Good afternoon. I'm Paul Gray, and
it's my pleasure to welcome you to this, the
seventh and final Ford/MIT Nobel Laureate Lecture. On behalf of the
Institute, I would like to express our gratitude
to the Ford Motor Corporation for its sponsorship of this
program over the last five years. Frank Wilczek received
the Nobel Prize in Physics in October 2004, and I
quote from the citation, "For the discovery
of asymptotic freedom and the theory of the strong
interaction," end quote. Professor Wilczek, who is
the Herman Feshbach Professor of Physics, came to MIT five
years ago in 2000, following appointments at UCSB-- University California,
Santa Barbara-- at Princeton, and at the
Institute for Advanced Study. He received his
bachelor's degree from the University of
Chicago, and his PhD from Princeton University. And I should note that the work
that is principally recognized by the Nobel committee
in this award was work that Professor Wilczek
while a graduate student at Princeton. No one would ever accuse the
Swedish Academy of Sciences of rushing to judgment. Professor Wilczek is one
of the world's most eminent theoretical physicists. He has received numerous
honors, fellowships, and prizes. And he is, beyond all that,
a very distinguished science writer. Before I ask him to come
up, let me remind you that there will be a
reception in the lobby of the auditorium following
the end of this presentation. Professor Wilczek
will take questions at the end of his presentation. I had the opportunity
last Friday to hear Professor Wilczek when
he addressed the Institute's governing board, and I know
that you're in for a treat as he speaks today on The
Universe is a Strange Place. Please join me in welcoming
Professor Wilczek. [APPLAUSE] All right. The universe is
stranger than I thought So my theme today is the
universe is a strange place. And I'd like to
start by justifying that with reference to
the part of the universe we do understand. And so we can be sure
it's a strange place. By describing the theory of
our part of the universe-- that is, the part that consists
of us among other things, the material we're made
out of, the material in our immediate environment,
the stuff that chemists and biologists deal with. Then we'll get onto the
really strange stuff later in the lecture. So the picture
that modern physics provides of ordinary matter
is strange in many ways. In quantum mechanics, atoms
appear as musical instruments. Not in a metaphorical way,
but in a very precise way. When Bohr introduced his
model of the hydrogen atom based on quantized
planetary orbits, the primary formula
of that model, the Bohr model of the
atom, was a formula for the frequencies
of light that's emitted in terms of
various physical constants and pure whole numbers-- these 1/n1 squared
minus 1/n2 squareds. So it was an appearance of
formulas for frequencies very reminiscent
of the formulas you would get for determining
the frequencies that musical
instruments can emit. But here it's the
frequencies of light. And because of that, when
Einstein learned of this model, and of some of its
successes, he called it, "The highest form of musicality
in the sphere of thought." Ironically, quantum mechanics
later became much more musical and Einstein didn't accept it. Let me show you in a way that's
more eloquent than equations. You can ignore this
thing streaming by. [LAUGHTER] This is a wonderful piece of
software by Dean Dauger called Atom in a Box that in real
time computes the wave function of the hydrogen
atom, of electrons circling a nucleus in a hydrogen
atom, and allows you to see how the patterns--
the stable wave patterns of electrons-- change as you
emit different kinds of light. You can also look at
more elaborate wave patterns by superposing. It's a wonderful program,
and you really ought to look into it and even pay
for it if you're-- [LAUGHS] it allows you
to play microcosmic God, spin the atom around. And the point is,
for those of you who's seen things
like Chladni patterns or sprinkled filings on a
drum and watch it be hit, these are the kinds
of things you see. These are wave patterns. In fact, the equations
of musical instruments are exactly the
equations one encounters in describing what happens
inside hydrogen atoms, according to the quantum theory,
the modern quantum theory. So that's the
physics of the 1920s. As things have developed
through the 20th century, we've succeeded in understanding
much more about matter. Not only about the structure
of the outer parts of atoms, the electron wave patterns
around the central nucleus, but also what the nuclei
themselves are made out of. And so we have a pretty complete
picture of ordinary matter. And according to
this picture, which has been rigorously
tested in many ways, matter is made from
electrons and photons-- or really fields named
the electron field and the photon field
that create and destroy photons and electrons. The photon field is also called
the electromagnetic field. And as we saw, it's really
fields in the description of electrons. The electrons are not to
be thought of as particles, but as spread out
objects, as wave patterns. And then you learn
in high school-- or even maybe in
grammar school-- that the other fact
about ordinary matter, the other constituent
of ordinary matter, the atomic nuclei is made
out of protons and neutrons. And that represents the physics
of the 1930s, when Chadwick discovered the neutron in
the early 1930s, in 1932, and people thought that that
was an elementary particle, as was a proton, and
you could build up the description of
matter by getting an accurate picture
of how protons and neutrons interacted. But when they looked
into it in more detail, they found that protons
and neutrons were actually very complicated objects. It was very hard to read
the message they described. Then thanks to work
by Jerry Friedman, among others, and
theoretical work by Murray Gell-Mann
and others, it became clear that there were
simpler objects inside protons and neutrons, inside what
are called nucleons that are quarks, and there
had to be something else to hold the quarks together. But that was
unclear what it was. And it was my fate-- sorry-- to figure out
that besides the quarks, there was something very
precise that we can describe-- gluons-- that make up the
protons and neutrons-- and nothing else. That's a complete description. And furthermore, it will
become important later to know that the theory
of electrons and photons is very, very much parallel
to the theory of quarks and gluons. The theory of quarks and
gluons is a more elaborate, mathematically complex version,
but a recognizable version of electrodynamics called
the nonabelian gauge theory, where the quarks play a
similar role to electrons and the gluons are a
generalization of the photons. How do we know
something like that? How do we come up with
a proof that those are the constituents of matter? And that's what I'd
like to describe in the next few minutes. This is a tremendously beautiful
picture, also due largely to MIT's physicist. I give a different version
of this talk elsewhere. This is a picture of
an event taking place at the CERN
accelerator near Geneva at the so-called Large
Electron-Positron Collider. This red stuff is all equipment. This is the beam pipe,
these are different magnets and detectors. The physical part are these
tracks of particles emerging. And what you're seeing here
are a quark, an antiquark, and a gluon. What's done at this
