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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coinventor 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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In 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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of Leonard Susskind, Sean Carroll, Michio Akaku,
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Max Stegmark, 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
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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,
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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,
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or simply connect with me on Twitter.
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Alex 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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and Cash App will also donate $10 to first,
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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 it another way.
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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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We don't know. This is science.
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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.
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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 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
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is merely a creation of our mind?
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So like, 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
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is something 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 was 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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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 what happens
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when there are fires, when there are not fires,
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what animals and plants are good to eat
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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 and incomplete information.
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So we judge quickly and we're often wrong.
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We're at least sometimes wrong,
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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 to be right.
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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 it'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 Firehub
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and 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?
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Can you elaborate, sorry if you were going to,
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but can you elaborate on the,
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what does it mean 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 Firehub, he was a student of Popper
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who taught Carl Popper and Firehub and argued
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both by logic and by historical example
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that you name anything that should be part of
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the practice of science.
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Say you should always make sure
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that your theories agree with all the data
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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
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contradicts that advice
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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 bound
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by certain ethical precepts, precepts, whatever that is.
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So in that community, a set of ideas they operate under.
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I'm meaning ethically of kind of the rules
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of the game 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, but there are tools
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both on the mathematics side and the experimental side
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to check and double check and triple 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, 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 the last, did you check this
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and did you check that and did you check this
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and what about a 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 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 the scientific method,
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but the final result, the hope of it
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is that you should be able to say with some confidence
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that a particular thing 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 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 weight is a principle of inertia
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and has an inertia in the direction
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with the earth isn't moving
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and the tower and the ball and the earth all move together.
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When the principle of inertia tells you at the bottom,
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it does look at, therefore, my principle of inertia is right.
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And Aristotelian says, no,
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our style of science is right, the earth is stationary.
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And so you've got to 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 till 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 strength theory
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and so on and kind of possible,
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when you might think of us dead ends and so on.
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Which is not the way I think of strength theory.
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We'll straighten out, we'll get our strength straight.
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But there is nevertheless in science,
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very often at least temporary dead ends.
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But if you look at the through centuries,
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you know, the century before Newton
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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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I think it's important to get the time, place is right.
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There was a scientific revolution
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that partly succeeded between about 1900 or late 1890s
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and into the 1930s, 1940s and maybe some
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if you stretch 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
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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
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with electrons going around
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and this is early 20th century.
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And then quantum mechanics was from 1905.
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It 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 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 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 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
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when you get something right, 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,
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your new book, before string theory,
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quantum mechanics and 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,
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which describes and explains exactly what happens
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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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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
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the fundamental world which had some chance in it.
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So 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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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,
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temporarily so, probably.
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Okay, so realism is the idea that
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while the ground 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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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,
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our human mind, consciousness, have a role in this
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realism view of the physical universe?
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There's two questions you could be asking.
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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,
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we can call it a naturalist view of the world
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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,
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is I hope so, 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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What about the anti realists?
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So what flavor, what are the differences
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What are the different camps of anti realists
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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 a very concrete
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real world, if there's divisions or there's a,
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it's messier than the realist view of the universe.
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What are the different camps?
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What are the different views?
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I'm not sure, I'm a good scholar
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and can talk about the different camps
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Many of the inventors of quantum physics
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were not realists, were anti realists.
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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
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an objective realist description of nature
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as it would be in our absence.
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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
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like particle or wave or causality
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If they're useful to us
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and they carry some intuitive implication
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but we shouldn't believe that they actually
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have to do with what nature would be like
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in our absence, 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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Do you find aspects of that kind of
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anti realist view of Niels Bohr compelling
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that we're fundamentally our 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
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Sure, I just would like to believe that
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it is 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
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lead us to discovering the real world as it is?
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It's perfection possible by the way, is it?
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You mean will we ever get there and know that we're there?
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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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again the sentence of apes for 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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There comes a point even with the help of the
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tools of physics that we just cannot grasp
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some fundamental aspects of that reality.
