Transcriber: Alexis Young Reviewer: Amanda Zhu
So there are lots of things frowned upon in Huxley’s Brave New World.
Two of them are thinking about fundamentals and having fun.
So let’s put one finger up to that
by talking about some fundamentals and having a bit of fun,
at least at the end of this talk.
So that’s my title:
Scientific Revolutions and the Truth about the Universe.
“The” scientific revolution of the 16th and 17th centuries
ushered in the age of enlightenment,
also sometimes called the age of reasoning,
starting the revolution,
starting with Copernicus at the bottom there
and culminating in the work and discoveries of Isaac Newton.
It ushered in that age of enlightenment
by seeming to show that human reason
was capable of discovering the truth about the universe.
We didn't need religion.
We didn’t need authority.
We didn’t need tradition.
Mankind,
through exercising its power of reason,
a fine scientific method could discover the truth about the universe.
And Newton’s theory, in particular, seems surely to be true,
And this was certainly what was widely taken to be the case.
There’s a famous couplet by Alexander Pope the poet,
“Nature, and Nature’s laws lay hid in night.
God said, Let Newton be! and all was light.”
Why was it thought to be true?
Why was Newton's theory thought to be true?
Well, basically, because of its amazing predictive successes.
It told us things
about that we could observe indeed to be the case
that we never suspected would be the case -
most spectacularly, the prediction of a new planet,
the existence of either two unsuspected planet,
its existence and its orbit.
And people, having noted that prediction from Newton’s theory,
then went and looked, and there is the planet,
and it was christened Neptune.
And there’s a sort of argument
that sometimes called in philosophy “no miracles argument,”
that a theory surely must be true
If it makes amazingly unlikely predictions that turn out to be correct.
It would be a miracle
if Newton’s theory saying something about the unobservable universe
turned out to predict the existence of Neptune correctly if it wasn’t true.
Well, that's all fine.
Just a bit of terminology:
So the philosophical claim that our best scientific theories are true
is usually called “scientific realism.”
And realism undoubtedly ruled the roost
so long as there was just “the” scientific revolution.
But of course, in the early 20th century,
along came this guy, wonderful looking guy,
Albert Einstein,
with his special and general theories of relativity.
Relativity has its own stunning empirical successes.
In addition to predicting everything that Newton did,
the most famous one
is bending of the light rays by the gravitational action of the sun,
which again turned out to be right.
And so, again, the no miracles argument applies.
Einstein’s theories must be true if it can make these predictions.
But it entails that Newton's theory,
which we’d already decided was true on the basis of its empirical success,
is false,
and false in certain seemingly, at least, fundamental ways.
In Newton’s theory, gravitational attraction is a ...
is an action-at-a-distance force - there’s no time evolved.
Gravity doesn’t spread out all the time.
In Einstein’s theory, action at a distance is explicitly banned.
In Newton’s theory, two events are either simultaneous or they’re not,
time is absolute,
and so either two events happened at the same time
or they don’t.
Whereas in relativity theory,
two events could be simultaneous
for one set of observers in one frame of reference
but occur at different times,
objectively, not a mistake.
It’s objectively the case
that for observers moving at high velocity relative to the first set of observers,
they will see those two events as not simultaneous.
[Infinite vs finite but unbounded universe]
Well, let’s just leave those two
because we don’t want to offend all the time.
So now we’ve got a bit of confusion.
What’s true now?
And this confusion was expressed by John Collings Squire,
who added to Pope’s famous couplet.
So remember: “Nature, and nature’s law lay hid in night.
God said, Let Newton be! and all was light.”
To which Squires added, after Einstein,
“It did not last, for Devil howling,
’Ho, let Einstein be!′ restored the status quo.”
So what's true?
Well, certainly not Newton,
because Newton’s theory is contradicted by Einstein
and Einstein’s theories are even better theory than Newton’s.
Einstein’s theory, well, maybe.
