#WhyTheQuantum?

Bonsoir, tweeps. Found a dinner place near the hotel. For once, not seated at the table reserved for parties of one.

Business travel dilemma: what looks better on the expense account, a meat-lovers pizza or a tankard of mead?

ZOMG! A dating disaster is unfolding at the next table over. The world must know!

She: blue hair, pierced lip, star-shaped earrings. He: smells faintly of AXE.

She swapped out fries and got a salad instead. He says, "I see you're trying to lose weight!"

The poker face this woman has, I cannot believe.

Now he's off talking about the restaurant. "Not bad, not bad." (I think she chose.) "Of course, I'm more used to the places downtown."

"Downtown?" she asks. "Yeah," he says. "Financial District. Bit more pricey, bit better vibe from the people around, but this isn't bad."

(I think I've just been negged by a guy I'm not even on a date with. Do dudebros try to capture en passant?)

She flags the server, asks for a glass of red wine. He mentions something about the song in the background, says the dubstep remix was better.

She keys off this, asks him if he has any favorite bands. Uh-oh. TACTICAL ERROR. The tap is open and flows freely.

We're halfway into the main course. He finally asks what she does. She brightens. "Quantum information theory!"

"Quantum? That's like, a cat that's half dead and half alive at the same time?"

She: "Uh, not really. It's---" He: "Yeah, I read how that works. You know, a quantum computer could, like, break codes by trying all the possibilities at once."

"The math doesn't imply that's how it works. And the image of trying everything in parallel isn't actually helpful. It's more that

> a quantum computer can be more efficient, because it carries less baggage than we thought a computer needed."

"Uh huh. And what do you do?"

"I seek seeks! S. I. C.s, also known as complex equi-angular lines."

(there is no emoji for the expression on his face right now)

She's pulling out an honest-to-God fountain pen and drawing on her napkin. It looks like the Mercedes symbol.

"Three lines," she says. "Pick any two of them. See the angle they make when they meet? How that angle is the same for each pair? They're equi-angular."

(trying to lean over without being obvious)

She: "You can't add in another line without spoiling that. Three is as many as you can get. Now: two changes."

Her hands are making shapes in the air. "First: what if you work in higher dimensions? Three, four, five, any number?"

(ow ow ow my brain--can you do that? I guess you can't see it, but you can, like, do it with math?)

She: "You can't visualize that, but you can do it with algebra." (Hooray!) "Just add more coordinates, x, y, z, on beyond zebra."

She: "Second change: what if you let your coordinates be complex numbers? As in, using the square root of minus one."

(ow ow ow my brain again--is that legal?)

She: "You can define the angle by

(my fingers can't fing--something about an "inner product"? is that like an inner tube? inner product, but I just met 'er!)

She: "The question is, how many equi-angular lines can you fit in, if you work in dimension N? With real numbers in dimension 2, we found 3 lines.

She: "With complex numbers in dimension N, what's the max in general? For every N that we can check, the answer is N squared."

(huh, that sounds, like, kind of simple!)

She: "We've checked it out to dimension 121, and it's always N squared, but we can't PROVE it will ALWAYS be N squared."

(bet you didn't know you'd be getting a math lesson tonight! only in Cambridge, amirite?)

He: "So, uh, what will that do?" She: "If we can prove it's always true, we'll have a new way of thinking about quantum probabilities."

(oops, my second beer showed up, I missed something about how quantum physics calculates probabilities using complex numbers)

She: "Max Born, who figured that out--his granddaughter is Olivia Newton-John. Hashtag TheMoreYouKnow!"

(she actually said "hashtag")

(there's a "let's get physical" joke in here somewhere that I'm totally too adult to make)

She picks up her drink, looks reflective, takes a sip. "We don't really know what quantum physics is really ABOUT."

Pulling out her phone and waving it: "We can USE it to do things, but when we TEACH it, the best we can do is to dump a lot of math on the poor students."

A gulp of wine. "And it's not because we're cruel. Well, we're not THAT cruel. We just don't know which ideas are THE ideas."

He looks at sea. She: "Like, what are the deep principles that all the details of the algebra would follow from, if you just thought carefully?"

She: "If we could solve this problem, we'd have a new way to think about quantum theory. We could get new answers, ask new questions. Do new things."

(dang, I've been staring for five minutes. he looks like he'd rather be HALOing)

She: "One day, after this and, you know, many other victories, we might answer John Wheeler's question: why the quantum?"

(ooh! hashtag for the evening! #WhyTheQuantum?!)

He: "Well, that sounds pretty cool, I guess. So you know all about this stuff?"

She: "More than some, less than others." He: "Now, I read a great thing online the other day about how quantum computers do everything in parallel--"

She: "..."

(she goes from #WhyTheQuantum to #WhyMe)