♪ [Music] ♪
 I'm in awe of reality,
 the very largest,
 the very smallest.
 I'm enthralled to cosmology.
 I'm a devotee of
 fundamental physics.
In cosmology, the very largest,
 the universe is now said to
 contain two trillion galaxies,
 that's just the
 visible universe.
 And no one thinks
 that the universe stops
 at what we can see.
 In fundamental physics,
 the very smallest,
 we search for deep harmony
 of all particles and forces,
 an ultimate unification,
 a final theory of everything.
How to discern the deep meaning
 of physics and cosmology.
 That's what philosophy
 is supposed to do.
 Why philosophy of
 physics and cosmology?
 I'm Robert Lawrence Kuhn,
 and Closer to Truth is
 my journey to find out.
♪ [Music] ♪
 To discern the deep meaning
 of physics and cosmology,
 I go to Banff, Canada,
 for a conference
 of the Foundational
 Questions Institute, FQXI,
 a gathering of physicists
 and cosmologists
 who dare to look over
 the scientific horizon.
 We're in the
 Canadian Rocky Mountains
 and with quantum
 theory on the agenda,
 I'm walking a rocky road,
 there are so many
 innovative thinkers here,
 I'm already frustrated
 I can't talk to them all.
 I begin with a
 philosopher of physics
 known for defending the
 many worlds interpretation
 of quantum theory,
 where all reality splits off
 into alternative
 future histories,
 David Wallace.
David, as someone
who is trained in science,
but as a non-physicist,
I've always been interested
in the deep implications
of physics and cosmology,
and philosophy of
physics and cosmology
seems like a way
to understand that,
but a lot of y
physicist friends say
that philosophy is at
best an interference
with what they do in science.
You are a philosopher
of physics,
so help me understand
what this field is
and why it's important.
Sure, what philosophy of
 physics is engaged with
is very much understanding
some of the more conceptual,
less calculational
aspects of physics,
and in that sense its
continuous with physics itself.
 And, I found,
 as a PhD student
 that the questions I
 was interested in in physics
ended up going so much more
towards those
conceptual questions
that it ended up
making more sense
to call myself a philosopher.
For example, what were
some of those questions.
Sure, so the
big three questions
that have dominated
the subject have been,
how do we think about
quantum mechanics,
how do we think
about space and time,
how do we think about
the emergence of laws
and physics on higher scales
from things on smaller scales.
And all of those
questions are questions
that at one point you'd have
said were pure philosophy,
and became parts of physics
as we got better at science.
 But they left behind
 conceptual questions
that physicists
care about as well,
but that, some of the methods
and practices of philosophy
come to play in.
And I'd say, this is
particularly relevant
for the FQXI
conference were at,
that, there's in recent years
been a sort of fourth branch
of that philosophy of cosmology
which is drawn on
all three of those,
but has asked some distinctive
 questions of its own.
So, what are some of those
distinctive questions,
because those are the ones
I've been interested in?
I think a lot of them have to
do with the nature of science
and the scientific
method in a domain
where the rules seem
to have changed a lot,
where it's really hard
to get evidence,
where our own place
in the universe
seems to be playing a role
in how we make predictions,
and where really
sober physicists
are starting to say for a
 bunch of different reasons,
that there are vast
numbers of universes,
most of them are lifeless,
and we need to understand
why we're in the one we're in.
So, four categories,
quantum mechanics, space-time,
something that seems
to me is emergence
in the broadest sense of
the term, and cosmology.
Just describe
each one of those
in terms of some of
the deep questions
 and how progress can be made,
because some physicist say
that as soon as any
progress can be made
that comes out of philosophy
and goes into physics.
Yeah, so in philosophy
of quantum mechanics,
the big question is the quantum
measurement problem.
Quantum mechanics seems
to say crazy things,
either that there are parallel
universes we can't see,
there are...that...all that
the observer is playing...
You're betraying
your theology...
 Some future role...my
 cards on the table,
the observe is playing
some crucial role
or that our fundamental theories
are wrong and need changing.
Okay, those are three
possibilities, very good. - Yup.
