What Is the Meaning of Life? | Sean Carroll

There are certain things we're very confident in that we really believe are true about the universe from the scientific perspective that should bear upon however it is. You want to set up your own view of the meaning of life and where it all came from. Let's get there. I want to start with the very beginning. If it were 2,500 years ago, if we were the ancient Greeks thinking about how stuff worked in the universe, the very first physics questions, right? Think about what Aristotle says about how things move. He says that if something is going to move, you have to push it. If there is motion, it's because there is a mover. There's a natural state of things, which is basically to sit where they want to be and then not move anymore. And guess what? Aristotle is correct if what you want to do is describe the world of your immediate senses. If you want this to move, you have to push it. If I stop pushing it, it will stop moving once again, right? He's not crazy. The car is not going to move unless someone is pushing it. Even if there's a very adorable little puppy dog pushing the car, driving the car, you need some fuel inside to get it to go, okay? It took hundreds of years, a lot of deep thought, to realize that as true as this is for our everyday lives, it's not how the world works at a fundamental level. And by fundamental in this sense, we mean what are the rules so that we can start with them and figure everything else out, rather than starting right at what we immediately see. So what Aristotle says successfully describes what we immediately see, but we can't go deeper with it. It was over a thousand years later that a Persian physicist, actually he was not a physicist, he was a doctor, a medical doctor named Ibn Sina. He's a medical doctor, but in his spare time, he came up with new laws of physics. So he invented something that we now call conservation of momentum. Ibn Sina was the first to point out that if you were moving, but you were moving in vacuum, in empty space, then what would happen is you would continue to move forever at the same velocity. The fact that when you push something and it moves and then stops, that's not a fundamental law of nature. That's just because there's friction in the room, right? There's air resistance, there's the force being acted upon you by the ground and so forth. These days we build spacecraft that are literally out there in empty space and indeed they will move in a straight line more or less at the same speed forever and ever or until something else bumps into them. Now this seems like a really good way to start torturing our undergraduate physics students with puzzles about incline planes and pendulums and things like that, but it's more than that. This is a very profound deep shift in how we think about the nature of the world. In the Aristotelian world, what we thought about at the most fundamental level was a world of purposes and goals, right? There was a reason why something was doing something in a different way. So Aristotle took this to his logical conclusion. The world moves, therefore there must be a mover for the world, a mover that was not itself moved, an unmoved mover, which you could identify with God if you wanted to. This point of view, which was then reified in classical mechanics with Isaac Newton and so forth, says something different. It says that the motion of the world is natural. It does not require an outside mover. It just is what the world wants to do. And as I mentioned, Isaac Newton developed this into a whole theory of mechanics, classical mechanics, right? That's what we really torture our little students with when we say, you know, two balls are hitting each other. You tell me, given where the balls are at the beginning, they're coming in at a certain position with a certain velocity. You tell me how they will scatter off of each other. It wasn't even Newton. It wasn't until quite a long while afterward that Pierre-Simone Laplace realized that there was an enormously important implication of Newtonian physics, of classical mechanics. What we torture our students with is the question, given that you start with two balls coming in at a certain angle, certain position, you tell me where they will go in the future. What Laplace says is, if I believe these equations you tell me, I could just as easily tell you what the balls were doing at the end of the experiment and ask you where they had come from. There is something called conservation of information. Not only is there conservation of momentum, which is pretty straightforward, there's something even deeper about the fundamental nature of reality that the amount of information you need to specify what the world is doing is the same at any one moment of time. And that information, in principle, specifies the entire past and future of the universe. So Laplace invented what we call Laplace's demon. Laplace didn't call it that. He was an atheist. He called it a vast intelligence. He said, imagine there's a vast intelligence that knew the position and velocity of everything in the universe, had infinite computing power, and knew all the laws of physics. To that vast intelligence, the future and the past would be as known and as clear as the present moment is. So what this does is, once and for all, removes the vocabulary of causes and purposes and goals from the fundamental laws of physics. The fundamental laws of physics, in this view, are ones of patterns. If this is happening at one moment, here's what will happen at the next moment. Here's what was happening at the last moment. Why is it that way? That's not a question you're supposed to ask, right? That's not part of the fundamental laws of physics. That's just what they are. Now, of course, this paradigm set up by Isaac Newton, we know better than Isaac Newton now, right? We have quantum mechanics, we have relativity, and so forth, but it's the same basic kind of idea. These days we have what is called the standard model of particle physics. Here's the standard model of particle physics in one short slide. This is the cartoon that you may have seen of an atom, okay? So there's a nucleus with protons and neutrons. Around the protons and neutrons, there are electrons, and the electrons are held to the nucleus by electromagnetism. Inside the protons and neutrons, there are quarks that are held together with gluons, and the spillover from that gluon force holds the protons and neutrons together. Occasionally, there's something called the weak nuclear force that turns a proton into a neutron or vice versa and spits out a neutrino. The whole thing has the property that everything is pulled to everything else by the force of gravity, and meanwhile, everything has a background which we call the Higgs field. That was the last piece of this puzzle. We discovered the vibrations of the Higgs field that we call the Higgs boson just in 2012, okay? So 2012 put the finishing touches on this picture that we now call the standard model of particle physics. Now what I want to claim, you don't have to believe me, right? I mean, I'm gonna say things that I think are true, and honestly you should believe me, but you don't have to. There's no normative force that you have to, but you should understand what I'm saying. What I'm saying is there's plenty that we don't know about the laws of physics, but there's something that we do know. There is a regime, an area of possible applications where we do understand the laws of physics, and that regime, that the domain of validity for the laws as we currently understand them, includes everything going on in this tent. Everything going on in this tent, and for that matter, everything you've ever seen with your eyes, heard with your ears, touched with your fingers, in your life, we understand the laws of physics that govern what those things are. This is what we call the core theory in physics. It's the standard model of particle physics plus Einstein's general relativity. You may have heard that gravity, which general relativity describes, does not play well with quantum mechanics. We don't have a quantum theory of gravity, and that's true, but we have a pretty good quantum theory of gravity. What we don't have is the final quantum theory of gravity. We can't explain the Big Bang or black holes, but if you want to explain why raindrops fall down rather than up, you can explain that in both quantum and gravitational terms right now. So everything that you've ever seen or touched, we have a theory that explains that. Of course, we don't understand dark matter, dark energy, the origin of the universe, and we certainly don't understand how these individual bits and pieces come together to make things like chemicals or aardvarks or financial systems and so forth, okay? Complex phenomena that are beyond the laws of fundamental physics, we certainly have a lot to do in understanding them, but whatever that work will eventually be, it better be compatible with the fundamental laws of physics. I don't understand how the human brain works in any great detail, but I know the brain is made of atoms. So if I'm going to come up with a theory of how the brain works, it better be compatible with the known laws of physics. Now, I know what you're thinking. I would only believe it if they showed me the underlying equations. You've come to the right place. Here you go. The good news is it's only one equation, okay? In Isaac Newton's time, it was F equals ma, Newton's second law, forces, mass times acceleration. If you were Laplace's demon, in a classical world, so someone gave you the billiard balls, the laws of physics you would have in your brain were Newton's laws, and you would know how the billiard balls bumped into each other. If you are a modern quantum mechanical Laplace's demon using the core theory to do your predictions, this is the equation you would use. For more debates, talks, and interviews, subscribe today to the Institute of Art and Ideas at IAI TV.