A Black Hole Is a Place, Not a Thing

People mix up how black holes form with what they are, Janna Levin tells Lex Fridman at the start of a three-hour conversation. When the objects first appeared as solutions, Einstein was surprised they could be found so quickly and still believed nature would protect us from making them. Nature found a way by killing massive stars. Levin wants that story kept separate from the concept. Dead stars are one manufacturing route. The black hole itself is more general and more fundamental than the corpse of a sun.

The whole idea began as a thought experiment. In 1915 and 1916 Einstein wrote the canonical form of general relativity, in the middle of World War I, and received a letter from the Eastern Front. Karl Schwarzschild, an astronomer who had enlisted in his forties, had solved the equations between trench duty and cannon fire. Colleagues joked that he was calculating ballistic trajectories; he was also reading the proceedings of the Prussian Academy of Sciences. He asked what happens if you crush all the mass of a star to a point. Do not ask how. Pretend, and see what spacetime does.

Matter and energy curve space and time; curved spacetime tells matter and energy how to fall. Schwarzschild found the first exact solution and, inside it, a demarcation beyond which not even light can escape. A hundred years later Levin still points at that line. The black hole is not the crushed mass. It is the event horizon, a surface that splits events: the outside can affect the inside, but nothing inside can affect the outside. You can throw a probe in. Someone who fell in cannot send one out. That one-way character is what is profound. At the horizon there is nothing there. It is an empty region of spacetime, more a place than a thing.

Einstein helped get the work published and still doubted such objects would form. The same solution describes the Earth’s orbit around the Sun from far away, almost overkill for that job, and it also marks where the theory dies. Go all the way to the center and the math starts to look wrong, like a dying man scratching a warning in the dirt. Roger Penrose later showed that once a horizon forms, a singularity is inevitable, then guessed that quantum mechanics, left out of the classical theory, would replace it. Levin says everybody would agree: you cannot talk about those curvatures and energy scales without quantum mechanics. The object she likes to name is still the empty horizon. Black holes, she says, are no thing.

Even in messy astrophysics, Levin says, nothing is left at the end of the day. Oppenheimer, in what she calls probably his most important theoretical work, asked why stars shine and whether they could collapse until light itself could not get out. A massive star is a fusion bomb, burning Earths of thermonuclear fuel. When it hits an iron core, fusion past iron costs energy, so the fuel stops. A star twenty or thirty times the mass of the Sun then collapses under its own weight, fast enough to drive a shock. That explosion is the supernova, and Levin is grateful for it: the star throws carbon and oxygen back into space, which is why we are not just hydrogen.

What remains may be a neutron star, superdense but still a thing, a giant nucleus of superconducting matter, electrons jammed into protons. If the leftover core is heavier than about twice the mass of the Sun, it keeps going. The Sun is a million and a half kilometers across. Imagine a remnant ten times as massive, squeezed to about sixty kilometers, city-sized. Spacetime there is so curved that light cannot escape. The horizon forms, but the star cannot sit in that dense state any more than it can race outward at light speed, because even light is forced to rain inward. The star continues to fall, leaves the horizon behind, and goes dark.

John Wheeler, the grandfather of American relativity, put it as a Cheshire Cat: the star fades from view and leaves only its grin, which is gravitational attraction. In 1967 he was lecturing above Tom’s Restaurant, the Seinfeld diner near Columbia, repeating the cumbersome phrase “the end-state of catastrophic gravitational collapse,” when someone in the back row reportedly shouted, “Well, how about black hole?” Wheeler foisted the name on the world. He had a talent for that. Fridman pulls up Oppenheimer’s 1939 paper with his student, three pages, published the day the Nazis advanced on Poland, opening with a line Levin calls gorgeous: “When all thermonuclear sources of energy are exhausted, a sufficiently heavy star will collapse.”

Wheeler thought Oppenheimer was wrong and said so for decades. The setup looked too idealized; a more realistic star, he believed, would not go all the way. Early computer work he had begun while thinking about nuclear weapons, then turned back to astrophysics in peacetime, reversed the conclusion. There is a story that Oppenheimer was sitting outside the auditorium when Wheeler announced that black holes were the likely end-state for very heavy stars. Asked about it, Oppenheimer said he had moved on to other things.

