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What's up everybody?
My guest today is Sean Carroll, a best selling
author and research professor of theoretical
physics at the California Institute of Technology.
He's written both as an author and as a researcher
about fundamental questions in physics and
cosmology, especially issues of dark matter,
dark energy, space time symmetries, and the
origin of the universe.
And more recently on the foundations of quantum
mechanics, the emergence of space time, and
the evolution of entropy and complexity.
Our focus today is on the subject of Dr. Carroll's
latest book, Something Deeply Hidden: Quantum
Worlds and the Emergence of Spacetime.
You'll notice that we jump around quite a
bit, and much of the conversation bends towards
the philosophical, including ontological questions
about the nature of reality, and the possible
limitations of science as an epistemological
tool for making definitive statements about
our own conscious experience of that reality.
There's a lot in this conversation to unpack.
And although I've tried my best to grasp the
various interpretations of quantum mechanics,
the implications of the theory are so at odds
with our own experience of the physical world,
that it's been a continuous struggle for me
to try and understand them.
And I want to understand them.
Or at least I want them to feel more accessible
to me.
And though I can't say that I've accomplished
that, I think there's value in trying to engage
with things that we struggle to understand.
This is something that came up in our recent
episode with David Epstein.
When you struggle to understand something,
when the learning process feels difficult,
it's often a sign that you're learning and
retaining that much more.
So just a thought to bear in mind, in case
like me, you struggle with this subject.
Now, for subscribers to our overtime feed,
we spend the balance of our time discussing
more off-the-wall subjects.
I mean, we start with the impact of quantum
mechanics in culture, but we move into discussions
about time travel, artificial intelligence,
aliens, Flat Earth Theory, and a little bit
of 1980s Sports trivia.
Carroll grew up in Philadelphia during the
Dr. J. Moses Malone and Charles Barkley era.
So we had a little fun with that.
And now, without any further ado, here is
my conversation with Dr. Sean Carroll.
Dr. Sean Carroll, welcome to Hidden Forces.
Thanks very much for having me.
It's so cool having you here.
I'm actually more geek than I thought I would
be.
Well, the word hidden appears in the name
of my book, Something Deeply Hidden, so there's
obviously an overlap here.
So, when I contacted, did you see that in
the podcast and say, just based on that word
alone...
[laughter] Yes, that's completely the reason
why.
Absolutely.
No matter what this person is doing, we have
something in common.
I mean, I've always been interested in quantum
mechanics because like everyone, it's quantum.
Yeah.
Exactly.
As part of the research I did for reading
my book is that I went to amazon.com, I typed
in the word quantum to the search bar, and
looked up all the crazy books with the word
quantum in the title.
Quantum yoga, quantum healing, quantum leadership,
quantum touch, quantum therapy.
It's an idea that is suffused into culture
without anyone understanding it.
So we need to do better.
Was that your lecture that brought up the
quantum like survival bed?
I don't think so.
Maybe it was somebody else because someone
else has done this.
Maybe it was Greene.
There's so many people.
The other thing that's amazing about this
subject, whether it be quantum mechanics,
whether it be something else in physics, is
that people are really interested in this
stuff.
Millions and millions of views each for these
videos.
No, absolutely.
I think that we underserved the desire for
people to have interesting, helpful, thought
provoking discussions about science.
We do certain things, but I think we underestimate
how much we people are willing to stretch
their minds a little bit to get their brains
around it.
I also wonder if it's also biased by the fact
that people probably watch those videos over
and over because they don't get it.
I don't think so.
No, I don't think so.
Because there's so many other videos for you
watching, right?
Like, you just skip to something else.
Even on TV, I've been very frustrated with
things, I don't want to mention any names,
but there's certain networks or rather cable
channels, I should say, that have science
shows, but no professional scientists are
involved in the making of the science shows.
Like on Gaia TV, you watch Gaia TV?
I don't watch that one actually.
But they'll be producers who go to Wikipedia
and look up black holes and make a TV show
based on that.
And they often do a pretty good job, but it
can be so much better if you actually trusted
the audience.
Yeah.
So the first time that I ever tried to learn
anything about quantum mechanics was, because
I thought about this, was in 2004, and I think
it was January or February, beginning of spring
semester in college.
There was a book out called Quantum Gravity
that year.
I didn't get it.
The only thing I remember-
You didn't buy it or you didn't understand
it?
I bought it.
And the only thing though that stuck out to
me was at the very beginning of the book,
where he talks about how in meeting after
meeting and dinner after dinner, the one thing
that is true is that they can all agree on
the mathematics and none of them can agree
on what it actually means in practice, or
what it means to actually live in a quantum
world.
And I feel like that sort of is just a big
part of what your book is about.
Yeah, except we don't even agree on the mathematics.
That's the thing.
We agree on the beginning and the end, we
disagree on what happens in between.
So if you set up a quantum mechanical system,
which by the way, is every system in the world,
right?
I mean, we see quantum mechanics manifest
itself when you look at electrons or atoms
or very tiny things, but it's the fundamental
way that the world works at the basic level.
And we can set up a system like an atom, we
can let it evolve for a little bit and then
we can observe it.
And we can predict with wonderful precision
what the probability is of getting different
measurement outcomes.
Really, really good precision.
Like, it's certainly right.
It's certainly on the right track.
But then if you ask, okay, what happened in
between when you set up the system and when
you looked at it?
What does it mean to look at it?
What was the interaction or the equation,
the laws of physics that governed you looking
at it?
We don't know.
We don't even know the math of there.
So it's not just that we know the math, but
not the physics, we don't even know either
one.
We don't know the math before we observe the
system?
Yeah.
If you say like, what is going on?
What is the physical stuff that is changing
while you're not looking at it?
We don't agree.
Different people have different ideas about
what the answer of that is.
So this is a really good time to maybe talk
about the measurement problem, because this
is part of the issue.
But also maybe we could start with kind of
foundationally, how did this theory even developed,
where did it come from?
Right.
I think that's the right way to start.
So let me give you, and not completely historically
accurate, but hopefully, comprehensible answer.
