Lee Smolin: Quantum Gravity and Einstein's Unfinished Revolution

00:00:00.000 | The following is a conversation with Lee Smolin.

00:00:02.880 | He's a theoretical physicist,

00:00:04.520 | co-inventor of loop quantum gravity,

00:00:06.680 | and a contributor of many interesting ideas

00:00:08.840 | to cosmology, quantum field theory,

00:00:11.320 | the foundations of quantum mechanics,

00:00:12.920 | theoretical biology, and the philosophy of science.

00:00:16.360 | He's the author of several books,

00:00:18.160 | including one that critiques the state of physics

00:00:21.000 | and its string theory called "The Trouble with Physics,"

00:00:24.080 | and his latest book, "Einstein's Unfinished Revolution,

00:00:27.080 | "The Search for What Lies Beyond the Quantum."

00:00:30.320 | He's an outspoken personality in the public debates

00:00:32.960 | on the nature of our universe,

00:00:34.680 | among the top minds in the theoretical physics community.

00:00:38.320 | This community has its respected academics,

00:00:41.080 | its naked emperors, its outcasts and its revolutionaries,

00:00:44.520 | its madmen and its dreamers.

00:00:46.980 | This is why it's an exciting world to explore

00:00:49.640 | through long-form conversation.

00:00:51.880 | I recommend you listen back to the episodes

00:00:53.880 | of Leonard Susskind, Sean Carroll, Michio Kaku,

00:00:57.240 | Max Stegmark, Eric Weinstein, and Jim Gates.

00:01:01.240 | You might be asking, "Why talk to physicists

00:01:03.840 | "if you're interested in AI?"

00:01:06.200 | To me, creating artificial intelligence systems

00:01:08.840 | requires more than Python and deep learning.

00:01:11.440 | It requires that we return to exploring

00:01:13.400 | the fundamental nature of the universe and the human mind.

00:01:18.400 | Theoretical physicists venture out into the dark,

00:01:21.240 | mysterious, psychologically challenging place

00:01:23.600 | to force principles more than almost any other discipline.

00:01:27.220 | This is the Artificial Intelligence Podcast.

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00:01:38.320 | @LexFriedman, spelled F-R-I-D-M-A-N.

00:01:41.520 | As usual, I'll do one or two minutes of ads now,

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00:02:58.840 | And now, here's my conversation with Lee Smolin.

00:03:02.220 | What is real?

00:03:05.080 | Let's start with an easy question.

00:03:06.440 | Put another way, how do we know what is real

00:03:09.160 | and what is merely a creation

00:03:10.680 | of our human perception and imagination?

00:03:14.200 | - We don't know.

00:03:15.640 | We don't know.

00:03:16.480 | This is science.

00:03:17.300 | I presume we're talking about science.

00:03:19.940 | And we believe, or I believe,

00:03:23.280 | that there is a world that is independent of my existence

00:03:28.520 | and my experience about it and my knowledge of it.

00:03:32.520 | And this I call the real world.

00:03:34.840 | - So you said science, but even bigger than science.

00:03:39.120 | - Sure, sure.

00:03:40.120 | I need not have said this is science.

00:03:42.380 | I just was warming up.

00:03:44.340 | - Warming up.

00:03:46.500 | Okay, now that we're warmed up,

00:03:47.820 | let's take a brief step outside of science.

00:03:51.060 | Is it completely a crazy idea to you

00:03:54.420 | that everything that exists

00:03:56.420 | is merely a creation of our mind?

00:03:58.800 | So there's a few, not many, this is outside of science now,

00:04:03.800 | people who believe perception

00:04:06.540 | is fundamentally what's in our human perception,

00:04:09.980 | the visual cortex and so on,

00:04:11.620 | the cognitive constructs that's being formed there,

00:04:16.260 | is the reality.

00:04:18.060 | And then anything outside

00:04:19.700 | is something that we can never really grasp.

00:04:22.500 | Is that a crazy idea to you?

00:04:24.100 | - There's a version of that that is not crazy at all.

00:04:27.760 | What we experience is constructed by our brains

00:04:32.340 | and by our brains in an active mode.

00:04:36.220 | So we don't see the raw world.

00:04:41.920 | We see a very processed world.

00:04:43.820 | We feel something that's very processed through our brains

00:04:47.500 | and our brains are incredible.

00:04:49.140 | But I still believe that behind that experience,

00:04:55.140 | that mirror or veil or whatever you wanna call it,

00:04:59.420 | there is a real world and I'm curious about it.

00:05:02.540 | - Can we truly, how do we get a sense of that real world?

00:05:06.720 | Is it through the tools of physics

00:05:08.620 | from theory to the experiments?

00:05:11.420 | Or can we actually grasp it in some intuitive way

00:05:15.340 | that's more connected to our ape ancestors?

00:05:20.340 | Or is it still fundamentally the tools of math and physics

00:05:25.180 | that really allow us to grasp it?

00:05:26.020 | - Well, let's talk about what tools they are.

00:05:29.060 | What you say are the tools of math and physics.

00:05:32.060 | I mean, I think we're in the same position

00:05:34.460 | as our ancestors in the caves

00:05:37.900 | or before the caves or whatever.

00:05:40.180 | We find ourselves in this world and we're curious.

00:05:43.340 | We also, it's important to be able to explain

00:05:47.940 | what happens when there are fires,

00:05:49.700 | when there are not fires,

00:05:50.840 | what animals and plants are good to eat and all that stuff.

00:05:55.040 | But we're also just curious.

00:05:57.700 | We look up in the sky and we see the sun

00:06:00.060 | and the moon and the stars and we see some of those move

00:06:03.980 | and we're very curious about that.

00:06:07.180 | And I think we're just naturally curious.

00:06:10.860 | So we make, this is my version of how we work.

00:06:15.860 | We make up stories and explanations.

00:06:19.060 | And there are two things which I think

00:06:25.020 | are just true of being human.

00:06:27.580 | We make judgments fast because we have to.

00:06:31.060 | We're to survive, is that a tiger or is that not a tiger?

00:06:36.500 | And we go.

00:06:37.460 | Act.

00:06:38.420 | We have to act fast on incomplete information.

00:06:41.180 | So we judge quickly and we're often wrong,

00:06:46.020 | or at least sometimes wrong,

00:06:47.220 | which is all I need for this.

00:06:49.140 | We're often wrong.

00:06:50.560 | So we fool ourselves and we fool other people readily.

00:06:55.560 | And so there's lots of stories that get told

00:06:59.940 | and some of them result in a concrete benefit

00:07:04.320 | and some of them don't.

00:07:06.620 | - So you said we're often wrong,

00:07:09.420 | but what does it mean to be right?

00:07:12.460 | - Right, that's an excellent question.

00:07:15.980 | To be right, well, since I believe

00:07:20.380 | that there is a real world,

00:07:22.220 | I believe that to be, you can challenge me on this

00:07:26.300 | if you're not a realist.

00:07:27.500 | A realist is somebody who believes

00:07:29.020 | in this real objective world

00:07:31.260 | which is independent of our perception.

00:07:33.060 | If I'm a realist, I think that to be right

00:07:37.660 | is to come closer.

00:07:40.220 | I think, first of all, there's a relative scale.

00:07:42.220 | There's not right and wrong.

00:07:43.500 | There's right or more right and less right.

00:07:46.960 | And you're more right if you come closer

00:07:49.100 | to an exact, true description of that real world.

00:07:53.060 | Now, can we know that for sure?

00:07:54.820 | No.

00:07:56.100 | - And the scientific method is ultimately

00:07:58.900 | what allows us to get a sense

00:08:00.660 | of how close we're getting to that real world?

00:08:03.060 | - No on two counts.

00:08:04.180 | First of all, I don't believe there's a scientific method.

00:08:07.020 | I was very influenced when I was in graduate school

00:08:10.740 | by the writings of Paul Feyerabend

00:08:12.820 | who was an important philosopher of science

00:08:15.740 | who argued that there isn't a scientific method.

00:08:18.340 | - There is or there isn't?

00:08:19.180 | - There is not.

00:08:20.020 | - There's not.

00:08:20.980 | Can you elaborate?

00:08:22.860 | Sorry if you were going to,

00:08:23.820 | but can you elaborate on the,

00:08:25.360 | what does it mean for there not to be a scientific method,

00:08:28.840 | this notion that I think a lot of people believe in

00:08:33.100 | in this day and age?

00:08:34.860 | - Sure.

00:08:36.100 | Paul Feyerabend, he was a student of Popper

00:08:39.780 | who taught Karl Popper.

00:08:42.340 | And Feyerabend argued both by logic

00:08:47.340 | and by historical example that you name anything

00:08:51.420 | that should be part of the practice of science,

00:08:55.060 | say you should always make sure that your theories

00:08:57.180 | agree with all the data that's already been taken.

00:09:01.240 | And he'll prove to you that there have to be times

00:09:03.640 | when science contradicts, when some scientist

00:09:07.320 | contradicts that advice for science to progress overall.

00:09:12.320 | So it's not a simple matter.

00:09:18.280 | I think that, I think of science as a community.

