The following is a conversation with Lee Smolin.
He's a theoretical physicist,
co-inventor of loop quantum gravity,
and a contributor of many interesting ideas
to cosmology, quantum field theory,
the foundations of quantum mechanics,
theoretical biology, and the philosophy of science.
He's the author of several books,
including one that critiques the state of physics
and string theory called The Trouble with Physics.
In his latest book, Einstein's Unfinished Revolution,
The Search for What Lies Beyond the Quantum.
He's an outspoken personality in the public debates
on the nature of our universe,
among the top minds in the theoretical physics community.
This community has its respected academics,
its naked emperors, its outcasts and its revolutionaries,
its madmen, and its dreamers.
This is why it's an exciting world to explore
through a long-form conversation.
I recommend you listen back to the episodes
of Leonard Susskind, Sean Carroll, Michio Akaku,
Max Stegmark, Eric Weinstein, and Jim Gates.
You might be asking, why talk to physicists
if you're interested in AI?
To me, creating artificial intelligence systems
requires more than Python and deep learning.
It requires that we return to exploring
the fundamental nature of the universe
and the human mind.
Theoretical physicists venture out
into the dark, mysterious, psychologically challenging place
of first principles,
more than almost any other discipline.
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Alex Friedman, spelled F-R-I-D-M-A-N.
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And now, here's my conversation with Lee Smolin.
What is real?
Let's start with an easy question.
Put it another way,
how do we know what is real
and what is merely a creation
of our human perception and imagination?
We don't know.
We don't know.
This is science.
I presume we're talking about science.
And we believe or I believe
that there is a world that is independent of my existence
and my experience about it and my knowledge of it.
And this I call the real world.
So you said science, but even bigger than science.
Sure, sure.
I need not have said this is science.
I just was warming up.
Warming up.
Okay, now that we warmed up,
let's take a brief step outside of science.
Is it completely a crazy idea to you
that everything that exists
is merely a creation of our mind?
So like, there's a few, not many,
this is outside of science now.
People who believe sort of perception
is fundamentally what's in our human perception,
the visual cortex and so on,
the cognitive constructs that's being formed there
is the reality.
And then anything outside is something
that we can never really grasp.
Is that a crazy idea to you?
There's a version of that that is not crazy at all.
What we experience is constructed by our brains
and by our brains in an active mode.
So we don't see the raw world.
We see a very processed world.
We feel something was very processed through our brains
and our brains are incredible.
But I still believe that behind that experience
that mirror or veil or whatever you wanna call it,
there is a real world and I'm curious about it.
Can we truly, how do we get a sense of that real world?
Is it through the tools of physics
from theory to the experiments?
Or can we actually grasp it in some intuitive way
that's more connected to our ape ancestors?
Or is it still fundamentally the tools of math and physics
that really allow us to grasp it?
Let's talk about what tools they are.
What you say are the tools of math and physics.
I mean, I think we're in the same position
as our ancestors in the caves
or before the caves or whatever.
We find ourselves in this world and we're curious.
We also, it's important to be able to explain what happens
when there are fires, when there are not fires,
what animals and plants are good to eat
and all that stuff.
But we're also just curious.
We look up in the sky and we see the sun and the moon
and the stars and we see some of those move
and we're very curious about that.
And I think we're just naturally curious.
So we make, this is my version of how we work.
We make up stories and explanations.
And where there are two things
which I think are just true of being human.
We make judgments fast because we have to.
Where to survive, is that a tiger or is that not a tiger?
And we go.
Act.
We have to act fast and incomplete information.
So we judge quickly and we're often wrong.
We're at least sometimes wrong,
which is all I need for this.
We're often wrong.
So we fool ourselves and we fool other people readily.
And so there's lots of stories that get told
and some of them result in a concrete benefit
and some of them don't.
So you said we're often wrong,
but what does it mean to be right?
Right, that's an excellent question to be right.
Well, since I believe that there is a real world,
I believe that to be, you can challenge me on this
if you're not a realist.
A realist is somebody who believes
in this real objective world,
which is independent of our perception.
If I'm a realist, I think that to be right
is to come closer.
I think, first of all, there's a relative scale.
There's not right and wrong.
There's right or more right and less right.
And you're more right if you come closer
to an exact true description of that real world.
Now, can we know that for sure?
No.
And the scientific method is ultimately
what allows us to get a sense
of how close we're getting to that real world.
No on two counts.
First of all, I don't believe it's a scientific method.
I was very influenced when I was in graduate school
by the writings of Paul Firehub
and who was an important philosopher of science
who argued that there isn't a scientific method.
There is or there is?
There is not.
There's not.
Can you elaborate, I'm sorry if you were going to,
but can you elaborate on the,
what does it mean for there not to be a scientific method,
this notion that I think a lot of people believe in
in this day and age?
Sure.
Paul Firehub, he was a student of Popper
who taught- Popper, yeah.
Carl Popper and Firehub and argued both by logic
and by historical example that you name anything
that should be part of the practice of science.
Say you should always make sure
that your theories agree with all the data
that's always been taken, that's already been taken.
And he'll prove to you that there have to be times
when science contradicts, when some scientist
contradicts that advice
for science to progress overall.
So it's not a simple matter.