We've all seen the cartoon picture of the
atom with like little nucleus at the center
and electrons going around in what looks like
orbits, right?
It looks like the solar system, a little tiny
solar system is what the atoms are like.
So that can't be right.
That was a picture that was put together in
the early 20th century around 1909.
Ernest Rutherford, especially.
And we know it can't be right, because if
electrons were orbiting atoms, the nucleus
of an atom, they would be giving off radiation.
They'd be giving off electromagnetic waves.
And they'd be losing energy and spiraling
into the middle of the nucleus.
So all of matter, like you and me and the
table and the Earth would be wildly unstable
and would just collapse into a point.
That's clearly-
Would the world be just one giant black hole?
Basically, yes.
That's right.
That's the prediction unambiguously.
So that's not right.
So what's going on?
And it took a lot of banging your head against
the wall to come up with a good theory, but
the theory eventually was, electrons are not
even particles.
Electrons are not orbiting like little planets
around the Solar System because they're actually
waves, which we cleverly called the wave function
of the electron.
The wave function of the electron is spread
out in the little cloud around the nucleus.
And there's different ways the cloud can vibrate.
But all of them have some heft to them, all
of them have some size, they don't just collapse
to the middle.
So that's the answer.
That was a good idea, it's the right answer.
That's all derived mathematically at first,
right?
I don't know what you mean.
I mean, we go back and forth between data
and ideas and math.
So it was a proposal, electrons are waves.
And then later Schrodinger came up with an
equation.
Erwin Schrodinger, the great physicist came
up with the Schrodinger equation, which says,
here's how wave functions evolve.
Here's how they behave, what they do, how
they evolve.
And it's all perfect until you look at it,
and that's the measurement problem that you
noticed.
So what Schrodinger's equation says is that
an electron within this little cloud, if you
remove it from the atom, if you just put it
out there and empty space, that wave function,
that cloud, should just spread out all across
the universe.
But when we look at electrons, we don't see
clouds of wave function spread out all across
the universe.
We see them in a particular location as if
they were a particle.
And that's the weird thing.
Quantum mechanics, unlike any other kind of
physics seems to require that electrons or
other quantum systems behave differently when
we are looking at them or when we are not.
Why?
Well, no one knows.
I mean, that's the measurement problem.
So we don't know what it means to measure
something.
We don't know, and when I say we don't know,
what I mean is, according to the conventional
wisdom, according to what we teach our students
in business courses, we don't agree, let's
put it that way.
And what it means to measure something when
a measurement happens, why wave functions
collapse to points, any of those things.
So I do want to talk about all those things
in detail.
And I think one place that they'll naturally
come up is when we talk about Many-Worlds
and some of these alternative hypotheses,
but give me a further continuum of the history.
Like, when did we first have the double-slit
experiment?
What was the initial reaction of that?
What were some of the early counter arguments?
Yeah.
So there's actually two tracks in the early
20th century.
One was people like Max Planck and Albert
Einstein were discovering that light, which
we had agreed in the 1800s was a wave, actually
had particle like properties.
So it was really Einstein more than anyone
else who should get credit for initiating
quantum mechanics.
It was really Einstein who said in 1905, out
loud, maybe light is just particles.
Okay.
Even though we had known, we had very good
evidence it was waves.
Einstein says, well, there's certain circumstances
under which it really acts like particles.
Meanwhile, on the political side of the ledger,
people like Louis de Broglie, who was a French
physicist, and Erwin Schrodinger said, maybe
electrons particles are really like waves.
So we had this confluence of ideas that were
saying that everything in the universe has
some particle like properties and some wave
like properties.
In around 1926, 1927, we settled on this idea
that the thing was that things really are
waves, those are the most important fundamental
things.
But when we look at them, they look like particles.
So that's the bizarre thing that we're trying
to deal with to this day, why does looking
at something have any role to play in the
fundamental formulation of a physical theory.
Now, the double-slit experiment we can talk
about, but let me just emphasize, it wasn't
done.
Like, no one did the double-slit experiment
to like the 70s or 80s.
It was a thought experiment.
Yeah, it was a thought experiment just to
illustrate exactly how crazy quantum mechanics
really is and exactly how important this role
of observation is.
So should I explain the experiment?
Yes.
Please explain.
Please, please.
You can do a double-slit experiment just classically
with water or with light.
So you basically take a light beam and shine
it through two slits in some sort of barrier.
And what happens if light were particles,
what you'd expect is that the light would
either go through one slit or the other.
And you would see if you put a screen on the
other side, you would see sort of one slit
lighting up.
Because when the photons, when the particles
went through one slit, or one slit lighting
up when it went to the other one.
If light-
Two lines of light against the wall.
Two lines of light on the screen.
Yeah, exactly.
And so if light were a wave like water or
something like that, then as soon as that
wave goes through either slit, it starts dispersing
in sort of a wave-like spherical pattern,
and you get an interference pattern on the
other side.
Because each wave is canceling each other
out wherever it-
Because waves go up and down, and so they
either are going to add together and you're
going to get a big bright thing or they're
going to cancel and you get nothing at all.
So that's the difference between waves and
particles, is that waves can cancel each other
and particles can't.
So seeing an interference pattern in that
double-slit experiment is evidence of wave-like
behavior.
So when you do the experiment, even though
they hadn't, they predicted what the result
would be and they turned out to be correct.
If you send light sufficiently, delicately
or even if you send electrons through a slit
like this, you see an interference pattern
on the other side.
You see if you build up lots of electrons
hitting it or lots of photons hitting it,
they appear to be bright and then dimmer and
dimmer and dimmer in lines as you get further
and further away.
So that seems to say that both light and electrons
are waves.
Okay.
But then the twist is the following, this
is easy to do for electrons, hard to do for
photons, put a little detector next to each
individual slit.
So you have double-slits, that's just what
the light or the electrons are going through
before they hit the screen on the other side,
but invent something that keeps track of which
slit the electron goes through.
At the slit before it goes through.
Before it actually hits the screen.
Okay.