Fridman asks what it means that the same physicists who asked utopian questions about stars also built a weapon that can end civilization. Levin calls it an excruciating moment in the history of science. There was hopeful talk that Heisenberg had quietly derailed the Nazi bomb; she says that story has been largely discredited. He would have made the weapon if he had not made simple errors about how much material was required. In Michael Frayn’s play *Copenhagen*, Bohr tells his wife that nobody has thought of a way to kill people using quantum mechanics. Then came the bomb. Science, Levin says, is agnostic. The same understanding of critical mass and thermonuclear fusion explains why the Sun is hot and how a city is destroyed. Lise Meitner’s fission of uranium was the first concrete demonstration of E=mc². Once the device exists, scientific reasoning no longer dictates its use.

Fridman plays the game theory. The Soviet Union, Nazi Germany, and the United States all had extraordinary scientists. He puts the chance that the bomb appeared first in America at about a third, and argues Hitler would have used it without question. In that version, Levin agrees, the American outcome was the least harmful, and no serious game theorist would play a world with no bomb at all. She will not grant the one-third. America was different. Scientists fled here; Americans were not fleeing to Nazi Germany. They had watched a free-spirited Berlin culture turn, almost overnight, into a repressive regime. Many particle-physics Nobelists later came from the Bronx, European immigrants who might otherwise have been laureates of the Soviet Union or the Eastern Bloc.

The world flocked here, she says, and that will not be the case if the country no longer has intellectual freedom. Fridman adds the cliché that is still operational: individual freedoms, at their best, make a scientific community vibrant, and the vibrancy of debate and funding is worth defending. The conversation glances at a twenty-first-century cold war with China and the need for free exchange of ideas. Then they go back to the collapsing star. Levin’s reminder is the same one she started with. If you are falling and you fire a photon straight outward exactly at the horizon, the light can hover like a fish swimming against Niagara. The star cannot. It rains in with the waterfall. From outside, all you should care about is the horizon. Matter and antimatter could annihilate into light on the inside and you would never know.

Levin is not an observer. She is happy to take the math at its word as a thought experiment. One of the most beautiful things the equations suggest, she says, is that space and time swap places inside the hole. Sit in a comfortable space station a hundred kilometers from a ten-solar-mass black hole sixty kilometers across. You are quite safe. It will not vacuum you up. Your astronaut friend jumps. From outside you see a spherical shadow, and you think the singularity is a point at the center of a sphere. From the friend’s point of view that direction is not a location in space. It is a location in time. The singularity is in the future. You can no more avoid it than you can avoid time coming at you. Rockets, orbits, and clever detours all fail. For a stellar-mass hole the wait is microseconds.

As the friend approaches, part of their space rotates into your time and part of their time into your space. Clocks that left the same factory now disagree. Years can pass on the station, plants dying, hair going gray, while minutes pass in the falling ship and the flowers have not wilted. At the horizon the effect is so extreme that, from outside, the clocks seem to stop. Generations could be born on the station watching the astronaut hover for millennia. They do fall in, because they have mass. The horizon bobbles and absorbs them in finite time. A perfectly light particle would take longer and longer; any perturbation still goes only one way.

From the astronaut’s side, almost no time has passed. You sail across. Nothing dramatic happens. You might not realize you have reached the point of no return, because there is no marker in that empty region. Outside, you can still fire rockets and maybe escape. Once you cross, all the energy in the universe will not save you. Fridman keeps holding his head. The surprise people least expect is that bigger holes are gentler. Stand on a basketball and you feel the curve under your feet. Stand on Earth and you have to be clever to prove the ground is round. A huge black hole can feel almost flat. There is still nothing there. In your own frame you may not know you have gone in.

There are hints. Black holes are dark from the outside and not necessarily dark inside. Galactic light falls in behind you and focuses, so you can see a bright white flash as you near the singularity. Levin jokes that it is a near-death experience, the light at the end of the tunnel, then adds that it is a total death experience. Outside clocks race. You could in principle watch the evolution of the galaxy unfold in one beam. A stellar-mass crossing is too fast for a human nervous system. A supermassive hole could let you hang around for months. You still expire in the center. You just take longer to do it.

