Randall grew up in Fresh Meadows, Queens, the second of three daughters, the first of whom had an undiagnosed disability, as well as the prodigious memory sometimes associated with Asperger’s syndrome. (Randall herself related to the Tom Cruise character in the movie “Rain Man,” and thought that his performance was underrated.) She and her younger sister, now a computer-science professor at Georgia Tech, both went to Stuyvesant, the specialized math-and-science high school in Manhattan. Randall describes fighting with her mother for permission to leave the house before it was light, in order to attend early-morning meetings of the math team, of which she was the first female captain. At seventeen, she won first place in the Westinghouse Science Talent Search, for a project on perfect Gaussian integers, a type of complex number.

When I asked Randall whether she felt there was a connection between her work and her older sister’s disability, Randall responded by e-mail, “It might be part of the reason I was so serious and retreated. Feeling responsible for talents I had if that makes sense.” She also remembered that for a period, around the time when she was five, she stopped speaking entirely. When a friend of her parents’—her father was a salesman for an engineering firm, her mother a third-grade teacher—suggested that this was strange, given her intelligence, her mother replied that she was just trying to get attention. Randall interprets it differently: “I think I only wanted to say things that were true.”

As an adult, Randall seems like someone who both wants attention and wants to say things that are true. You get the feeling that she might not always be easy to work with—she mentioned an argument with colleagues over a noisy coffee machine—but she is extremely patient in explaining her work to an interested party whose physics education never went beyond ninth-grade physical science. Her books rarely gloss over an explanation when it’s possible to supply it. “I wish this were less complicated, but I’m giving you the real story here,” she writes in her 2012 e-book about the search for the Higgs boson—a subatomic particle that is one of the most important discoveries of twenty-first-century physics so far.

Randall says that she writes for a general audience because it helps her connect with people in other fields, who suggest ideas she might not have considered. The novelist Cormac McCarthy was so interested in her work that he offered to edit her first book. What’s striking about Randall’s writing is its urgency, perhaps because of the way she feels about science, which she has described as analogous to religion; physics, she writes, “offers anyone some perspective when dealing with the foolishness of everyday life.”

Much of what theoretical physicists do is pure mathematics, so they often need analogies to explain their work to laypeople. While this might be a chore for some physicists, Randall clearly delights in it. Observing dark matter, she suggests, is like spotting a famous person: “Even if you don’t see George Clooney directly, the disruptive traffic generated by the waiting crowd armed with cell phones and cameras suffices to alert you to a celebrity’s proximity.” In the case of dark matter, it is the transparent stuff’s gravitational influence on ordinary matter that lets scientists know it’s there.

Making a plan with Randall is almost as difficult as (I imagine) it might be with Clooney, and every one of our meetings was scheduled and rescheduled several times. Randall is not only very busy but also has trouble deciding what she wants to do, as well as a habit of second-guessing those decisions. The first time I met her, she had interrupted a climbing trip to Devils Tower, in Wyoming, in order to attend a book festival in East Hampton—a decision she questioned after listening to the author of a book on entertaining speak about jumping out of a cake at a black-tie birthday party, in Dallas. The night after we went surfing, when I suggested we do something more in line with Randall’s vocation—I thought we could meet on the beach to look at the Milky Way—we texted for an hour to decide whether the sky was clear enough to see anything. I was a half-hour drive from where Randall was staying on the beach, and by the time I got there it was cloudy.

“If only you’d come an hour ago,” she said. I followed her down the nearly deserted surfing beach anyway. Randall walks in a determined, forward-tilting lope, somewhat self-consciously, as if walking in public were an unavoidable evil she would like to dispense with as quickly as possible. On the beach, two bonfires were burning, and for a moment a car in the parking lot illuminated a section of the water when its brights were turned on. Otherwise, the beach was dark, and you had to be careful not to fall in the holes that children had dug earlier in the day.

We sat on the sand and looked at the sky. Randall tried to show me a satellite through a gap in the clouds, but when I pointed she told me that what I was looking at was a plane. I asked her if, when she looked up there, she saw something different than what the average person would see; to me, I said, it always looks like a black sheet with holes poked in it.

“That’s what it looks like,” Randall agreed. “Most of the time we all behave as if what’s here on Earth is all there is.”

Randall told me that sometimes a model works, “but it’s not something that’s compelling. Yes, things could happen like that, but I don’t believe it. And sometimes it’s like, wow—this happened automatically. . . . Sometimes a model is like that—it has a life of its own.” I thought of the way that a fiction writer will sometimes say that the character has taken over her pen, a notion that has always struck me as overblown. But there is the sense that, in writing about a hypothetical situation, you sometimes forget yourself enough to put down something you might not otherwise have admitted—in other words, to say something true. I had misquoted Lorrie Moore during our conversation, and so, the next day, I e-mailed Randall her famous definition of fiction: “It’s the unlivable life, the strange room tacked onto the house, the extra moon that is circling the earth unbeknownst to science.” Randall was skeptical, and fired back a caveat: “Theoretical physics IS science. We are not just making stuff up. We are hypothesizing what might be true but we don’t yet know if it is. We look for ways to find evidence (or rule it out).”

In my newfound enthusiasm for particle physics, I tried to interest my mother in watching a Times video about the Large Hadron Collider, the most powerful particle accelerator in the world. “I’d love to watch it,” my mother said, “but I won’t understand it.” When I told Randall what my mother had said, she said that as long as it was socially acceptable for women to be intimidated by physics, it would be hard to change the discipline’s gender discrepancy. (As recently as 2010, women made up only fourteen per cent of American physics faculty.) “As long as it’s like, ‘Yeah, she can do this stuff, but she’s so weird.’ And of course we are weird. You’re not going to become a theoretical physicist, especially as a woman, and not be weird.” Randall pointed to Stephen Hawking and the way the popular notion of physicists as extraordinary sometimes allows the rest of us to give the whole discipline a pass: “To the extent that they can make you into the other, it makes people feel more comfortable.”

We were sitting on the porch of the cottage where she was staying. Seagulls complained in the background. Randall got up once to speculate about the workings of a recreational biplane, like something the Wright brothers might have flown. I got up once to help her with the controls on her host’s washing machine. Then we walked down to the beach one last time, where we ran into my kids climbing a lifeguard chair. Randall immediately scrambled up after them, concerned that they might fall. I hesitated, weighing a potential trip to the emergency room against the photo opportunity—the chance that I might someday be able to say, “There’s you with the Nobel laureate in physics!” The three of them reached the top. You could see only sky behind their heads. I stayed on the ground and took a picture.