So then, you imagine if the electron were
really a wave and were passing through both
slits and giving you an interference pattern,
then somehow the detector should say it went
through both slits.
And you see the interference pattern on the
other side.
That's not what happens.
What happens is, every time the detector says
the electron either went to the left slit
or the right slit, and because you did that
detection, the interference pattern disappears.
Now it's like a particle.
Now it's acting like it's just going to go
to the right or to the left, there's no more
interference pattern.
So this is supposed to be a vivid demonstration
of the idea that matter, whether it's light
or electrons or anything else, acts wave-like
as long as we choose not to look at it.
And it acts particle like when we observe
it.
So I have so many questions about this.
And I don't know where to start.
One obviously has to do with what qualifies
as a measurement or a detection, which we
won't forget to do, I'm sure.
Another thing that comes to mind, this you
didn't mention it, and you'll probably have
to explain to the audience.
But the density of the light or the area of
the light represents the probability that
you're going to find the electron in that
particular location.
And what I don't understand here is, if you're
going to shine light in the way we think about
it in a classical world, and you get these
two lines of light against the screen, there's
never been a case where there's light, let's
say, at the other end of the screen.
We have to be very careful here.
And this is why it took decades to actually
do the experiment, right?
With light, you can do the experiment.
And the easy part is sending it through two
slits and seeing an interference pattern on
the other side.
And that interference pattern, I mean, we
see interference patterns in light all the
time.
It depends on what the wavelength is.
The wavelength is very, very short.
Those interference patterns are going to be
really, really close together.
And if the slits are too far, you won't even
see interference.
But as long as you have the right wavelength
and the slits are close enough, and everything
is set up nicely, you will see an interference
pattern that fades off as you go left.
Okay.
So maybe I shouldn't have used light, maybe
I should have used the electron, right?
Good.
The discrete firing of electrons.
In what situation would we'd ever see an electron
at the other end of the screen if we're firing
straight?
What would account for that?
In other words, is that part of just ... There's
another example in your book and I've seen
this before somewhere else, which is that
we understand the world is being in tropic,
that you can't move in reverse.
But in Many-Worlds or in a quantum world,
it is possible for the chalk to jump off the
desk and write Beethoven's Ninth Symphony
on the chalkboard.
Is that sort of what-
It's sort of is like that.
I mean, one of the features of quantum mechanics
as we teach it is that you never know for
sure what's going to happen.
The best you can do is predict the probability
of certain things happening.
So if you say, you never see the electron
fly off way to the left or to the right, the
answer is, well, you could, it's just really
unlikely to see it there.
But if you waited long enough, you'd see some
electrons doing that.
That's the rules of quantum mechanics.
So does that mean that if we ... Now we're
jumping the gun here.
I don't want to go too far.
I do want to bring us back, bring some coherence
to it.
But in Many-Worlds type scenario, does that
mean that even though it's extremely unlikely
for me to see somebody, let's say burst into
flames, that there are many, many things that
are so unlikely.
In a classical world, if something is highly
improbable, it is practically impossible.
And there are many things that are practically
impossible.
But in a world where there are so many gazillion
practically impossible things, is it possible
that actually within our lifetime, we hear
about something that happened, that we say
could never possibly happened?
Like, there was like some ... You know what
I'm saying?
But it did.
Because actually if you think about it in
terms of probability in the context of Many-Worlds
scenario, it actually is likely that out of
all the unlikely events of the world, this
one thing actually did happen, and we considered
to be supernatural.
So the short answer is no.
Interesting.
And the longer answer is, you have to do the
math.
Like, forget about quantum mechanics, just
consider shuffling cards.
Let's imagine you shuffle cards and you were
actually really good at shuffling cards in
a random way.
So a good card shark can cheat and they can
rearrange the cards however they want.
But if you were really randomly shuffling
cards and you said, I shuffle it once, and
I look and I shuffle it again and I look,
how likely is it that the cards will just
arrange themselves in order?
Ace, king, queen, jack, et cetera.
Well, it will never happen in the lifetime
of the universe, okay?
The chances that if you did that once per
second, from the Big Bang to today, that the
cards would ever arrange themselves in the
right order is really, really tiny.
And even though it's really, really tiny,
it's still way bigger than a piece of chalk
jumping up and writing Beethoven's Fifth Symphony
on the board.
So when we say things are unlikely, these
things that are unlikely are so unlikely that
you've never seen them in the lifetime of
the universe.
Nobody's ever seen them in the lifetime of
the universe.
Don't worry about it.
Fascinating.
There was this other ... I read Gleick's,
The Information, years ago, which I really
loved and it really helped me a lot with information
theory.
And there was a part in the book where he
talked about a particular book that had been
published that actually generated random numbers.
And it was basically a chapter about what
is a random number.
You had talked about doing something similar
for the addition of your book.
And I think your point was like-
I did it.
So you did it?
That's right.
I actually have to check the book and I didn't
see that.
So what I did was while writing the book,
I generated a 50 digit, binary digits.
So 1001, et cetera.
Quantum random number, so every digit was
a single, yes, no measurement of the quantum
mechanical system.
And if you believe the Many-Worlds interpretation
of quantum mechanics, which I'm sure we we'll
get to, to specify, pretty soon, in different
branches of the wave function in the universe,
every possible string of digits came true.
So what I did was I printed that number that
I got in the book, and furthermore, we put
on the copyright page of the book, a version
number, which was the sort of decimal expansion
735 quadrillion, et cetera.
And so I think that my book has the largest
number of distinct editions of any book in
the history of the universe.
You were going to do that anyway, but did
Rob Reed convince you to do it after you guys
spoke?
You guys did an interview together, and you
had said that you wanted to do it-
I had the idea.
I just needed to convince the publisher to
do it.
And they actually loved the idea.
So, yeah.
They loved the idea.
So it was going to happen.
So everyone, if you have a copy of the book,
your version number is the same as all your
friends version number, because you all live
in the same universe.
But there's copies of you in other universes
that have different versions.
Fascinating.
