Factoring Humanity

4

Kyle remembered the day he’d learned that Heather was pregnant with their first child, Mary.

It had come as a complete shock. They’d been living together for about a year, sharing an apartment in St. Jamestown with a few hundred cockroaches. Kyle was in the second year of his master’s in computer science; Heather was just starting her master’s in psychology. They were in love—no doubt—and had talked about building a life together. But Kyle and Heather both knew they should each go somewhere other than U of T for their doctorates. Not that U of T wasn’t a fine place for grad school; indeed, if it really did have any claim to that “Harvard of the North” label, it was because of its graduate studies. But having all three degrees from the same institution would be an automatic red flag in future job interviews.

Then, suddenly, Heather was pregnant.

And they’d had tough decisions to make.

They’d talked about abortion. Although they did eventually want children, this was without doubt an unplanned pregnancy.

But…

But, hell, when would be the right time?

Not while they were finishing their masters’ degrees, of course.

And certainly not while doing their doctorates.

And, well, the starting salaries for associate professors were abysmal—Heather had already decided that an academic life was what she wanted, and Kyle, who didn’t enjoy stressful situations, was leaning toward that as well, rather than the high-pressure world of commercial computing.

And then of course they wouldn’t really be secure until at least one of them had tenure.

And by then—

By then, more than a decade would have slipped by, and Heather would be into the high-risk age for pregnancy.

Choices.

Turning points.

It could go one way or the other.

At last they’d opted to have the child; countless student couples had done the same over the years. It would be difficult—a stretch financially, an additional demand on their already overtaxed time.

But it would be worth it. Surely it would be worth it.

Kyle remembered vividly the class he’d been in the day Heather had told him she was pregnant. It had seemed so appropriate, somehow.

“Suppose,” Professor Papineau had said to the dozen students in the seminar that had seemed to start out a long way from computer science, “that you live just north of Queen’s Park and you work just south of it. Further suppose that you walk to work each day. You’re faced with a choice every morning. You can’t walk down the center line, since the Parliament Buildings get in the way. Of course, I’m sure there’ve been times when many of us have wanted to plow through the Legislature in a tank… but I digress.”

Laughter from the students. Papineau had been a wonderful prof; Kyle had gone to his retirement dinner fifteen years later, but hadn’t seen him since.

“No,” said Papineau, once the chuckling had stopped, “you have to go around the buildings—either to the east, or to the west. Each way is pretty much the same distance; you leave home at the same time and you arrive at work at the same time regardless of which route you choose. So, which route do you choose? You, there—Kyle. Which way would you go?”

Kyle had his beard even back then. As today, it was red, even though his hair was black. But in those days he’d kept it scruffy, unkempt—never trimming it, never shaving his neck beneath. He cringed now to think about it. “Down the west,” he said, shrugging to convey that it was a purely arbitrary selection.

“A fine choice,” said Papineau. “But it’s not the only choice. And in the many-worlds interpretation of quantum mechanics, we believe that any time a choice can be made one way, the alternative choice is also made—but in a parallel universe. If Kyle did indeed come down the west side in this universe, there would also exist a parallel universe in which he came down the east side.”

“But surely that’s just a metaphor,” said Glenda, a student Kyle sometimes thought he might have pursued had he not already met Heather. “Surely there’s really only one universe, no?”

“Or,” said D’Annunzio, a biker type who always seemed out of place in class, “even if another universe does exist, there’s no way to prove it, so it’s not a falsifiable hypothesis, and therefore not real science.”

Papineau grinned broadly. “You know,” he said, “if this were a nightclub performance, people would accuse me of having planted the two of you in the audience. Let’s look at that question: is there any direct evidence that multiple universes might exist? Roopshand, will you get the lights, please?”

A student in the back stood up and turned off the lights. Papineau moved next to a slide projector sitting on a metal cart; he turned it on. A diagram appeared on the screen.

“This picture shows some experimental apparatus,” said Papineau. “At the top, we have a lightbulb. In the middle there’s a bar representing a horizontal wall as seen from above. You see those two breaks in the bar? Those are two vertical slits that go right through the wall—one on the left and one on the right.” He used a small telescoping pointer to indicate these. “And at the bottom we have a horizontal line representing a sheet of photographic film seen edge-on from above. The wall in the middle is like Queen’s Park, and the two slits are like the two possible paths around the Parliament Buildings—one on the east and one on the west.” He paused while the students digested this. “Now, what happens when we turn on the light-bulb?”

He pushed a key; the carousel clicked around and a new slide came on. The photographic film at the bottom showed a zebra pattern of light and dark lines.

“You all know what that is from high-school physics, right? It’s an interference pattern. Light from the bulb, traveling like a wave, passes through the two slits—which behave now like two separate light sources, each with waves of light emanating from it. Well, when the two sets of waves crash against the photographic plate, some of the waves cancel out, leaving dark areas, and others reinforce each other, making the bright bands.”

Some students nodded.

“But you also know from high-school physics that light doesn’t always behave like a wave—sometimes it behaves like a particle, too. And, of course, we call particles of light ‘photons.’ Now, what happens if we turn down the power going to the lightbulb? What happens when the power is turned down so low that photons are coming out of the lightbulb one at a time? Anyone?”

A redheaded woman held up a hand.

“Yes, Tina?” said Papineau.

“Well, if only one photon is going through, then it should make one little spot of light on the photographic film—assuming it finds its way through one of the slits.”

Papineau smiled. “That’s what you’d expect, yes. But even when photons are released one at a time, you still get the light and dark bands. You still get interference patterns.”

“But how can you get interference if there’s only one particle passing through at a time?” asked Kyle. “I mean, what’s the particle interfering with?”

Papineau raised his index finger. “That is the question! And there are two possible answers. The one that’s simply weird is that in transit between the lightbulb and the film, the single photon breaks up into a series of waves, some of which go through one slit and some through the other, forming the interference pattern.

“But the other answer—the really interesting answer—is that the photon never breaks up, but rather remains a discrete particle, and as such, it has no choice but to go through only one of the two possible slits—in this universe. But just as you, Kyle, could have taken either route around Queen’s Park, so the photon could have taken the path through either slit—and in a parallel universe, it took the other path.”

“But how come we see the interference pattern?” asked D’Annunzio, chewing gum as he spoke. “I mean, if we stood south of the Parliament Buildings, we’d never see two versions of Graves, one coming around the east side and one around the west.”

“Excellent question!” crowed Papineau. “The answer is that the two-slit experiment is a very special example of parallel universes. The original single universe splits into two universes once the photon encounters the slits, but the two universes exist separately only so long as the photon is traveling. Since it makes no difference now or ever which path the photon actually took, the universes collapse back together into a single universe. The only evidence that the two universes ever existed is the interference pattern left behind on the film.”

“But what if it does make a difference which slit was chosen?” asked Roopshand from the back.

“In any experiment you can devise in which the choice of slit actually matters—indeed, in any experiment in which you can detect which slit the photon went through—you don’t get the interference pattern. If it matters at all, the universes never stitch back together into one; they continue on as two separate universes.

It had been a heady class—as all of Papineau’s were. And it had also been a metaphor that Kyle carried with him throughout his life: choices, branching paths.

Back then, back in 1996, even though he and Heather were still students, he knew which choice he wanted. He wanted to live in the universe in which they did have a baby.

And so that November, their first child, Mary Lorraine Graves, was born.