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M.S. Turner (University of Chicago)
Two independent lines of evidence point to accelerated expansion. Within Einstein's theory, the underlying cause is a component of energy with large negative pressure (p< -\rho /2), referred to as dark energy. Dark energy could be the energy associated with the quantum vacuum, the influence of extra dimensions, a slowly rolling scalar field or even an indication of a breakdown of Einstein's general relativity. Dark energy accounts for 2/3 of the mass--energy in the Universe, determines its destiny and perplexes even string theorists! It is a profound problem, a fantastic opportunity for deepening our understanding of the Universe and the laws that govern it, and cosmological measurements seem to be the only way to get at it.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.