It's wonderful to see you all of you back
and for those of you who are new, welcome. We are going to start off,
as Richard said, our seven week series with three weeks on atoms, quarks and
strings, the origin of matter. And the first week, that's this week, I'm gonna tell you about
everything from atoms to quarks. We're gonna start with things that all of
you know about, atoms and we're gonna end up with something that many of you have
probably heard about, namely quarks. And next week we're gonna talk
about the standard model, which is the most successful
model in modern science. It's been tested to 12 digits,
12 deciplaces, parts in a trillion and it describes how those quarks and all the
other particles interact with each other. And then in the third week, and that's
gonna be Professor Cyrus Taylor, the Dean of the College of Arts and Sciences and
the Michelson Professor of Physics. And then, in our third week, we're gonna
talk about things beyond the standard model, speculative ideas about physics,
and somewhere in there we'll end up talking
about the Large Hadron Collider. So let's jump right into it. And the way we're gonna work it is,
for those of you who are coming back, I'll talk for about 15 minutes. And then after 15 minutes
we'll have some questions. And then go back to the talk for
another 15 minutes, have some more time for questions,
and finish it off with the third part. Okay, so what are we gonna do today? We're gonna start with the periodic table
and since we're in the chemistry building, I was wondering if there would be
a periodic table on the wall somewhere. I'm sure we could find one, but
we'll see what it looks like and we're going to go from there to the modern
atom, and then we'll have some questions. Then we're gonna take a little
detour from our main story, which is we're gonna look in the mirror. And we're gonna see how nature can tell
us when we are looking in a mirror, which is kind of surprising. And in the third part we're gonna
talk about quarks and leptons, the building blocks of matter. So let's start out with
the periodic table. I bet most of you have seen this,
maybe it's been a couple of years, but what this is, is a table of all
of the known chemical elements. And they are lined up, all the columns are
things that have very similar chemistry, as we go down, they get heavier. But in each column those
have similar chemistry and those have similar chemistry. The creation of this table in 1869
by this fellow, Dmitri Mendeleev, was really a revolution in
understanding how to put what were then the fundamental particles of nature
together, to organize them, okay? So he didn't know about all of them,
a lot of them, many of them weren't discovered yet. And you can see all these ones
I have blocked out in gray, they weren't discovered. These ones here in orange we'll
talk about in a minute and as well as those ones in yellow. So but all of these, he organized in
this way that allowed us to understand their chemical relationships,
how the chemistry of fluorine and chlorine were similar,
the chemistry of oxygen and sulfur, etc. Now, these ones in this last column, those
are what are called the noble gasses, they weren't very reactive. We didn't know much about them,
in fact, the first one, the top right, that's helium. And it was discovered only in 1868, which was the year before
Mendeleev did this. But I guess communications back
then were maybe a little slow, people weren't quite sure about it yet
and so it wasn't widely accepted, so he didn't have that in his table yet. Argon, this, This one, two down, there have been hints
of that since the 18th century, but it wasn't actually isolated
until about 25 years later. And the other ones, argon, krypton,
and so neon, krypton and xenon, those didn't come around until
almost the turn of the 20th century. The four yellow ones, Mendeleev
was actually able to predict their existence and
they were very quickly found, okay? And over the next decades,
all of these others were produced, okay? Some of them are only made artificially,
many of the ones down here, they don't exist in nature and
we make them in accelerators. So this was the view of what were really,
fundamental particles. We didn't know that these
were made of things, they were just fundamental elements. That started to change with the work of
this fellow, this is Ernest Rutherford. And last year was the centenary of
probably his most famous experiment, he's considered the father
of nuclear physics and he had back then,
he had a large laboratory. Actually he had done some important
work in Montreal at McGill University, he had figured out how to make
beams of alpha particles, basically helium atoms
striped off their electrons. And he had one of his research associates,
and one of his students, the inventor of the Geiger counter,
Hans Geiger, and he had them shoot alpha-particles
at gold foil, okay? Here are those folks,
Hans Geiger and the fellow who later became Sir Ernest Marsden, so
they became very eminent physicists. What did we expect? Well, what we expected is that when you
shot those alpha particles at the gold, they'd kinda just go straight through. So here are the alpha particles
going through the gold atoms, we kind of expected. We kinda thought that atoms
consisted of electrons, maybe embedded in some
sort of positive matrix, and you could just shoot these