Stars are the most plentiful factory, not the only one. Levin estimates hundreds of millions, maybe a billion, black holes in the Milky Way, from the roughly one percent of stars that end that way. The surprise is the supermassive ones: millions to tens of billions, even hundreds of billions, of solar masses. The universe has not had enough time to grow them by merging stellar holes. The suspicion is that they formed a few hundred million years after the Big Bang by direct collapse out of primordial gas. Oddly, it is easier to make a very large hole out of something with the density of air if the region is big enough. There is thought to be one in the center of every galaxy, bound to the early formation of galaxies themselves.

Which came first, the hole or the galaxy, is still open. Early stars of hydrogen and helium, then black holes, then gassy clouds; jets from the central engine may have blown material out and curbed growth. The ordering is unfinished science. What is not unfinished is how little you need to specify the object. A black hole is completely described by electric charge, mass, and spin. Every hole with those three numbers is identical to every other. You cannot recognize yours by a little feature. Try to put Mount Everest on one and it will shake the mountain off in gravitational waves until it is perfect and quiet again.

That is another reason Levin resists calling them ordinary objects. They are closer, in an abstract way, to fundamental particles. An electron is a short list of properties. There is no electron that is a little different. You cannot recognize yours. Black holes share that featurelessness at macroscopic scales, which is why theoretical and mathematical physicists, not only astronomers with telescopes, use them as a terrain for thought experiments. General relativity, quantum mechanics, and the singularity meet there. The meeting is still out of reach for experiment. It is in reach for thought.

Fridman asks how a three-dimensional creature is supposed to picture spacetime. Levin cannot draw four dimensions. She can suppress one spatial direction and put the rest on paper, knowing the drawing is a misrepresentation the way a flat map of Earth is a misrepresentation. Time is not another Euclidean axis; the geometry is Minkowski. As long as you use the right rules for adding distances, you can still calculate how much time elapses between two observers. Einstein’s leap was not a catalog of solutions. It was a paradigm: matter and energy on one side of the equation, the deformation of space and time on the other. Schwarzschild found an elegant solution within a month. Einstein did not hunt every solution. He handed over the machine. One consequence, a surprise to him, was that a universe full of gas or light would expand. Distances between galaxies would grow.

He resisted the expansion. In 1905 he was twenty-five, unable to get a job as a physicist, writing papers on relativity and quantum mechanics. In 1915 he still did not know other galaxies existed. Kant had mused about island universes; Hubble’s confirmation came in the late 1920s. Relativity is often sold as a theory of relativism. Levin likes to call it a theory of absolutes. Einstein got there with almost no data by clinging to the absolute limit and constancy of the speed of light, a property only massless particles have. Everyone else tried to make light behave like cars on a road. He kept the speed fixed and gave up the absolute character of space and time instead.

The happiest thought of his life, the equivalence principle, is the short path Levin uses to teach the rest. You think you feel gravity in a chair. Cut the cable of an elevator and you float, unable to tell whether you are in empty space or falling around the Earth. Weightlessness is gravity unfettered by atoms. The Earth is in free-fall around the Sun with its engines off. The International Space Station does the same at something like 17,500 miles an hour; stop it and it drops like a stone. A thrown pen follows an arc until the ground interferes. In the Einsteinian picture it is following the curve the Earth inscribed. Newton already hated action at a distance. Relativity dissolves it: the tree is the problem, holding the apple away from its natural fall along a curve that already exists.

Fridman imagines a hippie telling Newton that gravity is just the curvature of spacetime. Every idea has its time; you have to stand on the shoulders of giants, and of those giants. Levin notes that Newton’s line was reportedly an unkind remark aimed at Hooke, who was short. The soap opera is not a side issue. People who think about cosmological forces still fight over offices, chairs, and the one woman in the department. Academic battles are so bitter, the old line goes, because the stakes are so low. Levin also defends the childlike part. The best scientists she knows ask the simplest questions and refuse to lie to themselves about what they do not understand. Had Newton lived another couple of centuries, she says, he would have invented relativity, because he never pretended he understood why the apple fell.