accelerator is, over and over again, electrons and positrons
are collided with one another. And what comes out is studied. It's a very profound point,
although not often remarked in this context that
the fact that you don't get the same thing coming out
every time even though you put the same thing in is a direct
manifestation of the quantum behavior of quantum mechanics. That there's a probability of
different things happening. You don't get a determinant
result from the same input. And one thing that
happens fairly frequently is that you get bunches
of particles coming out like this, so-called jets. Most often when you get jets,
you get two jets in equal and-- in two opposite directions
180 degrees apart. We interpret that as a
quark and an antiquark. When you get three
jets like this, we interpret it as a
quark, an antiquark. And a gluon. What does that mean interpreted? I mean, they're not particles. They're not single particles. They're these
conglomerates of particles. What gives us the right to make
that interpretation, much less think of it as evidence for the
idea that matter it is made out of quarks and gluons? And that's really where
asymptotic freedom comes in. Asymptotic freedom
is the property of our theory of quarks and
gluons, a very difficult property to property
to realize consistently in quantum mechanics
and special relativity. That in our particular theory of
how quarks and gluons interact with each other, radiation
events that significantly change the overall flow
of energy and momentum at high energy are very rare,
whereas radiation events that don't change the overall
flow of energy and momentum are quite common. That immediately gives
you the interpretation that what we're seeing here
is a single rare radiation event where the quark
and antiquark receding from the initial evolution,
initial annihilation event, emit a gluon that significantly
perturbs the overall flow of energy and momentum. But then all the
other radiation events are of the common variety that
produce particles, produce radiation of quarks, and
antiquarks, and gluons, but don't change
the overall flow. So the initial
direction and the amount of energy in these
different jets is set by the underlying
quarks and gluons and the hard radiation events. But then they get dressed up
by the common soft radiation events. So you don't see the single
particles-- literally-- but only as jets. However, if you do a
soft focus, and instead of following the
particles individually, just sum up all the energy
and momentum in these things-- in these jets-- then they should
have the predictable properties of individual quarks and gluons. And we have the precise
theory that describes that basic interaction. And that enables you to then-- comparing with the experiment,
comparing the probability of having two jets versus
three jets versus four jets, the different
angles at which they might emerge with different
relative energies, with different-- and how all that
changes is a function of the energy of the
initial annihilation, allows you to test in
great and rigorous detail the basic assumptions
of the theory and make sure that it's correct. So we can be pretty sure
that what we're viewing here is a quark, an
antiquark, and a gluon. We can't tell which is
which because that's obscured by the
dressing process that goes from the individual
particles to the jets. But if anyone tells you
that you can't see quarks, you can tell them that it's a
lie, that you do see quarks, and antiquarks, and gluons,
quite literally, just not as individual particles,
only as the imprint of energy and momentum in jets. So that's a little strange. But enables us to be sure that-- or that we have a
fruitful theory that's actually predicting
results of experiments and can be falsified--
could have been falsified. But in fact, by comparing
results of measurements at this experiment
and others like it, what you find is that
you can fit them all done at different energies-- here, this indicates
the overall energy-- different energies,
that the basic principle of asymptotic freedom that
enables the whole machine to run. That is, that radiation events
that take a lot of energy are rare, and so correspond
to a small coupling, small value of this coupling. So high energy radiation events
are rare whereas the radiation events that only involve
small changes in the flow, small transfers of
energy and momentum, we say are quite common. . So that's a gift
from heaven which enables us both to see
the basic interactions and to understand
why they were obscure before at lower energies,
why things get complicated. So that, I think, is
to the educated eye, a convincing demonstration that
there are quarks and gluons. And that they
interact in the way that this elegant
mathematical theory predicts. But it leaves a question
both of intellectual closure and of credibility or
the need for clarity. That is, we're claiming
that the things that make protons and neutrons, and you
and me, an ordinary matter, things that have mass, are these
strictly massless gluons that are like photons and quarks
that are almost massless, that have masses much, much
smaller than the protons and neutrons themselves. And we're claiming
that's all there is-- or at least, that's the
simplest form of the theory. How can we convince ourselves
of something like that? How can we rise to the
challenge of computing not only what happens at high energies,
but how these soft radiation events, these low-energy
radiation events, orchestrate themselves
into the particles, including protons and neutrons,
and you and me, that we see? How is it possible to
construct heavy objects out of objects that
don't weigh anything? And the answer to that challenge
comes from Einstein second law. Einstein's first law,
Einstein's famous law is E equals mc squared. Before telling you what
Einstein's second law is, I'd like to relate a story. During the Second
World War, the Army had to train a lot
of radio engineers rapidly from people
who didn't necessarily know much about radio
engineering or even basic electricity. And it's a job that they
managed to do very, very well and successfully. And we can look at the
textbooks they used at the time as models of teaching. And in the Army's
training manual for electrical engineers,
in the first chapter, you will find a description
of Ohm's three laws. Ohm's first law is V equals IR. Ohm's second law is I
equals V divided by R. And I'll leave it to
you as an exercise to figure out Ohm's third law. In a similar spirit,
together with Einstein's famous first law, E
equals mc squared, we have Einstein's second law,
m equals E divided by c squared. Now that may seem silly
to just rearrange things algebraically and consider
that as a different law. But it's not completely silly. It's a primitive version
of what the great physicist Paul Dirac called playing
with the equations, because writing essentially the
same equation in different ways can suggest different things. In this case, it's very true. If you think about
E equals mc squared, famously, what it suggests
is the possibility of getting large
amounts of energy from small amounts of mass. And so it suggests things
like the possibility of making nuclear weapons
or nuclear reactors that get a lot of energy out of
doing strange things to mass. But if you write it this way,
it suggests something different. It suggests the possibility
of explaining mass purely in terms of energy. In fact, really this should
be called Einstein's first law or maybe his zeroth
