Well let me thank you all very much for coming again and I also apologize again for speaking
in English but it will be better for us both and if I try to speak in German.
So let me get my technology straight, here we go, yes.
Okay my topic today is causation as folk science and I need to say a little bit to set things
up here because when people hear that I'm a causal skeptic it seems to cause a lot of
hilarity.
I think the favorite remark that I have is from a colleague who said to someone else
whispering, how does he think things happen?
Well I'm not that sort of causal skeptic.
What I hope to convince you of is that the view that I have is really quite a reasonable
view, it's the sort of view that I believe is held tacitly very widely amongst philosophers
of physics.
When I talk to my colleagues in philosophy of physics they tend not to be unhappy with
what I'm saying, they have a kind of gee isn't that what everybody thinks reaction.
When I talk to people who work in causal metaphysics they're the ones who think I'm crazy.
So there's a clear division here, I think it's a clash of two different cultures.
So as before I've put these transparencies up on the website so you can download the
PowerPoints and look at them at your leisure and I'm saying that because I'm going to skip
over this transparency, this has the principle claims, I'll come back to it in a moment because
I think the most important thing is for you to understand what the guiding intuitions
are behind what I'm going to say.
There's a very particular idea that I have and this is what I'm trying to give clear
and precise philosophical expression to you.
And so if there's one idea that is carried all the way through and the one idea that
I want to make work, it's exactly this idea here and that's the following.
Causation is about the causal connectedness of things in the world.
Things are connected in the world, things do relate to one another and theories of causation
are trying to talk about that.
The basic idea is this, that is the business of empirical science, it is not the business
of an a priori metaphysics.
The idea that we can come in advance and legislate how things are going to connect in the world
is a bad idea, it's not going to work and that I claim is what has been happening in
the metaphysics of causation.
People are trying to legislate ahead of time, ahead of experience in an a priori manner
how things are going to connect up in the world.
And that's just a flat out mistake that hasn't worked and it will continue to fail to work
and I'm trying to get that idea out.
So if that idea does not seem unreasonable to you, you'll be comfortable with the rest
of what I have to say.
If that idea seems crazy, you'll never be happy.
So let me add in a few more.
So that's the negative guiding intuition, then there's a positive intuition.
The positive intuition looks something like this.
Causal talk is pervasive, it's everywhere, I use it myself and every time I do this amongst
my colleagues in Pittsburgh they all laugh and point, but I do it and I do it for a very
particular reason.
It's very comfortable for us to do it.
We like to go to a particular domain and in order to get our heads around what's happening
in that domain, we like to think in terms of cause and effect.
What's causing, what's affecting, what controls, what's being controlled.
Causal talk comes about, I say, because we are very plastic in the way that we use these
causal ideas.
We can go to any domain and always find a way to graph this causal talk on so we get
a comfortable picture in our heads.
So that's the positive claim I'm going to try to advance, I'll make that a little more
precise in a moment.
Those are the two parts.
I'm not denying the admissibility of causal talk, I have no trouble with causal talk as
long as you understand what it is that you're doing.
And then finally I have a complaint about the modern philosophical literature.
There's an enormous literature on causation, it's exploding at the moment and the activity
is the wrong activity if you are interested in how things connect in the world.
If you're interested in understanding deeply how things connect in the world, this is the
wrong thing to do.
Get a small group of philosophers together and start quizzing each other about what you
mean when you say does this cause that.
Now if you've seen this literature you know the one that I'm referring to.
You might ask your colleague, so I have a railroad track and the railroad track forks
and there's a big fat man tied down to the railroad track here and there are seven little
children playing over there and the railroad is coming down and you have to choose whether
you throw the switch or not.
If you don't throw the switch did you cause the fat man to die?
Now this type of interrogation of one another is simply an exercise in learning how a very
small group of people happen to use words.
And the very exercise messes up the entire operation.
It's not even a good way of writing dictionary definitions because the probe destroys the
thing that you're trying to probe.
So at best this literature is writing tainted dictionary definitions.
Okay, I've said enough now to get myself into trouble with at least some people in the room
and let's see where that goes.
Now let me go back and I'll give you the principle claims which are simply my attempt to make
those intuitions into more precise philosophy.
This will be the major part of the talk.
I'll be going through these three claims.
First there's a negative thesis, I need to target a viewpoint that I believe is incorrect
and this viewpoint I call causal fundamentalism and I'll be expressing that more clearly later
and I'm going to try and make trouble for that with a dilemma.
Then I'm going to advance the positive thesis that I've described here and I'll be using
something like the notion of reduction relations as they appear in philosophy of science in
order to explicate a little further how I think causal ideas come about in our discourse
in science.
And then finally I'll have a fairly long discussion of this, the term causal or the adjective
causal and others like it appear very commonly in physics and so one of the things you might
wonder is has not physics established that there is a fundamental causal order in the
world?
In a way that would violate my denial of causal fundamentalism and by working through some
examples I'll suggest to you no this is not the case, it hasn't.
