Thanks Pat, thanks to the Royal Institution for having me back This is one of my favourite places to come visit and I thought that I would in the tradition of Michael Faraday and Humphrey Davy, and all the greats. Who’ve stood more or less in this place Begin the lecture by doing an experiment Now I’m a theoretical physicist. I’m not an experimenter, so don’t get your hopes up too high But I would like to do an experiment that illuminates the fundamental nature of motion Ok so you see here. We have an object It’s a book you can buy it and the finest book stores everywhere And we’re going to observe what happens to the object Nothing much happens to the object is the short answer to it it just sits there, but I can if I push on the object get it moving and Then if I stop pushing it stops moving the nature of motion there being demonstrated to you right there so if you were the kind of systematic thinker that lets say Aristotle was you would go from a demonstration like that To a very deep picture of how the world works at a fundamental level you would say that There is something called the natural state for the book to be in which is just sitting there motionless You would say that if you don’t do anything an object stays in its natural state But if you apply a force to it in impetus You can change its natural state you can cause it to start moving and you notice when I then stopped pushing It stopped it returns to its natural state So you invent what at what philosophers would call an ontology or a metaphysics of? Fundamental view of what the world is made of it’s made of things that have natural States And if they’re not staying stationary and unchanging in their natural States It is because something is changing them when there is motion there is a mover and you can go from this simple idea – a theory of physics as Aristotle did and you can in fact go beyond that to a theory of metaphysics that explains Not just the motion of things but more or less How everything changes and transforms at all you can even go all the way back you can say well, okay This thing is moving because this other thing is pushing it But what causes that other thing to be moving if you trace the chain of? Motion and movers backward you eventually would need to reach an unmoved mover and thereby prove the existence of God Without ever leaving the lecture hall right here this way of thinking is not only a Systematize ation of some very simple physics experiments you can do it also sort of accords well with our everyday experience when you see something moving or not moving it’s because something is moving it or not moving it so there became a philosophical tradition, which tried to go from the physics of it to a deeper understanding Claiming that everything that happens whether it’s motion or otherwise happens for a reason This is not just a bumper sticker you can buy this is a very venerable Philosophical maxim known as the principle of sufficient reason so here you have Aristotle Spinoza followed up with his version of the principle of sufficient reason and then live nets on the right german philosopher who also invented calculus They all put forward this idea that we can understand how the world works at a deep level by providing Explanations for everything we see in it nothing happens randomly nothing just happens There’s always a purpose a cause a reason why? Things happen you might be forgiven for thinking that the ultimate purpose was ever more grandiose hairstyles for professional philosophers Even if live Nets sort of had some artificial help there in in in his coffer The problem is that this is not right? The problem is that the world does not work this way at a fundamental level There’s two problems one is it’s not right the other is Despite the fact that it’s not right we haven’t abandoned it yet So we have learned a lot about how the world works because of the progress science and philosophy but we still talk a language that is handed down to us by Aristotle Spinoza and Leibniz now people have tried to fix the language here is a Bertrand Russell a more modern philosopher Trying to point out that the very idea of cause and effect is no longer Fundamental in our understanding of the world he says the law of causality I believe Like much that passes muster among philosophers is a relic of a bygone age Surviving like the monarchy. He couldn’t resist right like I’m just the messenger here. This is not. I’m not saying this Surviving like the monarchy only because it is erroneously supposed to do no harm Now many people would be surprised to hear the news that science has done away with the principle of cause and effect But I’m not gonna undo that it’s actually true It’s not that there is no such thing as causing effect. It’s that it is not a Fundamental principle of how reality works it is a very useful helpful way of thinking it about things at a macroscopic What we will call an emergent level of reality but it is nowhere to be found in the most fundamental laws of physics and That difference puts us in the position of Wiley coyote a famous American cartoon character I don’t know how popular the roadrunner is in uh in the UK good So wily coyote you will remember if you’re of the right age had this thing that he did every single episode where he would run off a cliff and Because it’s cartoon physics not either Aristotelian or Newtonian physics. He would not fall down Until he noticed that he was not standing on anything. He would look around and then oh and then he would fall down, okay We are all Wiley coyote in some sense and in the following sense this Cliff this solid surface that we used to be walking on is our old fashioned Aristotelian at all notion of causes and effects and purposes and meanings in the world We have left that behind the fundamental rules of nature according to our best scientific understanding. Don’t work that way but we haven’t adapted we still speak a language as if cause and effect purpose and Goals, and reasons. Why are the fundamental way the world works so one of our challenges should be to reconcile? The deep down vocabulary of the world given to us by physics and modern science with what philosophers call the manifest image the immediately accessible view of the world we have after all Physicists love to make fun of Aristotle and say how wrong he was but look The book does stop moving, right? That’s not a mistake That is an accurate way of talking about the world cause and effect are accurate useful ways of talking about the world you can be Accurate without being fundamental our goal is to show how at different levels of analysis different levels of squinting at the world? reveal different rules regularities and even vocabularies for speaking So I like to trace the origin of this shift from Aristotle to Bertrand Russell for example It’s actually a long series of very very interesting Thoughts and experiments over hundreds of years between Aristotle and let’s say Isaac Newton I like to give some credit to this guy even Cena Who sometimes? Romanized or latinized as Avicenna He was a persian polymath in the Islamic Golden Age and around the Year 1000 and as a modern day Theoretical physicist I find even Cina extremely annoying Because his day job was he was a doctor He was his interests were in health and human anatomy and he wrote many books about the human body and on Weekends he invented new fundamental laws of physics We can’t do that anymore, it’s more work now the low-hanging fruit has been picked so even Xena was thinking about Aristotelian notions of motion and so forth and what he pointed out for the very first time was that this idea that the book stops moving shouldn’t be thought of as the book returning