alpha particles straight through. But that's not what we saw as
hinted at in this picture, well as shown in this picture,
what did we actually see? We saw that many of the alpha
particles went through the gold foil, but a lot of them got deflected
a little bit off of that main path. So they came out of the alpha
particle emitter over here, they hit the gold foil and
they got deflected. And very occasionally one would
bounce back almost perfectly, okay? So instead of going straight through,
Many of them went straight through, some got deflected
and some seemed to bounce straight back. And it took a couple of years for Rutherford to figure out
what was happening there. What he realized was happening
eventually was that there was a very dense positive nucleus inside the atom and
then diffuse negative electrons kind of orbiting around
that positive nucleus, okay? So all of a sudden those elements
now have different parts, they have nuclei and
they have electrons, okay? Now that was still a situation
which there seemed to be, well at the time, tens of fundamental
particles in the universe. That each one had different properties,
each one had a different nucleus, okay, with no particular relationship to each
other in terms of one being made of another. And that started to get even worse in
the early part of the 20th century. So in 1912 radio chemist Fredrick Soddy,
he noticed that between lead and uranium where there should only
be 9 different nuclei there were instead 40 different nuclei
that he could measure. By looking at the decay of the uranium and
the various elements in here. So, instead of 9, 40 and
a fellow named JJ Thompson who won the 1906 Nobel Prize in physics,
he noticed that neon, there are actually two different
types of neon with different masses. And by the 1920s, there were more than 200 models, sorry, different nuclei, so far more than were originally thought. Now, Today, if we'd look at the same what's
called chart of the nucleoid, there are 200, in fact,
there are about 4100. So for each of those different
elements in the periodic table, there could be several even up to ten
different isotopes of those elements. So that was really a pretty
bad situation to have 4,100 different elementary particles. It didn't seem like we were really
understanding what was going on inside the atom, and so the same fellow,
Rutherford, he started to probe the atoms. So what he did is he took
some nitrogen atoms and he shot some more of these alpha
particles, these helium nuclei, at them. And what he noticed was, that when
he shot alpha particles at nitrogen, he got oxygen, but he got the nuclei
of hydrogen, protons, okay? So, again what we're showing
here is a nitrogen nucleus and it's being hit by an alpha particle
which is the nucleus of a helium atom. And what comes out is something bigger,
and then this little thing, and that's the nucleus of a hydrogen atom, in
other words, it's what we call a proton. And so he said, well, I could build
all of those different elements, all of those different chemical elements
and all the different isotopes if I took. Different numbers of protons, okay, so depending on how many protons there
are that's which element it would be. So that's where it would live
in the periodic table, but then I could add different amounts
of neutral particles, right? Now, no one had ever seen such neutral
particles, so he predicted them. He said, well, there must be neutral particles whose mass
is comparable to the mass of the proton, those are neutrons, and depending on
how many of those exactly you have. That will determine which isotope
of that chemical element you have. Okay, so now we have the number of protons
inside your nucleus tells you which element you have, and the number of
neutrons tells you which isotope you have. But we haven't seen these neutrons they
add new fact was a dozen years before this fellow, Sir James Chadwick detected
those neutrons and indeed, they were neutral and
about the mass of a proton. By the way, he was awarded the Nobel Prize
in physics for discovering the neutron. He was also the primary British scientist
who collaborated on the Manhattan Project during World War II. So, That meant that by 1932, sort of going into World War II, our world was all of a sudden much,
much simpler. Right, we had started with
this pretty complicated, it was a great revolution to be able
to organize all these elements into the periodic table, but
it was pretty complicated. It had a lot of different particles, and things were only getting worse
with the discovery of isotopes. But by 1932,
it seemed like there were just three fundamental particles of nature. The proton, which was positive and
heavy, the neutron, which was neutral and
heavy just like the same proton. And the electron which was negative and
much, in fact about 2,000 times lighter
than the proton or neutron. And so everything was made of those,
atoms consisted of dense nuclei containing protons and neutrons and
surrounded by these electrons. And the number of electrons which is
equal to the number of protons determine the chemistry of the element. And in fact, all of ordinary matter
is made of these three particles. >> Do we have to do something
artificial to create those isotopes? >> Yes, we so those are some of
those some of those isotopes exist naturally many of those are most
