back to indexLee Smolin: Quantum Gravity and Einstein's Unfinished Revolution | Lex Fridman Podcast #79
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The following is a conversation with Lee Smolin.
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He's a theoretical physicist,
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co inventor of loop quantum gravity,
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and a contributor of many interesting ideas
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to cosmology, quantum field theory,
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the foundations of quantum mechanics,
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theoretical biology, and the philosophy of science.
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He's the author of several books,
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including one that critiques the state of physics
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and string theory called The Trouble with Physics.
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And his latest book, Einstein's Unfinished Revolution,
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The Search for What Lies Beyond the Quantum.
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He's an outspoken personality in the public debates
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on the nature of our universe,
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among the top minds in the theoretical physics community.
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This community has its respected academics,
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its naked emperors, its outcasts and its revolutionaries,
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its madmen and its dreamers.
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This is why it's an exciting world to explore
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through a long form conversation.
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I recommend you listen back to the episodes
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with Leonard Susskind, Sean Carroll, Michio Okaku,
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Max Tegmark, Eric Weinstein, and Jim Gates.
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You might be asking, why talk to physicists
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if you're interested in AI?
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To me, creating artificial intelligence systems
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requires more than Python and deep learning.
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It requires that we return to exploring
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the fundamental nature of the universe and the human mind.
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Theoretical physicists venture out into the dark,
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mysterious, psychologically challenging place
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of first principles more than almost any other discipline.
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This is the Artificial Intelligence Podcast.
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If you enjoy it, subscribe on YouTube,
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give it five stars on Apple Podcast,
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support it on Patreon, or simply connect with me on Twitter
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at Lex Friedman, spelled F R I D M A N.
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As usual, I'll do one or two minutes of ads now
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and never any ads in the middle
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that can break the flow of the conversation.
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I hope that works for you
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and doesn't hurt the listening experience.
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This show is presented by Cash App,
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one of my favorite organizations
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that is helping to advance robotics and STEM education
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for young people around the world.
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And now, here's my conversation with Lee Smolin.
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Let's start with an easy question.
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Put another way, how do we know what is real
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and what is merely a creation
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of our human perception and imagination?
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I presume we're talking about science.
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And we believe, or I believe,
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that there is a world that is independent of my existence
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and my experience about it and my knowledge of it,
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and this I call the real world.
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So you said science, but even bigger than science, what?
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I need not have said this is science.
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I just was warming up.
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Okay, now that we're warmed up,
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let's take a brief step outside of science.
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Is it completely a crazy idea to you
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that everything that exists is merely a creation
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So there's a few, not many.
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This is outside of science now.
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People who believe sort of perception
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is fundamentally what's in our human perception,
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the visual cortex and so on,
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the cognitive constructs that's being formed there
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And then anything outside is something
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that we can never really grasp.
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Is that a crazy idea to you?
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There's a version of that that is not crazy at all.
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What we experience is constructed by our brains
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and by our brains in an active mode.
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So we don't see the raw world.
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We see a very processed world.
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We feel something that's very processed through our brains
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and our brains are incredible.
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But I still believe that behind that experience,
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that mirror or veil or whatever you wanna call it,
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there is a real world and I'm curious about it.
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Can we truly, how do we get a sense of that real world?
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Is it through the tools of physics,
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from theory to the experiments?
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Or can we actually grasp it in some intuitive way
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that's more connected to our ape ancestors?
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Or is it still fundamentally the tools of math and physics
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that really allow us to grasp it?
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Well, let's talk about what tools they are.
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What you say are the tools of math and physics.
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I mean, I think we're in the same position
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as our ancestors in the caves
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or before the caves or whatever.
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We find ourselves in this world and we're curious.
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We also, it's important to be able to explain
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what happens when there are fires, when there are not fires,
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what animals and plants are good to eat and all that stuff.
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But we're also just curious.
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We look up in the sky and we see the sun and the moon
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and the stars and we see some of those move
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and we're very curious about that.
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And I think we're just naturally curious.
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So we make, this is my version of how we work.
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We make up stories and explanations.
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And where there are two things
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which I think are just true of being human,
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we make judgments fast because we have to.
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Where to survive, is that a tiger or is that not a tiger?
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We have to act fast on incomplete information.
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So we judge quickly and we're often wrong
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or at least sometimes wrong, which is all I need for this.
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We're often wrong.
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So we fool ourselves and we fool other people readily.
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And so there's lots of stories that get told
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and some of them result in a concrete benefit
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and some of them don't.
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So you said we're often wrong,
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but what does it mean to be right?
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Right, that's an excellent question.
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To be right, well since I believe that there is a real world,
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I believe that to be, you can challenge me on this
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if you're not a realist.
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A realist is somebody who believes
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in this real objective world
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which is independent of our perception.
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If I'm a realist, I think that to be right
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is to come closer.
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I think first of all, there's a relative scale.
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There's not right and wrong.
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There's right or more right and less right.
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And you're more right if you come closer
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to an exact true description of that real world.
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Now can we know that for sure?
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And the scientific method is ultimately
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what allows us to get a sense
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of how close we're getting to that real world?
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First of all, I don't believe there's a scientific method.
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I was very influenced when I was in graduate school
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by the writings of Paul Fireman
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who was an important philosopher of science
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who argued that there isn't a scientific method.
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There is or there is not?
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Can you elaborate, I'm sorry if you were going to,
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but can you elaborate on what does it mean
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for there not to be a scientific method,
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this notion that I think a lot of people believe in
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in this day and age?
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Paul Fireman, he was a student of Popper
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who taught Karl Popper.
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And Fireman argued both by logic
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and by historical example that you name anything
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that should be part of the practice of science.
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Say you should always make sure that your theories agree
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with all the data that's already been taken.
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And he'll prove to you that there have to be times
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when science contradicts, when some scientist contradicts
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that advice for science to progress overall.
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So it's not a simple matter.
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I think that, I think of science as a community.
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Of people and as a community of people
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bound by certain ethical precepts,
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precepts, whatever that is.
