Harry Cliff: Particle Physics and the Large Hadron Collider
嘉宾：Harry Cliff
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本篇目录13 章节
§01Transcript · 00:00–07:59§02Transcript · 08:00–15:47§03Transcript · 15:49–23:12§04Transcript · 23:13–30:27§05Transcript · 30:28–37:52§06Transcript · 37:55–46:03§07Transcript · 46:05–53:15§08Transcript · 53:18–1:01:10§09Transcript · 1:01:11–1:08:30§10Transcript · 1:08:33–1:16:00§11Transcript · 1:16:02–1:23:12§12Transcript · 1:23:16–1:30:26§13Transcript · 1:30:27–1:38:13§01Transcript · 00:00–07:59
The following is a conversation with Harry Cliff,
a particle physicist at the University of Cambridge,
working on the Large Hadron Collider Beauty Experiment
that specializes in investigating the slight differences
between matter and antimatter by studying a type
of particle called the beauty quark or b quark.
In this way, he's part of the group of physicists
who are searching for the evidence of new particles
that can answer some of the biggest questions
in modern physics.
He's also an exceptional communicator of science
with some of the clearest and most captivating explanations
of basic concepts in particle physicists
that I've ever heard.
So when I visited London, I knew I had to talk to him.
And we did this conversation
at the Royal Institute Lecture Theater,
which has hosted lectures for over two centuries
from some of the greatest scientists
and science communicators in history,
from Michael Faraday to Carl Sagan.
This conversation was recorded
before the outbreak of the pandemic.
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And now, here's my conversation with Harry Cliff.
Let's start with probably one of the coolest things
that human beings have ever created,
the Large Hadron Collider, LHC.
What is it?
How does it work?
- Okay, so it's essentially this gigantic 27 kilometer
circumference particle accelerator.
It's this big ring.
It's buried about a hundred meters underneath the surface
in the countryside just outside Geneva in Switzerland.
And really what it's for ultimately
is to try to understand what are the basic building blocks
of the universe.
So you can think of it in a way
as like a gigantic microscope
and the analogy is actually fairly precise.
So-
- Gigantic microscope.
- Effectively, except it's a microscope
that looks at the structure of the vacuum.
- In order for this kind of thing to study particles,
which are the microscopic entities,
it has to be huge.
- Yes.
- It's a gigantic microscope.
What do you mean by studying vacuum?
- Okay, so I mean, so particle physics as a field
is kind of badly named in a way
because particles are not the fundamental ingredients
of the universe.
They're not fundamental at all.
So the things that we believe
are the real building blocks of the universe
are objects, invisible fluid-like objects
called quantum fields.
So these are fields like the magnetic field
around a magnet that exists everywhere in space.
They're always there.
In fact, actually, it's funny
that we're in the wrong institution
'cause this is where the idea of the field
was effectively invented by Michael Faraday
doing experiments with magnets and coils of wire.
So he noticed that,
if he was very famous experiment that he did
where he got a magnet and put it on top of it,
a piece of paper and then sprinkled iron filings.
And he found the iron filings arranged themselves
into these kind of loops,
which was actually mapping out
the invisible influence of this magnetic field,
which is the thing,
we've all experienced, we've all felt held a magnet
or two poles of magnet and pushing together
and felt this thing, this force pushing back.
So these are real physical objects.
And the way we think of particles in modern physics
is that they are essentially little vibrations,
little ripples in these otherwise invisible fields
that are everywhere.
They fill the whole universe.
- You know, I don't, I apologize,
perhaps for the ridiculous question.
Are you comfortable with the idea
of the fundamental nature of our reality being fields?
'Cause to me particles,
you know, a bunch of different building blocks
makes more sense sort of intellectually,
sort of visually, like it seems to,
I seem to be able to visualize that kind of idea easier.
- Yeah. - Are you comfortable
psychologically with the idea
that the basic building block is not a block, but a field?
- I think it's, I think it's quite a magical idea.
I find it quite appealing and it's,
well, it comes from a misunderstanding
of what particles are.
So like when you, when we do science at school
and we draw a picture of an atom,
you draw like, you know, a nucleus
with some protons and neutrons,
these little spheres in the middle,
and then you have some electrons
that are like little flies flying around the atom.
And that is a completely misleading picture
of what an atom is like.
It's nothing like that.
The electron is not like a little planet orbiting the atom.
It's this spread out, wibbly wobbly wave-like thing.
And we know we've known that since, you know,
the early 20th century, thanks to quantum mechanics.
So when we, we carry on using this word particle
because sometimes when we do experiments,
particles do behave like they're little marbles
or little bullets, you know?
So in the LHC, when we collide particles together,
you'll get, you know, you'll get like hundreds of particles
will fly out through the detector
and they all take a trajectory
and you can see from the detector where they've gone
and they look like they're little bullets.
So they behave that way, you know, a lot of the time.
But when you really study them carefully,
you'll see that they are not little spheres.
They are these ethereal disturbances
in these underlying fields.
So this is really how we think nature is,
which is surprising, but also I think kind of magic.
So, you know, we are, our bodies are basically made up of
like little knots of energy in these invisible objects
that are all around us.
§02Transcript · 08:00–15:47
- And what is the story of the vacuum when it comes to LHC?
So why did you mention the word vacuum?
- Okay, so if we just, if we go back to like
the physics we do know, so atoms are made of electrons,
which were discovered a hundred or so years ago.
And then in the nucleus of the atom,
you have two other types of particles.
There's an up, something called an up quark
and a down quark.
And those three particles make up every atom
in the universe.
So we think of these as ripples in fields.
So there is something called the electron field
and every electron in the universe is a ripple
moving about in this electron field.
So the electron field is all around us, we can't see it,
but every electron in our body is a little ripple
in this thing that's there all the time.
And the quark field is the same.
So there's an up quark field and an up quark
is a little ripple in the up quark field
and the down quark is a little ripple in something else
called the down quark field.
So these fields are always there.
Now there are potentially, we know about a certain number
of fields in what we call the standard model
of particle physics.
And the most recent one we discovered was the Higgs field.
And the way we discovered the Higgs field
was to make a little ripple in it.
So what the LHC did, it fired two protons into each other
very, very hard with enough energy that you could create
a disturbance in this Higgs field.
And that's what shows up as what we call the Higgs boson.
So this particle that everyone was going on about
eight or so years ago is proof really,
the particle in itself is, I mean, it's interesting,
but the thing that's really interesting is the field
because it's the Higgs field that we believe
is the reason that electrons and quarks have mass.
And it's that invisible field that's always there
that gives mass to the particles.
The Higgs boson is just our way of checking
it's there basically.
- So the Large Hadron Collider,
in order to get that ripple in the Higgs field,
it requires a huge amount of energy, I suppose.
And so that's why you need this huge,
that's why size matters here.
So maybe there's a million questions here,
but let's backtrack.
Why does size matter in the context of a particle?
Of a particle collider.
So why does bigger allow you for higher energy collisions?
- Right, so the reason, well, it's kind of simple really,
which is that there are two types of particle accelerator
that you can build.
One is circular, which is like the LHC,
the other is a great long line.
So the advantage of a circular machine
is that you can send particles around a ring
and you can give them a kick every time they go around.
So imagine you have a, there's actually a bit of the LHC
that's about only 30 meters long,
where you have a bunch of metal boxes,
which have oscillating 2 million volt
electric fields inside them,
which are timed so that when a proton
goes through one of these boxes,
the field it sees as it approaches is attractive.
