BY EMILY BALDWIN
Posted: 16 February, 2009
Scientists using the South Pole Telescope are set to put the theory of cosmic inflation to its most stringent observational test so far, by seeking out gravity waves.
"If you detect gravity waves, it tells you a whole lot about inflation for our Universe," says John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics at the University of Chicago. The theory of inflation proposes that a random, microscopic density fluctuation in the fabric of space and time gave birth to the Universe in a hot big bang approximately 13.7 billion years ago. Einstein's theory of general relativity predicts that cosmic inflation should produce gravity waves.
Detecting gravity waves would also rule out other competing theories for the origin of the Universe. "There are fewer than there used to be, but they don't predict that you have such an extreme, hot big bang, this quantum fluctuation, to start with," says Carlstrom. During the next decade, astronomers using the South Pole Telescope (SPT) could uncover these delicate signatures of the early Universe.
The eight metre South Pole Telescope takes advantage of the clear, dry skies at the National Science Foundation's South Pole Station to study the cosmic background radiation. Image: Jeff McMahon.
Carlstrom and colleagues are discussing these issues at the American Association for the Advancement of Science annual meeting in Chicago today, in a session titled "Origins and Endings: From the Beginning to the End of the Universe." Fellow panelists will include Alan Guth of the Massachusetts Institute of Technology, who in 1979 proposed the cosmic inflation theory. The theory also predicts the existence of an infinite number of universes, but this idea cannot be tested.
"Since these are separate universes, by definition that means we can never have any contact with them. Nothing that happens there has any impact on us," says Scott Dodelson, a scientist at Fermi National Accelerator Laboratory and a Professor in Astronomy & Astrophysics at the University of Chicago.
But there is still a way to probe the validity of cosmic inflation. Theories state that the phenomenon would have produced two classes of perturbations: one in the density of subatomic particles and one in the gravity waves.
Scientists have already observed the former. "Usually they're just taking place on the atomic scale. We never even notice them," says Dodelson. But inflation would instantaneously stretch these perturbations into cosmic proportions. "That picture actually works. We can calculate what those perturbations should look like, and it turns out they are exactly right to produce the galaxies we see in the Universe."
And given the right sensitivity of instruments, it may be possible to observe gravity waves with the SPT. Carlstrom and his associates are building a polarimeter in order to attempt this. The polarimeter operates at submillimeter wavelengths, between microwaves and the infrared on the electromagnetic spectrum.
The SPT is currently used to detect the cosmic microwave background (CMB) radiation, the afterglow of the big bang, and to shed light on the elusive force known as dark energy. A repulsive force, dark energy pushes the Universe apart and overwhelms gravity, the attractive force exerted by all matter. Dark energy is invisible, but astronomers are able to see its influence on clusters of galaxies that formed within the last few billion years.
"We have these key components to our picture of the Universe, but we really don't know what physics produces any of them," says Dodelson of inflation, dark energy and the equally mysterious dark matter. "The goal of the next decade is to identify the physics."
The much anticipated Planck mission, which is also destined to uncover the finer details of the CMB, is set for launch in April. Together, space- and ground-based experiments will endeavour to paint a picture of the birth and growth of our Universe.