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So in that community, a set of ideas they operate under,
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meaning ethically of kind of the rules of the game
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they operate under.
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Don't lie, report all your results,
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whether they agree or don't agree with your hypothesis.
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Check the training of a scientist.
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Mostly consists of methods of checking
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because again, we make lots of mistakes.
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We're very error prone.
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But there are tools both on the mathematics side
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and the experimental side to check and double check
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And a scientist goes through a training
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and I think this is part of it.
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You can't just walk off the street and say,
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yo, I'm a scientist.
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You have to go through the training
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and the training, the test that lets you be done
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with the training is can you form a convincing case
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for something that your colleagues
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will not be able to shout down
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because they'll ask, did you check this?
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And did you check that?
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And did you check this?
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And what about seeming contradiction with this?
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And you've got to have answers to all those things
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or you don't get taken seriously.
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And when you get to the point where you can produce
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that kind of defense and argument,
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then they give you a PhD.
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And you're kind of licensed.
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You're still gonna be questioned
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and you still may propose or publish mistakes.
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But the community is gonna have to waste less time
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fixing your mistakes.
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Yes, but if you can maybe linger on it a little longer,
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what's the gap between the thing that that community does
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and the ideal of the scientific method?
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The scientific method is you should be able
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to repeat and experiment.
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There's a lot of elements to what construes
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the scientific method, but the final result,
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the hope of it is that you should be able to say
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with some confidence that a particular thing
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is close to the truth.
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Right, but there's not a simple relationship
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between experiment and hypothesis or theory.
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For example, Galileo did this experiment
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of dropping a ball from the top of a tower
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and it falls right at the base of the tower.
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And an Aristotelian would say, wow,
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of course it falls right to the base of the tower.
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That shows that the earth isn't moving
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while the ball is falling.
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And Galileo says, no way, there's a principle of inertia
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and it has an inertia in the direction
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where the earth isn't moving and the tower
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and the ball and the earth all move together.
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When the principle of inertia tells you it hits the bottom,
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it does look, therefore my principle of inertia is right.
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And Aristotelian says, no, our style of science is right.
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The earth is stationary.
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And so you gotta get an interconnected bunch of cases
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and work hard to line up and explain.
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It took centuries to make the transition
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from Aristotelian physics to the new physics.
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It wasn't done until Newton in 1680 something, 1687.
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So what do you think is the nature of the process
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that seems to lead to progress?
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If we at least look at the long arc of science,
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of all the community of scientists,
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they seem to do a better job of coming up with ideas
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that engineers can then take on and build rockets with
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or build computers with or build cool stuff with.
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I don't know, a better job than what?
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Than this previous century.
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So century by century, we'll talk about string theory
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and so on and kind of possible,
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what you might think of as dead ends and so on.
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Which is not the way I think of string theory.
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We'll straighten out, we'll get all the strings straight.
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But there is, nevertheless in science, very often,
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at least temporary dead ends.
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But if you look at the, through centuries,
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the century before Newton and the century after Newton,
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it seems like a lot of ideas came closer to the truth
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that then could be usable by our civilization
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to build the iPhone, right?
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To build cool things that improve our quality of life.
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That's the progress I'm kind of referring to.
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Let me, can I say that more precisely?
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Yes, well, it's a low bar.
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Because I think it's important to get the time places right.
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There was a scientific revolution that partly succeeded
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between about 1900 or late 1890s
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and into the 1930s, 1940s and so.
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And maybe some, if you stretched it, into the 1970s.
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And the technology, this was the discovery of relativity
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and that included a lot of developments of electromagnetism.
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The confirmation, which wasn't really well confirmed
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into the 20th century, that matter was made of atoms.
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And the whole picture of nuclei with electrons going around,
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this is early 20th century.
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And then quantum mechanics was from 1905,
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took a long time to develop, to the late 1920s.
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And then it was basically in final form.
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And the basis of this partial revolution,
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and we can come back to why it's only a partial revolution,
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is the basis of the technologies that you mentioned.
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All of, I mean, electrical technology
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was being developed slowly with this.
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And in fact, there's a close relation
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between the development of electricity
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and the electrification of cities in the United States
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and Europe and so forth.
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And the development of the science.
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The fundamental physics since the early 1970s
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doesn't have a story like that so far.
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There's not a series of triumphs and progresses
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and there's not any practical application.
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So just to linger briefly on the early 20th century
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and the revolutions in science that happened there,
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what was the method by which the scientific community
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kept each other in check about when you get something right,
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when you get something wrong?
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Is experimental validation ultimately the final test?
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It's absolutely necessary.
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And the key things were all validated.
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The key predictions of quantum mechanics
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and of the theory of electricity and magnetism.
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So before we talk about Einstein, your new book,
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before String Theory, Quantum Mechanics, so on,
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let's take a step back at a higher level question.
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What is that you mentioned?
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What is anti realism?
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And maybe why do you find realism,
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as you mentioned, so compelling?
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Well, realism is the belief in an external world
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independent of our existence, our perception,
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our belief, our knowledge.
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A realist as a physicist is somebody who believes
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that there should be possible some completely objective
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description of each and every process
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at the fundamental level, which describes and explains
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exactly what happens and why it happens.
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That kind of implies that that system,
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in a realist view, is deterministic,
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meaning there's no fuzzy magic going on
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that you can never get to the bottom,
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or you can get to the bottom of anything
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and perfectly describe it.
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Some people would say that I'm not that interested
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in determinism, but I could live with the fundamental world,
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which had some chance in it.
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So do you, you said you could live with it,
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but do you think God plays dice in our universe?
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I think it's probably much worse than that.
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In which direction?
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I think that theories can change,
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and theories can change without warning.
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I think the future is open.
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You mean the fundamental laws of physics can change?
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Oh, okay, we'll get there.
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I thought we would be able to find some solid ground,
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but apparently the entirety of it, temporarily so, probably.
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Okay, so realism is the idea that while the ground
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is solid, you can describe it.
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What's the role of the human being,
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our beautiful, complex human mind in realism?
