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Sometimes when I run into people
from outside physics at least or
maybe -- or closely associated
sciences and people ask me what is
it that I do, I often get a very
sort of uncomprehending response. I
mean, they've heard of physics.
They've heard of particle physics,
and they think of it as going to
smaller and smaller things and
figuring out what the world is made
of at that level. And when I say
that I work in condensed matter
physics, I get sort of puzzlement.
On one notable occasion someone
thought that I was saying condensed
metaphysics. Which is pretty as -
Well, every once in a while you're
guilty of that. This is true. But
then I try and explain to them that
there's sort of a problem in
physics, which is instead of
starting, as it were, from laws
than you know at some level and
working your way back to the
universe that we see around us,
matter and life and issues like
that, they sound often slightly
surprised that something like that
is in fact a problem with physics
or in science generally. I don't
know if you've had that experience
in your field. Yeah, I have it all
the time. And usually I just face
it out and say I'm a condensed
matter physicist and leave it at
that. I have occasionally -- I even
have a lecture that I've given
every once in a while, saying what
in hell is a condensed matter
physicist. I think there are kind
of two responses actually. A lot of
lay people, and by lay people, I
mean people outside of physics, not
maybe not outside of science, a lot
of lay people, don't have any
concept of how complete an
intellectual structure physics is.
Of course, there are a lot of
people who have the other view. I
mean, why is it a problem? But I
think it's more common that people
don't recognize how much we really
know, how deeply we understand the
world on the level of everyday
objects. One way- It's interesting
since this is an understanding
that's almost, one might say
roughly a century old. Yes, yes. I
was going to say that it's a
strictly a 20th century phenomenon,
it's perhaps worthwhile to look
back on it from the point of view
of the end of the century because
if you look back in the 1890s,
you'll find that- find it very hard
to think yourself back to that time
when at the same time physicists
were pronouncing that they really
knew everything there was to know,
there were people, it was supposed
to be Lord Calvin but I don't think
it actually was, there were
physicists who said, there's
nothing for it but to look for more
decimal places. And they were so
wrong. They hadn't -- it was --
they were -- they were in a
complete blank as to the fact that
there was a problem. They hadn't
seen the existence of this problem.
I mean, what they saw as physics
was they took matter as a given.
They took, for instance, a planet.
They said, well, there's the
planet. How is it going to move?
And you used Newton's laws and you
derived that it goes around the sun
in an elliptical orbit. And that's
a great success and what more is
there to do? Or they studied the
laws of hydrodynamics, of water.
They studied -they had that
perfectly good description of how
water flows, invented by some 19th
century physicist named George
Stokes and said very much
elaborated by the great
hydrodynamicists of the end of the
century. But they had not the
slightest but very little idea of
where the numbers that went into
that equation came from and what
they represented. And then
suddenly, in the 1890s, they were
brought up short by something like
a number of phenomena that they'd
discovered. The big ones were
X-rays, radioactivity and cathode
rays. The discovery of the
electron. And the spectroline
theories. Yeah, and -- well, they'd
had spectrolines for many, many
years and they'd thought well,
spectrolines were another of these
things they'd catalogued, and they
had them measured to enormous
accuracy, but they just didn't
think that was their business and
they weren't really studying that.
Then suddenly they were brought up
short by these new phenomena and
they realized that there was whole
level of understanding and a level
of explanation that consisted of
questions they'd never asked
themselves. Do atoms -- in the
first place, they had the concept
of atoms, but they'd never thought
of an atom as something that they
could really understand. And they
certainly had never thought we
should look inside the atom and
find more and more, to find tinier
and tinier sub-particles to the
atom. And all of this became the
subject of physics rather than -and
a set of problems that they had
realized were there, they knew the
whole subject suddenly changed into
a new subject which was how do
atoms work? What do atoms really
do? And that is the great triumph
of the quantum theory. With the
quantum theory, we're able to
really look at the properties of,
well, not just ordinary matter, of
course, extraordinary matter. We
understand how the sun burns, how
the interiors of the stars work. We
understand how the interiors of the
elementary particles work, to a
great extent. But the really
enormous achievement that took
place beginning in the 1920s is
that you can hardly imagine, or
hardly know of, a piece of ordinary
matter, an ordinary system
consisting of the ordinary everyday
objects around us. That we don't
have quite a deep understanding of.