00:09:23.280 | - Of people.

00:09:26.440 | - Of people, and as a community of people

00:09:29.160 | bound by certain ethical precepts, percepts, whatever that is.

00:09:34.160 | - So in that community, a set of ideas they operate under,

00:09:40.540 | meaning ethically, of kind of the rules of the game

00:09:44.400 | they operate under.

00:09:45.480 | - Don't lie, report all your results,

00:09:48.020 | whether they agree or don't agree with your hypothesis.

00:09:51.020 | Check the training of a scientist,

00:09:56.040 | mostly consists of methods of checking,

00:09:59.320 | because again, we make lots of mistakes,

00:10:01.460 | we're very error prone.

00:10:03.700 | But there are tools, both on the mathematics side

00:10:06.640 | and the experimental side, to check and double check

00:10:09.380 | and triple check.

00:10:11.000 | And a scientist goes through a training,

00:10:14.400 | and I think this is part of it.

00:10:16.400 | You can't just walk off the street and say,

00:10:18.200 | "Yo, I'm a scientist."

00:10:20.640 | You have to go through the training,

00:10:22.280 | and the training, the test that lets you be done

00:10:27.280 | with the training is, can you form a convincing case

00:10:32.560 | for something that your colleagues

00:10:37.800 | will not be able to shout down,

00:10:40.560 | because they'll ask, "Did you check this,

00:10:42.440 | "and did you check that, and did you check this,

00:10:44.140 | "and what about a seeming contradiction with this?"

00:10:47.680 | And you've gotta have answers to all those things

00:10:52.240 | or you don't get taken seriously.

00:10:53.800 | And when you get to the point where you can produce

00:10:56.560 | that kind of defense and argument,

00:10:58.960 | then they give you a PhD.

00:11:00.480 | And you're kind of licensed.

00:11:03.900 | You're still gonna be questioned,

00:11:06.000 | and you still may propose or publish mistakes,

00:11:10.660 | but the community is gonna have to waste less time

00:11:14.480 | fixing your mistakes.

00:11:15.840 | - Yes, but if you can maybe linger on it a little longer,

00:11:20.240 | what's the gap between the thing that that community does

00:11:25.240 | and the ideal of the scientific method?

00:11:27.640 | The scientific method is you should be able

00:11:31.840 | to repeat an experiment.

00:11:33.840 | There's a lot of elements to what construes

00:11:39.440 | the scientific method, but the final result,

00:11:41.980 | the hope of it, is that you should be able to say

00:11:46.720 | with some confidence that a particular thing

00:11:50.160 | is close to the truth.

00:11:53.040 | - Right, but there's not a simple relationship

00:11:55.440 | between experiment and hypothesis or theory.

00:11:58.600 | For example, Galileo did this experiment

00:12:01.120 | of dropping a ball from the top of a tower,

00:12:04.460 | and it falls right at the base of the tower.

00:12:06.880 | And Aristotelian would say, "Wow, of course it falls

00:12:11.480 | "right to the base of the tower.

00:12:12.700 | "That shows that the Earth isn't moving

00:12:14.380 | "while the ball is falling."

00:12:16.760 | And Galileo says no weight is a principle of inertia

00:12:19.800 | and it has an inertia in the direction

00:12:22.320 | with the Earth isn't moving and the tower

00:12:24.400 | and the ball and the Earth all move together.

00:12:26.880 | When the principle of inertia tells you it hits the bottom,

00:12:30.120 | it does look, therefore my principle of inertia is right.

00:12:33.040 | And Aristotelian says no, Aristotle's science is right,

00:12:37.320 | the Earth is stationary.

00:12:39.440 | And so you've got to get an interconnected bunch of cases

00:12:44.440 | and work hard to line up and explain.

00:12:49.200 | It took centuries to make the transition

00:12:51.880 | from Aristotelian physics to the new physics.

00:12:55.920 | It wasn't done till Newton in 1680-something, 1687.

00:13:00.920 | - So what do you think is the nature of the process

00:13:05.000 | that seems to lead to progress?

00:13:08.000 | If we at least look at the long arc of science,

00:13:11.160 | of all the community of scientists,

00:13:13.420 | they seem to do a better job of coming up with ideas

00:13:17.000 | that engineers can then take on and build rockets with

00:13:21.160 | or build computers with or build cool stuff with.

00:13:26.160 | - I don't know, a better job than what?

00:13:28.620 | - Than this previous century.

00:13:32.520 | So century by century, we'll talk about string theory

00:13:35.840 | and so on and kind of possible,

00:13:38.040 | what you might think of as dead ends and so on.

00:13:41.040 | - Which is not the way I think of string theory.

00:13:42.640 | We'll straighten it out, we'll get on string straight.

00:13:45.880 | But there is, nevertheless, in science,

00:13:47.920 | very often at least temporary dead ends.

00:13:52.040 | But if you look through centuries,

00:13:57.040 | you know, the century before Newton

00:13:59.120 | and the century after Newton,

00:14:01.080 | it seems like a lot of ideas came closer to the truth

00:14:06.080 | that then could be usable by our civilization

00:14:10.240 | to build the iPhone, right?

00:14:12.920 | To build cool things that improve our quality of life.

00:14:15.900 | That's the progress I'm kind of referring to.

00:14:18.480 | - Let me, can I say that more precisely?

00:14:21.440 | - Yes.

00:14:22.280 | (laughing)

00:14:23.120 | It's a low bar.

00:14:23.940 | - 'Cause I think it's important to get

00:14:26.240 | the time places right.

00:14:28.680 | - Yes.

00:14:29.840 | - There was a scientific revolution that partly succeeded

00:14:34.640 | between about 1900 or late 1890s

00:14:39.520 | and into the 1930s, 1940s,

00:14:44.520 | and maybe some, if you stretched it, into the 1970s.

00:14:49.840 | And the technology, this was the discovery of relativity

00:14:54.520 | and that included a lot of developments

00:14:56.120 | of electromagnetism.

00:14:58.320 | The confirmation, which wasn't really well confirmed

00:15:02.600 | into the 20th century, that matter was made of atoms.

00:15:06.560 | And the whole picture of nuclei

00:15:08.680 | with electrons going around,

00:15:09.880 | this is early 20th century.

00:15:12.520 | And then quantum mechanics was from 1905,

00:15:17.520 | took a long time to develop to the late 1920s

00:15:21.760 | and then it was basically in final form.

00:15:25.280 | And the basis of this partial revolution,

00:15:29.440 | and we can come back to why it's only a partial revolution,

00:15:32.440 | is the basis of the technologies you mentioned.

00:15:37.060 | All of, I mean, electrical technology

00:15:40.840 | was being developed slowly with this.

00:15:42.880 | And in fact, there's a close relation

00:15:46.000 | between the development of electricity

00:15:49.560 | and the electrification of cities in the United States

00:15:54.120 | and Europe and so forth.

00:15:55.620 | And the development of the science.

00:15:59.300 | The fundamental physics,

00:16:06.060 | since the early 1970s,

00:16:08.540 | doesn't have a story like that so far.

00:16:11.220 | There's not a series of triumphs and progresses

00:16:16.220 | and there's not any practical application.

00:16:19.780 | - So just to linger briefly on the early 20th century

00:16:26.060 | and the revolutions in science that happened there,

00:16:29.080 | what was the method by which the scientific community

00:16:33.980 | kept each other in check about

00:16:37.940 | when you get something right, when you get something wrong?

00:16:40.160 | Is experimental validation ultimately the final test?

00:16:43.620 | - It's absolutely necessary.

00:16:45.340 | And the key things were all validated.

00:16:47.640 | The key predictions of quantum mechanics

00:16:50.940 | and of the theory of electricity and magnetism.

00:16:53.300 | - So before we talk about Einstein,

00:16:56.940 | your new book before string theory, quantum mechanics,

00:17:00.740 | let's take a step back at a higher level question.

00:17:04.060 | What is, that you mentioned, what is realism?

00:17:08.380 | What is anti-realism?

00:17:10.620 | And maybe why do you find realism,

00:17:13.860 | as you mentioned, so compelling?

00:17:15.720 | - Realism is the belief in an external world

00:17:22.180 | independent of our existence, our perception,

00:17:28.700 | our belief, our knowledge.

00:17:30.740 | A realist, as a physicist, is somebody who believes

00:17:35.540 | that there should be possible

00:17:38.340 | some completely objective description

00:17:42.260 | of each and every process at the fundamental level,

00:17:46.860 | which describes and explains exactly what happens

00:17:51.060 | and why it happens.

00:17:52.820 | - That kind of implies that that system,

00:17:55.700 | in a realist view, is deterministic,

00:17:58.340 | meaning there's no fuzzy magic going on

00:18:01.160 | that you can never get to the bottom of.

00:18:02.380 | You can get to the bottom of anything

00:18:04.340 | and perfectly describe it.

00:18:06.260 | - Some people would say that I'm not that interested

00:18:10.740 | in determinism, but I could live with the fundamental world,

00:18:15.740 | which had some chance in it.

00:18:18.580 | - So do you, you said you could live with it,

00:18:21.800 | but do you think God plays dice in our universe?