And then as it leaves the box, it flips and becomes repulsive
and the proton gets attracted and kicked out the other side.
So it gets a bit faster.
So you send it, but then you send it back around again.
- And it's incredible, like the timing of that,
the synchronization, wait, really?
- Yeah, yeah, yeah.
- I think there's going to be a multiplicative effect
on the questions I have.
Okay, let me just take that tangent for a second.
The orchestration of that,
is that a fundamentally a hardware problem
or a software problem?
Like what, how do you get that?
- I mean, I should first of all say, I'm not an engineer.
So the guys, I did not build the LHC.
So there are people much, much better at this stuff
than I could. - For sure, but maybe.
But from your sort of intuition,
from the echoes of what you understand,
what you heard of how it's designed, what's your sense?
What's the engineering aspects of it?
- The acceleration bit is not challenging.
Okay, I mean, okay, there is always challenges
with everything, but basically you have these,
the beams that go around the LHC,
the beams of particles are divided into little bunches.
So they're called, they're a bit like swarms of bees,
if you like.
And there are around, I think it's something of the order
of 2000 bunches spaced around the ring.
And they, if you're at a given point on the ring,
counting bunches, you get 40 million bunches
passing you every second.
So they come in like, you know,
like cars going past in a very fast motorway.
So you need to have, if you're electric fields
that you're using to accelerate the particles,
that needs to be timed so that as a bunch of protons arrives,
it's got the right sign to attract them
and then flips at the right moment.
But I think the voltage in those boxes
oscillates at hundreds of megahertz.
So the beams are like 40 megahertz,
but it's oscillating much more quickly than the beam.
So I think, you know, it's difficult engineering,
but in principle, it's not, you know,
a really serious challenge.
The bigger problem.
- There's probably engineers like screaming at you right now.
- Probably.
- Yeah.
- Well, I mean, okay.
So in terms of coming back to this thing,
why is it so big?
Well, the reason is you want to get the particles
through that accelerating element over and over again.
So you want to bring them back round.
That's why it's round.
The question is why couldn't you make it smaller?
Well, the basic answer is that these particles
are going unbelievably quickly.
So they travel at 99.9999991% of the speed of light
in the LHC.
And if you think about say driving your car
round a corner at high speed,
if you go fast, you need a lot of friction in the tires
to make sure you don't slide off the road.
So the limiting factor is how powerful a magnet can you make
'cause it's what we do is magnets are used
to bend the particles around the ring.
And essentially the LHC when it was designed
was designed with the most powerful magnets
that could conceivably be built at the time.
And so that's your kind of limiting factor.
So if you want to make the machines smaller,
that means a tighter bend,
you need to have a more powerful magnet.
So it's this toss up between how strong are your magnets
versus how big a tunnel can you afford.
The bigger the tunnel, the weaker the magnets can be.
The smaller the tunnel, the stronger they've got to be.
- Okay, so maybe can we backtrack to the standard model
and say what kind of particles there are period
and maybe the history of kind of assembling
that the standard model of physics
and then how that leads up to the hopes and dreams
and the accomplishments of the Large Hadron Collider.
- Yeah, sure, okay.
So all of 20th century physics in like five minutes.
- Yeah, please.
- Okay, so, okay, the story really begins properly
end of the 19th century,
the basic view of matter is that matter is made of atoms
and the atoms are indestructible, immutable little spheres,
like the things we were talking about
that don't really exist.
And there's one atom for every chemical element.
So there's an atom for hydrogen, for helium,
for carbon, for iron, et cetera, and they're all different.
Then in 1897, experiments done
at the Cavendish Laboratory in Cambridge,
which is where I'm still, where I'm based,
showed that there are actually smaller particles
inside the atom, which eventually became known as electrons.
These are these negatively charged things
that go around the outside.
A few years later, Ernest Rutherford,
very famous nuclear physicist,
one of the pioneers of nuclear physics,
shows that the atom has a tiny nugget in the center,
which we call the nucleus,
which is a positively charged object.
So then by like 1910, '11,
we have this model of the atom that we learn in school,
which is you've got a nucleus, electrons go around it.
Fast forward, you know, a few years,
the nucleus, people start doing experiments
with radioactivity where they use alpha particles
that are spat out of radioactive elements as bullets.
And they fire them at other atoms.
And by banging things into each other,
they see that they can knock bits out of the nucleus.
So these things come out called protons, first of all,
which are positively charged particles,
about 2000 times heavier than the electron.
And then 10 years later, more or less,
a neutral particle is discovered called the neutron.
So those are the three basic building blocks of atoms.
You have protons and neutrons in the nucleus
§03Transcript · 15:49–23:12
that are stuck together by something
called the strong force, the strong nuclear force.
You have electrons in orbit around that
held in by the electromagnetic force,
which is one of the forces of nature.
That's sort of where we get to by like 1932, more or less.
Then what happens is physics is nice and neat.
In 1932, everything looks great.
Got three particles and all the atoms are made of,
that's fine.
But then cloud chamber experiments.
So these are devices that can be used to,
the first device is capable of imaging subatomic particles.
So you can see their tracks
and they're used to study cosmic rays,
particles that come from out of space
and bang into the atmosphere.
And in these experiments,
people start to see a whole lot of new particles.
So they discover for one thing, antimatter,
which is the sort of a mirror image of the particles.
So we discover that there's also,
as well as a negatively charged electron,
there's something called a positron,
which is a positively charged version of the electron.
And there's an antiproton, which is negatively charged.
And then a whole load of other weird particles
start to get discovered
and no one really knows what they are.
This is known as the zoo of particles.
- Are these discoveries
some of the first theoretical discoveries
or are they discoveries in an experiment?
So like, yeah, what's the process of discovery
for these early sets of particles?
- It's a mixture.
I mean, the early stuff around the atom
is really experimentally driven.
It's not based on some theory.
It's exploration in the lab using equipment.
So it's really people just figuring out,
getting hands on with the phenomena,
figuring out what these things are.
And the theory comes a bit later.
That's not always the case.
So in the discovery of the anti-electron, the positron,
that was predicted from quantum mechanics and relativity
by a very clever theoretical physicist called Paul Dirac,
who was probably the second brightest physicist
of the 20th century apart from Einstein,
but isn't anywhere near as well known.
So he predicted the existence of the anti-electron
from basically a combination of the theories
of quantum mechanics and relativity.
And it was discovered about a year
after he made the prediction.
- What happens when an electron meets a positron?
- They annihilate each other.
So when you bring a particle and its antiparticle together,
they react, they just wipe each other out
and their mass is turned into energy,
usually in the form of photons.
So you get light produced.
- So when you have that kind of situation,
why does the universe exist at all
if there's matter in any matter?
- Oh God, now we're getting into the really big questions.
So, depends if you wanna go there now.
- Yeah, maybe let's go there later.
- 'Cause I mean, that is a very big question.
- Yeah, let's take it slow with the standard model.
So, okay, so there's matter and antimatter in the 30s.
So what else?
- So matter, antimatter, and then a load of new particles
start turning up in these cosmic ray experiments,
first of all.
And they don't seem to be particles that make up atoms.
They're something else.
They all mostly interact with a strong nuclear force.
So they're a bit like protons and neutrons.
And by in the 1960s, in America particularly,
but also in Europe and Russia,
scientists started to build particle accelerators.
So these are the forerunners of the LHC.
So big ring-shaped machines that were, you know,
hundreds of meters long,
which in those days was enormous.
You never, you know, most physics up until that point
had been done in labs, in universities, you know,
with small bits of kit.
So this is a big change.
