A Blink of Ordered Particles: Brian Greene on Entropy, Meaning, and Death

Lex Fridman opens with a line Brian Greene placed in *Until the End of Time*. In a 1948 debate about God, Bertrand Russell said that so far as scientific evidence goes, the universe has crawled by slow stages to a somewhat pitiful result on this earth, and is going to crawl by still more pitiful stages to a condition of universal death. If that is evidence of purpose, Russell added, the purpose does not appeal to him, and he sees no reason to believe in any sort of God. Lex calls it a bleak outlook on the universe and on the emergence of human consciousness.

Greene does not try to refute the physics. The second law of thermodynamics is what drove Russell's outlook: disorder, entropy in aggregate, is always on the rise, and over long enough timescales that is interpretable as disintegration and destruction. The hopeful move, he says, is to put that fact in a broader context, which is really what the book is about. There is a lot of truth in Russell's statement. The slant you take on it is the rest of the argument.

What the second law makes special, in Greene's view, is us. We are exquisitely ordered configurations of particles that will last only a blink of an eye in cosmological terms. The fact that we are here, can rise up, look around, and try to figure out where we are and what we should do with our time, inspires gratitude, wonder, and a sense of deep purpose. He would not disagree with Russell on the basic unfolding. It is a matter of what that unfolding means for the brief collections of particles that get to notice it.

Lex asks the biggest question: if complexity briefly arises from simple things and then, under the second law, returns to simplicity, what is the meaning of it all? Greene thinks there is meaning, but not a universal answer. Across the ages people have tried to settle the question with God, or love, or companionship. None of those, he says, is the one right answer.

Once you recognize that the universe does not care, the hunt for a final cosmic verdict becomes a fool's errand. It is not as though a more powerful telescope will make everything clear. The deeper we have looked, literally and metaphorically, the clearer it has become that we are a momentary byproduct of laws of physics with no emotional content and no intrinsic sense of meaning or purpose. Every individual, Greene says, has the capacity to make their own meaning and set their own purpose.

That is not a platitude, in his telling. It is what we are, because there is no fundamental answer. However much it sounds like a Hallmark card, he calls it the deep lesson of physics and of science more generally over the past few hundred years. Lex adds that whatever is happening on Earth still looks peculiar — hierarchical complexities forming more and more sophisticated biological systems — when you look at the observable universe we can actually see.

Erwin Schrödinger's 1944 lectures, later the little book *What Is Life?*, give Lex a way in. What is this pocket of complexity? Greene once put the question to Richard Dawkins and got roughly the answer he expected: if anyone could draw a line in the sand between the not living and the living, we might have the insight we yearn for. The fact of the matter, Greene says, is that it is a continuum, from the things we typically call inanimate to the things that are obviously full of the currents of life.

Somewhere in that range sit complexity of structure, the ability to take in raw material, and a metabolism that extracts energy and dumps entropy into the wider environment. Those look like necessary ingredients, but nobody can draw the line. Life may be unique; it may not. A well-ordered star, a planet bathed in that low-entropy energy, and a surface stocked with the commonplace leftovers of supernova explosions might be enough for life to form naturally. The James Webb Space Telescope, then due to launch in December, was supposed to look at atmospheres around distant planets and offer some sense of how special life as we know it really is.

Asked where, if he were a betting man, the path from rock to rabbit gets stuck, Greene puts the hard step at the onset of consciousness. That, too, is a continuum, but there are obvious creatures like ourselves with a self-reflective awareness. For billions of years this planet had life without that. A rock 65 million years ago slammed into Earth and wiped out the dinosaurs; without that accident, dinosaurs might still rule, and they may well not have developed the kind of awareness we have.

Greene can imagine a lot of life out there that is not wondering about the meaning of life, just going about the business of survival, which has been the dominant activity of life on this planet. We are a rare exception. He does not treat consciousness as a binary phase shift, and he is not even fully convinced, looking at Lex, that Lex is a conscious being. Behavior makes that the best explanation, but each of us has direct access only to our own awareness. Other creatures leave us in a similar state of ignorance about what is actually happening inside their heads, if they have heads.

Based on the best available data, Greene still thinks there is something special about us. He does not think fish are walking around inventing existentialism, or dogs working out general relativity. Asked which is more special, intelligence or consciousness, he picks consciousness. The two are distinct but deeply connected. Philosophers, David Chalmers among them, named the hard problem, and as a physicist Greene sees why the name stuck.