00:18:26.580 | - I think it's probably much worse than that.

00:18:28.820 | - In which direction?

00:18:32.120 | - I think that theories can change

00:18:33.940 | and theories can change without warning.

00:18:36.140 | I think the future is open.

00:18:38.540 | - You mean the fundamental laws of physics can change?

00:18:40.900 | - Yeah.

00:18:41.740 | - Okay, we'll get there.

00:18:43.860 | (laughs)

00:18:45.940 | I thought we would be able to find some solid ground,

00:18:49.700 | but apparently--

00:18:50.540 | - Well, the ground is pretty solid.

00:18:51.380 | - The entirety of it, temporarily so.

00:18:55.140 | Okay, so realism is the idea that while the ground is solid,

00:19:00.140 | you can describe it.

00:19:02.900 | What's the role of the human being,

00:19:04.660 | our beautiful, complex human mind in realism?

00:19:09.660 | Do we have a, are we just another set of molecules

00:19:14.780 | connected together in a clever way?

00:19:16.460 | Or the observer, does the observer,

00:19:21.060 | our human mind, consciousness, have a role

00:19:23.260 | in this realism view of the physical universe?

00:19:26.340 | - There's two ways, there's two questions

00:19:29.420 | you could be asking.

00:19:30.420 | Does our conscious mind, do our perceptions

00:19:35.700 | play a role in making things become,

00:19:38.860 | in making things real or things becoming?

00:19:42.340 | That's question one.

00:19:43.340 | Question two is, does this, we can call it

00:19:47.420 | a naturalist view of the world

00:19:51.580 | that is based on realism, allow a place

00:19:56.100 | to understand the existence of and the nature

00:19:58.820 | of perceptions and consciousness in mind?

00:20:01.820 | And that's question two.

00:20:03.260 | Question two, I do think a lot about,

00:20:06.660 | and my answer, which is not an answer, is I hope so.

00:20:11.180 | But it certainly doesn't yet.

00:20:12.700 | - So what-- - Question one,

00:20:15.180 | I don't think so.

00:20:17.060 | But of course, the answer to question one

00:20:18.740 | depends on question two.

00:20:20.180 | - Right.

00:20:21.820 | - So I'm not up to question one.

00:20:24.060 | - So question two is the thing that you can

00:20:25.780 | kind of struggle with at this time.

00:20:27.540 | What about the anti-realists?

00:20:32.100 | So what flavor, what are the different camps

00:20:36.260 | of anti-realists that you've talked about?

00:20:38.460 | I think it would be nice if you could articulate

00:20:40.980 | for the people for whom there is not

00:20:44.180 | a very concrete real world, or there's divisions,

00:20:47.500 | or it's messier than the realist view of the universe.

00:20:52.300 | What are the different camps?

00:20:53.300 | What are the different views?

00:20:54.700 | - I'm not sure I'm a good scholar

00:20:57.380 | and can talk about the different camps and analyze it.

00:21:00.020 | But some, many of the inventors of quantum physics

00:21:04.620 | were not realists, were anti-realists.

00:21:06.820 | And there are scholars, they lived in a very perilous time

00:21:11.060 | between the two world wars.

00:21:13.860 | And there were a lot of trends in culture

00:21:17.540 | which were going that way.

00:21:19.300 | But in any case, they said things like

00:21:21.900 | the purpose of science is not to give an objective

00:21:27.420 | realist description of nature as it would be in our absence.

00:21:30.780 | This might be saying Niels Bohr.

00:21:33.100 | The purpose of science is as an extension

00:21:36.380 | of our conversations with each other,

00:21:38.820 | to describe our interactions with nature.

00:21:41.380 | And we're free to invent and use terms like particle,

00:21:45.380 | or wave, or causality, or time, or space,

00:21:48.800 | if they're useful to us and they carry

00:21:53.000 | some intuitive implication.

00:21:56.520 | But we shouldn't believe that they actually have to do

00:21:59.400 | with what nature would be like in our absence,

00:22:02.540 | which we have nothing to say about.

00:22:04.640 | - Do you find any aspect of that,

00:22:08.140 | 'cause you kind of said that we human beings tell stories.

00:22:11.500 | Do you find aspects of that kind of anti-realist view

00:22:15.980 | of Niels Bohr compelling?

00:22:18.820 | That we're fundamentally are storytellers,

00:22:20.980 | and then we create tools of space and time,

00:22:24.540 | and causality, and whatever this fun

00:22:28.260 | quantum mechanics stuff is to help us

00:22:30.180 | tell the story of our world.

00:22:32.800 | - Sure, I just would like to believe

00:22:35.300 | it is an aspiration for the other thing.

00:22:38.520 | - The other thing being what?

00:22:41.420 | - The realist point of view.

00:22:44.020 | - Do you hope that the stories will eventually lead us

00:22:47.340 | to discovering the real world as it is?

00:22:52.340 | - Yeah.

00:22:57.560 | - Is perfection possible, by the way?

00:22:59.220 | - No.

00:23:00.060 | You mean, will we ever get there and know that we're there?

00:23:05.180 | - Yeah, exactly.

00:23:06.500 | - That's for people 5,000 years in the future.

00:23:09.820 | We're certainly nowhere near there yet.

00:23:11.780 | - Do you think reality that exists outside of our mind,

00:23:19.220 | do you think there's a limit to our cognitive abilities,

00:23:24.620 | as again, descendants of apes,

00:23:26.820 | who are just biological systems?

00:23:28.820 | Is there a limit to our mind's capability

00:23:31.780 | to actually understand reality?

00:23:35.740 | There comes a point, even with the help

00:23:40.380 | of the tools of physics, that we just cannot grasp

00:23:45.060 | some fundamental aspects of that reality.

00:23:46.820 | - Again, I think that's a question

00:23:48.220 | for 5,000 years in the future.

00:23:49.820 | - We're not even close to that limit.

00:23:51.140 | - I think there is a universality.

00:23:54.060 | Here, I don't agree with David Deutsch about everything,

00:23:56.900 | but I admire the way he put things in his last book.

00:24:01.260 | And he talked about the role of explanation.

00:24:04.540 | And he talked about the universality of certain languages,

00:24:08.820 | or the universality of mathematics,

00:24:11.060 | or of computing, and so forth.

00:24:15.740 | And he believed that universality,

00:24:18.420 | which is something real, which somehow comes out

00:24:22.260 | of the fact that a symbolic system,

00:24:24.020 | or a mathematical system, can refer to itself,

00:24:27.580 | and can, I forget what that's called,

00:24:30.140 | can reference back to itself.

00:24:32.700 | And build, in which he argued for a universality

00:24:37.020 | of possibility for our understanding,

00:24:39.500 | whatever is out there.

00:24:41.380 | But I admire that argument.

00:24:45.300 | But it seems to me we're doing okay so far,

00:24:50.300 | but we'll have to see.

00:24:53.860 | - Whether there is a limit or not.

00:24:55.180 | For now, we've got plenty to play with.

00:24:57.260 | - Yeah.

00:24:58.340 | There are things which are right there in front of us,

00:25:01.780 | which we miss.

00:25:03.660 | And I'll quote my friend Eric Weinstein in saying,

00:25:07.620 | look, Einstein carried his luggage.

00:25:10.540 | Freud carried his luggage.

00:25:12.060 | Marx carried his luggage.

00:25:13.420 | Martha Graham carried her luggage, et cetera.

00:25:17.020 | Edison carried his luggage.

00:25:19.260 | All these geniuses carried their luggage.

00:25:22.020 | And not once before, relatively recently,

00:25:25.620 | did it occur to anybody to put a wheel on luggage

00:25:28.180 | and pull it.

00:25:29.020 | (laughing)

00:25:30.500 | And it was right there waiting to be invented

00:25:33.060 | for centuries.

00:25:34.620 | - So this is Eric Weinstein.

00:25:37.980 | Yeah, what do the wheels represent?

00:25:40.540 | Are you basically saying that there's stuff

00:25:42.180 | right in front of our eyes that once we,

00:25:45.180 | it just clicks, we put the wheels in the luggage,

00:25:48.260 | a lot of things will fall into place?

00:25:49.900 | - Yes, I do, I do.

00:25:52.420 | And every day I wake up and think,

00:25:55.140 | why can't I be that guy who was walking through the airport?

00:25:59.420 | - What do you think it takes to be that guy?

00:26:02.700 | Because like you said, a lot of really smart people

00:26:07.140 | carried their luggage.

00:26:08.580 | What, just psychologically speaking,

00:26:12.460 | so Eric Weinstein is a good example of a person

00:26:14.580 | who thinks outside the box.

00:26:16.140 | - Yes.

00:26:16.980 | - Who resists almost conventional thinking.

00:26:21.060 | You're an example of a person who,

00:26:23.460 | by habit, by psychology, by upbringing, I don't know,

00:26:28.900 | but resists conventional thinking as well, just by nature.

00:26:31.980 | - Thank you, that's a compliment.

00:26:32.900 | - That's a compliment?

00:26:34.100 | Good, so what do you think it takes to do that?