Okay so that's where we're going here at the intuitions again.
Let's start with the negative thesis causal anti-fundamentalism.
This is the doctrine that I wish to criticise and I'll read it to you because the wording
is important and we will keep coming back to this I guarantee you at least once in question
time I'll say but remember the view I'm criticising, this is the view.
Nature is governed by cause and effect and the burden of individual sciences is to find
the particular expression of the general notion in the realm of their specialised subject
matter.
There is a universally applicable principle of causality.
Now this is a view that I think is widely accepted amongst causal metaphysicians that
that is the way the world is put together.
The world is fundamentally causal, this is a fact about the world and when the sciences
go out to do their investigations they're finding the particular expression of that
general idea in the individual sciences, that's the view that I want to criticise.
So causation is factually about the connectedness of things in the world and there is a unity
of meaning to causal talk in all the different places.
In cause and effect I talked about in biology or in physics or wherever it appears it's
the same idea, it's the same notion all the way through.
Now okay that is what I'm denying, I'm saying no this is wrong and the challenge comes in
the form of a dilemma.
Okay let's take a science and we are going to expect that science to conform to the idea
of cause and effect.
Does conforming to the idea of cause and effect place a factual restriction on what the science
can say or does it not?
You have to say yes or no, there's nothing in the middle there.
Does being causal make a factual difference, does it restrict you factually or does it
not?
And I'm going to say that if you're a causal fundamentalist either of these possibilities
is unappealing, either of them will get you into trouble.
So let's take the first horn.
Okay if the claim is that there is some factual restriction placed on the content of the science
then you have to find some assertion that will express that.
What is the factual restriction?
I mean it's nice to say there is a factual restriction but I want to know what is it?
And you know what's going to happen next, I'm going to give you a history of failed
attempts to do this.
If there's one lesson you can learn from the history none of them work.
They fail over and over and over again and there's I think no hope that it's ever going
to get any better, the history is coming.
What about the other?
What happens if you say it does not place a factual restriction on the science?
Well I think it's game over at this point for causal fundamentalism because then all
that you're doing is you're not changing anything by imposing a causal framework onto some science.
All you're doing is naming things, you're not changing.
There's no restriction to the factual content, it's simply a matter that every science
no matter what it might be, no matter what its content can be given causal labeling
because being causal places no factual restriction.
Now I rather like that, I actually think that's the correct thing that happens but it doesn't
look good for causal fundamentalism because one doesn't have this fundamental fact of
causal structure.
Okay, let's go through the first one.
Being causal places a factual restriction on the science.
What is it?
Well we've tried to find this for a very long time.
Let me give you a very short history of the trouble that we've gotten into.
As everyone knows in the 4th century BC Aristotle declared that there were four causes, the
material, formal, efficient and final cause.
They didn't fare so well.
In the 17th century there was a very strong movement that pushed to say no, three of them
are wrong and there's only one and that's the efficient cause.
In particular there's no place for final causes.
Now I won't say that's the final verdict on the matter but I will say there was a very
strong movement that wanted to overturn the ancient idea of four causes.
If it wasn't Aristotle can we look to other luminaries to tell us things that are just
incontrovertible factual statements about cause.
Let me give you one of my favorite examples.
This is Isaac Newton writing about action at a distance in the 17th century and this
is what he said about action at a distance.
It's so great an absurdity that no man who has in philosophical matters a competent faculty
of thinking can ever fall into it and in other places.
I think it's Clark at one point says that it's a contradiction that something should
act where it is not.
So this seemed to be an incontrovertible factual limitation about causation.
It has to be local.
It can't be at a distance but of course you know what happened in the centuries that followed.
Work on gravitation theory was unable to find any mechanism of propagation for gravitational
effects and in the 18th and 19th century de facto gravity became an action at a distance
to affect to the point that nowadays people who don't work in history of science don't
realize that Newton absolutely condemned the idea.
So let's move on.
In the 19th century there was a great deal more thought about the nature of causation
and the 19th century theorists, people like John Stuart Mill, affected a very great simplification
and purification of the notion of causation.
They purged it of all of the scholastic furniture that came with it.
There was no difference now between cause and effect, between agent and patient.
One didn't need the continued existence of a cause for the effect to be present.
All that mattered was the following.
Causation is determinism.
Causes simply guarantee their effects or in another place I think Laplace at one point
has the future, the present fixes the future and in that way it causes the future.
The effect of this in the 19th century was to equate causation with determinism.
The present fixes the future and that looked pretty good in the 19th century.
That was philosophically minded thinkers, a very great simplification of the idea of
causation and places a very definite factual limit on what there can be in our physical
science.
But of course you know what happened next, along comes quantum mechanics and all of that
goes away.
You might notice by the way that we now understand quantum theory as violating determinism but
in the 1920s when the physicists were complaining about the disaster that had happened they
talked about the violation of causality and the reason they were talking that way was
that they had the 19th century definition.