And when these accelerators are built,
they start to find they can produce
even more of these particles.
So I don't know the exact numbers, but by around 1960,
there are of order 100 of these things
that have been discovered.
And physicists are kind of tearing their hair out
because physics is all about simplification.
And suddenly what was simple has become messy
and complicated and everyone sort of wants to understand
what's going on.
- As a quick kind of aside,
and probably a really dumb question,
but how is it possible to take something like a photon
or electron and be able to control it enough,
like to be able to do a controlled experiment
where you collide it against something else?
- Yeah.
- Is that, that seems like an exceptionally difficult
engineering challenge, 'cause you mentioned vacuum too.
So you basically want to remove every other distraction
and really focus on this collision.
How difficult of an engineering challenge is that,
just to get a sense?
- It is very hard.
I mean, in the early days,
particularly when the first accelerators are being built
in like 1932, Ernest Lawrence builds the first,
what we call a cyclotron,
which is like a little accelerator, this big or so.
There's another one. - Literally that big?
- This tiny little thing, yeah.
I mean, so most of the first accelerators
were what we call fixed target experiments.
So you had a ring,
you accelerate particles around the ring
and then you fire them out the side into some target.
So that makes the kind of,
the colliding bit is relatively straightforward
'cause you just fire it,
whatever it is you want to fire it at.
The hard bit is the steering the beams
with the magnetic fields,
getting strong enough electric fields to accelerate them,
all that kind of stuff.
The first colliders where you have two beams
colliding head on, that comes later.
And I don't think it's done until maybe the 1980s.
I'm not entirely sure, but it takes,
it's a much harder problem.
- That's crazy 'cause you have to like perfectly
get them to hit each other.
I mean, we're talking about, I mean, what scale,
what's the, I mean, the temporal thing is a giant mess,
but the spatially, like the size, it's tiny.
- Well, to give you a sense of the LHC beams,
the cross-sectional diameter is,
I think, around a dozen or so microns.
So, you know, 10 millionths of a meter.
- And a beam, sorry, just to clarify,
a beam contains how many,
is it the bunches that you mentioned?
Is it multiple parts or is it just one part?
- Oh, no, no, the bunches contain,
say, a hundred billion protons each.
So a bunch is, it's not really bunch-shaped.
They're actually quite long.
They're like 30 centimeters long,
but thinner than a human hair.
So like very, very narrow, long sort of objects.
Those are the things.
So what happens in the LHC is you steer the beams
so that they cross in the middle of the detector.
So basically you have these swarms of protons
that are flying through each other.
And most of that, you have, sorry,
a hundred billion coming one way,
a hundred billion another way,
maybe 10 of them will hit each other.
- Oh, okay, so this, okay, that makes a lot more sense.
That's nice.
So you're trying to use sort of,
it's like probabilistically, you're not-
- You can't make a single particle
collide with a single other particle.
- Yeah, so- - That's not an efficient way
to do it.
You'd be waiting a very long time to get anything.
- Yeah, so you're basically, right,
so you're relying on probability to be
that some fraction of them are gonna collide.
And then you know which,
'cause it's a swarm of the same kind of particle.
- So it doesn't matter which ones hit each other exactly.
I mean, that's not to say it's not hard.
You've got to, one of the challenges
to make the collisions work
is you have to squash these beams to very, very,
basically the narrower they are, the better,
'cause the higher chances of them colliding.
If you think about two flocks of birds
flying through each other,
the birds are all far apart in the flocks.
There's not much chance that they'll collide.
If they're all flying densely together,
then they're much more likely to collide with each other.
So that's the sort of problem.
And it's tuning those magnetic fields,
getting the magnetic fields powerful enough
§04Transcript · 23:13–30:27
that you squash the beams and focus them
so that you get enough collisions.
- That's super cool.
Do you know how much software is involved here?
I mean, so if I come from the software world
and it's fascinating,
this seems like,
it's the software's buggy and messy.
So you almost don't want to rely on software too much.
Like if you do, it has to be low level,
like Fortran style programming.
Do you know how much software
is in a large Hadron Collider?
- I mean, it depends at which level, a lot.
I mean, the whole thing is obviously computer controlled.
So, I mean, I don't know a huge amount
about how the software for the actual accelerator works,
but I've been in the control center.
So at CERN, there's this big control room,
which is a bit like a NASA mission control
with big banks of desks where the engineers sit
and they monitor the LHC
'cause you obviously can't be in the tunnel
when it's running, so everything's remote.
I mean, one sort of anecdote about the sort of software side
in 2008, when the LHC first switched on,
they had this big launch event
and then, you know, big press conference party
to inaugurate the machine.
And about 10 days after that,
they were doing some tests
and this dramatic event happened
where a huge explosion basically took place in a tunnel
that destroyed or damaged, badly damaged
about half a kilometer of the machine.
But the story is,
the engineers are in the control room that day.
One guy told me this story about, you know,
basically all these screens they have in the control room
started going red.
So all these alarms, like, you know,
kind of in software going off
and then they assumed that there's something wrong
with the software 'cause there's no way
something this catastrophic could have happened.
But I mean, when I worked on,
when I was a PhD student,
one of my jobs was to help to maintain the software
that's used to control the detector that we work on.
And that was, it's relatively robust,
not so, you don't want it to be too fancy.
You don't want it to sort of fall over too easily.
The more clever stuff comes
when you're talking about analyzing the data
and that's where the sort of, you know.
- Are we jumping around too much?
Did we finish with the standard model?
- We didn't, no.
- We didn't.
So have we even started talking about quarks?
- We haven't talked to them yet, no.
We got to the messy zoo of particles.
- Let me, let's go back there if it's okay.
- Okay, that's fine.
- Can you take us to the rest of the history
of physics in the 20th century?
- Okay.
- Sure.
Okay, so circa 1960, you have this,
you have these a hundred or so particles.
It's a bit like the periodic table all over again.
So you've got like having a hundred elements,
sort of a bit like that.
And people start to try to impose some order.
So Murray Gelman,
he's a theoretical physicist American from New York.
He realizes that there are these symmetries
in these particles that if you arrange them
in certain ways, they relate to each other
and he uses these symmetry principles
to predict the existence of particles
that haven't been discovered,
which are then discovered in accelerators.
So this starts to suggest
there's not just random collections of crap.
There's like, you know, actually some order
to this underlying it.
A little bit later in 1960,
again, it's around the 1960s.
He proposes along with another physicist
called George Zweig that these symmetries arise
because just like the patterns in the periodic table arise
because atoms are made of electrons and protons,
that these patterns are due to the fact
that these particles are made of smaller things
and they are called quarks.
So these are the particles that predicted from theory
for a long time, no one really believes they're real.
A lot of people think that they're a kind
of theoretical convenience that happened to fit the data
but there's no evidence.
No one's ever seen a quark in any experiment.
And lots of experiments are done to try to find quarks,
to try to knock a quark out of a...
So the idea, if protons and neutrons are made of quarks,
you should be able to knock a quark out and see the quark.
That never happens.
And we still have never actually managed to do that.
- Wait, really?
- No.
So the way that it's done in the end
is this machine that's built in California
at the Stanford Lab, Stanford Linear Accelerator,
which is essentially a gigantic
three kilometer long electron gun.
It fires electrons almost the speed of light at protons.
And when you do these experiments,
what you find is at very high energy,
the electrons bounce off small hard objects
inside the proton.
So it's a bit like taking an X-ray of the proton.
You're firing these very light, high energy particles
and they're pinging off little things inside the proton
that are like ball bearings, if you like.