to its natural state of motion Because if the book was not on the table here in a room But rather out in space like the spacecraft if it were in the vacuum The book would just keep moving at a constant velocity what we now call conservation of momentum or servation of inertia now Even Sina didn’t like this idea. He didn’t even like the idea of a vacuum in the year 1000 We weren’t sure whether there were any vacuum Vacuums so he put forward this idea, but it was seized upon by later thinkers There’s no such thing as natural motion versus being pushed the natural motion of things is just to keep moving You don’t need to keep things pushed and of course Galileo helped develop this idea he pointed out that if you think of the fundamental starting point of motion as constant motion with the uniform velocity And then put in things like friction and dissipation and air resistance Afterward you get a much more accurate precise quantitative feeling for what happens in the world So the secret thing that sneaks in is not just a new way to torture first-year physics students with inclined planes and pulleys and so forth there’s a Fundamentally new way of looking at the world the world is not made of motions that have a mover Effects that have causes there are things that are doing their thing according to some rigorous mathematical laws of physics some conservation laws very often such as conservation of momentum and of course once Isaac Newton came along and put together his theory of physics and motion and mechanics we had a much deeper version of conservation But you could call conservation of information and even though it’s sort of in some implicit Sense due to Isaac Newton it was really Pierre Simone Laplace who stuck his neck out and really understood the implications of Newtonian mechanics Laplace points out the following thing let’s imagine that we believed Newton’s laws of motion Which they did at the time and in fact? I’ll point out we updated them since then but it’s not in a fundamentally another way that really changes this particular analysis Laplace says look think of two billiard balls bouncing into each other and scattering off now He think takes these in the tradition of even Cena and Galileo and so forth to be physicists billiard balls They make no noise They have no air resistance or on a frictionless surface So they scatter off and they go their own way the traditional question we would ask of our students is if you Gave me the information at the start of the experiment So where the balls were and how they were moving I? Could tell you I could solve the equations and tell you how they would evolve thereafter But what Laplace points out is that in fact you could give me the? Information about what the billiard balls are doing at any moment in time you Could not only tell what’s going to happen next according to Newton’s laws. You could say what did happen before that? The information necessary to tell you what’s happening in those billiard balls is contained equally well in every moment of their Existence so he says imagine a vast intellect Later commentators thought that vast intellect was insufficiently sexy, so they said imagine a demon Which we now call Laplace’s demon and of course if we had been at 20 if a 21st century commentator would have been Imagine a really big computer That knew the position and the velocity of everything in the universe and all the laws of physics and had apparently infinite calculational abilities computational capacity to this vast intellect Laplace says There is no difference between the present the past and the future the future in the past or equally Transparent and known as the present is because they are determined by the laws of nature So this sets up a whole long centuries long debate about determinism and freewill and etc But there’s something deeper that gets glossed over sometimes it is worth bringing out It’s not that anything goes, but the vocabulary has changed Aristotle would have said if things are moving. There’s something moving them. There’s a cause or a reason why they are moving Laplace as they just obey equations What that means is that rather than a cause-and-effect relationship? we had patterns in the universe think about the Integers write the number zero one two three and also negative minus one minus two minus three There’s a pattern there if you tell me any one number if you say three I know what the number before that was was two I know the number after that’s gonna be it’s gonna be four But I don’t think that three is the cause of four or vice-versa There’s just a pattern that relates all those numbers to each other Laplace is saying the laws of physics are like that It’s not that there is an impulse an enchantment a guiding force it’s just there’s a pattern that says if this then that and vice versa and This way of thinking about how the world works at a deep level is something we have yet to truly absorb of Course Laplace was not right. He didn’t know about the true laws of physics He thought that Newton’s laws were more or less correct it every reason to believe that was true But since then we have relativity and quantum mechanics And so forth so we have a better idea now of what the law is Fundamentally are in fact one of the bold claims I want to make and you’re willing to disbelieve me if you want, but you would be incorrect is That the laws of physics underlying Everyday life are today completely known Here, I put on a slide just in case This sounds very much like one of those incredibly Dopey pretentious statements that scientists have made for hundreds of years right scientists especially Physicists my tribe are very very famous for saying you know any day now. We’ll have it all figured out We’ll have the theory of everything This is especially common in the late 19th century people were saying yes We have you know mechanics and thermodynamics and electromagnetism any day now We’ll have all the physics figured out and then of course it all Went to hell because they invented relativity and quantum mechanics and so forth I’m not saying that I’m not making any statement whatsoever about how close we are to Understanding all of the laws of physics or everything we are made of what I’m saying is we know some of the laws of physics some of the things that we are made of and more importantly the regime that we do understand the domain of validity of our current knowledge includes everything in this room Includes everything that you experience in the everyday Regime of your life as long as your everyday regime is not that of an experimental particle physicist But you you are made of atoms you are made of particles Electrons protons neutrons those protons, and neutrons are made of quarks up and down quarks And these particles feel forces and there’s basically four forces that are relevant here. Gravity pulling everything together electromagnetism pulling together unlike charges and pushing away like charges There’s a strong nuclear force that binds those quarks together to make the proton in the neutron and there’s a weak nuclear force which is Almost dil rel almost irrelevant except it Helps the sunshine so that’s kind of important the weak nuclear force converts Protons to neutrons and vice versa by spitting out a particle called a neutrino Okay, so for particles electron up quark down quark neutrino four forces gravity electromagnetism strong and weak And that’s it We know there are other particles. There are muons. There are top quarks etc You can argue over the exact cutoff for everyday life, okay? But you’re made of these particles and everything you see with your eyes touch with your fingers taste with your tongue Made of these particles and