Okay so we can move on, things still work and I'll lump these two together.
So in the 20th century we've now recovered, we've now redefined what it is to be causal
to incorporate some kind of probabilistic notion of causation and I'll talk about this
one here.
And so now we've gotten used to the idea that causal processes are processes that a probability
raises.
That's still only useful as a means of labeling things, it doesn't work as a factual restriction
on the world because one of the lesser known facts about our physical theories is that
virtually all of them are indeterministic and they do not give probabilities for what
the future might be.
Virtually all of our physical theories, if you fix the present they will not fix the
future as well.
Curiously about one of the few cases of a physical theory that is deterministic is a
no collapse version of quantum mechanics.
One theory has lots of counter examples, general relativity is a real mess this way,
there are space times that don't have Cauchy surfaces if anyone does relativity.
You don't have determinism universally in physics.
So that's the basic idea, this is simply a continued history of failure, it doesn't seem
to be going anywhere.
When I look at the history, what I'm seeing are people learning new theories, learning
new ways that the world is connected, that things in the world are connected together
and then they're finding ways to graft causal talk onto that so they can keep talking about
it as though there are causes and effects and it's a very comfortable thing to do.
But there's no sense that there's a prior constraint that the fundamentalist wants that's
being implemented in these sciences as we move through.
So what about the second horn?
Well I've already really said what has to be said there.
If you accept the second horn so there's no factual restriction on a science from being
causal then any possible science no matter how odd can be conformed to causality.
Now I think that's what happens, I'm quite comfortable with that idea.
There are other approaches that you can use here and I mentioned, this isn't so far from
a Kantian view although I'm certainly not a Kantian, or Nagel said this is the principle
of causality, he says it is an analytic consequence of what is commonly meant by theoretical science.
It's a maxim for inquiry rather than a statement with definite empirical content.
And so you can figure out what you make of that.
It's not telling us about the world but about our definitions and our own psychology.
So now let me move on.
I've gotten the idea that I'm a skeptic about causation.
I find that when people hear I'm a skeptic about causation that triggers a program and
the program is Hume and they say oh he's a Humean, no I'm not a Humean, I'm probably
as far as you could possibly be from a Humean and I want to go through that briefly now.
This is Humean skepticism and this is my version of skepticism, yes that's really me too and
I think that's Hume, I don't know if the internet can be trusted but anyway.
So if you match up these two viewpoints you'll see the difference.
So Hume and the positivist tradition that he started is essentially anti-metaphysical.
Now I'm not so directly anti-metaphysical as I'm simply anti a priori.
Hume's tradition is epistemically pessimistic.
You never learn anything really other than what you experience directly.
It's very hard for a Humean or a positivist to believe that you know something that goes
beyond experience.
You have to really push hard to get them to admit they know a little bit more.
Maybe what about that missing shade of blue, do you know about that or not?
Whereas I'm epistemically very optimistic.
I think science has done a terrific job.
I think we know vast amounts of the way that the world is put together that goes beyond
our direct experience.
I'm an optimist when it comes to this.
Hume then has a definition of causation.
It is constant conjunction or the later positivist tradition, functional dependence on the facts.
Whereas I'm saying here that the causal theories I see are simply an attempt to preempt discovery.
Okay, now there's a viewpoint that many causal skeptics share in common.
I'm calling this a limitivism.
It's been stated very clearly by Russell.
He points out that you could eliminate all causal talk from science and the science would
still manage pretty well.
And Marx says the same thing.
Science of the future will discard the idea of cause and effect as being formally obscure.
Now I think causal skeptics share the idea that you can purge science of causal talk.
Personally, I think it would be an awkward and ill-advised thing to do, but it could
be done.
But that isn't the basis of the skepticism.
That's a consequence of the skepticism.
It's something that we share.
It doesn't mean we have the same viewpoint.
Okay, so that's the negative thesis.
So you're saying, well, what's left?
How can we still use causal talk in science without being philosophically unrespectable?
Well, here's the story that I want to tell.
I want to think in terms of an analogy, and I think it's about as close as I can get to
it.
Let's look at the relationship between general relativity and Newtonian theory.
According to general relativity, fundamentally, when you get down to it, there are no gravitational
forces in the world.
It's all space-time curvature of the space-time geometry.
There are no gravitational forces.
Fundamentally there's no such thing.
But one of the most important results of general relativity is that if you restrict yourself
to weak fields and non-cosmic scales and all the usual conditions that you need, then the
theory reverts into something in which gravitational effects look just like there are gravitational
forces.
So in these special limiting cases, you get the forces back.
Now, there are numerous examples of this sort of behavior.
I'll give you a second one.
General physics tells us that fundamentally there's no such thing as heat.
When you have something that's very hot, you simply have energy randomly distributed over
very many degrees of freedom of some system.
That's really what thermal systems are, the systems with energy distributed over very
many degrees of freedom.