So you actually, that way they resolve
that there are three things inside the proton,
which are quarks, the quarks that Gell-Mann
and Zweig had predicted.
So that's really the evidence that convinces people
that these things are real.
The fact that we've never seen one
in an experiment directly,
they're always stuck inside other particles.
And the reason for that is essentially
to do with a strong force.
The strong force is the force that holds quarks together.
And it's so strong, it's impossible
to actually liberate a quark.
So if you try and pull a quark out of a proton,
what actually ends up happening
is that you kind of create this spring-like bond
in the strong force.
You imagine two quarks that are held together
by a very powerful spring.
You pull and pull and pull,
more and more energy gets stored in that bond,
like stretching a spring.
And eventually the tension gets so great,
the spring snaps and the energy in that bond
gets turned into two new quarks
that go on the broken ends.
So you started with two quarks,
you end up with four quarks.
So you never actually get to take a quark out,
you just end up making loads more quarks in the process.
- So how do we, again, forgive the dumb question,
how do we know quarks are real then?
- Well, A, from these experiments where we can scatter,
you fire electrons into the protons,
they can burrow into the proton and knock off,
and they can bounce off these quarks.
So you can see from the angles the electrons come out.
- I see, you can infer.
- You can infer that these things are there.
The quark model can also be used,
it has a lot of success,
so you can use it to predict the existence
of new particles that hadn't been seen.
So, and it basically, there's lots of data
basically showing from, you know,
when we fire protons at each other at the LHC,
a lot of quarks get knocked all over the place,
and every time they try and escape from, say,
one of their protons,
they make a whole jet of quarks that go flying off,
bound up in other sorts of particles made of quarks.
So all the sort of the theoretical predictions
from the basic theory of the strong force and the quarks
all agrees with what we are seeing in experiments.
We've just never seen an actual quark on its own,
because unfortunately it's impossible
to get them out on their own.
- So quarks, these crazy smaller things
that are hard to imagine are real.
So what else?
What else is part of the story here?
- So the other thing that's going on at the time,
around the '60s, is an attempt to understand the forces
that make these particles interact with each other.
So you have the electromagnetic force,
which is the force that was sort of discovered
to some extent in this room, or at least in this building.
So the first, what we call quantum field theory
of the electromagnetic force is developed in the 1940s
and '50s by Feynman, Richard Feynman,
amongst other people, Julian Schwinger, Tomonaga,
who come up with the first, what we call
a quantum field theory of the electromagnetic force.
And this is where this description of,
which I gave you at the beginning,
§05Transcript · 30:28–37:52
that particles are ripples in fields.
Well, in this theory, the photon, the particle of light,
is described as a ripple in this quantum field
called the electromagnetic field.
And the attempt then is made to try,
well, can we come up with a quantum field theory
of the other forces, of the strong force
and the weak, the third force, which we haven't discussed,
which is the weak force, which is a nuclear force.
We don't really experience it in our everyday lives,
but it's responsible for radioactive decay.
It's the force that allows, you know,
in a radioactive atom to turn into a different element,
for example.
- And I don't know if you've explicitly mentioned,
but so there's technically four forces.
- Yes.
- I guess three of them would be in the standard model,
like the weak, the strong, and the electromagnetic,
and then there's gravity.
- And there's gravity, which we don't worry about that,
'cause it's too hard.
- Who cares?
- Maybe we bring that up at the end, but yeah.
Gravity so far, we don't have a quantum theory of,
and if you can solve that problem,
you'll win a Nobel Prize.
- Well, we're gonna have to bring up the graviton
at some point, I'm gonna ask you,
but let's leave that to the side for now.
So those three, okay, Feynman, electromagnetic force,
the quantum field.
- Yeah.
- And where does the weak force come in?
- So yeah, well, first of all,
I mean, the strong force is the easiest.
The strong force is a little bit like
the electromagnetic force.
It's a force that binds things together.
So that's the force that holds quarks together
inside the proton, for example.
So a quantum field theory of that force is discovered
in the, I think it's in the '60s,
and it predicts the existence of new force particles
called gluons.
So gluons are a bit like the photon.
The photon is the particle of electromagnetism.
Gluons are the particles of the strong force.
So there's, just like there's an electromagnetic field,
there's something called a gluon field,
which is also all around us.
- So these, some of these particles, I guess,
are the force carriers or whatever.
They carry the-
- Well, it depends how you wanna think about it.
I mean, really the field, the strong force field,
the gluon field is the thing that binds the quarks together.
The gluons are the little ripples in that field.
So that like, in the same way that the photon
is a ripple in the electromagnetic field.
But the thing that really does the binding is the field.
I mean, you may have heard people talk about things like,
I don't know if you've heard the phrase virtual particle.
So sometimes in some, if you hear people describing
how forces are exchanged between particles,
they quite often talk about the idea that, you know,
if you have an electron and another electron, say,
and they're repelling each other
through the electromagnetic force,
you can think of that as if they're exchanging photons.
So they're kind of firing photons backwards and forwards
between each other and that causes them to repel.
- That photon is then a virtual particle.
- Yes, that's what we call a virtual particle.
In other words, it's not a real thing.
It doesn't actually exist.
So it's an artifact of the way theorists do calculations.
So when they do calculations in quantum field theory,
rather than, no one's discovered a way
of just treating the whole field.
You have to break the field down into simpler things.
So you can basically treat the field
as if it's made up of lots of these virtual photons,
but there's no experiment that you can do
that can detect these particles being exchanged.
What's really happening in reality
is that the electromagnetic field
is warped by the charge of the electron
and that causes the force.
But the way we do calculations involves particles.
So it's a bit confusing,
but it's really a mathematical technique.
It's not something that corresponds to reality.
- I mean, that's part, I guess, of the Feynman diagrams.
- Yes.
- Is this these virtual particles, okay.
- That's right, yeah.
- Some of these have mass, some of them don't.
Is that, what does that even mean, not to have mass?
And maybe you can say,
which one of them have mass and which don't?
- Okay, so--
- And why is mass important or relevant
in this field view of the universe?
- Well, there are actually only two particles
in the standard model that don't have mass,
which are the photon and the gluons.
So they are massless particles,
but the electron, the quarks,
and there are a bunch of other particles
that I haven't discussed.
There's something called a muon and a tau,
which are basically heavy versions of the electron
that are unstable.
You can make them in accelerators,
but they don't form atoms or anything.
They don't exist for long enough.
But all the matter particles, there are 12 of them,
six quarks and six, what we call leptons,
which includes the electron and its two heavy versions
and three neutrinos.
All of them have mass.
And so do, this is the critical bit.
So the weak force,
which is the third of these quantum forces,
which is one of the hardest to understand,
the force particles of that force have very large masses.
And there are three of them.
They're called the W plus, the W minus, and the Z boson.
And they have masses of between 80 and 90 times
that of the protons.
So they're very heavy.
- Wow.
- They're very heavy things.
- So they're what, the heaviest, I guess?
- They're not the heaviest.
The heaviest particle is the top quark,
which has a mass of about 175-ish protons.
So that's really massive.
And we don't know why it's so massive.
But coming back to the weak force,
so the problem in the '60s and '70s was that
the reason that the electromagnetic force
is a force that we can experience in our everyday lives.
So if we have a magnet and a piece of metal,
you can hold it a meter apart if it's powerful enough
and you'll feel a force.
Whereas the weak force only becomes apparent
when you basically have two particles touching
at the scale of a nucleus.
So we get to very short distances
before this force becomes manifest.