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Again, I think that's a question 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
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of certain languages or the universality of mathematics
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or of computing and so forth.
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He believed that universality, which is something real,
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which somehow comes out of the fact that a symbolic system
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or a mathematical system can refer to itself
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and can, I forget what that's called,
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can reference back to itself.
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And build in which he argued for a universality
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of possibility for our understanding, whatever is out there.
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I admire that argument, but it seems to me
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we're doing okay so far, 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, Derek 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.
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Edison carried his luggage.
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All these geniuses carried their luggage.
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Not once before, relatively recently,
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did it occur to anybody to put a wheel on luggage and pull it.
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And it was right there waiting to be invented for centuries.
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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 right in front of our eyes
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that once it just clicks, we put the wheels in 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 carry their luggage.
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What, just psychologically speaking,
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so Eric Weinstein is a good example of a person 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, by psychology,
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by upbringing, I don't know,
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but resists conventional thinking as well, just by nature.
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That's a compliment.
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That's a compliment? Good.
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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 Weinstein
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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 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, there are ways to fail.
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But if you somehow have the right luck,
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the right confidence and arrogance,
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I think Weinstein cared to understand nature
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with a ferocity and a commitment
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that exceeded 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
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or can be developed 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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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,
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have you found yourself walking that nice edge of too much
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or too little, so being overconfident
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and therefore leaning yourself astray
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or not sufficiently confident to throw away
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the conventional thinking of whatever the theory of the day,
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of theoretical physics?
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I don't know if...
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I mean, I've contributed what I've contributed,
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whether if I had had more confidence in something,
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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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When 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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what is Einstein's Unfinished Revolution
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and also how do we finish it?
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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 theories,
link |
special and especially general relativity,
link |
and quantum theory,
link |
which he was the first person to realize in 1905
link |
that there would have to be a radically different theory
link |
which somehow realized or resolved the paradox
link |
of duality of particle and wave for photons.
link |
People, I think, don't always associate Einstein
link |
with quantum mechanics
link |
because I think his connection with it,
link |
as one of the founders, 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 but incomplete
link |
and that also is my view.
link |
It needs, for various reasons,
link |
to have additional degrees of freedom,
link |
particles, forces, something
link |
to reach the stage where it gives a complete description
link |
of each phenomenon as I was saying,
link |
So what aspect of quantum mechanics
link |
bothers you and Einstein the most?
link |
Is it some aspect of the wave function
link |
collapse discussions, the measurement problem?
link |
The measurement problem.
link |
I'm not going to speak for Einstein.
link |
The measurement problem, basically,
link |
and the fact that...
link |
What is the measurement problem, sorry?
link |
The basic formulation of quantum mechanics
link |
gives you two ways to evolve situations and time.
link |
One of them is explicitly when no observer is observing
link |
or no measurement is taking place.
link |
And the other is when a measurement or an observation
link |
They basically contradict each other.
link |
But there's another reason why the revolution wasn't complete,
link |
which is we don't understand the relationship
link |
between these two parts.
link |
The 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,
link |
general relativity describes big things.
link |
Quantum theory describes little things.
link |
And that's the revolution that we found.
link |
Really powerful tools to describe big things and little things.
link |
And it's unfinished because
link |
we have two totally separate things.
link |
We need to figure out how to connect them so we can describe everything.
link |
Right. And we either do that
link |
if we believe quantum mechanics, as understood now,
link |
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.
link |
Then part of the job 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,
link |
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 |
you mentioned space time.
link |
What is space time?
link |
Space time, you talked about a construction.
link |
So I believe the space time
link |
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
link |
and a connection and satisfies
link |
the equations that Einstein wrote.
link |
It's a good description to some scale.
link |
It's a good approximation.
link |
It captures some 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 going to allow me to link around that.
link |
So the universe has events.
link |
Events cause other events.
link |
This is the idea of causality.
