NASA Once Spent 5 Percent of the Economy to Go 250,000 Miles. Mars Is a Hundred Times Farther.

At eight, Gates realized the stars were places. Getting a human body outside the solar system, he tells Lex Fridman, will be extraordinarily difficult if today’s physics stays valid. He is a science-fiction fan who loves to dream of starships; the barriers are still formidable. Multi-generational ships are imaginable with current technology. The body is the part people forget. Even Mars is a radiation problem. Earth is a wonderful home with a magnetosphere. Leave that shield for something like a two-year round trip and you are bombarded — which probably means cancer. Fix every technical problem and the bioengineering is what he worries about most: engineer the ship, the body, or both, so that something still recognizably human survives interplanetary space.

He is extraordinarily convinced there will not be a human on Mars by 2030, a date that lives in public debate. The simple slice is money. He was at MIT for the first Moon landing. NASA, an extraordinary technical agency, consumed about 5 percent of the country’s economic output. Five percent over about ten years got 250,000 miles. Mars is about a hundred times farther, and the government is spending about a tenth of those funds. His claim: it is at least a thousand times harder. He still loves Kennedy’s line about doing things because they are hard. He will go out on a limb for a later window: around 2090, or 2100, say 2120, he suspects there will be a human on Mars.

Fridman asks whether Elon Musk and Jeff Bezos can bend the cost curve. Bending it, Gates says, is the anchor of the whole challenge. He is disappointed in the routes he sees. Reusable rockets that go up and land on their fins, like the science-fiction movies of his childhood, are astounding. The technology is not really that different from what went to the Moon. There is an alternative he calls a flare engine: a traditional rocket nozzle looks like a bell; this one looks like a long, elongated exhaust pipe on a fancy car. Preliminary tests show it works. It is more economical because you can vary thrust as you rise in a way a bell cannot. You would think an entrepreneur trying to bend the cost curve would bet on flared nozzles. What he sees instead is incremental change, and incremental change, in his view, will not bend the curve.

Are we alone? Gates reaches for Carl Sagan: if we are the only conscious life in the universe, it is a terrible waste of space. When Sagan said it, we did not know about the profusion of planets. In the last decade, he says, we have discovered over a thousand, a substantial number of them Earth-like in the Goldilocks zone. It is practically inconceivable to him that we are the only conscious form of life. That does not mean they have come to visit. The two claims have very different strengths, and he refuses to fuse them.

Would we recognize them? It depends on the native environment. Biology has a principle called convergence: systems that never met, facing similar conditions, tend to converge on similar solutions. A place like this place might grow something like us. He will not grant carbon a monopoly. Carbon is the backbone because of how it interacts, a reflection of its electronic structure. Look down the periodic table and you find similar elements; science fiction has long mentioned silicon. It is presumptuous, he says, to think we are the template by which all life has to appear. Weirder things can spring from the same laws of physics.

Fridman asks for the most beautiful, surprising idea in physics. Gates does not name a theory. The most surprising idea is that we can actually do physics. The universe did not have to be constructed so that limited intellects, put together as we are, could delve incredibly deeply into its structure. That, to him, is pretty close to a miracle. Relatively simple equations compress the functioning of the universe. He can imagine worlds where everything is a lot more complicated.

People ask whether mathematics is the language of the universe. His response: mathematics is the language humans are capable of using to describe the universe. It may have little to do with the universe itself. In terms of our capacity it is the microscope, the telescope, the lens that lets us view nature with a precision no other human language allows. Computer scientists compress big packets, transmit the small ones, and unpack them at the other end. It looks to him as if the universe did us a favor: it constructed our minds with mathematics, which then teaches us how to carry out that compression. The feeling physicists call beauty is close to the relief of a compression that worked.

Can the human mind be compressed and sent at the speed of light? Gates unpacks the question. He does not believe wetware biology has an exclusive patent on intellectual consciousness. Other structures in the universe are perfectly capable of producing the data streams we use for observing the world and being aware of ourselves. Panpsychists who treat consciousness as a fundamental law, and Gaia-style planetary life-force ideas, he has encountered; he does not know what to make of them, and he probably will not live to know. He will be 69 in about two months. A lifetime of watching mathematics interact with nature leaves him with one integrated report: there is something extraordinarily mysterious about the universe. Einstein said something similar. The mysteriousness almost feels as if the universe is our parent — a strange thing for a scientist to say, except there are so many strange coincidences that you get a sense something is going on.