law because this is the form that he actually
had in his original paper. In the original
paper, you will not find the equation E equals
mc squared, but rather this equation, m equals
E divided by c squared. And the title of the
paper was a question, can the inertia of a body-- or "Does the Inertia of a Body
Depend on its Energy Content?" So right from the
beginning, Einstein was thinking of the possibility
of creating mass out of pure energy. And remarkably enough,
that's what actually happens in our modern theory
of quarks and gluons and the strong interactions. I won't try to describe
that in technical detail, but I'll show you
some pictures that suggest some of the mechanisms
that come into play, which are really very, very beautiful,
and very, very unexpected, and very, very
different from what you learn in elementary physics. In quantum field
theory, we discover that what appears to us as empty
space is in reality, a wildly dynamical medium, as well
as the famous uncertainty in position and momentum that
is encoded in Heisenberg's uncertainty relation. In relativity, there
is a related form of the uncertainty relation
that relates energy and time. That is, if you study things
for short enough times, you'll find that the
energy fluctuates. And in particular,
that means that you can borrow energy for
very short amounts of time to create particles
and antiparticles, so-called virtual particles. And so if we look at
even an empty space with a very high
resolution in time, we find that it's full
of all kinds of particles and antiparticles, and
forms a dynamical medium because these particles and
antiparticles, while they exist, can interact
with each other and affect also the
properties of other-- real particles that
happen to be around. These virtual particles
are so important that I wrote a sonnet about them. And with very little
prompting, I'll recite it. OK. Virtual particles, beware
of thinking nothing's there. Remove what you can,
despite your care. Behind remains a mindless
seething of mindless clones beyond conceiving. You'll get the right version
if you buy the book, actually. They come in a wink
and dance about. Whatever they touch
is moved by doubt. What am I doing here? What should I weigh? These thoughts can
induce rapid decay. Fear not, the terminology
is misleading. Decay is virtual
particle breeding. And seething, though
mindless, conserved noble ends, this
clone stuff exchanged is a bond between friends. To be or not, the choice
seems clear enough, but Hamlet vacillated,
and so does this stuff. So that's the poetic
version And here's-- [APPLAUSE] Oh, thank you. [LAUGHS] And here's the
even more poetic version due to Derek Leinweber,
this is actual calculation of virtual particles. That is, fluctuations--
actually taking the equations of this basic
theory, quantum chromodynamics, discretizing them,
putting them on a lattice and just solving for
these quantum mechanical fluctuations. And this is what you find. This is not an artist's
impression, this is data. Well, the data is somewhat
massaged, of course. They don't really
come in colors, they're not really this big. They're not really this
smooth, most important. But for experts,
what this is, is this is smooth topological
charge density. And this QCD lava lamp is
what's going on in empty space all the time within
you and me, according to our correct theory of the
strong interactions, QCD. And this dynamical vacuum
has many consequences. One of the consequences
is asymptotic freedom, which I mentioned, that
this is the kind of dynamics that underlies that phenomenon. But it very much
relates to this problem of calculating the masses of
particles and an accounting for the mass of the
protons and neutron, and ultimately, ordinary matter. Because I told you that
mass corresponds directly to energy-- or Einstein told you that,
actually, but I agreed. So the different particles we
observe therefore correspond-- well, they correspond to
different vibration patterns, different stable vibration
patterns in space. Remember, the description of
particles, even for electrons, was waves, so they're
all vibration patterns moving in different ways. And stable particles that
we identify as particles and can reproduce are just
vibration patterns that have a particularly long
lifetime that we can identify over and over Again. And so in that language,
the different particles we observe correspond
to vibration patterns that occur in this
dynamical void when it's disturbed
in various ways. This language is extravagant
if you're just doing ordinary quantum mechanics. But if you're doing quantum
field theory and doing QCD, it really is the right language. You have to use it. And here's an example. This is how one produces-- again, in these
numerical experiments, and again, this is data-- a particle. We notionally plunk down a
quark and an antiquark here. You can do that very
conveniently numerically, even though it would be quite
a challenge to do it cleanly in a laboratory. So then they run free,
they settle down, they create disturbances in
those fluctuating fields-- their presence. They have influence and
they create disturbances in those fluctuating fields. If we average over
the fluctuations and just keep the net
disturbance created by having an extra quark
and an antiquark around, this is the extra
disturbance in the field. This is much smaller than
the fluctuations, by the way. But you average over
the fluctuations because that's empty space. We measure energies
relative to that. And this tells you
what the particle is. The particle is this
particular excitation in empty space,
otherwise empty space. It's this pattern that
persists over time. This is actually the pion. There would be similar
pictures if you looked at protons and neutrons. So this is our
deepest understanding of what protons
and neutrons are. They're these stable vibration
patterns in the dynamical void. Now let's play with
equations a little bit because it leads to a very
beautiful realization. So we had this, m equals
E divided by c squared. If we actually want to use
this numerical experiment to calculate the
mass, well, we don't get to weigh those things,
those numerical patterns. It would be complicated to
build in a gravitational field and see the response. What's much easier to do is
to exploit the Planck relation between energy and frequency. So you see the frequency
of vibrations of the field and relate that to
the energy they're carrying, according to E
equals Planck's constant times the frequency. And so when we actually want
to measure the masses, what we actually look at numerically
is these frequencies, and use this equation. Now if we call that the first
law of determining masses, then the second law would be
this one, which expresses that every mass is
associated uniquely with a corresponding frequency. And that suggests
something different. That suggests something very
beautiful and poetic, actually. The masses of particles are-- not are like, not
are similar to, not are metaphorically
suggested by-- they are the tones, the
frequencies, of these vibration patterns in the dynamical void. Here's what comes out of the
calculations numerically. And these calculations, by
the way, are very hard work. Mostly hard work by
computers, but also some hard work by the
people who program them. And it's a very
important activity in which MIT plays
a leading role with John Negele and Andrew
Pochinsky, especially. What comes out of these
kinds of calculations is convincing evidence that
