“Nope. Don’t know it,” I say.

“Okay. Let’s say you have an evil grandfather.”

“He’s dead. I only met him once in Korea. He seemed nice.”

“Are you Korean?” she asks.

“Korean American. I was born here.”

“I’m Jamaican,” she says. “I was born there.”

“But you don’t have an accent.”

“Well, I’ve been here for a while.” She tightens her hold on her cup and I can feel her mood starting to shift.

“Tell me about this paradox,” I prod, trying to distract her. It works and she brightens up again.

“Okay. Yes. Let’s say your grandfather was alive, and he was evil.”

“Alive and evil,” I say, nodding.

“He’s really evil, so you invent a time machine and go back in time to kill him. Say you kill him before he meets your grandmother. That would mean that one of your parents is never born and that you are never born, so you can’t go back in time to kill him. But! If you kill him after he meets your grandmother, then you will be born, and then you’ll invent a time machine to go back in time to kill him. This loop will go on forever.”

“Huh. Yes, we’re definitely ignoring that.”

“And the Novikov self-consistency principle too, I guess?”

I thought she was cute before, but she’s even cuter now. Her face is animated, her hair is bouncing, and her eyes are sparking. She’s gesturing with her hands, talking about researchers at MIT and probability bending to prevent paradoxes.

“So theoretically, you wouldn’t be able to kill your grandfather at all, because the gun would misfire at just the right moment, or you would have a heart attack—”

“Or a cute Jamaican girl would walk into the room and bowl me over.”

“Yes. Something strange and improbable would happen so that the impossible couldn’t.”

“Huh,” I say again.

“That’s more than a ‘huh,’ ” she says, smiling.

It is more than a huh, but I can’t think of anything clever or witty to say. I’m having trouble thinking and looking at her at the same time.

There’s a Japanese phrase that I like: koi no yokan. It doesn’t mean love at first sight. It’s closer to love at second sight. It’s the feeling when you meet someone that you’re going to fall in love with them. Maybe you don’t love them right away, but it’s inevitable that you will.

I’m pretty sure that’s what I’m experiencing right now. The only slight (possibly insurmountable) problem is that I’m pretty sure that Natasha is not.

I DON’T TELL RED TIE the complete truth about what I would do with a time machine if I had one. I would travel back in time and make it so the greatest day of my father’s life never happened at all. It is completely selfish, but it’s what I would do so my future wouldn’t have to be erased.

Instead, I explain all the science to him. By the time I’m done, he’s giving me a look like he’s in love with me. It turns out he’s never heard of the grandfather paradox or the Novikov self-consistency principle, which kind of surprises me. I guess I assumed he’d be nerdy because he’s Asian, which is crappy of me because I hate when other people assume things about me like I like rap music or I’m good at sports. For the record, only one of those things is true.

Besides the fact that I’m being deported today, I am really not a girl to fall in love with. For one thing, I don’t like temporary, nonprovable things, and romantic love is both temporary and nonprovable.

The other, secret thing that I don’t say to anyone is this: I’m not sure I’m capable of love. Even temporarily. When I was with Rob, I never felt the way the songs say you’re supposed to feel. I didn’t feel swept away or consumed. I didn’t need him like I needed air. I really liked him. I liked looking at him. I liked kissing him. But I always knew I could live without him.

“Red Tie,” I say.

“Daniel,” he insists.

“Don’t fall in love with me, Daniel.”

He actually sputters out his coffee. “Who says I’m going to?”

“That little black notebook I saw you scribbling in, and your face. Your big, wide-open, couldn’t-fool-anybody-about-anything face says you’re going to.”

He blushes again, because blushing is his entire state of being. “And why shouldn’t I?” he asks.

“Because I’m not going to fall in love with you.”

“How do you know?”

“I don’t believe in love.”

“It’s not a religion,” he says. “It exists whether you believe in it or not.”

“Oh, really? Can you prove it?”

“Love songs. Poetry. The institution of marriage.”

“Please. Words on paper. Can you use the scientific method on it? Can you observe it, measure it, experiment with it, and repeat your experiments? You cannot. Can you slice it and stain it and study it under a microscope? You cannot. Can you grow it in a petri dish or map its gene sequence?”

“You cannot,” he says, mimicking my voice and laughing.

I can’t help laughing too. Sometimes I take myself a little seriously.

He spoons a layer of foam off his coffee and into his mouth. “You say it’s just words on paper, but you have to admit all those people are feeling something.”

I nod. “Something temporary and not at all measurable. People just want to believe. Otherwise they would have to admit that life is just a random series of good and bad things that happen until one day you die.”