00:26:37.260 | Is that something you were just born with?

00:26:39.360 | - I doubt it.

00:26:42.060 | Well, from my studying some cases,

00:26:47.020 | 'cause I'm curious about that, obviously,

00:26:49.860 | and just in a more concrete way,

00:26:52.520 | when I started out in physics,

00:26:54.420 | 'cause I started a long way from physics,

00:26:57.860 | so it took me a long, not a long time,

00:27:00.820 | but a lot of work to get to study it and get into it,

00:27:04.300 | so I did wonder about that.

00:27:05.860 | And so I read the biographies,

00:27:10.420 | and in fact, I started with the autobiography of Weinstein

00:27:12.980 | and Newton and Galileo and all those people.

00:27:17.980 | And I think there's a couple things.

00:27:22.780 | Some of it is luck, being in the right place

00:27:24.900 | at the right time.

00:27:26.340 | Some of it is stubbornness and arrogance,

00:27:28.820 | which can easily go wrong.

00:27:30.460 | - Yes.

00:27:31.980 | - And I know all of these are doorways,

00:27:36.300 | if you go through them slightly at the wrong speed

00:27:38.980 | or in the wrong angle, they're ways to fail.

00:27:43.980 | But if you somehow have the right luck,

00:27:47.620 | the right confidence and arrogance, caring,

00:27:52.060 | I think Einstein cared to understand nature

00:27:56.020 | with a ferocity and a commitment

00:28:00.140 | that exceeded other people of his time.

00:28:02.220 | So he asked more stubborn questions,

00:28:05.060 | he asked deeper questions.

00:28:08.120 | I think, and there's a level of ability,

00:28:14.940 | and whether ability is born in or can be developed

00:28:20.020 | to the extent to which it can be developed,

00:28:21.700 | like any of these things, like musical talent.

00:28:25.620 | - You mentioned ego.

00:28:27.060 | What's the role of ego in that process?

00:28:28.980 | - Confidence.

00:28:30.060 | - Confidence, but in your own life,

00:28:33.740 | have you found yourself walking that nice edge

00:28:36.440 | of too much or too little?

00:28:38.900 | So being overconfident and therefore leading yourself astray

00:28:42.520 | or not sufficiently confident to throw away

00:28:45.820 | the conventional thinking of whatever the theory of the day,

00:28:49.260 | of theoretical physics?

00:28:50.540 | - I don't know if I, I mean, I've contributed

00:28:54.260 | where I've contributed, whether if I had had

00:28:57.380 | more confidence in something, I would have gotten further.

00:29:01.340 | I don't know.

00:29:02.220 | Certainly, I'm sitting here at this moment

00:29:08.980 | with very much my own approach to nearly everything.

00:29:14.500 | And I'm calm, I'm happy about that.

00:29:17.860 | But on the other hand, I know people

00:29:22.420 | whose self-confidence vastly exceeds mine,

00:29:26.660 | and sometimes I think it's justified,

00:29:28.500 | and sometimes I think it's not justified.

00:29:31.660 | - Your most recent book titled

00:29:35.220 | "Einstein's Unfinished Revolution,"

00:29:37.740 | so I have to ask, what is Einstein's unfinished revolution?

00:29:42.220 | And also, how do we finish it?

00:29:45.420 | - Well, that's something I've been trying

00:29:47.260 | to do my whole life.

00:29:48.380 | But Einstein's unfinished revolution

00:29:51.220 | is the twin revolutions which invented relativity theory,

00:29:54.860 | special and especially general relativity,

00:29:58.140 | and quantum theory, which he was the first person

00:30:01.260 | to realize in 1905 that there would have to be

00:30:04.900 | a radically different theory which somehow realized

00:30:09.860 | or resolved the paradox of the duality

00:30:12.220 | of particle and wave for photons.

00:30:14.320 | - And he was, I mean, people, I think,

00:30:18.060 | don't always associate Einstein with quantum mechanics,

00:30:21.180 | 'cause I think his connection with it,

00:30:23.380 | founding, as one of the founders, I would say,

00:30:27.420 | of quantum mechanics, he kind of put it in the closet.

00:30:30.460 | Is it--

00:30:31.300 | - Well, he didn't believe that the quantum mechanics,

00:30:33.980 | as it was developed in the late 19th, middle late 1920s,

00:30:38.160 | was completely correct.

00:30:39.540 | At first, he didn't believe it at all.

00:30:42.140 | Then he was convinced that it's consistent but incomplete,

00:30:45.180 | and that also is my view.

00:30:47.260 | It needs, for various reasons I can elucidate,

00:30:52.060 | to have additional degrees of freedom,

00:30:56.020 | particles, forces, something, to reach the stage

00:31:00.680 | where it gives a complete description of each phenomenon,

00:31:03.980 | as I was saying, realism demands.

00:31:07.620 | - So what aspect of quantum mechanics bothers you

00:31:11.260 | and Einstein the most?

00:31:12.940 | Is it some aspect of the wave function collapse discussions,

00:31:17.940 | the measurement problem?

00:31:19.860 | Is it the--

00:31:21.580 | - The measurement problem.

00:31:24.140 | I'm not gonna speak for Einstein.

00:31:26.140 | (Lex laughing)

00:31:27.700 | The measurement problem, basically, and the fact that--

00:31:31.900 | - What is the measurement problem, sorry?

00:31:34.100 | - The basic formulation of quantum mechanics

00:31:36.860 | gives you two ways to evolve situations in time.

00:31:41.100 | One of them is explicitly when no observer is observing

00:31:44.900 | or no measurement is taking place,

00:31:47.180 | and the other is when a measurement

00:31:48.700 | or an observation is taking place,

00:31:50.460 | and they basically contradict each other.

00:31:53.940 | But there's another reason why the revolution

00:31:56.700 | was incomplete, which is we don't understand

00:31:58.660 | the relationship between these two parts,

00:32:01.220 | general relativity, which became our best theory

00:32:04.700 | of space and time and gravitation and cosmology,

00:32:08.700 | and quantum theory.

00:32:11.600 | - So for the most part, general relativity

00:32:14.120 | describes big things, quantum theory describes

00:32:16.960 | little things, and that's the revolution

00:32:19.680 | that we found really powerful tools

00:32:21.360 | to describe big things and little things,

00:32:24.040 | and it's unfinished because we have

00:32:27.400 | two totally separate things, and we need to figure out

00:32:30.080 | how to connect them so it can describe everything.

00:32:32.360 | - Right, and we either do that,

00:32:35.120 | if we believe quantum mechanics, as understood now,

00:32:38.480 | is correct, by bringing general relativity

00:32:42.120 | or some extension of general relativity

00:32:44.160 | that describes gravity and so forth

00:32:46.520 | into the quantum domain that's called quantized,

00:32:49.680 | the theory of gravity, or if you believe

00:32:54.440 | with Einstein that quantum mechanics

00:32:56.880 | needs to be completed, and this is my view,

00:33:01.400 | then part of the job of finding the right completion

00:33:04.880 | or extension of quantum mechanics

00:33:07.120 | would be one that incorporated space-time and gravity.

00:33:10.340 | - So, where do we begin?

00:33:14.960 | So first, let me ask, perhaps you can give me a chance,

00:33:19.640 | if I could ask you some just really basic questions,

00:33:22.120 | well, they're not at all, the basic questions

00:33:24.320 | are the hardest, but you mentioned space-time.

00:33:26.760 | What is space-time?

00:33:28.920 | - Space-time, you talked about a construction,

00:33:32.280 | so I believe that space-time is an intellectual construction

00:33:36.440 | that we make of the events in the universe.

00:33:39.200 | I believe the events are real,

00:33:40.680 | and the relationships between the events,

00:33:43.520 | which cause which are real, but the idea

00:33:46.440 | that there's a four-dimensional smooth geometry

00:33:51.440 | which has a metric and a connection

00:33:54.000 | and satisfies the equations that Einstein wrote,

00:33:57.320 | it's a good description to some scale,

00:34:00.400 | it's a good approximation, it captures

00:34:02.440 | some of what's really going on in nature,

00:34:05.080 | but I don't believe it for a minute is fundamental.

00:34:08.600 | - So, okay, we're gonna, allow me to linger on that.

00:34:12.440 | So the universe has events, events cause other events,

00:34:16.720 | this is the idea of causality, okay, so that's real.

00:34:21.720 | - That's in my-- - In your view, is real.

00:34:25.520 | - Or hypothesis, or the theories that I have been

00:34:29.100 | working to develop make that assumption.

00:34:32.200 | So space-time, you said four-dimensional space

00:34:35.320 | is kind of the location of things,

00:34:37.200 | and time is whatever the heck time is,

00:34:42.240 | and you're saying that space-time is,

00:34:47.240 | both space and time are emergent and not fundamental?

00:34:51.480 | - No. - Sorry, before you correct me,

00:34:54.460 | what does it mean to be fundamental or emergent?

00:34:58.760 | - Fundamental means it's part of the description

00:35:01.500 | as far down as you go, we have this notion.

00:35:03.720 | - As real. - Yes.

00:35:05.160 | - As real as real could be.