But why shouldn’t there be another revolution
coming somewhere down the pike that replaces Einstein’s theory
in just the same way that Einstein’s theory replaced Newton’s.
So it looks like we can’t say any theory is true.
So, the pessimistic induction that people talk about in philosophy of science
says, indeed, we can’t.
It’s likely, on inductive grounds, that it will be -
For any scientific theory currently accepted,
no matter how predictably powerful,
it’s likely that it will be replaced by another theory that contradicts it
sometime in the future.
So the problem is, can we have the best of both worlds?
That is, can we respect the no miracles intuition
while accepting that they have indeed been scientific revolutions -
changes of fundamental theory.
Well, I could talk about the Einstein-Newton case,
but it’s quite complex.
So let’s take an equally revolutionary but more manageable example,
and this concerns this guy,
a French physicist called Augustin-Jean Fresnel,
operating in the early 19th century.
Fresnel’s theory was that light consists of waves -
Fresnel’s theory of light was that it consists of waves,
transmitted through an elastic solid medium.
So luminous sources, like the Sun, set up certain vibrations atomically,
And these vibrations get carried through a medium that infuses everything -
it’s in the Sun, it’s in the empty space -
and it’s vibrations in that medium that constitute the light,
and eventually, those vibrations get picked up by light sensitive structures,
such as our retinas.
And Fresnel’s theory has amazing predictive successes.
The most famous of which is the “Poisson’s spot.”
The theory, it turns out to predict, much to Fresnel’s own amazement actually -
he didn’t know it -
that if you hold an opaque disk, a small opaque disk,
let’s say a five-pence coin,
in the light diverging from a point source
and look at its shadow,
you’d think on commonsense grounds,
geometrical optics,
there’ll be a solid shadow created by the opaque disk.
In fact, if you look at the shadow properly and carefully,
there’s a white spot right at its center,
and in fact, at the center of that, what should be a shadow,
it’s illuminated just as strongly when the opaque disk is in the light
as when there’s no opaque disk there.
And that turns out to be correct.
If we look at the one on the right,
that is the picture of the Poisson’s spot.
And so again, we’ve got an argument
that Fresnel’s theoretical claims must be correct,
how otherwise could they have turned out
to entail such surprising and, of course, correct results?
Again, no miracles argument applies.
But now, Newton had to wait two centuries
for his theory to be contradicted by a still better one.
It happened within two decades for Fresnel’s theory.
Because along came this guy,
James Clerk Maxwell,
Maxwell’s theory is that light consists of vibrations all right,
just like Fresnel’s,
but vibrations not in an elastic solid medium -
there’s no such thing on Maxwell’s theory -
but rather vibrations in an electromagnetic field.
The field is sui generis.
It’s just a fact about the universe,
that at every point in space,
there are always well-defined values of electric and magnetic field vectors,
and these vibrate in certain ways
when they vibrate with a certain frequency that’s visible light.
So Maxwell’s theory tells that Fresnel’s theory
was quite wrong about what waves to produce optical effects.
So again, what’s true?
Surely, not Fresnel,
because it’s contradicted by Maxwell’s theory,
which is even better on predictive success.
Maxwell, well, you have to sort of suppose
that there might be a revolution later than the Newton-Einsteins case.
But here, we do have further revolutions in light theory,
principally the photon theory developed by Einstein
in the early 20th century again.
So we know that Maxwell’s theory is not true either.
So, that poses this dilemma that I’ve addressed in various papers:
We’re pulled two ways regarding our current theories,
best theories, in science.
On the one hand, they are massively predictively successful.
And so we get this no miracles intuition.
It means surely that there’s something right about them.
On the other hand,
we surely have to admit that these theories may be just as wrong
as Fresnel’s theory turned out to be,
in the light of facts about this, about theory change in science.
Well, the answer to sort of resolving that dilemma
is to think a little bit more about how wrong exactly that is.