this theory of quarks and gluons really-- and nothing else-- really
does account for the vast bulk of the mass of ordinary matter. Here and in terms of very,
very few parameters-- I haven't emphasized
it, and it would be hard to do justice to
it in a talk like this-- but the theory is so
symmetrical, so tight, so on the verge of being
inconsistent that it's difficult to change in any way. It has very few
adjustable parameters. If we fix the
adjustable parameters, the mass of the up and down
quarks from the pion mass, the mass of the strange
quark from the kaon mass, then nothing else
remains to be fixed and you get predictions--
unique predictions-- for the masses of a
lot of other particles, strongly interacting
particles that have been measured, including N here. N is the nucleon. Those are the
protons and neutron. And so we really have
accounted quantitatively using this mathematically
simple, but profound theory of quarks and gluons for the
mass of protons, neutrons, and ultimately, you and me,
and everything around us in our immediate vicinity. So the ancient
dream that there was a music of the spheres
emitted by planets circling around the sun-- or even earlier,
I guess, planets circling around the Earth-- that "ancient dream" which
always was nothing but a dream, it didn't have any
rigorous content, and so has quotation
marks, has become something quite rigorous, quite
literal, and even true, that there's a
music of the void. And to read it, to hear
it, what you have to do is look at the table
of particle masses. That's it. Those are the tones
emitted by the void. So from this little survey
of our strange understanding of the part of
the universe we do understand in a
profound way, I think we can draw two great lessons. First of all, if we
work to understand, then we can understand. Even as late as the late
1960s and early 1970s, physicists despaired-- some physicists,
the faint of heart-- despaired of ever
understanding this mass of the strong interactions. Freeman Dyson, who was probably
the most brilliant person I ever met and a
very distinguished physical physicist, said--
predicted famously in 1969 that it would be 100 years
before we began to understand the strong interaction. But four years later,
we had the theory. And it came about because
there was freewheeling research along many, many
lines, some of which seemed unpromising, some of
which was hard to assess, and much of which did
turn out to be unfruitful. But by a vast effort involving
many, many physicists, experimentalists and theorists,
over an international community, sharing values
of openness and honesty so that they could
correct each other and learn from each
other, we humans did manage to
understand and find this world which is so remote
from our everyday experience. And then secondly, that part
of the world we understand is, by any standard,
strange, and also I think quite beautiful. It's even more beautiful
if you study the equations and understand it properly. But I hope even these
pictures and rough indications have indicated some of it. So that's the part
we do understand. Now I'd like to-- and
that's ordinary matter, things around us. We really understand
quite profoundly. In the reductionist
sense, I think we're close to closing on that. We really do understand the
behavior of ordinary matter and its basic
properties in principle under ordinary conditions with
a very, very wide definition of what ordinary means. That would include everything
relevant to chemistry, biology, astrophysics. But in cosmology,
we meet our match. And in cosmology, we don't
know what's going on. Astronomers recently have
found that ordinary matter-- the stuff I've been talking
about so rhapsodically-- contributes only about 5% of
the total mass in the universe. So that makes stars, galaxies,
nebulae, planets, people, frogs, things like that. But it's only 5% of
the universe as a whole if you count by mass. 25% is in some
mysterious dark matter. It's-- well, we don't
know what it is. It's not really dark,
it's transparent. If it were dark, then by
studying how it absorbs light, we could determine
its properties. But in fact, its
impervious to light. It's been impervious so far
to all the normal methods of astronomy-- optical astronomy,
radio astronomy, even neutrino astronomy. The dark matter has
only been detected through its
gravitational influence on ordinary matter
which we can see. From that, we learned how much
there is, and that it clumps, and that it exerts
very little pressure. And then of course, we learn
from what it doesn't do, that it interacts very, very
weakly with ordinary matter. There are some ideas
about what that might be, some very good
and exciting ideas which I'll come to momentarily. 70% of the matter
in the universe-- 70% of the mass,
I should say, when you average over the universe
as a whole on very large scales, is in something called
dark energy, which is even more weird. This is evenly
spaced as if it's not clumping at all, as
if in other words, it were an intrinsic
property of space and time that space weighs a little bit. Every little volume
has a little bit of weight-- a very
little bit of weight, but it adds up over
enormous volumes. And even stranger, this stuff
exerts negative pressure. It pushes things apart and
makes the universe actually have an accelerated expansion
instead of a slowing down expansion,
which is what you'd expect from ordinary gravity
on very large scales. So the challenge is, what is it? And we don't know. How do you go about answering
a question like that or coming to terms with it? Well, one way is
to do experiments, and that's very important. But if you have no
idea of what it is, and your attempts to do
experiments to find out have been frustrating-- you find
that you're measuring zero over and over again-- you search for an alternative. Or if you're a
theorist who doesn't know how to do
experiments, also, you have to consider a
different strategy. So another strategy is to
try to improve the equations of the part of physics we know. What does that mean
to improve them? Well, before I
get to that, we're in a fortunate
situation that way because we think we understand
the behavior of matter and extreme conditions. That's another aspect
of asymptotic freedom-- things simplify at
very, very high energies or at short distances. So our description which
simplifies in those regimes is perfectly tailored to the
needs of Big Bang cosmology, where in the early
moments of the universe you had a lot of stuff which
was very hot, very energetic, and very stuffed together. So that's what we
really understand well-- geology is hard,
cosmology is very easy. And here's the proof. That's how simple the
early universe looks. Here's an experiment at the
so-called RHIC accelerator, where people collide heavy
nuclei together at extreme energies, and over very limited
volumes for very limited times, produce the sorts of
temperatures and conditions that haven't been seen in
the universe for the last 10 to the 10 or 11 seconds-- years, rather. And it looks complicated. But if you follow
that strategy I mentioned of looking at the
flows of energy and momentum rather than trying to resolve
every single particle, then you can reconstruct
even from such a complicated topology
of events with thousands of different tracks
emerging that there was in that initial collision
down there, a hot fireball that had the kind of properties when
described in terms of quarks and gluons, that we