00:35:07.280 | - Yeah, so I think that time is fundamental,

00:35:10.200 | and quote goes all the way down, and space does not,

00:35:14.480 | and the combination of them we use in general relativity

00:35:17.680 | that we call space-time also does not.

00:35:20.840 | - But what is time, then?

00:35:24.120 | - I think that time, the activity of time

00:35:29.480 | is a continual creation of events from existing events.

00:35:34.380 | - So if there's no events, there's no time.

00:35:37.580 | - Then there's not only no time, there's no nothing.

00:35:41.120 | - So-- - So I believe the universe

00:35:44.460 | has a history which goes to the past.

00:35:48.780 | I believe the future does not exist.

00:35:51.740 | There's a notion of a present and a notion of the past,

00:35:55.500 | and the past consists of, is a story about events

00:36:00.380 | that took place to our past.

00:36:03.640 | - So you said the future doesn't exist.

00:36:05.540 | - Yes.

00:36:06.380 | - Could you say that again?

00:36:10.220 | Can you try to give me a chance to understand that

00:36:14.100 | one more time?

00:36:15.280 | So events cause other events.

00:36:18.480 | What is this universe?

00:36:19.420 | 'Cause we'll talk about locality and non-locality.

00:36:23.580 | - Good.

00:36:25.100 | 'Cause it's a crazy, I mean, it's not crazy,

00:36:27.140 | it's a beautiful set of ideas that you propose.

00:36:32.140 | But, and if causality is fundamental,

00:36:34.660 | I'd just like to understand it better.

00:36:37.100 | What is the past, what is the future,

00:36:39.980 | what is the flow of time, even the error of time

00:36:44.580 | in our universe, in your view?

00:36:46.680 | And maybe what's an event?

00:36:49.300 | Right? - Oh, an event is

00:36:51.660 | where something changes, or where two,

00:36:55.860 | it's hard to say because it's a primitive concept.

00:37:02.220 | An event is a moment of time within space,

00:37:07.220 | this is the view in general relativity,

00:37:11.480 | where two particles intersect in their paths,

00:37:15.460 | or something changes in the path of a particle.

00:37:19.740 | Now, we are postulating that there is,

00:37:23.600 | at the fundamental level, a notion,

00:37:25.620 | which is an elementary notion,

00:37:27.220 | so it doesn't have a definition in terms of other things,

00:37:31.460 | but it is something elementary happening.

00:37:34.780 | - And it doesn't have a connection to energy,

00:37:36.900 | or matter, or exchange of any--

00:37:37.740 | - It does have a connection to energy and matter.

00:37:40.140 | - So it's at that level.

00:37:41.700 | - Yes, it involves, and that's why the version

00:37:44.980 | of a theory of events that I've developed

00:37:49.700 | with Marina Cortes, and by the way,

00:37:51.540 | I want to mention my collaborators,

00:37:54.040 | because they've been at least as important

00:37:55.940 | in this work as I have, as Marina Cortes

00:37:59.100 | in all the works since about 2013, 2012, 2013,

00:38:04.100 | about causality, causal sets, and in the period

00:38:08.260 | before that, Roberto Manguibara Unger,

00:38:11.220 | who is a philosopher and a professor of law.

00:38:14.780 | - And that's in your efforts together

00:38:16.900 | with your collaborators to finish the unfinished revolution.

00:38:20.100 | - Yes. - And focus on causality

00:38:22.100 | as a fundamental-- - Yes.

00:38:24.380 | - As fundamental to physics.

00:38:25.860 | - And there's certainly other people we've worked with,

00:38:30.380 | but those two people's thinking

00:38:32.700 | had a huge influence on my own thinking.

00:38:34.940 | - So in the way you describe causality,

00:38:36.780 | that's what you mean of time being fundamental,

00:38:39.460 | that causality is fundamental.

00:38:41.700 | - Yes.

00:38:43.680 | - And what does it mean for space to not be fundamental,

00:38:47.360 | to be emergent? - That's very good.

00:38:48.880 | That there's a level of description

00:38:51.280 | in which there are events, there are events

00:38:54.920 | create other events, but there's no space.

00:38:59.320 | They don't live in space.

00:39:00.760 | They have an order in which they caused each other,

00:39:04.040 | and that is part of the nature of time for us.

00:39:10.080 | But there is an emergent approximate description,

00:39:13.720 | and you asked me to define emergent, I didn't.

00:39:16.120 | An emergent property is a property

00:39:22.160 | that arises at some level of complexity,

00:39:26.500 | larger than and more complex than the fundamental level,

00:39:31.280 | which requires some property to describe it,

00:39:36.160 | which is not directly explicable or derivable,

00:39:41.160 | is the word I want,

00:39:44.640 | from the properties of the fundamental things.

00:39:48.680 | - And space is one of those things

00:39:50.860 | in a sufficiently complex universe,

00:39:53.160 | space, three-dimensional position of things emerged.

00:39:58.160 | - Yes, and we have this, we saw how this happens in detail

00:40:03.000 | in some models, both computationally and analytically.

00:40:07.680 | - Okay, so connected to space is the idea of locality.

00:40:11.280 | - Yes.

00:40:12.120 | - So we talked about realism.

00:40:15.240 | So I live in this world, I like sports.

00:40:19.860 | Locality is a thing that you can affect things close to you

00:40:25.440 | and don't have an effect on things that are far away.

00:40:29.880 | It's the thing that bothers me about gravity in general,

00:40:32.880 | or action at a distance.

00:40:35.120 | Same thing that probably bothered Newton,

00:40:37.400 | or at least he said a little bit about it.

00:40:40.080 | Okay, so what do you think about locality?

00:40:45.560 | Is it just a construct?

00:40:46.980 | Is it us humans just like this idea

00:40:51.680 | and are connected to it because we exist in it,

00:40:54.200 | we need it for our survival, but it's not fundamental?

00:40:57.120 | I mean, it seems crazy for it not to be

00:40:58.920 | a fundamental aspect of our reality.

00:41:01.920 | - It does.

00:41:02.760 | - So can you comfort me, sort of as a therapist?

00:41:05.840 | - I'm not a good therapist, but I'll do my best.

00:41:10.440 | - Okay.

00:41:11.280 | - There are several different definitions of locality

00:41:16.820 | when you come to talk about locality in physics.

00:41:19.620 | In quantum field theory, which is a mixture

00:41:25.520 | of special relativity and quantum mechanics,

00:41:29.640 | there is a precise definition of locality.

00:41:32.640 | Field operators corresponding to events in space-time,

00:41:37.560 | which are spaced like separated commute

00:41:39.320 | with each other as operators.

00:41:41.440 | - So in quantum mechanics, you think about

00:41:44.240 | the nature of reality as fields,

00:41:46.200 | and things that are close in a field

00:41:48.760 | have an impact on each other more than farther away.

00:41:53.000 | - That's, yes.

00:41:54.200 | That's very comforting.

00:41:55.560 | That makes sense.

00:41:56.400 | - So that's a property of quantum field theory,

00:41:58.400 | and it's well-tested.

00:42:00.360 | Unfortunately, there's another definition of local,

00:42:04.920 | which was expressed by Einstein,

00:42:07.680 | and expressed more precisely by John Bell,

00:42:11.100 | which has been tested experimentally and found to fail.

00:42:15.740 | And this setup is you take two particles.

00:42:19.620 | So one thing that's really weird about quantum mechanics

00:42:24.000 | is a property called entanglement.

00:42:26.520 | You can have two particles interact

00:42:28.920 | and then share a property without it being a property

00:42:32.720 | of either one of the two particles.

00:42:35.440 | And if you take such a system,

00:42:38.520 | and then you make a measurement on particle A,

00:42:43.480 | which is over here on my right side,

00:42:46.080 | and particle B, which is over here,

00:42:48.240 | somebody else makes a measurement on particle B,

00:42:52.140 | you can ask that wherever is the real reality of particle B,

00:42:57.140 | it not be affected by the choice

00:43:01.980 | the observer at particle A makes about what to measure.

00:43:04.660 | Not the outcome, just the choice

00:43:07.100 | of the different things they might measure.

00:43:09.680 | And that's a notion of locality,

00:43:11.420 | because it assumes that these things

00:43:13.220 | are very far space-like separated,

00:43:16.060 | and it's gonna take a while for any information

00:43:19.060 | about the choice made by the people here at A

00:43:22.180 | to affect the reality at B.

00:43:24.100 | But you make that assumption, that's called Bell locality.

00:43:27.620 | And you derive a certain inequality

00:43:30.140 | that some correlations,

00:43:32.460 | functions of correlations have to satisfy.

00:43:36.060 | And then you can test that pretty directly

00:43:39.380 | in experiments which create pairs of photons

00:43:42.300 | or other particles.

00:43:44.020 | And it's wrong by many sigma.

00:43:46.820 | - In experiment, it doesn't match.

00:43:49.940 | So what does that mean?

00:43:51.860 | - That means that that definition

00:43:53.860 | of locality I stated is false.

00:43:56.460 | - The one that Einstein was playing with?