It's not, we don't get weak forces going on in this room.
We don't notice them.
And the reason for that is that the particle,
well, the field that transmits the weak force,
the particle that's associated with that field
has a very large mass,
which means that the field dies off very quickly.
So as you, whereas an electric charge,
if you were to look at the shape of the electromagnetic field
it would fall off with this,
you have this thing called the inverse square law,
which is the idea that the force halves
every time you double the distance.
No, sorry, it doesn't half, it quarters
every time you double the distance
between say the two particles.
Whereas the weak force kind of,
you move a little bit away from the nucleus
and it just disappears.
The reason for that is because these fields,
the particles that go with them have a very large mass.
But the problem that theorists faced in the '60s
was that if you tried to introduce massive force fields,
the theory gave you nonsensical answers.
So you'd end up with infinite results
for a lot of the calculations you tried to do.
So the basically, it turned out,
it seemed that quantum field theory was incompatible
with having massive particles.
Not just the force particles actually,
but even the electron was a problem.
So this is where the Higgs
that we sort of alluded to comes in.
And the solution was to say, okay, well,
actually all the particles in the standard model are mass,
they have no mass.
So the quarks, the electron, they don't have a mass.
Neither do these weak particles,
they don't have mass either.
What happens is they actually acquire mass
through another process.
They get it from somewhere else.
They don't actually have it intrinsically.
So this idea that was introduced by,
well, Peter Higgs is the most famous,
but actually there are about six people
that came up with the idea more or less at the same time,
is that you introduce a new quantum field,
§06Transcript · 37:55–46:03
which is another one of these invisible things
that's everywhere.
And it's through the interaction with this field
that particles get mass.
So you can think of, say, an electron in the Higgs field,
it kind of Higgs field kind of bunches around the electron.
It's sort of drawn towards the electron.
And that energy that's stored in that field
around the electron is what we see
as the mass of the electron.
But if you could somehow turn off the Higgs field,
then all the particles in nature would become massless
and fly around at the speed of light.
So this idea of the Higgs field allowed other people,
other theorists to come up with a, well,
it was another, basically a unified theory
of the electromagnetic force and the weak force.
So once you bring in the Higgs field,
you can combine two of the forces into one.
So it turns out the electromagnetic force
and the weak force are just two aspects
of the same fundamental force.
And at the LHC, we go to high enough energies
that you see these two forces unifying effectively.
- So first of all, it started as a theoretical notion,
like this is something, and then,
I mean, wasn't the Higgs called the god particle
at some point?
- It was by a guy trying to sell popular science books, yeah.
- Yeah, but I mean, I remember,
'cause when I was hearing it,
I thought it would, I mean, that would solve a lot of,
that unify a lot of our ideas of physics,
is what was my notion.
But maybe you can speak to that.
Is it as big of a leap?
Is it a god particle, or is it a Jesus particle?
(laughing)
Which, you know, what's the big contribution of Higgs
in terms of this unification power?
- Yeah, I mean, to understand that,
it maybe helps to know the history a little bit.
So when the, what we call electroweak theory
is put together, which is where you unify electromagnetism
with the weak force, and Higgs is involved in all of that.
So that theory, which was written in the mid '70s,
predicted the existence of four new particles,
the W plus boson, the W minus boson,
the Z boson, and the Higgs boson.
So there were these four particles
that came with the theory,
that were predicted by the theory.
In 1983, '84, the Ws and the Z particles were discovered
at an accelerator at CERN,
called the super proton synchrotron,
which was a seven kilometer particle collider.
So three of the bits of this theory had already been found.
So people were pretty confident from the '80s
that the Higgs must exist,
because it was a part of this family of particles
that this theoretical structure only works
if the Higgs is there.
So what then happens,
and so you have this question about why is the LHC
the size it is? - Yes.
- Well, actually the tunnel that the LHC is in
was not built for the LHC.
It was built for a previous accelerator
called the large electron positron collider.
So that began operation in the late '80s, early '90s.
They basically, that's when they dug
the 27 kilometer tunnel.
They put this accelerator into it,
the collider that fires electrons and anti electrons
at each other, electrons and positrons.
So the purpose of that machine was,
well, it was actually to look for the Higgs.
That was one of the things it was trying to do.
It didn't have enough energy to do it in the end.
But the main thing it achieved was it studied
the W and the Z particles at very high precision.
So it made loads of these things.
Previously you could only make a few of them
at the previous accelerator.
So you could study these really, really precisely.
And by studying their properties,
you could really test this electroweak theory
that had been invented in the '70s
and really make sure that it worked.
So actually by 1999, when this machine turned off,
people knew, well, okay, you never know
until you find the thing.
But people were really confident
that this electroweak theory was right.
And that the Higgs almost,
the Higgs or something very like the Higgs had to exist
because otherwise the whole thing doesn't work.
It'd be really weird if you could discover
and these particles, they all behave exactly
as your theory tells you they should.
But somehow this key piece of the picture is not there.
So in a way, it depends how you look at it.
The discovery of the Higgs on its own
is obviously a huge achievement in many,
both experimentally and theoretically.
On the other hand, it's like having a jigsaw puzzle
where every piece has been filled in.
You have this beautiful image, there's one gap
and you kind of know that piece must be there somewhere.
- Yeah. - Right.
So the discovery in itself, although it's important,
is not so interesting.
- It's like a confirmation of the obvious at that point.
- But what makes it interesting
is not that it just completes the standard model,
which is a theory that we've known
had the basic layout of for 40 years or more now.
It's that the Higgs actually is a unique particle.
It's very different to any of the other particles
in the standard model.
And it's a theoretically very troublesome particle.
There are a lot of nasty things to do with the Higgs,
but also opportunities.
So that we basically, we don't really understand
how such an object can exist in the form that it does.
So there are lots of reasons for thinking
that the Higgs must come with a bunch of other particles
or that it's perhaps made of other things.
So it's not a fundamental particle
that it's made of smaller things.
I can talk about that if you like a bit.
- That's still a notion.
So the Higgs might not be a fundamental particle,
that there might be some, oh man.
- So that is an idea.
It's not been demonstrated to be true.
But I mean, all of these ideas basically come
from the fact that this is a problem that motivated
a lot of development in physics in the last 30 years or so.
And it's this basic fact that the Higgs field,
which is this field that's everywhere in the universe,
this is the thing that gives mass to the particles.
And the Higgs field is different
from all the other fields in that,
let's say you take the electromagnetic field,
which is, if we actually were to measure
the electromagnetic field in this room,
we would measure all kinds of stuff going on
'cause there's light, there's gonna be microwaves
and radio waves and stuff.
But let's say we could go to a really, really remote part
of empty space and shield it and put a big box around it
and then measure the electromagnetic field in that box.
The field would be almost zero,
apart from some little quantum fluctuations,
but basically it goes to naught.
The Higgs field has a value everywhere.
So it's a bit like the whole,
it's like the entire space has got this energy
stored in the Higgs field, which is not zero,
it's finite, it's got some,
it's a bit like having the temperature of space raised
to some background temperature.
And it's that energy that gives mass to the particles.
So the reason that electrons and quarks have mass
is through the interaction with this energy
that's stored in the Higgs field.
Now, it turns out that the precise value this energy has
has to be very carefully tuned if you want a universe
where interesting stuff can happen.
So if you push the Higgs field down,
it has a tendency to collapse to,
well, there's a tendency,
if you do your sort of naive calculations,
there are basically two possible likely configurations
for the Higgs field, which is either it's zero everywhere,
in which case you have a universe
which is just particles with no mass that can't form atoms
and just fly about at the speed of light,
or it explodes to an enormous value,
what we call the Planck scale,
which is the scale of quantum gravity.