Right. Sort of interesting in some
ways that, as always with a great
moment, sort of change in physics,
that it was a combination of
advances and experimental
techniques. And, as you were
saying, although spectrolines were
known, but still, this conjunction
of discoveries of the electron by
Thompson and then the nucleus by
Rutherford, suddenly posed the
problem in a way that was not
possible to pose before you really
understood what you might mean by
an atom. And once you had posed the
problem in terms of, let's say, a
planetary solar system like a model
of the atom, it became rapidly
clear that the classical mechanical
account of it couldn't possibly be
correct. Such an atom would not be
stable. And in fact, once you pose
the problem that way, then it's
clear that even the stability of
the matter, the fact that anything
exists at all instead of collapsing
onto itself, is something that
requires ideas that the quantum
theory is then able to provide --
the notion of having particles with
Ferme Statistics; things that can't
be in the same place at the same
time, roughly speaking. So it's
again, although since we're both
theoretical physicists, it's
natural for us to look at it sort
of from the perspective of theory,
but I think the advances in
experimental technique that made it
possible probably played a crucial
role, as they often do such as the
discovery of the telescope and the
move away from classical mechanics.
Yes. That's an -- or remarkably
true. That's the way physics works
and you can understand -we will be
talking, I think, in the course of
this conversation, we'll be talking
about why it is that we so often
need experiment to stimulate theory
and theory to guide experiment.
There are a couple of, well, there
are in fact two aspects to this
problem. In the first place, of
course, we have this wonderful
success story. Beginning in 1925,
and certainly not before 1925, we
were able to understand the
properties of first of atoms and
then of molecules and then of solid
matter and now we're even beginning
to deal sensibly with polymers and
glass and liquids and all that. So
we've had a remarkable success
story, but if the story were
nothing but that, then the two of
us would be out of a job. We'd just
be redundant. And there's even a --
an eminent journalist of science,
named John Horgan who claims that
we are out of a job, that we've
reached the end of science. So
there are other questions that are
-- That would put science
journalists out of a job, too.
(laughter). Yeah, it -- yeah, it
would put science journalists out
of a job. Fortunately, there's a
gentleman I would be glad to see
out of a job. But there are also
deep problems. There are things
that we don't, haven't completely
solved, even within condensed
matter physics. And they keep
cropping up. The notorious example
and everyone's favorite example, is
the phenomenon of
superconductivity. We had this
marvelous experience of discovering
the quantum theory, which, within
five years, we had the basic
explanation of why ordinary metals
exist and why other substances
aren't metals and insulate, but
there was one class of metal that
was a complete mystery and had been
a mystery since it was discovered
in 1911. And that was the
superconductors. It was discovered
by Kamerlingh Onnes that lead and
mercury were superconductors. They
conducted electricity -- Without --
-- without showing any resistance
at all. And if you make a ring of
lead, you can start a current
flowing in that ring and it will
continue to circulate --
Essentially forever. -- for, I
calculated once the age of the
universe, if you keep the lead
cold. Of course, then Kamerlingh
Onnes measured gold and he claimed
that that was superconducting too,
but he corrected himself -- I see.
-- in 1912, so he didn't stay
permanently wrong. But it wasn't
until 1957 that we had even the
hint of a theory, theoretical
explanation for this. So that took
46 years after the discovery and
something like over 30 years
between the discovery of the
fundamental equations that explain
it and the understanding of the
phenomenon. But that wasn't the end
of the story. In 1987, a kind of
superconductor was discovered, the
so-called high DC superconductor
and awarded a Nobel Prize in
remarkably short time of 1988. And
those we still don't understand.
Those we find are in the center of
a tremendous congeries of
controversies, questions, puzzles,
puzzlements and so on. Maybe if I
can -- So there are still problems.