use in our description of the early universe. That they're weakly
interacting, that they form a kind of quark-gluon plasma. So the early universe
is user-friendly to us, which means that if you have
some guess for how to improve the equations that has
consequences producing new kinds of
particles, we can trace through the evolution
of the universe to see how those particles
would have been produced during the Big Bang. And then we can go
out and look for them. We can go out and look
for exotic properties. For instance, we could-- if you have a theory that
predicts a new kind of particle that interacts very, very
weakly with ordinary matter and is produced roughly enough
to make the dark matter, well, maybe it is
the dark matter. So that's how the
aesthetic quest for improving the
equations can tie up with the physical quest for
understanding the universe. Now the main strategy
that physicists have employed very
successfully over the course of the 20th century in trying
to improve their equations is to try to extend the amount
of symmetry that they have. Special relativity
was an example of this, where you tried
to make the laws look the same to observers
moving at different speeds. Electrodynamics is a
more intricate example, where there's something
called gauge invariance, which very roughly speaking, is
the possibility of adjusting the zeroth-- the electric potential,
independently at different places, which
has a profound implementation in quantum mechanics. QCD was an extension
of electrodynamics to have an even more extensive
symmetry, and so forth. General relativity
was a postulate that even more extensive
motions than uniform motions at a constant velocity leave
the equations the same. So I'll go through this quickly. There are many exciting and
interesting attempts now-- or suggestions-- for how
to improve the equations. One is based on the
similarity I mentioned between the strong interaction
and the electrodynamic interaction, where quarks
are similar to electrons, and gluons are a
generalization of photons. That suggests since they are
described in the same way, that there could be a
more profound theory that had those as subtheories, where
they would be manifestations, like different sides of one
die, different ways of looking at one richer overlying reality. They could be combined or
unified into an encompassing theory. Doing that in detail suggests
new kinds of experiments-- proton decay-- because,
well, I won't go into why-- and supersymmetry. Supersymmetry is another
kind of symmetry, which postulates the
possibility of extra dimensions, extra dimensions of
a different character than the ordinary
dimensions of space and time that we deal with in
a familiar experience, or even in special relativity. These extra dimensions
are quantum dimensions. They're very small. If you move into the extra
dimensions, what happens is that your spin changes. You change from a
spin zero particle into a spin one-half
particle, for example. And if supersymmetry is
an approximate property of the world,
that's very exciting because it means that
there have to be many more particles corresponding
to the particles we know boosted into
those extra dimensions. So when they peek out
of the extra dimensions, they have to look different. And also implementing
supersymmetry gives you a candidate for
what the dark matter is. Improving the equations of QCD-- and improving the spelling here. It should be QCD protection-- gives you another suggestion
for a new kind of particle, which remarkably enough
also is a candidate to form dark matter. Beautifying the
equations of the electric and the electroweak interactions
suggest the existence of new kinds of particles
called the Higgs particles, which are a big
target of future accelerators. So this theme of extending the
symmetries of the equations is a very rich one, and suggests
the way to make progress in the future of physics. But physics is ultimately
an empirical science, and these beautifications
of the equations wouldn't be fertile
if they didn't lead to definite predictions. Now each of the
things I mentioned does lead to
definite predictions. But it would take me four
more colloquia of this size to explain them properly. I just want to give you the
merest hint of one of the most compelling ideas, and I think
one of the most exciting ones as a way of climaxing. So I mentioned the idea that the
different kinds of interactions are described by mathematically
similar theories. So we have the
electromagnetic interaction. Actually, this is
not quite that. It's the so-called
hypercharge interaction. But let's just say it's the
electromagnetic interaction for simplicity. The strong interaction, which
is mathematically similar and described just by
a different coupling constant and a
different symmetry, and the weak interaction,
which is also described by similar mathematics. And we would like to think that
they are all aspects of one unified theory. But there's a big barrier
to that at first sight. If they were really all
aspects of the same thing, they should have a
similar strength. That would be part
of implementing an extended symmetry
that includes all these symmetries of
the separate interactions as subsymmetries. However, when you
study the strength of the different interactions
at accelerators here, you find that they don't
have the same strength. There's a reason that
the strong interaction is called the strong interaction
and the electromagnetic interaction isn't, and the
weak interaction is even called the weak interaction. The reason is that the strong
interaction is stronger. So its inverse coupling,
which is pictured here, is smaller than the inverse of
the electromagnetic coupling. And so the unification does
this-- possible unification of these seems to
be a nonstarter. However, the great lesson
from asymptotic freedom was that the power
of these interactions changes with energy or
equivalently changes with distance. And we would expect the
most basic interactions to be the ones that occur
at the highest energies or the shortest distances. So what we need to do to see if
this hypothesis of unification really works, whether
it can be made to work, is to extend this calculation
for the strong interaction, which is experimentally
verified and shows how the interaction gets
weaker at higher energies or equivalently
shorter distances, to extend this to the
other interactions and to extend the
whole calculation to much higher energies. And we can do that with
the stroke of a pen. It's the same sort
of calculation. And when we do that, using
the kinds of dynamical vacuum we know about for sure, the
kinds of virtual particles we know about for sure, it
almost, but not quite works. But if we do it, including that
hypothesis of supersymmetry I mentioned, then it seems
to work quite accurately. And we get an unexpected
bonus that not only do the different interactions
of the standard model that we study ordinarily
at accelerators, the weak strong and
electromagnetic interactions unify. But if we plotted on this
same graph also gravity, which acting as a force
between elementary particles is ridiculously small between-- compared to the
other interactions. So its inverse coupling
would start out way up here somewhere-- maybe over there. It also changes with distance
in a way we can calculate. And it turns out that
it unifies very nearly with these other ones, too. So we're encouraged
in our speculations. And beautifying the
equations leads to-- leads to not ugly consequences,
