes and understanding the fundamental nature of matter, space, and time. In this chapter the next steps that must be taken to realize the opportunities are discussed.
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From page 165... ...
. The portion of the polarization of the CMB that is produced by primordial gravitational waves offers great promise in testing further and understanding the inflationary era that may have occurred shortly after the birth of the universe.
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From page 166... ...
Both telescopes will also help to elucidate our understanding of the distribution of dark matter. In this quest to solve one of the great puzzles of physics and astronomy, NASA and NSF have their traditional roles to play in space-based and ground-based astronomy, respectively.
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From page 167... ...
Recommendation on Exploring the Unification of the Forces from Underground Three of the committee's 11 questions the nature of the dark matter, the question of neutrino masses, and the possible instability of the proton must be addressed by carrying out experiments in a deep underground laboratory that is isolated from the constant bombardment of cosmic-ray particles. One of the most important discoveries in the past 10 years, that neutrinos have mass, was made in an underground laboratory.
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From page 168... ...
Constellation-X is a sensitive, high-resolution x-ray spectroscopy mission. Among its many potential targets are the gas disks orbiting black holes and the surfaces of neutron stars at nearly the speed of light, which will enable it to test general relativity and measure how matter behaves at high density.
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From page 169... ...
The committee supports the Constellation-X and LISA missions, which have high promise for studying black holes and for testing Einstein's theory in new regimes. The committee further recommends that the agencies proceed with an advanced technology program to develop instruments capable of detecting gravitational waves from the early universe.
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From page 170... ...
They challenge laboratory physicists to devise and perform experiments that will uncover the physical principles that can be scaled up to understand the most powerful astronomical sources, like quasars, neutron stars supernova explosions uamma-rav bursts and the bin band.
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From page 171... ...
, the Cryogenic Dark Matter Search (NSF and DOE) , the BOOMERanG and MAXIMA cosmic microwave background experiments (NASA and NSF)
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From page 172... ...
New funds will be needed to realize the grand opportunities before us. In addition, the committee believes that it is essential that an interagency initiative on the physics of the universe maintain a balanced approach that provides opportunities for investigator-initiated experiments, detector R&D, theoretical work, and computational efforts that address the committee's scientific questions but that do not necessarily fit within major program themes and their related large projects.
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