Yes. If I can synthesize some of
the things you've been saying. So
one thing that you sort didn't say
is probably worth repeating that
modern chemistry and modern
molecular biology were simply
inconceivable as subjects before
the discovery of the quantum
theory. So in -- what you were
saying about not being able to
understand the world around us,
it's completely changed the way we
look at vast areas of our life and
most importantly ourselves. Yes, I
guess I was jumping ahead. I think
that's what you're trying point out
and you're right. And I was jumping
ahead because I didn't explain how
much we knew before I explained how
much we don't -- We don't know. And
that was -has been a remarkable
achievement. But what's interesting
is again this notion that it was
impossible, and Schrˆdinger, one of
the founders of the quantum theory,
unsurprisingly was perhaps the
first person to guess that once you
had this understanding of atoms and
molecules, that it was very natural
to look for the basis of heredity,
which had been indirectly guessed
by the tradition of genetics and
following Mendel. Have you ever
read the book? I had it sort of
summarized, I haven't actually read
it. Actually, what is surprising
about it is that he had it the
other way around? He did? He
personally felt that probably there
was something in life that couldn't
be explained by simple chemistry. I
see. He was asking "What is life?"
And his answer was, well, so far we
can't explain it. I mean, it was
very influential because it asked
the question. But he gave the wrong
answer. I see. It was my
understanding that he at least
suggested -- Well, he presented the
two possibilities. Possibilities. I
see. But he certainly did not
decide between them. Because just
recently, we had a talk by an
eminent biologist who pages quoting
from Schrˆdinger and essentially
held him as one of the founders of
modern electron -- Well, he was in
that sense that he asked the
question. Asked the right
questions. And he didn't. Well, I'm
not sure whether he didn't. Well,
he certainly finessed the question,
he did not actually settle it
finally one way or another. But
coming back to your second thing
just to sort of try and put it
together, so, as you were saying,
so there's an enormous amount that
we came to understand about the
nature of the everyday level, the
macroscopic level and starting with
this understanding of atoms and
molecules due to the quantum
theory. But, as you were saying the
output -- We understand how
chemistry works and not just that
there is chemistry. And we
understand in very great detail how
chemistry works and how the
fundamental empirical rules of
chemistry that had to have been
discovered before the quantum
theory all follow -- So, having
said all of this, we then want to
turn around and say, nevertheless,
problems remain. Yes. And, as you
were saying, the example of
superconductivity, that it took so
long for a phenomenon to be
understood. So that is due to what
after all, we know the fundamental
equations, I might as you sort of
naively, and we knew then back in
the 1920s, and so why is it that it
took us so long to figure out how
the traditional superconductors
worked? What is the obstruction?
The obstruction -- well, it's
something that -- and biologists
invented the word for, it's
emergence, and another, well, the
kind of phenomenon that occurs in
superconductivity is something that
I would classify as an emergent
phenomenon, but it's a specific
kind of an emergent phenomenon
called broken symmetry. Emergence,
perhaps, I don't know whether it's
come up in other discussions in
this series, but emergence is a
terribly important concept. An
emergent phenomenon is one
which occurs in a - a system of
individual parts, simpler parts,
but only when you put the different
parts together is it even possible
to conceive of the existence of the
conceptual structure of the new
phenomenon. The original, the first
example where this word was used
was by the 19th century biologists
about Darwinian evolution, they
said modern life is an emergent
phenomenon from primitive life. And
then if you're brave enough, you
say, well, primitive life is an
emergent phenomenon from the laws
of physics and chemistry. So it's
-- In the case of
superconductivity, you would say
that a single atom of lead can in
no sense be superconducting. Yeah,
you can't, I mean, you can't even
conceive of the possibility --
Conceive. right. -- of an atom of
lead or you can conceive of the
possibility of an atom of lead
being metal, and lead becomes metal
only when you put all the atoms
together. Together. But, in
addition, it has a - having -take
lead, put a lot of atoms together, you
have either molten lead or ordinary
metallic lead. And these are
both metals, different kinds of
metals. Then you lower the
temperature still further and you
get down to about six -- is it six
or -- eight degrees, I believe, in
the case of lead. Eight degrees
Kelvin. Eight degrees above the
absolute zero. And it suddenly
stops showing any resistance to the
flow of electricity. But more
important, it does what we call
breaking symmetry. The state of the
lead below this transition
temperature has a new kind of
asymmetry, if you like, any of it,
a different symmetry from the state
of the lead above this phase
transition. This symmetry is of a
sort that really we hadn't
conceived before we first - before
superconductivity was first
explained. It was something that
was just inconceivable. As a matter
of fact, there were mathematical
theorems that had been derived -- I
see. -- that proved that that
theorem, that symmetry couldn't
exist. It was proved right here in
Princeton, didn't you know? No, I
didn't. And there it was called,
not supersymmetry, superselection
rule. The superselection rule says
there can be no coherence between
states -- With a different particle
-- -- with a different particle
number. I see. And that is why,
and, as a matter of fact, Eugene
Vigner, opposed the theory of
superconductivity for the rest of
his life. This is well before my
time, I didn't realize it.