So let's go back to this thing about the detector
and what constitutes a measurement because
something else I learned in preparing for
this episode is that there is a lot of ... I
kind of already knew it, I guess to some degree,
but it was formalized.
That there is a lot of confusion about quantum
mechanics and a lot of people use it.
It's like a blank slate on which people can
project whatever their desires are.
One of the popular interpretations is that
quantum mechanics basically proves that consciousness
is integral to the universe because without
a conscious observer, nothing actually happens.
Yeah.
So that's incorrect but you can understand
why people would say something like that.
And they are perfectly respectable physicists
who used to think about that.
Does Chalmers still think way in his understanding
of-
So David Chalmers, who's a well known philosopher
of consciousness is too cagey to ever say
what he believes.
And I'll give him credit.
He's open minded about these things.
So he wants to insist that we should take
certain ideas seriously.
But he's not going to say because they're
true, he's going to say, because we don't
know and they have a chance to be true.
So he's absolutely open to the possibility
that quantum mechanics and consciousness do
have something to do with-
He's more like Cartesian a little bit.
No?
Not really.
So a good Cartesian would say that the mind
is a whole separate substance, right?
There's the body, the physical world, obeys
the laws of physics.
And there's the mind which is not located
in time or space and somehow interacts with
the body.
Chalmers is way too sophisticated to buy into
anything like that.
Well, actually, this is what I meant.
I meant that he ascribes to the idea that
there could be a Cartesian demon?
No, he doesn't.
[crosstalk 00:23:08].
What he's more likely to believe, again, what
he actually believes is difficult to pin down.
But what he's more sympathetic to, is something
called property dualism, where the only things
that exist are physical objects like you and
me and the electrons are made of and so forth.
But these things have both physical properties
and mental properties.
So in addition to an electron in your body,
having electric charge and a location and
a spin and things like that, it has a mental
state.
Maybe its mental state is very primitive,
like it's a little bit happier or a little
bit sad, but that's it.
Everything's a little conscious.
Is that kind of like panpsychism?
It builds up to panpsychism.
That's right.
And so the conscious experiences that you
and I have subjectively, introspectively in
our first person perspective, build up because
we're made of many different particles interacting
in a certain way, all of which have a little
bit of consciousness.
I think this is completely wrong.
But it is a perspective that people have.
And how does that thread in with like Tononi's
Integrated Information Theory?
So Giulio Tononi has this idea called Integrated
Information Theory, which I think is a good
try that didn't work.
And it's a try to define exactly what you
mean by consciousness.
And basically, he came up with a mathematical
formula that describes how integrated the
information within a system is.
So you can ask if you have a country like
the United States, so that country is made
of states, and the states have people in them,
and the people have cells in them, and the
cells have molecules in them, and the molecules
have particles.
And at every one of those levels, you can
ask, how does the information within that
system integrate into itself?
And what he argues is that the individual
self is the high point of integrated information.
There's less information when you go to smaller
systems and it's less integrated when you
go to bigger systems.
So that's the locus of consciousness.
It's interesting.
So he actually converges on-
That's the argument.
It's so interesting.
You can even imagine-
That takes geocentrism to like a new level.
Well, but you can also imagine that under
the right circumstances, a mob of people might
be the right conscious agent to pinpoint,
right?
The mob sort of take on a mind of their own,
as we say, because people become so connected
to each other when in certain circumstances.
But people like Scott Aaronson have pointed
out that if you took the information in the
human brain and printed it out on piece of
paper, that would be just as conscious by
Tononi's definition.
Really?
Yeah.
That doesn't work.
It probably doesn't work, right?
And Erickson also has a bunch of other examples,
which we'd all, most of us would agree, are
not conscious, but would have very high integrated
information.
And Tononi's response is, how do you know
they're not conscious?
And so that's where the panpsychism comes
in.
That everything by this construction count
as a little bit conscious because there's
a little bit of integrated information, but
less than you and I do.
So I listened to a bunch of ... You have a
great podcast.
Congratulations.
It's fantastic.
MindScape.
In fact, we just had-
MindScape Podcast.
Just had an episode with Philip Goff whose
a big proponent of panpsychism.
Couldn't follow it.
But if you want to know what it's about, I
think it's a good-
Couldn't follow it.
I listened to a number of them.
It's super heady, obviously.
And I'm sure if I didn't have all this prep
stuff that I do every week, I bet that I would
be listening to your podcast constantly, because
it would give me that dosage.
It stretches your brain.
But I heard the episode on panpsychism, couldn't
really follow it.
I also listened to ... I mean, I first came
across David Chalmers back when the third
episode of the Matrix came out, and they had
the installment of those documentaries.
I don't know if you're familiar with it, but
he was in that.
He had long hair back then.
I remember.
Yeah.
So I've always liked his stuff.
But again, I can't follow his theory that
well.
I mean, I come from a point of view that I
don't know that it makes sense that anything
can be said definitively about our own conscious
experience using science because sciences
requires some objective measurement and conscious
is entirely subjective.
I mean, you're halfway to agreeing with Chalmers
because people like him who, again, I disagree
with, but I try to understand what they're
saying.
The main point that they want to emphasize
following people like Tom Nagel, who's a philosopher
at NYU also, is that there's something that
is purely first person about consciousness.
Something that I can experience and I can
tell you what I'm experiencing, I can act
in certain ways that indicate I'm experiencing,
but you have no direct access to what I'm
experiencing.
And they say that's where consciousness lies,
the experience of different things.
And by definition, according to this way of
thinking, can't be probed by outside observers
doing ordinary scientific things.
So that puts it in kind of a special category.People
like me say that's just not right.
Sure.
If I'm sad, I'm experiencing something.
But clearly, that has an impact on how we
behave, also.
I behave differently when I'm sad than when
I'm happy.
So these inner experiences are not completely
decoupled from the external, observable world.
But like to kind of squish together the Cartesian
demon thing and this, how on earth would you
be able to prove if you were not in a simulation
by some diabolical demon that some demon had
created?
You can't prove it.
You can't prove it.
So that's kind of what I'm trying to say,
basically, which is that fundamentally, we
can't make definitive statements about the
subjective experience of conscious.