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Do we have a, are we just another set of molecules
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connected together in a clever way,
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or the observer, does the observer, our human mind,
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consciousness, have a role in this realism view
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of the physical universe?
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There's two ways, there's two questions you could be asking.
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One, does our conscious mind, do our perceptions
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play a role in making things become,
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in making things real or things becoming?
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That's question one.
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Question two is, does this, we can call it
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a naturalist view of the world that is based on realism,
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allow a place to understand the existence of
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and the nature of perceptions and consciousness in mind,
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and that's question two.
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Question two, I do think a lot about,
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and my answer, which is not an answer, is I hope so,
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but it certainly doesn't yet.
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Question one, I don't think so.
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But of course, the answer to question one
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depends on question two.
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So I'm not up to question one yet.
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So question two is the thing that you can kind of
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struggle with at this time.
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That's, what about the anti realists?
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So what flavor, what are the different camps
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of anti realists that you've talked about?
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I think it would be nice if you can articulate
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for the people for whom there is not
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a very concrete real world, or there's divisions,
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or it's messier than the realist view of the universe,
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what are the different camps, what are the different views?
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I'm not sure I'm a good scholar and can talk about
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the different camps and analyze it,
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but some, many of the inventors of quantum physics
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were not realists, were anti realists.
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Their scholars, they lived in a very perilous time
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between the two world wars.
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And there were a lot of trends in culture
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which were going that way.
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But in any case, they said things like,
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the purpose of science is not to give an objective
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realist description of nature as it would be
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This might be saying Niels Bohr.
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The purpose of science is as an extension
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of our conversations with each other
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to describe our interactions with nature.
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And we're free to invent and use terms like
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particle, or wave, or causality, or time, or space.
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If they're useful to us, and they carry some
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intuitive implication, but we shouldn't believe
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that they actually have to do with what nature
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would be like in our absence,
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which we have nothing to say about.
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Do you find any aspect of that,
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because you kind of said that we human beings
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tell stories, do you find aspects of that
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kind of anti realist view of Niels Bohr compelling?
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That we fundamentally are storytellers,
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and then we create tools of space, and time,
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and causality, and whatever this fun quantum
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mechanic stuff is to help us tell the story of our world.
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Sure, I just would like to believe that there's
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an aspiration for the other thing.
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The other thing being what?
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The realist point of view.
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Do you hope that the stories will eventually lead us
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to discovering the real world as it is?
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Is perfection possible, by the way?
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Well that's, you mean will we ever get there
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and know that we're there?
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That's not my, that's for people 5,000 years in the future.
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We're certainly nowhere near there yet.
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Do you think reality that exists outside of our mind,
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do you think there's a limit to our cognitive abilities?
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Is, again, descendants of apes,
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who are just biological systems,
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is there a limit to our mind's capability
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to actually understand reality?
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Sort of, there comes a point,
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even with the help of the tools of physics,
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that we just cannot grasp some fundamental aspects
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Again, I think that's a question
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for 5,000 years in the future.
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We're not even close to that limit.
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I think there is a universality.
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Here, I don't agree with David Deutsch about everything,
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but I admire the way he put things in his last book.
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And he talked about the role of explanation.
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And he talked about the universality of certain languages
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or the universality of mathematics
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or of computing and so forth.
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And he believed that universality,
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which is something real,
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which somehow comes out of the fact
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that a symbolic system or a mathematical system
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can refer to itself and can,
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I forget what that's called,
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can reference back to itself and build,
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in which he argued for a universality of possibility
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for our understanding, whatever is out there.
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But I admire that argument,
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but it seems to me we're doing okay so far,
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but we'll have to see.
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Whether there is a limit or not.
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For now, we've got plenty to play with.
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There are things which are right there in front of us
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And I'll quote my friend, Eric Weinstein,
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in saying, look, Einstein carried his luggage.
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Freud carried his luggage.
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Marx carried his luggage.
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Martha Graham carried her luggage, et cetera.
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Edison carried his luggage.
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All these geniuses carried their luggage.
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And not once before relatively recently
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did it occur to anybody to put a wheel on luggage
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And it was right there waiting to be invented
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So this is Eric Weinstein.
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What do the wheels represent?
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Are you basically saying that there's stuff
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right in front of our eyes?
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That once we, it just clicks,
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we put the wheels on the luggage,
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a lot of things will fall into place.
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And every day I wake up and think,
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why can't I be that guy who was walking through the airport?
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What do you think it takes to be that guy?
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Because like you said,
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a lot of really smart people carried their luggage.
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What, just psychologically speaking,
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so Eric Weinstein is a good example of a person
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who thinks outside the box.
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Who resists almost conventional thinking.
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You're an example of a person who by habit,
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by psychology, by upbringing, I don't know,
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but resists conventional thinking as well,
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Thank you, that's a compliment.
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That's a compliment?
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So what do you think it takes to do that?
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Is that something you were just born with?
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Well, from my studying some cases,
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because I'm curious about that, obviously,
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and just in a more concrete way,
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when I started out in physics,
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because I started a long way from physics,
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so it took me a long, not a long time,
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but a lot of work to get to study it and get into it,
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so I did wonder about that.
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And so I read the biographies,
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and in fact, I started with the autobiography of Einstein
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and Newton and Galileo and all those people.
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And I think there's a couple of things.
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Some of it is luck, being in the right place
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at the right time.
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Some of it is stubbornness and arrogance,
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which can easily go wrong.
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And I know all of these are doorways.
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If you go through them slightly at the wrong speed
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or in the wrong angle, they're ways to fail.
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But if you somehow have the right luck,
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the right confidence or arrogance, caring,
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I think Einstein cared to understand nature
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with ferocity and a commitment that exceeded
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other people of his time.
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So he asked more stubborn questions.
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He asked deeper questions.
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I think, and there's a level of ability
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and whether ability is born in or can be developed
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to the extent to which it can be developed,
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like any of these things like musical talent.
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So you mentioned ego.
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What's the role of ego in that process?
