He turned to a fresh page and drew a tiny circle. “You ever hear of an electron?”
I nodded. “It’s a particle, right? Like, an atom?”
“Subatomic, actually. But for our purposes, you only have to know it behaves like a sphere. And one thing we know about spheres is that they can spin, right? Either clockwise or counterclockwise.” He drew a second circle on the page. “The thing is, electrons are supercool because they can spin clockwiseandcounterclockwise at the same time.”
“I call BS.”
“I don’t blame you. But, actually, there have been tons of experiments that can only be explained with this phenomenon. For example—imagine taking an opaque screen that blocks out all light. Now cut two little holes in that screen—let’s call them slit 1 and slit 2. If you shine a laser beam onto the slits, and you block slit 1, you’d expect to see a little blotch of light on the wall in the distance aligned with slit 2. If you block slit 2, you’d expect to see a little blotch of light on the wall in the distance aligned with slit 1. What happens when we open both slits at the same time?”
“You see two blotches?”
His eyes lit up. “You’d think so, right? But no. You get a whole row of blotches of light uniformly spaced out in various intensities. It’s called an interference pattern. The only way physicists can explain it is that the light that comes out of slit 1 must be interacting with the light that comes out of slit 2, because we know that when only one slit is open you get a single blotch on the wall…when the other slit is open you get a single blotch on the wall…and when they’re both open, you get something you’ve never seen before. Then Einstein came along and told us light isn’t a jet stream, it’s all individual particles, so maybe the pattern comes from individual particles from different slits hitting each other. Scientists slowed the laser to a point where only one photon was going through a slit at a time, figuring that the weird pattern would disappear. But it didn’t. And physicists were left with the explanation that the one photon actually does go through both slits simultaneously, interfering with itself. Even though every evolutionary instinct bred into us revolts against the idea.” He glanced at me. “That interference phenomenon is what makes your laptop work, in case you still think I’m bullshitting.”
“What does this have to do with the electrons?” I asked.
“We know they spin both clockwise and counterclockwise,” Brian said. “So let’s say you put an electron in a box. There’s a little trigger next to the electron that will activate if the electron spins clockwise, but it won’t activate if the electron spins counterclockwise. If the trigger activates, it will send a signal to a gun, which will fire, and kill a cat.”
“That’s a big box.”
“Work with me,” Brian said. “So if the electron goes clockwise…”
“The trigger activates, the gun goes off, the cat dies.”
“And if the electron goes counterclockwise?”
“Nothing happens.”
“Exactly.” He looked up at me. “But what happens if that electron spins both clockwise and counterclockwise at the same time—as weknowit can?”
“Either the cat is dead or it isn’t?”
“Actually,” Brian corrected, “the cat is both alive and dead.”
“How postapocalyptic,” I murmured. “Nice story, but I’ve never seen a zombie cat.”
“That’s pretty much what Niels Bohr said, too. He knew that the math said this was happening, but he had never seen a live-dead cat either. So he figured that there had to be something special about the act of observation that made the cat stop being both aliveanddead, and instead become just aliveordead.”
“Like human consciousness?”
“That’s what John von Neumann suggested. But what makes humans so special that they can determine the outcome of a quantum system to collapse into a single defined state? What if it’s not a human…what if a ferret is watching? Or what about the cat in the box? Youknowit has a vested interest in the outcome. So does it have the power to collapse the state of the electron, or trigger, or gun?” Brian said. “The collapse theory was the one the cool kids believed until the 1950s, when Hugh Everett III came up with another reason why we don’t see zombie cats walking the earth. He said that just like the electron and the trigger and the gun and the cat are quantum objects, so is whoever or whatever is observing what’s in that box.” He drew a little stick figure wearing a skirt, waving. “At first, she is standing outside the box, and doesn’t know what she’s going to see when she looks inside. But the minute she lifts the lid…she is split into two distinct copies of herself. In one version she sees a cat with its brains exploded all over the box. In another, she hears a meow. If you asked her what she saw, one version is going to say the cat is dead, and the other will say the cat is alive. The observer only ever sees one outcome, but never both, even though the laws of quantum mechanics tell us that both versions of that poor damn cat exist. And the reason she sees only one outcome is because she’s trapped in one of the timelines and is unable to see the other one.” He grinned at me. “That’s Everett’s whole deal. The reason we don’t see zombie cats or electrons spinning both ways at the same time is because the minute we look at them, we become part of that mathematical equation and we ourselves get split into multiple timelines, where different versions of us see different, concrete outcomes.”
“Like a parallel universe,” I said.
“Exactly. I’ve been using the wordtimelinebut you could easily sayuniverse. And the reason this matters isn’t because there are cats in boxes, but because we’re all made up of molecules, like those electrons. If you zoom in and zoom in and zoom in, everything we do is explained by quantum mechanics.”
“What happens to those two different timelines?”
“They get farther and farther apart. For example, the observer who sees the dead cat might be so bummed out she drops out of grad school and becomes a meth addict and never invents the technology that would help us develop a cure for cancer. Meanwhile, the observer who sees the live cat thinks she is onto something and becomes the dean of physics at Oxford.” He ran a thumb over the stack of papers he had been working on. “That’s what I’m doing. Slowly destroying my career by insisting that the multiverse is constantly branching off, creating a new timeline whenever we make a decision or have an interaction.”
“Why would that ruin your career?”
“Let’s just say the physicists who believe it are outliers. But one day—”
“One day they’ll be calling you a genius.” I hesitated. “Or maybe that’s already happening in some other timeline.”
“Exactly. Everything thatcanhappendoeshappen—in another life.”
I tilted my head, staring at him. “So in another universe, my mother isn’t dying.”