I think that, I think of science as a community
and- Of people.
Of people and as a community of people bound
by certain ethical precepts, precepts, whatever that is.
So in that community, a set of ideas they operate under,
I'm meaning ethically of kind of the rules
of the game they operate under.
Don't lie, report all your results,
whether they agree or don't agree with your hypothesis.
Check, the training of a scientist mostly consists
of methods of checking because again,
we make lots of mistakes.
We're very error prone, but there are tools
both on the mathematics side and the experimental side
to check and double check and triple check.
And a scientist goes through a training
and I think this is part of it.
You can't just walk off the street and say,
yo, I'm a scientist, you have to go through the training.
And the training, the test that lets you be done
with the training is can you form a convincing case
for something that your colleagues
will not be able to shout down
because the last, did you check this
and did you check that and did you check this
and what about a seeming contradiction with this?
And you've got to have answers to all those things
or you don't get taken seriously.
And when you get to the point where you can produce
that kind of defense and argument,
then they give you a PhD and you're kind of licensed.
You're still gonna be questioned
and you still may propose or publish mistakes,
but the community is gonna have to waste less time
fixing your mistakes.
Yes, but if you can maybe linger on it a little longer,
what's the gap between the thing that that community does
and the ideal of the scientific method?
The scientific method is you should be able
to repeat and experiment.
There's a lot of elements to what the scientific method,
but the final result, the hope of it
is that you should be able to say with some confidence
that a particular thing is close to the truth.
Right, but there's not a simple relationship
between experiment and hypothesis or theory.
For example, Galileo did this experiment
of dropping a ball from the top of a tower
and it falls right at the base of the tower.
And Aristotelian would say, wow,
of course it falls right to the base of the tower.
That shows that the earth isn't moving
while the ball is falling.
And Galileo says, no weight is a principle of inertia
and has an inertia in the direction
with the earth isn't moving
and the tower and the ball and the earth all move together.
When the principle of inertia tells you at the bottom,
it does look at, therefore, my principle of inertia is right.
And Aristotelian says, no,
our style of science is right, the earth is stationary.
And so you've got to get an interconnected bunch of cases
and work hard to line up and explain.
It took centuries to make the transition
from Aristotelian physics to the new physics.
It wasn't done till Newton in 1680 something, 1687.
So what do you think is the nature of the process
that seems to lead to progress?
If we at least look at the long arc of science
of all the community of scientists,
they seem to do a better job of coming up with ideas
that engineers can then take on and build rockets with
or build computers with or build cool stuff with.
I don't know, a better job than what?
Than this previous century.
So century by century, we'll talk about strength theory
and so on and kind of possible,
when you might think of us dead ends and so on.
Which is not the way I think of strength theory.
We'll straighten out, we'll get our strength straight.
But there is nevertheless in science,
very often at least temporary dead ends.
But if you look at the through centuries,
you know, the century before Newton
and the century after Newton,
it seems like a lot of ideas came closer to the truth
that then could be usable by our civilization
to build the iPhone, right?
To build cool things that improve our quality of life.
That's the progress I'm kind of referring to.
Let me, can I say that more precisely?
Yes.
It's a low bar.
I think it's important to get the time, place is right.
There was a scientific revolution
that partly succeeded between about 1900 or late 1890s
and into the 1930s, 1940s and so,
and maybe some if you stretch it into the 1970s.
And the technology, this was the discovery of relativity
and that included a lot of developments
of electromagnetism.
The confirmation which wasn't really well-confirmed
into the 20th century that matter was made of atoms
and the whole picture of nuclei with electrons going around
and this is early 20th century.
And then quantum mechanics was from 1905.
It took a long time to develop to the late 1920s.
And then it was basically in final form.
And the basis of this partial revolution
and we can come back to why it's only a partial revolution
is the basis of the technologies you mentioned.
All of, I mean, electrical technology
was being developed slowly with this.
And in fact, there's a close relation
between development of electricity
and the electrification of cities in the United States
and Europe and so forth and the development of the science.
The fundamental physics since the early 1970s
doesn't have a story like that so far.
There's not a series of triumphs and progresses
and there's not any practical application.
So just to linger briefly on the early 20th century
and the revolutions in science that happened there,
what was the method by which the scientific community
kept each other in check about when you get something right,
when you get something wrong?
Is experimental validation ultimately the final test?
It's absolutely necessary and the key things
were all validated to keep predictions
of quantum mechanics and of the theory
of electricity and magnetism.
So before we talk about Einstein,
yeah, your new book before string theory,
quantum mechanics and so on,
let's take a step back at a higher level question.
What is that you mentioned?
What is realism?
What is anti-realism?
And maybe why do you find realism
as you mentioned so compelling?
Realism is the belief in an external world
independent of our existence, our perception,
our belief, our knowledge.
A realist as a physicist is somebody who believes
that there should be possible
some completely objective description
of each and every process at the fundamental level
which describes and explains exactly what happens
and why it happens.
That kind of implies that that system
in a realist view is deterministic,
meaning there's no fuzzy magic going on
that you can never get to the bottom.
You can get to the bottom of anything
and perfectly describe it.
Some people would say that I'm not that interested
in determinism but I could live with the fundamental world
which had some chance in it.