The information paradox is what catapulted Stephen Hawking’s fame. As a young researcher he did not attempt full quantum gravity. He asked what happens if you let the vacuum around an event horizon have ordinary quantum properties, just a little. Heisenberg’s uncertainty principle says you cannot know a particle’s position and momentum exactly at once, and the limit is foundational, not a laboratory defect. You also cannot say with perfect confidence that a region contains zero particles. The vacuum is a seething sea. Pairs froth into existence, entangled so their charges and spins cancel, then vanish again. That is the best empty space can do in a quantum universe.

Put an event horizon through the pair and the story breaks. If one partner falls in and the other does not, the survivor cannot return to the vacuum. It has a charge or a spin it no longer shares. The black hole has stolen one virtual particle and forced the other to live. To a distant observer the hole has radiated. The particle did not come from inside; it was taken from the nothingness of the horizon. Because of the swap of space and time, the absorbed partner carries negative energy from the outside view. The hole’s mass drops. It does more than radiate. It evaporates.

Hawking said the radiation would look thermal, the most featureless spectrum you can write, a temperature that depends only on the mass you could already measure from outside. It carries no information about what fell in. Not everyone saw how naughty that was. People who love quantum mechanics, Leonard Susskind and Gerard ’t Hooft among them, were furious. Quantum mechanics does not allow information to poof out of the universe. Unitarity is as sacred as conservation of energy, Levin says, in this setting more sacred, because the uncertainty principle already lets you fudge energy a little. The fight was coined the Black Hole Wars. Susskind’s book is subtitled as a battle with Hawking to make the world safe for quantum mechanics.

The temperature falls as the mass rises, so the holes we see are far too cold to evaporate in anything like a human age. As they shrink they get hotter. Near the end, after a time much longer than the age of the universe, the horizon is yanked up. The object explodes. Everything that went in is gone, because it was never in the radiation. The debate was productive, Levin says, because any future quantum gravity has to get the temperature and the entropy of a black hole right. The hole is the place on which you test the theory. It has not been fully resolved.

Fridman reads through the candidate resolutions. Information really is lost: quantum mechanics fails under extreme gravity. Levin is unhappy with that. Her gut is that unitarity will be preserved. Fuzzballs, from string theory, say there is no interior and no true horizon, only a tangled ball of strings and branes the size of the would-be horizon. Near the hole, time dilation acts like a magnifying glass; strings smear and catch, and nothing falls through. Information never went in, so it does not have to come out. Levin does not buy it, but she calls the statement strong. Soft hair, revived by Hawking, Perry, and Strominger, gives the hole low-energy quantum excitations that store what fell in. That challenges the no-hair theorems, which are formal proofs in general relativity. Worth trying, she says. She does not think that is the answer either.

The firewall paper by Almheiri, Marolf, Polchinski, and Sully argued that unitarity requires the horizon to be a highly energetic sheet that incinerates anything crossing it. Levin finds the papers fascinating and does not think the authors believed firewalls were real. They were saying too much had been brushed under the rug, including a complementarity story in which one observer falls in and another never does, and both can be right. AMPS showed those escapes do not work. She does not believe you will find a firewall at the horizon. She does think the paper stopped the subject from stalling and pushed people toward entangled wormholes.

The idea she takes seriously is ER = EPR: Einstein-Rosen bridges as the geometric face of Einstein-Podolsky-Rosen entanglement. You cannot follow the chalk from the first line to the last. Juan Maldacena and Susskind landed on an intuition and are still formalizing it. The setup is holography. Black hole entropy grows with area, not volume. Pack more information into a region than its surface can hold and you make a hole. Susskind called that a hologram. Maldacena’s late-1990s paper, the most cited in the history of physics, with an opaque title, showed that a universe in a box, anti-de Sitter space, with gravity and black holes, is equivalent to a gravity-free, fully unitary quantum theory on the boundary. If the dictionary holds, information cannot be lost, even if you cannot yet see how in the interior description.

ER = EPR fills that gap by saying the interior is quantum-entangled with the escaping Hawking radiation. Information does not have to crawl out through the horizon. Look closely and the shadow on the sky is embroidered with tiny non-traversable wormholes. Levin will go back to the empty, beautiful horizon and give up locality. The implication is larger than a paradox solved. If the horizon only exists when it is sewn from quantum threads, gravity may not be something you quantize. It may emerge from a quantum description, the way temperature emerges from molecular motion and is not stamped on any molecule. That would be a bad day for anyone hoping for a single clean equation of everything, because emergent quantities are usually hard to compute. Collect all the Hawking radiation, in principle, and the information is there, the way the words of a burned page are still in the smoke. Practically you cannot recover them. Fundamentally they were never gone.