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But in your own life, have you found yourself
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walking that nice edge of too much or too little,
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so being overconfident and therefore
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leaning yourself astray or not sufficiently confident
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to throw away the conventional thinking
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of whatever the theory of the day, of theoretical physics?
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I don't know if I, I mean, I've contributed
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where I've contributed, whether if I had had
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more confidence in something, I would have gotten further.
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Certainly, I'm sitting here at this moment
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with very much my own approach to nearly everything.
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And I'm calm, I'm happy about that.
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But on the other hand, I know people
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whose self confidence vastly exceeds mine.
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And sometimes I think it's justified
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and sometimes I think it's not justified.
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Your most recent book titled
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Einstein's Unfinished Revolution.
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So I have to ask, what is Einstein's unfinished revolution
link |
and also how do we finish it?
link |
Well, that's something I've been trying to do my whole life,
link |
but Einstein's unfinished revolution
link |
is the twin revolutions which invented relativity theory,
link |
special and especially general relativity,
link |
and quantum theory, which he was the first person
link |
to realize in 1905 that there would have to be
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a radically different theory which somehow realized
link |
or resolved the paradox of the duality
link |
of particle and wave for photons.
link |
And he was, I mean, people I think don't always
link |
associate Einstein with quantum mechanics
link |
because I think his connection with it,
link |
founding as one of the founders,
link |
I would say, of quantum mechanics,
link |
he kind of put it in the closet.
link |
Well, he didn't believe that the quantum mechanics
link |
as it was developed in the mid to late 1920s
link |
was completely correct.
link |
At first, he didn't believe it at all.
link |
Then he was convinced that it's consistent,
link |
but incomplete, and that also is my view.
link |
It needs, for various reasons, I can elucidate,
link |
to have additional degrees of freedom, particles,
link |
forces, something to reach the stage
link |
where it gives a complete description of each phenomenon,
link |
as I was saying, realism demands.
link |
So what aspect of quantum mechanics
link |
bothers you and Einstein the most?
link |
Is it some aspect of the wave function collapse discussions,
link |
the measurement problem?
link |
The measurement problem.
link |
I'm not gonna speak for Einstein.
link |
But the measurement problem, basically, and the fact that.
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What is the measurement problem, sorry?
link |
The basic formulation of quantum mechanics
link |
gives you two ways to evolve situations in time.
link |
One of them is explicitly when no observer is observing
link |
and no measurement is taking place.
link |
And the other is when a measurement
link |
or an observation is taking place.
link |
And they basically contradict each other.
link |
But there's another reason why the revolution
link |
was incomplete, which is we don't understand
link |
the relationship between these two parts.
link |
General relativity, which became our best theory
link |
of space and time and gravitation and cosmology,
link |
and quantum theory.
link |
So for the most part, general relativity
link |
describes big things.
link |
Quantum theory describes little things.
link |
And that's the revolution that we found
link |
really powerful tools to describe
link |
big things and little things.
link |
And it's unfinished because we have
link |
two totally separate things and we need to figure out
link |
how to connect them so we can describe everything.
link |
Right, and we either do that if we believe quantum mechanics
link |
as understood now is correct by bringing general relativity
link |
or some extension of general relativity
link |
that describes gravity and so forth
link |
into the quantum domain that's called quantize,
link |
the theory of gravity.
link |
Or if you believe with Einstein
link |
that quantum mechanics needs to be completed,
link |
and this is my view, then part of the job
link |
of finding the right completion
link |
or extension of quantum mechanics
link |
would be one that incorporated space, time, and gravity.
link |
So, where do we begin?
link |
So first, let me ask, perhaps you can give me a chance,
link |
if I could ask you some just really basic questions.
link |
Well, they're not at all.
link |
The basic questions are the hardest,
link |
but you mentioned space, time.
link |
What is space, time?
link |
Space, time, you talked about a construction.
link |
So I believe the space, time is an intellectual construction
link |
that we make of the events in the universe.
link |
I believe the events are real,
link |
and the relationships between the events,
link |
which cause which are real.
link |
But the idea that there's a four dimensional
link |
smooth geometry which has a metric and a connection
link |
and satisfies the equations that Einstein wrote,
link |
it's a good description to some scale.
link |
It's a good approximation, it captures some
link |
of what's really going on in nature.
link |
But I don't believe it for a minute is fundamental.
link |
So, okay, we're gonna allow me to linger on that.
link |
So the universe has events, events cause other events.
link |
This is the idea of causality.
link |
Okay, so that's real.
link |
In your view is real.
link |
Or hypothesis, or the theories that I have been working
link |
to develop make that assumption.
link |
So space, time, you said four dimensional space
link |
is kind of the location of things,
link |
and time is whatever the heck time is.
link |
And you're saying that space, time is,
link |
both space and time are emergent and not fundamental?
link |
Sorry, before you correct me,
link |
what does it mean to be fundamental or emergent?
link |
Fundamental means it's part of the description
link |
as far down as you go.
link |
We have this notion.
link |
As real as real it could be.
link |
Yeah, so I think that time is fundamental,
link |
and quote goes all the way down,
link |
and space does not, and the combination of them
link |
we use in general relativity that we call space time
link |
But what is time then?
link |
I think that time, the activity of time
link |
is a continual creation of events from existing events.
link |
So if there's no events, there's no time.
link |
Then there's not only no time, there's no nothing.
link |
So I believe the universe has a history
link |
which goes to the past.
link |
I believe the future does not exist.
link |
There's a notion of the present
link |
and a notion of the past,
link |
and the past consists of,
link |
is a story about events that took place to our past.
link |
So you said the future doesn't exist.
link |
Could you say that again?
link |
Can you try to give me a chance to understand that
link |
So events cause other events.
link |
What is this universe?
link |
Cause we'll talk about locality and nonlocality.
link |
Cause it's a crazy, I mean it's not crazy,
link |
it's a beautiful set of ideas that you propose.
link |
But, and if Kozali is fundamental,
link |
I'd just like to understand it better.