(laughter). It was well before your
time. And he was wrong. But he
firmly believed in his
superselection rules, which were
violated by the theory of
superconductivity. This phenomenon
of broken symmetry -- well, perhaps
then the example of
superconductivity is too esoteric
and outside of people's common
experience. But there
are other examples of broken
symmetry which are very simple.
Right. The magnetism would be --
Magnetism would be one. -- would be
one of the examples. If you look at
iron, there's a sense in which each
individual electron has a magnetic
moment, a little magnet attached to
it, if you will. And had high
temperatures, the electrons don't
really agree among themselves, and
which their little moments should
point, but there comes a
temperature Curie point below which
they suddenly decide to agree over
macroscopic scales over the size of
a piece of iron. And that's when
the iron goes magnetic and then is
able to stick to our refrigerators.
And so this distinction that, as
you're saying, so the symmetry is
broken in the sense that in the
high temperature phase of iron is
essentially, if you look over some
suitably average period, you find
locally no signs of magnetism.
But the moment you go below the
temperature, you do, and the iron
does that presumably for reasons of
energetics or, more technically,
free energetics in which it decides
to give up on some of this global
symmetric freedom in order to
achieve a more -- And there's some
very important properties that the
iron acquires that are consequences
of this broken symmetry. It
acquires a certain rigidity. I
mean, the reason for the magnetism
is that it requires a certain
rigidity. It costs energy. It
twists the magnetization in one
part relative to another, the
magnetization in another part. So
it has stiffness. It has another
phenomenon. It can transmit waves.
It has waves of magnetization that
pass through it called spin waves.
And these are very fundamental to
the phenomenon of broken symmetry.
And so this phenomenon of broken
symmetry is not just the
observation that there is a
different symmetry, which is an
important observation, but it's the
observation that there are a
cluster of properties which it
implies. In superconductivity,
there is something like this
rigidity and it is the rigidity of
this new symmetry, which causes the
perfect conduction. It's kind of a
stiffness or an elasticity of the
electric fluid in the same sense
that there's a stiffness of a steel
bar, or the stiffness of
magnetization of a steel bar. But
this tends to -- well, perhaps, we
should move on from there to this
idea of the hierarchical nature of
metal -- Right. But I was going to
say, it leads naturally to sort of
two things that are worth perhaps
discussing. One is that -- so we've
sort of crystallized the notion
that what makes condensed matter
physics, let's say, a discipline is
the fact that there are these
properties that emerge when we go
from the microscopic to the
macroscopic. And since these are
qualitatively new properties,
emergent properties, as you said --
in order to learn about them by
studying three atoms or four atoms,
you have to study an incredibly
large number of atoms and know what
to look for. So that naturally sort
of leads to two questions. And
that's why we call it condensed
matter physics, as a matter of fact
because it isn't interesting if it
isn't condensed, if it isn't a lot
of atoms. Right. So that leads to
sort of two things. One is it leads
to question of: well, if it's not
something that you're able to get
by simply taking a large number of
atoms and let's say putting their
equations and motion on the
computer and solving for them, then
how is it that condensed matter
physicists ever figured out
emergent properties? What is the
nature of an explanation in our
field? And the second sort of thing
it leads to is that, which is also
related, which is: why are these
properties comprehensible at all?
