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Photo, caption follows:

An artist's conception of our "stop and go" universe, in which the cosmic expansion slowed under the influence of gravity before accelerating again due to an unexplained dark energy. This brief history extends from the Big Bang and the recombination epoch that created the microwave background (bottom), through the formation of galactic superclusters and galaxies themselves (top). The dramatic flaring in the upper reaches of the diagram emphasizes that the universe's expansion currently is speeding up.
Credit: David A. Aguilar, Harvard-Smithsonian Center for Astrophysics

The
                            Physics of the Universe
During the past two decades, scientists have made astonishing discoveries and raised profound questions about the contents and evolution of the universe. These new insights – derived from observation of exploding stars called supernovae, from analysis of the cosmic microwave background (CMB), from measurements of ghostly particles called neutrinos and examination of ultra-high-energy collisions of atomic nuclei, from wide-angle sky surveys, and from many other sources – are so revolutionary that they cannot be explained by traditional ideas and methods.

To name only a few: About 95 percent of all the matter and energy in the cosmos exists in one or more “dark” forms radically different from the familiar protons, neutrons, electrons and forces we know. The universe is expanding at an accelerating rate, apparently driven by some exotic force called dark energy. The “empty” vacuum of space is actually seething with activity that researchers do not fully understand. And that same empty space is also pervaded by super-high-energy particles such as gamma rays and cosmic rays, whose origins are still unclear.

Comprehending these and other mysteries requires far more than astronomy. It demands an integrated approach in which particle physics, cosmology, quantum theory, nuclear physics, deep underground experiments and pioneering theoretical ideas combine with space- and ground-based celestial observations to create a synthesis.

NSF already supports many such efforts, including projects to further analyze the cosmic microwave background; detect and characterize the dark matter that holds galaxies together; investigate dark energy through several kinds of observations; and study those mysterious high-energy cosmic rays, which have presumably been propelled to by some equally mysterious sort of cosmic accelerator.

In addition, NSF funds the world’s largest and most ambitious gravity-wave observatory, LIGO, which is devoted to detecting and categorizing evidence for one of the extraordinary predictions of Einstein’s general theory of relativity: the ripples in space-time caused by acceleration of enormous masses, such as black holes or neutron stars.

In the future, NSF plans to collaborate with other federal agencies to invest in the highly sensitive instruments and technologies – and the improved experimental sophistication – that will be needed to address the most pressing questions in the physics of the universe. Among them are experiments to test the prediction that protons ultimately decay, measure the masses of the three “flavors” of neutrinos, understand the origin of elements heavier than iron (which are not created naturally in stellar fusion), determine how cosmic accelerators work, and describe the behavior of light and matter in extreme energy-density conditions.

These are exhilarating times in cosmology and physics. With NSF’s help, scientists are on the verge of revelations that will be every bit as significant as those that produced the Copernican revolution, the Newtonian era, and the age of Einstein.

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