Sean Carroll Blows Joe Rogan's Mind With Laplace's Demon

the Joe Rogan experience I remember there's a woman who came to the Comedy Store after the last podcast that we did and she apparently is also working on it and she was trying to explain it to me her version of it you know after hearing your version of it was very similar but I believe she was from Romania so she was struggling a little bit with English okay so excited to discuss it it's so fascinating when you see someone who's like for the limited number of how many of you guys there are and gals there are out there I mean whatever the number is when that spark gets ignited and other people start tuning into it she was so excited that this was being discussed on a podcast and she wanted to talk to me about yet to say you know please have more people on please talk about this more you know we need support we need you know it's it is it's it does baffle me a little bit how difficult it is swimming uphill to get more support for this kind of thing because it is just an enormous privilege to be able to call your job thinking about the fundamental nature of reality right like you know I gave my first book tour talk was last Tuesday and I had dinner the night before with you know several philosophers of physics in the New York area if you know from Columbia NYU and Everett and and you know we're all friends and we could talk about you know our cats and our cars but every single word discussed at the table all night long was about the philosophy of his because you guys work in isolation essentially and then when you get together you just you're so pumped up to be discussing these things behind it Souls you know in part yeah I mean I there's no one else in the physics department at Caltech who cares about these issues I mean some of them care in the sense that they are happy that I'm doing it but no one does it ourselves yeah well there's a couple other people in the philosophy department who care about these and the folks you were saying get pushed into philosophy and why why is that I mean is it just because it's so complex that it's so esoteric there's so many people that just they don't do the the support for it's not there but the support for philosophy is more common in mainstream yeah you know there's different kinds of support one kind of support in academia is who do you hire right what what areas do you want like a physics department will generally say yeah we should have some people doing particle physics some people doing astrophysics some people doing condensed matter in solid-state physics and and then and then it becomes hard do we need people doing biophysics do we need people doing this and by the time they get to the foundations of quantum mechanics there's there's usually very little support philosophers there their job is being patient and clarifying difficult conceptual questions and so they get that quantum mechanics is fertile territory for philosophy like it you know one of the big problems in philosophy compared to science is that many of the questions that they're asking cannot be tested experimentally right what is infinity well you know it's hard to do an experiment there but it's important questions right and so you need patience but also it's harder to make progress because it's easy to be trapped by your intuition right like when it's just you thinking and trying to think hard and be rational and so forth it's easy to fall into a trap of well this looks reasonable to me and quantum mechanics doesn't look reasonable to anybody so it's a wonderful corrective it's a wonderful reality check when you think well reality has to be this way and then someone can say well look at quantum mechanics that's different than what you said so philosophy and quantum mechanics they sort of they they share some sort of a border yeah oh yeah absolutely I mean the things so I was always a big fan of philosophy ever since I was an undergraduate and I discovered it for the first time but when I was undergraduate and my favorite philosophy classes were like the philosophy of morality or political philosophy right I took philosophy of science classes but they seemed to be kind of dry to me because they were all about how scientific theories are constructed and chosen you know the structure of scientific revolutions is the famous book that everyone reads people like Thomas Kuhn and Paul fire abend and so forth okay that's interesting but it's sort of meta science right it's like how science is done not how the world and it wasn't until you know circa 2000 that I discovered that there are philosophers of physics who are kind of really doing physics you know that they're not asking how physics works they're asking how the world works but they're asking in a way that is comfortably located in philosophy departments and right now not so much in physics departments there was a part of the book that that shocked me because I had a ridiculous idea once and this idea was not my idea apparently La Paz had a very similar idea as a thought experiment I had an idea once that if one day there was a computer that was so powerful that it could accurately describe every single object on earth that we would be able to figure out the past and La Paz was saying that not only that would he propose for the entire universe like every single object electron everything in the atom in the entire universe that you would not only be able to show the past but also predict the future that's right so this is called Laplace's daemon although he never called to that Pierre Simone Laplace was a brilliant guy he deserves to be much more well known so I base I think I've mentioned him his name in every book that I've ever written for totally different reasons he helped invent probability as we currently understand it for example but yeah so Isaac Newton came up with the rules of classical mechanics in the 1600s but it wasn't until Laplace around the Year 1800 that this implication of classical mechanics was realized it's a clockwork universe that the way classical mechanics works is if you tell me the state of a system right now at one moment by which in classical mechanics you would mean the position and the velocity of every part and you knew the laws of physics and you had arbitrarily large computational capacity Laplace said of vast intelligence okay then to that vast intelligence the past and future would be as determined and known as the present was because that's the clockwork universe as deterministic everything is fixed