of those Isotopes exist naturally. So you can have a certain number
of protons, and then you can have, a typical isotope would have about
the same number of neutrons and protons, not exactly, but you can have one more,
one less, and it can still be stable. Or sometimes it's unstable and
that means it's radioactive, okay? So it'll decay into other things either
by emitting alpha particles, by emitting the nuclei of helium or by emitting
electrons or by emitting other particles. So we'll have radiation coming
out of the unstable ones but many, many of them are stable. Some of the higher ones in that list,
those are only made in the accelerators by smashing particles
together, some of those rise to the top, some may exist for
a very short fraction of a second. >> Judging by this three loads,
why would so much of the fundamental
research done in England? >> Well, remember that, for example,
the first important scientific experiment in the United States was
done here, about 125 years ago. Until then, really until the early 1900s, the center of gravity for
most science was in Europe, and really until World War II. Or just before World War Two when a lot
of scientists started to come over, but really,
Europe was the center for research. And in particular, I'd say Germany and
England in this field were really the places where a lot of
the fundamental science was being done. Rutherford was actually up in Montreal for
a lot of his early work, but as soon as he could get in a good position in England,
in Manchester, he went over there. >> What did he know about the nature
of alpha particles, their constituency? >> That's a good question,
I actually don't know, I'm not sure, I think he got them from helium. Okay so, we've now found we have
these three fundamental particles. But now we're gonna take a detour and
we're gonna look in the mirror, and I'll try to explain what
that means in a few minutes. So, by the 1920s this fellow
who was one of the most influential scientist of the 20th century,
Niels Bohr, had told us, by the way,
he's a Danish physicist. And won the Nobel Prize in 1922, really
for getting quantum mechanics going, okay? So, but one of the ways he got
quantum mechanics going was telling us that electrons orbit nuclei in
a discrete set of possible orbits. In other words, unlike in the solar
system, where you could have a body orbiting, pretty much any
distance from the sun In an atom, you had to have your electrons
orbiting on particular orbits. That's called the Bohr model of the atom. And that orbiting gave
rise to magnetic fields. When you have charged particles moving,
creating currents, those currents create magnetic fields, and
you could measure those magnetic fields. It turned out when we measured
those magnetic fields, the motion of the electrons didn't account
for all the magnetic fields we saw. And so, we realized that the electrons
had to have intrinsic magnetic fields. And the way to think of that is that
the electrons not only were orbiting the nuclei, not only were they going
around the atom, they were also spinning. That's what's called a classical picture
of something quantum mechanical. They aren't really little spinning
objects, but a convenient way for us to think of them is as
spinning objects, okay? And when they're spinning,
that creates a current, as well, and that current creates a magnetic field. So we could detect the magnetic field
of these spinning electrons, okay? So and the electrons could
spin in different directions, and we were able to detect that
extra magnetic contribution. So the magnetic field could either add or subtract to the magnetic field due to
their motion depending on whether they were spinning in such a way that
it was adding or subtracting. So I've drawn these little kind
of orange arrows to suggest that the electrons are spinning
either this way or this way. And if they're spinning this way, the way
I figure this out is I take my right hand, if they're spinning this way, I'm gonna put a little arrow
the direction my thumb is pointing. And if they're spinning this way I'm
gonna put an arrow down the way my thumb is pointing. So we say they either spin up or
spin down. Now eventually, we realized that
not only were the electrons, did they have spin, but so did
the protons and so did the neutrons and that also meant that
they had magnetic fields. So now we have electrons with spin and
we have protons with spin and we have neutrons with spin. [COUGH] And it turns out that
when particles have spin, especially when they're moving fast, we can talk about them as being either
right-handed or left-handed, okay? Now, we call a particle,
for example an electron, right-handed when it's spinning this way,
the electrons' spinning this way. Its spin arrow is pointing that way,
if it's also moving in that direction, we call it,
a right-handed electron, okay? But if it's spinning the other way,
this way, so that spin arrow is pointing that way, so if its spin
arrow is pointing to the left but it's moving to the right, we call it,
left-handed instead of right-handed, okay? So electrons can be right-handed or they
can be left-handed depending whether their spin is lined up or
opposite to the direction they're moving. [COUGH] Now [COUGH] that is a property
that changes when you look in a mirror. Most of physics does not change when