And so maybe if I could start on
the second one, I think an
important insight that has come and
perhaps was formalized in the work
of Kenneth Wilson, who got the
Nobel Prize for that, is what we
call in technical language, the
normalization group idea, which is
sort of an unfortunate name since
it can raise almost nothing even to
people inside the field. Yes. But
it's the idea that physics is
organized by scales. So if I look
at short distances, which in some
sense are also high energies,
there's some physics appropriate to
that level because I work my way
up. So let's say there might be
physics appropriate to the quarks
inside a nucleus, it was my
colleagues, the other levels, are
interested in studying in terms of
quantum chromodynamics or theories
of that kind, work your way to sort
of nuclear level, and then to the
atomic level. And, essentially, if
you've gone far enough in scale
that only some of the details that
were known at one scale are truly
important as input parameters into
the physics of the other scale, but
in the process not everything is
relevant and properties emerged. So
that physics separates by scale,
which of course is responsible for
two things -- one, the richness of
phenomena. It's not just - the
universe is not a giant atom. And
also in some sense makes it
comprehensible, because you're able
to organize physics by scale, and
you can sort of leave some details
aside and start. Somehow nature has
been enormously complex and every
scale was linked to every other
scale, perhaps we wouldn't exist to
be able to ask these questions in
the first place. But the thing that
perhaps you might address, I think,
since you've thought about these
questions yourself, is how this
question of explanation of
condensed matter physics, how one
understands a phenomenon and in
particular the importance of what
people call model building. Well,
as you were implying, the worst way
to go about it is to pile one atom
on top of the next one, on top of
the next one and then just compute.
Very seldom can you ever arrive at
any -- any useful conclusion. One
of the important insights about
that process is one is always
finding in the discussions of
philosophers, not in the
discussions of condensed matter
physicists, I must say, the idea of
the perfect computer, and you have
a perfect computer and you have
Newton's laws or -- as we now know,
Newton's laws won't do, you have
quantum mechanics. So if you have
quantum mechanics, you can just
compute the behavior of all these
atoms and eventually arrive at the
answer. There are two things with
that - wrong with that. One is you
can't do it but even in principle,
it's not right because even if you
succeeded, all you would be able to
do is to say, okay, this piece of
lead is superconducting. And I
calculate that it has all the
properties that I already know
exist and they earned their
superconductivity. In some sense,
you have to find an explanation
that explains something to you,
that somehow simplifies it. So we
have this problem of what is the
nature of an explanation. And I
don't think we always know exactly,
but one of the best ways of
arriving at an explanation is the
process of abstraction, to take
from this detailed structure,
details, all the details of how you
have put all the atoms together, to
take from this the important pieces
and abstract some kind of model
which may be much easier to solve,
that exhibits the phenomenon you're
looking for but doesn't show a lot
of side issues. One example of this
kind of abstraction is the simplest
one, the one with which condensed
matter physics began, which used to
be called solid state physics. Any
real piece of lead or iron or
whatever has to be, to some extent,
impure. It will be full of defects
of various kinds. It won't have an
exactly regular crystal lattice, so
a very simple abstraction is to
say, well, let's imagine that it
really is a perfect lattice, then
what are its properties? And that
turns out to be -- at least, in
some degree, a problem that we can
solve a lot more easily than we can
this complicated imperfect system.
Once we've solved the perfect
system, we can say what are the
properties of this perfect system?
One example of a property is that
it turns out that electrons can
move as freely through a perfect
lattice as they can move through a
vacuum. And so we now want to know
what do the impurities do to these
electrons. We can make an
abstraction, we can say forget
about the perfect part of the
lattice, let's just drop that out
and pretend that we have electrons
flowing through a vacuum and that
these electrons are scattering on
the imperfections in the lattice or
they encounter imperfections of one
kind or another and that causes
resistivity and various other
properties, or if we're worrying
about how light is propagated in
this lattice, we can ask how is
light scattered by the
imperfections in the lattice
without bothering too much about
the properties of the background.
So we abstract- first, we make the
abstraction of the perfect lattice,
then we discover that's so simple
that we can just drop it out and
pretend that it's really a vacuum.
And again and again and again in
condensed matter physics, that was
one of the earliest techniques
invented in the -actually, as late
as the 1940s by Landau, we make
this equivalent vacuum and then we
study how things move within that,
forgetting about the absolutely
regular structure and asking now,
what are the things which are
wiggly inside this regular
structure? Quasi-particle motion.