So you said you could live with it
but do you think God plays dice in our universe?
I think it's probably much worse than that.
In which direction?
I think that theories can change
and theories can change without warning.
I think the future is open.
You mean the fundamental laws of physics can change?
Yeah.
Okay, we'll get there.
I thought we would be able to find some solid ground
but apparently the entirety of it, temporarily so.
Okay, so realism is the idea
that while the ground is solid, you can describe it.
What's the role of the human being,
our beautiful complex human mind in realism?
Do we have a, are we just another set of molecules
connected together in a clever way
or the observer, does the observer, our human mind,
consciousness have a role in this realism view
of the physical universe?
There's two ways, there's two questions you can be asking.
Does our conscious mind do our perceptions play a role
in making things become, in making things real
or things becoming?
That's question one.
Question two is, does this, we can call it
a naturalist view of the world
that is based on realism, allow a place to understand
the existence of and the nature of perceptions
and consciousness in mind.
And that's question two.
Question two, I do think a lot about
and my answer, which is not an answer is I hope so
but it certainly doesn't yet.
So what?
Question one, I don't think so.
But of course the answer to question one
depends on question two.
Right.
So I'm not up to question one yet.
So question two is the thing that you can kind of struggle
with at this time.
What about the anti-realists?
So what flavor, what are the different camps
of anti-realists that you've talked about?
I think it would be nice if you can articulate
for the people for whom there is not a very concrete
real world or there's divisions or there's a,
it's messier than the realist view of the universe.
What are the different camps?
What are the different views?
I'm not sure, I'm a good scholar and can talk about
the different camps and analyze it.
But some, many of the inventors of quantum physics
were not realists, were anti-realists in.
They're scholars, they lived in a very perilous time
between the two world wars.
And there were a lot of trends in culture
which were going that way.
But in any case, they said things like
the purpose of science is not to give
an objective realist description of nature
as it would be in our absence.
This might be saying Niels Bohr.
The purpose of science is as an extension
of our conversations with each other
to describe our interactions with nature.
And we're free to invent and use terms like
particle or wave or causality or time or space.
If they're useful to us and they carry
some intuitive implication, but we shouldn't believe
that they actually have to do with what nature
would be like in our absence,
which we have nothing to say about.
Do you find any aspect of that?
Because you kind of said that we human beings tell stories.
Do you find aspects of that kind of
anti-realist view of Niels Bohr compelling?
That we're fundamentally our storytellers
and then we create tools of space and time and causality
and whatever this fun quantum mechanic stuff is
to help us tell the story of our world?
Sure, I just would like to believe
that this is an aspiration for the other thing.
The other thing being what?
The realist point of view.
Do you hope that the stories will eventually lead us
to discovering the real world as it is?
Yeah.
It's perfection possible by the way, is it?
No, well that's, you mean will we ever get there
and know that we're there?
Yeah, exactly.
That's not my, that's for people
of 5,000 years in the future.
We're certainly nowhere near there yet.
Do you think reality that exists outside of our mind,
do you think there's a limit to our cognitive abilities?
Is again the sentence of apes for just biological systems?
Is there a limit to our mind's capability
to actually understand reality?
Sort of there comes a point even with the help
of the tools of physics,
that we just cannot grasp some fundamental aspects
of that reality.
Again, I think that's the question
for 5,000 years in the future.
We're not even close to that limit.
I think there is a universality.
Here, I don't agree with David Deutsch about everything,
but I admire the way he put things in his last book.
And he talked about the role of explanation.
And he talked about the universality of certain languages
or the universality of mathematics
or of computing and so forth.
And he believed that universality,
which is something real, which is somehow comes out
of the fact that a symbolic system
or a mathematical system can refer to itself
and can, I forget what that's called,
can reference back to itself and build
in which he argued for a universality
of possibility for our understanding,
whatever is out there.
But I admire that argument,
but it seems to me we're doing okay so far,
but we'll have to see.
Whether there is a limit or not,
for now we've got plenty to play with.
Yeah.
There are things which are right there in front of us,
which we miss.
And I'll quote my friend, Derek Weinstein,
in saying, look, Einstein carried his luggage.
Freud carried his luggage.
Marx carried his luggage.
Martha Graham carried her luggage, et cetera.
Edison carried his luggage.
All these geniuses carried their luggage.
And not once before, relatively recently,
did it occur to anybody to put a wheel on luggage and pull it.
And it was right there waiting to be invented for centuries.
So this is Eric Weinstein.
Yeah.
What do the wheels represent?
Are you basically saying that there's stuff
right in front of our eyes,
that once we, it just clicks,
we put the wheels in the luggage,
a lot of things will fall into place?
Yes, I do, I do.
And every day I wake up and think,
why can't I be that guy who was walking through the airport?
What do you think it takes to be that guy?
Because, like you said,
a lot of really smart people carry their luggage.
What, just psychologically speaking,
so Eric Weinstein is a good example of a person
who thinks outside the box,
who resists almost conventional thinking.
You're an example of a person who, by habit, by psychology,
by upbringing, I don't know,
but resists conventional thinking as well, just by nature.
Thank you, that's a compliment.
That's a compliment?
Good. So what do you think it takes to do that?
