June 21, 2012
Charles Bennett And WMAP Team To Receive 2012 Gruber Cosmology Prize For Pinning Down The Universe
Charles L. Bennett and the Wilkinson Microwave Anisotropy Probe (WMAP) team are the recipients of the 2012 Gruber Cosmology Prize. Their observations and analyses of ancient light have provided the unprecedentedly rigorous measurements of the age, content, geometry, and origin of the universe that now comprise the Standard Cosmological Model.
The Prize citation further recognizes that the exquisite specificity of these results has helped transform cosmology itself from “appealing scenario into precise science.”
Bennett, a professor of physics and astronomy at Johns Hopkins University, stresses the team nature of the collaboration. “There are so many heroes who stand up at just the right time and make something happen,” Bennett says, “and they all deserve credit for that.”
Modern cosmology was born in 1916 with Einstein´s relativity theory. In the 1920s Alexander Friedmann and Georges LemaÃ®tre each found that Einstein´s theory implies that the universe should be evolving. Incorporating data on the velocities of galaxies by the astronomer Vesto Slipher, LemaÃ®tre gave the form of a universal expansion with distance from Einstein´s theory of relativity and in 1929 Hubble presented data that galaxies are receding from us at rates directly proportional to their distances–the farther, the faster. The expanding universe gave rise to the Big Bang theory. (Contrary to common usage, the “Big Bang Theory” technically describes the expansion and cooling of the universe from a hot and dense early state, not to an initial explosive event.)
One of the theoretical consequences of the Big Bang interpretation is that when the universe was 378,000 years old, it would have cooled enough for the fog of electrons to be swept up into neutral hydrogen atoms so photons could decouple and go their separate ways. At that moment, the fog lifted so the photons we see today constitute a sort of snapshot of that moment the light broke free (as when we look at the bottom of a cloud) –a “baby picture” of the universe–though after all this time the expansion of space would have stretched the light from the image all the way into the microwave end of the electromagnetic spectrum. In 1948, Ralph Alpher, Robert Herman, and George Gamow calculated the Big Bang prediction of the abundances of the light elements and they predicted that the universe should be filled with a cosmic microwave background radiation. Then, in 1964, two Bell Laboratories astronomers discovered the cosmic microwave background–a nearly uniform glow suffusing all of space.
“Nearly” is the key. Because everything that is in the universe now would have to have been there when the universe was 378,000 years old, some extraordinarily subtle fluctuations in the microwave background would have to have been present–variations that would represent the seeds that would evolve into the galaxies, clusters of galaxies, and superclusters of galaxies that populate the universe as we know it.
A generation later, the Cosmic Background Explorer (COBE), a satellite telescope, began to fill in those details. In 1992, the COBE team announced the discovery of those relic wrinkles in space–an historic scientific achievement in itself, and a momentous step in cosmology´s long march from metaphysics to physics. Only follow-up observations of those wrinkles at far greater sensitivity and resolution, however, would allow scientists to pin down the fundamental cosmology of the universe.
Bennett, then at NASA and the deputy principal investigator of the COBE experiment that discovered the relic wrinkles, soon became the principal investigator of the Microwave Anisotropy Probe, later renamed the Wilkinson Microwave Anisotropy Probe after the death of pioneering cosmologist and MAP team member David Wilkinson of Princeton. (“Anisotropy” means “having a different value when measured in different directions”, referring here to the fluctuations in the microwave signal that represent the wrinkles in space.) The satellite launched in 2001, and the team released the analysis of the first year´s worth of data in February 2003.
“Every astronomer will remember the moment he heard the results from WMAP,” said John Bahcall of The Institute for Advanced Study in Princeton, NJ (now deceased).
Bennett and the WMAP team have released further data analyses in two-year increments. The latest, in 2011, showed that, within very tight margins of error, the universe:
is within 1 percent of 13.75 billion years old;
consists of 22.7 percent dark matter, 72.8 percent dark energy, and only 4.6 percent “ordinary” matter;
seems to have undergone a period of “inflation” in the first trillionth of a trillionth of a trillionth of a second of its existence, just as many theorists have been predicting;
has a flat geometry, to within 0.6 percent.
So precise are these findings that WMAP´s version of the universe is now commonly known as the Standard Cosmological Model.
One of the principal investigators on COBE, John Mather (who received the 2006 Gruber Prize in Cosmology and shared the Nobel Prize in Physics that same year), has commented on the selection of Bennett and the WMAP team for this year´s Gruber Prize. “Dr. Bennett´s discoveries,” Mather said, “have literally changed the scientific universe.”
Science magazine awarded WMAP its “Breakthrough of the Year” honor in 2003: “All the arguments of the last few decades about the basic properties of the universe–its age, its expansion rate, its composition, its density–have been settled in one fell swoop.”
Having far exceeded expectations for the quality and quantity of science it produced, the WMAP science team chose to stop taking data in August 2010. Although nobody expects that the release of the final data analysis in late 2012 will contain surprises, it will nonetheless mark the end of an era–an era that itself marked the dawn of the age of precision cosmology.
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