He looks at the world and sees particles governed by physical law: electrons, quarks of various flavors, a list of ingredients and a list of rules. Nowhere in there is there even a hint that putting those particles together in the right way should switch on an inner world. It is not only that there is no hint. "It's insane," he says. How could a thoughtless, passionless, emotionless particle, grouped with its compatriots, yield something so deeply foreign to the ingredients themselves?

The hard problem, in the technical sense, is that the thing to be explained seems unavailable to third-party analysis. Greene can tell Lex a lot about what is happening in his head, but Lex cannot get inside it the way Greene can. That is a different kind of problem from measuring the Moon or the spectrum of hydrogen. He still thinks the eventual explanation will be that consciousness is just a thing that happens when particles come together. A hundred years from now, or maybe a thousand, people will smile at those who found it incredibly mysterious.

The mystery will start to evaporate, he suspects, when we build artificial systems that report they are sad, or anxious, or that there is a world going on inside. Lex, who has built robots that do emotional-type things, says the mystery recedes immediately: you no longer need to solve the hard problem, because the thing sure as heck looks conscious. The same is true with a dog or another person. He wonders whether rich subjective experience is a social trick, deeply coupled to language and poetry, that helps us describe the world to one another.

Princeton's Michael Graziano has developed ideas that, Greene says, do not solve the problem but illuminate it. We are not aware of the physiochemical processes that make our inner worlds tick. Because of that dissociation, the mind feels untethered, floating in the gray matter. Greene's image: if you are in a dark room and he has glow-in-the-dark paint on his fingers, the dancing fingers look mysterious. Turn on the light, and there is an arm underneath. What we are missing is that deep physical connection. Consciousness feels mysterious because we suppress the underlying science responsible for it.

Lex wonders whether mystery is an important component of enjoyment — whether, once we know how the thing works, we will stop enjoying the conversation. Greene answers with a Richard Feynman interview. Some people feel that once science explains something, the beauty goes away. Feynman disagreed. Looking at a rose, he could still enjoy the aroma, the color, the texture; what a physicist can add is a deeper look at where the red and the scent and the structure come from. That only augments wonder. It does not flatten it.

Greene takes that as a motto. There is a wonder that comes from not knowing, and another that comes from deep knowing, with its own special character, perhaps more gratifying. Lex notes that you never get to the bottom; peel the onion and more mystery remains. Nature, unlike a magician whose trick looks ridiculous once you know it, can increase awe when the curtain is pulled back: electrons changing orbitals, photons at particular wavelengths, the equations of quantum electrodynamics that Feynman helped develop.

If physics one day arrives at a unifying account of the fabric of reality, from the Big Bang to now, Greene thinks that understanding will only elevate appreciation. It has so far. Certain categories of questions will end: he expects we will close the book on nature's ingredients and fundamental laws, though he cannot prove it. That is one chapter. Then we use the knowledge to understand how the world builds planets, people, black holes, and possibly other universes. The set of questions we know we do not understand keeps blossoming, so the ratio of what we understand to what we know we don't keeps getting smaller.

Lex asks whether there is hope of solving the puzzle in the next few decades. Experimental tests of quantum gravity need effects that are brutally hard to measure; theoretically, gravity and quantum mechanics still refuse to sit together. Greene has to have hope: part of his professional life is spent trying to make progress. He dislikes "theory of everything" as a phrase, because it makes other scientists feel that biology is leftover details. Call it what it is: putting gravity and quantum mechanics together.

He has been on the problem for thirty years, since he was a student fired up by the idea that physicists were stumped. There has been progress. String theory is one possible scenario, a vibrant field making incredible progress — except on experimental verification, which is a vital part of the story. Interviewed in the 1980s as a wild, bright-eyed kid working eighteen-hour days, he would have said that by 2021 we would know whether the idea was right.

That contact with experiment has not happened. Other things he would have said were impossible did happen: detailed talk about the qualities of black holes, and an exact formulation of string theory in certain circumstances. You never know where the progress will land. He would love to know the answer before he leaves the earth, though he does not think there is an after. Science and the universe are not about pleasing any individual. They are what they are, and the work is to press onward.