Is that something you were just born with?
I doubt it.
Well, from my studying some cases,
because I'm curious about that, obviously.
And just in a more concrete way,
when I started out in physics,
because I started a long way from physics,
so it took me a long, not a long time,
but a lot of work to get, to study it and get into it.
So I did wonder about that.
And so I read the biographies,
and in fact, I started with the autobiography of Weinstein
and Newton and Galileo and all those people.
And I think there's a couple of things.
Some of it is luck, being in the right place at the right time.
Some of it is stubbornness and arrogance,
which can easily go wrong.
And I know all of these are doorways.
If you go through them slightly at the wrong speed
or in the wrong angle, there are ways to fail.
But if you somehow have the right luck,
the right confidence, or arrogance, caring,
I think Weinstein cared to understand nature
with a ferocity and a commitment
that exceeded other people of his time.
So he asked more stubborn questions.
He asked deeper questions.
And there's a level of ability
and whether ability is born in
or can be developed to the extent to which it can be developed,
like any of these things, like musical talent.
You mentioned ego.
What's the role of ego in that process?
Confidence.
Confidence, but do you, in your own life,
have you found yourself walking that nice edge
of too much or too little, so being overconfident
and therefore leaning yourself astray
or not sufficiently confident to throw away
the conventional thinking of whatever
the theory of the day, of theoretical physics?
I don't know if, I mean, I've contributed
where I've contributed, whether,
if I had had more confidence in something,
I would have gotten further.
I don't know.
Certainly I'm sitting here at this moment
with very much my own approach to nearly everything.
And I'm calm, I'm happy about that.
But on the other hand, I know people
whose self-confidence vastly exceeds mine.
And sometimes I think it's justified
and sometimes I think it's not justified.
Your most recent book titled Einstein's Unfinished Revolution.
So I have to ask, what is Einstein's Unfinished Revolution
and also how do we finish it?
Well, that's something I've been trying to do my whole life.
But Einstein's Unfinished Revolution
is the twin revolutions which invented relativity theory,
special and especially general relativity.
And quantum theory, which he was the first person
to realize in 1905 that there would have to be
a radically different theory which somehow realized
or resolved the paradox of the duality
of particle and wave for photons.
And he was, I mean, people I think don't always
associate Einstein with quantum mechanics
because I think his connection with it,
as one of the founders, I would say of quantum mechanics,
he kind of put it in the closet, is it?
Well, he didn't believe that the quantum mechanics
as it was developed in the late 19, middle late 1920s
was completely correct.
At first he didn't believe it at all.
Then he was convinced that it's consistent but incomplete
and that also is my view.
It needs, for various reasons, I can elucidate,
to have additional degrees of freedom,
particles, forces, something to reach the stage
where it gives a complete description
of each phenomenon as I was saying, realism, demands.
So what aspect of quantum mechanics bothers you
and Einstein the most?
Is it some aspect of the wave function collapse discussions,
the measurement problem?
Is it the?
The measurement problem.
I'm not gonna speak for Einstein.
But the measurement problem basically
and the fact that- What is the measurement problem, sorry?
The basic formulation of quantum mechanics
gives you two ways to evolve situations in time.
One of them is explicitly when no observer is observing
or no measurement is taking place.
And the other is when a measurement
or an observation is taking place.
And they basically contradict each other.
But there's another reason why the revolution
wasn't complete, which is we don't understand
the relationship between these two parts.
General relativity, which became our best theory
of space and time and gravitation and cosmology
and the quantum theory.
So for the most part, general relativity describes big things.
Quantum theory describes little things.
And that's the revolution that we found
really powerful tools to describe big things
and little things.
And it's unfinished because we have
two totally separate things.
We need to figure out how to connect them
so we can describe everything.
Right, and we either do that
if we believe quantum mechanics, as understood now,
is correct by bringing general relativity
or some extension of general relativity
that describes gravity and so forth
into the quantum domain that's called quantize,
the theory of gravity.
Or if you believe with Einstein
that quantum mechanics needs to be completed,
and this is my view,
then part of the job of finding the right completion
or extension of quantum mechanics
would be one that incorporated spacetime and gravity.
So where do we begin?
So first, let me ask,
perhaps you can give me a chance
if I could ask you some just really basic questions.
Well, they're not at all.
The basic questions are the hardest,
but you mentioned spacetime.
What is spacetime?
Spacetime, you talked about a construction.
So I believe the spacetime
is a intellectual construction that we make
of the events in the universe.
I believe the events are real
and the relationships between the events
which cause which are real.
But the idea that there's a four-dimensional
smooth geometry which has a metric and a connection
and satisfies the equations that Einstein wrote,
it's a good description to some scale.
It's a good approximation.
It captures some of what's really going on in nature.
But I don't believe it for a minute is fundamental.
So, okay, we're gonna allow me to linger on that.
So the universe has events.
Events cause other events.
This is the idea of causality.
Okay, so that's real.
That's in my- In your view, Israel.
Or hypothesis or the theories that I have been working
to develop make that assumption.
So spacetime, you said four-dimensional space
is kind of the location of things
and time is whatever the heck time is.
And you're saying that spacetime is,
both space and time are emergent and not fundamental?
No.
