If I keep observing the uranium, which means a little more than keeping my eyes on the pot on my desk and involves something akin to surrounding it with a whole system of Geiger counters, I can freeze it in such a way that it stops emitting radiation.Although Turing first suggested the idea as a theoretical construct, it turns out that it is not just mathematical fiction. Experiments in the last decade have demonstrated the real possibility of using observation to inhibit the progress of a quantum system.

Robert Oppenheimer used to tell of the pioneer mysteries of building reliable Geiger counters that had low background noise. Among his friends, he said, there were two schools of thought. One school firmly held that the final step before one sealed off the Geiger tube was to peel a banana and wave the skin three times, sharply to the left.The other school was equally confident that success would follow if one waved the banana peel twice to the left and then, once, smartly to the right. (My counters were unbelievably bad because I didn't use either of these techniques.).