And at that point, if the Higgs field was that strong,
even an electron would become so massive
that it would collapse into a black hole.
And then you have a universe made of black holes
and nothing like us.
So it seems that the strength of the Higgs field
is to achieve the value that we see
requires what we call fine tuning of the laws of physics.
You have to fiddle around with the other fields
in the standard model and their properties
to just get it to this right sort of Goldilocks value
that allows atoms to exist.
This is deeply fishy.
People really dislike this.
- Well, yeah, I guess, so what would be,
so two explanations.
One, there's a God that designed this perfectly,
and two is there's an infinite number
§07Transcript · 46:05–53:15
of alternate universes, and we just happen
to be in the one in which life is possible.
- Yeah, yeah. - Complexity.
So when you say, I mean, life, any kind of complexity,
that's not either complete chaos or black holes.
- Yeah, yeah.
- I mean, how does that make you feel?
What do you make of that?
That's such a fascinating notion
that this perfectly tuned field
that's the same everywhere is there.
What do you make of that?
Yeah, what do you make of that?
- I mean, yeah, so you laid out
two of the possible explanations.
- Really? - Somewhat.
Yeah, I mean, well, someone,
some cosmic creator went, yeah, let's fix that
to be at the right level.
That's one possibility, I guess.
It's not a scientifically testable one,
but theoretically, I guess it's possible.
- Sorry to interrupt, but there could also be
not a designer, but couldn't there be just,
I guess I'm not sure what that would be,
but some kind of force that,
some kind of mechanism by which
this kind of field is enforced
in order to create complexity,
basically forces that pull the universe
towards an interesting complexity.
- I mean, yeah, I mean, there are people
who have those ideas.
I don't really subscribe to them.
- As I'm saying, it sounds really stupid.
- No, I mean, there are definitely people
that make those kind of arguments.
There's ideas that, I think it's Lee Smolin's idea,
one, I think, that universes are born inside black holes.
And so universes, they basically have
like Darwinian evolution of the universe
where universes give birth to other universes.
And if universes where black holes can form
are more likely to give birth to more universes,
so you end up with universes which have similar laws.
I mean, I don't know, whatever.
- But I talked to Lee recently on this podcast
and he's a reminder to me that the physics community
has like so many interesting characters.
It's fascinating.
Anyway, sorry, so.
- I mean, as an experimentalist,
I tend to sort of think, these are interesting ideas,
but they're not really testable.
So I tend not to think about them very much.
So, I mean, going back to the science of this,
there is an explanation.
There is a possible solution to this problem of the Higgs,
which doesn't involve multiverses
or creators fiddling about with the laws of physics.
If the most popular solution
was something called supersymmetry,
which is a theory which involves
a new type of symmetry of the universe.
In fact, it's one of the last types of symmetries
that is possible to have
that we haven't already seen in nature,
which is a symmetry between force particles
and matter particles.
So what we call fermions,
which are the matter particles
and bosons, which are force particles.
And if you have supersymmetry,
then there is a super partner for every particle
in the standard model.
And without going into the details,
the effect of this basically is that
you have a whole bunch of other fields,
and these fields cancel out
the effect of the standard model fields,
and they stabilize the Higgs field
at a nice sensible value.
So in supersymmetry, you naturally,
without any tinkering about
with the constants of nature or anything,
you get a Higgs field with a nice value,
which is the one we see.
So this is one of the reasons,
and supersymmetry has also got lots
of other things going for it.
It predicts the existence of a dark matter particle,
which would be great.
It potentially suggests that the strong force
and the electroweak force unify at high energy.
So lots of reasons people thought
this was a productive idea.
And when the LHC was, just before it was turned on,
there was a lot of hype, I guess,
a lot of an expectation that we would discover
these super partners, because,
and particularly the main reason was
that if supersymmetry stabilizes the Higgs field
at this nice Goldilocks value,
these super particles should have a mass
around the energy that we're probing at the LHC,
around the energy of the Higgs.
So it was kind of thought, you discover the Higgs,
you probably discover super partners as well.
- So once you start creating ripples in this Higgs field,
you should be able to see these kinds of,
you should be, yeah.
- So these super fields would be there.
When at the very beginning I said
we're probing the vacuum,
what I mean is really that,
okay, let's say these super fields exist.
The vacuum contains super fields,
they're there, these supersymmetric fields.
If we hit them hard enough, we can make them vibrate.
We see super particles come flying out.
That's the sort of, that's the idea.
- That's the whole, okay.
- That's the whole point.
- But we haven't.
- But we haven't.
So, so far at least, I mean, we've had now
a decade of data taking at the LHC.
No signs of super partners,
have supersymmetric particles have been found.
In fact, no signs of any physics,
any new particles beyond the standard model
have been found.
So supersymmetry is not the only thing that can do this.
There are other theories that involve
additional dimensions of space
or potentially involve the Higgs boson
being made of smaller things,
being made of other particles.
- Yeah, that's an interesting,
I haven't heard that before.
That's really, that's an interesting point.
Could you maybe linger on that?
Like what, what could be,
what could the Higgs particle be made of?
- Well, so the oldest,
I think the original ideas about this
was these theories called technicolor,
which were basically like an analogy
with the strong force.
So the idea was the Higgs boson
was a bound state of two
very strongly interacting particles
that were a bit like quarks.
So like quarks, but I guess higher energy things
with a super strong force.
So not the strong force,
but a new force that was very strong.
And the Higgs was a bound state of these, these objects.
And the Higgs would in principle, if that was right,
would be the first in a series of
technicolor particles.
Technicolor, I think, not being a theorist,
but it's not, it's basically not done very well,
particularly since the LHC found the Higgs,
that kind of, it rules out, you know,
a lot of these technicolor theories.
But there are other things
that are a bit like technicolor.
So there's a theory called partial compositeness,
which is an idea that some of my colleagues
at Cambridge have worked on,
which is a similar sort of idea
that the Higgs is a bound state
of some strongly interacting particles.
And that the standard model particles themselves,
the more exotic ones like the top quark
are also sort of mixtures of these composite particles.
So it's a kind of an extension to the standard model,
which explains this problem with the Higgs bosons,
Goldilocks value, but also helps us understand.
We have, we're in a situation now, again,
a bit like the periodic table where we have six quarks,
six leptons in this kind of,
you can arrange in this nice table
and there you can see these columns
where the patterns repeat and you go,
"Okay, maybe there's something deeper going on here."
And so this would potentially be something
this partial compositeness theory could explain,
sort of enlarge this picture
that allows us to see the whole symmetrical pattern
and understand what the ingredients, why do we have,
so one of the big questions in particle physics is,
why are there three copies of the matter particles?
So in what we call the first generation,
which is what we're made of,
there's the electron, the electron neutrino,
the up quark and the down quark,
they're the most common matter particles in the universe,
but then there are copies of these four particles
§08Transcript · 53:18–1:01:10
in the second and the third generations.
So things like muons and top quarks and other stuff,
we don't know why, we see these patterns,
we have no idea where it comes from.
So that's another big question,
can we find out the deeper order
that explains this particular periodic table
of particles that we see?
- Is it possible that the deeper order
includes like almost a single entity?
So like something that I guess like string theory
dreams about, is this essentially the dream?
Is to discover something simple, beautiful and unifying?
- Yeah, I mean, that is the dream.
And I think for some people, for a lot of people,
it still is the dream.