Artificial intelligence, he argues, will probably develop something indistinguishable from consciousness, because the architecture that supports ours holds no patent. As far as he can tell, we are self-actuating, self-learning data streams. That is the most accurate description he can give of humans at the level of consciousness. Export that peculiar data stream to metal or electronics and that kind of mind could get to Mars quickly; it does not have our radiation problems. Sending it at light speed is harder. That is no longer about having a data stream. It is about preserving the information in it. The internet itself is a miracle most people do not notice, built on message packaging. Unless you can expand that packaging in some exponential way so the stream does not corrupt, the dream does not hold.

Does replacement by machines scare or excite him? He tells a story about sitting near Eric Schmidt at a meeting. Schmidt said something like: Jim, in a decade or so we will have computers that do what you do. Gates’s response was: not unless they can dream. Human creativity, in his lived experience and in watching creative people, is connected to the irrational parts of what goes on in our heads. Dreaming is part of that irrationality. Unless you can build an AI that dreams, he has a strong suspicion you will not get something fully conscious by a definition he would accept.

In the mathematical workspace where he is charged with inventing ideas about nature, Gates has watched several modes of creativity. One looks normal: Chinese water torture, drop, drop, drop, until information congeals and the picture clears. That is how most technical people think problems get solved. He has also seen a second mode, far more powerful. As an MIT freshman in Baker House, in course 18.01, differential calculus yielded to the drip method. Integral calculus was different. He could memorize the formulas. The problem was why, in his own mind, the formulas worked. He was emotionally involved in his education. Multiple substitutions produced an emotional crisis.

One night in the dorm, nowhere on a problem set, he got a terrific headache, went to sleep, and had a very strange dream. When he woke he could do three- and four-substitution integrals with relative ease. He had never understood that a subconscious could be harnessed to do mathematics. It was not the only time. Wickedly tough problems, he thinks, need this second variety, the kind that comes from dreaming. Fridman, romanticizing suffering as a Russian, asks whether pain is in the equation. Gates is convinced it is a crucible. The mind is struggling to get out; even when you are not consciously solving, something is going on. He likens it to a thermonuclear weapon: two bombs, an atomic first stage that does the compression, then fusion. Emotional pressure is the first stage. The military metaphor is not accidental. His father served 27 years in the U.S. Army; Gates started life on bases, and a lot of what wanders around in his subconscious is connected to that.

Will we always have war? He is not sure we will be able to afford it — not in money, in consequences. Non-state actors can already acquire bioterrorism whose impact is roughly what it used to take nations to inflict on a population. He thinks the cost of war may work like the Cold War. The species survived fifty or sixty years with weapons that could have ended this form of life. Why didn’t they? Mutually assured destruction. The cost was so great people figured out you cannot really use them. He thinks it may have been Schrödinger who said nuclear weapons are not really weapons but political implements. Spread that lesson across biology and materials science and you can imagine technologies so terrible they cannot be used. That might cure us. As a scientist collating data on the species, it is not clear to him we will avoid a catastrophic self-induced ending. As a person: he would not bet against us.

Physicists sort the smallest objects they can mathematically conceive and experimentally check into two buckets. One is matter: electrons, quarks inside protons — 18 quarks, and six electron-like objects called leptons. The other is force carriers. The familiar one is the photon. Gravity’s carrier, the graviton, is a mathematical object physicists have known about essentially since Einstein wrote general relativity; it has not been experimentally verified. Four fundamental forces: gravity (graviton), electromagnetism (photon), the strong nuclear force (eight gluons), the weak nuclear force (W plus, W minus, and Z bosons). The most precise experiments the species can run test these ideas to at least one part in a billion. Force carriers are not a trivial idea. Newton, who invented physics out of natural philosophy when he wrote the *Principia*, was puzzled that an object in one place could magically affect another with nothing intervening. James Clerk Maxwell, between Newton and Einstein, taught electric and magnetic forces; from his equations, around 1860, physicists could see the photon.

Bosons and fermions are how the buckets behave. In a dusty room, two flashlight beams pass through each other; they do not bounce. That is a boson, and the particle of light is the simplest example. Throw two buckets of balls so they meet and they bounce — partly charge, but even with charge mathematically turned off, fermions still repel. Everything in those two buckets has been hypothesized and then verified, the Higgs boson the most recent. The graviton is the holdout. Space-time is enough like a rubber sheet that when it oscillates you get waves; LIGO has seen those waves from colliding black holes and neutron stars. A graviton would mean the waves carry energy in packets. We do not yet have the technology to show that. Why gravity is so much weaker than the other forces is a deep mystery. Some facts in nature are accidents, like planetary orbits. The ordering of the forces may be like that, or there may be a deep reason. We do not know.