the statement. I want to make is that? understanding of what you’re made of the particles and the forces the laws that they obey is True it’s not gonna go away it’s not like epicycles or Phlogiston or caloric these ideas that we had in the past that we showed later were completely wrong It’s an idea that a thousand years from now or a million years from now We’re still going to believe that these particles exist that the rules that we now know are Accurate ways of talking about how they behave inside you we might get a deeper understanding You might realize that space and time themselves aren’t fundamental We certainly don’t know how to take these laws and build them up to make biology in chemistry and economics or anything like that but at this particular level What are the particles and forces that you and I are made out of what are the equations that tell us how they behave? we know that and I know that you don’t believe me because I’m just showing you a cartoon. You’re thinking to yourself I’m not gonna believe this until I see the equation so here you go This is the equation I’m very grateful to the Royal Institution for giving me these six hours, so I can explain All of the terms in this equation in great detail, but that’s okay you don’t need to know all the details as you see from the labels on the equation this is a single equation that more or less is the information that the modern-day version of Laplace’s daemon would need to tell you what happens in the world This is the answer to the question you tell me what the configuration of stuff in the world is right now This equation tells you what it will be a little bit in the future what it was a little bit in the past It’s a quantum mechanical equation so if you observe the system one of the things about quantum mechanics is you can only predict probabilities not certainties But this is the equation that tells you what those probabilities are it includes quantum mechanics space-time All the matter particles that were made of as well as all the forces that we know about and of course the Higgs field Lurking in the background that we finally had evidence for back in 2012 What you don’t see in this picture? Is anything that Aristotle would recognize as a final cause or anything that Leibniz would recognize as the? Reason why a certain event is happening the language being spoken here, is that of patterns and differential equations? not of causes purposes Meanings, and there’s no values here. There’s no judgments this equation what we call the core theory of physics Which has all the particle physics and also all the gravity that we know about the core theory doesn’t pass judgment on you Or me, it doesn’t tell us. What is right from wrong. It just tells you what is going to happen? Now even though. I show you the equation you might still not be happy because you say well I only trust equations that can fit on a t-shirt So I had the experimental evidence that The core theory can fit on a t-shirt. We’re in good shape now I Know what you’re thinking. I’ve given this talk before different forms You’re thinking fine you guys you physicists you have your particles and your forces But it’s just the same kind of hubris to say that we’re not going to discover new Particles and forces that you don’t know about yet. How do you know that there’s not new particles mr.? smartypants physicist, and of course, there’s two answers for that one is it’s almost certainly true that there are New particles and forces that we’ve not yet discovered remember all I’m claiming is that we’ve discovered the particles and forces relevant to our everyday lives as a Working theoretical physicist, I certainly hope there are new particles and forces in understanding I’m I’m just saying that whatever we discover along those lines is not going to affect your biology It’s not gonna affect your psychology It’s not gonna affect the motion of the particles that do make up you that we know about right now So how do we know that that’s a very grandiose claim? It’s one that we really could not have made in years past it turns out to be a very specific feature of the way That this equation works, it is based on the principles of what we call quantum field theory field theory is the idea that what you think is a particle like an electron or a photon is really a vibration in a field filling all of space Why does it look like a particle instead of looking like a field? That’s where the quantum comes in quantum says that when you look at these things that make up the world They come to you in discrete packets of stuff we call those packets of stuff Particles so quantum field theory says the world is made of fields But quantum mechanics gives us the rules for observing them so we can talk about them in terms of particles And then it goes on to draw implications from that idea So here’s one simple implication of quantum field theory called crossing symmetries that Usually taught is a little technical tool in quantum field theory, but it actually has extremely profound implications So let’s say we imagine that there is a particle or a force or a field that we haven’t yet found in our Experiments that might in fact play an important role in human biology or neuroscience. How would that work? Well the first thing that a physicists would do given the proposition that there’s a new particle is started drawing these pictures What are called Fineman diagrams named after richard fineman my predecessor at Caltech my most famous? Accomplishment as a physicist is I sit at the desk at Richard iemon used to sit at it Is the desk given to the most senior theoretical physicist at Caltech? Who is not senior enough to get a brand new desk when they get there so I got that one These fireman diagrams do two things the number one show us what can happen they are pictures of actual Processes so the diagram on the left you have an ordinary particle at the bottom Let’s say a proton at the top the red line is some new particles some particle that we’ve hypothesized And we’re imagining there’s some new interaction or some old interaction maybe electromagnetism or the weak nuclear force via which this new particle can interact with the particle that we know about the proton so you read the diagram from left to right it says that the new particle comes in a proton comes in and they scatter off of each other by exchanging Some bows on some photon or some new boson that we haven’t heard about okay Number one the diet the diagram tells you that can happen but number two there are rules for attaching numbers to these diagrams So if you’re a graduate student in physics this diagram Will strike fear into your heart because you go oh no I have to calculate a scattering amplitude and the diagram lets you do that it tells you the probability the two particles will come in and scatter off Now crossing symmetry is a feature of quantum field theory that says given this diagram given some new particle They could in principle interact with an old particle that I know I have inside me I can rotate the diagram by 90 degrees and I get a new diagram That is a little bit different when I rotate it. You know time goes from left to right in these diagrams There’s this There’s a little technical rule that if a line gets flipped from going left to right from to going right to left I exchange a particle with an anti particle We’re not at that level of detail here, but the point is that rotated diagram gives me a new process with the same probability The same quantum amplitude as the old process has in other words if the thing on the Left can happen where the new particle and the old particles scatter off each other then the thing on the right can happen where to existing