once you know the present moment now quantum mechanics comes along and throws a spanner into the works a little bit if you're a many-worlds person Laplace is demon still possible so if you know the wave function of the universe exactly and you have infinite calculational capacity you could predict the past and the future with perfect accuracy but what you're predicting is all of the branches of the wave function so any individual person inside the wave function still experiences apparently random events right so you can't predict what will happen to you even if you can predict what will happen to the entire universe whoo Shawn care my goodness there's a lot of people pause in this podcast right now just shaking their head like you know I wrote a little article that just appeared in quantum magazine which by the way if anyone here is a science fan quantum magazine is the best online magazine for science these days they have really really good high-level our articles about all sorts of things and so I wrote an article called what is probability because you know again this is a philosophers kind of question like you're physicist we'll just put it to use and get on with their lives philosophers will say well what do you really mean by probability the traditional answer is if you're flipping a coin and you say it's 5050 what you mean by that is that if you flipped it an infinite number of times half the time it would be heads half the time it would be tails that's what you mean it's called the frequentist idea probability but then what do you say like well what is the probability that Donald Trump wins reelection that's not gonna happen infinite number of times you're not gonna do the experiment or even better what was the probability that Lee Harvey Oswald actually was the lone shooter of JFK that already happened that's in the past right right but we can easily say well I think it was an 80% chance that that's true right so this is called Bayesian probability where rather than thinking of an infinite number of things going on you're assigning a degree of confidence to your lack of perfect knowledge right like I don't know exact there's something yeah there's something going on I don't know what it is so I assign a probability and and that just like a frequency that you know those the the credence as we say that you assigned to these different ideas is a positive number then all the credence is add up to one because something happened so in quantum mechanics is is probability more like frequentist probability or is it more like Bayesian probability the answer is it depends on what your favorite version of quantum mechanics is in one of these spontaneous collapse theories it's very much like a frequency like you know you just things happen randomly and it's purely objective in something like many world well sorry I should say in something like hidden variables its Laplace is demon all over again so Laplace is demon doesn't work in a spontaneous collapse theory because you the laws of physics are not deterministic you don't know when things are gonna collapse all by themselves in a hidden variable Theory the hidden variables and the wavefunction of all deterministically but you don't know what the hidden variables are so you can assign some probability to having them be different things so there's some ignorant involved many-worlds is the coolest idea because it's it's kind of then this is what is kind of hard to wrap your mind around on the one hand there is only the wavefunction it describes the universe exactly but imagine that I measure the spin of an electron okay so I actually do know what the wavefunction is going to evolve into it's gonna evolve into a 50/50 split of I observe that spinning up and I observed it spinning down and then but I only ever find myself in one side or the other so there is always a moment in between when the wavefunction splits and when I know about it it splits much faster than I can know about it the the rate the speed of a wavefunction branching is some incredibly tiny number 10 to the minus 20 seconds or something like that and the timescale of things happening in my brain is like 10 to the minus 3 seconds at best okay so there will always be a time when there are two copies of me one on the branch where the spin was up one on the branch where the spin was down but they're both identical they don't know which branch they're on yet so they need to be good Bayesian z' and say well what probability should I assign that I'm on one branch or the other and it turns out that the probabilities work exactly like the textbook quantum mechanics tells you the probability should work out how's that the wave function squared is the probabilities so there's a function square this is a rule called the born rule after Max Born who was a physicist who invented it so I mean read the book of course but like like you said it to very start the history of quantum mechanics is just so fascinating in hilarious Schrodinger urban furniture of Schrodinger's cat Fame invented the idea of the wavefunction and wrote down the equation that it obeys okay but what he hoped was that if you had the wavefunction of electron all by itself if you solved his equation it would sort of show that the wave function becomes localized peaked at one location the electron kind of acts like a point particle and that's why we see particles that was his hope what actually happens when you solve the equation is that the electron spreads out all throughout the universe so he was his hope was dashed and then he's like alright I had this equation what is it like what is the wave function do and it was Max Born a whole nother guy who said what the wave function does is you square it and that's the probability of seeing something somewhere like if the wave function looks like this it's some spread-out thing there's very small probability over here and large probability over there because the probability is the wave function squared and Schrodinger said like oh my god that's awful I'm sad I had anything to do with it he regretted happy being involved with this whole idea of probabilities and collapses and all that stuff [Applause]

Channel: JRE Clips

Views: 4,142,841

Rating: 4.8517714 out of 5

Keywords: Joe Rogan, JRE, Joe Rogan Experience, JRE Clips, PowerfulJRE, Joe Rogan Fan Page, Joe Rogan Podcast, podcast, MMA, Joe Rogan MMA Show, UFC, comedy, comedian, stand up, funny, clip, favorite, best of

Id: odpq1vjWUXA

Length: 12min 27sec (747 seconds)

Published: Mon Sep 16 2019