link |
Okay, so that's real.
link |
In your view, Israel.
link |
Or hypothesis or the theories
link |
that I have been working to develop
link |
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
link |
is both space and time are emergent
link |
and not fundamental.
link |
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 |
So I think the time is fundamental
link |
and quote goes all the way down
link |
and space does not.
link |
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,
link |
the activity of time
link |
is the continual creation of events
link |
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
link |
which goes to the past.
link |
I believe the future does not exist.
link |
There's a notion of a present and a notion of the past.
link |
And the past consists of
link |
is a story about events that took place
link |
So you said the future doesn't exist.
link |
Could you say that again?
link |
give me a chance to understand that one more time?
link |
So the events cause other events.
link |
What is this universe?
link |
Because we'll talk about locality
link |
Because it's a crazy, I mean it's not crazy,
link |
it's a beautiful set of ideas
link |
And if causality 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
link |
in our universe, in your view.
link |
And maybe what's an event?
link |
Oh, an event is where
link |
something changes.
link |
because it's a primitive concept.
link |
This is the view in general relativity
link |
where two particles intersect
link |
or something changes
link |
in the path of a particle.
link |
postulating that there is
link |
at the fundamental level a notion
link |
which is an elementary notion
link |
so it doesn't have
link |
a definition in terms of other things
link |
but it is something elementary
link |
And it doesn't have a connection to energy
link |
or matter or exchange of energy?
link |
Because it's at that level.
link |
and that's why the version of
link |
events that I've developed
link |
with Marina Cortez.
link |
And by the way, I want to mention
link |
my collaborators because they've been
link |
at least as important in this work as I have.
link |
There's Marina Cortez
link |
in all the work since about
link |
causality, causal sets
link |
in the period before that, Roberta
link |
who is a philosopher and a professor
link |
And that's in your efforts together
link |
with your collaborators to finish the unfinished revolution
link |
and focus on causality
link |
as fundamental to physics.
link |
And there's certainly other people
link |
we've worked with but those two people's
link |
thinking had a huge influence
link |
on my own thinking.
link |
That's why 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
link |
to not be fundamental?
link |
There's a level of description
link |
in which there are events
link |
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 |
of the nature of time for us.
link |
But there is an emergent
link |
approximate description
link |
and you asked me to find an emergent.
link |
property is a property
link |
at some level of complexity
link |
and more complex than the fundamental level
link |
which is not directly
link |
or derivable is the word I want
link |
from the properties of the fundamental
link |
And space is one of those things
link |
in a sufficiently complex
link |
position of things emerged.
link |
Yes and we have this
link |
we saw how this happens
link |
in detail in some models
link |
both computationally
link |
Okay so connected to space
link |
is the idea of locality.
link |
So we talked about realism.
link |
live in this world that like sports
link |
locality is a thing that
link |
you can affect things close to you
link |
and don't have an effect
link |
on things that are far away.
link |
It's a thing that bothers me about gravity
link |
in general or action
link |
Same thing that probably bothered Newton
link |
or at least he said a little bit
link |
Okay so what do you think about locality
link |
is it just a construct
link |
just like this idea
link |
and are connected to it because we exist
link |
and we need it for our survival
link |
but it's not fundamental.
link |
I mean it seems crazy for it not to be a fundamental
link |
aspect of our reality.
link |
Can you comfort me on a sort of as a therapist
link |
I'm not a good therapist.
link |
There are several different definitions
link |
of locality when you come
link |
to talk about locality in physics
link |
quantum field theory
link |
which is a mixture
link |
of special relativity
link |
and quantum mechanics.
link |
There is a precise definition
link |
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 realities
link |
fields and things that are close
link |
in a field have an impact
link |
on each other more
link |
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
link |
which was expressed by Einstein
link |
and expressed more precisely
link |
which has been tested experimentally
link |
and found to fail.
link |
is you take two particles
link |
that's really weird about quantum mechanics
link |
is a property called entanglement.