It's kind of my point.
You could be in a simulation and still be
conscious?
Yes.
Right.
So the reason why this has anything to do
with quantum mechanics is back in the battle
days, when we knew that quantum mechanics
had this rule that wave functions collapsed
when they were observed, people definitely
wondered about what do you mean by observing
or measuring?
And then they said, well, maybe it requires
a conscious observer to do the measuring.
And so very good physicist like Eugene Wigner,
a Nobel Prize winner, set up entire strategies
to figure out how consciousness causes collapse
of the wave function.
Now, Wigner later repudiated his ideas, but
others still believe it.
And it opened the door for people thinking
that somehow consciousness creates the entirety
of reality, one way or the other.
And then you can make movies like What the
Bleep Do We Know!? and stuff like that?
Yeah, that was wild.
It's all down there.
That was wild.
That was like some woman that was demonized
or something, was in it.
Like some person from like the world of Atlantis
that had inhabited her body and she was called
the Rom or something?
Yeah, she channeled the spirit warriors, I
recall.
Yeah.
There were various people of dubious legitimacy
in there, and but people loved that movie.
It was good PR for this point of view.
Well, I think that speaks to the need for
mystery in life, maybe.
I think people ... That's a whole larger question
about what's missing.
Can we live in a world where we feel like
everything is knowable?
There need to be a certain amount of mystery
for us to-
I think that's part of it, but it's also if
someone dispelled the mystery and said, yes,
consciousness is central, it creates the universe,
it creates reality.
And here's how to use that lose weight and
win friends, right?
Then most of the people would say, that's
great.
I'm all for dispelling the mystery in that
case.
I think it's less about the mystery and more
about the reluctance to give up on certain
imagined powers that human people have.
People like me think that we're constrained
by the laws of physics and certain things
we're never going to be able to do, including,
for that matter, life after death.
Right?
So what causes the wave function to collapse?
Again, that's what we don't know.
That's what there are different proposals
on the board in the battle days, in the Copenhagen
interpretation, you're just not allowed to
ask that question.
You know it when you see it, that's the measurement
problem.
Like, when exactly does it happen?
What causes it?
How quickly does it happen?
Now, these days, we have much better theories
than the Copenhagen interpretation.
They're rigorously defined, mathematically
precise, and they get precise answers to the
question, when does the wave function collapse
or appear to collapse?
But the answers are different in all the theories.
And we don't know which theory is right.
Do you think anyone is right in particular?
I do.
So thank you for the leading question.
Yeah, no, I think the Many-Worlds interpretation
is right.
And in many worlds, the answer is simple,
wave functions never collapse.
That's just not what happens.
We apparently see wave functions collapse
because when we look at quantum systems, what
really happens is there's nothing special
about looking or measuring or consciousness
or perception.
You are a quantum mechanical system just like
the electron is and you become entangled with
the electron.
And if you're going to see the electron here
or see it there, Many-World says, what really
happens is that there are multiple copies
of you that come into existence, and in each
copy, there's a copy of you that saw it somewhere.
And all the different places you might have
seen it are realized in these different universes.
So how does that work?
So this is the part that's so challenging.
For me, personally, I think Most people, right?
Yeah.
And I wonder, Is it because we've grown up
with a classical model of the world in our
heads that we've been taught?
Is it that there's something innately not
right about this theory in the way that we
experience the world?
Or is it some combination that because we've
also been taught Newtonian mechanics that
it's sort of really ingrained in us?
I think it's because it's ingrained in us,
and not only because we've been taught, but
it is our, as philosophers say, pre-theoretic
view of the world, right?
Like, you have to be taught anything to see
like, here's a table, here's a chair, they're
located somewhere in space, they move or they
don't move or whatever.
All of these concepts long before you learn
about Newtonian mechanics, these concepts
make sense to you.
They're objects and they have locations.
And quantum mechanics says, none of that is
true.
It's much more subtle than that.
But if you back up and ask why in the world
anyone would believe this craziness of the
Many-Worlds interpretation, it's much simpler
than any other approach to understanding quantum
mechanics.
So first you have to admit that quantum systems
can be in superpositions.
What we mean by that is, you can think of
the electron, I said it's a wave.
And if you observe it, you can see it in different
positions.
One way of saying exactly that, but just in
different words is, the electron is in a superposition
of every possible location that it can be
in.
It's not in any one location, it's in the
superposition of all of them.
Or Schrdinger's cat is in a superposition
to being alive and being dead.
Or the spin of an electron is in a superposition
of spinning clockwise, spinning counterclockwise.
So it's not just that the electron is clockwise
or counterclockwise spinning, we don't know,
it really is in a superposition of both.
How does time relate to that?
If we're looking, for example, at the entire
universe, does that mean that every single
possible thing that can and will happen in
the universe is there at this moment?
No.
I mean, the wave function of the universe
says that certain possibilities are realized
and certain ones are not.
So it's not just anything goes.
The wave function says there's more of some
things happening than other things happening.
And so the superposition is not equal.
Like, when you think of the electron as being
a little cloud localized near the nucleus,
you can think of it as a superposition of
every single possible location.
But the chances, were you to observe it, that
it will be far away from the nucleus or infinitesimally
small.
Also, the amplitude of the wave function is
the total set of probabilities.
The amplitude squared gives you the probability.
It's the amplitude squared.
So when you're talking about the entire electron
field being the quantum field or all the positions
of the electron around the nucleus is the
wave function.
Is that a physical statement?
Or is it mathematical that it's ... Because
you're saying it's not, in fact, empty space?
Right.
But does that mean it's actually there and
it's actually there in a physical form?
Well, this depends on what your favorite version
of quantum mechanics is.
So I would say yes, that's exactly what it
means.
And that's your interpretation.
It's there in a physical form.
Does that mean the universe is more dense
than we think it is?
Well, it means that the world is not made
of stuff with locations in space.
The world is one big giant wave function.
That's what it is.
And this where we talk about Hilbert space,
the whole world is Hilbert space.
That's right.
The Hilbert space is the set of all possible
wave functions.
