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Sean Carroll: Are we living in a clockwork universe? | Big Think | YouTubeToText
YouTube Transcript: Sean Carroll: Are we living in a clockwork universe?
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Classical mechanics, as formulated by Newton and elaborated by Laplace, suggests a deterministic universe where knowing the exact state of every particle at one moment allows for perfect prediction of the past and future. However, the practical impossibility of such knowledge, coupled with the emergence of quantum mechanics, leads to a nuanced understanding of free will and agency.
- The structure of classical mechanics
implies that if you knew the position and velocity,
not just of one particle,
but of every particle in the universe,
then the laws of physics would determine what happens next,
at the next moment and the next moment,
and infinitely far into the future,
and for that matter, indefinitely far into the past.
Now, this might bother you a little bit
if you wanna think, well, wait a minute,
I'm a person, I'm a human being,
I have the ability to make choices.
I'm not determined by the laws of physics.
And both scientists and philosophers thought about that.
They still don't agree
on what the right way to think about it is.
I'm Sean Carroll.
I'm a physicist and philosopher at Johns Hopkins University,
host of the "Mindscape Podcast,"
and also author of a bunch of books.
Most recently, "The Biggest Ideas in the Universe" series,
including "Space, Time, and Motion" and "Quanta and Fields."
- [Narrator] Is reality just a clockwork machine?
I like to say that physics is hard because physics is easy,
by which I mean we actually think about physics as students.
You know, we took classes, we read books, and it was hard
because there's all this new stuff, all these ideas,
all these equations that we don't come across
in our everyday lives.
But the reason those ideas are hard
and those equations are there,
is because physicists have a technique
that has been amazingly successful,
which is to take all the messy world around us
with all its peculiarities and specificities,
and to boil it down to really, really simple systems.
You might imagine or remember
when you were taking physics courses,
there were frictionless surfaces,
there were pendula that rocked back and forth perfectly.
We're always idealizing,
we're always imagining there are no complications,
and then we're putting them back in.
That's a strategy that would completely fail
if you tried to do it for psychology
or biology or political science.
But for physics, it turns out to work incredibly well.
There's a joke that physicists like to tell each other.
They don't like to tell it to others
'cause it's not very funny.
But the idea is that a dairy farmer
wants to improve his yield, more milk out of the cows,
and for some reason, he approaches a physicist and says,
"Could you look at my farm
and tell me how to get more milk out of the cows?"
And the physicist thinks about it,
and he comes back with a sheaf of calculations
and he says, "Okay, first imagine a spherical cow."
The idea, I know it's not that funny, but the idea is
that the first thing the physicist is gonna do
is try to imagine a simpler situation.
Real cows are not spherical.
It would be a very different dairy farm
if the cows were spherical,
but you can calculate the volume of the cow
and the metabolic rate of the cow much more easily
if it were spherical.
And the joke, of course, is that
that doesn't work in dairy farming,
but it works really well when you're considering
a spherical universe
or a spherical solar system or a spherical atom.
The first really huge revolution in physics
was the existence of classical mechanics
handed down by Isaac Newton and others.
It took a while.
Newton was building on the shoulders of giants.
But before Newton, there was Aristotle.
And Aristotle says that things have natural places
they wanna be, natural ways they want to move.
And Newton says something completely different.
He says, if something is not acted on by a force,
it's gonna continue in a straight line
at a constant velocity forever.
And if it is acted on by a force,
I can tell you how it'll move.
I have an equation to do that.
Physicists like to simplify things a great deal.
But billiards, you know, the pool game,
is pretty close to being simple.
It's not exactly, because you know,
when you hear those balls click against each other,
that sound is giving off energy, and it's kind of wasteful.
But in principle, if you had no friction, no sound,
no air resistance, the balls bouncing around the pool table,
let's also imagine there's no pockets,
so the balls can just bounce off
the edges of the table forever.
They would go forever.
They wouldn't stop, right?
The energy contained in the system remains constant.