particles two protons or two electron or something like that can annihilate into each other and create this new particle you can produce the new particle it can’t hide from you and This idea that we smash particles together and look to see what comes out and hope that new particles comes out That is what particle physicists do we’ve been smashing particles together for decades electrons and other electrons electrons and positrons protons and protons protons and antiprotons Neutrons, we’ve smashed everything together that we have in the core theory of particle physics We’ve seen what comes out? That’s how we discovered the Higgs boson at the Large Hadron Collider in 2012 is It possible that there are particles that exist that haven’t yet been produced in this way sure But we know what that would mean either They interact with ordinary matters, so weakly that you can’t make them Then you smash literally billions of particles together and no none of these new particles are created. That’s possible But if that’s possible then they’re not gonna play an important role in you there. You can’t make them They’re just irrelevant to the processes that describe the atoms and the molecules inside you The other possibility is that you do make them, but then they quickly decay away That’s what happens with the Higgs boson for example the Higgs boson you make it then it decays away in one Zepto second Zepto second is a very short period of time 10 to the minus 21 seconds so we say we’ve discovered the Higgs boson at CERN. We’ve never seen a Higgs boson We’ve seen the thing the Higgs bosons decay into and if that’s the way that these particles have avoided being seen then again They’re not relevant to you. And me if you did have any in your brain. They would decay away in a Zepto second or less This is why we can make this kind of statement about our knowledge of the laws of physics underlying everyday life It’s certainly you’re welcome to imagine other new particles and forces But if they were there, and they were strongly interacting enough with you and me to be relevant to our everyday lives We would have seen them already and we do not So we know what you and I are made out What is remaining to do is to match this underlying core theory? equation to the everyday life that we see and that’s where this principle called emergence comes in that we have different Vocabularies different stories we can tell about the world at different levels of detail The story of the core theory with the particles the electrons and the quantum fields bumping into each other. That’s the microscopic Version of reality our best current microscopic description we may in the future do get even deeper layers But the layer that we have right now won’t go away and that microscopic description is a story of particles fields differential equations the macroscopic world that we are familiar with in our everyday lives that Aristotle knew about Speaks a completely different language There is dissipation there’s cause and effect There’s a natural state for things to move in there are reasons why? Things happen rather than not happen and much of this is due to this first Item on the list here the arrow of time the difference between past and future The arrow of time is something that is absolutely central to how we think about the world it is so central that you don’t notice It is a thing Aristotle who wrote books on absolutely everything from metaphysics to drama Never talked about the arrow of time of course the past is different from the future. That’s just an obvious thing. What is it? What are you even asking that question about? But there’s no arrow of time in the core theory equation there was no arrow of time in Newton’s equations for describing the world The best since the time of Isaac Newton the best ways we have of describing the world at the most fundamental Microscopic level do not distinguish between past and future in any way Despite that the world in which we live obviously does Just doing distinguish between the past and future in many ways we remember what happened yesterday. We don’t remember the future I hope nobody here remembers the future You can make choices right so like right now you could decide That you think this is the most boring lecture you’ve ever heard you can leave you don’t need to be here for the next half of the lecture But you cannot right now decide not to have come to the lecture you Cannot make a decision that affects the past right there’s an asymmetry of influence where does that come from? If the underlying law is to treat the past and future symmetrically Well, it’s all comes down to this egg breaking if you understand the egg breaking you understand Why all these things are true this egg breaking illustrates the increase of entropy or disorderliness the second law of? Thermodynamics, which is going to be a theme of the Royal Institution advent calendar entropy increases You clean your room you leave it to its own devices your room gets Messier over time That’s a fundamental law of physics of course you can clean it again But that’s because your room is not a closed system in an isolated system or in the universe as a whole entropy increases the universe becomes more disorderly the reason why is because there are more ways to be Low and more ways to be high Entropy than to be low entropy you give me an orderly arrangement like an unbroken egg. It is easy to break it There’s a lot more ways to arrange the molecules in the egg in the form of a broken egg or scrambled eggs Then there are in a very delicately chosen arrangement of the unbroken egg That’s half of the reason why there is an arrow of time There’s more ways to be high entropy to be low entropy, but the other half is the universe was low entropy in the past That’s more of a puzzle. Why was the universe lower entropy more orderly yesterday than it is today? I can tell you the answer. It’s because it was even lower Entropy the day before yesterday And the reason why that’s true is because it was even lower entropy the day before that and this logic goes back 13.8 billion years to the Big Bang there’s no fundamental arrow of time or just like there’s no fundamental arrow of space in the laws of physics if you were an Astronaut doing experiments, there’d be no difference being up down left right forward backward in front of you You could rotate yourself out there in space it wouldn’t make any difference Here in this room. There’s an arrow of space if I let go the book it falls. I could predict What direction it’s gonna fall in it goes down? We don’t think that’s built into the nature of reality? We think it’s because we live in the vicinity of an influential object namely the earth What I’m telling you is that the arrow of time is exactly the same way. It’s tempting It’s natural to think that the difference between past and future is somehow inherent in the net in the nature of reality But it’s not it’s because we live in the aftermath of an influential event the Big Bang That had a very low entropy was a very organised system We don’t know why if you want to know why well no one knows Why if you want to think about why I wrote a book that was the first book I wrote from eternity here You can buy that that’s where this figure is from So what this is revealing to us. Is that unlike an Aristotelian view which was? Teleological things were directed toward a future goal. They were headed toward going back to their natural state of being if Anything the macroscopic world is? Economical which is from the greek words start or beginning the special state of the universe was where it began? We don’t know why it began in such a special state, but since then it’s just been winding