So there's a great book by Steven Weinberg,
who is one of the theoretical physicists
who was instrumental in building the standard model.
So he came up with some others with the electroweak theory,
the theory that unified electromagnetism
and the weak force.
And he wrote this book,
I think it was towards the end of the 80s, early 90s,
called "Dreams of a Final Theory,"
which is a very lovely, quite short book
about this idea of a final unifying theory
that brings everything together.
And I think you get a sense reading his book
written at the end of the 80s, early 90s,
that there was this feeling that such a theory was coming.
And that was the time when string theory
had been, was very exciting.
So string theory, there's been this thing
called the super string revolution
and theoretical physics getting very excited.
They discovered these theoretical objects,
these little vibrating loops of string that in principle,
not only was a quantum theory of gravity,
but could explain all the particles in the standard model
and bring it all together.
And as you say, you have one object, the string,
and you can pluck it and the way it vibrates
gives you these different notes,
each of which is a different particle.
So it's a very lovely idea.
But the problem is that, well, there's a few,
people discover that mathematics is very difficult.
So people have spent three decades or more
trying to understand string theory.
And I think, you know,
if you spoke to most string theorists,
they would probably freely admit
that no one really knows what string theory is yet.
I mean, there's been a lot of work,
but it's not really understood.
And the other problem is that string theory
mostly makes predictions about physics
that occurs at energies far beyond
what we will ever be able to probe in the laboratory.
Yeah, probably ever.
- By the way, so sorry, take a million tangents,
but is there room for complete innovation
of how to build a particle collider
that could give us an order of magnitude increase
in the kind of energies,
or do we need to keep just increasing the size of things?
- I mean, maybe, yeah.
I mean, there are ideas,
to give you a sense of the gulf that has to be bridged.
So the LHC collides particles at an energy
of what we call 14 tera electron volts.
So that's basically the equivalent
of you've accelerated a proton through 14 trillion volts.
That gets us to the energies where the Higgs
and these weak particles live.
They're very massive.
The scale where strings become manifest
is something called the Planck scale,
which I think is of the order 10 to the,
hang on, get this right,
is 10 to the 18 giga electron volts.
So about 10 to the 15 tera electron volts.
So you're talking trillions of times more energy.
- Yeah, 10 to the 15, or 10 to the 14th larger.
- I may be wrong, but it's of that order.
It's a very big number.
So we're not talking just an order
of magnitude increase in energy.
We're talking 14 orders of magnitude energy increase.
So to give you a sense of what that would look like,
were you to build a particle accelerator
with today's technology.
- Bigger or smaller than our solar system.
- As the size of the galaxy.
- The galaxy.
- So you need to put a particle accelerator
that circled the Milky Way to get to the energies
where you would see strings if they exist.
So that is a fundamental problem,
which is that most of the predictions of the unified,
these unified theories, quantum theories of gravity,
only make statements that are testable
at energies that we will not be able to probe.
And barring some unbelievable,
completely unexpected technological
or scientific breakthrough,
which is almost impossible to imagine.
You never say never, but it seems very unlikely.
- Yeah, I can just see the news story.
Elon Musk decides to build a particle collider
the size of our--
- It would have to be, we'd have to get together
with all our galactic neighbors to pay for it, I think.
- What is the exciting possibilities
of the Large Hadron Collider?
What is there to be discovered
in this order of magnitude of scale?
Is there other bigger efforts on the horizon?
In this space, what are the open problems,
exciting possibilities?
You mentioned supersymmetry.
- Yeah, so well, there are lots of new ideas.
Well, there are lots of problems that we're facing.
So there's a problem with the Higgs field,
which supersymmetry was supposed to solve.
There's the fact that 95% of the universe
we know from cosmology, astrophysics is invisible,
that it's made of dark matter and dark energy,
which are really just words for things
that we don't know what they are.
It's what Donald Rumsfeld called a known unknown.
So we know we don't know what they are.
- Well, that's better than unknown unknown.
- Yeah, well, there may be some unknown unknowns,
but by definition, we don't know what those are.
So yeah.
- But the hope is a particle accelerator
could help us make sense of dark energy, dark matter.
There's still some hope for that?
- There's hope for that, yeah.
So one of the hopes is the LHC could produce
a dark matter particle in its collisions.
And it may be that the LHC will still discover new particles,
that supersymmetry could still be there.
It's just maybe more difficult to find
than we thought originally.
And dark matter particles might be being produced,
but we're just not looking
in the right part of the data for them.
That's possible.
It might be that we need more data,
that these processes are very rare
and we need to collect lots and lots of data
before we see them.
But I think a lot of people would say now
that the chances of the LHC
directly discovering new particles
in the near future is quite slim.
It may be that we need a decade more data
before we can see something, or we may not see anything.
That's where we are.
So I mean, the physics, the experiments that I work on,
so I work on a detector called LHCb,
which is one of these four big detectors
that are spaced around the ring.
And we do slightly different stuff to the big guys.
There's two big experiments called Atlas and CMS,
3,000 physicists and scientists
and computer scientists on them each.
They are the ones that discovered the Higgs
and they look for supersymmetry in dark matter and so on.
What we look at are standard model particles
called bquarks, which depending on your preferences,
either bottom or beauty, we tend to say beauty
'cause it sounds sexier.
- Yeah, for sure.
- But these particles are interesting
because we can make lots of them.
We make billions or hundreds of billions of these things.
You can therefore measure their properties very precisely.
So you can make these really lovely precision measurements.
And what we are doing really is a sort of complimentary thing
to the other big experiments, which is,
if you think of the sort of analogy they often use is,
if you imagine you're in the jungle
and you're looking for an elephant, say,
and you are a hunter and you're kind of like,
let's say there's the elephant's very rare,
you don't know where in the jungle, the jungle's big.
So there's two ways you go about this.
Either you can go wandering around the jungle
and try and find the elephant.
The problem is if there's only one elephant
and the jungle's big,
the chances of running into it are very small.
Or you could look on the ground
and see if you see footprints left by the elephant.
And if the elephant's moving around,
you've got a chance,
§09Transcript · 1:01:11–1:08:30
you've got a chance maybe of seeing the elephant's footprints
if you see the footprints, you go, okay, there's an elephant.
I maybe don't know what kind of elephant it is,
but I got a sense there's something out there.
So that's sort of what we do.
We are the footprint people.
We are, we're looking for the footprints,
the impressions that quantum fields
that we haven't managed to directly create the particle of,
the effects these quantum fields have
on the ordinary standard model fields
that we already know about.
So these B particles,
the way they behave can be influenced by the presence
of say super fields or dark matter fields
or whatever you like.
And the way they decay and behave can be altered slightly
from what our theory tells us they ought to behave.
- Gotcha.
And it's easier to collect huge amounts of data
on B quarks.
- We get billions and billions of these things.
You can make very precise measurements.
And the only place really at the LHC
or in really in high energy physics at the moment
where there's fairly compelling evidence
that there might be something beyond the standard model
is in these B, these beauty quarks decays.
- Just to clarify,
which is the difference between the different,
the four experiments, for example, that you mentioned,
is it the kind of particles that are being collided?
Is it the energies of which they're collided?
What's the fundamental difference
between the different experiments?
- The collisions are the same.
What's different is the design of the detectors.
So Atlas and CMS are called,
they're called what are called general purpose detectors.
And they are basically barrel shaped machines.
And the collisions happen in the middle of the barrel.
And the barrel captures all the particles
that go flying out in every direction.
So in a sphere effectively, they come flying out
and it can record all of those particles.