Yeah, quasi-particle approximation
of an elementary excitation
approximation. That was really
invented by the great Russian
physicist Landau. Just as a
footnote, actually, it strikes me
that one of the great and parallel
insights in modern economics also
seems to have been the study of
relatively simple models in which
the abstracts, and of course they
have much more sort of stricter
system to study, the actual economy
that keeps changing on them. But
much of the post war progress in
economics seems to have come from a
sort of similar meta-insight about
how to proceed. I could differ.
(laughter) I think there also has
been a great tendency for
economists to be guilty of
physics-envy and to make
oversimplified models which then
don't really -- Don't really --
well, there's more at stake when
they go wrong. Yes, yes, well not
only is more at stake, but there is
a tendency, for instance, for them
to try to make models that behave
like statistic mechanics where all
the actors are the same in
statistic mechanics. In our
physics, every atom is the same as
every other atom in some deep
sense. In economics, every actor is
not the same as every other actor.
And there's a very wide
distribution of sizes of actors.
And up until recently, they totally
neglected this, or many of their
models totally neglect this. That's
reality. Sure, but going back to
what you were saying -- They'll fix
it with some help from physicists.
Well, perhaps. That'll keep us
employed for a while to come. Yes.
I wanted to bring up something
which is related to this issue of
the complexity of trying to solve
for new properties of macroscopic,
let's say assemblies of atoms,
which is -- it is, of course, true
that many of our colleagues have
made really an enormous amount of
progress with the help of modern
computers in calculating many of
the properties of real materials.
For example, the properties of iron
at zero temperature, if you wanted
to have some sense of how the size
of a magnetic moment is, is
something that they're able to do
using modern computers plus some
amount of analytic sophistication.
Yes -- -- to be fairly -- -- and if
you had asked me 30 years ago, I
would have been very pessimistic
about reaching the level of --
Right. Precision that we have. --
sophistication that they've reached
now. So that's impressive
achievement that I think really
deserves its due, and undoubtedly
as computers get more and more
powerful, they will undoubtedly get
better and better at it. But it's
also an interesting way to
illustrate some of the limitations
of looking for emergent properties
by the sort of brute force
approach. You mentioned the example
of the magnet and the Curie point
where the magnet is in first
release sets in. And there's this
sort of remarkable universality
associated with the behavior near
this point. In fact, that's what
Mr. Wilson got his prize for. And
the remarkable thing that came out
of that understanding was that the
self-organization of the electronic
spins near this Curie point where
magnetism first sets in is
mathematically identical to the
self-organization of molecules in a
liquid and gas near what's called
the liquid-gas critical point,
where the difference between a
liquid and a gas just about
disappears. These are two
completely different systems that
would require completely different
microscopic technologies, and I bet
no one, starting with borrowed
computers, that two of them would
ever discover -- That's right. Of
course. -- the contributing factor.
And this illustrates another thing
which is the power of abstracting a
model from the -- From the details.
-- from the details, and saying
actually what I have to solve in
order to get this very complicated
behavior is a model doesn't contain
either the magnets or the atoms in
any real detail. But we also should
say something about the role of
experiment. Which is -- well -- for
instance, in the case of
superconductivity, I am sure that
no one would ever have invented a
theory of superconductivity if he
hadn't had the experiment sort of
facing him down and forcing him to
find an explanation for this
phenomenon. The experiment, well,
in a field that you've played with
or worked with, experiment has
played a very important role also.
Oh, that's right. No, I mean, I
think you're referring to the
quantum particle for which our
colleague Dan Tsui got the Nobel
Prize this year, and I think it's
fair to say that although there
were mild, extremely mild
intimations, that something special
might happen for a set of electrons
in two dimensions placed in a
magnetic field. Before the
experimental discovery of the
phenomenon, no one had a clue that
anything like that was possible,
this thing called the Quantum Hall
Effect. And it's remarkable
phenomenon in many ways. I mean,
physics is remarkable. You take a
set of 2D electrons, two
dimensional electrons, you put them
in a magnetic field, which kind of
is perpendicular to the plane that
we live in, and they have an
incredibly intricate sense of set
of phases that they're able to
organize themselves into sort of
collective dancing patterns, as one
of our colleagues, Sargon Wen
calls them. And it's remarkable.