First, sorry, before you correct me,
what does it mean to be fundamental or emergent?
Fundamental means it's part of the description
as far down as you go.
We have this notion.
It's real.
Yes.
As real as real it could be.
So I think the time is fundamental
and quote goes all the way down and space does not.
And the combination of them we use in general relativity
that we call spacetime also does not.
But what is time then?
I think that time, the activity of time
is a continual creation of events from existing events.
So if there's no events, there's no time.
Then there's not only no time, there's no nothing.
So I believe the universe has a history
which goes to the past.
I believe the future does not exist.
There's a notion of a present and a notion of the past.
And the past consists of,
is a story about events that took place to our past.
So you said the future doesn't exist?
Yes.
Could you say that again?
Can you try to give me a chance to understand that
one more time?
So the events cause other events.
What is this universe?
Cause we'll talk about locality and non-locality.
Good.
Cause it's a crazy, I mean, it's not crazy.
It's a beautiful set of ideas that you propose.
But, and if causality is fundamental,
I'd just like to understand it better.
What is the past?
What is the future?
What is the flow of time?
Even the error of time in our universe, in your view.
And maybe what's an event, right?
Oh, an event is where something changes or where,
to, it's hard to say because it's a primitive concept.
An event is a moment of time within space.
This is the view in general relativity,
where two particles intersect in their paths
or something changes in the path of a particle.
Now, we are postulating the theories
at the fundamental level, a notion,
which is an elementary notion.
So it doesn't have a definition in terms of other things,
but it is something elementary happening.
And it's, it doesn't have a connection to energy
or matter or exchange of any.
It does have a connection to energy and matter.
Which is at that level.
Yeah.
It involves, and that's why the version
of a theory of events that I've developed
with Marina Cortez, and it's, by the way,
I wanna mention my collaborators
because they've been at least as important
in this work as I have.
It's Marina Cortez in all the work since about 2013,
2012, 2013, about causality, causal sets.
And in the period before that,
Roberta Mangibara-Hunger, who is a philosopher
and a professor of law.
And that's in your efforts, together with your collaborators
to finish the unfinished revolution.
So, and focused on causality as a fundamental.
Yes.
As fundamental to physics.
So.
And there's certainly other people we've worked with,
but those two people's thinking
had a huge influence on my own thinking.
So in the way you describe causality,
that's what you mean of time being fundamental.
That causality is fundamental.
Yes.
And what does it mean for space
to not be fundamental to be?
That's very good.
This is a level of description
in which there are events,
there are events create other events,
but there's no space.
They don't live in space.
They have an order in which they caused each other.
And that is part of the nature of time for us.
But there is an emergent approximate description.
And you asked me to find an emergent.
I didn't.
An emergent property is a property
that arises at some level of complexity,
larger than and more complex than the fundamental level,
which requires some property to describe it,
which is not directly
explicable or derivable, is the word I want,
from the properties of the fundamental things.
And space is one of those things
in a sufficiently complex universe,
space, three-dimensional position of things emerged.
Yes.
And we saw how this happens in detail in some models,
both computationally and analytically.
Okay, so connected to space is the idea of locality.
Yes.
That, so we talked about realism.
So I live in this world that like sports,
locality is a thing that,
you can affect things close to you
and don't have an effect on things that are far away.
It's the thing that bothers me about gravity in general
or action at a distance.
Same thing that probably bothered Newton
or at least he said a little bit about it.
Okay, so what do you think about locality?
Is it just a construct?
Is it us humans just like this idea
and are connected to it because we exist in it?
We need it for our survival, but it's not fundamental.
I mean, it seems crazy for it not to be a fundamental
aspect of our reality.
It does.
And can you comfort me on a sort of as a therapist?
Like, how do I?
I'm not a good therapist, I'll do my best.
There are several different definitions of locality
when you come to talk about locality in physics.
In quantum field theory,
which is a mixture of special relativity
and quantum mechanics,
there is a precise definition of locality.
Field operators corresponding to events in space time,
which are space like separated commute
with each other as operators.
So in quantum mechanics,
you think about the nature realities fields
and things that are close in a field
have an impact on each other more than farther away.
That's, yes.
That's very comforting, that makes sense.
So that's a property of quantum field theory
and it's well tested.
Unfortunately, there's another definition of local,
which was expressed by Einstein
and expressed more precisely by John Bell,
which has been tested experimentally and found to fail.
And this setup is you take two particles.
So one thing that's really weird about quantum mechanics
is a property called entanglement.
You can have two particles interact
and then share a property without being a property
of either one of the two particles.
And if you take such a system
and then you make a measurement on particle A,
which is over here on my right side,
and particle B, which is over here on what somebody else
makes a measurement on particle B,
you can ask that whatever is the real reality
of particle B, it not be affected by the choice
the observer particle A makes about what to measure,
not the outcome, just the choice
of the different things they might measure.
And that's a notion of locality
because it assumes that these things
are very far spaced like separated.
And it's gonna take a while for any information
about the choice made by the people here at A
to affect the reality at B.
But you make that assumption, that's called bell locality.
And you derive a certain inequality
that some correlations, functions of correlations
have to satisfy.
And then you can test that pretty directly
in experiments which create pairs of photons
or other particles.