So the world is one element of Hilbert space.
One element.
The universe is one element of Hilbert space.
But Hilbert space is a mathematical construction.
Well, it's always velocity.
But that doesn't make it less real.
The math is just the language we use to talk
about reality.
When I say that the world is a wave function,
if you want to be a little bit more careful,
what I really mean is, there's a world and
it can be mathematically precisely represented
by a corresponding wave function.
But there's the world.
It's not math, it's-
Right, exactly.
It's the world.
It's reality.
Okay.
So flushes out a bit more for me, because
I think you actually, hadn't fully completed,
I interrupted you when you were building out
what the Many-Worlds system would look like.
So there's three ingredients you need to bring.
One is that quantum mechanics describes systems
as being in superpositions.
Okay.
Number two, you are a quantum system.
Back in the battle days with the Copenhagen
interpretation, they said that you the observer
are actually classical.
You obey Isaac Newton's laws, whereas the
thing you're looking at is quantum.
And people like Hugh Everett who pioneered
the Many-Worlds interpretation said like,
come on, you're made of atoms.
Atoms obey quantum mechanics, you obey quantum
mechanics, too.
So you are part of the wave function.
And number three, the third ingredient is
this thing called entanglement.
So it's not that different parts of the universe,
electrons or people or cats or whatever, have
different wave functions.
There's only one wave function for the whole
universe, all at once.
And that wave function says, well, if this
is observed to be true, then we know something
else.
So it's like you have two spins, you can have
two spins, where you know that the two spins
are aligned in opposite directions.
But you don't know which direction either
one of them is aligned in.
So possible spin one is up and spin two is
down.
Possible spend two is down, spin is one is
up.
The reality is a superposition of both.
So those three ingredients, things are in
superpositions, you are quantum mechanical
and entanglement happens.
And then you just plug into the equations
and see what happens.
So whatever it says is, when you measure the
spin of an electron, it's not that it's wave
function collapses into being spinning clockwise
or spinning counterclockwise, what happens
is you are a physical system that has a wave
function that is part of the wave function
of the universe.
You become entangled with the electron and
the wave function of the universe becomes
the electron is spin up, plus you saw it spin
up, plus the electron was spin down and you
saw it spin down.
And both of those possibilities are still
there in the wave function.
And everyone agrees on that.
Everyone agrees that if you follow the equations,
that is what happens.
Where people disagree is, what are you going
to do about that?
Whatever it does about it says, accept it.
Deal with it.
Chill out.
Don't deny it.
Just accept that.
And what you say is that there are two separate
worlds, one which says you saw the electron
spinning clockwise.
The other one, you saw it spinning counterclockwise.
Every other version of quantum mechanics says
is somehow we have to get rid of the other
worlds.
The other worlds are there.
We all agree on that.
So we have to sort of delete them somehow.
And so there's different strategies for actually
doing that.
Because the Copenhagen view is, first of all,
it differentiates between not only that you
as an individual are living in a classical
world or a classical system, that you are
a classical system.
But that in effect, the macroscopic world
is classical and the microscopic world is
quantum.
And that you're kind of opening your little
quantum window from your classical house,
and you're viewing something in the quantum
world.
And then your classical observation collapses
the wave function.
That's exactly right.
That's the Copenhagen story.
And Everett says, you don't get the right
to be classical.
You have a wave function or you're part of
the universal wave function.
And that wave function branches into different
possibilities when you become entangled with
the small quantum system.
So, this mystery in Copenhagen, what do you
mean by measure or look at or observed is
answered in many worlds by you become entangled
with that small quantum system?
That's the answer.
So what does this mean in practical terms?
Let's say it is in fact true.
And there are so many other universes.
By the way, another thing I mentioned, last
night I was on Twitter and in preparation
for this conversation, I put out a tweet because
I had a question, which I already asked, which
had to do with like supernatural phenomenon
probability.
But no one actually even wanted to hear the
question I tweeted-
Tweeter is not the best way to get new information.
Everyone started giving me answers, I hadn't
even asked the question.
It was very funny.
But back to this question, which is what does
this mean in practical terms?
How does this impact the way that we think
about the world?
Are you saying that if in practical terms
the world is classical or our personal world
is classical, but because the actual world
is quantum that there are lots of other "classical
worlds"?
Yeah.
Now, this is actually a great question.
So one really important thing for supporters
of Everett like myself to admit, is that the
fundamental formulation of the theory is really,
really simple.
But connecting it to the world we see is the
tricky part.
That's the difference.
It's a vast distance between the formalism
and our reality.
So what you would like to show is that out
of this very austere, pure, simple, elegant
formalism comes a world that more or less
acts classically, except for some occasional
quantum probabilities, poking their heads
in.
So when a radioactive decay happens, we can't
predict when it's going to happen, right?
There's a probability for any individual nucleus
to decay.
And so if you have something like a Geiger
counter that is clicking, because it's detecting
radioactive particles, the laws of classical
mechanics are not up to the job to predict
exactly when that's going to happen.
So basically, you hope that the individual
worlds within the Everettian wave function
act classically, except for some occasional
probabilistic quantum interventions.
Can I ask you something?
First of all, when did you become interested
in physics?
Very young, 10 years old, maybe.
Okay.
So, as you progressed, I'm sure there were
periods or moments where you came upon some
significant realization about the world based
on the things that you were reading.
Over that time as your life has progressed
and you've learned more and more, spend more
and more time with this, and you speak with
so many different people and you have all
these conversations.
How has this impacted the way you view life,
your place on Earth, the world, et cetera?
Well, I mean, that's always a give and take.
I think that the way that we have assembling
our view of life and our place in the world
is not a straight line, usually, right?
Like we have a lot of different influences
coming at us.
So for me part of that influence is how the
world works, the laws of physics and so forth.
Part of it is reading and part of it is philosophy
and part of it is talking to other people,
and part of it is just thinking for myself.
So I do think that my familiarity with how
physics works, gives me great confidence in
what we unimaginably call physicalism as a
view of the world.
