CPU Study Issues Final Report

The CPU study group identified 11 questions that they be-lieve encapsulate most of the topics at the physics and astro-physics interface that we have a good chance of answering inthe next few decades. Taken as a whole, the questions belowaddress an emerging model of the universe that connects phys-ics at the most microscopic scales to the properties of theuniverse and its contents on the largest physical scales. 1. What is the dark matter? 2. What is the nature of the dark energy? 3. How did the universe begin? 4. Did Einstein have the last word on gravity? 5. What are the masses of the neutrinos, and how have they shapedthe evolution of the universe? 6. How do cosmic accelerators work and what are they accelerating? 7. Are protons unstable? 8. Are there new states of matter at exceedingly high density andtemperature? 9. Are there additional spacetime dimensions? 10. How were the elements from iron to uranium made? 11. Is a new theory of matter and light needed at the highest energies?

The National Academy of Sciences' Committee on the Physics of the Universe has completed its two- year-long study of physics and astronomy research and issued a final report, presented at the APS April Meeting in Albuquerque. Entitled "Connecting Quarks to the Cosmos," the final report outlines seven specific recommendations for research and research coordination to address 11 specific science questions at the interface of physics and astronomy [see box to the right].

Chief among the recommendations are three new initiatives. Potentially most controversial is the construction of a deep underground laboratory (at least 4000 meters of water equivalent) aimed at determining neutrino masses and mixings, measuring the lifetime of the proton, and determining the constituents of dark matter. "[These issues] are all predictions of theories that unify the forces of Nature," said Michael Turner (University of Chicago), who chaired the study group. "Fully addressing all three requires a laboratory that is well shielded from the cosmic ray particles that constantly bombard the surface of the Earth." The committee identified three possible sites, including an extension of the existing Sudbury Neutrino Observatory in Ontario, Canada, and construction of a new facility in the San Jacinto mountains in Southern California. The Homestake mine in South Dakota is another possibility.

A second new initiative is the construction of a wide-field telescope in space to determine the expansion history of the universe and fully probe and characterize the nature of the dark energy. The third new project calls for the creation of a cosmic microwave polarization experiment, in the hope that measuring the polarization of the cosmic microwave background will help scientists detect the signature of inflation.

In addition, the committee added its support to three projects previously recommended by the National Research Council's 2001 survey report, "Astronomy and Astrophysics in the New Millennium," on the basis of their ability to address important problems in astronomy. The CPU group determined they would also address science at the interface of physics and astronomy. They are the Large Synoptic Survey Telescope (LSST), intended to probe the dark energy by weak gravitational lensing; the Laser Interferometer Space Antenna (LISA), designed to test GR by detecting gravity waves from colliding massive black holes; and the Constellation X {CON-X) Observatory's mission, aimed at probing the event horizon of black holes.

Finally, the report calls for determining the origin of the highest energy gamma rays, neutrinos and cosmic rays, adding its support for the broad approach currently in place and recommending that the U.S. ensure the timely completion and operation of the Southern Auger array in Argentina, which the committee deems "crucial for solving the mystery of the highest energy cosmic rays.

"The committee recommended the establishment of an Interagency Initiative on the Physics of the Universe, with the participation of the DOE, NASA and NSF, intended to provide structures for the joint planning and mechanisms for joint implementation of cross-agency topics. The agencies should also cooperate in bringing together the different scientific communities that can foster the rapidly developing field of extreme astrophysical environments through the laboratory study of high-energy-density physics. "The field is in its infancy, and to fulfill its potential, it must draw on expertise from astrophysics, laser physics, magnetic confinement and particle beam research, numerical simulation and atomic physics," said Turner.

Editor's Note: Copies of the full CPU report, "Connecting Quarks to the Cosmos," can be obtained by contacting Joel Parriott at the NAS, 202-334-3520, Jparriot@nas.edu, or Dick Rowberg, 202-334-3226, Rrowberg@nas.edu.