And there’s a crucial fact,
namely, that Fresnel’s mathematical equations
are retained within Maxwell and subsequent theories.
So let me just give briefly an example -
partial reflection.
You pass a beam of light to an interface between air and glass.
It gets reflected.
Some of it is reflected.
Some of it is reflected into the medium.
These equations -
Let’s not worry about what they say,
about what the r’s and the i’s and the x’s mean for the minute.
Those equations completely characterize that process,
and they’re derived from Fresnel’s theory
and they’re derived equally from Maxwell’s theory.
So the equations are completely intact.
So, the idea of structural realism,
hinted at by Poincaré and developed by this bald guy -
I’m not quite sure what his name is -
(Chuckles)
says that Fresnel was right ...
Points were that Fresnel was right about structure.
The light effects do indeed depend on something that vibrates
at right angles to the direction of transmission.
He was just wrong about what it is that vibrates.
And his equations correctly describe how that vibration occurs
and is modified as the light goes from medium to medium
or is subject to various interventions,
just, quote, unquote, wrong about what it is that vibrates.
So there’s something
that vibrates at right angles to the direction of propagation
that accounts for the optical effect.
So there’s no miracle that Fresnel got this,
because he was right about that,
no miracle that he got these phenomena right.
On the other hand, he got it wrong about what was doing the, uh ...
what was doing the vibrating.
But “we can be realistic about structure” is what structural realism says
even if we can’t be realists about metaphysics, about the content.
OK, so structure is retained across scientific revolutions.
Correctness of structure explains the predictive success,
So the success is no miracle.
Structural realism,
which says that we can be realist about mathematical structure,
that we really have captured that our best theories do really capture
even though they might get replaced later on by other theories.
We know that they’ll turn out to be structurally correct
even though we suppose that they’ll be structurally correct
in the light of those later theories.
OK, “Solves our dilemma
and hence constitutes the best of both worlds.”
OK, well, lots more to be said, obviously, but I’ve already said a lot.
And you deserve a recapitulation.
But rather than just do a po-faced recapitulation,
let me do it via a song that I wrote.
This is the fun.
I hope it’s fun.
(Music)
(Singing) I woke up this morning,
science’s success on my mind.
I woke up this morning,
science’s success on my mind.
If you don’t believe in miracles, you’ve got to be a realist of some kind.
But in the middle of the night, the pessimistic induction got me!
Yeah, in the middle of the night, the pessimistic induction got me!
It seems a realist can’t handle theory change in history.
So I tossed and I turned till I thought my mind would rupture.
Yeah, I tossed and I turned till I thought my mind would rupture.
And then I heard the word, and the word was “structure.”
I say, Think of Fresnel.
Think of Maxwell.
Oh, my theory fits them so well.
You see, the equations are completely preserved.
So come on and give structural realism a whirl.
Metaphysics, it comes and it goes.
Yeah, metaphysics, it comes and it goes.
But the content in the structure,
the structure, it just grows and grows.
So if you want to have the very best of both worlds,
Yeah, if you want to have the very best of both worlds,
come on and give structural realism a whirl.
Come on and give structural realism a whirl.
Come on and give structural realism
a whirl.
Yeah!
(Applause)
(Speaker) Yeah, so performed by the Philosophy Department here in LSE,
its one and only rock and roll band, The Critique of Pure Rhythm,
and involved these guys here, some of which are still around.
Some of you may have been taught by Roman Frigg,
who’s the drummer on that.
Uh, this ... I think it’s ... uh, good, it doesn’t start again.
This is ... uh ... We can’t have been playing Structural Realism,
because you can see I’m not having fun.
(Laughter)
And Structural Realism is very straightforward,
Structural Realism Blues is very ...
You can’t get that wrong.
This face is
“What the hell is the next chord change?”
And this song that looks as -
I’m having fun underneath,
but it doesn’t look like that.
Anyway, thank you very much.
Thanks for listening to the song. (Cheers) (Applause)