Physicalism as in meaning, there's not extra
properties that are mental properties that
the world has.
There's not extra non physical stuff, whether
it's-
Is that like materialism?
The same ideas?
Materialism, physicalism, are almost synonymous
except the materialism says everything is
matter or material.
And I don't even want to go that far, because
is a wave function matter?
I don't know.
Like, it doesn't really count.
But whatever it is, the idea of physicalism
is, it's stuff obeying laws of physics.
That's the idea of physicalism.
And it can really only be defined in contrast
to alternatives.
But I believe that.
The success of the laws of physics is overwhelming.
In my previous book, The Big Picture, I have
an appendix where I write down this humongous
equation, which encapsulates what we call
The Core Theory, all of the laws of physics
that apply to our everyday life as we currently
understand it.
And this theory is completely compatible with
every experiment, everything you've seen here
on Earth.
[crosstalk 00:43:28].
So we know the laws of physics governing you
and me, here in this room.
We know why the sun shines.
We know why the planets orbit the sun, trees
and puppies and all that.
We know the underlying laws of physics.
So there's no room for extra stuff, influence
and everything.
And so that definitely affects how I think
about purpose and mattering in life.
I think, going back to the thing I said at
the very beginning, this idea of the matrix
or whatever.
I think another way of putting it, I think,
would be to say that I agree, but I agree
with that in terms of epistemologically as
an explanation.
But I think because of the point about subjectivity,
I don't know if we can use physics or science
to make ontological statements about the nature
of reality, you know what I mean?
I do.
[crosstalk] how you could better than physics
when he made ontological statements.
In fact, historically again and again, we've
tried to guess at the ontology of the universe,
and physics has proved us wrong over and over
again.
Yeah.
But what I mean is, though, again, like you
can have a simulation that operates perfectly
that obeys all the laws of physics, you could
be living in that simulation.
And ultimately, it's not what you thought
it was.
So this is also another way of saying-
That's an epistemological question.
Yeah.
So that's a very good question.
But I think it's a separate question.
Like, if we had the theory of everything,
the perfect laws of physics that really ... The
core theory that I talked about in my previous
book, I'm very careful to say that it applies
within a certain regime, which includes our
everyday life, but it doesn't include the
Big Bang and black holes and dark matter and
all these other things.
So maybe someday we get the theory that does
include all those things, we still wouldn't
know that we weren't brains in vats or living
in a simulation or anything like that.
And so what are we going to do about that?
How much credence are we going to put on that
possibility?
That's an excellent question.
Yeah.
It's interesting that it matters for a lot
of us.
I'm going to give a talk on the philosophical
question of how do we know what kind of universe
we live in?
How do we know where we live in the universe?
If the universe is so big, there could be
multiple copies of us.
How do we know that we didn't randomly fluctuate
into existence?
How do we know we're not brains in vats?
Can you use cosmology to figure out how likely
it is that the laws of physics have different
actual manifestation?
So these are all really ripe topics for the
intersection of physics and philosophy.
I think it's a fascinating set of questions.
When are you giving that talk?
Next Tuesday.
Next Tuesday.
Okay.
This won't be out by then.
So little will have happened.
But I can link the-
Any time travelers listening should go back
in time.
I can link to that in the description.
I have no idea whether it'll be recorded or
not, but hopefully.
Two questions popped into my head when we
were talking.
The first was more I bet you get cornered
a lot at cocktail parties.
That's sort of the first-
There's some people who run away and some
people who are fascinated.
Yeah, it's two types of people in the world.
Because if you were like creating a party,
dropping you in would be like probably a good
bet anywhere.
Because there are not many people that can
do that.
I would probably just go play with the cat.
Schrödinger's cat.
I wonder also to what degree when people wonder
about these things.
Some like from the backdoor, from the side,
their underlying questions about what happens
to me when I die?
Yeah, absolutely.
Do you find that to be true with a lot of
people that you talk to?
Well, yeah.
People don't want to die.
I don't want to die.
that's a very natural thing.
Impermanence.
Well, there's a lot going on here.
I think that people don't quite appreciate
what it would even mean to live even within
an afterlife, literally forever.
Right?
We can't really tell the difference between
a million years and infinity years, but there's
a big difference there, right?
I think you get bored after infinity years.
But the fact that we all want to continue
our existence makes it very natural that in
circumstances of incomplete knowledge, we're
going to bet that hopefully we do, continue
our existence.
But I think that the laws of physics provide
really strong evidence that that's not what
actually happens.
Like entropy.
Although that probably is also a bit dubious
when we think about a quantum universe or
no?
Does that ... Or our notions of entropy change?
Notions of entropy don't change, but there
are unlikely things that happen.
But again, those unlikely things are so really,
really, really, really unlikely that for all
intents and purposes, forget about.
Something else popped into my head when we
were talking about this immortality, is it
really about death?
Or is it even more fundamentally about not
knowing the uncertainty of what comes after
that?
I don't know.
I think people want to live forever.
Yeah.
So you don't think there's less anxiety around
that within the physics community, because
you guys are actively dealing with these questions?
And so trying to work through that gives you
a sense of catharsis around these issues,
because you're-
Sadly, no.
I mean, that would be great.
I think that effectively, the vast majority
of working physicists are physicalists and
atheists.
And if you ask them, they would think that
there is no life after death.
But they don't spend a lot of time thinking
about it, because there's another thing going
on, which is that physicists are highly trained
to spend their time thinking about physics,
and not worry about questions that might distract
them from physics.
So I have another question that kind of comes
into this.
Well, actually, maybe an easy way to get into
it is talk about QBism.
Because it doesn't QBism view quantum mechanics
or the observations that come out of quantum
mechanics as being basically just another
way of describing probabilities?
Yeah.
So for those of you out there who are not
experts or haven't read my book yet, QBism
is spelled with a Q, not with a C, so it's
not the art movement.
Quantum Bayesianism is the phrase from which
QBism was derived.
And it's basically an approach that says,
forget about reality.
Forget about the real world, forget about
ontology, forget about what's really going
on.
Limit yourself to saying we are agents who
make predictions for what is going to be observed.