we look in the mirror, for example, suppose I showed you a movie,
people playing pool. And I asked you to tell me, did I take
this movie directly with my camera or did I shoot into a mirror that
was looking at the pool table. Well, if it's a really, really good mirror,
there's almost no way that you could tell. The only way you could tell is,
you might guess that it's in a mirror if all the players
and all the audience were left handed. But that's a peculiarity of biology
that it manage us to choose right-handedness over left-handedness. But in terms of the fundamental physics,
the way the balls are bouncing, the way the balls hit the wall,
the way they fall into the pockets, you can not tell whether you
are watching the movie of the game or or you are watching the movie of
a reflection of the game, okay? And, that is how we believed physics was. We believed the world did not care
whether you watched it through a mirror. Okay, well, let's look at these
particles now these right-handed and left-handed electrons in the mirror. So here I stuck a mirror down the middle
and here I have a right-handed electron. So that means, remember it's spinning this
way and it's moving to the right, okay? But if I look in a mirror, then it's going
to be moving towards the mirror still and it's still gonna be turning
spinning to the right. And if you try to think, is that right, go home look in the mirror
do something like this. So if I am standing on this side of
the mirror, if I turn my hands like this, then if you look at me in the mirror my
hands are still going around this way. But as I approach the mirror, I'm moving
towards the mirror from this side and my reflection is moving to the other way. So the direction you're moving reverses
but the direction you're spinning doesn't, and that means that a right-handed
electron a right-handed particle when viewed in a mirror
is a left-handed particle, okay? It looks like a left-handed electron,
and similarly, a left-handed electron looks like a right-handed electron
when looked out in the mirror, okay? So what does that mean? It means that if it's in fact true that we can't tell the difference
when looking in a mirror, then right-handed and left-handed
electrons should behave exactly the same. We shouldn't be able to tell
the difference in how they behave. They should behave exactly the same. And so the question is, can we tell when we're watching a mirror
image when we watch how electrons behave? Now this fellow R.T. Cox, who was a later
professor of physics at Johns Hopkins. He decided that was going
to bounce some electrons. He was gonna take some radium and he was gonna bounce some
electrons off of some mirrors. And he was gonna measure what
happens to the electrons. So what did he do? He had some radium, this is in 1928, he had some radium which
was an electron source. And he would shoot electrons out, bounce
them off a mirror, bounce them up here. And sometimes he would aim this
mirror over to this direction, and sometimes he would flip
it off in this direction. And he would count how many of the
electrons actually manage to get into this particle counter that he had over there. Some of them would get up there and
some would go in and slash, make the particle counter flash,
but some of them would miss, okay? And so he would do this, shoot the electrons, out of the electrons
source, they bounce off the mirror. And some of them would get in but
some of them would actually miss and he would do this over and over again,
many, many, many times, okay? And then after a while he would flip the
mirror and do it some more, and some of them would hit and some of them would
miss, but when they hit, they would flash. Now the peculiar thing was that
the electrons more often hit even though he let the same number of electrons
come out of the radium source, when he had the mirror
pointing to the right, the electrons hit more often than when
he had the mirror pointing to the left. So electrons would go right more
often than they would go left, okay? In other words, you could tell this wasn't You could whether we're looking at
the said mirror, because the right hand part of the experiment was behaving
different than the left hand part. He did it over and
over again that the other people did it. And the people who did it with the radium
source got the same answer, and other people who didn't
about the radium source, they boiled electrons off the filament and
it didn't work. So no one believed them, and people
ignored the experiment for 30 years, okay? Actually until these
two folks repeated it, we actually did a different experiment,
but saw the same thing. This Madam Wu, C.S Wu, and
she was actually the only chinese physicist who worked on
the Manhattan project. And the fellow to the right is Richard
Garwin, who was born here in Cleveland in 1928, and graduated from
Case Institute of Technology in 1947. And he also did an experiment like this,
and what they found was that nature indeed can tell
the difference between left and right. That nature, when viewed through a mirror,
is not the same. So, all those people who did not believe
that result from 1928 were wrong. It was a completely unexpected result,
our theory of physics had allowed for that possibility, and so people just
assumed that the experiment was wrong. And, in fact, I think most physicists, I just learned about this