link |
You can have two particles
link |
interact and then share
link |
without being a property of either one
link |
of the two particles.
link |
And if you take such a system
link |
you make a measurement
link |
which is over here on my right side
link |
and somebody else makes a measurement
link |
the real reality of particle B
link |
it not be affected
link |
the observer at particle A
link |
makes about what to measure. Not the outcome
link |
just the choice of the different
link |
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 going to take a while
link |
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 |
correlations, functions of correlations
link |
And then you can test that
link |
in experiments which create pairs
link |
of photons or other particles
link |
and it's wrong by many
link |
In experiment it doesn't match.
link |
What does that mean?
link |
That means that that definition
link |
of locality I stated is false.
link |
The one that Einstein
link |
The one that I stated that is
link |
it's not true that
link |
whatever is real about particle B
link |
by the choice that the observer makes
link |
as to what to measure in particle A.
link |
No matter how long they've been
link |
propagating at almost the speed of light
link |
or the speed of light
link |
away from each other.
link |
No matter, so like the distance between them?
link |
Well, it's been tested of course
link |
if you want to have hope
link |
for quantum mechanics
link |
being incomplete or wrong
link |
and corrected by something that changes this.
link |
It's been tested over
link |
a number of kilometers.
link |
whether it's 25 kilometers
link |
or 170 kilometers.
link |
in trying to solve the
link |
unsolved revolution
link |
in trying to come up with the theory of everything
link |
causality, fundamental
link |
breaking away from locality?
link |
In your book essentially those are the
link |
two things we really need to
link |
think about as a community.
link |
Especially the physics community has to think about
link |
I guess my question is
link |
how do we finish the unfinished
link |
I can only tell you what I'm trying to do
link |
and what I've abandoned
link |
As one ant, smart ant
link |
and an ant colony?
link |
Or maybe dumb, that's why.
link |
we've had some nice
link |
theories invented.
link |
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 |
understanding they
link |
none of them completely
link |
solve the problems that I care about.
link |
so we're in a situation
link |
is either terrifying for a student
link |
or full of opportunity for the right
link |
student in which we've got
link |
And I never thought, I don't think anybody
link |
anticipated would work out this way.
link |
Which work partly and then at some point
link |
they have an issue
link |
that nobody can figure out how to go around
link |
that's the situation we're in.
link |
My reaction to that
link |
One of them is to try to
link |
bring people, we evolved
link |
into this unfortunate
link |
sociological situation in which there are
link |
communities around some
link |
of these approaches. And to borrow
link |
again a metaphor from Eric
link |
they sit on top of hills
link |
in the landscape of theories
link |
and throw rocks at each other.
link |
we need two things. We need people
link |
to get off their hills
link |
and come down into the valleys
link |
and party and talk
link |
and become friendly and
link |
yes, your idea goes this far
link |
but maybe if we put it together with my idea
link |
we can go further.
link |
several times with Sean Carroll
link |
who's also written
link |
an excellent book recently
link |
and he plays around
link |
as a big fan of the many worlds interpretation
link |
of quantum mechanics.
link |
So I'm a troublemaker
link |
what's your sense of
link |
Sean and the idea of many worlds interpretation?
link |
the commentary back and forth
link |
you guys are friendly
link |
but have a lot of fun debating.
link |
not, he's articulate
link |
and he's a great representative
link |
or ambassador of science
link |
for different fields of science to each other.
link |
like I do takes philosophy
link |
in all cases he's really done the homework.
link |
he knows the people
link |
he exposes his arguments to them
link |
there's this mysterious thing
link |
that we so often end up
link |
on the opposite sides of these issues.
link |
I'd love to have a conversation
link |
about that but I would want to include him.
link |
I see about many worlds
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 actually told Sean
link |
I would love to hear you guys just going back and forth
link |
I hope you can make that happen eventually
link |
you and Sean. I want to tell you what it is
link |
but there's something that Sean said to me
link |
my whole approach to a problem
link |
but I have to tell him first.
