Scientists have known for a hundred years now that atoms behave oddly. On the smallest scales of nature, the common-sense laws of science are overthrown by the strange house rules of quantum mechanics, in which physical systems are represented by mathematical formulations called wave functions that encapsulate all the possibilities of some event or object.

Light or a subatomic particle like an electron could be a wave or a particle depending on how you want to look at it, and causes are not guaranteed to be linked to effects. An electron could be in two places at once, or everywhere until someone measures it, courtesy of the Heisenberg uncertainty principle, which caused a cranky Einstein to grumble that God did not play dice.

Erwin Schrödinger, one of the founders of the theory — as was Einstein, for that matter — once complained that according to quantum principles a cat in a box would be both alive and dead until somebody looked at it.

Until recent years this was all philosophy, and physicists could comfort themselves with the realization that quantum mechanics works so spectacularly well — every time you turn on your computer, for example — that for some of them the real problem is why the ordinary world does not work that way; why, for example, your sunglasses are not simultaneously in the car, back at the summer cabin or on the shelf when you want them.

Now scientists are able to direct experiments and catch nature in the act of being quantum and thus explore the boundary between quantum reality and normal life. Their work involves isolating the individual nuggets of nature — atoms and the particles that transmit light, known as photons — and making them play with each other.