but still more beautiful-- the beautiful surprise. It works better than
it should have worked-- or than we had a
right to anticipate. But is it true? Ultimately, experiment
is the arbiter. And in this case,
we'll find out soon because these ideas
of supersymmetry require that there be a
new world of particles that are not too heavy. And in fact their masses
are such that they should be accessible at
the next great accelerator, the Large Hadron Collider,
being built again at CERN near Geneva. The US has shirked
its responsibilities in recent years here. But that's due to start
operating in 2007. And within a few
years after that, we'll see if these
beautiful ideas about improving the equations
by improving their symmetry, unifying the different
interactions, including the possibility of
extra quantum dimensions and supersymmetry,
whether all those would seem to come together and
form a beautiful package, really govern the world-- or not. It's a very exciting situation. So I had two great
lessons before, now I'm prepared to add one
more in conclusion. I stick by this one. If we work to understand,
we can understand. We learn that even more
difficult and seemingly inaccessible problems-- like
what is the dark matter-- can start yielding to
theoretical insight. By demanding more
beautiful equations, we get candidates we get
possibilities for understanding what the dark matter is. The part of the
world we understand is strange and beautiful. That hasn't changed. We're only trying to
make it more beautiful. But the third lesson is-- I hope you'll agree-- we still have a lot to learn. Thank you. [APPLAUSE] OK. So now I'll take
questions, either about the subject of this
talk or anything else. I may not answer them, but
I'll take the questions here. I can't see very well,
so you'll have to-- someone who has a question,
just come to the mic and we'll [INAUDIBLE]. All right. This lady would like to-- [INAUDIBLE] I understand there was
an interesting work done on the theory of
space and time that is during the Nobel banquet,
and I wonder if you could [INAUDIBLE] Yep. Yeah. Strange things
happen in Stockholm at the time of the Nobel Prize,
including some strange events in space and time. I'd like to show you that
here is the banquet hall-- let me expand this a bit-- where the great banquet is held. This is basically a
town square covered up so that you can have
town events in the winter. And the Nobel Banquet, which
is a banquet for 1,400 people, including the Swedish
royal family down to third cousins, the prize
winners and their guests, and a lot of the government, and
members of the Royal Academy, people like that-- it's a difficult ticket to get. But 1,400 means very
elaborate preparations, and because these are
such august people, they don't like to wait
around for their food. So there have to be a lot
of waiters prepared to serve everybody simultaneously. The king goes first
that, but then everybody else gets the same-- at the same time. So the logistics
are quite daunting. Preparations go on
for a long time. To record-- to do justice
to this whole event would take quite
a lot of patience. But to aid us, what they've
done is make a photo by taking pictures
every 15 seconds and then running it as a movie. So here are the preparations
and the occasion of the Nobel Banquet. [MUSIC PLAYING] That middle table is the table
where the king and queen, Nobel Prize winners sit. You can lights going and off. That's rehearsals of
the opera comes together with the banquet. The whole banquet is accompanied
by themes from The Magic Flute this year. And now you'll see the
waiting staff rehearsing. There's the [INAUDIBLE]. Here's the opera. The places are set. The waitstaff, the
dress rehearsal. Candles are lit, and now
people start arriving. People eat very fast. The Magic Flute. The student union [INAUDIBLE]. So I hope you'll agree that-- [APPLAUSE] You see the universe really
is a very strange place. OK. Yes? Does string theory answer
some of these questions? OK. The question is,
does string theory answer some of these questions? I think in its present
form, it doesn't really answer any questions. It poses a lot of
questions and gives a lot of-- some hints about
what the answers might be. But it doesn't really
supply algorithms or definite predictions. So it's a very interesting and
promising thing to work on, but at present, it's more
questions than answers. I was wondering, what
does it actually mean-- the energy at a particular
point-- to be oscillating? What is the energy
of a point in space? Can you describe that
any more than that? Well, yeah. In principle, what
you're supposed to do is surround the
point by a scale-- well, scale is a little-- OK. In principle-- in principle--
the right way to do it is you look at the
neighborhood of your point, see how much it's curved by
throwing gravitons at it, and scattering, and
seeing how it's curved. And that gives you a
measurement of the curvature of space time, which is directly
proportional to the energy momentum density. And then you look at
smaller and smaller volumes, and that gives you the
energy momentum density. Of course, you don't actually
have energy at a point. You have a certain
density at a point. That's a highly
idealized description of how operationally
you would do it. I'm afraid in this-- in this context, I
think that's as deep as I want to go into it. We could discuss it privately. There's much more
to say about it. Yes? Thank you for this
great lecture, and I was really
intrigued by the point you made that the mass
is the frequency itself. And I was wondering,
could you comment on how that relates to how
does the internal state of mind and thoughts relate to the
external state and matter because their internal
state is more frequencies of different vibrations and
external states as well. Yeah. This suggests-- I mean, what
I've told you about is hard scientific facts-- until the very end, where
things were labeled speculative and are speculative. Certainly, the first
part of the lecture, I was talking about
ordinary matter. These are very hard,
rigorously tested, battle worn consequences. So scientific facts as
hard as they get, I think. So there really is
that rigorous sense in which mass is frequency. The masses of
particles really do correspond to frequencies of
stable vibrations in the void. And we really are, in a
sense, children of light. That is, we, made out
of protons and neutrons primarily, which we seem to be
very heavy and weighed down, were actually produced out
of very light particles. It was gluons and
almost massless quarks. Now then it's up to you
how poetic you find it. It does not, in
itself, I think lead to metaphysical or
theological consequences. So when we discovered that
we are children of light, I wouldn't want to put a
theological spin on it. But having said that,
what does emerge-- clearly, as I've said-- is
that the world is very strange and very beautiful. And then we can admire it
and be happy to live in it, and happy that we can
learn about it, too. Oh yes? I don't think this
is on-- is it? Yeah. I can hear you. I'll repeat the question. My question is, you talked
about gravitons earlier. What do you think would
be the implications if we were to actually
experimentally detect gravitons? Like how much of
an impact would it have on the questions
you discussed? OK. So the question is, if
we actually detected gravitons, what would that-- what implications
would that have for questions that I discussed? So let me put that