link |
That will be great
link |
to tell him on his podcast.
link |
I can't invite myself to his podcast
link |
We'll make it happen.
link |
We talked about non locality.
link |
Many worlds is also a very
link |
uncomfortable idea
link |
or beautiful depending
link |
on your perspective.
link |
there's a realist aspect to it
link |
I think you called it magical realist
link |
it's just a beautiful line
link |
at the same time it's very difficult to
link |
far limit a human mind to comprehend
link |
so what are your thoughts about it?
link |
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
link |
and it does so to such a
link |
strong case that when Roberto
link |
Mangibar Anger and I
link |
began looking for principles
link |
and I want to come back and talk about the use of principles
link |
in science because that's the other thing
link |
I was going to say 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
link |
and it happens once
link |
personal approach to my personal
link |
agenda but of course
link |
I'm part of a community
link |
the many worlds interpretation I have
link |
thought a lot about it and struggled a lot
link |
first of all there's Everett himself
link |
there's what's in Everett
link |
and there are several
link |
connected with the
link |
derivation of the born rule
link |
which is the rule that gives probabilities
link |
and the reasons why there is a
link |
problem with probability
link |
I mentioned the two ways that
link |
physical systems can evolve
link |
the many worlds interpretation
link |
cuts off one the one having
link |
to do with measurement
link |
and just has the other one the Schrodinger evolution
link |
which is the smooth evolution
link |
of the quantum state
link |
but the notion of probability
link |
the second rule which we've thrown away
link |
probability come from and you have to answer the
link |
experimentalists use probabilities
link |
to check the theory
link |
side you get very confused because there seems
link |
to be a real problem
link |
because in the many worlds interpretation
link |
branches is not quite precise but I'll
link |
there's a branch in which
link |
everything that might happen does
link |
happen with probability one
link |
you might think you could count the
link |
number of branches
link |
in which things do and don't happen
link |
and get numbers that
link |
you can define as something like
link |
frequentist probabilities
link |
ever did have an argument in that direction
link |
the argument gets very subtle when
link |
there are an infinite number of possibilities
link |
as is the case in most quantum
link |
understanding although
link |
I'm not as much of an expert as some other
link |
people is that ever
link |
failed did not work
link |
if it doesn't stop there
link |
an important idea that ever
link |
didn't know about which is decoherence
link |
and it is a phenomenon that
link |
might be very much relevant
link |
a number of people
link |
tried to make versions of what you
link |
might call many worlds quantum mechanics
link |
is a big area and it's subtle
link |
and it's not the kind of thing that
link |
that's why there's two chapters
link |
on this in the book I wrote
link |
chapter 10 which is about everett's version
link |
there's a very good group
link |
of philosophers of physics in oxford
link |
and a number of others and of course
link |
there's david deutch
link |
and those people have developed
link |
and put a lot of work
link |
into a very sophisticated
link |
set of ideas designed to come back
link |
and answer that question
link |
they have the flavor of
link |
there are really no probabilities
link |
we admit that but imagine
link |
if the everett story was true
link |
and you were living in that
link |
multiverse how would you make
link |
decision theory from the theory
link |
of probability and gambling and so forth
link |
you would bet if you were
link |
inside an everett in the universe
link |
and there's a debate
link |
among those experts
link |
they or somebody else has really
link |
and when I checked in
link |
as I was finishing the book with some of those
link |
people like simon who's a good friend
link |
that they weren't sure that any of them
link |
so that's what I put in my book
link |
now to add to that
link |
approach to that problem in what's called
link |
self referencing or self locating
link |
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 shawn
link |
I didn't do the things that I would do
link |
so I had nothing to say about in the book
link |
whether it's right or not
link |
let's talk a little bit about
link |
science you mentioned
link |
the use of principles in science
link |
to have a principle and
link |
why is that important
link |
when I feel very frustrated
link |
about quantum gravity I like to go back
link |
Einstein's achievements are
link |
something like a role model and it's very clear
link |
thought that the first job
link |
enter a new domain of theoretical
link |
physics is to discover and invent
link |
and then make models of how those
link |
principles might be applied in some
link |
experimental situation
link |
where the mathematics comes in
link |
unified space and time
link |
Minkowski invented this idea of
link |
for Einstein it was a model of his
link |
principles or his postulates
link |
that we don't know
link |
the principles of quantum gravity
link |
candidates and I have some papers where I
link |
candidates and I'm happy to discuss them
link |
belief now is that
link |
those partially successful approaches
link |
which might describe
link |
indeed some quantum gravity
link |
physics in some domain in some
link |
would be important because they
link |
model the principles and
link |
the first job is to tie down those
link |
principles so that's the approach
link |
so speaking of principles
link |
The Trouble with Physics
link |
criticized a bit string theory
link |
for taking us away from the
link |
rigors of the scientific method
link |
or whatever you would call it but
link |
the trouble with physics
link |
today and how do we fix it
link |
how I read that book
link |
this of course has to be
link |
you can't as an author claim
link |
after all the work you put in that you are
link |
say that many of the reviewers
link |
personally involved and even many
link |
who were working on string theory
link |
some other approach to quantum gravity
link |
told me, communicated with me
link |
and told me they thought that I was
link |
balance was the word
link |
that was usually used so let me tell you
link |
what my purpose was in writing that
link |
book which clearly
link |
because there was already
link |
a rather hot argument
link |
going on and this is
link |
on which topic on string theory specifically
link |
or in general in physics
link |
more specifically than string theory
link |
since we're in Cambridge can I say that
link |
we're doing this in Cambridge
link |
just to be clear, Massachusetts
link |
is a good friend of mine and has been
link |
for many many years
link |
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
link |
a way to break that
link |
symmetries of one of those string
link |
theories and discover the standard
link |
all the properties of standard model particles
link |
like their masses and charges
link |
and so forth, coupling constant
link |
and then there was a bunch
link |
to string theory found which led
link |
each of them to a different version
link |
of particle physics with a different phenomenology
