AS LONG AS THE TECHNOLOGY WORKS, THE SCIENCE IS IMMATERIAL:

My quantum experiment, which has consumed me for more than a year now, has dredged up a creepy, long-buried memory. It dates back to the late 1970s, when I was a housepainter living in Denver. One day I found myself in a grungy saloon on Denver's dusty eastern outskirts. Behind the bar was an aquarium with a single, nasty-looking fish hovering in it. A silver, saucer-sized, snaggle-toothed, milky-eyed, blind piranha.

Now and then, the bartender netted a few minnows from a fishbowl and dropped them into the piranha's cubicle. The piranha froze for an instant, then darted this way and that, jaws snapping, as the minnows fled. The piranha kept bumping, with audible thuds, into the glass walls of its prison. That explained the protuberance on its snout, which resembled a tiny battering ram. Sooner or later the piranha gobbled all the hapless minnows, whereupon it returned to its listless, suspended state.

What does this poor creature have to do with quantum mechanics? Here's what. Our modern scientific worldview and much of our technology--including the laptop on which I'm writing these words--is based on quantum principles. And yet a century after its invention, physicists and philosophers cannot agree on what quantum mechanics means. The theory raises deep and, I'm guessing, unanswerable questions about matter, mind and "reality," whatever that is.

More than a half century ago, Richard Feynman advised us to accept that nature makes no sense. "Do not keep saying to yourself ... 'But how can [nature] be like that?'" Feynman warns in The Character of Physical Law, "because you will get 'down the drain,' into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that." Most physicists have followed Feynman's advice. Ignoring the oddness of quantum mechanics, they simply apply it to accomplish various tasks, such as predicting new particles or building more powerful computers.

Another deep-thinking physicist, John Bell, deplored this situation. In his classic 1987 work Speakable and Unspeakable in Quantum Mechanics, Bell chides physicists who apply quantum mechanics while blithely disregarding its "fundamental obscurity"; he calls them "sleepwalkers." But Bell acknowledges that efforts to "interpret" quantum mechanics so that it makes sense have failed. He likens interpretations such as the many-world hypothesis and pilot-wave theory to "literary fiction."

Today, there are more interpretations than ever, but they deepen rather than dispel the mystery at the heart of things. The more I dwell on puzzles such as superposition, entanglement and the measurement problem, the more I identify with the piranha.

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