You change the magnetic field a
little bit and the collective
pattern changes completely. You
find organizations nested within
organizations, hierarchical
organizations in which the
electrons first organized
themselves, then make small
defects, and the defects organize
themselves. I mean, it's an
incredibly rich structure that you
could never have guessed. But the
field is also remarkable for
several other reasons. Another
purely physical reason, which I
think was perhaps heavily
influenced the Nobel committee in
their decision, was the fact that
when you think of adding an
electron to such a system, it
actually doesn't go in as an
electron in some sense, and in
another sense, it breaks into, for
example, three pieces. For example,
the sort of rich behavior that you
can get in a macroscopic system
that again, at the level of an
electron and an electron isn't
going to split into three, but the
level of 10 to the 12 electrons, it
does indeed. I think something else
that's remarkable about the field
is its sort of connection to
technology. You were there at Bell
Labs in the good old days when
modern condensed matter physics was
launched -- the study of
semi-conductors which has had this
sort of enormous impact on our
lives through semi-conductor
technology. The Hall Effect is an
example of a field which, in fact,
the flow goes the other way.
Advances in technology have made it
possible to fabricate an
experimental system that we'd be
hard put to make otherwise. That
happened again and again, as it was
a kind of a relay race, if you
like. Many of, or several of Bell
Labs, early in Nobel Prizes, were
actually a consequence in a real
sense, a consequence of the
technology that was developed --
well, when you started with a
quantum theory, from the quantum
theory eventually arose the
semi-conductor industry. But from
the semi-conductor industry arose
very exciting developments in the
quantum theory. Not just the one
that you're talking about, the
Quantum Hall Effect, but even my
own private Nobel Prize was I was
stimulated by the very beautiful
measurements of a physicist named
George Faire on semi-conductor
samples that we were
investigating because they were the
semi-conductors, silicon and
germanium, that we were trying to
make transistors out of. So they
have samples he was using were
available only because we had
developed the technology of dealing
with these samples. So even that
one was technology-driven as well
as science-driven. And it's
fascinating. Well, like what you
were talking about, the Quantum
Hall Effect, that you can find
areas in which the range of
relevance goes all the way from
direct hard rock technology, if
want to call it that, transistors,
computers, materials, fuzzy
materials, sticky materials and so
on, to these serious questions of
how do you interpret, how do you
understand how something happens or
how you understand the
fractionalization of the electron
in your Quantum Hall sample -- The
joke I sometimes like to make is
that our field goes all the way
from material science to immaterial
science. Immaterial science.
(laughter). But there is one other
thing, that in addition, we learn
things about the tools we're using.
We learn things about the Quantum
Field Theory. And so what you learn
about the Quantum Hall Effect can
be relevant, is probably relevant,
and is certainly using the same
mathematics as our friends who are
trying to understand the elementary
particles by means of String
Theory, topology, terms
and so on and so on. So
essentially by trying to build a
better transistor, you can learn
how strings work. Also by learning
how strings work -- You've seen the
universe in a transistor. Yes, you
can see the universe in a
transistor. Well, actually I was
thinking of that Vilesov, the
Russian physicist named Vilesov who
has written -- recently written a
paper called "Seeing the Universe
in a Drop of Helium Stream." The
strange thing about it is he's not
above himself; he really can see
many of the things that happen in
the universe, happening in this
droplet of one of the simplest
liquids that we know of. Right. So
this might be a good point to sort
of look ahead a little bit, which
is that we've talked about sort of
this development really across the
science, but from the perspective
of our own field, starting with the
quantum theory discussion, the
discovery of the microscopic
structure kind of working, so
there's of course being those set
of our colleagues who've gone the
other way, who've gone to smaller
and smaller scales, so that's why
the fascinating enterprise for
their discoveries. Or -- or
disappeared back into the first
microsecond of time also. Right.