00:43:58.860 | - Yeah, and the one that I stated,

00:44:00.740 | that is, it's not true that whatever is real

00:44:04.780 | about particle B is unaffected by the choice

00:44:08.700 | that the observer makes as to what to measure

00:44:10.980 | in particle A, no matter how long they've been propagating

00:44:14.620 | at almost the speed of light,

00:44:15.980 | or the speed of light away from each other.

00:44:18.460 | - No matter, so like the distance between them?

00:44:22.020 | - Well, it's been tested, of course,

00:44:23.660 | if you want to have hope for quantum mechanics

00:44:27.540 | being incomplete or wrong,

00:44:29.140 | and corrected by something that changes this.

00:44:32.460 | It's been tested over a number of kilometers.

00:44:35.900 | I don't remember whether it's 25 kilometers

00:44:39.420 | or 100 and something kilometers.

00:44:42.140 | So in trying to solve the unsolved revolution,

00:44:47.140 | in trying to come up with a theory for everything,

00:44:50.180 | is causality fundamental and breaking away from locality?

00:44:55.180 | - Absolutely.

00:44:58.380 | - A crucial step.

00:45:00.420 | So in your book, essentially,

00:45:02.460 | those are the two things we really need

00:45:04.660 | to think about as a community,

00:45:07.860 | especially the physics community has to think about this.

00:45:11.500 | So I guess my question is, how do we solve,

00:45:15.700 | how do we finish the unfinished revolution?

00:45:19.140 | - Well, that's, I can only tell you what I'm trying to do,

00:45:22.780 | and what I have abandoned.

00:45:24.380 | - Yes, exactly.

00:45:26.080 | - As not working.

00:45:27.900 | - As one ant, smart ant in an ant colony.

00:45:30.920 | - Or maybe dumb, that's why, who knows?

00:45:35.940 | But anyway, my view of the,

00:45:40.260 | we've had some nice theories invented.

00:45:43.100 | There's a bunch of different ones,

00:45:47.220 | both relate to quantum mechanics,

00:45:49.620 | relate to quantum gravity.

00:45:51.900 | There's a lot to admire in many of these different approaches

00:45:56.780 | but to my understanding,

00:45:58.580 | none of them completely solve the problems that I care about.

00:46:04.100 | And so we're in a situation

00:46:08.900 | which is either terrifying for a student

00:46:11.860 | or full of opportunity for the right student,

00:46:14.980 | in which we've got more than a dozen attempts,

00:46:19.580 | and I never thought, I don't think anybody anticipated

00:46:22.180 | it would work out this way, which worked partly,

00:46:24.940 | and then at some point, they have an issue

00:46:27.640 | that nobody can figure out how to go around

00:46:29.900 | or how to solve.

00:46:30.940 | And that's the situation we're in.

00:46:36.120 | My reaction to that is twofold.

00:46:39.560 | One of them is to try to bring people,

00:46:42.680 | we evolved into this unfortunate sociological situation

00:46:46.940 | in which there are communities

00:46:48.840 | around some of these approaches.

00:46:50.700 | And to borrow again a metaphor from Eric,

00:46:53.780 | they sit on top of hills in the landscape of theories

00:46:58.020 | and throw rocks at each other.

00:47:00.420 | And as Eric says, we need two things.

00:47:02.900 | We need people to get off their hills

00:47:05.460 | and come down into the valleys and party and talk

00:47:08.700 | and become friendly and learn to say

00:47:12.940 | not no but, but yes and.

00:47:17.860 | Yes, your idea goes this far,

00:47:19.700 | but maybe if we put it together with my idea,

00:47:21.840 | we can go further.

00:47:22.980 | - Yes.

00:47:23.820 | So in that spirit, I've talked several times

00:47:29.340 | with Sean Carroll, who's also written

00:47:32.700 | an excellent book recently.

00:47:34.260 | And he kind of, he plays around,

00:47:36.900 | is a big fan of the many worlds interpretation

00:47:39.020 | of quantum mechanics.

00:47:40.460 | So I'm a troublemaker, so let me ask,

00:47:44.460 | what's your sense of Sean

00:47:47.300 | and the idea of many worlds interpretation?

00:47:50.020 | I've read many, the commentary back and forth.

00:47:52.780 | You guys are friendly, respect each other,

00:47:55.820 | but have a lot of fun debating.

00:47:57.420 | - I love Sean and he, no, I really,

00:48:02.300 | he's articulate and he's a great representative

00:48:07.300 | or ambassador of science to the public

00:48:10.300 | and for different fields of science to each other.

00:48:13.400 | He also, like I do, takes philosophy seriously.

00:48:19.300 | And unlike what I do in all cases,

00:48:24.380 | he's really done the homework.

00:48:26.460 | He's read a lot, he knows the people,

00:48:29.160 | he talks to them, he exposes his arguments to them.

00:48:34.160 | And I, there's this mysterious thing

00:48:37.540 | that we so often end up on the opposite sides

00:48:40.700 | of one of these issues.

00:48:41.820 | - It's fun though.

00:48:43.100 | - It's fun and I'd love to have a conversation about that,

00:48:47.740 | but I would want to include him.

00:48:50.140 | - I see, about many worlds.

00:48:51.660 | Well--

00:48:52.500 | - No, I can tell you what I think about many worlds.

00:48:54.060 | - I'd love to, but actually on that, let me pause.

00:48:56.220 | Sean has a podcast, you should definitely figure out

00:48:58.960 | how to talk to Sean.

00:49:00.700 | I actually told Sean I would love to hear you guys

00:49:03.060 | just going back and forth.

00:49:05.060 | So I hope you can make that happen eventually,

00:49:07.540 | you and Sean.

00:49:08.380 | - I won't tell you what it is,

00:49:09.600 | but there's something that Sean said to me

00:49:12.180 | in June of 2016 that changed my whole approach to a problem.

00:49:17.180 | But I have to tell him first.

00:49:19.260 | - Yes, and that'll be great to tell him on his podcast.

00:49:23.300 | So--

00:49:24.140 | - I can invite myself to his podcast.

00:49:26.260 | - I told him, yeah, okay, we'll make it happen.

00:49:28.580 | So many worlds.

00:49:30.020 | - Anyway.

00:49:30.860 | - What's your view?

00:49:32.560 | Many worlds, we talked about non-locality.

00:49:34.840 | Many worlds is also a very uncomfortable idea

00:49:39.800 | or beautiful, depending on your perspective.

00:49:43.440 | It's very nice in terms of,

00:49:48.440 | I mean, there's a realist aspect to it.

00:49:50.600 | I think you called it magical realism.

00:49:52.580 | - Yeah.

00:49:53.420 | (laughing)

00:49:54.260 | - It's just a beautiful line.

00:49:55.760 | But at the same time, it's very difficult

00:49:58.880 | to for our limited human minds to comprehend.

00:50:01.400 | So what are your thoughts about it?

00:50:03.240 | - Let me start with the easy and obvious

00:50:08.640 | and then go to the scientific.

00:50:10.760 | - Okay.

00:50:12.280 | - It doesn't appeal to me.

00:50:13.520 | It doesn't answer the questions that I want answered.

00:50:17.720 | And it does so to such a strong case

00:50:20.460 | that when Roberto Manguibar-Anger and I

00:50:23.280 | began looking for principles,

00:50:24.960 | and I want to come back and talk about

00:50:26.400 | the use of principles in science,

00:50:28.560 | 'cause that's the other thing I was gonna say,

00:50:30.180 | and I don't want to lose that.

00:50:31.680 | When we started looking for principles,

00:50:34.640 | we made our first principle, there is just one world,

00:50:37.660 | and it happens once.

00:50:39.000 | But so it's not helpful to my personal approach,

00:50:44.880 | to my personal agenda.

00:50:49.040 | But of course, I'm part of a community.

00:50:52.360 | And my sense of the many worlds interpretation,

00:50:57.040 | I have thought a lot about it and struggled a lot with it,

00:51:00.800 | is the following.

00:51:02.860 | First of all, there's Everett himself,

00:51:07.820 | there's what's in Everett.

00:51:09.400 | And there are several issues there

00:51:13.560 | connected with the derivation of the Born Rule,

00:51:16.880 | which is the rule that gives probabilities to events.

00:51:20.960 | And the reasons why there is a problem with probability

00:51:25.420 | is that I mentioned the two ways

00:51:28.480 | that physical systems can evolve.

00:51:31.280 | The many worlds interpretation cuts off,

00:51:34.360 | one, the one having to do with measurement,

00:51:37.080 | and just has the other one, the Schrodinger evolution,

00:51:39.740 | which is this smooth evolution of the quantum state.

00:51:43.020 | But the notion of probability is only in the second rule,

00:51:48.720 | which we've thrown away.

00:51:50.820 | So where does probability come from?

00:51:52.560 | You have to answer the question,

00:51:54.920 | because experimentalists use probabilities

00:51:57.680 | to check the theory.

00:51:58.880 | Now, at first sight, you get very confused,

00:52:05.000 | 'cause there seems to be a real problem.