Now draw a pie in four quadrants. Put matter in one, force carriers in another, leave two empty. Does that look symmetrical? No. Humans have a deeply programmed sense of symmetry; that, too, is part of the universe’s mystery. Fill the empty quadrants and you have supersymmetry. The idea was born in Ukraine in the late 1960s behind the Iron Curtain; in the early 1970s Bruno Zumino and Julius Wess rediscovered it in the West. Gates started graduate school at MIT in 1973, surveying ideas for a thesis, and in 1975 the mathematics bowled him over. He already had an undergraduate degree in mathematics and one in physics. No one else at MIT found the idea interesting. He became the first person there to really study it, and in 1977 wrote the physics department’s first PhD thesis on it, drawn to the balance.

The most beautiful idea in the math–physics interplay, he says, is symmetry itself: an innate sense lining up with incredible mathematics. It is very strange but true that if symmetries were perfect we would not exist. Balance is a scaffold for reality, not the entirety of it. The magic happens when you break it — humans, planets, stars. Filling the empty slices is a composer’s variation on a theme. Take Maxwell’s photon, change a term so the force carrier bounces like an electron, and it no longer belongs in the force-carrier bucket; you are forced to put it in an empty quadrant. That companion is a photino. Start from Dirac’s electron, change the term that makes two electrons bounce even with charge off, and you get a selectron. Quarks get squarks. A graduate student in 1975 could see the pie coming into balance. Supersymmetry is closer to experimental reach than string theory, he says, and it is still not validated. That is how deep modern physics works: write equations, predict an object, go looking, as with the Higgs in the late 1960s and early 1970s.

In 2005, with a colleague named Michael Fox, Gates was looking at a class of equations they could not solve. Beating your head against the wall is a bad philosophy; you change your frame of reference. They figured out that all the data in those equations could be put in pictures: little balls, white for the light-like bucket, black for the electron-like one, connected by lines. He has no physical model for the lines. If you are a mathematician, they are the orbit of the representation under the action of the symmetry generators; nobody else in their right mind needs that sentence. The pictures were stunning, and encouraging, because of problems in the equations he had first learned about in 1979 at Harvard and then at Caltech with John Schwarz. He now had an alternative language. The language was not known to mathematicians, which meant teaching them a piece of mathematics. Their rigor made the ideas better. He named the graphs Adinkra, after a Ghanaian symbol system that already carried proverbs and concepts.

The simplest Adinkra is one white ball, one black ball, and a single line — the same balance that fills the empty quadrants. People who work with mathematics call such concepts objects, even though there is nothing objective about them. You cannot see or touch them; they occupy interior life so thoroughly it is as if you could. Then the collaboration found ones and zeros buried in the graphs. Digital information is strings of bits. On a rainy day, or through foggy windows, a zero arrives as a one. In the 1940s Richard Hamming showed how to send extra ones and zeros in a particular pattern so the receiver, knowing the pattern, can tell which bit flipped. That is an error-correcting code. The ones and zeros in the Adinkra graphs were not random. They were in the pattern of error-correcting codes. The first attempt to publish took three years; other physicists had to be convinced the authors were not crazy. Eventually a paper went out with mathematicians and other physicists on it.

The craziest property, to him, is this: when you try to write equations in these extra-supersymmetric systems so that information gets transmitted reliably, it does not happen unless an error-correcting code is present. It is as if the universe says you do not really transmit information unless something about an error-correcting code is there. That is the craziest thing he has personally encountered in his research. The only place in nature we know error-correcting codes is genetics, where we think evolution put them in genomes. Does that mean some form of evolution acted on the mathematical laws of the physics of our universe? A bizarre idea; he has wondered about it since. He does not know whether it is fundamental or emergent, and he probably will not live to find out. The Adinkra line of work sits two steps from talking about electrons — a long way around, trying to get back to reality. It is also the concrete source of that feeling that the universe is a parent: a structure you cannot explain, in the same family as a trick humans invented in the 1940s to beat noise.

Gates doubts he can clarify the public fight over string theory, partly because it did something he has never seen physics do: break into general consciousness before it was finished. People know it because of *The Big Bang Theory*. String theory, he says, does not actually exist — not if *theory* means an overarching paradigm that explains what you are doing. No such paradigm exists. What exists is an enormously large, mutually reinforcing collection of mathematical facts in which researchers can find no contradictions. They do not know why it is there. Finding a piece of mathematics does not mean it applies to nature. The heated debate is whether this is hysteria among theorists or something fundamental about the universe. We do not yet know.