But if you take certain very simple cases, and the sort of case I have in mind is the
following, cases where there's no conversion of heat into work, where heat is, for example,
only conducted along an iron bar, then the heat now becomes a conserved quantity and
takes on the properties of the caloric that Lavoisier and others wrote about a long time
ago.
So you see the pattern here.
You have a theory which fundamentally doesn't give you some entity, but when you restrict
it down to some narrow domain, then that domain looks as though there is that entity
there.
Right?
Gravitational forces, the heat as a fluid are two examples of that.
And the program is simply to say it's the same idea with cause.
When you take at the broadest level, there is no fundamental principle of causation.
But when you restrict down the sciences that you happen to be concerned with to a small
domain, those small domains will take on regularities that you will be able to label with causal
talk.
Now, why am I interested in narrowing things down to one domain?
Well, the key thing is that as you go to different domains, you'll get different little mini-theories
of causation, or as I'll call them, folk theories of causation.
There is no single theory that works across the board.
So let me give you an example of how that goes.
So this is how we can generate multiple theories of causation.
I'm just going to think of a greater science that is not fundamentally causal.
The science I have in mind is something mechanical with a few fluids and things in it.
And so here's one way that you might restrict things down.
You might restrict your mechanics to the ordinary Newtonian theory of bodies with finitely many
degrees of freedom.
You have to pick, as those of you who will come tomorrow, ordinary sorts of systems,
nothing too fancy.
And then you recover determinism.
The present state will fix the future, and you can call that fixing that determinism
causation.
Now, let's take a different example.
If you restrict yourself to dissipative systems, these are systems that have friction.
For example, you have a bowl and you throw a ball in and the ball starts to roll around
rattling and rubbing and gradually dissipating its energy so that you know that it will eventually
end up in the bottom of the bowl.
In dissipative systems, then you can say that the states of lowest energy function as final
causes because you know that's where the process is going.
And so the final cause talk now becomes, in my view, perfectly respectable, as long as
you realize that you're dealing with this restricted example of dissipative systems.
Well, let's take another example.
If you have a vacuous surrounded by fluids, it's a very, very common thing for people
to attribute causal powers to the vacuum.
People tell you that the vacuum will suck things in.
It will draw things in.
Now, of course, you know that literally the vacuum can't draw things in, a classical vacuum,
right?
Because it's nothing.
It's not a thing to do any drawing.
But I don't think there's any problem in talking that way as long as you understand what you're
doing.
You know, the classical vacuum does not have that sort of causal power, but you can talk
about it as though it does, and we all do, and not get into trouble, right?
So that gives you an idea of how I think positively that causal talk can be used in science, and
I'm quite comfortable if it's used this way as long as you realize what you're committing
to when you do that in a cave.
So I have a few remarks here on analogies to, and I'm just looking at my watch and thinking
that maybe I'll pass over this quickly.
It's in the papers that I've written elsewhere, and you can get this.
And also I ask the question here of whether causes are real or not, and I don't have a
very strongly worked out answer for this.
I don't like either extreme view, and I'll go through very quickly.
One extreme view you might have is that nothing is real unless it's part of the most fundamental
science that we have, and if you say that, then causes do not come out as real, but I
don't think anything else does either because we don't have the final science.
So if that's your condition of reality, and I ask you what's real, you can't point to
anything and tell me what it is.
You might go in the other direction and be a strong realist and say that every entity
of a functioning science should be construed literally and should be regarded as real.
Well, I think that goes too far in the other direction because in the end, heat is not
a conserved fluid, and you need to bear that in mind.
It just behaves as if it were a conserved fluid.
And so I try and find something in the middle here and say that causes have a kind of derivative
reality.
And the best I can really do is to say that causes are as real as gravitational forces
and caloric.
Everyone has their own particular take on realism.
Philosophers of science have been debating the realism, anti-realism issue for 30 years,
and wherever it is that you come down on that, just take that viewpoint, ask what you think
about gravitational forces and caloric, and then that's what I'd urge you to think about
causes, whatever that view is.
Okay, perhaps an analogy, just a lighter analogy, you get a sense of how I think it's working.
Here are three images of clouds, and you see the face there, and you see the ghost-like
figure here, and there's another face here somewhere which eventually pops out if you
keep staring at it.
Now, fundamentally, there are no figures here, there are no faces, there are no heads, but
we all see them, and once they're pointed out, they jump out at you fairly clearly.
So there's a kind of reality to this.
The thing that is the nose here really is a cloudy material that's sitting there, and
that's the sort of thing that's happening with causes as well.
Okay, well that ends just the straight analysis of the idea of causation as folk science,
and now I want to take up the next issue, and that is this.
How is it that someone who works in philosophy and history of physics as well could possibly
think all of that when you go to space-time theories and theories of quantum mechanics
and the word causal is all the way through?
Aren't these fundamentally causal theories in a sense that contradict what I'm saying?
So that's the challenge, and my claim is going to be no, there's no contradiction between
the causal anti-fundamentalism that I espouse and the way that causal talk appears in modern
physics.
