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A problem of cosmic proportionsA problem of cosmic proportions.doc

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A problem of cosmic proportionsA problem of cosmic proportions

A problem of cosmic proportions Three experiments are starting to study dark energy, the most abundant stuff in the universe. But a theory has just been published purporting to show it does not exist Aug 24th 2013?|?From the print edition IN THE 1920s astronomers realised that the universe was running away from them. The farther off a galaxy was, the faster it retreated. Logically, this implied everything had once been in one place. That discovery, which led to the Big Bang theory, was the start of modern cosmology. In 1998, however, a new generation of astronomers discovered that not only is the universe expanding, it is doing so at an ever faster clip. No one knows what is causing this accelerating expansion, but whatever it is has been given a name. It is known as dark energy, and even though its nature is mysterious, its effect is such that its quantity can be calculated. As far as can be determined, it makes up two-thirds of the mass (and therefore, E being equal to mc2, two-thirds of the energy) in the universe. It is thus, literally, a big deal. If you do not understand dark energy, you cannot truly understand reality. Cosmologists are therefore keen to lighten their darkness about dark energy, and three new experiments—two based in Chile and the third in Hawaii—should help them do so. These experiments will look back almost to the beginning of the universe, and will measure the relationships between galaxies, and clusters of galaxies, in unprecedented detail. When they are done, though the nature of dark energy may remain unresolved, it should at least be clearer. If, that is, it actually exists. For a core of cosmological refuseniks still do not believe in it. They do not deny the observations that led others to hypothesise dark energy, but they do deny the conclusion. For them, then, these experiments provide an opportunity to test alternative theories. Darkness and dawn The most advanced of the new experiments is the five-tonne, 570-megapixel Dark En