link |
What is the future?
link |
What is the flow of time?
link |
Even the error of time in our universe, in your view.
link |
And maybe what's an event, right?
link |
Oh, an event is where something changes,
link |
it's hard to say because it's a primitive concept.
link |
An event is a moment of time within space.
link |
This is the view in general relativity,
link |
where two particles intersect in their paths,
link |
or something changes in the path of a particle.
link |
Now, we are postulating that there is,
link |
at the fundamental level, a notion,
link |
which is an elementary notion,
link |
so it doesn't have a definition in terms of other things,
link |
but it is something elementary happening.
link |
And it doesn't have a connection to energy,
link |
or matter, or exchange of energy?
link |
It does have a connection to energy and matter.
link |
So it's at that level.
link |
Yeah, it involves,
link |
and that's why the version of a theory of events
link |
that I've developed with Marina Cortez,
link |
and it's, by the way, I wanna mention my collaborators,
link |
because they've been at least as important
link |
in this work as I have.
link |
It's Marina Cortez in all the work since about 2013,
link |
2012, 2013, about causality, causal sets.
link |
And in the period before that, Roberta Mangibera Unger,
link |
who is a philosopher and a professor of law.
link |
And that's in your efforts,
link |
together with your collaborators,
link |
to finish the unfinished revolution.
link |
And focus on causality as a fundamental.
link |
As fundamental to physics.
link |
And there's certainly other people we've worked with,
link |
but those two people's thinking
link |
had a huge influence on my own thinking.
link |
So in the way you describe causality,
link |
that's what you mean of time being fundamental.
link |
That causality is fundamental.
link |
And what does it mean for space to not be fundamental,
link |
There's a level of description in which there are events,
link |
there are events create other events,
link |
but there's no space.
link |
They don't live in space.
link |
They have an order in which they caused each other.
link |
And that is part of the nature of time for us.
link |
But there is an emergent approximate description.
link |
And you asked me to define emergent.
link |
An emergent property is a property
link |
that arises at some level of complexity,
link |
larger than and more complex than the fundamental level,
link |
which requires some property to describe it,
link |
which is not directly
link |
explicable or derivable is the word I want
link |
from the properties of the fundamental things.
link |
And space is one of those things
link |
in a sufficiently complex universe,
link |
space, three dimensional position of things emerged.
link |
Yes, and we have this,
link |
we saw how this happens in detail in some models,
link |
both computationally and analytically.
link |
Okay, so connected to space is the idea of locality.
link |
So we've talked about realism.
link |
So I live in this world that like sports.
link |
Locality is a thing that you can affect things close to you
link |
and don't have an effect on things that are far away.
link |
It's the thing that bothers me about gravity in general
link |
or action at a distance.
link |
Same thing that probably bothered Newton,
link |
or at least he said a little bit about it.
link |
Okay, so what do you think about locality?
link |
Is it just a construct?
link |
Is it us humans just like this idea
link |
and are connected to it because we exist in it,
link |
we need it for our survival, but it's not fundamental?
link |
I mean, it seems crazy for it not to be
link |
a fundamental aspect of our reality.
link |
Can you comfort me on a sort of as a therapist,
link |
I'm not a good therapist, but I'll do my best.
link |
There are several different definitions of locality
link |
when you come to talk about locality in physics.
link |
In quantum field theory,
link |
which is a mixture of special relativity
link |
and quantum mechanics,
link |
there is a precise definition of locality.
link |
Field operators corresponding to events in space time,
link |
which are space like separated,
link |
commute with each other as operators.
link |
So in quantum mechanics,
link |
you think about the nature of reality as fields
link |
and things that are close in a field
link |
have an impact on each other more than farther away.
link |
That's very comforting.
link |
So that's a property of quantum field theory
link |
and it's well tested.
link |
Unfortunately, there's another definition of local,
link |
which was expressed by Einstein
link |
and expressed more precisely by John Bell,
link |
which has been tested experimentally and found to fail.
link |
And this set up is you take two particles.
link |
So one thing that's really weird about quantum mechanics
link |
is a property called entanglement.
link |
You can have two particles interact
link |
and then share a property
link |
without it being a property
link |
of either one of the two particles.
link |
And if you take such a system
link |
and then you make a measurement on particle A,
link |
which is over here on my right side,
link |
and particle B, which is over here.
link |
Somebody else makes a measurement of particle B.
link |
You can ask that whatever is the real reality
link |
of particle B, it not be affected by the choice
link |
the observer at particle A makes about what to measure,
link |
just the choice of the different things they might measure.
link |
And that's a notion of locality
link |
because it assumes that these things
link |
are very far spaced like separated.
link |
And it's gonna take a while for any information
link |
about the choice made by the people here at A
link |
to affect the reality at B.
link |
But you make that assumption,
link |
that's called Bell locality.
link |
And you derive a certain inequality
link |
that some correlations,
link |
functions of correlations have to satisfy.
link |
And then you can test that pretty directly
link |
in experiments which create pairs of photons
link |
or other particles.
link |
And it's wrong by many sigma.
link |
In experiment, it doesn't match.
link |
So what does that mean?
link |
That means that that definition of locality
link |
I stated is false.
link |
The one that Einstein was playing with.
link |
Yeah, and the one that I stated,
link |
that is it's not true that whatever is real
link |
about particle B is unaffected by the choice
link |
that the observer makes as to what to measure
link |
No matter how long they've been propagating
link |
at almost the speed of light or the speed of light
link |
away from each other, it's no matter.
link |
So like the distance between them.
link |
Well, it's been tested, of course,
link |
if you want to have hope for quantum mechanics
link |
being incomplete or wrong and corrected
link |
by something that changes this.
link |
It's been tested over a number of kilometers.
link |
I don't remember whether it's 25 kilometers
link |
or a hundred and something kilometers, but.
link |
So in trying to solve the unsolved revolution,
link |
in trying to come up with the theory for everything,
link |
is causality fundamental and breaking away from locality?
link |
So in your book, essentially, those are the two things
link |
we really need to think about as a community.
