Sunday, September 13, 2015

Einstein’s Parable of Quantum Insanity

From Quanta Magazine:
Quantized A monthly column in which top researchers explore the process of discovery. This month’s columnist, Frank Wilczek, is a Nobel Prize-winning physicist at the Massachusetts Institute of Technology.
Einstein refused to believe in the inherent unpredictability of the world. Is the subatomic world insane, or just subtle?
“Insanity is doing the same thing over and over and expecting different results.”

That witticism — I’ll call it “Einstein Insanity” — is usually attributed to Albert Einstein. Though the Matthew effect may be operating here, it is undeniably the sort of clever, memorable one-liner that Einstein often tossed off. And I’m happy to give him the credit, because doing so takes us in interesting directions.

First of all, note that what Einstein describes as insanity is, according to quantum theory, the way the world actually works. In quantum mechanics you can do the same thing many times and get different results. Indeed, that is the premise underlying great high-energy particle colliders. In those colliders, physicists bash together the same particles in precisely the same way, trillions upon trillions of times. Are they all insane to do so? It would seem they are not, since they have garnered a stupendous variety of results.

Of course Einstein, famously, did not believe in the inherent unpredictability of the world, saying “God does not play dice.” Yet in playing dice, we act out Einstein Insanity: We do the same thing over and over — namely, roll the dice — and we correctly anticipate different results. Is it really insane to play dice? If so, it’s a very common form of madness!

We can evade the diagnosis by arguing that in practice one never throws the dice in precisely the same way. Very small changes in the initial conditions can alter the results. The underlying idea here is that in situations where we can’t predict precisely what’s going to happen next, it’s because there are aspects of the current situation that we haven’t taken into account. Similar pleas of ignorance can defend many other applications of probability from the accusation of Einstein Insanity to which they are all exposed. If we did have full access to reality, according to this argument, the results of our actions would never be in doubt.

This doctrine, known as determinism, was advocated passionately by the philosopher Baruch Spinoza, whom Einstein considered a great hero. But for a better perspective, we need to venture even further back in history.

Parmenides was an influential ancient Greek philosopher, admired by Plato (who refers to “father Parmenides” in his dialogue the Sophist). Parmenides advocated the puzzling view that reality is unchanging and indivisible and that all movement is an illusion. Zeno, a student of Parmenides, devised four famous paradoxes to illustrate the logical difficulties in the very concept of motion. Translated into modern terms, Zeno’s arrow paradox runs as follows:...MORE