link |
metaphors named after
link |
Yao who was also here
link |
certainly we've been friends at some time in the past
link |
and then there were nobody was sure
link |
but hundreds of thousands of different
link |
versions of string theory
link |
found there was a way to put a certain kind
link |
of mathematical curvature called
link |
into the solutions and he wrote a paper
link |
of string theory with torsion
link |
in which he discovered there was
link |
uncountable but he was unable to invent
link |
the number of solutions or classify
link |
the diverse solutions
link |
and he wrote that this is
link |
doing phenomenology the old fashioned way
link |
by solving the theory
link |
is not going to work because
link |
there's going to be
link |
loads of solutions for editing
link |
proposed phenomenology for anything
link |
of the experiments
link |
it hasn't quite worked out that way
link |
but nonetheless he took
link |
we spoke at least once
link |
maybe two or three times about that
link |
and I got seriously
link |
worried about that
link |
and this is a little
link |
sounds like an anecdote that
link |
inspired your worry
link |
about string theory in general
link |
well I tried to solve the problem
link |
and I tried to solve the problem
link |
at that time a lot of biology
link |
a lot of evolutionary theory like
link |
Lindmerg Gullis and
link |
Steve Gould and so
link |
could take your time to go through
link |
things but it occurred to me maybe
link |
physics was like evolutionary biology
link |
and maybe the laws
link |
evolved and there was
link |
the biologists talk about a landscape
link |
a fitness landscape
link |
DNA sequences or protein
link |
sequences or a species
link |
or something like that
link |
and I took their concept and the word
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landscape from theoretical biology
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and made a scenario about how the
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physics as a whole
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parameters of the standard model
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and I'm happy to discuss that's called
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cosmological natural selection
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cosmological natural selection
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of the standard model so the laws
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of physics are changing
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this idea would say that
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the laws of physics are changing
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that of natural selection or just
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it adjusts in some way
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I wrote the paper in
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8 or 89 the paper was published
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my first book in 1997 the life of the
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cosmos was explicitly
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and I was very clear
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that what was important
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you would develop an ensemble
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of universes but they were
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related by descent
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through natural selection
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universe would share the property
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its fitness was maximized
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to some extent or at least close
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to maximum and I could deduce
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predictions that could be tested
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of that out and I compared it to the
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happy principle where you weren't
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able to make tests
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or make falsifications all of this
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was in the late 80s
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that's a really compelling notion but
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how does that help you arrive
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I'm coming to where
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the book came from
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I worked on string theory
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worked on loop current gravity
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and that was one of the inventors of loop current gravity
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strong belief in some other principles
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which led to this notion of wanting a quantum
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theory of gravity to be what we call
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relational or background
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I tried very hard to make
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string theory background independent
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and in an up developing a bunch of tools
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which then could apply directly
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to general relativity and that became loop current gravity
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so the things were
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very closely related and have always been
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very closely related in my mind
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the idea that there were two communities
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one devoted to strings and one devoted
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to loops is nuts and has always
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there's this nuts community of loops and strings
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that are all beautiful and compelling
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and mathematically speaking
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and what's the trouble with all that
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why is that such a problem
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so I was interested
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in developing that notion of how science
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works based on the community
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and ethics that I told you about
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a draft of a book about that
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several chapters on methodology
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of science and it was
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rather academically oriented