From the outside, string theory looks as if it has fallen out of favor after decades of popularity. Greene challenges that. Any new field is a bright, shiny bicycle nobody has seen on the block: news coverage, students flocking in. As it matures, it sheds those qualities. Judge it by whether it is making progress on foundational issues, and he thinks it scores very high. Judge it by contact with experiment, and it is still challenged. Many string theorists, himself included, are sober about the theory.

The tremendous progress of thirty or forty years ago has not gone away, but they are better at assessing the long journey ahead. When Greene was starting out there was a sense that physics was about to end, that string theory would be the final unified theory. He thinks it was mostly younger physicists saying that. Founders like John Schwarz, Michael Green — no relation — and Edward Witten knew it would be a long haul. Quick hits that resolve everything are few and far between. People who wanted the quick solution were disappointed and moved on; people in it the way Einstein was in for a lifetime have found a rich source of material.

What attracted him, beyond putting gravity and quantum mechanics together on paper, was extra dimensions of space. Even before he understood what that meant, Einstein's curved spacetime had spoken to him in a strange emotional way. Then he learned that extra dimensions might explain why certain forces and particles exist and behave as they do. When he learned that string theory embraced general relativity, quantum mechanics, and extra dimensions, he was hooked. As a graduate student at Oxford he and a couple of classmates worked enormous hours trying to understand the shapes of those dimensions and what they would imply for the world we see.

Nobody really knows whether the extra dimensions are physical reality or a mathematical trick, but the most straightforward reading treats them as real — as real as left-right, back-forth, and up-down, only different in shape and size, perhaps tightly coiled and too small to detect, still leaving an imprint. Hopes of seeing a signature at the Large Hadron Collider have not been fulfilled: debris slipping into other dimensions would have shown up as missing energy after a proton collision. A Nobel Prize, Greene says, would have surprised him. He is sympathetic to the view that calling it a theory degrades the word; it should be the string hypothesis. Asked about critics such as Peter Woit and Sabine Hossenfelder, he is more drawn to people who offer a better idea than to people who start by cutting one down.

Greene likes to think of time as emergent. He does not have a solid reason, only hints from string theory and quantum gravity. Time is the most familiar quality of experience, because nothing happens outside an interval of it, and perhaps the most mysterious quality of the world. If you ask him what time is, he does not really know, and he does not think anybody does. He can say what it gives us: a language for change, a way to spread events on a timeline and see patterns. Laboratories measure this thing called time to spectacular precision, and he is not sure the people running those clocks can articulate what they are actually measuring.

On one-way causality, his guess is that at the macroscopic level of human experience there is a fundamental notion of cause and effect that emerges from a starting point that may not have causality built in. The deepest description of reality, when we have it, may not show causality directly. Einstein already wiped away the old picture: if you and I move relative to each other, our clocks — and therefore time itself — tick at different rates; if we sit in different gravitational potentials, time elapses differently. Those strange properties give rise to a scientific notion of time travel. Greene does not think we will ever wipe away causality at the macroscopic level.

The universe certainly allows time travel to the future, not the mundane second-by-second kind but the Hollywood net effect. Want to see Earth a million years from now? Build a ship, go out near the speed of light for six months, turn around, come back. Einstein tells you how close to light speed you need to be so that, when you step out, a million years have passed on Earth. This, Greene says, is not controversial. It is bread-and-butter physics. The engineering, the g-forces, the biology are details. Lex notes that extending the human lifespan is another, biological, way for a conscious observer to travel forward.

Coming back from such a journey is another matter. The dominant perspective in physics is that you cannot get back, though serious people have written papers on hypothetical routes. Wormholes appear in Einstein's equations; in principle you could manipulate the openings so they fall out of sync, one ahead and one behind. Einstein himself was quick to say that math allowing something does not make it real — he did not believe in black holes or the Big Bang. People who have studied wormholes ask whether you could keep one open, or whether you would need exotic matter that may not exist. Greene's general sentiment is that this scenario is unlikely to survive a deeper understanding of physics, which is not quite the same as a closed door.

Another macroscopic feeling Greene writes about is free will. His take, as Lex summarizes it, is that there is no physics-based free will, but there is an experience of freedom, and that experience is real. Assume the physical universe is stuff governed by laws. A human being is a particular collection of those ingredients. Every thought and action is the motion of particles, fully governed. That leaves no opportunity to break free from physical law. The intuitive notion that we are the ultimate authors of our actions — that the buck stops with us when we choose vanilla or chocolate, left or right, live or die — has no basis in the physical world.