So let me give you the basic claim here.
There are essentially two notions that once you see it, they pick up virtually all the
uses of the term cause in physics.
The first notion is this, it's the claim that there exists a finite invariant velocity in
space-time, the velocity of light.
This is a fundamental part of the structure of space-time, it has this preferred velocity.
Or in more geometrical language, it is the claim that space-time has a light-cone structure.
And then there's a second idea that the propagation of matter always happens within and on the
light-cone.
The slogan is there's no propagation outside the light-cone.
And my claim is that virtually all of the uses of the term causation as they appear
in fundamental physics are expressions of these two ideas.
Now these are simple empirical claims about the way the world is.
These are not a priori claims.
The world does not have to be this way.
And when we thought that the world was different, we didn't think the world was a-causal.
So if this is necessarily what it is to be properly causal, then we have a tremendous
embarrassment on our hands.
Newtonian theory, the theory that persisted from say the 17th to the end of the 19th century,
was regarded as the paradigm of a causally perfect theory, yet it was a theory that violated
all of this.
So if being causal requires this, then we made a humongous mistake when we thought that
Newtonian theory was causal.
So you'll see I'm just summarizing the argument in a nutshell for you.
So you'll see where I'm going with this.
Calling these facts causal is simply another exercise in naming.
We've gone to a theory.
It has a light-cone structure.
It requires material propagation to respect the light-cone structure.
It becomes very comfortable for us to call that causal structure for reasons that you
can understand.
Because if you fix the present, then the future will be fixed if you have a deterministic system
by propagations that will respect the light-cone structure.
So let me fill in a few of the details about how it is that these two ideas get expressed
in the science.
If you go to special relativity, you'll find that the adjective causally connectable just
means timelike or light-like connected, and then the adjective propagates all the way
through the structure of special relativity, and it always has that meaning.
Causal simply means timelike or light-like, and that's the use all the way through.
When you move to general relativity, you have a similar effect.
I worked through Hawking analysis, and I just pulled out.
It's quite easy to work through a book and pull out.
Every time the word causation appears, pull it out and see what's being defined.
These are the terms that are defined here.
The term local causality is defined on page 60, and it's simply the requirement that there
is no propagation of fields outside of the light-cone, and that's formulated as a standard
Cauchy problem for differential equations.
If you know general relativity, you've seen this 1,000 times, and I don't need to tell
you anymore.
If you've not seen it before, I'm not going to try.
There are global extensions of this idea, and these are the so-called causality conditions,
which I've listed three of them here.
Essentially what they're telling you is how it is that this light-cone structure is going
to be spread around a big space-type.
In general relativity, you start to get odd topologies.
Space times can wrap back onto themselves, and so you want to start to make restrictions
about how this light-cone structure is going to be disposed when you go through the larger
space-time, and that's what these conditions are doing.
Let's move over to quantum mechanics.
One of the big causality principles is the so-called locality principle, and I take the
definition of this here from Michael Redhead's wonderful little book on philosophy of quantum
mechanics.
The basic claim is that elements of reality pertaining to one system cannot be affected
by measurement performed at a distance on another system.
Then you read on, and you discover that for Bell locality, at a distance means in the
absence of causal influences recognized by current physical theory, so it actually doesn't
tell you what these things mean, because there's an empty slot there for a current physical
theory that has to be put in, and then finally, for Einstein locality, one particular thing
is slotted in.
At a distance means space-like separation, so we're back to where we started before.
The one case where locality is properly defined, it is defined again in terms of time-like
or light-like connection, and of course I should mention that the locality principle
here is not a principle of quantum mechanics, it's simply another principle that someone's
written down that they wish would be true, and of course the difficulty in quantum mechanics
is to see if it really is true or not, and people are obviously struggling with that.
Let's move on.
I went to the Weitman axioms for quantum field theory.
There are two of them that are called causal.
This one here is just called causality by itself, and that's the familiar requirement
from quantum field theory that field operators need to commute when their supports are space-like
separated, so it's again the same idea of space-like separation, no causal interaction.
Not being causal means space-like separated.
Then there's the time slice axiom, primitive causality, and when you finally figure out
what that one's about, it turns out to be just telling you that the quantum field operators
have to be propagated through space-time according to a well-behaved Cauchy problem, exactly
as we had for the locality condition that Hawking and Ellis had earlier on, or at least
that's the best that I can make of it.
I should mention briefly Reichenbach's common cause principle.
It's another causal principle that comes up.
It's not something, as I say here, that defines the nature of causation.
It's actually a rule for detecting causal connection without saying what it is.
It's a detection principle, and of course it's fallible because there's always a measure
zero or a small probability that it can say that there's a causal connection when there
isn't.
Okay, so let's move on.
So let me summarize this part, and then I have one more part that'll go for a while.
So I'm saying the causal talk that I've reviewed in modern physics does not conform to the
first horn.
It's not producing a universal factual principle of causality that we can expect to be applied
everywhere.