down That’s all it’s been doing. There is no future goal or place toward which we’re going that increase of entropy is Sufficient to explain all the differences between past and future And we can’t go through all of them that would require another book or another lecture But let’s think about the idea of a memory or a record Some artifact some feature of the present day that gives us knowledge of the past in a reliable way So maybe that’s literally a memory in your head, maybe it’s a photograph maybe you’re walking down the street on the sidewalk you see a broken egg I Claim that the evidence that you have there’s an egg broken on the sidewalk Gives you different leverage over the past than over the future you can ask yourself. What is the future of the egg hold? Well many things are possible right it could just sit there someone could clean it up But dog could come by and eat it. It could be washed away. There’s many different possible futures What was the past of the egg probably like well with very large probability there was an unbroken egg and somebody dropped it right We can say something much more specific and informative about the past given this evidence of the egg right now Then we can about the future. Why is that? Again, if all you knew were the deepest laws of physics that equation I showed you or Newton’s laws or whatever your ability to extrapolate Toward the past and future would be identical you have some knowledge of the worlds present state, but it is incomplete you have this macroscopic configuration of the egg But you don’t know what all the atoms and molecules are doing the number of things the egg could possibly do toward the future is exactly equal to The number of things that could have been doing in the past if all you know is the fundamental laws of physics But you know something else you know that the early universe had a low entropy you know that our past Something that philosophers have sadly labelled the past. Hypothesis is most boring label. I’ve ever heard, but the past. I pathi says the universe started with low entropy and that provides an anchor that provides an Asymmetry between what we know about the past and what we know about the future so you have not only the present information But also that past anchor and that lets you infer features of what actually happened in the past If you have an egg broken on the sidewalk there used to be an unbroken egg if you have a photograph of you Ten years old wearing a red sweater. You probably were wearing a red sweater that day we all know that we’ve all heard right that there’s this general tendency of the universe to wind down and Evolve toward its heat death over time and there is in my country. There’s a controversy over What is called creationism? Some people think that if you think that there’s a fundamental feature of the world where things just go to more more disorderly states that is incompatible with the appearance over a cosmological history of things like you and me Because we’re not low entropy how is it possible that such highly organized things like you and me could just pop into existence in a world that is generally becoming more and more disorganized and Scientists have an immediate glib answer to this the earth and its biosphere is not a closed system It’s not isolated. You can clean your room There are things called refrigerators if you put your bottle of champagne in the refrigerator its entropy will go down as it cools, okay? So therefore there’s no contradiction with the second law of thermodynamics That low entropy things like you and me came to be as the universe expanded and cooled on the other hand Just because you can clean your room doesn’t mean you will Clean your room some of you may have experienced this with children or even yourselves so The fact that the earth is not a closed system allows for the appearance of organized systems like you and me But it doesn’t explain. Why it happened the explanation is of course incomplete We don’t know the full answer But it relies on the fact that there’s a difference between simplicity and complexity there’s an axis if you like between simple systems and complex systems another axis between low entropy organized things and high entropy Disorganized things being disorganized does not mean being simple or being complex Think about one of my favorite examples mixing cream into coffee on the left, you have a low entropy situation all the creams on the top all the coffee’s on the bottom as Time goes on the cream mixes into the coffee on the right you have a high entropy situation everything is mixed together That’s a natural flow of time from past to future But think about the system on the left it is very simple here the technical definition of simplicity vs. Complexity is how long do you have to talk to me? To describe the system in full detail how many bytes of information? Do you need on the Left all the creams on the top all the coffees on the bottom? It’s very simple on the right? Everything is mixed together It’s also very simple It’s in between it’s where those tendrils of cream and coffee are mixing together in some intricate fractal pattern That’s when things look complex So there’s a natural tendency as the universe ages for entropy to increase But at the same time complexity first increases and then decreases It’s not only that complex complex systems are allowed to come into existence When entropy is increasing in a very real sense they do come into existence Because entropy is increasing or at least they can maintain themselves They can maintain structure in order and self-repair Because we’re in a very low entropy universe that is only gradually becoming more and more disorderly And it’s not just cups of coffee and cream that this is true for this is true for the universe So here is the history of our observable universe and a very brief presentation it started out We don’t know what happened at the Big Bang, but one second after the Big Bang We know what the universe was like it was hot dense and smooth That’s it. That’s a very simple explanation a very simple description. I didn’t take that many bites to give it to you as the universe expands and cools It becomes increasingly lumpier because gravity pulls things together So a few hundred thousand years after the Big Bang we get the cosmic background radiation A snapshot of what the universe looked like when it first became transparent Tiny variations in density from place to place, but still pretty smooth Now fourteen billion years after the Big Bang the universe is very complicated. We’ve formed galaxies and stars and planets and Biospheres and lecture halls. It’s a very complicated part of the universe But we can keep going we discovered in 1998 of the universe is not only expanding, but accelerating It’s expanding faster and faster, which means it’s never gonna stop According to our best current theories what will happen is the stars will burn out? 10 to the 15 years 1 quadrillion years from now the last star will stop shining Sorry All those stars are gonna fall into black holes and Stephen Hawking taught us in 1970s that even black holes don’t last forever. They give off radiation So 10 to the 100 years from now What used to be called a Google before the search engine took over the term 10 to 100 years from now? There’ll be nothing left in the observable universe it will literally be nothing but empty space Nothing, but empty space is very simple But it is very high entropy everything’s very far apart, so there’s lots of different arrangements for the things that do exist in the universe So the entropy of this universe just increases, but the complexity first increases and then decreases This is a natural