Philosophy of space-time,
I say these days the
most crucial questions
are how do we continue
to think about the nature
of space and time,
in the context of quantum
theories of gravity...
-Are they discreet?
- Are they discreet?
-Emergent?
- Exactly,
 is our fundamental theory
something that's not describe of
the language of space and time,
since every physics
we've ever done
is described by the
language of space and time,
that kind of looks
like a problem.
Biggest question
in the philosophy
of, of what you call
philosophy of emergence,
what I think is fine,
but sometimes gets called
the philosophy of
statistical mechanics,
I'd say the biggest
question is about
the distinction between
the past and the future
How come the
 microphysics we have,
 which doesn't seem to care,
 gives rise to a macrophysics
that seems to care a lot?
-So, there's an arrow of time?
-Exactly.
So, arrow of time
is a subset of this kind of
emergent area of physics?
That's right, because what
emerges has an era of time in,
and what it emerges
it seems, doesn't.
And seems almost
like a contradiction.
Okay, okay.
And philosophy of cosmology.
I kind of think
we don't yet know
what the biggest question is,
but I'd say, a good
contender for first place
is just how do we modify
our scientific methodology
to allow for the very different
context of observations
we find ourselves in cosmology
And this is a place I think
where, even hard-nosed
physicists
have found themselves having
to be quite philosophical
to say things about the
observer and the mind
that you wouldn't have
managed to get published
in serious physics journals
even maybe 15 years ago.
-And today can.
- And today can.
I mean not that everyone's
happy with that.
Yeah, how do you see the
development of the field?
I think the optimist
in me thinks that
what really matters is
that philosophy of physics
gets better than it is now
at really engaging with
and talking to physics
and listening to what
physics says back.
Frankly, I think the field
 needs to up its game a bit.
♪ [Music] ♪
 In the philosophy of
 physics and cosmology,
 I hear four categories
 of questions.
 One, how does quantum
 mechanics work?
 Two, what is space-time?
 Three, how does our
 ordinary macroscopic world
 with all its complexity
 and normality
 emerge from the fundamental
 microscopic world
 with all its simplicity
 and strangeness?
 Four, what counts for
 science in cosmology?
 Great questions, robing
 the deep meaning of reality,
 I need to dig deeper.
 I start with the mystery
 of our ordinary world.
 How does complexity
 come from simplicity?
 I speak with a big picture
 physicist and cosmologist,
 author of, unsurprisingly,
 The Big Picture:
 On the Origins of Life,
 Meaning, and the universe,
 Sean Carrol.
Sean, what's the philosophy
of physics or cosmology?
And one of the big
questions is that,
in any start to the system,
everything is extremely simple.
And so, the question is,
how do you go from the extremely
simple to what we have now,
which is extremely complex,
especially when you have the
second law of thermodynamics,
pushing seemingly in the
opposite direction.
Yeah, I mean there's an old
kind of silly question, right?
Which says, if you claim
that the universe is
just winding down,
becoming more disorganized
entropy is increasing,
the second law,
then how in the
world do you explain
the coming into being
without some
transcendent purpose
of these exquisitely organized
systems, like you and me.
And of course, scientists had
a cut and dry answer to that.
The Earth, and its biosphere
is not a closed system.
And in open systems,
in ones that are interacting
with their environments,
entropy can do down.
I can put a bottle of champagne
in the refrigerator, cool it,
its entropy will go down.
And that's true,
but it doesn't explain why
it actually does happen,
it says it's okay,
its allowed by the
laws of physics
for complex structures to come
into existence here on Earth.
But it doesn't
say why it does.
And I think the answer to
that lies in the distinction
between entropy,
low entropy being orderly,
high entropy
being disorderly,
and simplicity
versus complexity.
These are two very,
very different things.
I would, I would argue
that not only is it allowed
that complex structures
come into existence
as the universe expands
and entropy increases.
But it is necessary for
that process to happen
in order to allow
complexity to arise.
It's definitely an interplay
of the different forces.
The fact that we have gravity
which only pulls
things together.
Nuclear force which holds
nuclei together,
and electromagnetism which
kind of can push or pull,
depending on the situation.