It's simply reporting the fact to us that our present physics employs a light cone structure
in the space time and requires that propagations have to respect that light cone structure.
It could not be a universal a priori principle because if you believe that, you would then
have to believe that Newtonian theory was never properly causal, even though everyone
thought it was the paradigm of perfect causation.
And then also you might wonder about what you're going to do with sciences that don't
talk about light cone structures.
What of geology, for example, how are causes in geology to be understood?
Really things moving at the speed of light are not an issue when you come there.
So what I think it does conform to is the second horn in which causal talk is an honorific.
What we've done is go to a theory, look at certain processes, and find it comfortable
and convenient to talk about it using causal language.
Why we find that comfortable is I think ultimately a matter of psychology.
I certainly find it comfortable.
I imagine you find it comfortable as well, but that's all we're doing.
I think at this point you have to be convinced.
In principle, I could stop the talk right here and we could just all go home.
There's really nothing more to say.
That would be terribly boring if that were the case.
So I have to thank my colleague, Matthias Frisch, who insists there is more to say.
He's come up with this rather wonderful example that he believes is a fatal counter example
to everything that I've told you.
So I want to work through the example and explain to you why I think he's wrong.
I think it's an ingenious example.
I think it's terrific that he found it.
It's unfortunate that it's wrong, but you'll see.
The process that he's discussed is the process of scattering from a dielectric.
Let me just briefly indicate what scattering looks like.
Here we have a total field.
This is an electromagnetic wave and the wave is propagating from left to right.
It's moving in this direction.
About here is a dielectric that will scatter the wave when it comes in, perhaps a few little
charges sitting there.
The wave will come through and here's the wave coming through.
It hits the little charges here.
These are the secondary waves that have been excited by the incident wave.
When you put this together with the incident wave, you get something that looks like this.
This is the phenomenon of scattering.
The wave passes through and you're left with secondary radiation propagating outwards.
You can see what the claim's going to be.
This incoming wave causes that.
We're going to get more interested in how that comes about.
There is a basic theory of scattering.
This is simply drawn directly from an introductory textbook in classical electrodynamics.
The basic rule is the following.
You pick some position.
You just pick some position in the field here, x, and you want to know at any particular
time what is the intensity of the field at that point.
The answer is you use a particular formula to add up the field intensities at other times.
This is the formula.
It's a very simple linear formula.
The intensity of the scattered field at the position x at time t is given as an integration
over the incident field at the same position but at different times.
Then you wait by this Green's function here which then tells you which contributions to
take from which different times.
It's called Lin because this is a linear relationship that we have here.
The important fact about scattering is that the scattered field at some time can only
have contributions coming from earlier times.
The scattered field doesn't know about what's going to happen later.
You have an asymmetry in time and this is the no influence from future rule which tells
you that the Green's function is equal to zero whenever s.
This is in the time slot of the function whenever s is less than zero.
This says when you are summing to produce your scattered field, forget about the future
only add up components from the past and put them in to get the final result.
The issue is going to be this.
How do we arrive at that?
How do we arrive at that condition?
That's a condition that's asymmetric in time.
What Matthias did was to go to the ... There he is.
He tells me that is the correct spelling.
What he's done is to go to Jackson which is a standard widely used electrodynamics text.
Note that in Jackson the origin of that particular principle, no influence from the future, is
attributed directly to causal ideas.
So this is now quoting Jackson, not Matthias, that's a typo, is in accord with our fundamental
idea of causality in physical phenomena.
He says that put the two together, the most general spatially local linear and causal
relation that can be written down between the scattered field and the incoming in a
uniform isotropic medium.
Its validity transcends any specific model of the dielectric.
You get the idea.
Jackson's not the only one.
When you look around in the literature, you'll find this no influence from the future principle
being justified by an appeal to causation.
So of course Matthias loves this.
He says, see, they're using a principle of causation after all.
So he knows what's coming next.
So he has to state what that principle is.
And here's the principle.
He postulates as an additional constraint on all causally possible models, and this
is it, an effect cannot temporally precede its cause, an effect cannot temporally precede
its cause.
So there's no causation, no causal processes going into the past.
That's the principle.
You're probably already thinking, well, we need to hear a little bit more about how this
works, but it's not going to get better.
It's going to get worse.
You can already see that there's a problem here because he's going to allow that this
principle doesn't apply everywhere.
It only holds sometimes.
But he's going to say he thinks that that is OK.
So what do I think about this?
Well, it's not at all clear to me when you go and read what Jackson does, and you look
at the other accounts, that they are using an independent principle of causation.
The way the text actually works is the following.
What Jackson does is to look at the simplest possible case.
And it's been a while since I've looked at it, so I don't recall exactly what that case
was.
But you can imagine it was something like an incoming plane wave with a single charge
sitting there being held by a harmonic oscillator.
And then he sets up and solves that case.
He does not use anything resembling a principle of causation anywhere in that.