And it's wrong by many sigma.
In experiment, it doesn't match.
So what does that mean?
That means that that definition of locality
I stated is false.
The one that Einstein was playing with.
And the one that I stated, that is,
it's not true that whatever is real about particle B
is unaffected by the choice that the observer makes
as to what to measure in particle A.
No matter how long they've been propagating
at almost the speed of light or the speed of light
away from each other.
No matter, so like the distance between them.
Well, it's been tested, of course,
if you want to have hope for quantum mechanics
being incomplete or wrong and corrected
by something that changes this.
It's been tested over a number of kilometers.
I don't remember whether it's 25 kilometers
or a hundred and something kilometers.
So in trying to solve the unsolved revolution,
in trying to come up with the theory of everything
is causality fundamental and breaking away
from locality, a crucial step.
So in your book, essentially those are the two things
we really need to think about as a community.
Especially the physics community has to think about this.
So I guess my question is, how do we solve?
How do we finish the unfinished revolution?
Well, that's, I can only tell you what I'm trying to do
and what I've abandoned as not working.
As one ant, smart ant and an ant colony, yep.
Or maybe dumb, that's why, who knows.
But anyway, my view of the,
we've had some nice theories invented.
There's a bunch of different ones,
both related to quantum mechanics,
related to quantum gravity.
There's a lot to admire in many of these different approaches.
But to my understanding, none of them completely solve
the problems that I care about.
And so we're in a situation
which is either terrifying for a student
or full of opportunity for the right student,
in which we've got more than a dozen attempts.
And I never thought,
I don't think anybody anticipated would work out this way.
Which work partly and then at some point,
they have an issue that nobody can figure out
how to go around or how to solve.
And that's the situation we're in.
My reaction to that is two-fold.
One of them is to try to bring people,
we evolved into this unfortunate sociological situation
in which there are communities
around some of these approaches.
And to borrow again a metaphor from Eric,
they sit on top of hills in the landscape of theories
and throw rocks at each other.
And as Eric says, we need two things.
We need people to get off their hills
and come down into the valleys and party and talk
and become friendly and learn to say,
not no but, but yes and yes,
your idea goes this far,
but maybe if we put it together with my idea,
we can go further.
Yes.
So in that spirit of talked several times with Sean Carroll,
who's also written an excellent book recently.
And he kind of, he plays around as a big fan
of the many worlds interpretation of quantum mechanics.
So I'm a troublemaker.
So let me ask, what's your sense of Sean
and the idea of many worlds interpretation?
I've read many of the commentary back and forth.
You guys are friendly, respect each other,
but have a lot of fun debating.
I love Sean and he, no, I really,
he's not, he's articulate and he's a great representative
or ambassador of science to the public
and for different fields of science to each other.
He also, like I do, takes philosophy seriously.
And unlike what I do in all cases,
he's really done the homework.
He's read a lot.
He knows the people.
He talks to them.
He exposes his arguments to them.
And I, there's this mysterious thing
that we so often end up on the opposite sides
of one of these issues.
It's fun though.
It's fun.
And I'd love to have a conversation about that,
but I would want to include him.
I see, about many worlds.
Well, no, I can tell you what I think about many worlds.
I'd love to, but actually on that, let me pause.
Sean has a podcast.
You should definitely figure out how to talk to Sean.
I actually told Sean I would love to hear you guys
just going back and forth.
So I hope you can make that happen eventually.
You and Sean.
I won't tell you what it is,
but there's something that Sean said to me
in June of 2016 that changed my whole approach
to a problem, but I have to tell him first.
Yes.
And that'll be great to tell him on his podcast.
So.
I can't invite myself to his podcast.
I told him, yeah, okay, we'll make it happen.
So many worlds.
Anyway, what's your view?
Many worlds, we talked about non-locality.
Many worlds is also a very uncomfortable idea
or beautiful, depending on your perspective.
It's very nice in terms of,
I mean, there's a realist aspect to it.
I think you called it magical realism.
Yeah.
It's just a beautiful line.
But at the same time, it's very difficult
to far limit a human mind to comprehend.
So what are your thoughts about it?
Let me start with the easy and obvious
and then go to the scientific.
Okay.
It doesn't appeal to me.
It doesn't answer the questions that I want answered.
And it does so to such a strong case
that when Roberto, Mangibar, Anger and I
began looking for principles,
and I want to come back and talk about
the use of principles in science,
because that's the other thing I was going to say
and I don't want to lose that.
When we started looking for principles,
we made our first principle, there is just one world
and it happens once.
But so it's not helpful to my personal approach
to my personal agenda,
but of course I'm part of a community.
And my sense of the many worlds interpretation,
I have thought a lot about it
and struggled a lot with it, is the following.
First of all, there's Everett himself,
there's what's in Everett.
And there are several issues there
connected with the derivation of the born rule,
which is the rule that gives probabilities to events.
And the reasons why there is a problem with probability
is that I mentioned the two ways
that physical systems can evolve.
The many worlds interpretation cuts off
one, the one having to do with measurement
and just has the other one, the Schrodinger evolution,
which is this smooth evolution of the quantum state.
But the notion of probability is only in the second rule,
which we've thrown away.