All of these play together
to allow the complexity
to come into being.
But its temporary.
The analogy I'd like to use
is cream and coffee
mixing together.
When the cream and
coffee are separate,
that's a low entropy,
organized system.
It's also very, very simple.
When they're all mixed together
its high entropy disorganized
but again very, very simple.
It's in between, when the
tendrils of the cream and coffee
are mixing into each other,
that's when its complex,
it's the fact that
entropy is increasing
that lets this complexity
come into being,
at least for a little while
until it eventually
fades away again.
And is that your metaphor for
the entire universe and for...
The universe does
exactly the same thing.
The universe starts very simple,
very organized and low entropy.
It will end in the far
future, billions and
billions of years from now,
simple again,
because the universe is going to
expand and cool and empty out.
It will be very high entropy,
but once again simple.
It's this in between phase
in the middle
that you see complexity.
You and I are those cream
and coffee tendrils
mixing into each other.
And this is the time that
we can see other Galaxies
they haven't flown away
from each other,
so, doesn't that make you
wonder about this time
and this oddity that the
universe goes from
utter simplicity to
utter simplicity? -Well...
And, here we have this time,
isn't that a strange
way for reality to be?
The fact that the
universe started
in such an extremely simple
low entropy state,
is indeed very, very puzzling.
This is one of the
primary things
that cosmologists spend their
waking hours worrying about.
The fact that given
that we did that,
complex structures come into
being in the aftermath,
and that's the era of the
universe's history
which we find ourselves
is the least surprising
thing in the world.
I mean there's clearly
a selection effect,
we're very complicated.
What's the universe
going to look like
when we wake up
and look at it?
It's going to be in
the complicated...
Right, but you're assuming
the existence of those forces?
-Yeah, oh Yeah.
Gravity and electromagnetism
and the strong force,
and weak force,
and quantum wave functions,
and all sorts of things!
Yes, you need a universe
that is rich enough in
its fundamental dynamics
to have pushing and pulling
on different scales.
Without both
pushing and pulling,
you're not going to get
complex structures for me,
in fact, we simulated cream and
coffee mixing into each other
and we found that,
for some versions,
they just sort of smoothly
spread into each other
and complexity never arose.
For different quote,
unquote laws of physics,
they become very complicated.
-...of physics, yeah.
But you know, there wasn't
a lot of fine tuning involved,
it wasn't hard to find
versions of those laws
where they became every
intricate and complex
But doesn't it strike
you in some odd way
that you have these very
complicated things
and quantum wave function,
and the four forces of nature,
gravity, electromagnetism,
we talked about them,
and then going from simplicity
back to simplicity.
I mean, that's the
way reality is.
Yeah, that's right.
That's the way reality is.
-Doesn't that bother you?
-No.
It makes me curious,
I'm wondering why it's like
that versus some other ways,
I'm not sure whether there's
a good answer to that.
I have no idea how
surprised we should be
that the fundamental
laws of physics
seem to allow for
enough complexity
to give us not only intricate
structures in the universe,
but self-aware
information processing,
future predicting,
substructures of the universe.
And then disappearing?
And then we'll go away,
yup, that's right.
And then disappearing,
it seems like a cosmic joke.
Well, it certainly is absurd
in the existentialist
sense, right,
there's no reason why it's
like that, as far as we know.
Fortunately, that's what it is.
♪ [Music] ♪
 How complexity emerges
 from simplicity
 makes scientific sense.
 But then for complexity to
 devolve back into simplicity,
 as the universe expands
 and dilutes into emptiness,
 and for such simplicity
 to remain static forever?
 I cannot help but wonder
 what an odd way for
 the universe to end.
 Explaining the odd ending,
 or is alternatives,
 that's for philosophy.
 Another oddity is
 how the universe began,
 the origin of space and time,
 as well as matter and energy.
 I speak with physicist
 James Hartle,
 who developed the
 Hartle-Hawking wave function
 of the universe,
 before what we call
 the Beginning,
 he proposes, there was
 no time, only space.
 The universe had no beginning.
