Research on Gravitation, Relativity and Cosmology

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The Princeton experimental program is centered on measurements of the angular distribution of the thermal cosmic background radiation (the CBR) and its spectrum and absolute temperature. These are a proving ground for scenarios of galaxy formation; if the scenario is simple we may find encoded in the angular distribution the values of key cosmological parameters. The spectrum at wavelengths greater than about 3 cm should be better explored to improve constraints on the history of interactions of matter and radiation. This group's measurements from Saskatoon detect the power spectrum of irregularities in the CBR on angular scales from about 0.5 to 3. They will improve these detections with their ground-based telescope and to build a balloon-borne instrument that produces a map of the anisotropy. Better measurements of the CBR anisotropy require more sensitive and stable detectors and radiometers. They will build and test a new 90 Ghz HEMT-based (High Electron Mobility Transistor) radiometer and to develop a small array of broad-band SIS receivers for 90 Ghz. They will also continue developing the techniques to search for long-wavelength distortions in the spectrum. The objective of this research is to advance knowledge, through both theory and experiment, of the evolution and large-scale structure of the universe. New telescopes and improvements in detector sensitivities over a broad range of energies have yielded a much enlarged fund of data that confront a multitude of options within the standard cosmological model. The Princeton group expects that within a decade additions to the data and a careful evaluation of the theoretical options the data allow will yield a new test of general relativity theory, and, through an improved check of consistency of the cosmological model, will sharply restrict models for the formation of galaxies and their large-scale distribution, and perhaps tell us whether the universe is open or closed. Education is central t o this research. The group places a strong emphasis on undergraduate teaching; on average, the group supervises six undergraduates each summer and ten independent research projects during the school year. Though many go on in physics, quite a few continue their education in medicine, engineering, or law. Educating graduate students also has high priority.