robust generic way that complexity can come into being Well we want to do that’s the easy part well we want to do is take that natural bust simple story and apply to the real evolution of complicated structures like life here on earth so For me the Epiphany was one day I was taking a plane ride to a conference and I was actually interested in the origin of life I was reading a paper a technical paper on the relationship between physics and the origin of life So I’m sitting there reading my paper the guy in the plane seat next to me starts talking And you know as a theoretical physicists and cosmologists you need a lot of people who have furies About the universe that they would like to explain to you So this guy looks at my paper, and he says oh, yes, I’m familiar with that work in fact I can tell you the purpose of life Like okay, long plane ride ahead lay it on me. He said the purpose of life is to hydrogenate carbon dioxide Not what I expected his theory to be Turns out the guy sitting next to me was dr. Michael Russell the Jet Propulsion Laboratory in Pasadena one of the world’s leading researchers on the origin of life What are the odds we turns out we’re going to the same conference so it’s not completely a coincidence everything happens for a reason remember So Mike Russell’s theory which is not universally accepted. We don’t know how life began there are different competing ideas He has one of the good ideas his idea. Is that in certain environments of the early Earth? Were in a low entropy configuration In particular all the carbon atoms were in the form of carbon dioxide which happens to be relatively low entropy Given all the water and hydrogen around them. They could be in the form of methane ch4 That would be a higher entropy configuration in some sense To be a little bit poetic about it it wants to be in the form of methane that would be higher entropy But there is no simple chemical reaction That goes from carbon dioxide to methane while increasing the entropy all along there’s a barrier in between You need to first lower the entropy to get to the higher entropy state So Mike Russell’s idea is that even though? There’s no simple chemical reaction? There is a network of complex chemical reactions that could do the trick and that in the right circumstances that could happen and be self-sustaining and that self-sustaining Metabolism could then break free of its original environment and become the precursor to life So it’s more than just a pretty story. He actually made a prediction He’s a geologist by training And he said you know if this is true there must exist under the ocean floor certain kind of geological formations warm alkaline hydrothermal event hydrothermal vents where this kind of Chemistry is going on and after he made the prediction they found them. This is what you live for in science This is a picture of the lost city hydrothermal formation deep underneath the Atlantic Ocean in the mid-atlantic ridge It’s been it lasts for tens of thousands of years so Mike Russell and other people think that maybe This is the kind of place where life began We don’t know I’m not pushing this theory necessarily what I’m pointing out is that rather than saying? But entropy increases why should something as complex as life ever come to be The it’s very very plausible that the appearance of life Depended on the fact that entropy tends to increase so you actually find the complexity depends on entropy increasing and vice versa the reason why entropy could increase in this system is only because you had a complex Network of reactions and that of course continues to the present day. We live in an open system We live here on earth you ask yourself What good is the Sun? What does the Sun do for us here on earth you might think well we get energy from the Sun? But that’s not quite right It’s true that we get energy from the Sun go we give the same amount of energy back To the universe we radiate back into the universe the same amount of energy that we get from solar radiation The difference is that for every one photon of light we get from the Sun Visible light we radiate twenty photons of infrared light back to the universe with on average one twentieth of the energy each But twenty times the entropy The thing that the Sun gives us is not just energy, but energy in a concentrated low entropy form and we then photosynthesize chew our cod eat our cows give lectures write books all of that all those processes Increase the entropy of the universe along the way then we give it back to the universe in the form of infrared radiation So we are sustained by increasing entropy back in the 1800s. It was a reasonable hypothesis that life Was a thing We thought for instance that heat was a thing if you put a hot object next to a cold object they equilibrates They come to the same temperature, so people said well, that’s kind of like putting two Vessels with a fluid in it the fluid comes to the same level there must be a heat fluid that flows From the hot thing to the cold thing not true. Don’t believe anything I just said heat is not a fluid heat is a feature It is a way of talking about the motions of the atoms and molecules Life is the same way life is not a force or a substance that is in your body And then leaves it is a feature It is a way of talking about what is happening inside you the bad news is that that means it will end someday But we’ll get to that in a second. I have lots of bad news. Don’t don’t worry The good news is that once this happens once you get life once you get this chemical reaction that sustains itself and reproduces and Wants to keep going there’s this wonderful thing that kicks in called evolution If there’s different ways the chemical reaction could arrange itself and some of them will more robust and more likely to survive Professor Darwin would tell you that’s what’s going to happen Those more robust ones are likely to dominate the future ecosystem in that particular environment And what that means is that we can once again change our? vocabularies just as we change our vocabulary – going from particles and atoms to eggs and entropy and and time We can change our vocabulary when we start talking about biology and evolution because the new words that creep into our Vocabulary are words of purpose and reasons why? Why is it that a giraffe has a very long neck? You could say if you want to be annoying about it. Well because of the laws of physics and the initial conditions of the universe That’s why giraffe has its long necks. That’s the answer to every question Why is something true laws of physics and the initial conditions of the universe? But it’s not the only possible answer in fact. It’s not a very sensible Answer right there’s another answer that says well Giraffes had mutations in their genes and some of them got longer necks and those were able to reach Sources of food up on trees that other animals with which they were competing were not able to reach and therefore over successive generations the longer and longer necks survived and flourished And they were naturally selected to be like that so in a very real sense the purpose of the giraffes long neck Is to help it reach food sources that it couldn’t otherwise reach? Where did that purpose come in did it did someone put it there? No it evolved naturally, but that doesn’t mean it’s fake It doesn’t mean it’s an illusion It is a useful emergent vocabulary for talking about what happens at the macroscopic level And you’re probably willing to believe that if I’m just talking about life and biology. It’s where it comes to thinking and Neuroscience and consciousness that people tend to get off the bus and of course just like with the origin of life