In order to get the excitement in the outward propagating scattered wave, he uses a standard
boundary condition.
That is, the little charge there of the dielectric is at rest up until the time when the incoming
wave arrives.
So it's all secured through a boundary condition.
So in this one simple case, everything works out.
Everything works out.
Well, the wave comes in.
There's the dielectric sitting there not doing anything minding its own business.
The wave excites it.
It starts oscillating.
As a result, it produces secondary radiation.
The scattering effect happens.
All of this gets calculated.
It's a bit of a slog to go through the calculation.
It's a fairly messy calculation.
Lots of approximations are being used, and then eventually the result comes out at the
end.
But it's still the simplest possible case.
What do you do with the other cases?
Well, if you've calculated that one case, you're pretty sure it's going to go the same
way if you could calculate the harder cases.
What if there are many charges and they're maybe not held by harmonic oscillators, but
slightly anharmonic oscillators, and just keep adding in complications of all sorts
of forms?
Once you've seen the way the simple calculation goes, you kind of know what's going to happen
in the complicated case.
You just want to say, look, it's always going to look like that.
You're going to have this quiescent system.
The wave's going to come in.
It's going to get excited.
The waves, secondary waves will be scattered.
You'll have the scattering things.
The formulas are going to be different, but the basic process is going to go that way.
That's what Jackson should have said, but I can understand that that's an awkward thing
to say.
He says, wait a minute, if it went any other way, this would violate causality.
Now, of course, he's a physicist, and so he's completely innocent of the long history of
people trying to make sense of the notion of causation in philosophical circles.
He thinks, and I would not wish to disabuse him of this, he thinks that we philosophers
have got all this figured out, and all he has to do is say, the principle of causation
is going to make all of this work.
Don't ask me to say anything more, because, well, that's philosophers, they've done all
that stuff.
Well, I want to tell you he's wrong.
He would have been better if he just said, by analogy, you can kind of see that it's
very likely to go the same way if he hadn't called up this other realm of causation, because
what I'm going to try and do is see what's involved in making it work, and when you try
to make it work, things get worse, they don't get better.
So it's not clear, I say here, that Jackson does use an independent principle of causality,
and I don't think he could have used an independent principle of causality.
Now let's start looking at the sorts of problems that we face.
That's the principle that Matthias has given us, and effect cannot temporarily precede
its cause.
That's the principle.
But now he says that this may only hold sometimes.
He doesn't think it holds universally.
Well, so now you've got a very serious problem.
When does it hold, and when does it not hold?
And Matthias has not given us any guidelines for saying when it holds.
The simplest thing is to say that it holds only for scattering phenomena.
Well, but now you've reduced the whole thing to a circularity, because your principle of
causality simply is the assertion that you wanted to get out of it.
So that's no good.
But if you want to say the principle applies more broadly but not universally, well then
you have to tell me where's the fence?
Where does it stop working?
Matthias has certainly not done that.
So if you want to say it's broader, I think we've ended up with the principle that in
effect holds except when it doesn't.
And that isn't much of a principle.
Let me keep going.
There are further problems.
This principle of causality, in effect, has to pick out forward direction in time.
And that's awkward, because electrodynamics is time reversible.
And to give you a sense of that, here's the idea.
If you have any system that goes in a forward direction, there's a correspondingly Lisset
model in electrodynamics that goes in the reverse direction.
So here's the forward scattering.
You've got the same incoming wave it passes through.
And you see here, this is just the scattered wave.
The scattered wave is propagating outwards, as you expect.
If that is an admissible system in Maxwell's electrodynamics, then the time reverse of
that system is also an admissible system in Maxwell's electrodynamics, equally admissible.
And here you can see you've got the scattered wave collapsing down onto a point.
And it's then sending energy into the incident wave that is now moving in this direction.
Now, of course, I've stuck the label forward and reverse on the top there, but there's
nothing in either of these systems other than convention that makes one the forward
and one the reverse.
I could have just switched the labels around if I want.
Now, if you think that you can look into this and find some property, some characteristic
of it that tells you absolutely this is the forward process, there's a complete isomorphism
between these two systems.
Any property that this has has a correlate over here.
So this isn't going to work.
And moreover, I'd suggest you wouldn't want it to work.
You wouldn't want to say that this is an illegitimate process, that this going forward in time is
illegitimate.
And here's why you wouldn't want it to work.
This process has been assembled from many small pieces.
Just look at a very, very tiny little piece of that wave as it's collapsing down.
That just looks to arbitrarily good approximation, like a plane wave moving, because it's a very
very tiny piece of a much bigger piece.
The way electrodynamics works, it's the basic idea is that you assemble the allowed systems
from many, many smaller allowed pieces.
And any system that you can assemble from many smaller allowed pieces is then going
to be an allowed system.
So in effect, you have to say that there's going to be some grander selection principle
that will let you pick between, which is the correct forward process and which is the
correct reverse process.
Now in this particular case here, you've got a kind of idea.
