The field of non-accelerator physics uses naturally occurring particles and phenomena to explore particle and astroparticle physics. High-energy cosmic rays, celestial gamma rays and neutrinos from the Sun, supernovae and terrestrial nuclear reactors serve as some of the non-accelerator-based particle sources used in this area of research.
In the past decade, experiments like these have revealed a Universe far stranger than scientists ever imagined. Ordinary matter—everything that makes up the things we are, see and touch—forms only about 4% of the matter-energy composition of the Universe. The remainder consists of mysterious substances called dark energy (73%) and dark matter (23%). Physicists believe that dark matter holds the galaxies together, but it is a form of matter that does not emit light and interacts very weakly with ordinary matter making it difficult to detect with ordinary observation methods. Dark energy may be responsible for the accelerated expansion of the universe.
Non-accelerator-based programs are playing an increasingly important role in this area of high energy physics. Research from such projects as Sudbury Neutrino Observatory (SNO) in Canada, the Pierre Auger Observatory in Argentina, and the Super-K observatory in Japan have provided experimental data, new ideas and techniques complementary to those provided by accelerator-based research on the Energy Frontier.
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