We don’t understand the origin of consciousness or what it really is well. We can do is suggest occasional steps in the history of life which might help us understand why consciousness became an interesting part of Biology this guy up here the C elegans Nematode kind of flat worm is a little model organism That biologists like to study in your brain the cells doing the thinking are the neurons There’s something like 85 billion neurons in your brain and different neurons are connected to each other and a big project for modern Neuroscience is studying the connectome the way that all the neurons in your brain are connected to each other We’re gonna start with a simpler system. We’re going to start with C elegans. We have its connect on We’ve mapped it out C elegans flatworm has exactly 302 neurons So you can actually count them, and then now you counted them and see how they connect to each other We’re trying to figure out what they’re for what they do in the flatworm. There is a paper that came out I’m not sure if it’s correct or not theoretical physicists remember But there’s a claim that is very interesting one that says they can identify one of those neurons Whose job it is to tell the nematode whether it’s looking at itself or the rest of the world Is this thing in front of me is this dirt does this water, or is this just my tail right? This this one part of one neuron its job is to sort of Have a little bit of self-awareness a little bit of well This is me not the rest of the world and you can see why if that developed just through the natural Fluctuations and mutations of evolution it would be an advantageous thing to keep around we have much more highly developed Self-awareness and you can imagine other steps along the way Malcolm McIver who is a mechanical engineer at Northwestern he studies fish and How in particular fish sense their surroundings? So he points out that a fish with its eyes eyes are very ubiquitous in life They developed multiple independent times in the course of evolution But eyes aren’t that great if you’re underwater you know you can see tens of meters at most the attenuation length of light is just not that far and You’re swimming at meters per second So if you’re a fish every time you see something new you have seconds to react to it Maybe a second right so the evolutionary pressure is to make a decision really quickly is this Food is this friendly, or is this foe and I should run away So you don’t need to think too much if you’re a fish, but when you hop onto land Now the attenuation length of photons is kilometers. You can see off to the horizon. You can see essentially forever It’s possible that you now see something coming long before you need to react So there’s a new evolutionary pressure that starts exerting itself that if you just threw the randomness of evolution develop the ability to contemplate different hypothetical scenarios Then you have a new way of winning the struggle for survival that is to say up on land it pays to develop an imagination not just an awareness of yourself, but the ability to put yourself Hypothetically into different situations and say what is the right thing to do? We don’t know if any of this is right, okay? We don’t know how consciousness evolved or even we don’t even know the right definition of consciousness, but you can imagine stories like this will be put together by the progress of biology and neuroscience over the years the only thing that I really care about I really want to stress is that there’s nothing that we know about? Consciousness that is incompatible with the idea that we are made of the particles and fields of the core theory obeying that equation Here I have a picture of my brain. This is actually my it’s not my brain it’s the skull so I was in it’s not to scale either but I was in a machine M eg Magneto and cephalo gram machine and there were Sensors placed on my skull that looked for magnetic fields you’ve seen fMRI Pictures which are able very very good at locating things spatially in the brain But their time resolution is not very good an M eg has great time resolution because what happens is Your brain is made of particles in the core theory in that includes your neurons so when your neurons talk to each other electrically charged particles race down the neurons and as people who stood at this desk long before me could tell you when charged particles start moving you create a magnetic field so This sense is the magnetic field that those blue, and red splotches are the magnetic Fields the south and north poles coming in and out of my skull when I think a thought This is just a reminder of something you already know which is that thoughts are associated with real physical things happening in your brain They’re not abstract things outside our physical bodies there used to be a theory that they were right Rene Descartes very famously promulgated a theory of mind-body dualism He was a skeptic and he came up with a “Cogito, ergo sum” argument, I think therefore I am, I cannot doubt the existence of my mind because it is the thing doing the doubting But he says it’s very easy for me to doubt the existence of my body so if I can doubt the existence of my body But not the existence of my mind they must be two separate things he wrote books about this became very famous died a tragic death in the cold, but that’s a whole another story, so… There weren’t a lot of tenured faculty ositions at the time of Descartes in the 1600s so one had to be nice to potential patrons So he got to know this young lady Princess Elizabeth of Bohemia His his aim wasn’t very good. They were in exile and didn’t have a lot of money Princess Elizabeth and her family, but fortunately Princess Elizabeth was a genius. She was a wonderful thinker very highly educated She devoured de cartes books and she didn’t agree with what he said And they struck up a correspondence which is a wonderful thing to read I encourage you to go look up Princess Elizabeth’s correspondence with Descartes and Elizabeth says look this mind-body stuff I just don’t know you’re saying that there’s a mind that is literally Immaterial that has no location in space and yet it clearly Influences what our bodies do when I talk presumably my mind has something to do with the words, I’m saying So Elizabeth wants to know how does the immaterial mind? causally affect the material body and Descartes in response drew pictures like this. This is yeah. It was back in the days They were just begin to open people up right so they knew that your brain came in two different hemispheres There seemed to be one organ in the brain that there’s only one of them It was not broken into that was the pineal gland that little teardrop shaped thing right there, so Descartes says well You only have one mind one soul so I bet that the soul talks to your body via the pineal gland Yeah, no one else believed that either in the 1600s. It was not a very effective Hypothesis for understanding. What was going on and so Elizabeth kept pushing on him, and he never really gave a very good answer today We would have a much sharper version of Elizabeth’s question Remember this I know you love this equation right if Princess Elizabeth were here today. She would say Renee Tell me how the immaterial mind pushes around the quantum fields of the core theory this Equation tells me what’s going to happen in the quantum fields of the core theory without any reference to an immaterial mind So you must be saying this equation is wrong in some way. Tell me how and there’s still no answer to that So the conclusion that I want to draw is not that I understand what consciousness is or how it came about But that we should be able to understand it without invoking violations of the physical laws that make up you and me Does that mean that we are non-autonomous robots?