link |
Especially the physics community has to think about this.
link |
I guess my question is, how do we solve?
link |
How do we finish the unfinished revolution?
link |
Well, that's, I can only tell you what I'm trying to do
link |
and what I've abandoned as not working.
link |
As one ant, smart ant in an ant colony.
link |
Or maybe dumb, that's why, who knows?
link |
But anyway, my view of the,
link |
we've had some nice theories invented.
link |
There's a bunch of different ones.
link |
Both relate to quantum mechanics,
link |
relate to quantum gravity.
link |
There's a lot to admire
link |
in many of these different approaches.
link |
But to my understanding,
link |
they, none of them completely solve the problems
link |
that I care about.
link |
And so we're in a situation
link |
which is either terrifying for a student
link |
or full of opportunity for the right student,
link |
in which we've got more than a dozen attempts.
link |
And I never thought, I don't think anybody anticipated
link |
it would work out this way.
link |
Which work partly and then at some point,
link |
they have an issue that nobody can figure out
link |
how to go around or how to solve.
link |
And that's the situation we're in.
link |
My reaction to that is twofold.
link |
One of them is to try to bring people,
link |
we evolved into this unfortunate sociological situation
link |
in which there are communities
link |
around some of these approaches.
link |
And to borrow again, a metaphor from Eric,
link |
they sit on top of hills in the landscape of theories
link |
and throw rocks at each other.
link |
And as Eric says, we need two things.
link |
We need people to get off their hills
link |
and come down into the valleys and party and talk
link |
and become friendly and learn to say,
link |
not no but, but yes and yes.
link |
Your idea goes this far,
link |
but maybe if we put it together with my idea,
link |
we can go further.
link |
So in that spirit, I've talked several times
link |
with Sean Carroll, who's also written
link |
an excellent book recently.
link |
And he kind of, he plays around,
link |
is a big fan of the many worlds interpretation
link |
of quantum mechanics.
link |
So I'm a troublemaker.
link |
So let me ask, what's your sense of Sean
link |
and the idea of many worlds interpretation?
link |
I've read many the commentary back and forth.
link |
You guys are friendly, respect each other,
link |
but have a lot of fun debating.
link |
I love Sean and he, no, I really,
link |
he's articulate and he's a great representative
link |
or ambassador of science to the public
link |
and for different fields of science to each other.
link |
He also, like I do, takes philosophy seriously.
link |
And unlike what I do in all cases,
link |
he has really done the homework.
link |
He's read a lot, he knows the people,
link |
he talks to them, he exposes his arguments to them.
link |
And I, there's this mysterious thing
link |
that we so often end up on the opposite sides
link |
of one of these issues.
link |
It's fun and I'd love to have a conversation about that,
link |
but I would want to include him.
link |
I see, about many worlds, well.
link |
No, I can tell you what I think about many worlds.
link |
I'd love to, but actually on that, let me pause.
link |
Sean has a podcast.
link |
You should definitely figure out how to talk to Sean.
link |
I would, I actually told Sean,
link |
I would love to hear you guys just going back and forth.
link |
So I hope you can make that happen eventually,
link |
I won't tell you what it is,
link |
but there's something that Sean said to me
link |
in June of 2016 that changed my whole approach to a problem.
link |
But I'll have to tell him first.
link |
Yes, and that, that'll be great to tell him on his podcast.
link |
I can't invite myself to his podcast.
link |
But I told him, yeah, okay, we'll make it happen.
link |
Many worlds, we talk about nonlocality.
link |
Many worlds is also a very uncomfortable idea
link |
or beautiful depending on your perspective.
link |
It's very nice in terms of,
link |
I mean, there's a realist aspect to it.
link |
I think you called it magical realism.
link |
It's just a beautiful line.
link |
But at the same time,
link |
it's very difficult to far limited human minds
link |
So what are your thoughts about it?
link |
Let me start with the easy and obvious
link |
and then go to the scientific.
link |
It doesn't appeal to me.
link |
It doesn't answer the questions that I want answered.
link |
And it does so to such a strong case
link |
that when Roberto Mangueber Anger and I
link |
began looking for principles,
link |
and I want to come back and talk about
link |
the use of principles in science,
link |
because that's the other thing I was going to say,
link |
and I don't want to lose that.
link |
When we started looking for principles,
link |
we made our first principle,
link |
there is just one world and it happens once.
link |
But so it's not helpful to my personal approach,
link |
to my personal agenda,
link |
but of course I'm part of a community.
link |
And my sense of the many worlds interpretation,
link |
I have thought a lot about it and struggled a lot with it,
link |
First of all, there's Everett himself,
link |
there's what's in Everett.
link |
And there are several issues there
link |
connected with the derivation of the Born Rule,
link |
which is the rule that gives probabilities to events.
link |
And the reasons why there is a problem with probability
link |
is that I mentioned the two ways
link |
that physical systems can evolve.
link |
The many worlds interpretation cuts off,
link |
one, the one having to do with measurement,
link |
and just has the other one, the Schrodinger evolution,
link |
which is this smooth evolution of the quantum state.
link |
But the notion of probability is only in the second rule,
link |
which we've thrown away.
link |
So where does probability come from?
link |
And you have to answer the question
link |
because experimentalists use probabilities
link |
to check the theory.
link |
Now, at first sight, you get very confused
link |
because there seems to be a real problem
link |
because in the many worlds interpretation,
link |
this talk about branches is not quite precise,
link |
There's a branch in which everything that might happen
link |
does happen with probability one in that branch.
link |
You might think you could count the number of branches
link |
in which things do and don't happen
link |
and get numbers that you can define
link |
as something like frequentist probabilities.
link |
And Everett did have an argument in that direction,
link |
but the argument gets very subtle
link |
when there are an infinite number of possibilities,
link |
as is the case in most quantum systems.
link |
And my understanding,
link |
although I'm not as much of an expert as some other people,
link |
is that Everett's own proposal failed, did not work.
link |
There are then, but it doesn't stop there.
