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Research

The Institute for Gravitation and the Cosmos (IGC) promotes interdisciplinary effort to create and develop fundamental theories and study their manifestations in the observable universe. The Institute is also developing new realms of inquiry that use novel types of astronomy to guide theoretical investigations.

Members of the IGC belong to one or more of its three centers. Specific information about research in each of the centers is available at these links:

However, with its emphasis on interdisciplinary studies, the IGC is more than the sum of these centers. It stimulates collaborative research between centers as well as within each center. The history of physical science testifies to the constructive resonance between empirical results and advances in theory. The IGC provides bridges between different observational theaters, bridges between different theoretical paradigms, and an overarching structure to connect observations with theory.

Theoretical research at the Institute spans astroparticle physics, cosmology, general relativity, quantum gravity, string theory and the interface of geometry and physics. We seek to illuminate the dynamics that fuel the most energetic explosions in the universe, to elucidate aftermaths of black hole collisions, and to study the death dance of binary neutron stars as they spiral in an ever tightening embrace. General relativity and quantum physics, the great pillars of 20th century physics, have succeeded brilliantly in their own domains. But they provide strikingly different pictures of the physical universe. To unify them, we pursue both leading approaches — loop quantum gravity and string theory — as potential, possibly complementary, frameworks. These investigations are guided by the expertise in geometry and topology at the IGC and in turn inspire new developments in these areas.

Cosmology has developed over the past century from philosophical speculation to a science of precision measurements. The IGC initiatives span all aspects of the study of the very early universe, ranging from observational missions such as the Sloan Digital Sky Survey (SDSS) and the Large Synoptic Survey Telescope (LSST), to numerical simulations of the first structures, to theoretical paradigms for the earliest instants of the universe, with emphasis on confronting theories with observations. Black holes appear in a multitude of ways in the cosmic riddle. They provide engines that drive extreme astronomical phenomena, they have emerged as the most promising sources of gravitational radiation and they serve to bring out some of the deepest puzzles that lie at the interface of gravity, thermodynamics and quantum mechanics. The IGC researchers use ideas and methods from geometry, astrophysics, computational science and fundamental theory to address this diverse array of challenges.

On the observational front, the IGC is unique in helping to develop new windows on the cosmos using each of the four forces of Nature:

(1) Gravitational force
Gravitational waves from collapsing stars, from merging black holes and neutron stars, and from the first moment of the universe are targets of study using LIGO (Laser Interferometer Gravitational-Wave Observatory), a Pulsar Timing Array (NANOGrav) which constitutes a galactic scale detector, and the future LISA (Laser Interferometer Space Antenna). IGC scientists have played central roles in the development of theoretical underpinnings for the new discipline of gravitational wave astronomy.
(2) Electromagnetic force
IGC faculty are involved in observations of gamma-rays with energies spanning more than 9 decades of the spectrum. With its Mission Operation Center at Penn State, the Swift Gamma-Ray Burst Mission has been revolutionizing our knowledge of the powerful gamma ray bursts that can be detected from the edge of the observable universe, and IGC scientists are leading the way in deriving new understandings from the Swift data. High energy gamma rays are measured by the Fermi Gamma-Ray Space Telescope. For very high energy gamma-rays of 100 GeV and above, VERITAS targets individual sources with high resolution, while HAWC (now under construction in Mexico) will monitor the entire exposed sky. IGC is well represented in all these projects.
(3) Strong nuclear force
The Pierre Auger Cosmic Ray Observatory in Argentina monitors the arrivals of nature's most energetic particles through their nuclear interactions in the atmosphere. This new field of astronomy using neutrons, protons, and nuclei provides direct information about the extreme conditions that produce the highest energy cosmic rays, and IGC faculty are prominent members of the international Auger Collaboration.
(4) Weak nuclear force
The IceCube Neutrino Observatory at the South Pole studies high energy neutrinos which penetrate the earth because they are immune to electromagnetic and strong nuclear forces. The neutrinos are detected by their weak nuclear interactions in the ice. IGC members are major players in the IceCube operations, data analysis and the development of enhancements to the observatory.

The Institute for Gravitation and the Cosmos is a catalyst that brings together research in different specialties where cross fertilization can produce major discoveries. The four novel windows on the cosmos are observing dynamic cosmic occurrences through different techniques. A holistic analysis of the collective observations provides insights that are not apparent using any one window by itself. Similarly, string theory and loop quantum gravity provide complementary perspectives which together are leading to new understandings and theoretical breakthroughs. The Institute is designed to develop such synergy between its complementary specialties and to foster new interdisciplinary fields of research.

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