I’ve described this quantum confusion before (in my book The Bit and the Pendulum) by relating it to television. In the old days, TV signals traveled through the air, all the possible channels passing through your living room at the same time. (Nowadays they usually arrive via cable.) By turning the dial on your TV set (or punching a button on the remote control), you can make one of those shows—one of many possible realities—come to life on your screen. The realm of atoms, molecules, and particles even smaller works in a similar way. Left to themselves, particles buzz about like waves, and their properties are not sharply defined. In particular, you cannot say that a particle occupies any specific location. An atom can literally be in two places at once—until you look at it. An observation will find it located in one of the many possible positions that the quantum equations allow.

An important issue here, one that has occupied physicists for decades, involves defining just what constitutes an “observation.” In recent years, it has become generally agreed that humans are not necessary to perform an observation or measurement on a particle. Other particles bouncing off it can accomplish the same effect. That is to say, an atom, on its own, cannot be said to occupy a specific location. But once other atoms start hitting it, the atom will become localized in a position consistent with the altered paths of the other atoms. This phenomenon is known as decoherence. As long as decoherence can be avoided (for example, by isolating a particle from other influences, maintained at very low temperatures), the weird multiplicity of quantum realities can be sustained.

This feature of quantum physics has been an endless source of controversy and consternation for physicists and nonphysicists alike. But experimental tests have left no room for doubt on this point. In the subatomic world, reality is fuzzy, encompassing a multiplicity of possibilities. And those possibilities all have a claim to being real. It’s not just that you don’t know where an atom is— it occupies no definite location, but rather occupies many locations simultaneously.

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