a couple of weeks ago. So most people have completely
forgotten this experiment but in fact, the fact that when we look in the mirror
we get a different answer for physics, was discovered in 1928, not in 1957 which is what we
always credit Wu and Garwin for. And so it turns out that left handed and
right handed electrons behave different. And that radium was emitting
more left hands electrons than right handed electrons. Because of the way that we will learn
next week that weak interactions work. When things decay, they emit
left-handed electrons exclusively, not right-handed electrons, okay? So nature knows the difference
between left-handed electrons, left-handed particles and
right-handed particles. In fact, the thing we call electron is actually
two completely different particles. The left handed electron but
I think that was spinning this way and traveling that way,
is not at all related to the particle called the right-hand electron, which is
spinning this way and moving that way. It's just that they can turn into one
another by emitting another particle. We don't see that other particle, that
particle called the Higgs particle, and we're going to talk about that next week. You've probably heard about
people looking for the Higgs. So, our confusion about the nature
manages to relate the left and right-handed electron and
make us fool us into thinking that there's only one particle,
but there's actually two. And it was these two people who
taught us this, even though back in the year that he was born,
we should have figured it out all ready. >> What's says so what? What are the implications of this? >> What's the implications, well,
that's a great question, so what. So the first thing is that
it's surprising, okay? So, people had studied physics by at this
point, studied science at this point for doing this kind of science,
detailed science for maybe 100 years. And had no idea that this was possible,
that looking in a mirror you could tell when you were looking in a mirror and
doing science. But you could say, you're right, so what? It'll turn out that if that wasn't true,
none of us would be here, okay? It turns out that in order
to make more matter, which is what we're made of,
than this stuff called antimatter, which we need to stay far away from cuz
if we touch it we'll get destroyed. You need this property, you need for there
to be what's called parity violation. You need there to not be a symmetry
between left and right-handed particles. They have to behave differently, okay? So, our existence actually relies on
the fact that there is difference between left and right. And we didn't appreciate that, and we actually didn't appreciate
that until mid-1960s. A fellow named Sakharov, who many of you know as the father
of the Russian hydrogen bomb. He was the one who pointed out that we
needed this parity violation in order to make more matter than anti-matter. >> Assuming you have a sodium atom,
do all sodium atoms have left and right spins to the same degrees? >> No, so this property of being left and
right handed, it turns out that because of this
Higgs field that we're gonna talk about next time,
that people are looking for particles of now, left and
right get mixed up very easily. And that's why we don't notice on a
day-to-day basis that there's a difference between left and right in chemistry,
and in a normal particle physics. It's why we're so hard to really see. So in that sodium atom, those electrons,
they flip between left and right constantly, okay? In order to get them not to
flip between left and right, they have to be going really,
really close to the speed of light, then that makes it harder for
them to not flip, okay? So, the electrons coming out of the radium
were going fast enough that basically they did weren't flipping,. They were coming out as
left-handed electrons, and they were staying left-handed long enough
that they knew whether that there was a difference between going left and
right on the mirrors, okay? But inside the sodium atom, they're moving
too slowly to preserve their left-handed or right-handed identifies. >> Boy, you answered my question. I was gonna ask if there was, hydrogen
has both right-hand and left-hand- >> Same reason, no. >> And there's no difference? >> No, the electrons inside of
atoms actually move pretty slowly. What do I mean by slowly? In a hydrogen atom, the electron is
going about 1% at the speed of light. That's what we call slowly, okay? So, speed of light is the maximum speed. Imagine if you're driving on the freeway,
you're driving at 60 miles an hour, maybe a little bit more, and someone
is going along at half a mile an hour. What is half an hour and hour look like? Just like this, and
it's pretty slow, right? So, electrons are moving really
slowly compared to the speed that would be needed in order for
them to preserve that handedness. And the same thing, the protons,
as we'll learn in a minute, they're not even fundamental particles. So there isn't such thing as a left-handed
proton and right-handed proton. >> It's sort of fun sometimes to try and
think back, how these guys were thinking when they do these experiments, and
particularly when they make mistake. And, makes you wonder, there are two things in these experiments
that were done by Wong Garner. There's the particle, but
then there's the deflector. That's material.
