Alamos, New Mexico, and Dugway, Utah, offer the hope of confirming the detection of 1014-eV gamma rays and extending the observations to new objects. The development of new gamma-ray airshower detectors is recommended in Chapter 1 (see Table 1.3).

The existing Fly's Eye telescope has convincingly measured cosmic rays with energies greater than 1019 eV, whose origin is still a puzzle. The new Fly's Eye telescope recommended by the committee in Chapter 1 represents an outgrowth of this exciting work. These ongoing programs, which lay the groundwork for more ambitious projects that may be required later in the decade, should be pursued vigorously.

The 1980s saw many interactions between astronomers and physicists on important theoretical questions, such as the origin of the predominance of matter over antimatter and the evolution of large-scale structure in the universe. Only in the first few microseconds after the “Big Bang” were the conditions of density and temperature extreme enough to produce some of the reactions predicted by modern theories of elementary particle physics. Some particle physics models can be tested by comparing their predictions for cosmology and for elemental abundances with astronomical observations.

One of the most striking examples of these interactions involves the existence and nature of “dark matter.” As discussed in Chapter 2, a feature of much of the recent work connecting cosmology and particle physics is the requirement that the universe contains much more matter than is seen. In fact, for many years astronomers have quite independently been obtaining observations of galaxies and clusters of galaxies that suggest that as much as 90 percent of the matter inferred to be present from its gravitational effects has not been seen. Many of the explanations involve exotic particles such as massive neutrinos, axions, or weakly interacting massive particles. Imaginative experiments have been proposed to detect contributions to the missing mass from various particles. The committee has recommended (see Table 1.3) that the technology for various dark matter detectors be developed in the 1990s.

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