“I don’t know. People do like to try to link quantum mechanics to something more tangible. Tangible or mystical.”
“You don’t?”
“I suppose I do. The thing about quantum mechanics is that when you try to make it make sense by analogy to something at our level of perception, it’s always a misrepresentation, so the real thing slips out of your grasp. You’re getting it wrong. So for a long time I preferred to keep it at the level of the math, and not try to explain it at all.”
“For a long time? And then something happened?”
“Well, yes.” Fred sat up on the couch, stirred by the thought. “People are using the math to design and build machines. More and more qubits are being stabilized in various ways. So something real is happening, something physical. So I started thinking about what the quantum realm was really doing, I mean in the physical world. I mean clearly it’s doing something. And the idea that it’s an entirely statistical probability state, that takes consciousness or measurement to make it collapse to an event—or that there are new universes branching out of every moment—none of that was working for me. There are several different interpretations of what the math is describing, because it’s so weird, but most of them just struck me as crazy.”
After he was silent for what might have been some time, thinking about this, she said sharply, “And then?”
Fred thought about it some more. “Then,” he said, “I started thinking more about the pilot wave interpretation. Have you heard of that one?”
She shook her head. “Tell me.”
“Well, people talk about the Copenhagen interpretation, which came mostly from Niels Bohr. His idea was that physical reality was a matter of probabilities, like the equations are, and that things at the subatomic level are undetermined until measured, at which point they become one thing or the other. Waves become particles, and particles add up to waves, but not in ways that make sense according to our senses, so in the end it’s too strange to understand.”
“That’s not much of an interpretation?”
“No. Einstein didn’t like it, Penrose didn’t like it. But the math definitely works, right down to the parts-per-trillion range. So it’s been hard to say how Bohr’s take on it is wrong. But right from the beginning, a physicist named de Broglie said there was another way of understanding it, which was that quantum particles were disturbing fields they were moving in, mostly by creating waves that moved ahead of the particles, like a pilot wave that you see in front of a boat. I’ve seen those from this window, looking at the boats on this bay. So, David Bohm talked about that as being disturbances in quantum fields. Then later they did some analog experiments that were like sending a droplet of oil skipping over a sheet of water, to show the kinds of effects that de Broglie suggested were happening at the quantum level.”
“Wait, what? Oil on water?”
“Yeah, you know how oil and water don’t mix, so when you shoot a droplet of oil across water, there’s a wave—”
“Show me,” she said.
“Well, I think it’s at a pretty small scale—”
“Show me!”
She was standing over him, hand out; when he took it, she pulled him to his feet. And then they had something to do.
They found the biggest pan in the apartment’s kitchen cabinets, a metal sheet pan about two feet long and a foot wide. “I don’t know if this will be big enough,” Fred said.
“It’s what we’ve got. Just make it work.”
“Okay, I’ll try.”
One of the few things Fred had done in his youth was to serve as teaching assistant to his high school physics teacher. The teacher had been a nice guy, and had probably given Fred the job to try to get him out of his shell a little. So Fred had worked on wave-tank experiments for a semester of his senior year, and now, remembering those, he found that ceramic chopsticks could be used to create dams across water filling the pan very shallowly; he could place three of them to make the two slits of the two-slit experiment. When they got that arranged, they put this apparatus on the coffee table and started making waves and observing them. It was a little messy, but waves on water can be counted on to spread and rebound in their usual way, and they had time to adjust the amount of water and the intensity of the initiating splashes until these effects were pretty clear, even the secondary waves that got through the two slits and interacted with each other on the other side of the dam. Interference patterns appeared, just as predicted, and interesting as such.
The oil droplets were not so easy. There was some sesame oil in the kitchen cabinet above the sink, but no obvious way to send a droplet of it skittering across the surface of their water to make the pilot wave. They tried a lot of methods, and ended up laughing a lot. Throwing; flicking; spitting; squeezing out of a basting bulb; shooting out of a red plastic water pistol found in a drawer—they kept trying things, they didn’t want it to end. The room smelled of sesame oil. Sometimes the drop would ooze across the top of the water with enough momentum to send a little wave across the water ahead of it. Once that wave hit the two slits hard enough that the little waves on the other sides of the slits were high enough to be seen interfering with each other, and Fred said,
“Yes! That’s the two-slit experiment. Now see, if the oil droplet were then to follow that wave on a certain trajectory, it would only go through one slit, but its wave already went through both. And on the other side, it would get pushed around by the interference pattern of that wave, and where it went then would be stochastic, meaning probabilistic, but its location would always fit the equations, just like they really do in quantum behaviors. And you don’t need an observer making an observation to make that happen. It will happen without an observer. It’s not just a probability state.”
“So—pilot wave!” Qi said, looking pleased. “So you’re an advocate of that interpretation, and it helps you in your work?”
Fred sat back on the couch, shook his head. “No. I don’t know if it helps or not. The math is the same either way. The quantum fields can’t be entered into the equations, and David Bohm was always suggesting they were contiguous to the entire universe. And judging by analogy to gravitational waves, the pilot waves are likely to be really small.”
“Like how small?”
“Like, if two black holes hundreds of times more massive than the sun collide, they make a gravitational wave that by the time it gets to us squeezes the Earth about the width of one proton. So how big of a wave can a photon make in a quantum field the size of the universe?”
“Wow,” Qi said after pondering this for a while. “Pretty small, I’m guessing.”
“Right. So I end up working on things that derive from the usual math. What the math is describing in physical terms doesn’t help me that much.” He waved at their wave tank. “Actually I’m not sure seeing it this way has ever helped me. I mostly try to leave that part blank.”
She sat in the armchair looking at him, he could tell; he continued to look at their wave tank. She was amused, he guessed, but maybe exasperated too.
“And you’re very good at leaving things blank,” she said.
“Yes?” He was pretty sure she would think this was a bad thing. “I feel kind of blank, pretty often. Or,” he confessed, “maybe baffled, you might say.”
She was nodding. “I bet you find me baffling!”
“Yes!”
She laughed at him. “Do you know about Yiman Wang’s yellow yellowface?”
“No.”
“How about Edward Said’s Orientalism?”
“No.”
“Of course not. Well, you should read them. They talk about how Westerners, when they look at Asians, they see a stranger, a big other. Some kind of blank that isn’t at all like them, and then they fill that blank in with a story they make up. Exotic inscrutable dragon lady! That’s me all right!” She laughed again.