Jim, what are some of the
most important
contributional theories
that together can give
us an understanding
of the meaning of cosmology.
What's important, right,
is to understand our universe,
how it evolved, right?
What are the laws that
govern the regularities
that we see in it? Right?
From the point of view
of fundamental physics
that means quantum gravity
and it means a theory of a
quantum state of the universe.
It's two pieces,
a theory of dynamics
and a theory of the state.
And then to see what we can
predict from realistic theories
and test them against what
we see of the universe today.
It's not really different
from what human beings
have been doing
for thousands of years
trying to understand
whatever the universe
seems to them as a whole
in terms of basic physical laws.
We have a better
appreciation today,
because we're able
to do more experiments
of the nature of those laws.
It's a big extrapolation
to apply them to the universe,
but a necessary one to
continue this tradition,
and hopefully
we'll be successful
in discovering what
theories really compress
all the discussions of
the regularities we see
all over the universe,
and explain those that
aren't the results of that,
but are the result of quantum
accidents like evolution
that have occurred over
the course of Existence.
What can we explain,
and how do we explain it?
So, we deal with an initial
state and then a process,
a dynamic process to have
that state go forward in time?
Except for the word initial
I'm with you on this,
because there's
no time, right?
The world is four dimensional,
as far as we can tell,
or ten dimensional if
we're...or more of less.
So, we need to understand
not only evolution,
that comes later.
We need to understand the
prerequisite for evolution,
which is a classical space time.
Why classical space-times
come out of a quantum universe?
What are the importance
of some of the areas
that you've focused on,
the wave function
of the universe,
the Hartle-Hawking state?
How are these big,
interesting original ideas
affect that overall philosophy
of state and dynamism?
They tell us
that the evidence in the
observations of the universe
are that it was much
simpler earlier,
than it is now.
More homogenous, more isotropic,
more nearly in equilibrium.
The light from the
Big Bang, right,
shows very tiny fluctuations
to the order of one part
in ten thousand of
the temperature.
Yet those fluctuations
are important
because the collapse
of those fluctuations
gave rise to the
stars, galaxies,
and ultimate the biota and
human beings that we see today.
It's the standard effort,
I think of human society,
to try to put what
we see in order.
As Bohr said, the task of
physics is to extend its range
and reduce the
phenomena to order,
and that's exactly what we're
doing in quantum cosmology.
We're extending it on the
biggest possible range,
the whole thing,
and were trying to reduce
it to Order, right?
That explains what we see today.
♪ [Music] ♪
 Trying to find my way
 amidst the astonishing reach
 of human knowledge,
 I remain transfixed.
 It's not just me,
 this increasingly
 public fascination
 with physics and cosmology.
 That's good for the
 support of science,
 but is there larger meaning?
 That, only philosophy
 can provide.
 That's why I seek the author
 of 7 Brief Lessons in Physics,
 an expert in quantum gravity,
 Carlo Rovelli.
Carlo, I like to talk
about the philosophy of physics,
the philosophy of cosmology,
in order to see the
broader implications
of the scientific theory.
Reflect for me the importance
of communicating the essence
of physics to large audiences.
People want to know,
and, what is happening
in modern science,
quantum gravity, cosmology,
particle physics,
quantum mechanics,
general relativity.
But also, want to know
the implications of that.
Also, I think that's what is
most meaningful and significant
in the science that we do.
A conference like
the conference here,
it's not a technical conference
about adding details
to some information
about physics.
It's trying to go to
the deep questions,
to the core questions.
What do we know about reality,
what do we know about time?
What do we know
about the observable?
Or what we know...
And I think that
the distance between physics
and philosophy is small,
it's very small.
Physics nourishes
itself from philosophy.
The best philosophy finds
nourishment in physics.
Why? Because our understanding
of the world is one.
It's not broken.
We don't have a physics...
a philosophical religious...
we're unitary beings
which try to bring together
a vison of the world
based on everything we know.
You've picked 7 ideas.
So, what are the seven,
and why do they
express fundamentally
the philosophy of physics?
The first chapters on
general relativity,
because it has changed in depth
what we mean about
space and time.