>> Well, they in fact looked at it in a completely different way, they did a completely different
experiment than Cox actually. >> It's another piece of material,
>> Right. >> Whose structure and properties may
explain either call it anomalous result or what turned out to be an important result. >> Right. Well, I think it's also interesting how important the role theory
plays in experiments. If you don't have a theory to
explain your anomalous result, you think your result is wrong. So for example, who here has heard about the neutrinos
that go faster than the speed of light? Okay, so that was in the news for
a long time. That there were neutrinos that
moved fast in the speed of light. And if you ask pretty much any physicist,
he or she will tell you that that
experiment is wrong, okay? Now, in fact, it's turned out to be wrong. But even before we knew why it was wrong,
because there was some bad cable connections, pretty much everyone
was convinced it was wrong. Everyone was also convinced that
Dr Cox's experiment was wrong because there was no good
theory to explain it. So we have a little bit
of humility when we're so confident that what seem to be
wrong experiments really are wrong. Sometimes they turn out to be right. So let's get back to our main story. And you'll see why our digression wasn't
completely a digression because we learned in our digression that those particles
that we think of one particle, the electron, is really two different
particles, the left-handed electron and the right-handed electron. But what I want to do now is
talk about the case for quarks. So let's remember where we started
which was with this periodic table of the elements that has over 100 what
could have been fundamental particles, and how life got even worse when it
turned into the chart of the nuclides with 4,100 fundamental particles,
different isotopes. But how life got wonderfully simpler
when we understood that, really, everything was made out of electrons,
and protons, and neutrons. So that going into World War II,
going to the early '30s, we thought we knew the fundamental
constituents of matter. Electrons, protons, and neutrons. And if we had listened to Cox,
we would have realized that the electrons at least were
actually two different particles. But we didn't listen to him,
we ignored him. So what happened, though,
is that we very quickly realized that there are other particles. In fact, in 1928 to 1931, Dirac,
a very famous physicists, and he went on, so many of these people won the Nobel
Prize for the work they're doing. There's probably a couple of tens of 20 or
30 Nobel prizes given out for this stuff. So I'm not always gonna mention when
everyone won a Nobel Prize for it. But Dirac, he predicted that there was
gonna be another particle just like the electron, exactly the same math,
that could also spin left or right, but have a positive charge
instead of a negative charge. Just the opposite charge. And in 1932, Carl Anderson, an American
physicist who won the 1936 Nobel Prize for this, discovered that, indeed, in cosmic
rays, in particles coming from the sky, coming from outer space,
he saw positively charged electrons. Electrons that curved the wrong
way in magnetic fields, but otherwise behaved exactly like electrons. So all a sudden, now we have not three
fundamental particles, but four. Now, that wasn't so bad. In fact, we'll see Dirac also predicted
that there would be an antimatter version of the proton, the anti-proton. But something bad happened, and that was that just a few years later,
Anderson found another particle that was just like the
electron, except it was 200 times heavier. And as another one of the collection of
people who won Nobel Prizes in this period said Who ordered that? Nothing we knew on Earth
was made of muons. In fact, muons decay in
a tiny fraction of a second. But by the way, this fellow, Robbie,
he's the one who invented MRI. Although, at the time it was called
nuclear magnetic resonance, okay? So his Nobel Prize was in 1944. All right, so now, we have the electron,
and the proton, and the neutron. We've discovered antimatter,
that's the positron. But now we have another
copy of the electron. That's the muon. And things are starting to get messy,
okay? And then, this fellow, this Japanese
theorist, Yukawa, in 1935 said, you know what, we're gonna need some
particles to help mediate the force, to bind together protons and
neutrons inside nuclei. And those are gonna be called pions, okay? And sure enough, in 1947,
and again in these cosmic rays coming from outer space,
he saw, well, we saw, pions. All right, so now, we have, that's
called the pi plus and the pi minus. Those are the two pions. And a few years later, in an accelerator, the first particle produced
in an accelerator for the first time, in 1950,
we saw a neutral version of the pion. About the same mass,
but no electric charge. And then, as I said, Dirac, just like he had predicted the positron,
he predicted the anti-proton. And in 1955, we managed to see that, okay? Again, in cosmic rays. And so here,
let me get rid of all those circles and arrows and just put a chart up here. So there's now three
basic types of particles. There are light particles,
those are called leptons, that means light particles. And heavy particles, those are called
baryons, which means heavy particles. And there are particles of middling mass,
those are called mesons, which means middle, middling. So now, we have all of these
