(intro music)
My name is Richard[br]Holton, and I teach at MIT
in the Linguistics and[br]Philosophy Department.
And today I'd like to talk about
the problem of free will.
Or, more precisely, about[br]a couple of problems
surrounding free will,
which I think tend to[br]get muddled up together.
And part of what I want to do today
is to draw those two problems apart.
So the first problem of free will
is probably the one[br]most people think about.
And that is the idea that
if all the laws of[br]nature are deterministic,
then if the initial conditions are fixed,
everything that will[br]happen thereafter is fixed,
by those conditions and[br]by the laws of nature.
People have thought,[br]understandably enough,
that that puts a real[br]problem on free will.
Because part of the intuitive[br]idea of free will is that
when I'm faced with some choice, decision,
I could choose one way and act that way,
or I could choose the[br]other way and act that way.
And those two choices are free.
But let me mention,[br]now, the second problem.
Which I think gets tied[br]up with this first one.
So the first one is a metaphysical issue,
it's about determinism.
The second one is basically[br]an epistemological issue,
that is it's an issue[br]about what we can know.
And this is actually an idea[br]that goes back much further.
It goes back certainly to the stoics,
and it's come up time and[br]again in Christian thought.
So this is the problem,[br]really, of foreknowledge.
That is,
if things are determined in[br]the way we talked about before,
then, if we know the initial conditions,
and we know the laws of nature,
then it looks as though[br]we'll be able to predict
everything that happens.
So Laplace phrased this very neatly,
and came up with this idea[br]called "Laplace's demon,"
who is able to predict everything[br]that you're going to do.
So there you are, thinking[br]you're acting freely,
and this little demon[br]knows what you're gonna do.
And you can make the problem even worse.
So, suppose you could get a book
in which all this was written down.
a Book of Life as it's sometimes called.
You can open the book and you can
look at your history and you can see
everything you've done,[br]it's catalogued perfectly.
You flick through the[br]pages, you get to today,
you run your finger down the ledger,
and you get to the entry which says,
"You are reading the Book of Life."
It's the end of the page.
And you think, "If I turn over the page,
I'm gonna know exactly[br]what I'm going to do.
How can I hang onto any[br]conception that I'm free,
if when I turn the page, I'm going to see
everything that I'm going to do."
This second problem, I think,
is in many ways worse than the first.
What I want to suggest is actually that
the second idea doesn't[br]follow from the first.
And in order to illustrate[br]that difference,
I want to think about a[br]very, very simple device,
in a very, very simple game.
This is a challenge I offer to you.
I have this device, and[br]on the top of the device,
is a light bulb.
And what I want you to do is to predict
whether or not that light[br]bulb will be on or off
at exactly noon today.
And I'm going to make[br]it rather easy for you.
I'm going to give you a[br]lot of resources to tell
whether or not that[br]light bulb is on or off.
I'm going to tell you exactly[br]what the configuration
of the machine under the light bulb is.
I can tell you all about the circuitry,
all about the power coming into it,
so you'll know exactly how that works.
And in fact, I'm gonna tell you about
anything else in the universe[br]you might want to know.
So I'll tell you all of[br]the initial conditions.
And I'm gonna tell you[br]all of the laws of nature.
And if that's not good enough,
I'm going to give you something else.
I'm going to give you
all the computing power you can ask for.
And my challenge to you then is,
using all of this, predict whether or not
the light bulb will be on or off
at noon today.
Small catch though.
In fact, there are two small catches.
First catch is this.
You have to make your prediction
before 12:00.
You have to make it at[br]exactly five minutes to 12:00.
Secondly, you have to make your prediction
by putting on a light bulb of your own,
which is quite close to[br]my light bulb on my box.
If you put that light bulb on,
then that's an indicator that you believe
the light bulb on the[br]box will be on at noon.
If you leave it off,
that's an indicator that you believe
the light bulb will be[br]off on the box at noon.
So that's the challenge.
Sounds easy, right?
You've got all that power,[br]you've got all that knowledge,
you should be able to predict whether
the light bulb's going to be on or off.
But now let me tell you what's in the box.
Let me reveal some of the wiring.
What's in the box is[br]a little light sensor.
And it's directed at your light bulb.
So if your light bulb goes on,
that sensor will sense that it's on,
and that will trip a switch,
which will ensure that the light bulb
on the top of the box will be off.
Reversely, if your light bulb is off,
the sensor will sense that,
and that will trip a switch[br]which will ensure that
at noon the light on the top of the box
will be on.
Now it doesn't seem so easy[br]to win the competition.
Because what this machine[br]is, is a frustrator.
It's designed to frustrate[br]whatever prediction you make,
it's designed to make it go false.
But now think what we've got.
I've given you all the initial knowledge,
I've given you all of the
resources to compute,
and yet you still can't come up with
an accurate prediction
once you're in a world[br]with a frustrator in it.
Two things to say about this.
First thing to say:
it seems to me that many many things,
but particularly human beings,
may well be frustrators.
In fact, you might be[br]a frustrator yourself.
You might look at what's[br]predicted for you to do
when you turn that page[br]in the Book of Life
and you see what's predicted for you,
and you might do the opposite,
because you want to show[br]that you're no puppet
of what's happening in the Book of Life.
Secondly, of course,[br]someone outside the system,
if they have all the predictive abilities,
they could predict what would happen.
But of course what they'd be predicting
is just that you were[br]going to lose the game
when you are stuck inside the system.
So what conclusion can we draw?
Well, I think the conclusion to draw
is that if we are creatures[br]who are inside the system,
which in some obvious sense we are,
and if we or others[br]around us are predictors,
then we can't infer from[br]the truth of determinism
to the possibility of foreknowledge.
That doesn't show, I think,
that free will is home and dry,
but I think it does remove one of the most
worrying aspects to free will.
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