Magazine article Science News

Time Proves Not Reversible at Deepest Level

Magazine article Science News

Time Proves Not Reversible at Deepest Level

Article excerpt

Sometimes scientists stir excitement not by discovering something fundamentally new but by unveiling something stunningly fundamental--such as the machinery of time.

New results from two independent physics teams at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Ill., and the European Laboratory for Particle Physics (CERN) near Geneva do just that. They show directly for the first time that "there is a distinction between going forward and backward in time, even at the most fundamental level," says Alan Kostelecky of Indiana University in Bloomington. "The work is truly spectacular."

Until the mid-1950s, physicists thought that, for elementary particles, the physical laws still applied even if three key qualities of the universe were reversed: spatial directions flip-flopping with their mirror images, matter swapping with antimatter, and time running in reverse. Experiments subsequently shattered that notion.

First, scientists found differences in particle behavior when directions are reflected in a mirror. Then, a landmark 1964 experiment found that the asymmetry remains when both the directions and matter and antimatter were exchanged. Because of an overarching theory uniting all three reversals, it follows that time symmetry must also collapse, but that effect has not been observed until now.

In the new experiments, "we have not assumed anything from theory," says Panagiotis Pavlopoulos, spokesman for the experiment at CERN. By allowing antiprotons and liquid hydrogen atoms to annihilate each other in matter-antimatter collisions, the group generated particles known as kaons and antikaons, which can transform into one another. …

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