fundamental particles. And hence, we start to get more. Actually, you should think of
the negative pion as the antiparticle of the positive pion. And the neutral one is
it's own antiparticle. Well, it kept getting worse and worse. In 1947 to 1950, we found four new mesons called the K plus,
the K zero, the K minus. And the anti-particle of the K
zero called the K zero bar. The plus means it's positively charged,
the minus negatively charged, and the zero uncharged. And another baryon, another heavy
particle, called the lambda zero. And these were strange in that they
decayed more slowly than we expected to. So we named the property
called strangeness, which explained why they were strange. >> [LAUGH]
>> And It kept going. In 1951 through 1954, in Chicago, Enrico Fermi,
the famous Italian-American physicist, another Nobel Prize winner,
he made four new baryons, the deltas. And then in 1952, in cosmic rays,
we saw three more. And then, in 1959, the final one of these
what are called cascade particles, so four new baryons. And in 1930,
Pauli predicted that the electron should have a partner called the neutrino that
would be neutral and very hard to see. And it was. But in 1956, Cowan and
Reines, at a nuclear reactor, managed to detect neutrinos. That was in 1956. Reines, they of course
won the Nobel prize. Well, Reines did, much,
much later in 19 1995, I believe. >> Go read the plaque. >> And you can go read
the plaque out there, right? Because he was chair of the Physics
department here from 1959 to 1966, okay? And he won his Nobel Prize in 1995. Okay, so you notice that there we're
getting a lot of new particles. In 1962, Leon Lederman noticed that there were
actually two different types of neutrinos, these incredibly hard to find particles
that we can only see in nuclear reactors. There is one called the muon neutrino,
that's what we named it. And so really an awful lot
of different particles. And yeah,
1960-61 we added some more mesons. So this is kind of a lot
of particles to have. Remember, we had this nice picture of
electrons, protons, and neutrons and now we have this whole mess. And it really only gets worse. Because here are the leptons,
there are six of them now. Actually by that point, we actually
didn't know about the tau minus, another copy of the lepton. We would have learned about that later. This doesn't look so bad,
these four leptons and their anti-leptons. But here is the list of all the mesons and
baryons that we know about. It doesn't look a whole
lot simpler than that. It looks worse than the periodic
table because it's just a list and not even organized. And it almost looks as bad
as that chart of the nuclei. Again, since this is just a list,
it's probably even worse So as Enrico Fermi, who's already come up,
says to Leon Lederman, young man, if I could remember the names of these
particles, I would have been a botanist. >> [LAUGH]
>> So it was a mess again. And I imagine it was a very disturbing
time to be a particle physicist, because the point of being a particle
physicist was to investigate the fundamental particles of nature,
the fundamental forces between them. And here you have this absolute zoo, with
no relationship between these particles. Every week, someone discovers another one. And you just add it to your list. And it was really fundamentally
this fellow, Murray Gell-Mann, an American physicist,
who won his Nobel Prize in 1969 for the work I'm gonna describe along
with a bunch of other people, but it was really primarily him. Here are some of the others. Unfortunately, they're coming off
the bottom of the screen, but Kazuhiko Nishijima,
who was a Japanese physicist. Yuval Ne'Eman, an Israeli physicist,
and his fellow, George Zweig,
who now works somewhere on Wall Street. So Gell-Man had the revolutionary idea that all of those mesons and
baryons aren't fundamental particles. It's not really that revolutionary
if you think going back to that what we have learned from history
about the periodic table and nucleo atoms and nucleo nuclides. When you end up with a lot of stuff,
maybe they aren't really fundamental. Maybe they're made of things. And so his idea was that these baryons,
neutrons and protons and all those others, and those mesons, the
pions and all those others, are composite. In other words,
they're made of more fundamental things. [COUGH] So this is the model he built
of a baryon, like a neutron or proton. He said there are three quarks. Why quarks? Well, because he was
reading Finnegans Wake, and there's a line in Finnegan's Wake,
three quarks for Mr. March, and he liked that because he liked the sound
of it, he said, and he liked the number. It had the number three, and
he needed three of them so he decided to name them quarks. And there are many, many stories
told about this fellow, Marigo Man, none of which I'll tell on camera, but
I'm happy to tell some of them afterwards. But it's very much in keeping
this personality to go off and name something for
a line from Finnegans Wake. So three quarks, he said, and they're going to have spin
just like electrons to do. And so for example,
if we put three of them together, if two of them are spinning one way and
the other the opposite way, that will add up to give the spin
of a baryon like the proton. We're gonna give them some charge, and we can give them a charge in such a way
that we're gonna get protons and neutrons. How do we do that? Well, [COUGH] we'll say our ordinary
baryons, the proton and neutron, are gonna be made of two what are called
