A joint Fermilab/SLAC publication

Nobel Prize for discovery of accelerating universe; mysterious origin still unknown


The 2011 Nobel Prize in Physics has been awarded to three scientists: Saul Perlmutter, Brian Schmidt and Adam Riess. Their observations of distant exploding stars led them to the startling discovery that the expansion of the universe is accelerating. This discovery laid the groundwork for the idea that a mysterious force called dark energy, which makes up 75 percent of the universe – yet has never been detected – is fueling the acceleration.

Perlmutter, a researcher at Lawrence Berkeley National Laboratory and the University of California, headed the Supernova Cosmology Project, which began observations in 1988. Schmidt, of the Australian National University, started the High-Z Supernova Search Team in 1994; it was later joined by Riess, of Johns Hopkins University and the Space Telescope Science Institute, who played a crucial role in the observations.

Between them, the two teams found more than 50 supernovae whose light was weaker than expected – an indication not only that the universe was expanding, as had been expected, but that it was expanding ever faster. The discovery came as a complete surprise, even to the discoverers, and its announcement in 1998 profoundly shook our view of the universe. In 2007, symmetry published a scan of the page of Riess’s logbook with the data and notes that led to his Nobel Prize-winning discovery.

"I'm thrilled for Adam, Brian and Saul and the teams they have led,” said Roger Blandford, director of the Kavli Institute of Particle Astrophysics and Cosmology at SLAC National Accelerator Laboratory. “It was a great discovery, and it's looking like a vindication of the original proposal Albert Einstein made 94 years ago."

Several research projects are aiming to find out the origin of the force that drives the universe apart. The SDSS-II collaboration, which includes Riess, used the telescope of the Sloan Digital Sky Survey, located in New Mexico, to gather information on supernovae and the expansion of the universe. Earlier this year, SDSS scientists published the largest color image of the sky ever made.

Perlmutter is a member of the Dark Energy Survey, which will use a powerful digital camera mounted on a telescope in Chile to record 300 million galaxies. The survey will start taking data in 2012. The Dark Energy Camera, built at Fermilab in Batavia, Ill., will peer deeper into the sky and unveil more galaxies at greater distances than any previous project, including the Sloan Digital Sky Survey.

"The origin of cosmic acceleration presents a deep mystery for cosmology and fundamental physics," said Joshua Frieman, director of the Dark Energy Survey. "Is the universe filled with gravitationally repulsive dark energy? Do we need a new theory of gravity to replace Einstein's? The Dark Energy Survey aims to address these questions by measuring the 14-billion-year history of cosmic expansion with high precision."

This symmetry article describes the DES in more detail. It says:

[The Dark Energy Survey] will collect data on the distances of supernovae from Earth; the large-scale clustering of galaxies; the abundance of massive galaxy clusters; and the bending of light caused by galaxies and clusters of galaxies. DES scientists will use these four methods to determine how fast the universe has been expanding and the rate at which galaxies and clusters formed over cosmic time. Two of those methods will yield answers that are independent of the role that gravity played in the evolution of the universe. The other two will provide answers that depend on the theory of gravity.

Another group of scientists is advancing plans for the Large Synoptic Survey Telescope. The LSST will meet the need for more dark energy data over its estimated 10-year lifetime by collecting some 2000 images of each of five billion galaxies. The LSST project has about 400 members and expects to grow to more than 1000. Led by a team at SLAC, LSST collaborating institutions from all over the world are working on pieces for the LSST digital camera. According to this article:

The LSST mirrors will capture and focus starlight down into the largest— and perhaps the most expensive—digital camera ever built. Six feet tall, weighing more than 6000 pounds, the LSST camera will produce 3.2-billion-pixel images and generate, on an average viewing night, about 15 terabytes of raw data, or 25,000 CDs worth. To display one of the LSST full-sky images on a television would require not just a high-definition screen, but 1500 of them.

Much of the initial funding to get the LSST rolling came from private sources, primarily the Charles Simonyi Fund for Arts and Science and from Microsoft founder Bill Gates. Long-term plans show the bulk of LSST funding coming from the National Science Foundation and the US Department of Energy.

Kurt Riesselmann contributed to this article.

A short version of this article first appeared in
SLAC Today.

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