The camp that studies it will tell you it has been extraordinarily productive even on mathematics that is not string theory. Spin-offs have, for almost two decades, let physicists more accurately calculate the force between electrons in the presence of quantum mechanics — weak-strong duality, coming directly from strings, and not something you hear about in public. Holography lets you look at equations on the boundary of a space and know about the inside without calculating there. Take those ideas to math already known and you suddenly find yourself more powerful. That is a pretty good indication something interesting is going on. It is the early days of a powerful mathematical framework. That is what we have right now.

What is a string? Start with Newton’s particle: imagine a little ball, shrink its size until it has no extent, keep the mass. That mathematical limit underlies all of physics. For a string, start with a piece of spaghetti and shrink the thickness until it has none. In words that makes no sense; mathematically it works. The object can wiggle and jiggle and also move collectively, like pasta. The mathematics of those objects is string theory. Extra dimensions are not, for Gates, the strangest part, partly because of his own research. Adinkras do not really care how many dimensions you are in; they have an internal consistency that lets them show up in many. Supersymmetry is part of string theory, so you would expect the inheritance. A little-known fact not in the public debate: there are strings that are only four-dimensional, discovered at the end of the 1980s by three groups independently. Gates and Warren Siegel, then at the University of Maryland, proved there is mathematics that looks totally four-dimensional and is still a string. A group in Germany used slightly different math and found the same result; a group at Cornell used a third piece of mathematics and found it again. Extra dimensions are the story the public was told. There are alternatives.

Gates nods when Fridman asks whether general relativity’s early years echo in string theory. That is one reason he wanted to tell how Einstein became a global superstar. In 1915 Einstein wrote equations different from Newton’s, made calculations, and issued a prediction. Making a prediction is not enough; someone has to measure. String theory sits in that in-between zone. Einstein had made an incorrect prediction about the same thing in 1911 and corrected himself in 1915. By 1919 the first observational data said he was not wrong; by 1922 the observational argument was overwhelming. The book *Proving Einstein Right*, written with novelist Cathy Pelletier — a conjoined brain; she called them Professor Higgins and Eliza Doolittle — had two motives. Young people should see that the alien giants were people: they marry, divorce, do terrible things and great things. And Gates, who can create mathematics and will not pretend to be a great writer, wanted readers to feel how science feels from the inside.

The first magical moment in the research was Einstein’s struggle. The 1911 wrong prediction about bending starlight is what set the astronomers off. In 1914 there was an eclipse; war, weather, and accidents transporting equipment stopped anyone from measuring. If they had, the result would have disagreed with 1911, because nature has one answer. He corrects himself in 1915 and hands them a different number — the number nature agrees with. Circumstance, place, and accident are the lens through which we view him. The story could have been: a professor made a prediction, 1914 disagreed, and that is who he was. Eclipses themselves drove science in a very young United States, even before it was a nation. Fortune and misfortune shove the progress of radical ideas.

General relativity was trying to answer what left Newton puzzled: gravity magically going from one place to another. Newton did not believe it; the mathematics was so good you threw your qualms away. That math got a man from the Earth to the Moon. Einstein did not even create the mathematics he harnessed; it was created roughly fifty years earlier, and a friend had to teach it to him. Why no Nobel for relativity, only for the photoelectric effect? The physics prize is never given for purely proposing an idea, only for an idea with observational support. Alfred Nobel’s provisions blocked special and general relativity at the time of the award. Validation really arrives in the 1920s, and the theory had vociferous critics into the 1950s. Einstein died in 1955. A committee that wanted to give the prize would have had to face those critics.

String theorists, Gates thinks, will retrace that path, far longer and more torturous. When the idea becomes acceptable it will be a confluence of observations, not a single one. The day before the taping he gave a seminar at MIT on an idea that string theory can leave signatures in the cosmic microwave background. If those observations are borne out, and perhaps others related to supersymmetry, they would be the first powerful, observationally based pieces of evidence — beginning to do what the Eddington expedition did in 1919. That may take several decades. Nobel Prizes for string theory? No, because the arc will exceed a normal human lifetime. There are other prizes. Yuri Milner’s Breakthrough Prize is three times the Nobel money and is awarded every year. Something like that is likely to arrive far earlier.