So where does probability come from?
You have to answer the question
because experimentalists use probabilities
to check the theory.
Now, at first sight, you get very confused
because there seems to be a real problem
because in the many worlds interpretation,
this talk about branches is not quite precise,
but I'll use it.
There's a branch in which everything
that might happen does happen
with probability one in that branch.
You might think you could count the number of branches
in which things do and don't happen
and get numbers that you can define
as something like frequentist probabilities.
And Everett did have an argument in that direction,
but the argument gets very subtle
when there are an infinite number of possibilities,
as is the case in most quantum systems.
And my understanding, although I'm not as much
of an expert as some other people,
is that Everett's own proposal failed, did not work.
There are then, but it doesn't stop there.
There is an important idea that Everett didn't know about,
which is decoherence, and it is a phenomenon
that might be very much relevant.
And so a number of people post-Everett
have tried to make versions of what you might call
many worlds quantum mechanics.
And this is a big area and it's subtle
and it's not the kind of thing that I do well.
So I consulted, that's why there's two chapters
on this in the book I wrote, chapter 10,
which is about Everett's version, chapter 11.
There's a very good group of philosophers
of physics in Oxford, Simon Saunders, David Wallace,
Harvey Brown, and a number of others.
And of course, there's David Deutsch, who is there.
And those people have developed and put a lot of work
into a very sophisticated set of ideas
designed to come back and answer that question.
They have the flavor of, there are really no probabilities,
we admit that, but imagine if the Everett story was true
and you were living in that multiverse,
how would you make bets?
And so they use decision theory
from the theory of probability and gambling and so forth
to shape a story of how you would bet
if you were inside Everett in the universe and you knew that.
And there's a debate among those experts
as to whether they or somebody else has really succeeded.
And when I checked in as I was finishing the book
with some of those people, like Simon,
who's a good friend of mine, and David Wallace,
they told me that they weren't sure
that any of them was yet correct.
So that's what I put in my book.
Now, to add to that,
Sean has his own approach to that problem
in what's called self-referencing or self-locating observers.
And it doesn't, I tried to read it
and it didn't make sense to me,
but I didn't study it hard.
I didn't communicate with Sean.
I didn't do the things that I would do.
So I had nothing to say about in the book.
I don't, I don't know whether it's right or not.
Let's talk a little bit about science.
You mentioned the use of principles in science.
What does it mean to have a principle?
And why is that important?
When I feel very frustrated about quantum gravity,
I like to go back and read history.
And of course, Einstein and his achievements
are a huge lesson and hopefully something like a role model.
And it's very clear that Einstein thought
that the first job when you want to enter a new domain
of theoretical physics is to discover and invent principles
and then make models of how those principles
might be applied in some experimental situation,
which is where the mathematics comes in.
So for Einstein, there was no unified space and time.
Minkowski invented this idea of space time.
For Einstein, it was a model of his principles
or his postulates.
And I've taken the view that we don't know
the principles of quantum gravity.
I can think about candidates and I have some papers
where I discuss different candidates
and I'm happy to discuss them.
But my belief now is that those partially successful approaches
are all models which might describe indeed
some quantum gravity physics in some domain, in some aspect.
But ultimately it would be important
because they model the principles.
And the first job is to tie down those principles.
So that's the approach that I'm taking.
So speaking of principles, in your 2006 book,
The Trouble with Physics,
you criticized a bit string theory for taking us away
from the rigors of the scientific method
or whatever you would call it.
But what's the trouble with physics today
and how do we fix it?
Can I say how I read that book?
Sure.
And I'm not, this of course has to be my fault
because you can't as an author claim
after all the work you put in that you are misread.
But I will say that many of the reviewers
who were not personally involved
and even many who were working on string theory
or some other approach to quantum gravity
told me, communicated with me and told me
they thought that I was fair
and balance was the word that was usually used.
So let me tell you what my purpose was in writing that book
which clearly got diverted by,
because there was already a rather hot argument going on.
And this is...
On which topic? On string theory specifically
or in general in physics?
No, more specifically than string theory.
So since we're in Cambridge, can I say that?
We're doing this in...
Yeah, of course.
Cambridge, just to be clear, Massachusetts
and on Harvard campus.
Right.
So Andy Stromminger is a good friend of mine
and has been for many, many years.
And Andy...
So originally there was this beautiful idea
that there were five string theories
and maybe they would be unified into one.
And we would discover a way to break that
symmetries of one of those string theories
and discover the standard model
and predict all the properties of standard model particles
like their masses and charges and so forth,
coupling constants.
And then there was a bunch of solutions
to string theory found
which led each of them to a different version of particle physics
with a different phenomenology.
These are called the Kalabi Yao manifolds
named after Yao who was also here.
Certainly we've been friends at some time in the past anyway.
And then there were, nobody was sure,
but hundreds of thousands of different versions of string theory.
And then Andy found there was a way
to put a certain kind of mathematical curvature
called torsion into the solutions.
And he wrote a paper, a string theory with torsion
in which he discovered there was...
not formally uncountable,
but he was unable to invent any way to count
the number of solutions or classify the diverse solutions.
And he wrote that this is worrying
because doing phenomenology the old-fashioned way
of solving the theory is not going to work
because there's going to be loads of solutions
for editing proposed phenomenology
for anything of the experiments.