in a broader context. One of the exciting frontiers--
one of the main frontiers, including here at MIT-- of experimental
astrophysical research is the quest to detect
gravitational waves. Now gravitational waves are
not individual gravitons. They consist of many, many
gravitons acting together in a sort of Bose-Einstein
condensate, if you like, or just a coherent wave. And there are firm
theoretical predictions that gravitational
waves really do exist. There are estimates of the
strength that they have. They're very weakly
interacting with matter, as I sort of alluded
to, so they're very difficult to detect. But people are optimistic. They've worked very hard to
make very sensitive detectors. They're optimistic
that they'll start detecting gravitational
waves before too many more decades are out. And that would be very exciting. It would teach you-- it would be like a whole
new form of telescope that's especially attuned
to the most violent events in the universe because it's
only violent events that produce enough of these very,
very weakly interacting waves to be detectable. And furthermore, since the
waves are so weakly interacting, they penetrate, so
you can indirectly see what's going on deep
inside exploding stars, for instance, or maybe
from the early universe. So that would be very exciting. But that wouldn't be the
detection of single gravitons. The detection of really
quantum effects in gravity-- so you have to worry about-- small numbers of gravitons
would be a real surprise because, well, it would mean
that that gravity is behaving very differently than a
conventional extrapolation of what we know. Because if you start estimating
based on what we know, the interaction of individual
gravitons with any detector that we're likely to have-- not just for decades,
but for many centuries-- is too feeble to be practical. Now having said that, there
are some heterodox ideas about gravity that
indicate that maybe very high-energy gravitons
interact more strongly. I don't think they're
very likely, but just because of that, if those
ideas turned out to be true, and we found at accelerators
gravitons being emitted, that would indicate that
high-energy gravitons behave in a way that's very
different from what's suggested by the
low-energy forms of gravity we've observed so far. That would really be
a dramatic discovery that would dramatically impact
and basically falsify what I was telling you at the end. But I don't think
it's likely because I think what I told you at the
end is really compelling. Excuse me. I'm not a trained
scientist, I've never-- so what I have-- my
question is probably trivial in light of what
you've been talking about, but I still can't wrap my
head around Planck's constant. Could you kind of
summarize briefly what that is, if possible? OK. The Planck's constant that
appeared in my equation-- the equation I used-- relates energy to frequency. So it's the idea
that when you have-- well, in its simplest
and original form that Planck invented it, it
says that when you have light, that light is really created-- is composed of particles,
so-called photons. And that the energy
of each photon is proportional to the
frequency of the light. And since energy and frequency
have different units, you need a conversion factor. And Planck's constant is
the conversion factor. So it's E equals-- the energy is Planck's
constant times the frequency. And it's that which
enables us to really make this connection between
frequencies of vibrations, and energies, and masses now. I'm fascinated that you
did the work for which you won the Nobel Prize doing
your graduate studies. And I'm thinking I'm
not going to win one. I'm curious if you knew the
implications of that work at the time. I had a pretty good
idea that this-- I didn't have confidence
that it was correct. But I did know that-- that is, that it was a correct
description of nature-- but I did have confidence
even at that time that if it were correct,
it was very important and would represent,
well, potentially, Nobel Prize material. Right-- didn't I say
something like that, yes? Now it's much
clearer in retrospect what the significance of
our calculations were. And the smooth-- the
nice pictures of jets that I showed you of course,
weren't available then. The clues were much, much
more indirect and harder to interpret. Any fool could have
discovered the theory if they had those pictures. And so the experimental evidence
was much more ambiguous or-- not as compelling. It took several years
to really do that. Also the ideas we
were proposing that the fundamental ingredients
were of the strong interaction where these particles
you never saw-- famously-- no one had ever
discovered a quark or a gluon. And on the other
hand, our theory did not contain any of
the particles you did see. Didn't have protons explicitly,
or neutrons, or anything else. It was a little
nerve-wracking But what was a gift from heaven that
made all this possible, and made me think right
from the very beginning that this might be the
answer is that the property of asymptotic freedom, that the
interaction should get weaker at short distances and/or at
high energies equivalently, was something you
really needed to have the consistency of special
relativity and quantum mechanics work to the bitter
end in quantum field theory. And also it was something
that was strongly hinted at by the experiments
that professors Friedman, Kendall and Taylor later
won the Nobel Prize for. And that requirement
of asymptotic freedom was so difficult to achieve
that there was basically only one theory that
even remotely looked like it had simultaneously
had that property and could describe the
strong interactions. So it was all or nothing--
either this was correct or it was not. So that was a good situation. It really focused the research
effort and ultimately paid off. Hi. Could you comment
on the significance of the Nobel Prize to you, not
as a scientist but as a person? Maybe some anecdotes or
you're the same person, but so many things have changed? Well, I haven't really
absorbed it yet. Things are still changing,
so I haven't reached any kind of steady state. I don't know how it's
going to play out. I liked the life I had before. I'd like to keep it and add. There's certainly many
opportunities to add. The question is trying to-- making sure it doesn't edge
out the things I liked before. But having said, that, I
mean, there's no turning back. I was very unhappy not to have
this marvelous work recognized for so long. So there's no-- well, be
careful what you wish for. But I definitely wished for it. And it's a lot of fun. So there are huge pluses
and some potential dangers that I'm going to have to
learn how to cope with. That's a vague
answer, but I'll have a much more concrete
answer in a year or so when I understand it better. Have you got a
favorite physics joke? What's that? A favorite physics joke? Well, I'll tell you Albert
Einstein's favorite joke, which I like very much. Although it's not it's not
directly about physics, it is profoundly about physics. It involves a man who can't
get his car to start-- with or more accurately, he can
get his car to start, but only after a lot of effort. And this is an old
story, so he has to crank, and sort of
kick the car, and push it. But he can get it
to the mechanic. And he takes it to
various mechanics and asks them to fix the car. And none of them can fix it. He tries one mechanic after
another, and each of them examines the car,