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those chapters were the first
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part of the book the first third of it
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and you can find their remnants
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in what's now the last
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the trouble with physics and then I described
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a number of test cases
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case studies and one of them
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which I knew was the search for
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quantum gravity and string theory and so forth
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I was unable to get that
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the suggestion of flipping it around
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the story of string theory which was already
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controversial this was
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I was very careful
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papers and not people you won't
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find me criticizing individuals
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you'll find me criticizing
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certain writing but in any
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here's what I regret
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let me make a program
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with the exception of not understanding
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the applications to condense matters
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diagnosis of string theory
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has stood up since 2006
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the same critique I was using
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string theory as an example
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and the same critique applies
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to many other communities
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in science and all of
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including and this is what I regret
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my own community that is a community
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of people working on quantum gravity
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outside string theory
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but and I considered
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saying that explicitly
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but to say that explicitly since I'm
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it's a small intimate community
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I would be telling stories
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and naming names of
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of history that I have no right
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to write so I stayed away
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from that but was misunderstood
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ask is there a hopeful message
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for theoretical physics
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that we can take from that book
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sort of that looks at the community
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work on now with causality
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and nonlocality but just
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broadly in understanding the fundamental
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nature of our reality
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what's your hope for the
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21st century in physics
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What do we solve the problem?
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unfinished problem of Einstein's
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that's certainly the thing
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that I care about most
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let me say one thing among the young
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people that I work with
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a total disinterest in these
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arguments that we older scientists
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and an interest in what each other is doing
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and this is starting to appear
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where the young people interested
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in quantum gravity make a
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conference they invite loops
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and strings and causal dynamical
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triangulations and causal set people
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a conference like this next week
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at perimeter and I guess I'm
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out of tidiness and then in
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the summer we're having a big
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full on conference
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which is just quantum gravity it's not strings
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it's not loops but
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the organizers and the speakers will be
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from all the different communities
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and this to me is very helpful
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that the different ideas
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are coming together?
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At least people are expressing an interest
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talking to you Lee thanks so much
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for your time today
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Thanks for listening to this conversation
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and thank you to our presenting sponsor
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If you enjoy this podcast
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also connect with me on Twitter
link |
and now let me leave you with some words
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One possibility is
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God is nothing but
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the power of the universe to organize
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Thanks for listening and hope to see you