Now, it hasn't quite worked out that way.
But nonetheless, he took that word to me.
We spoke at least once, maybe two or three times about that.
And I got seriously worried about that.
And this is a little...
It sounds like an anecdote that inspired
your worry about string theory in general.
Well, I tried to solve the problem.
And I tried to solve the problem.
I was reading at that time a lot of biology,
a lot of evolutionary theory,
like Lin-Margoulis and Steve Gould and so forth.
And I could take your time to go through the things
but it occurred to me maybe physics was like evolutionary biology
and maybe the laws evolved.
And there was...
The biologists talked about a landscape, a fitness landscape
of DNA sequences or protein sequences
or a species or something like that.
And I took their concept and the word landscape
from theoretical biology and made a scenario
about how the universe as a whole
could evolve to discover the parameters of the standard model.
And I'm happy to discuss...
That's called cosmological natural selection.
Cosmological natural selection.
So the parameters of the standard model...
So the laws of physics are changing.
This idea would say that the laws of physics
are changing in some way that echoes that of natural selection
and just it adjusts in some way towards some goal.
Yes.
And I published that.
I wrote the paper in 1888 or 1889.
The paper was published in 1992.
My first book in 1997,
The Life of the Cosmos, was explicitly about that.
And I was very clear that what was important
is that because you would develop an ensemble of universes,
but they were related by descent through natural selection,
almost every universe would share the property
that its fitness was maximized to some extent,
or at least close to maximum.
And I could deduce predictions that could be tested from that.
And I worked all of that out
and I compared it to the Anthropic Principle
where you weren't able to make tests
or make falsifications.
All of this was in the late 80s and early 90s.
That's a really compelling notion,
but how does that help you arrive at a...
I'm coming to where the book came from.
Yes.
So what got me...
I worked on string theory.
I also worked on loop pattern gravity
and I was one of the inventors of loop pattern gravity.
And because of my strong belief in some other principles
which led to this notion of wanting a quantum theory of gravity
to be what we call relational or background independent,
I tried very hard to make string theory background independent
and ended up developing a bunch of tools
which then could apply directly to general relativity
and that became loop pattern gravity.
So the things were very closely related
and have always been very closely related in my mind.
The idea that there were two communities,
one devoted to strings and one devoted to loops,
is nuts and has always been nuts.
Okay, so...
So anyway...
There's this nuts community of loops and strings
that are all beautiful and compelling and mathematically speaking
and what's the trouble with all that?
Why is that such a problem?
So I was interested in developing that notion
of how science works based on the community and ethics
that I told you about.
And I wrote a draft of a book about that
which had several chapters on methodology of science
and it was a rather academically oriented book
and those chapters were the first part of the book,
the first third of it and you can find their remnants
in what's now the last part of the trouble with physics
and then I described a number of test cases,
case studies and one of them,
which I knew was the search for quantum gravity
and string theory and so forth.
And I was unable to get that book published.
So somebody made the suggestion of flipping it around
and starting with the story of string theory
which was already controversial.
This was 2004, 2005.
But I was very careful to be detailed,
to criticize papers and not people.
You won't find me criticizing individuals,
you'll find me criticizing certain writing.
But in any case, here's what I regret.
Let me make a program worthwhile.
As far as I know, with the exception of not understanding
how large the applications to condense matter,
say, ADMCFT would get,
I think largely my diagnosis of string theory
as it was then has stood up since 2006.
What I regret is that the same critique,
I was using string theory as an example
and the same critique applies to many other communities
in science and all of, including,
and this is what I regret, my own community,
that is a community of people working on quantum gravity,
outside string theory.
And I considered saying that explicitly.
But to say that explicitly,
since I'm a small, intimate community,
I would be telling stories and naming names
and making a kind of history that I have no right to write.
So I stayed away from that, but was misunderstood.
But if I may ask,
is there a hopeful message for theoretical physics
that we can take from that book,
sort of that looks at the community,
not just your own work now with causality and nonlocality,
but just broadly in understanding
the fundamental nature of our reality,
what's your hope for the 21st century in physics?
Well, do we solve the problem?
We solve the unfinished problem of Einstein's.
That's certainly the thing that I care about most
and hope for most.
Let me say one thing.
Among the young people that I work with,
I hear very often and sense a total disinterest
in these arguments that we older scientists have
and an interest in what each other is doing.
And this is starting to appear in conferences
where the young people interested in quantum gravity
make a conference.
They invite loops and strings and causal dynamical triangulations
and causal set people.
And we're having a conference like this next week,
a small workshop at Perimeter.
I guess I'm advertising this.
And then in the summer,
we're having a big full-on conference,
which is just quantum gravity.
It's not strings, it's not loops.
But the organizers and the speakers
will be from all the different communities.
And this to me is very helpful.
That the different ideas are coming together?
At least people are expressing an interest in that.
That's a huge honor talking to you, Lee.
Thanks so much for your time today.
Thank you.
Thanks for listening to this conversation.
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And now, let me leave you with some words from Lee Smolin.
One possibility is God is nothing but
the power of the universe to organize itself.
Thanks for listening and hope to see you next time.