The Physics of the Cosmos (PCOS) Program lies at the intersection of physics and astronomy. Its purpose is to explore some of the most fundamental questions regarding the physical forces and laws of the universe: the validity of Einstein's General Theory of Relativity and the nature of spacetime; the behavior of matter and energy in extreme environments; the cosmological parameters governing inflation and the evolution of the universe; and the nature of dark matter and dark energy. PCOS takes us beyond Einstein and beyond the Standard Model.
The PCOS Program consists of a suite of operating science missions and possible future missions that focus on specific aspects of these questions. The Chandra and XMM-Newton observatories probe the universe in X-rays using detailed images and spectroscopy to study matter under a broad range of physical conditions. INTEGRAL and now Fermi study the phenomena with the highest energy emission looking for new physics in the gamma-ray regime. Planck provides an order of magnitude increase in the precision with which we measure the Cosmic Microwave Background. The next generation of PCOS missions will build on the discoveries of these missions and take us to the next stages of discovery.