The other kind of freedom, if you focus on it intently, is the one we actually feel. Inanimate objects have a very limited behavioral repertoire because their internal organization is too coarse. Talk to a glass of water and it may vibrate; that is about it. We are different because eons of natural selection refined our inner organization until we have a huge repertoire of behaviors finely attuned to stimuli. Lex asks a question; particle processes go into action; the answer is the result.

The freedom we have is not freedom from physical law. It is freedom from the constrained behavior that has long governed inanimate objects. We are liberated from the limited repertoire of rocks and bottles of water. Do we pick the responses? We do not. Do we freely choose them? We do not. But we have them, and we can marvel at those behaviors. That, Greene says, is the freedom we have.

Lex loves cellular automata, Game of Life worlds where simple rules yield complexity that looks like little organisms making decisions. Is that emergence physics or poetry? Greene is a physicalist: beauty, wonder, consciousness, all of it is ultimately explainable from particles and laws. That is usually the worst language for talking about what emerges. Describe a baseball in flight as 10^28 quarks and electrons with coordinates in time, and you hand someone a mountain of data they cannot use. "A baseball flying through the air" is the insightful sentence. Human emotion and the sensation of free will belong to that useful macroscopic language. The risk is forgetting that emergent phenomena still come from the reductionist account — and that, in that account, the freedom of will you thought you had is not real.

When the first image of a black hole came out, Greene felt amazement mixed with longing, not quite jealousy. The story starts with Einstein's 1915 equations, then Karl Schwarzschild seeing the possibility, then John Wheeler and others developing the idea. It remained hypothetical, then nearly real through stars whipping around the center of our galaxy, still indirect. Then there was a photograph you could look at. That narrative arc from the theoretical to the established is what he hopes for in string theory: still a wholly mathematical subject, waiting for the picture you can point at and say it is real.

Lex finds the picture exciting at first and more terrifying the longer he sits with it: a gigantic hole, darkness at the center, a mass he gropes to name in billions of Suns. Greene shares a kind of terrified awe. Day to day he writes equations on a blackboard and the ideas live in a mathematical corner of the brain. In quiet it hits that this is not a game, that there are monsters out there. It is not fear for his life. It is how extraordinary, how stupendously powerful nature is, and a deep humility if you let the ideas sink in.

The most stupendously powerful event is the Big Bang. A millionth of a second afterward, Greene says, the story is no longer very controversial; much earlier than that, the field is in a heated fight. Inflationary cosmology has been the dominant paradigm since the early 1980s, using Einstein's result that gravity can be repulsive, not only attractive. Alan Guth, Andrei Linde, and at the time Paul Steinhardt and Andreas Albrecht imagined a nugget of that repulsive stuff as the bang itself; the math predicted tiny temperature differences across the sky, and satellites measured a matching statistical pattern. Steinhardt, one of the builders, has since lost confidence, citing other universes and length scales below the Planck length. Greene would still bet on inflation, but not as loudly as he would have three or four years earlier.

Dark energy, the push that is accelerating expansion, looks like leftover repulsive gravity, but in quantum-gravity units it is a decimal point, about 120 zeros, then a one — a number so strange Greene says something must be wrong. Cyclic cosmologies claim a more natural home for that number. Roger Penrose's idea that information bleeds through the Bang, conformal cyclic cosmology, feels to Greene like a solution built to order; he does not rate it as close a competitor as Steinhardt's alternatives. The deeper obstacle is the singularity: math that breaks down, like one divided by zero, and Greene does not see a consensus that it has been cured. Talking about the whole universe has always meant throwing away features; the next step, already starting, is to put cosmology on computers the way astrophysics already simulates stars and galaxies.

The Drake equation is Lex's prompt for the highest-level question: looking out there, how many alien civilizations — zero, one, or many? If the word is civilization, Greene brings the number way down; it could be zero. If the word is life, he thinks it could be many. The move from life to the kind of consciousness that would build what we recognize as a civilization may be extraordinarily rare. As a kid he loved *Star Trek* and the idea of a universal community. Earth's own record of separated groups trying to live together is mixed, but as an optimist he finds the thought of comparing notes on physics and cosmology wonderful. Asked for a likelihood, he errs toward rare.

