Physicists Learn to Turn Back Time

By Maia Weinstock|Sunday, December 01, 2002
According to the Second Law of Thermodynamics, any isolated system tends to grow more disorderly over time—the fundamental reason the mess in your sink only gets worse if you don't wash the dishes. But Denis Evans, a physicist at the Australian National University, has found that the second law can sometimes be forced to run backward. To physicists, this is a discovery equivalent to finding that the dishes washed themselves while you waited.

Evans and his colleagues searched for flaws in the second law by adding fine latex beads, each less than a millionth of an inch wide, to a water-filled cell big enough to fit on a microscopic stage. The researchers shook the cell in a precise rhythm and used a laser beam to track the progress of a single bead within the chamber. They found that when they observed the bead for periods of no more than a tenth of a second, the bead's path caused the system to become more orderly—the opposite of what is supposed to happen.

The experiment proved what Evans and his colleague Debra Searles had predicted nine years earlier: Measurable violations of the second law are possible at extremely small scales; at larger scales, however, they vanish into the overall trend toward disorder. This loophole could eventually help engineers design miniature machines, such as rotors built from a single protein molecule. It could also aid in the investigation of the very nature of causality. The second law defines the arrow of time—why those dishes do not get un-dirty, or why you cannot un-spill spilled milk. The existence of some flexibility in the law hints that events could temporarily run backward but only over minuscule distances. Humans will not be able to make themselves young again. Current theory "still prohibits time reversal for large systems," Evans says.




 
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