link |
There is an important idea that Everett didn't know about,
link |
which is decoherence,
link |
and it is a phenomenon that might be very much relevant.
link |
And so a number of people post Everett
link |
have tried to make versions of what you might call
link |
many worlds quantum mechanics.
link |
And this is a big area and it's subtle,
link |
and it's not the kind of thing that I do well.
link |
So I consulted, that's why there's two chapters on this
link |
in the book I wrote.
link |
Chapter 10, which is about Everett's version,
link |
chapter 11, there's a very good group of philosophers
link |
of physics in Oxford, Simon Saunders, David Wallace,
link |
Harvey Brown, and a number of others.
link |
And of course there's David Deutsch, who is there.
link |
And those people have developed and put a lot of work
link |
into a very sophisticated set of ideas
link |
designed to come back and answer that question.
link |
They have the flavor of there are really no probabilities,
link |
we admit that, but imagine if the Everett story was true
link |
and you were living in that multiverse,
link |
how would you make bets?
link |
And so they use decision theory
link |
from the theory of probability and gambling and so forth
link |
to shape a story of how you would bet
link |
if you were inside an Everett in the universe
link |
and you knew that.
link |
And there's a debate among those experts
link |
as to whether they or somebody else has really succeeded.
link |
And when I checked in as I was finishing the book
link |
with some of those people, like Simon,
link |
who's a good friend of mine, and David Wallace,
link |
they told me that they weren't sure
link |
that any of them was yet correct.
link |
So that's what I put in my book.
link |
Now, to add to that, Sean has his own approach
link |
to that problem in what's called self referencing
link |
or self locating observers.
link |
And it doesn't, I tried to read it
link |
and it didn't make sense to me,
link |
but I didn't study it hard,
link |
I didn't communicate with Sean,
link |
I didn't do the things that I would do,
link |
so I had nothing to say about it in the book.
link |
I don't know whether it's right or not.
link |
Let's talk a little bit about science.
link |
You mentioned the use of principles in science.
link |
What does it mean to have a principle
link |
and why is that important?
link |
When I feel very frustrated about quantum gravity,
link |
I like to go back and read history.
link |
And of course, Einstein, his achievements
link |
are a huge lesson and hopefully something
link |
like a role model.
link |
And it's very clear that Einstein thought
link |
that the first job when you wanna enter a new domain
link |
of theoretical physics is to discover and invent principles
link |
and then make models of how those principles
link |
might be applied in some experimental situation,
link |
which is where the mathematics comes in.
link |
So for Einstein, there was no unified space and time.
link |
Minkowski invented this idea of space time.
link |
For Einstein, it was a model of his principles
link |
or his postulates.
link |
And I've taken the view that we don't know
link |
the principles of quantum gravity.
link |
I can think about candidates and I have some papers
link |
where I discuss different candidates
link |
and I'm happy to discuss them.
link |
But my belief now is that those partially successful
link |
approaches are all models,
link |
which might describe indeed some quantum gravity physics
link |
in some domain, in some aspect,
link |
but ultimately would be important
link |
because they model the principles
link |
and the first job is to tie down those principles.
link |
So that's the approach that I'm taking.
link |
So speaking of principles, in your 2006 book,
link |
The Trouble with Physics, you criticized a bit
link |
string theory for taking us away from the rigors
link |
of the scientific method or whatever you would call it.
link |
But what's the trouble with physics today
link |
and how do we fix it?
link |
Can I say how I read that book?
link |
Because I, and I'm not, this of course has to be my fault
link |
because you can't as an author claim
link |
after all the work you put in that you are misread.
link |
But I will say that many of the reviewers
link |
who are not personally involved
link |
and even many who were working on string theory
link |
or some other approach to quantum gravity
link |
told me, communicated with me and told me
link |
they thought that I was fair
link |
and balance was the word that was usually used.
link |
So let me tell you what my purpose was in writing that book,
link |
which clearly got diverted by,
link |
because there was already a rather hot argument going on.
link |
On string theory specifically?
link |
Or in general in physics?
link |
No, more specifically than string theory.
link |
So since we're in Cambridge, can I say that?
link |
We're doing this in Cambridge.
link |
Yeah, yeah, of course.
link |
Cambridge, just to be clear, Massachusetts.
link |
And on Harvard campus.
link |
Right, so Andy Straminger is a good friend of mine
link |
and has been for many, many years.
link |
And Andy, so originally there was this beautiful idea
link |
that there were five string theories
link |
and maybe they would be unified into one.
link |
And we would discover a way to break that symmetries
link |
of one of those string theories
link |
and discover the standard model
link |
and predict all the properties
link |
of standard model particles,
link |
like their masses and charges and so forth,
link |
coupling constants.
link |
And then there was a bunch of solutions
link |
to string theory found,
link |
which led each of them to a different version
link |
of particle physics with a different phenomenology.
link |
These are called the Calabi Yao manifolds,
link |
named after Yao, who is also here.
link |
Not, certainly we've been friends
link |
at some time in the past anyway.
link |
And then there were, nobody was sure,
link |
but hundreds of thousands of different versions
link |
And then Andy found there was a way
link |
to put a certain kind of mathematical curvature
link |
called torsion into the solutions.
link |
And he wrote a paper, String Theory with Torsion,
link |
in which he discovered there was,
link |
and not formally uncountable,
link |
but he was unable to invent any way
link |
to count the number of solutions
link |
or classify the diverse solutions.
link |
And he wrote that this is worrying
link |
because doing phenomenology the old fashioned way
link |
by solving the theory is not gonna work
link |
because there's gonna be loads of solutions
link |
for every proposed phenomenology
link |
for anything the experiments discovered.
link |
And it hasn't quite worked out that way.
link |
But nonetheless, he took that worry to me.