00:52:07.480 | Because in the many worlds interpretation,

00:52:10.880 | this talk about branches is not quite precise,

00:52:13.460 | but I'll use it.

00:52:14.500 | There's a branch in which everything that might happen

00:52:19.200 | does happen, with probability one in that branch.

00:52:23.840 | You might think you could count the number of branches

00:52:27.420 | in which things do and don't happen,

00:52:30.240 | and get numbers that you can define

00:52:32.340 | as something like frequentist probabilities.

00:52:34.860 | And Everett did have an argument in that direction.

00:52:40.200 | But the argument gets very subtle

00:52:43.260 | when there are an infinite number of possibilities,

00:52:45.780 | as is the case in most quantum systems.

00:52:48.940 | And my understanding, although I'm not as much of an expert

00:52:53.220 | as some other people, is that Everett's own proposal failed,

00:52:58.220 | did not work.

00:52:59.420 | There are then, but it doesn't stop there.

00:53:05.420 | There is an important idea that Everett didn't know about,

00:53:08.540 | which is decoherence, and it is a phenomenon

00:53:11.260 | that might be very much relevant.

00:53:14.840 | And so a number of people post-Everett

00:53:19.140 | have tried to make versions of what you might call

00:53:22.320 | many worlds quantum mechanics.

00:53:24.260 | And this is a big area, and it's subtle,

00:53:29.720 | and it's not the kind of thing that I do well.

00:53:33.140 | So I consulted, that's why there's two chapters on this

00:53:36.260 | in the book I wrote, chapter 10,

00:53:38.300 | which is about Everett's version, and chapter 11.

00:53:41.720 | There's a very good group of philosophers of physics

00:53:45.200 | in Oxford, Simon Saunders, David Wallace,

00:53:49.480 | Harvey Brown, and a number of others.

00:53:52.840 | And of course, there's David Deutsch, who is there.

00:53:57.160 | And those people have developed and put a lot of work

00:54:01.520 | into a very sophisticated set of ideas

00:54:04.320 | designed to come back and answer that question.

00:54:07.620 | They have the flavor of, there are really no probabilities,

00:54:11.440 | we admit that, but imagine if the Everett story was true

00:54:15.760 | and you were living in that multiverse,

00:54:18.800 | how would you make bets?

00:54:21.000 | And so they use decision theory

00:54:24.680 | from the theory of probability and gambling and so forth

00:54:28.680 | to shape a story of how you would bet

00:54:33.080 | if you were inside an Everettian universe and you knew that.

00:54:37.840 | And there's a debate among those experts

00:54:41.960 | as to whether they or somebody else has really succeeded.

00:54:46.600 | And when I checked in as I was finishing the book

00:54:50.800 | with some of those people, like Simon,

00:54:52.840 | who's a good friend of mine, and David Wallace,

00:54:56.640 | they told me that they weren't sure

00:54:59.280 | that any of them was yet correct.

00:55:02.180 | So that's what I put in my book.

00:55:04.880 | Now, to add to that, Sean has his own approach

00:55:08.160 | to that problem in what's called self-referencing

00:55:10.760 | or self-locating observers.

00:55:13.480 | And it doesn't, I tried to read it

00:55:19.680 | and it didn't make sense to me,

00:55:22.560 | but I didn't study it hard, I didn't communicate with Sean,

00:55:25.540 | I didn't do the things that I would do,

00:55:27.040 | so I had nothing to say about it in the book.

00:55:29.360 | I don't know whether it's right or not.

00:55:34.440 | - Let's talk a little bit about science.

00:55:36.560 | You mentioned the use of principles in science.

00:55:39.820 | What does it mean to have a principle

00:55:43.100 | and why is that important?

00:55:45.400 | - When I feel very frustrated about quantum gravity,

00:55:48.480 | I like to go back and read history.

00:55:50.740 | And of course, Einstein, his achievements are a huge lesson

00:55:56.880 | and hopefully something like a role model.

00:56:00.880 | And it's very clear that Einstein thought

00:56:05.200 | that the first job when you want to enter a new domain

00:56:09.080 | of theoretical physics is to discover and invent principles

00:56:13.360 | and then make models of how those principles

00:56:15.880 | might be applied in some experimental situation,

00:56:19.260 | which is where the mathematics comes in.

00:56:22.440 | So for Einstein, there was no unified space and time.

00:56:27.560 | Minkowski invented this idea of space time.

00:56:30.880 | For Einstein, it was a model of his principles

00:56:33.880 | or his postulates.

00:56:35.320 | And I've taken the view that we don't know the principles

00:56:41.280 | of quantum gravity.

00:56:43.600 | I can think about candidates and I have some papers

00:56:47.060 | where I discuss different candidates

00:56:50.280 | and I'm happy to discuss them.

00:56:51.840 | But my belief now is that those partially successful

00:56:57.000 | approaches are all models which might describe indeed

00:57:02.000 | some quantum gravity physics in some domain,

00:57:07.160 | in some aspect, but ultimately would be important

00:57:12.160 | because they model the principles

00:57:15.360 | and the first job is to tie down those principles.

00:57:18.360 | So that's the approach that I'm taking.

00:57:21.440 | - So speaking of principles, in your 2006 book,

00:57:26.440 | The Trouble with Physics, you criticized a bit

00:57:30.920 | string theory for taking us away from the rigors

00:57:34.160 | of the scientific method or whatever you would call it.

00:57:37.120 | But what's the trouble with physics today

00:57:42.120 | and how do we fix it?

00:57:44.240 | - Can I say how I read that book?

00:57:47.400 | - Sure.

00:57:48.240 | - Because I, and I'm not, this of course has to be my fault

00:57:52.440 | because you can't as an author claim

00:57:55.680 | after all the work you put in that you were misread.

00:57:58.320 | But I will say that many of the reviewers

00:58:04.480 | who are not personally involved and even many

00:58:07.520 | who were working on string theory

00:58:09.720 | or some other approach to quantum gravity

00:58:12.400 | told me, communicated with me and told me

00:58:14.360 | they thought that I was fair

00:58:16.120 | and balance was the word that was usually used.

00:58:20.840 | So let me tell you what my purpose was

00:58:23.120 | in writing that book, which clearly got diverted by,

00:58:28.120 | because there was already a rather hot argument going on.

00:58:33.760 | And this is--

00:58:36.000 | - On which topic, on string theory specifically

00:58:38.600 | or in general in physics?

00:58:40.180 | - No, more specifically than string theory.

00:58:44.060 | So since we're in Cambridge, can I say that?

00:58:47.680 | We're doing this in Cambridge.

00:58:48.520 | - Yeah, of course, Cambridge, just to be clear,

00:58:51.120 | Massachusetts and on Harvard campus.

00:58:55.600 | - Right, so Andy Strominger is a good friend of mine

00:59:00.600 | and has been for many, many years.

00:59:03.460 | And Andy, so originally there was this beautiful idea

00:59:08.460 | that there were five string theories

00:59:11.360 | and maybe they would be unified into one.

00:59:14.400 | And we would discover a way to break that,

00:59:17.560 | the symmetries of one of those string theories

00:59:20.640 | and discover the standard model

00:59:22.800 | and predict all the properties

00:59:24.560 | of the standard model particles,

00:59:26.280 | like their masses and charges and so forth, coupling constant.

00:59:30.080 | And then there was a bunch of solutions

00:59:34.860 | to string theory found, which led each of them

00:59:38.500 | to a different version of particle physics

00:59:40.560 | with a different phenomenology.

00:59:42.700 | These are called the Calabi-Yau metaphors,

00:59:46.560 | named after Yau, who was also here.

00:59:50.280 | Not, certainly we've been friends

00:59:52.520 | sometime in the past anyway.

00:59:54.260 | And then there were, nobody was sure,

00:59:57.880 | but hundreds of thousands of different versions

01:00:00.200 | of string theory.

01:00:01.840 | And then Andy found there was a way

01:00:04.620 | to put a certain kind of mathematical curvature

01:00:07.480 | called torsion into the solutions.

01:00:10.440 | And he wrote a paper, "String Theory with Torsion,"

01:00:13.860 | in which he discovered there was

01:00:18.640 | not formally uncountable, but he was unable

01:00:21.040 | to invent any way to count the number of solutions

01:00:24.560 | or classify the diverse solutions.

01:00:27.480 | And he wrote that this is worrying

01:00:31.100 | because doing phenomenology the old-fashioned way

01:00:33.880 | by solving the theory is not gonna work

01:00:37.400 | because there's gonna be loads of solutions

01:00:41.100 | for editing proposed phenomenology

01:00:42.940 | for anything in the experiments.

01:00:44.840 | This hasn't quite worked out that way.

01:00:47.480 | But nonetheless, he took that worry to me.

01:00:50.640 | We spoke at least once, maybe two or three times about that.

01:00:56.640 | And I got seriously worried about that.

01:00:59.040 | And this is a little--

01:01:02.440 | - Sounds like an anecdote that inspired

01:01:05.020 | your worry about string theory in general.

01:01:07.280 | - Well, I tried to solve the problem,

01:01:10.080 | and I tried to solve the problem.