And then in that case, you say the wave function
doesn't represent reality at all.
It's just a tool we use, we agents, we use
this tool to make observations of reality
and make predictions.
And even two different people could have two
different wave functions for the same system.
They might know different amounts of stuff.
And then they use this philosophy to build
up an elaborate set of mathematical relationships,
improved theorems and things like that.
And for someone like me, it's just wildly
unsatisfying.
Like, I want to know what reality is.
That's the whole point.
And some quantum Bayesians or people who work
on epistemic approaches to quantum mechanics
more broadly, where you say the wave function
is not reality, is just a way of making predictions.
Some of them say, yes, there is a reality
out there, we haven't quite figured out what
it should be within this picture.
But people who've tried have failed to come
up with any reality other than something like
the wave function.
But QBists would say that reality is classical,
right?
I don't even think they would say that.
They wouldn't say that.
They would say, why are you talking about
reality?
Talk about measurement and outcomes.
So they actually have that embedded in their
philosophy?
Yeah.
Can you take the operational framework or
model of QBism and apply it, and at the same
time also believe that the world is classical?
In other words, because this is giving you-
But believing that the world is classical
is a statement of ontology of what the world
really is.
Quantum Bayesians want to say that all the
world is a set of measurement outcomes.
So reality comes into being as a result of
our measurement outcomes.
That's interesting.
Man is the measure of all things, it's quite
literally.
Christopher Fuchs is one of the founders of
quantum Bayesianism, calls it, participatory
realism.
Because by the sum of all of our measurement
outcomes, we bring reality into existence.
Highly relative.
Yeah.
I can't even claim to fairly characterize
it, honestly.
So I don't even like talking about quantum
Bayesianism, because even if I tried to be
fair, I'm going to mess it up.
This reminds of something else.
I took, sad to admit it, because I feel like
I should have done better.
But I took an online course by Leonard Susskind
some years ago.
Of course, there's the famous phrase that
Richard Fineman said that, pretty confident,
that no one understands quantum mechanics.
Yes.
And that goes back to the point that I said
early on when I read that book on quantum
gravity where it said everyone's sitting at
dinner, and putting aside the point about
mathematics, no one can agree on what it actually
is.
But he had said something else that really
resonated with me, which was that Fineman
was reported to have said, "It's so confusing.
I can't even tell if there's a problem."
Right.
That's right.
Yeah.
And I think that this is another message of
my book, is that physicists, forget about
the fact that we don't understand quantum
mechanics.
That's fine.
There's plenty of things we don't understand,
right?
I mean, that's how science makes progress
by not understanding things, recognizing we
don't understand them, and trying to tackle
the problem.
The problem with quantum mechanics is we're
not trying to tackle the problem.
It's not that we don't understand it, it's
that we are in denial about the fact we don't
understand it.
And there's a whole bunch of working physicists
who say, it's fine that we don't understand
it.
Who wants to understand things?
That's not why we're here.
We just want to make predictions.
So I have another question and it kind of
intersects with something that I discussed
with Patrick Grim on our episode on Mind-Body
Philosophy, and that had to do with notions
of the self.
Who am I?
And there were some thought experiments we
worked through.
And one example would be if I made a literal
copy of myself, and that copy was recreated,
who would I be?
And that stems from your interpretation of
many worlds.
It's an example.
Yeah.
So this is exactly what I'll be talking about
in my philosophy lecture.
This idea of personal identity over time,
to the extent that we think of the world as
classical and having, for that matter, just
any single world version of reality.
Again, even if we don't define it rigorously,
we know what we mean when we say our self,
right?
You have a self and it's connected in an obvious
way to what that self was doing a year ago,
for example.
But if we are really, really careful about
it, yourself now, is it a different person
than yourself a year ago?
This is a person who knows different things,
who's made of different atoms, right?
Who has different knowledge and experience.
So what's more rigorously true is there is
a relationship between yourself now and yourself
in the past.
So Many-Worlds says that relationship is many-to-one.
It's not one-to-one.
There's one self in the past and as many selves
right now.
That's fine.
That whole talk about what the relationship
is and psychological continuity and the sharing
of memories, still goes through unaffected.
So it's an updated version of what you mean
by personal identity, but it's a perfectly
coherent version.
So what do you think consciousness is?
I think consciousness is an emergent phenomenon.
It's a useful way of talking about the fact
that we are made of atoms, we're a physical
system that has the property that we contain
information about ourselves.
That we represent ourselves.
That we have some form of self-awareness.
And we can sort of check back on ourselves
to figure out what is going on and that self-awareness.
Doesn't it complicate you when you think about
that, ultimately, consciousness was what's
creating all of these theories?
I don't know.
I guess, the theories that I come across that
try to explain consciousness ... Again, I
think, here's where Chalmers makes more sense
to me.
I feel like consciousness somehow needs to
be at the center.
But again, even if it's at the center, I think
where I disagree is I don't know that you
can say anything definitively, if you put
it at the center, because then it's just all
theoretical.
Right?
I don't know because they don't put it at
the center.
So I don't want to speak for people who do.
I think that consciousness ... The universe
would be fine without consciousness in it.
So how in the world can we put it at center.
All right.
So I'm going to move us to the overtime, Dr.
Carroll, and I want to drill more into this
maybe from a more practical standpoint or
maybe popular culture standpoint, maybe talk
a little bit more about the simulation, reverse
engineering intelligence and stuff like that.
For regular listeners, you know the drill.
If you're new to the program or if you haven't
subscribed yet, head over to patreon.com/hiddenforces,
or go directly into the description for this
week's episode and click on the link, and
you can access our audio file autodidact or
super nerd tiers and get access to this week's
overtime and my conversation with Dr. Carroll.
As well as to the transcript of today's conversation,
as well as to the rundown, which was my attempt
at bringing some level of preparedness in
order to this conversation.
Dr. Carroll, stick around.
I will.
Thanks.
Today's episode of Hidden Forces was recorded
at Creative Media Design studio in New York
City.
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As always, thanks for listening.
We'll see you next week.
