Researchers at the Cosmic Frontier seek to understand the nature of the overwhelming majority of the contents of the universe. Ordinary matter—including all stars, planets, interstellar gas, and all living things—accounts for only five percent of the universe while the remaining 95% is comprised of dark matter and dark energy. In 1933, Fritz Zwicky, a faculty member of Caltech, coined the term ?dark matter? to describe the unseen matter that must dominate the Coma Galaxy Cluster in order to match his observations of the motion of its galaxies. Overwhelming indirect evidence for dark matter now exists, from galaxy rotation dynamics to the large-scale structure of the universe, but its nature remains a mystery. The surprising discovery in 1998 that the expansion of the universe is accelerating, instead of slowing down due to gravity, has posed another significant question: what is the ?dark energy? that is pushing our universe apart? While it may be an inherent feature of the universe, it could be something dynamic related to new particles or forces, or a failure of Einstein?s theory of General Relativity. Cosmic Frontier researchers use diverse tools and technologies, from space-based observatories to ground?based telescopes and large detectors deep underground, to probe fundamental physics questions and offer new insight about the nature of dark matter, dark energy, and other phenomena.
Dark matter accounts for five times as much of the universe as ordinary matter, but little is known about it other than that it interacts through gravity. Although there are a few theoretically favored candidate particles for dark matter, it is possible that a rich and complex set of dark matter particles exist. Cosmic Frontier researchers use large, sensitive detectors located deep underground to directly search for the dark matter particles that may be continually passing through Earth. Dark matter may also be detected indirectly through specific signatures within cosmic rays and gamma rays that may be seen by space-based and ground-based observatories.
Cosmic Frontier scientists study two distinct periods of cosmic acceleration, an early moment of cosmic expansion called inflation that occurred a fraction of a second after the Big Bang and an extended period of acceleration that began about 9 billion years later and continues today. Experiments measuring the polarization of the cosmic microwave background may provide clues about the early inflation of the universe. Dark energy may explain why the expansion of the universe continues to accelerate rather than slow down, as would be expected if gravity predominated. Large scale ground-based telescope surveys that study the cosmos with both optical and spectroscopic techniques will improve our understanding of the long term expansion history of the universe and help address the question of what drives cosmic acceleration.
While neutrinos are the lightest known particles, they are one of the most numerous and their gravitational influence has affected the evolution of the universe. Cosmic observations provide important indirect information on the total mass of the number of types of neutrinos.
A suite of experiments observing extra-terrestrial ultra-high energy gamma rays and cosmic rays allow Cosmic Frontier scientists to explore for new particles and interactions beyond those in Standard Model. Cosmic accelerators produce particles with much higher energies than can be produced by particle accelerators on Earth, and studying these particles may give physicists a way of exploring energy scales far beyond what current or planned future particle accelerators can achieve.
The Cosmic Frontier supports a wide variety of fabrication projects and operates experiments that further the science and enable discovery. The High Energy Physics Advisory Panel (HEPAP) advises the DOE on cosmic frontier program status and direction. The Astronomy and Astrophysics Advisory Committee (AAAC) advises the DOE, NASA, and NSF on programmatic areas of overlap.