Levin will not predict when the information paradox, the origin of life, or consciousness will break. Extra dimensions, dark matter, and dark energy might all be linked in a dark sector, and that is work she loves, but it would still be a clue rather than a solution. We do not know why there are three large spatial dimensions. String theory needs more of them to make sense; even people hostile to strings have reasons to consider extras. Most models roll them into a tiny origami that can trap quantum energy, with numerology that might line up with dark energy or dark matter and is not yet perfect. The live question is why three dimensions grew and the others stayed small. Some models wrap strings and branes so that only three directions loosen. Others put us on a three-dimensional membrane moving through a bulk that need not be small at all. We do not notice the extra directions because we cannot leave the brane.

Fridman asks whether other civilizations could live on other membranes. Mathematically you can write a higher-dimensional universe with more than one brane. If something can be written, Levin often wonders whether nature will try it. That is how people slide into a multiverse: searches for a unique beautiful law that includes gravity produced a proliferation of descriptions that all did okay, or equally badly. Communication is not obviously impossible. We are glued to the brane, but gravity can move through the bulk. You could in principle build a gravitational transmitter and send waves the way SETI sends light, telling the neighbors where we are and singing songs. In practice it is wildly expensive, hard to localize, long in wavelength, and hungry for energy.

You do not need brane worlds to make aliens plausible. In the past thirty years the count of exoplanets has exploded. There are probably more planets in the Milky Way than stars. Levin agrees it is hard to imagine life was never sparked elsewhere, even within a few hundred light years. Fridman’s gut is that bacterial-type life is common and that he finds no great-filter story convincing; advanced civilizations, he thinks, should avoid self-destruction. Levin finds the 50/50 he grants humanity appalling. We have been around a couple of hundred thousand years and have already invented the means to wipe ourselves out. Whales have not. He treats that as a feature of cosmic natural selection: give everyone nuclear weapons, half figure it out, half do not. She answers that the bar is then very high.

Dinosaurs lasted 250 million years, not very bright, no fire, no sonnets, no contemplation of origins, and they did not confront demise at their own hooves. Jellyfish have no localized brain, she thinks no heart or blood, and some can revert after a bad wound and start over, a kind of immortality. Life can flourish without wanting to manipulate its environment. We are attached to creatures like us. The only sure thing she will say about life is that it has something to do with moving electrons, in nerves and in metabolism. Extremophiles eat rocks. Multicellularity, an energy problem, looks to her like the hard step; the jump from inanimate to animate is probably gray. Viruses and prions scramble any bullet list. Carbon is cool because it combines. Maybe sulfur would do. Membranes, she adds, will not explain why we do not see anyone in this galaxy. That problem we are stuck with.

Wormholes, Einstein-Rosen bridges, are just curves in spacetime. Topology, the global connectedness, is trickier, because Einstein’s theory speaks to local distortion and is silent on whether the universe wraps around. You could travel in a straight line, watch the Virgo Cluster drift behind you, and find yourself coming home. That connectedness needs something beyond the field equations. Wormholes add handles, Swiss cheese. Levin sees nothing abusive about them as laws. You can reverse-engineer: choose the architecture, run Einstein’s equations backward, and ask what matter and energy you need. Kip Thorne did that imaginative work. The bummer is that the matter looks like nothing we have ever seen. It needs negative energy. There are conjectures that such stuff should not be allowed if you want stability. Quantum mechanics already offers examples. The Casimir effect between metal plates can be a negative energy. You can imagine wormholes propped up by that kind of vacuum. Levin is not ready to call it an engineering problem. She will call it plausible physics. Sending a person through would take a lot of the weird matter.