And the laws of physics, as Laplace points out,
suffice it to predict exactly what the balls are gonna do
at every moment, given what they're doing right now.
So to the extent that it's okay to ignore friction and noise
and things like that, not only is it true
that if you imagine hitting the balls
and watching them move,
you could predict exactly what's gonna happen
on the basis of the laws of physics.
If somehow you could take a snapshot later in their motion
so you know both where they are and how fast they're moving,
so maybe a little clip of a movie,
then the laws of physics would let you
go backwards and reverse engineer
what exact configuration the balls were in.
We don't perceive that in our everyday world
because the world is full of noise and dissipation
and air resistance and things like that.
But in the pristine, perfect world
of imagined classical mechanics,
the past and future work equally well.
You can go from any one moment to any other moment.
It's interesting that Newton came up
with the framework of classical mechanics in the 1600s,
and people were very excited,
you know, physicists, mathematicians, philosophers.
They didn't really have physicists at the time.
They were all considered to be natural philosophers,
but they worked on it, you know, they thought
about the motions of the planets and things like that.
And the implications of this idea are profound
for how we think about what physics is,
what physics tells us.
Because it wasn't realized until Pierre-Simon Laplace
over a hundred years after Newton.
But the structure of classical mechanics
implies that if you knew the position and velocity,
not just of one particle,
but of every particle in the universe,
and you knew the laws of physics
and you had infinite calculational abilities,
none of these are at all plausible,
but we're imagining right now.
Then the laws of physics would determine what happens next
at the next and the next moment
and infinitely far into the future,
and for that matter, indefinitely far into the past.
So you can take any one moment
in the history of the universe
according to classical mechanics,
and the information contained
in what is going on at that moment
is sufficient to fix what will happen
at every other moment in history.
And Laplace, who is quite imaginative about these things,
put it in terms of a metaphor.
He says, "Imagine a vast intelligence."
Later, commentators dubbed it Laplace's demon.
He didn't call it that, he was famously an atheist.
He didn't like to talk about demons.
But the demon, the vast intelligence
who could know everything about the universe
at any one moment, Laplace says to that vast intelligence,
the past and future are an open book.
You would know everything because what happens now
fixes the entirety of space and time.
The idea that the laws of physics
fix what's going to happen
in principle precisely and exactly
if you know what's happening right now.
So this became known as the clockwork universe paradigm.
The universe clicks along
in perfect accord with the laws of physics forever.
Now, this might bother you a little bit if you wanna think,
well, wait a minute, I'm a person, I'm a human being,
I have the ability to make choices.
I'm not determined by the laws of physics.
And both scientists and philosophers thought about that.
They still don't agree
on what the right way to think about it is.
But the favorite way to think about it is the following.
In principle, if you knew
exactly everything that was going on in the universe,
you could predict the future.
Now, classical mechanics isn't quite right.
Eventually, we're gonna talk about quantum mechanics,
so that's another thing you have to keep in mind.
But to the approximation that classical mechanics is good,
you are determined in what is going to happen.
But guess what?
You don't know all the positions of all the atoms
and all the molecules that make up you.
Indeed, you literally cannot know them
because the memory storage capacity to know all that
would be at least as big as your brain, if not bigger.
And if you made your brain bigger,
now you just have more molecules to keep track of.
It is impossible to actually have
a real Laplace's demon in the universe.
It's just a thought experiment
to make vivid the implications of determinism.
So philosophers have settled on what they decided to call
compatibilism in the sense that on the one hand,
the deep down microscopic laws of physics
are perfectly deterministic,
or they're not if you're in quantum mechanics,
but they're pretty deterministic anyway.
But since you don't know it,
you should be asking yourself, what is the best I can do?
What is the best way that I can try to understand
human beings given the vastly incomplete information I have?
I know about, you know, my friends' personality,
and you know their predilections and their traits,
but I don't know every neuron in their brain.
And under those circumstances, you will model,
you will think about a fellow human being or about yourself
as an agent capable of making choices.
Everyone does that, and that's the right thing to do
because you are not Laplace's demon.
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