Early in the 20th Century, the study of cosmic rays—highly energetic, charged particles from space—provided the first evidence for the richness of particle physics. By discovering the positron, the antiparticle of the electron, these first observations revealed the existence of antimatter. Cosmic rays also enabled physicists to discover the muon, the unexpected heavier cousin of the electron.
As high-energy particle accelerators became increasingly capable of producing exotic particles in a controlled laboratory setting, scientists migrated from the Cosmic Frontier, using natural sources, to the energy frontier, using powerful beams of electrons and protons. With an increasingly set of sophisticated techniques that complement the accelerator-based research, the Cosmic Frontier is experiencing a resurgence, creating a diverse program of experiments.
A number of experiments aim to solve the mystery of dark matter and dark energy. These components of the universe do not shine like stars and galaxies; they are “dark.” Scientists have thus far only indirect evidence of their existence of dark matter through its gravitational influence on both the motion of galaxies. The direct detection of dark matter might be possible by searching for Weakly Interacting Massive Particles (WIMPS). Physicists consider these WIMPs to be one of the leading candidates for the constituents of dark matter.
Fermilab's Cryogenic Dark Matter Search experiment is searching for WIMPs half a mile below ground where the detector is well shielded from background noise. High-energy gamma ray observations from the Large Array Telescope using the Fermi Gamma-ray Space Telescope (FGST), a NASA space telescope, and VERITAS, a ground-based telescope in Arizona, present another approach for shedding light on dark matter.
In the case of dark energy, measurements of its properties rely on the impact it has on how distant galaxies move over large amounts of space and time. Such measurements require telescopes capable of surveying large portions of the sky in great detail. The Dark Energy Survey will map the distances of 300 million galaxies, helping chart the geometry of the universe. The Large Synoptic space Telescope (LSST) will be able to chart the distribution of mass in the universe using the “weak lensing” technique and thereby provide crucial information on the nature of dark energy
Neutrinos present another research area on the Cosmic Frontier. Though trillions of neutrinos pass through our bodies each second, they hardly leave a trace. Only now are these particles—first detected in the 1950s—beginning to reveal their secrets. For example, only in the past few years have physicists discovered at the Sudbury Neutrino Observatory in Canada and the Super-K observatory in Japan the first evidence for neutrino mixing, an observation that can be understood only if neutrinos have mass. Scientists are still analyzing data from these observatories, but their results indicate a need for a deeper understanding of fundamental physics than that contained in the Standard Model. And of course new questions arise: What are the masses of the various types of neutrinos and why are they so small? And, Are there other types of neutrinos than the three already known? The physics of neutrinos—whether from astrophysical or terrestrial sources--may even hold answers to even deeper questions such as, Where has all the antimatter gone? and Do all the forces become one? Results from new, highly precise experiments designed to observe neutrinos from controlled sources including accelerators as well as nuclear reactors such as Daya Bay in China, may help scientists answer these questions.