Quantum Zeno Effect

The Quantum Zeno Effect actually does stop the world

ESTHER INGLIS-ARKELL

http://io9.com/

Zeno of Elea was a Greek philosopher who suggested that if you could slice time into small enough increments, the world would freeze in place. It turns out that he was right — at least, from a quantum mechanics perspective.

University of Texas physicists George Sudarshan and Baidyanath Misra offer evidence of the Zeno Effect by showing that you can stop an atom from decaying, if you just check on it enough.

Zeno of Elea was a philosopher who went around southern Italy two-and-a-half thousand years ago proving that nothing was true. He did this by setting up a series of paradoxes that showed, among other things, that half a given span of time is equal to twice that given span of time, that time and space are neither continuous nor discrete, and that nothing ever moves. Ever. With this last one, he was able to anticipate quantum mechanics by over two millennia. It was only in 1977 that science caught on.

The official name for the modern scientific theory is the Quantum Zeno Effect, and it's based on the Arrow Paradox. An arrow flies through the air. It flies in a series of instants. An instant is defined as the shortest moment of time possible. In any given instant, the arrow has to appear motionless. If it wasn't motionless, there would be two instants, one in which the arrow was at one position and one in which the arrow was in another position. This presents a problem. There is no other way to define an instant, but if time is made up of a number of instants, and the arrow doesn't move in any of them, the arrow can't move through the air at all.

From Everyday Movement to Quantum Movement

This idea of shrinking down the measurement of motion to the point at which it can never move struck a chord with two researchers at the University of Texas. George Sudarshan and Baidyanath Misra realized that the behavior of some decaying atoms could be manipulated by a version of the Arrow Paradox. An unwatched atom that has the potential to decay eventually slips, from our point of view, into a superposition of states. It is both decayed and not decayed until someone checks on it. When they do, it slips into one of those states. Checking on it isn't a coin flip. There isn't always a straight fifty-fifty chance of the atom having decayed. At some points in time, very soon after it has slipped into this superposition of states, it is more likely to not be decayed when someone checks on it. At others, it more likely to be decayed.

Let's say an atom is very likely to have decayed after three seconds, but very unlikely to have decayed after one. Check on it after three seconds, and it probably will have decayed. But, Misra and Sudarshan argue, check on it three times in one second intervals, and it will most likely not have decayed. Every time you check on it, it will revert to its "original" measured state, and the clock will start over. Amazingly, this actually does happen. Researchers observing sodium atoms observed that, "Depending on the frequency of measurements we observe a decay that is suppressed or enhanced as compared to the unperturbed system." The "enhanced" decay is the result of the Quantum Anti-Zeno Effect. Time your measurements just right and you can actually push a system to decay faster than it would if it were unobserved. Zeno was correct. It is possible to freeze the world, if you manage to measure it just right. It's just also possible to hurry it along.