But of course it does have these
unexpected connections, as you were
alluding, through helium 3 to the
large-scale structure of space-time
itself and of the universe. In
fact, they're looking both at the
very small and the very big. But
for ourselves, in our neck of the
woods, you've been involved at the
Santa Fe Institute in setting up
and so on. So there's a certain
vision of where studies of our kind
would naturally lead to, namely
higher and higher levels of
complexity, perhaps with the
ultimate end, in some sense, of
understanding life itself as the
ultimate complex behavior. Do you
think that - how do you see the
sort of tools and tricks of
condensed matter physics and its
body of insights sort of
dovetailing into this project?
Well, they already do in a number
of ways. When they think what one
likes of Herr Bach [phonetic], I
think he's made the case that there
are aspects of these
renormalization group methods, and
aspects of the study of phase
transitions and things like that,
that can be generalized to very
complex systems. He studies
traffic, clothes. He studies
extinctions of species. He studies
all kinds of things on the basis of
what many of us feel is this
considerably oversimplified model
that comes from condensed matter
physics. There's a big movement in
evolutionary theory in biology that
is studying evolution as what they
call motion or optimization on a
rugged landscape. The first rugged
landscape was in condensed matter
physics. That's the energy of a
so-called spin glass -- Spin glass,
right. --- as a function of the
orientations of the spins. So how
does this work in evolutionary
biology? You simply postulate that
the fitness landscape is a rugged
landscape. And it explains a great
many of the general rules - general
ideas in evolutionary biology. How
well it explains them and whether
it is any more than a metaphor is
still a question under discussion.
But at the American Physical
Society in Atlanta, to which
neither of us went -- -- Went,
unfortunately. -- there was a
session on rugged landscapes in
biophysics. And that's a serious -
well, there are certain areas where
it is well-established that this
approach, this condensed matter
approach makes a great deal of
sense; other areas where it's still
under contention. But there are
ideas that we develop that
certainly have application in
broader fields. An example, a good
example is computer science. The
question of complex optimization
has had a very strong interaction
with spin glass physics again. I
don't know how far this can be
taken but certainly the
intellectual structure is
transferable. The intellectual
structure of starting or thinking
of a simple substrate, thinking of
emergent things that the simple
objects in the substrate can do
together, making a new level of the
hierarchy, for instance. Start with
physics of atoms, the atoms make
molecules. That's simple. But then
the molecules can get together and
make the secret of life, the
heredity and the proteins, the
complex set of catalysts that life
is based upon. And the complex
network of proteins turning on
genes turning on proteins turning
genes -- this complex network that
life is based upon. Then life
develops nervous systems or it
develops morphology and we begin to
understand that. But then when we
get to the nervous system, which is
perhaps the next stage beyond
morphology, that's where the
frontier is at the moment. And, of
course, once you have organisms
that can think, more or less.
Right. Once you have intelligent
life on earth -- On earth. If you
say we have intelligent life on
earth, then we have sociology and
we have the organization of more
and more complex states and so on.
So you can see the hierarchy
working all through the different
areas of science, and you'll also
see this unifying thread which
Edward Wilson has called
consilience, which is the
requirement that at each stage in
the hierarchy, you have to look
downward and see whether and what
you think about the stage where
you're at is consistent with the
laws that you know are true at the
smaller, at the lower stage, and so
on. Right. I think he makes the
point in that book, which is clear
to most practicing science but is
probably worth, even for us, for
him to say it in the detail in
which he has that we really are at
the risk again of some hyper-belief
stage where, I think we're about to
start understanding ourselves at a
level of detail that's really going
to be quite staggering, this sort
of marriage of microbiology and
perhaps ideas from computer science
and, as you said, from physics
about complex systems and their --
Of course, I'm always a pessimist
about these things. I'm usually
wrong. I was wrong, for instance,
about morphology, about the
remarkable progress that's been
made in the past ten years and
learning how bodies are organized.
I thought that was one of the
insoluble problems that was going
to have to wait for the 21st
century. Right. I think there are
just two rules in this regard. One,
it often takes longer than you
think, and second, it often happens
sooner than you than you think. Of
course. And perhaps we'll come back
fairly soon and -- Well, the
trouble with the future is, of
course, or the trouble with
prediction is that it's very easy
so long as you aren't trying to
predict the future. So maybe on
that note -- Okay. -- we'll call it
quits for today. 