You can say, oh, everything's collapsing down to a point, so that can't be right.
But there are going to be much messier processes where you won't have this obvious rule to
guide you.
And I don't know what the rule is that you're going to work on.
Now let me keep going.
The principle says that an effect cannot temporarily precede its cause.
Now there are a lot of words there, and we have to get precise correlates for that.
You have physics.
Physics deals with fields and particles and waves and things like that.
And then you have a sentence that uses the term cause and the sentence that uses the
term effect.
Somehow these two terms have to be mapped onto things in the physics.
And I don't see exactly how that's being done, exactly what state is going to count
as the effect and which is going to count as the cause.
You have to go to the process and say, oh, this one's a cause, this one's an effect.
How do you know when you have processes that are interacting with one another, which one
you attach the label cause to, which one you attach the label effect to?
Well, the simple thing to do is to pick the earlier one as the cause and the later one
as the effect, but now all you've done is to render the entire principle a definition
because that's all the principle says.
An effect cannot temporarily precede its cause.
So if by definition the earlier of the two Rolata is the cause, you've just made the
thing true by definition.
But if not that, how are you going to single out which is the cause and which is the effect?
How do you know independently what they are?
You need to provide this or you don't have a rule that can be used.
And then what in the theory is going to count as a cause and effect?
Are we looking at states over time?
We're looking at localized states?
Are we looking at states at an instant on some hypersurface?
If so, which hypersurface?
As you know, in special relativity, picking out the hypersurfaces is not so straightforward.
I don't want to say that these questions are unanswerable.
I do want to say they are unanswered.
We need answers for them.
And then finally, what sorts of processes are going to count as properly causal?
We've talked about processes being causal and knowing when we have a causal process
and that's as it were built into the principle.
But how do you identify principles that look like that?
So what, for example, if we happen to give a Lagrangian formulation of our mechanics?
And as you know with the Lagrangian formulation, you take histories through time in their entirety
and then you optimize the Lagrange function in order to figure out which is the time development
that has been allowed by your theory.
Now this doesn't look like earlier states causing later states, that later states are
independent of earlier states because in that Lagrange type formulation, if you mess
around with things in the future, that's going to affect the particular history that you
pick out.
So are we saying that there is a proper and correct way to formulate these theories or
not?
Okay, so I think there are lots of issues here to be dealt with and let me go through
the principle claims once again.
Positive thesis is the denial of causal fundamentalism which asserts that the world is governed by
a principle of cause and effect, of causality.
The basic argument comes down to this.
We simply haven't been able to identify what the fact is that being causal places on what
the factual restriction is that being causal places on physical theories.
The positive thesis is that whenever you do take a science that is not fundamentally
causal, restrict it down to some domain, it proves quite easy for us to graft causal talk
onto it and the type of regularities that arise in association with that talk, I'm calling
it the folk theory of causation, I'm perfectly happy with you doing that, it doesn't bother
me at all as long as you remember what you're doing.
It's an honorific labeling that's at work here.
And then finally I've suggested that causal anti-fundamentalism, the skeptical view that
I hold, is compatible with the way that causal talk is used in modern physics.
Okay, so you can read all about it.
I've got a rather rich website which has lots of stuff on it.
And for this particular lecture series there's a section on it.
Let me see if we go back here.
If you click on this thing that says lectures, you'll get to it.
Or if you go to the website that looks like this with that picture, you can also link
to it from there.
And there are a few of the papers that I've talked about that can be downloaded from there.
So one of them, the first paper I wrote, Causation as Folk Science, was reprinted in an Australian
volume.
And since I'm also Australian, you can understand that this was the way the proof pages came
back to me.
So the next one you might want to look at is the paper on causal anti-fundamentalism
in physics.
This is the paper in which I talk about Matthias Frisch.
By the way, Matthias and I got on very well and what we did was we wrote two papers together.
We could see that a big debate was coming and so I sat down with him and I said, look,
we don't need to debate this at great length.
And so we both wrote our parts and we exchanged them backwards and forwards and backwards
and forwards and backwards and forwards until we converged.
And then we sent them off as a hold to the journal.
So this is my end of it.
You can find his end back to back in the paper.
And then finally, I need to make a short commercial.
As some of you may know, my colleagues in Pittsburgh are not infallible.
And one of the less wise things they did a number of years ago was to make me director
of the Center for Philosophy of Science.
So now, wherever I go, I try and entice people to come and visit me in Pittsburgh.
And to make it easier to visit, we have all sorts of wonderful programs.
So you can come and be a visiting fellow and we give you all sorts of good stuff.
You get an office, you get a bit of money, you get a computer, and it's a great office
on just in the best part of the university.
We have a post-doctoral fellowship program as well, which pays real money.
And most recently, we've just started a new thing, a one-off.
We're looking for someone who does philosophy of risk.
And we're looking for someone who will do that for next year.
And we're looking for someone in a mid-level academic.
And we have a nice, healthy stipend.
Okay, enough commercials, thank you.