Well, I don’t think so so the philosophy that I try to elucidate in the book is called poetic naturalism The idea is that there’s naturalism says there’s only one world the natural world But poetic means there’s many ways of talking about the world there’s many different levels of description whether it’s atoms versus gas in a room or Emergent purpose for the neck of the giraffe or even things like making choices you can describe yourself as a set of particles and forces obeying the core theory or you can describe yourself as a person and People make choices if you choose to describe yourself using only Atoms and molecules, then there is no such thing as free will and there’s no such thing as the ability to make a choice But if as real actual people do you describe yourself as a person then you can’t help? But attribute to yourself the ability to make choices So if you want to say can free will the ability to make choices be real and true even though we are made of atoms Yes, of course it can in the same way that any emergent property can be real the different vocabularies work within themselves you can’t start a sentence in one language, and then end it in another one and Once you accept that then the same thing goes true for more judgmental value-laden Propositions is there right and wrong is there a way to live in the world with meaning and compassion. Well yes It’s nowhere to be found in the fundamental atoms but nowhere to be found in fundamentals of tables either or water right these are higher level emergent properties and carrying an meaning and purpose are the same kind of thing Now that bothers people because they want things like right and wrong to be objective right even the most hardcore Scientifically minded person wants to say well. I will someday do so much science that I will tell you right from wrong I will discover how to live as a human being I’m here to say that it’s never going to happen more bad news Sorry The good news is that you can choose What to label right and wrong and no one can stop you you construct your own morality the analogy I like to use is think of the rules of chess The rules of chess are not fixed by the laws of physics. We made them up We all agree on that, but that doesn’t mean they’re arbitrary that doesn’t mean you could make up any old rules And they’d be just as good When we made up the rules of chess we had goals in mind And when we make up the rules of right and wrong and living together in the world we likewise have Goals in mind we will not always agree there will always be people who would rather play go than play chess We might have to sort of come to an understanding of what our overlap is, but that doesn’t mean that we’re adrift It doesn’t mean that just because the universe doesn’t tell us how to behave there is no way to behave All right the final piece of bad news. I already sort of foreshadowed this, but you are all going to die so Biologists like to study these scaling relations. How one biological property depends on another one so it turns out that larger animals live longer But their hearts beat slower, and it is particular kind of animals like mammals for example, these effects cancel out, in mammals very roughly speaking Every mammal is granted one and a half billion heartbeats for their lifetime on this axis you can figure out you tell me how heavy an object is a Mammal is I will tell you how fast its heart beats And how long it’s gonna live now we human beings heart beats and you know once per second right 60 or 70 times a minute so that puts us at about 40 years and That’s about right That’s how long we used to live back in the state of nature of course these days we have Obamacare and the National Health and pasteurized milk So we have increased our lifespan We live twice as long as we should so that gives us three billion heartbeats to our lives before we die And if you believe in the core theory do you believe that we are made of particles obeying the laws of physics? Then there is no life after death there’s no place for the information That is contained in your neurons to go when you die because I think neurons and the atoms that are there they stay in your body even when you you die and That can be sad you you might want to be I would have liked to live not maybe forever forever is a long time But I think I could keep things interesting for a few hundred thousand years before they got boring I only get three billion heartbeats and three billion is an interesting number It’s sort of a big number, but it’s not that big. I mean you’ve squandered a couple thousand heartbeats Just over the course of this lecture Knowing that you have about 3 billion heartbeats allocated to you Makes every heartbeat seem precious, right? It’s not just like a little thing that will grow into something After we die because this is it every one of those heartbeats is meaningful to you Because you only have a finite number So the good news. This is not going to sound like good news after all that bad news, but the good news is On the one hand we are very very small ok this is the famous Hubble Ultra Deep Field an image of galaxies if you take us telescope and point it at the sky and You click the shutter on the camera, and you just leave it open This is what you will see if your telescope is the Hubble Space Telescope. This is what you will see Our universe is alive with galaxies our our galaxy the Milky Way has about a hundred billion stars Before last week I was able to say there’s about a hundred billion Galaxies in the observable universe, I don’t know if you following the news But they discovered that the density of galaxies is actually 20 times higher than we thought it was There’s about two trillion galaxies in the observable universe Every one of these dots even tiny dots. That’s a galaxy with a hundred billion stars Who knows how many royal institutions? They have where there’s a lecture going on there with a picture of us up there. We seem very small That’s the that’s the last piece of bad news the good news is We took this picture Right we’re exactly there. You go appreciate the good news We are very very tiny insignificant the universe is not about us if the universe was about us There was some purpose to the world that was for our greater. Glory. We would not be Around a medium sized planet around a medium sized star in a galaxy with 100 billion stars in a universe with two trillion galaxies We’d be more central And if you look at the ancient pictures of the world we were always much more central than the modern view had it despite that we are the little part of the universe in this age when things are complex and interesting that has developed the capacity for self-awareness and Reflection and thinking and rational thought and writing books and buying books by the way and that Should make us feel pretty good. We don’t always do very well at it I think both in my country in yours there are examples in recent political history where things have gone Not right But we have the ability to be rational to think to invent to discover to create new things to care about each other in ways That other parts of the universe just don’t care about each other and that’s that capacity that we have as fleeting as Life is it’s up to us What to make of it the fact that we are made of atoms and particles obeying the laws of physics doesn’t stop us From caring about ourselves the rest of the world our legacies the people next to us right now So that’s a choice that we can make completely compatible with the laws of physics I urge you all to choose very wisely. Thank you