Connecting two black holes tends to give you non-traversable bridges, the ER = EPR sort, not a subway. Thorne’s recipes, enlarging quantum foam, mixing classical geometry with quantum gravity, all start the same way: draw the building, then demand the materials. That is how they learned they must violate energy conditions we usually assume. Either you throw the idea out or you notice that quantum fields already violate those conditions a little. Fridman wants faster-than-light travel. Levin sometimes assigns a warp-drive problem in advanced general relativity: contract the space in front of you, skip, push it back, something antithetical to dark energy. She cannot find the energy that does it. She also cannot find dark energy. We look at spacetime expanding ever faster, name the pressure we need, and call the name a proxy. The stuff is in this room. It is not dark. It is invisible, she says, and the name was a misnomer.

Dark energy has positive energy and negative pressure, a rubber-band quality: as things move outward you feel more energy, not less. Vacuum energy would be an excellent answer except that every calculation gives either a number vastly too large or zero. Extra dimensions are one attempt to foist a weird value on us through topology. Nobody has landed a version friends like as much as the author does. Levin hopes dark matter and dark energy are tied together, a single dark sector, maybe even dark dimensions. Dark matter at least clumps. It sits in a halo around the galaxy. Images of colliding clusters show luminous matter slamming and lighting up while lensing maps the mass sailing straight through, which is what non-interacting stuff should do. She finds that compelling.

People outside physics sometimes say dark matter and dark energy were invented to label ignorance. There is some truth in the naming, Levin says, and it misses the point. Precision cosmology is stunning. When COBE measured leftover light from the Big Bang in the 1980s, people applauded. Because of that precision we can stare down a fact: everything anyone has ever seen makes up less than five percent of what is out there. Neutrinos are real dark matter raining through this room, just not with the right mass to be the missing component. The Higgs field could have acted like dark energy; its energy is too high. Leon Lederman wanted to call his book *The Goddamn Particle* because he could not find it. The publisher made him say *The God Particle*, offending people who believed in God and people who did not. The particle showed up at CERN where it was expected. The mismatch that remains is not a license to sneer at the measurement.

Gravity is weak. The whole Earth pulls on Levin and she can still get out of a chair. To make gravity do something interesting you need huge masses in violent motion, black holes among them. If holes curve spacetime and then move, the curves have to follow, but not faster than light. Two holes in orbit raise a wave in the shape of space. In simulations the horizons bobble, merge, and the remnant rings away its imperfections until it is one quiescent, spinning, silent hole. The final mass is less than the sum of the two starters. The difference leaves as E=mc² in that ringing. None of it is light. X-rays, gamma rays, infrared, optical, the whole electromagnetic spectrum, stay dark. Levin likes a sound analogy she has not anatomically checked: near enough, the frequency sits in the human auditory range. The shape of space could squeeze and stretch an eardrum even in vacuum. You could literally hear the collision.

Riding the wave would feel like squeezing and stretching, with your orbit tossed about. For years people were not even sure the waves carried energy. Levin likens the holes to mallets and spacetime to a drum. The waves interfere with almost nothing, so they can travel a couple of billion years and arrive quieter, a little stretched by cosmic expansion, but preserved. LIGO is a gigantic musical instrument, an electric guitar that records the shape of the string. Two vacuum tunnels, four kilometers on a side, form an L. They are among the largest holes ever pulled in Earth’s atmosphere. The wobble they hunt is less than a ten-thousandth the width of a proton over that baseline. Levin still cannot believe they succeeded. People started in their thirties and forties and were in their eighties when it worked.

She walked the tunnels with Rai Weiss, who shared the Nobel Prize with Kip Thorne and Barry Barish. About a month before success, Weiss told her that if they did not detect black holes the whole project was a failure, and they had led the country down the wrong path. That sentence is why her book is called *Black Hole Blues*. His first prototype sat on a tabletop outside MIT. Colleagues said he would not get tenure. The first-generation machine, just after 2000, detected nothing. Crickets. They kept going. In September 2015 they postponed the first science run because they were not ready. Experimentalists spent the night banging on the instruments, driving trucks, slamming brakes to see how much noise the thing could tolerate. They went home tired, left the interferometer locked, and within about an hour of that drive a wave washed over Louisiana, crossed the United States, and rang the detector in Washington state.