Lex lays out Fermi-paradox stories. A hopeful one: life itself is hard, which we might falsify soon by finding it elsewhere. A scary one: life is easy, intelligent civilizations are common, and we have not made contact because intelligence comes with the power and the tendency to destroy itself. A milder one: we are being watched, primitive villages left under a protective layer. Greene lands on the most straightforward explanation: there aren't any. He cannot be dogmatic about a gut feel. He also cannot resist a favorite *Twilight Zone* episode: aliens arrive with a book, cryptographers finally read the title as *To Serve Man*, and as the last decoder boards the ship his assistant shouts that the rest of the book is a cookbook.

After James Webb, he thinks, this conversation would be better informed. Current estimates put on the order of one planet per star, which, given hundreds of billions of stars and hundreds of billions of galaxies, is a staggering census. If survey after survey finds no biological markers, that would at least speak to the life question, though life could take a radically different form. Civilization and consciousness, he suspects, will not yield to that kind of survey without a direct connection. If consciousness were ubiquitous, he does not understand why they have not been here. It would be a strangely special place for human beings to be the most advanced. He thinks we are run-of-the-mill, that many would be far more advanced, and that they would not expend the energy to hide. They do not care enough.

Lex believes we are limited in our senses and our tools, that there could be stuff in front of our noses we are too young and too ignorant to see. Greene is on board with that as a possibility, but notes that we can already look back across most of cosmic time. If we are ants on the cosmological landscape, he can imagine super-advanced aliens declining to stoop and chat, as he would not stop on a Manhattan sidewalk to interview ants. Lex thinks the deeper problem is language: our linguistic club may be a niche product of our kind of brain, and everything could be lost in translation. Greene allows it. Part of why he leans toward a silent cosmos is romantic: eternal quiet appeals to him at an emotional level. Nobody knows. There may simply be a radical mismatch between what we can detect and the structures that actually permeate the universe.

If we are alone, Lex says, it is on us to spread out. Greene treats colonization as fundamentally an engineering problem so long as we are not building wormholes or flying near light speed — though relativity's punch line is that near light speed you can go arbitrarily far in a human lifetime. Terraforming, solar sails, and a first step to Mars are, in that frame, engineering. He thinks the dream is worth fighting for. We have long been explorers, walking from one part of the world to another and, metaphorically, traveling through our minds to the quantum realm, the Bang, and the insides of black holes.

A child born on Mars, learning Earth's origin story, will probably not read it in a book. It will be uploaded into the head, Greene jokes, or imprinted in DNA. The vital obstacle is the one Lex already named: maybe any sufficiently advanced civilization destroys itself, another answer to Fermi, and not hard to imagine from Earth's own history. Put that aside, and we will surmount the engineering, which then makes the physics relevant — near-light travel, manipulating the shape of spacetime. Lex, born in the Soviet Union and raised on the dream of joining the stars, says it was Elon Musk talking about colonizing Mars that made him realize humans could actually do it. Saying the impossible out loud, planting it in millions of minds and in kids' heads, is how it becomes real.

Dreaming, Greene says, is what makes the seemingly impossible possible for the next generation. Mars is concrete, and soon: a semi-permanent presence will not wait for the twenty-fifth century. It could be in Lex's lifetime, unlikely in Greene's, that a child is born who looks back at Earth through a telescope. Greene would love to go on an early mission, even one-way; he is single, he jokes, and ready if anyone wants to start a family there. Lex, placing himself in a world he cannot leave, finds the thought pure terror.

Greene knows that terror from ordinary goodbyes — the Kerouac feeling that driving over the hill is really farewell — and he thinks terror of mortality sits underneath human motivation, a slant he took from Ernest Becker's *The Denial of Death*. Terror-management experiments still find measurable differences when one group is merely interviewed across from a funeral home; most people can ignore that because culture, over some ten thousand years, has taught them how. Lex suspects you cannot build a mind that fits in human society without engineering in a similar scarcity and dread. Greene adds that any system which understands the second law will see that even robust parts disintegrate, and on the scale of eternity any finite life is effectively zero. Then, he says, it will be us and robots drinking beers under the stars, having a good laugh in awe of the whole thing.