The second is about
quantum mechanics.
Quantum mechanics has changed
and is still changing,
and that's what
we think about matter.
Matter is different than
what we thought before.
So, it's this...
And it's the fundamental
basis for everything
that exists, obviously.
Exactly, exactly.
So, but you know,
quantum mechanics tell us
that the world is
made up of stones,
by things, so,
it's a new work...
So, both of the first
two are different ways
of thinking about things
that we thought were
obvious and self evident.
Basic, exactly, exactly.
And they're both neither.
Third is about cosmology.
We, it's basically a
chapter with pictures,
we saw the world, you know,
the ground and the sky,
and then the Earth
and then the sky,
and then the Earth,
then all of a sudden the galaxy,
and thousands of galaxies
and they're always...
And then the, the story...
immense expansion.
The scope of reality.
The scope of reality.
And, smallness of ourselves
in the universe we see.
The universe is
incredibly large.
And then there's on chapter
about quantum field theory.
Because quantum field theory,
particles, particles physics.
That's, I mean, quantum
physics is often presented
in the form of, you know,
there are these particles
or these particles in this
field. -Yeah, it's like a zoo.
It's a zoo, that's not
the interesting part,
that's a list of things.
The interesting part
is that particles are
not really particles.
The things that exist,
don't exist, exist, don't exist,
the vacuum is full of stuff.
So, there is this
sort of vibration,
the universe is like the...
the universe of the
hippies of the 60s, right?
It's all vibrations,
something like that.
So again, it's sort of
relativistic quantum mechanics,
but has changed our sense
of all this stuff.
Okay.
And, up to now, it's mostly,
established physics.
Then you go to
quantum gravity,
which is you know, I see a
cleavage, it's a boundary,
now I tell you what
we're trying to do.
And I talk about
quantum gravity,
quantum, granular space,
I talk about new
quantum gravity,
the structure of
space and time,
the quantum structure
of space and time.
And then there's one
chapter about heat,
and the relation between
heat and time.
Heat and time and gravity,
you know, gravity changes time,
changed the meaning of heat,
black hole. All that.
There is a last lecture,
which is not about
physics really,
but is about, what are we?
In this funny world,
this world of
champion particles,
curved space, immense universe,
what is human beings, that feel,
that know, that learn,
that have understood all that?
What are we, how can
we think about that?
And my own take is that
we're part of this nature.
And, personally, emotionally,
I find this immensely
reassuring and calming.
I'm home.
I'm not in the natural
world as an outsider.
I'm in the natural
world as part of it.
I admire your serenity,
but I personally, after living
through the 6 prior chapters,
I'm agitated.
Because I want to know
what it all means.
You're very calm to be subsumed
in this very natural World
and enjoy that,
but people are different
and they're not.
I'm agitated, I was calm before
I heard your 6 chapters...
-I'm sorry...
-Now I'm very agitated.
I'm sorry,
it makes me more quiet,
by thinking there are
things I don't know.
I'm partial in the setting
of reality, and that's it.
I'm limited, I'm mortal.
I think I'm going to die,
and that's it.
And this is an incredibly
reassuring thing for me.
I don't have to
worry about eternity.
♪ [Music] ♪
 I'm stunned by infinity.
 I shudder before eternity.
 I marvel that we humans can
 comprehend endless time.
 It's part of the philosophy
 of physics and cosmology,
 a clear, if twisting
 road to reality.
 The four big questions.
 One, quantum mechanics,
 two, space-time,
 three, our emergent world,
 four cosmology.
 The puzzle of complexity
 from simplicity,
and the relatively brief period
 when complexity exists.
 The vast size of the cosmos.
 We must never tire of
 this ultimate fact.
 Quantum gravity shaping cosmic
 structure and evolution,
 what any final
 theory must explain.
 The unity of knowledge,
 the deep truths
 when philosophy intersects
 physics and cosmology.
 On all this, I've two minds.
 One is awed by the beauty,
 the elegance of the science.
 The other is overwhelmed
 by the oddity,
the strangeness of the reality.
 Perhaps both are
 Closer to Truth.
♪ [Music] ♪
