"Time keeps on slippin', slippin', slippin' into the future" went the popular hit song "Fly Like an Eagle" by the Steve Miller Band in 1976. Hold that thought about our perception of time always moving forward.
A team of 365 physicists, including five from the University of Oregon, at the BaBar experiment at the Department of Energy's SLAC National Accelerator Laboratory at Stanford University pored through 10 years of data from billions of particle collisions.
The group confirmed a preferred direction for some subatomic processes to take in time. But they also report "a violation of time reversal symmetry." That violation is the first direct observation of a long-theorized exception to a fundamental physics rule involving fundamental symmetries.
The findings were published in the journal Physical Review Letters in November, creating a buzz in the physics community. And now Physics World has placed the BaBar discovery in its Top 10 breakthroughs in the physical sciences during 2012. The winners were chosen from more than 350 research papers.
Physics World also -- and not surprisingly -- named the possible discovery of the Higgs boson at the Large Hadron Collider, where the UO also has a leading presence, in its list of Top 10 breakthroughs.
What the BaBar discovery involving time means is not easily explainable, but the UO's James Brau, Knight Professor of Natural Science, approaches the challenge briefly.
"Are the laws of physics the same whether time is going forward or backward? This is a long standing question in the theory of fundamental particles," says Brau, who heads the Center for High Energy Physics and one of the winning paper's co-authors. "Until this year, no direct evidence for a difference has been seen. This year a collaboration involving the University of Oregon has produced such direct evidence."
From 1999 to 2008, the UO's experimental high-energy group and other collaborators with the BaBar experiment collected a lot of data on particle interactions, which when scrutinized, Brau said, provided important insights on the behavior of bottom mesons and the difference between bottom and anti-bottom mesons (so-called CP violation). The results already were directly involved in the 2008 Nobel Prize in Physics.
"This year the BaBar collaboration completed and published an analysis of the data which for the first time provides a direct observation of a violation in the symmetry of the laws of physics in the forward and backward directions, which is called time-reversal violation," Brau says. "In other words, it shows some subatomic processes prefer one direction of time over the other."
Other UO co-authors on the research team were Raymond Frey, Nikolai Sinev, David Strom and Eric Torrence. Along the way, several UO graduate students completed their doctoral theses based on data from the BaBar experiment, and several postdoctoral research associates worked with the UO team before moving to permanent positions with other universities and laboratories around the world.
The Oregon team worked on gaseous detectors and data selection (so-called trigger) for the experiment, and studied various important physics decay modes of bottom mesons and tau leptons.
An interesting view on the discovery can be found in a Discover Magazine blog. Look for the part about scrambled eggs.
(Graphic is by Alan Stonebraker/American Physical Society. More details)