Gravitational waves provide a laboratory for general relativity and a windowto energetic astrophysical phenomena invisible with electromagnetic radiation.Several terrestrial detectors are currently under construction, and aspace-based interferometer is envisioned for launch early next century todetect test-mass motions induced by waves of relatively short wavelength.Very-long-wavelength gravitational waves can be detected using the plasma inthe early Universe as test masses; the motion induced in the plasma by a waveis imprinted onto the cosmic microwave background (CMB). While the signature ofgravitational waves on the CMB temperature fluctuations is not unique, thepolarization pattern can be used to unambiguously detect gravitationalradiation. Thus, forthcoming CMB polarization experiments, such as MAP andPlanck, will be the first space-based gravitational-wave detectors.
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