At Caltech, Gates interacted with Richard Feynman. He has a fair number of stories and is not prepared to tell them; they are not all politically correct. What he will say is that the books, starting with *Surely You’re Joking, Mr. Feynman!*, portray the man he met with startling accuracy: irreverent, fun, deeply intelligent, deeply human.

He did not hear Feynman say the line himself, but it is reputed: if you are on a barstool as a physicist and you cannot explain to the person next to you what you are doing, you do not understand what you are doing. When you truly understand something as complicated as string theory, in its fully formed final development, it should be something you could tell that person. The line shapes how Gates does science and how he talks to the public. Einstein said related things: when the answer is simple, God is speaking; his work was the distillation of common sense; make things as simple as possible, but no simpler. Seeing that attitude exemplified around Feynman is, for Gates, the origin of a career-long search for simplicity.

Gates served seven years on President Obama’s Council of Advisors on Science and Technology, in a room that included Eric Schmidt, whom he first met when the council convened in 2009. The idea of service comes from his father, who spent 27 years in the Army, going off in 1942–43 in the supply corps that fed Patton’s tanks across Western Europe toward a meeting with Soviet forces pushing from Stalingrad. As an adult Gates studied the war from both sides, names like Zhukov and Rokossovsky as well as Patton, in conversations with many Russian friends. In 2009 a Nobel laureate in biology, Harold Varmus, emailed that he needed to talk, then went silent through several cycles. Gates had just stepped off a plane to give a physics talk at the University of Florida when the phone rang. Why, he asked, do you keep saying you want to talk and never call? After the small talk Varmus asked: if you were offered the chance to serve on the President’s science council, what would be your answer?

Gates was amused at the formulation, then understood it was not a joke. It was one of the few times in his life his knees went weak and he had to hold himself up against a wall. As a beneficiary of the country he could not say no. He was frightened — his policy work went back to the 1980s, but he had never advised a president — and he would not have slept if he had chickened out. He took the plunge. There are things from those seven years of which he is extraordinarily proud. If you have seen the *Schoolhouse Rock* cartoon about how a bill becomes a law, he has kind of lived it: some of what he worked on is now codified in U.S. law. Not everybody gets that chance.

He has met other presidents. Obama is the most extraordinary he has encountered, “despite the fact that he went to Harvard.” Thinking about him is a deep mystery in the same way the universe is a mystery: Gates does not really understand how that constellation of personality traits fits in one individual. He watched for seven years, so he is convinced it was not fake news. Obama was not afraid to sit with really smart people, completely comfortable asking some of the world’s greatest experts what to do about a problem. He would not just take the answer; he would listen. He internalized complicated ideas in real time with a speed that stunned the entire council, then came back with really good questions. In artificial intelligence, an area Gates knows better, Obama would integrate the briefing and come out with Feynman-like insights. What takes graduate students four years on a topic, Gates says, he does in a few minutes.

Fridman asks for problems just within reach in the next two decades. On the immediate horizon, Gates says, is quantum computing, and if we get there it will be extraordinarily interesting. It is no longer a problem of theory. It is in the space of engineering. A couple of months before the taping, as a vice president of the American Physical Society, he visited Microsoft’s quantum research facility in Santa Barbara, heard lectures on what they were doing, and came away thinking they knew what they were doing and were close to major breakthroughs.

Does he ponder shuffling off this mortal coil? The phrase is from Hamlet’s soliloquy, which he still does not fully understand; the expression is beautiful. He does not ponder his own mortality. His mother died when he was eleven. He immediately knew the end of the story for all of us, and has never spent much time thinking about death. It will come in its own good time. The job of every human is to make the best of the time given, not for selfish gain, but to make the place better for someone else. The why of life? He has no idea and has never worried about it. The local, apparent why for him was that he is supposed to do physics.

Two dreams were born when he was four, simultaneously: astronaut and theoretical physicist. If both paths had stayed open it would have been the worst choice of his life. The universe helped, the way war and weather helped Einstein in 1914, and not only in that — it helped him pick the right dad. Asked for a day he would relive because it made him truly happy, he says being a theoretical physicist is like having Christmas every day. Moments of invention and revelation sit high; only family experiences, like the births of his kids, exceed them. Fridman closes with Einstein, for the rebels: unthinking respect for authority is the greatest enemy of truth. That is the method Gates has been demonstrating — disappointed in incremental rockets, unwilling to call a pile of math a theory, more interested in Einstein’s 1911 miss than in the halo, and still shocked, after a career of equations good to a billionth, that the universe was constructed so it could be understood at all.