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Riding the gravitational wave

Lawrence Krauss speaking at ASU Origins event
October 30, 2014

Detecting the elusive gravity wave has both inspired and confounded physicists for decades. Last March a team of scientists at the BICEP2 (Background Imaging of Cosmic Extragalactic Polarization 2) experiment said they detected gravity waves, which theory says were produced immediately after the Big Bang creation of the universe. But since then the euphoria has faded and concern over the measurements has set in.

Was it really the faint aftermath of gravity waves that they detected or were the signals distorted by nearby galactic dust?

In the cover story of the October issue of Scientific American, Arizona State University Foundation Professor and cosmologist Lawrence Krauss describes the quest to detect the elusive gravitational wave and what is at stake in its detection. Everything from how the universe acts on a cosmic scale down to the submicron (quantum) level could be put into a clearer light if, and when, gravity waves are detected. Detection of gravity waves could point to the unification of several forces of nature and help us understand the early evolution of the universe and its operation.

“The observation, if confirmed, would be one of the most important in decades,” Krauss writes in ‘A Beacon from the Big Bang.’ “It would allow us to test ideas about how the universe came to be that hitherto scientists have only been able to speculate about. It would help us connect our best theories of the subatomic (quantum) world with the best theories of the massive cosmos – those based on Einstein’s general theory of relativity. And it might even provide compelling (though indirect) evidence of the existence of other universes.”

In the article, Krauss describes the recent discovery from the BICEP2, which was reported in March 2014.

Born in the Big Bang

It is generally believed that in the first fraction of a second after the Big Bang the universe underwent rapid and dramatic growth during a period called “inflation.” According to Einstein’s general theory of relativity, inflation would generate gravitational waves, which stretch space-time along one direction while contracting it along the other direction.

This would affect how electromagnetic radiation in the cosmic microwave background radiation left behind by the Big Bang, is produced causing it to become polarized. The results from BICEP2 were the first indication of this CMB polarization and thus the existence of gravitational waves.

“Polarization observations are very difficult,” Krauss writes, “and although statistically the signal is clear, other possible astrophysical processes could produce effects that might mimic gravitational wave signal from inflation.” He added that while the BICEP2 team examined a number of possible contaminants the hardest to discount is radiation emitted by polarized dust in our own galaxy.

Currently, researchers are analyzing results from the European Space Agency’s Planck satellite also searching for this “imprint” of inflation in the polarization of the cosmic microwave background, Krauss said. This would provide collaborating evidence of gravitational waves, or it could demonstrate that the BICEP2 signal is due to foreground contaminants in our galaxy.

What it means

If the existence of gravitational waves can be proved, then it opens up several new realms for physicists and cosmologists, and would likely lead to a much greater fundamental understanding of the universe, how it came to be and how it operates, Krauss said.

For one, it could help demonstrate that the three nongravitational forces in nature fit together in a grand unified theory, but only if a new symmetry in nature, called super symmetry, exists. A second idea would be that it could lead to proof of the existence of gravitons, the theorized single unit of a quantum theory of gravity that acts much like photons, which carry the electromagnetic force.

Krauss said that either of these results would dramatically improve our understanding of the universe at its most basic levels, helping us unravel the nature of fundamental forces and perhaps even explain the origin of the Big Bang.

Implications for the multiverse

Sensing gravity waves, relics of the earliest microseconds of the universe, also could lead physicists to the idea that our universe may not be the only one in existence. It may imply the existence of a “multiverse.” Because of the mechanics of eternal inflation (the universe will forever expand), there are ideas that this universe is but one in an unaccountable number of universes that exist, with each in existence under its own physical rules born in each Big Bang.

“Determining even indirectly that our universe is not unique would completely change our perspective on our place in the cosmos,” Krauss said.

“Will BICEP2 provide as revolutionary guideposts to understanding the physics of the future as early experiments that led to quantum theory of atoms did,” Krauss asks. “We do not yet know. But the possibility is very real that it, or perhaps a subsequent CMB polarization probe, could open a new window on the universe that will take us back to the beginning of time and out to distances and phenomena that may make the wild ride that physics provided in the 20th Century pale by comparison.”