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We spoke at least once, maybe two or three times about that.
link |
And I got seriously worried about that.
link |
And this is just a little.
link |
So it's like an anecdote that inspired
link |
your worry about string theory in general?
link |
Well, I tried to solve the problem
link |
and I tried to solve the problem.
link |
I was reading at that time, a lot of biology,
link |
a lot of evolutionary theory,
link |
like Linmar Gullis and Steve Gould and so forth.
link |
And I could take your time to go through the things,
link |
but it occurred to me,
link |
maybe physics was like evolutionary biology
link |
and maybe the laws evolved.
link |
And there was, the biologists talk about a landscape,
link |
a fitness landscape of DNA sequences
link |
or protein sequences or species or something like that.
link |
And I took their concept and the word landscape
link |
from theoretical biology and made a scenario
link |
about how the universe as a whole could evolve
link |
to discover the parameters of the standard model.
link |
And I'm happy to discuss,
link |
that's called cosmological natural selection.
link |
Cosmological natural selection.
link |
Wow, so the parameters of the standard model,
link |
so the laws of physics are changing.
link |
This idea would say that the laws of physics
link |
are changing in some way that echoes
link |
that of natural selection,
link |
or just it adjusts in some way towards some goal.
link |
And I published that,
link |
I wrote the paper in 1888 or 89,
link |
the paper was published in 92.
link |
My first book in 1997,
link |
The Life of the Cosmos was explicitly about that.
link |
And I was very clear that what was important
link |
is that because you would develop an ensemble of universes,
link |
but they were related by descent to natural selection,
link |
almost every universe would share the property
link |
that it was, its fitness was maximized to some extent,
link |
or at least close to maximum.
link |
And I could deduce predictions
link |
that could be tested from that.
link |
And I worked all of that out
link |
and I compared it to the anthropic principle
link |
where you weren't able to make tests
link |
or make falsifications.
link |
All of this was in the late 80s and early 90s.
link |
That's a really compelling notion,
link |
but how does that help you arrive?
link |
I'm coming to where the book came from.
link |
I worked on string theory.
link |
I also worked on loop quantum gravity.
link |
And I was one of the inventors of loop quantum gravity.
link |
And because of my strong belief in some other principles,
link |
which led to this notion of wanting a quantum theory
link |
of gravity to be what we call relational
link |
or background independent,
link |
I tried very hard to make string theory
link |
background independent.
link |
And it ended up developing a bunch of tools
link |
which then could apply directly to general relativity
link |
and that became loop quantum gravity.
link |
So the things were very closely related
link |
and have always been very closely related in my mind.
link |
The idea that there were two communities,
link |
one devoted to strings and one devoted to loops is nuts
link |
and has always been nuts.
link |
Okay, so anyway, there's this nuts community
link |
of loops and strings that are all beautiful
link |
and compelling and mathematically speaking.
link |
And what's the trouble with all that?
link |
Why is that such a problem?
link |
So I was interested in developing that notion
link |
of how science works based on a community
link |
and ethics that I told you about.
link |
And I wrote a draft of a book about that,
link |
which had several chapters on methodology of science.
link |
And it was a rather academically oriented book.
link |
And those chapters were the first part of the book,
link |
the first third of it.
link |
And you didn't find their remnants
link |
in what's now the last part of the trouble with physics.
link |
And then I described a number of test cases, case studies.
link |
And one of them, which I knew was the search
link |
for quantum gravity and string theory and so forth.
link |
And I wasn't able to get that book published.
link |
So somebody made the suggestion of flipping it around
link |
and starting with a story of string theory,
link |
which was already controversial.
link |
This was 2004, 2005.
link |
But I was very careful to be detailed,
link |
to criticize papers and not people.
link |
You won't find me criticizing individuals.
link |
You'll find me criticizing certain writing.
link |
But in any case, here's what I regret.
link |
Let me make your program worthwhile.
link |
As far as I know, with the exception of not understanding
link |
how large the applications to condensed matter,
link |
say ADS CFT would get,
link |
I think largely my diagnosis of string theory
link |
as it was then has stood up since 2006.
link |
What I regret is that the same critique,
link |
I was using string theory as an example,
link |
and the same critique applies to many other communities
link |
in science and all of, including,
link |
and this is where I regret my own community,
link |
that is a community of people working on quantum gravity.
link |
Not science string theory.
link |
But, and I considered saying that explicitly.
link |
But to say that explicitly,
link |
since it's a small, intimate community,
link |
I would be telling stories and naming names
link |
and making a kind of history
link |
that I have no right to write.
link |
So I stayed away from that, but was misunderstood.
link |
But if I may ask, is there a hopeful message
link |
for theoretical physics that we can take from that book,
link |
sort of that looks at the community,
link |
not just your own work on,
link |
now with causality and nonlocality,
link |
but just broadly in understanding
link |
the fundamental nature of our reality,
link |
what's your hope for the 21st century in physics?
link |
Well, that we solve the problem.
link |
That we solve the unfinished problem of Einstein's.
link |
That's certainly the thing that I care about most in.
link |
Let me say one thing.
link |
Among the young people that I work with,
link |
I hear very often and sense a total disinterest
link |
in these arguments that we older scientists have.
link |
And an interest in what each other is doing.
link |
And this is starting to appear in conferences
link |
where the young people interested in quantum gravity
link |
make a conference, they invite loops and strings
link |
and causal dynamical triangulations and causal set people.
link |
And we're having a conference like this next week,
link |
a small workshop at perimeter.
link |
And I guess I'm advertising this.
link |
And then in the summer,
link |
we're having a big full on conference,
link |
which is just quantum gravity.
link |
It's not strings, it's not loops.
link |
But the organizers and the speakers
link |
will be from all the different communities.
link |
And this to me is very helpful.
link |
That the different ideas are coming together.
link |
At least people are expressing an interest in that.
link |
It's a huge honor talking to you, Lee.
link |
Thanks so much for your time today.
link |
Thanks for listening to this conversation.
link |
And thank you to our presenting sponsor, Cash App.
link |
Download it, use code LexPodcast.
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link |
And now let me leave you with some words from Lee Smolin.
link |
One possibility is God is nothing but
link |
the power of the universe to organize itself.
link |
Thanks for listening and hope to see you next time.