flavors of quark, up and down. That's just the names he gave them. A proton is gonna be made up of
two up quarks and one down quark. And if we let up quarks have charge
plus two-thirds and down quarks have charge minus a third, then two-thirds
plus two-thirds is four-thirds and four-thirds minus one-third is
three-thirds, and three-thirds is one. So protons have charge one. And a neutron is gonna be made of
an up quark and two down quarks. And so that's two-thirds minus a third
minus a third, and that's zero, and now we know why protons are charge
one and neutrons are charge zero. Now that doesn't sound so remarkable. But remember he had to explain not
just the proton and the neutron, but all of those other baryons and
all of those mesons. And his explanation for
mesons is pretty simple. A meson, like a pion, those are made
of a quark and an anti-quark. So here is a picture of a positive pion. It's just an up quark bound
to an anti-down quark. So that's two-thirds and
a down quirk is minus a third. So an anti-down is plus a third. And two-thirds plus one-third is one. That's a positive pion. And a negative pion is an anti-up
quark plus a down quirk and that's minus two-thirds minus one-third,
and it's minus one. And so he can now build baryons,
like protons and neutrons, and mesons like pions,
out of his quarks and anti-quarks. And remember, there was a neutral pion. Well, that's, say, an up quark, and
an anti-up quark and those add up to zero. Or a down quark and an anti-down quark,
and those also add up to zero. And it turns out that the neutral pion is
kind of a mixture of those two things. And in fact,
he could explain all the baryons, well, he had to add a third flavor of quark. And here's where that
strangeness comes in. He called it the strange quark. And once he had done that, he could make
all the baryons and mesons that we saw. So our new list of fundamental
particles is once again much shorter. Here they are, the electron and
its neutrino, the muon and its neutrino, and three types of quarks. That's not too bad, that's seven. And then of course there
are anti-particles. But still, that's relatively tiny. It's much better than that huge
list that we came up with. Well, things don't stay simple. It was quickly realized that you actually
couldn't just have that strange quark, you needed another quark. This was noticed by three folks named
Glashowm Iliopoulos, and Maiani. They invented something called
the GIM mechanism for their names, and in 1970 they said, you're gonna go
out and you're gonna find another quark. We're gonna call it charm. And that was discovered in 1974 by
Burt Richter and Sam King at Stanford and at Brookhaven. And guess what? They won the Nobel Prize. And then some other folks said, well,
you actually need more quarks here. You're gonna need a bottom quark. And indeed,
the bottom quark was predicted in 1973, and discovered in 1977. And then people said, well,
you're also gonna find some more of these. Another copy of the electron that's
even more massive than the muon, and it's neutrino, and
those were discovered in the mid 1970s. Remember what we learned about
there being left and right? So really,
each of those quarks is not one quark, but two different, one left and
one right-handed. And each of those electron, muon and tau, there's actually a left-handed and
a right-handed one. And then this fellow by
the name of Yoichiro Nambu, who I'm particularly proud of,
he's actually my grandfather. Not my real biological grandfather. My intellectual grandfather. He's the advisor of my advisor. He pointed out that we were actually
gonna need to take those quarks, and we're gonna have to make three
different colors of each one. But let's ignore that for a while. We're gonna talk about that next week. This really is the list of fundamental particles that make up
all sorts of matter. The matter in this room is made only
of these four, and the two electrons. All of this stuff exists only in
accelerators and out in space. So everything that we know and love is made on this side,
not including the neutrino. Neutrinos kind of wiz through stuff. And they're held together by these 12 particles that we're
gonna focus on next week. And by the last particle out of the zoo of
34 fundamental particles of the standard model that we have yet to find. But of which there are finally
after decades of looking, hints called the Higgs. So, where did we start? We started at the periodic
table as this great organizing principle derived from chemical
knowledge that Mendeleev had. And we saw that the world got much, much
messier before it got much, much neater. But it didn't stay neat,
it got messy again, and we have this terrible list in
the 1960s of things that we really had no understanding,
just lists and lists of particles. And we've now managed to reduce it
to at least a manageable number, 34 particles of the standard model. Now you might be wondering, and this is
what we'll talk about in the last week, does this suggest that there is
more fundamental understanding? That we're ready one more time for
a revolution in which we understand all of these particles to be
different aspects of the same thing. Composites or
some other relationship to each other. But that has to wait for
two weeks from now. Next week, this fellow,
Cyrus Taylor is gonna tell us about the standard model, the fundamental
forces and the origins of mass. And you'll have to wait for two weeks for
physics beyond the standard model. Thank you. >> [APPLAUSE]
