Later I learned about Hawking’s work. I learned that in the 1970s he had performed a remarkable calculation, in an attempt to disprove the work of another physicist who had annoyed him. The result ended up proving three things. First, that revenge is an excellent fuel for genius. Second, that I was a moron, because if anything, Hawking is underrated. His physics was brilliant and the only thing that was disproportionate was the fact that everyone has heard of Stephen Hawking but few people know what he really did that was so great. Something about black holes? The universe? Time? The profound meaning of his work is all too often overlooked. The meaning, that is, of the third thing he proved: that particles are not ultimately real.

Physicists define something as “real”—truly, ultimately, fundamentally real—if it remains invariant across reference frames. If that sounds abstract, it’s not—in fact, it’s how normal people define reality, too. Say you suddenly see a purple elephant in the corner of the room. You might wonder whether the elephant is really there or if you’re having some kind of breakdown. Instinctively, you know there are two ways to find out. The first is to get up, walk over to the elephant and tread a careful circle around it, viewing it from every angle, eyeing it suspiciously. If at some angle it disappears, you’ll know it was more likely a mirage than a mammal. The other strategy is to turn to the guy next to you and ask, “Do you see an elephant?” If he says no (or stares at you blankly), you’ll probably want to call a neurologist. Because you know, intuitively, that something is only real if it persists in every point of view.

Just because something’s not ultimately real doesn’t mean it’s a hallucination. Take a rainbow. Is it real? Not really. It’s not a hallucination, but it’s also not a physical object hanging in the sky. You can’t go touch it because it’s a product of your reference frame, a lucky confluence of circumstance, your standing in the right place at the right time with the sun streaming in from behind you and the light being refracted by the moisture in the air. Ask the guy next to you, “Do you see that rainbow?” and he’ll probably say yes, but run the test of walking around it, and you’ll see it disappear. Its existence is dependent on your reference frame. It’s a product of physics, but it’s not invariant. If you want to find the fundamental ingredients of ultimate reality, you have to find the invariants.

Particles always seemed like good candidates. After all, they comprise all the stuff in the universe. They give things heft and solidity and object-hood. They’re the reason there are things at all.

But Hawking’s calculation suggested otherwise.

To appreciate what Hawking did, there’s one more thing you need to know. According to quantum mechanics, empty space isn’t really empty. The so-called uncertainty principle tells us that there’s a trade-off between time and energy—the more defined the one, the vaguer the other. That means that on very short timescales—fractions of fractions of fractions of seconds—large amounts of energy can (and do) bubble up out of empty space. To ensure it’s all paid back in full, the energy manifests as pairs of particles and antiparticles, which, in the blink of an eye, will collide and annihilate, the existence of one canceling out the existence of the other, returning the energy back to the emptiness from whence it came. This cycle of creation and destruction is happening all the time, right now, all around us, particles emerging in pairs and disappearing, but it all happens so quickly that we call them “virtual particles”—not because they’re fundamentally different from ordinary particles, but because they don’t stick around long enough to count.