tries different things, takes it apart,
puts it together, but they can't fix the problem. Then finally, he finds
the seventh mechanic, who looks at the car, takes out
his wrench, tightens a bolt, and says, now your
car will work. And it does work. Then it works perfectly. So the man is delighted that
his car works, drives it home. But then he's very unhappy
when a few days later, he gets the bill. The bill is $150. He can't believe it-- $150 for screwing a simple
bolt. He's so outraged that he storms back to the
mechanic and says, how dare you charge me $150-- this is when money was
really money, so you should said multiply by 50 probably-- how dare you charge me
$150 for that repair? It took you about 30
seconds to fix that. Very little labor was involved. All you did was take out your
wrench and tighten a bolt. I want an itemized bill
that accounts for $150. So the mechanic
takes out his pad and itemizes the bill,
parts, $0, labor, $0.15 for turning screw. Knowing how to turn
screw, $149.85. I'm sorry-- I blew it-- knowing
which screw to turn, $149.85. Do you believe that in
the observable future, or ever at all, we'll
be able to control reactions between elements-- like elementary
particles the way we do chemical reactions to get
some practical use of them-- say, like energy sources? Yes. So the question is whether
we'll get practical results from understanding these
fundamental interactions better. And well, let me answer
that in several ways because it's a question
I'm often asked, and it is a profound question. First of all, there
are direct implications for the rest of physics
because as I showed you, it opens the early
universe to examination because things simplify. It suggests how to unify
the different interactions. And it also is a great help
in interpreting experiments because most of what happens
at high-energy accelerators is this strong interaction. We need to understand that
very, very well if we're looking for the rare
events that correspond to something fundamentally new. Those are applications
within physics that are very real and
very actively pursued. As to sort of
engineering applications, I think the direct applications
are not yet visible, and may never really be visible. But I'm not sure about that. I think as time goes on
and as petroleum dries up as an energy source-- becomes very expensive or
unavailable altogether-- and also its pollution starts to
have markedly horrible effects, mankind, if it's going to
maintain its current standard of living, will have
to turn more and more to nuclear energies. And knowing the
fundamental theory of how the nuclei
interact may turn out to be important in understanding
that kind of nuclear chemistry as opposed to ordinary
chemical chemistry. Certainly, that
hasn't happened yet. But as I told you, our ability
to calculate these things-- which relies on powerful
computer technologies-- has recently come into fruition. We can now actually
calculate the mass of the proton and other
things from first principles. So I don't think it's at
all absurd to think that 10 or 20 years
from now, we'll be able to calculate
properties of atomic nuclei from first principles. And that will really help. But much more immediate
and maybe more important is the fact that doing fundamental
research like this inspires some of the brightest
people in the world-- bright young people-- to work very hard,
learn difficult things, work together, push
the possibilities of what's possible-- push the frontiers
of what's possible. And time and again, that kind
of focus, that kind of effort, has paid off in ways that are
unexpected with vast multiples of the amount of capital
that was invested. So for instance, Faraday's
investigations into the force of electromagnetism, which
were just pure research-- and big science at
the time, by the way-- ultimately led to all the
electrical and radio technology we have today. Similarly, basic investigations
in quantum mechanics have led to microelectronics,
and computers, and lasers. And in this even more abstract
stuff of fundamental particle interactions, it was in order
to facilitate communications among large collaborations
of experimentalists at CERN that the world wide
web was developed. Tim Berners-Lee developed
the hypertext protocols and browsers, and for
that very purpose. So these investments
in pure research pay off in unexpected ways. Since they're unexpected, I
can't tell you exactly what they're going to be. But history indicates, I
think very convincingly, that putting-- challenging talented people
to stretch their imaginations and work hard pays off. Thanks. I was wondering about the
T-shirt on that you have on underneath your suit jacket. This T-shirt? Yeah. The question is the T-shirt. All right. I think we-- right. Well, I'll keep answering
questions, but yeah. This T-shirt comes from
a head shop in Amsterdam. I don't know what it means. But if you take the
appropriate drugs, you may be able
to figure it out. [LAUGHS] Fantastic talk, by the way. Thank you. I heard some questions that
maybe the next generation of particle colliders
would create conditions in which you might-- Create what? --create high enough energy
conditions that for some reason a tiny black hole might
spontaneously be created, which could be very dangerous. Is this plausible at all
or is it completely unreal? Well, there are two
questions there. So the first question was-- or statement was--
that you've read that there are
theoretical speculations that at very high--
at the next generation of high-energy
accelerators, one might produce small black holes. And that's true. Otherwise respectable
physicists have suggested that kind of thing. In an earlier
question, I was asked about the possibility of
detecting single gravitons, and I alluded to
the fact that there are heterodox theories where
high-energy gravitons behave quite differently than
what you would naively guess by extrapolating
what we know about low-energy gravitons. It's in those kinds of theories
that you would possibly produce black holes, because
the high-energy gravitons are interacting stronger. So those go together. And I've told you that I
don't like those theories-- but some people do. And we don't know. But even in those theories,
that black holes-- the so-called black holes
that you would produce would actually be so small that
they would be highly unstable. They'd evaporate very
rapidly by Hawking radiation. So they wouldn't
look very much-- they wouldn't look grossly
different from particles. They'd just be heavy
particles with-- that would decay very fast. The details of their
behavior would be different. So you could try to
convince yourself that they were well-described
as rapidly evaporating black holes. But they would be
evaporating very rapidly and would not create any hazard. That's not to say
that nature is not so inventive and malicious
that it's a logical-- it's always a
logical possibility when you do something
that's never been done before that it'll
lead to a catastrophe. But there's no real indication
that we're close to that-- famous last words. Just to conclude, I've never
been so confident, though, of making a prediction
as when I was called to sit on a panel about the
possibility of an accelerator turning on and ending the world. Predicting that it won't is very
safe because if your prediction is wrong-- [LAUGHTER AND APPLAUSE] OK. So I think with that,
it's appropriate to end. And I'll answer other
questions in private. Thank you. [APPLAUSE]