The signal had been traveling for more than a billion and a half years, from before multicellular organisms on Earth. It was the centenary of Einstein’s general relativity. When he wrote the theory in 1915, that wave was already on its way, almost here. Fridman asks which is cooler, the theory or LIGO. Levin will not disparage her friends, and relativity is all-encompassing, and then she concedes they built it. Weiss had just left the site. He woke in the night, looked at the log, and wondered what the hell that was. She does not know, in the end, whether the greater feat is the equation or the instrument that made the equation ring in a control room.

Levin’s novel *A Madman Dreams of Turing Machines* pairs Kurt Gödel and Alan Turing, two minds she found mesmerizing. Mathematicians once believed every mathematical fact could in principle be proved. Hilbert made it a program. Gödel, a Platonist who trusted mathematical objects more than physical reality, showed that even among the numbers there are truths that can never be theorems. It is a way of saying mathematics has no theory of everything. Turing started from uncomputable numbers, strings with no rule that generates them, and proved such numbers exist. Then he turned almost the opposite way: he asked what a proof is, what it means to think, and imagined a machine that executes orders. The universal machine, one piece of hardware that takes different software, is the computer. In the war he helped break Enigma, a code widely thought uncrackable. People believe that small group turned the tide for the Allies. His further leap was that we ourselves might be biological machines, replicable, a long way from Gödel’s distrust of this world.

She does not want the trite trope of the mad genius. She does think people who refuse ordinary gratification, money, comfort, fame, and chase something elusive can become unstable. Gödel had a wife, walked with Einstein every day at the Institute for Advanced Study, and produced a rotating-universe solution in which you can travel backward in time, mathematically correct. He was probably paranoid schizophrenic, feared poisoned food, and starved himself to death. Turing was openly gay when it was illegal in Britain. After a petty robbery he went to the police and was himself arrested. The man who had helped win the Atlantic war was chemically castrated. Depressed, obsessed with *Snow White* and the chant about dipping the apple in the brew, he is believed to have bitten a cyanide apple; some say so his mother could think it an accident. Apple’s logo is sometimes read as a nod. The company has denied it. Levin put the two men in a novel because a factual biography cannot capture them. That elusiveness felt isomorphic to incompleteness and uncomputability: things we can believe and never quite know.

Fridman talks about being self-critical and open, and about advice to armor up. Levin believes in the tragic flaw the Greeks described. What makes a person great is also the downfall. The choice may be not to be great. Character traits that built the work built the demise. For every Gödel or Turing, he notes, millions try, destroy themselves, and fail without reason. The story should not be romanticized. If you are already weird and already suffering, use the friction. Levin cannot imagine abandoning a discovery she can see her way through, even from fear of misuse. Bohr could not think of a way for quantum mechanics to kill people either. Terence Tao, Fridman says, is better than anyone he has met at putting a problem down and labeling it a weekend problem. Levin can kill most of her own ideas; any self-respecting theorist should. Andrew Wiles spent some seven years on Fermat’s last theorem, not wrong, asymptotically approaching a proof that might never land, then survived a gap that took a year to check. Grigori Perelman proved the Poincaré conjecture alone, refused the Fields Medal and the Millennium Prize, and walked away. A recluse who enjoys solitude, Levin smiles, does not want to talk to a man in a tie.

She is chief science officer at Pioneer Works, an old ironworks in Brooklyn that the artist Dustin Yellin bought as a utopian collage of artists and scientists. Hurricane Sandy left a waterline on the brick. Gabriel Florenz, the founding artistic director, builds with his hands. Levin does not like the labels outreach or education. She is doing culture. Nobody asks a painter why the show is pedagogical. If you have seen something from the summit, you bring it back. They run live events and a magazine, *Broadcast*, and she interviews people, CRISPR biologists included, because she does not understand them and wants to. She wears Andrea Lauer’s Risen Division jumpsuits and event patches of string theory and consciousness. Theoretical physics is mostly solitary, even with collaborators such as Brian Greene, Massimo Porrati, and Dan Kabat. Pioneer Works is the rare place she actually makes things with other people. She reads fiction more than sci-fi: Ishiguro’s *Never Let Me Go*, Martin Amis’s *Time’s Arrow*, Orwell, Hitchens on Orwell, and Cormac McCarthy’s *The Road*, science as a way of structuring a world in which a father and child still walk. Fridman keeps returning to *Animal Farm*. Levin answers that some animals are more equal than others, and in Turing some infinities are bigger than others.