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. I’m blindly thrashing about for insights, epiphanies, revelations. Every now and then I think I’ve grasped some slippery truth, but my satisfaction is always fleeting. Sooner or later, I end up crashing into an invisible barrier. I don’t really know where I am or what’s going on. I’m in the dark.

The main difference between me and piranha is that it is inside the aquarium, and I’m on the outside, looking in. I can take solace from the fact that my world is much bigger than the piranha’s, and that I know many things that the fish cannot. But it’s all too easy to imagine some enlightened, superintelligent being standing outside our world, looking at us with the same pity and smug superiority that we feel toward the piranha.

Plato presents himself as this enlightened being in his famous parable of the cave, which I make my freshman humanities classes read every semester. The parable describes people confined to a cave for their entire lives. They are prisoners, but they don’t know they are prisoners. An evil trickster behind them has built a fire, by means of which he projects shadows of everything from aardvarks to zebras onto the cave wall in front of the prisoners. The cave dwellers mistake these shadows for reality. Only by escaping the cave can the prisoners discover the brilliant, sunlit reality beyond it.

We are the benighted prisoners in the cave, and Plato, the enlightened philosopher, is trying to drag us into the light. But isn’t it possible, even probable, that Plato and other self-appointed saviors, who say they’ve seen the light and want us to see it too, are charlatans? Or loons? Given our profound capacity for self-deception, isn’t it likely that when you think you’ve left the cave, you’ve actually just swapped one set of illusions for another? These are the questions with which I torment my students. Here are some of their responses:

  • Clearly, some people are ignorant and deluded, like flat-earthers, and others are well-informed. So yes, we can and do escape the cave of ignorance by going to college and studying physics, chemistry, history, philosophy and so on. We can reduce our ignorance still further with the help of reliable news sources, such as the New York Times and Fox News, and traveling to other countries to learn how other people see the world.
  • Yes, we can escape the cave by studying physics and other fields, but we only end up in another cave, with equations projected on the walls instead of silhouettes of aardvarks and so on. The new cave may be more interesting, comfortable and better-illuminated than the cave we were in before, but it’s still a cave. Only a few rare souls experience ultimate reality, like Buddha, Jesus and Einstein.
  • Plato wasn’t really talking about worldly knowledge, he was talking about spiritual knowledge, or enlightenment. So yes, we can leave the cave and see the light of truth, but only by accepting the teachings of great sages such as Buddha, Moses, Jesus or Muhammad, and perhaps by practicing spiritual disciplines such as prayer and meditation.
  • With the help of philosophy, art, meditation and psychedelics, we can become more aware that we are in a cave, in a state of illusion; we can know, sort of, what we don’t know. But no mere human ever escapes the cave, not even the greatest sages and scientists. Not even Plato, Stephen Hawking or L. Ron Hubbard. Only God, if there is a God, can perceive absolute truth. And maybe not even God.
  • Who cares if we’re in a cave or not? If we’re having fun, that’s all that matters. (Although only a few of my students have the courage to voice this option, I suspect it’s what many of them think, especially the business majors.)

To be honest, the fourth option—that not even God can escape the cave, plus the references to psychedelics, Stephen Hawking and L. Ron Hubbard—is mine. But my students come up with the other options on their own, with minimal prodding from me. By the time we’re done with this exercise, I start feeling guilty about rubbing the young, innocent faces of the non–business majors in the world’s inscrutability. To make them feel a little better, I bring up another possibility that usually doesn’t occur to them:

If we realize we’re in the cave, isn’t that the same, sort of, as escaping from it? Actually, if “ultimate reality” is inaccessible to us, isn’t that the same, sort of, as saying that it doesn’t exist? And hence that the cave, the world in which we live each and every day, is the one and only reality? And hence that the business majors are right, and we should just chill out and enjoy ourselves?

Maybe. On good days, I look out the window of my apartment at the shining Hudson River, crisscrossed by boats, and at the Manhattan skyline, a symbol of humanity’s ever-growing knowledge of and power over nature, and I think, Yes, this is reality, there is nothing else. But then I remember the quantum mist at the core of reality, which not even the smartest sages can penetrate, and to which most of us are oblivious. And I remember the piranha, bumping over and over again into the walls of its world, blind to its own blindness.

This is an opinion and analysis article; the views expressed by the author or authors are not necessarily those of Scientific American.

Further Reading:

Is the Schrödinger Equation True?

Quantum Mechanics, the Chinese Room Experiment and the Limits of Understanding

Quantum Mechanics, the Mind-Body Problem and Negative Theology

I explore the limits of knowledge in my two most recent books, Mind-Body Problems, available for free online, and Pay Attention: Sex, Death, and Science.

See my recent chat with Russian writer/artist Nikita Petrov, in which we talk about the blind piranha, Plato’s cave and psychedelics.