01:01:12.960 | I was reading at that time a lot of biology,

01:01:15.720 | a lot of evolutionary theory,

01:01:17.280 | like Lin-Margulis and Steve Gould and so forth.

01:01:22.280 | And I could take your time to go through the things,

01:01:28.080 | but it occurred to me maybe physics

01:01:31.400 | was like evolutionary biology,

01:01:33.960 | and maybe the laws evolved.

01:01:36.040 | And there was, the biologists talk about a landscape,

01:01:40.040 | a fitness landscape of DNA sequences

01:01:44.040 | or protein sequences or species or something like that.

01:01:48.800 | And I took their concept and the word landscape

01:01:51.360 | from theoretical biology and made a scenario

01:01:54.560 | about how the universe as a whole could evolve

01:01:59.080 | to discover the parameters of the standard model.

01:02:03.520 | And I'm happy to discuss,

01:02:04.640 | that's called cosmological natural selection.

01:02:07.240 | - Cosmological natural selection.

01:02:09.920 | - Yeah, and I--

01:02:10.760 | - Wow, so the parameters of the standard model,

01:02:12.600 | so it's the laws of physics are changing.

01:02:15.520 | This idea would say that the laws of physics

01:02:18.960 | are changing in some way that echoes

01:02:23.400 | that of natural selection,

01:02:24.880 | or just it adjusts in some way towards some goal.

01:02:28.840 | - Yes, and I published that,

01:02:32.560 | I wrote the paper in '88 or '89,

01:02:36.600 | the paper was published in '92.

01:02:39.120 | My first book in 1997,

01:02:41.040 | The Life of the Cosmos was explicitly about that.

01:02:45.480 | And I was very clear that what was important

01:02:49.280 | is that because you would develop an ensemble of universes,

01:02:54.280 | but they were related by descent through natural selection,

01:02:59.260 | almost every universe would share the property

01:03:03.500 | that it was, its fitness was maximized to some extent,

01:03:08.500 | or at least close to maximum.

01:03:10.920 | And I could deduce predictions

01:03:12.480 | that could be tested from that.

01:03:16.080 | And I worked all of that out,

01:03:18.240 | and I compared it to the anthropic principle

01:03:20.440 | where you weren't able to make tests

01:03:23.320 | or make falsifications.

01:03:24.480 | All of this was in the late '80s and early '90s.

01:03:28.400 | - That's a really compelling notion,

01:03:30.000 | but how does that help you arrive--

01:03:32.840 | - I'm coming to where the book came from.

01:03:36.060 | - Yes.

01:03:37.000 | - So what got me,

01:03:41.080 | I worked on string theory.

01:03:42.720 | I also worked on loop quantum gravity,

01:03:47.480 | and I was one of the inventors of loop quantum gravity.

01:03:50.640 | And because of my strong belief in some other principles,

01:03:55.480 | which led to this notion of wanting a quantum theory

01:03:58.040 | of gravity to be what we call relational

01:04:00.900 | or background independent,

01:04:03.000 | I tried very hard to make string theory

01:04:05.960 | background independent,

01:04:07.600 | and ended up developing a bunch of tools

01:04:09.840 | which then could apply directly to general relativity,

01:04:12.600 | and that became loop quantum gravity.

01:04:15.040 | So the things were very closely related,

01:04:17.280 | and have always been very closely related in my mind.

01:04:20.440 | The idea that there were two communities,

01:04:22.160 | one devoted to strings and one devoted to loops,

01:04:24.640 | is nuts and has always been nuts.

01:04:27.720 | - Okay, so--

01:04:30.440 | - So anyway--

01:04:31.360 | - There's this nuts community of loops and strings

01:04:34.000 | that are all beautiful and compelling

01:04:35.680 | and mathematically speaking,

01:04:37.400 | and what's the trouble with all that?

01:04:38.800 | Why is that such a problem?

01:04:40.800 | - So I was interested in developing that notion

01:04:45.640 | of how science works based on a community and ethics

01:04:48.400 | that I told you about.

01:04:49.700 | And I wrote a draft of a book about that,

01:04:54.780 | which had several chapters on methodology of science,

01:04:58.840 | and it was a rather academically oriented book.

01:05:02.520 | And those chapters were the first part of the book,

01:05:06.600 | the first third of it,

01:05:07.720 | and you can find their remnants

01:05:09.880 | in what's now the last part of "The Trouble with Physics."

01:05:14.560 | And then I described a number of test cases, case studies,

01:05:18.720 | and one of them, which I knew,

01:05:20.220 | was the search for quantum gravity

01:05:22.440 | and string theory and so forth.

01:05:24.120 | And I was unable to get that book published.

01:05:29.660 | So somebody made the suggestion of flipping it around

01:05:34.660 | and starting with the story of string theory,

01:05:36.780 | which was already controversial.

01:05:38.580 | This was 2004, 2005.

01:05:41.580 | But I was very careful to be detailed,

01:05:47.420 | to criticize papers and not people.

01:05:52.860 | You won't find me criticizing individuals,

01:05:55.500 | you'll find me criticizing certain writing.

01:05:59.060 | But in any case, here's what I regret.

01:06:04.060 | Let me make your program worthwhile.

01:06:06.500 | - Yes.

01:06:07.340 | - As far as I know, with the exception of not understanding

01:06:11.940 | how large the applications to condensed matter,

01:06:15.340 | say, of ADS-CFT would get,

01:06:20.340 | I think largely my diagnosis of string theory,

01:06:26.580 | as it was then, has stood up since 2006.

01:06:30.340 | What I regret is that the same critique,

01:06:34.940 | I was using string theory as an example,

01:06:37.500 | and the same critique applies to many other communities

01:06:41.780 | in science and all of, including,

01:06:44.380 | and this is where I regret my own community,

01:06:46.500 | that is a community of people working on quantum gravity

01:06:49.860 | outside string theory.

01:06:52.220 | But, and I considered saying that explicitly.

01:06:55.880 | But to say that explicitly,

01:06:57.220 | since it's a small, intimate community,

01:07:00.460 | I would be telling stories and naming names of,

01:07:04.100 | and making a kind of history that I have no right to write.

01:07:08.900 | So I stayed away from that, but was misunderstood.

01:07:12.060 | - But if I may ask, is there a hopeful message

01:07:16.380 | for theoretical physics that we can take from that book,

01:07:20.260 | sort of that looks at the community,

01:07:22.080 | not just your own work on,

01:07:24.780 | not with causality and non-locality,

01:07:26.800 | but just broadly in understanding

01:07:29.060 | the fundamental nature of our reality,

01:07:32.060 | what's your hope for the 21st century in physics

01:07:36.060 | that we can take?

01:07:37.060 | - Well, that we solve the problem.

01:07:38.760 | - That we solve the unfinished problem of life science.

01:07:44.260 | - That's certainly the thing that I care about most,

01:07:46.980 | and hope for most.

01:07:49.180 | Let me say one thing.

01:07:50.620 | Among the young people that I work with,

01:07:53.740 | I hear very often and sense a total disinterest

01:07:58.740 | in these arguments that we older scientists have.

01:08:03.420 | And an interest in what each other is doing,

01:08:05.800 | and this is starting to appear in conferences

01:08:09.860 | where the young people interested in quantum gravity

01:08:13.300 | make a conference, they invite loops and strings

01:08:16.300 | and causal dynamical triangulations and causal set people.

01:08:20.540 | And we're having a conference like this next week,

01:08:24.060 | a small workshop at Perimeter,

01:08:26.980 | and I guess I'm advertising this,

01:08:28.380 | and then in the summer,

01:08:30.460 | we're having a big full-on conference,

01:08:33.460 | which is just quantum gravity.

01:08:34.900 | It's not strings, it's not loops.

01:08:37.260 | But the organizers and the speakers

01:08:39.420 | will be from all the different communities.

01:08:41.780 | And this to me is very helpful.

01:08:43.420 | - That the different ideas are coming together.

01:08:49.020 | At least people are expressing an interest in that.

01:08:52.300 | - It's a huge honor talking to you, Lee.

01:08:56.300 | Thanks so much for your time today.

01:08:57.660 | - Thank you.

01:08:59.180 | - Thanks for listening to this conversation,

01:09:01.300 | and thank you to our presenting sponsor, Cash App.

01:09:04.180 | Download it, use code LEXPODCAST,

01:09:06.820 | you'll get $10, and $10 will go to FIRST,

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01:09:12.820 | to become science and technology innovators of tomorrow.

01:09:16.300 | If you enjoy this podcast, subscribe on YouTube,

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01:09:23.340 | or simply connect with me on Twitter @LexFriedman.

01:09:27.220 | And now, let me leave you with some words from Lee Smolin.

01:09:30.420 | One possibility is,

01:09:33.380 | God is nothing but the power of the universe

01:09:36.540 | to organize itself.

01:09:38.300 | Thanks for listening, and hope to see you next time.

01:09:42.380 | (upbeat music)

01:09:44.980 | (upbeat music)

01:09:47.580 | [BLANK_AUDIO]

Lee Smolin: Quantum Gravity and Einstein's Unfinished Revolution | Lex Fridman Podcast #79

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