And-
- What's the, sorry to be interrupting,
but what's the mechanism of the recording?
- Oh, so these detectors,
if you've seen pictures of them, they're huge.
Like Atlas is 25 meters high and 45 meters long.
They're vast machines,
instruments, I guess you should call them really.
They are, they're kind of like onions.
So they have layers, concentric layers of detectors,
different sorts of detectors.
So close into the beam pipe,
you have what are called usually made of silicon,
they're tracking detectors.
So they're little, made of strips of silicon
or pixels of silicon.
And when a particle goes through the silicon,
it gives a little electrical signal
and you get these dots, you know,
electrical dots through your detector,
which allows you to reconstruct
the trajectory of the particle.
So that's the middle.
And then the outsides of these detectors,
you have things called calorimeters,
which measure the energies of the particles.
And then very edge,
you have things called muon chambers,
which basically these muon particles,
which are the heavy version of the electron,
they are like high velocity bullets
and they can get right to the edge of the detectors.
If you see something at the edge, that's a muon.
So that's broadly how they work.
- And all of that is being recorded.
- That's all being fed out to, you know, computers.
- Data must be awesome.
Okay.
- So LHCb is different.
So we, because we're looking for these b-quarks,
b-quarks tend to be produced along the beam line.
So in a collision,
the b-quark tend to fly sort of close to the beam pipe.
So we built a detector that sort of pyramid,
cone shaped basically, that just looks in one direction.
So we ignore, if you have your collision,
stuff goes everywhere.
We ignore all the stuff over here and going off sideways.
We're just looking in this little region
close to the beam pipe
where most of these b-quarks are made.
So.
- Is there a different aspect of the sensors involved
in the collection of the b-quark trajectories?
- There are some differences.
So one of the differences is that
one of the ways you know you've seen a b-quark
is that b-quarks are actually quite long lived
by particle standards.
So they live for 1.5 trillionths of a second,
which is if you're a fundamental particle
is a very long time.
'Cause you know, the Higgs boson,
I think lives for about a trillionth of a trillionth
of a second, or maybe even less than that.
So these are quite long lived things
and they will actually fly a little distance
before they decay.
So they will fly, you know, a few centimeters,
maybe if you're lucky, then they'll decay into other stuff.
So what we need to do in the middle of the detector,
you wanna be able to see,
you have your place where the protons crash into each other
and that produces loads of particles that come flying out.
So you have loads of lines,
loads of tracks that point back to that proton collision.
And then you're looking for a couple of other tracks,
maybe two or three that point back to a different place
that's maybe a few centimeters away
from the proton collision.
And that's the sign that little b particle
has flown a few centimeters and decayed somewhere else.
So we need to be able to very accurately resolve
the proton collision from the b particle decay.
So we are, the middle of our detector is very sensitive
and it gets very close to the collision.
So you have this really beautiful, delicate silicon detector
that sits, I think it's seven mil millimeters from the beam.
And the LHC beam has as much energy as a jumbo jet
at takeoff.
So it's enough to melt a ton of copper.
So you have this furiously powerful thing sitting next
to this tiny, delicate, you know, silicon sensor.
So those aspects of our detector that are specialized
to measure these particular b quarks
that we're interested in.
- And is there, I mean, I remember seeing somewhere
that there's some mention of matter and antimatter
connected to the b, these beautiful quarks.
Is that, what's the connection?
Yeah, what's the connection there?
- Yeah, so there is a connection,
which is that when you produce these b particles,
these particles, 'cause you don't see the b quark,
you see the thing that b quark is inside.
So they're bound up inside what we call beauty particles,
where the b quark is joined together with another quark
or two, maybe two other quarks, depending on what it is.
There are a particular set of these b particles
that exhibit this property called oscillation.
So if you make a, for the sake of argument,
a matter version of one of these b particles,
as it travels, because of the magic of quantum mechanics,
it oscillates backwards and forwards
between its matter and antimatter versions.
So it does this weird flipping about backwards and forwards.
And what we can use this for is a laboratory
for testing the symmetry between matter and antimatter.
So if the symmetry between antimatter is precise,
it's exact, then we should see these b particles decaying
as often as matter as they do as antimatter,
'cause this oscillation should be even.
It should spend as much time in each state.
But what we actually see is that one of the states
it spends more time in,
it's more likely to decay in one state than the other.
So this gives us a way of testing this fundamental symmetry
between matter and antimatter.
- So what can you, sort of returning to the question
we were before about this fundamental symmetry,
it seems like if there's perfect symmetry
between matter and antimatter,
if we have the equal amount of each in our universe,
it would just destroy itself.
And just like you mentioned,
we seem to live in a very unlikely universe
where it doesn't destroy itself.
So do you have some intuition about why that is?
- I mean, well, I'm not a theorist.
I don't have any particular ideas myself.
I mean, I sort of do measurements
to try and test these things.
But I mean, so in terms of the basic problem
is that in the Big Bang,
if you use the standard model
to figure out what ought to have happened,
you should have got equal amounts of matter
and antimatter made.
'Cause whenever you make a particle,
in our collisions, for example,
when we collide stuff together,
you make a particle, you make an antiparticle.
They always come together.
They always annihilate together.
So there's no way of making more matter than antimatter
§10Transcript · 1:08:33–1:16:00
that we've discovered so far.
So that means in the Big Bang,
you get equal amounts of matter and antimatter.
As the universe expands and cools down
during the Big Bang,
not very long after the Big Bang,
I think a few seconds after the Big Bang,
you have this event called the Great Annihilation,
which is where all the particles and antiparticles
smack into each other,
annihilate, turn into light mostly,
and you end up with a universe later on.
If that was what happened,
then the universe we live in today
would be black and empty,
apart from some photons, that would be it.
So there's stuff in the,
there is stuff in the universe.
It appears to be just made of matter.
So there's this big mystery as to where the,
how did this happen?
And there are various ideas
which all involve sort of physics going on
in the first trillionth of a second or so of the Big Bang.
So it could be that one possibility
is that the Higgs field is somehow implicated in this,
that there was this event that took place
in the early universe
where the Higgs field basically switched on.
It acquired its modern value.
And when that happened,
this caused all the particles to acquire mass.
And the universe basically went through a phase transition
where you had a hot plasma of massless particles.
And then in that plasma,
it's almost like a gas turning into droplets of water.
You get kind of these little bubbles forming in the universe
where the Higgs field has acquired its modern value.
The particles have got mass.
And this phase transition in some models
can cause more matter than antimatter to be produced
depending on how matter bounces off these bubbles
in the early universe.
So that's one idea.
There's other ideas to do with neutrinos,
that there are exotic types of neutrinos
that can decay in a biased way to just matter
and not to antimatter.
So people are trying to test these ideas.
That's what we're trying to do at LHCb.
There's neutrino experiments planned
that are trying to do these sorts of things as well.
So yeah, there are ideas,
but at the moment no clear evidence
for which of these ideas might be right.
- So we're talking about some incredible ideas.
By the way, never heard anyone be so eloquent
about describing even just the standard model.
So I'm in awe just listening.
- Oh, thank you.
- Interesting, just having fun enjoying it.
So yes, the theoretical,
the particle physics is fascinating here.
To me, one of the most fascinating things
about the Large Hadron Collider is the human side of it,
that a bunch of sort of brilliant people
that probably have egos got together
and were collaborating together.
And countries, I guess, collaborated together
for the funds and everything.
Just collaboration everywhere.
'Cause you may be,
I don't know what the right question here to ask,
but what's your intuition about how it's possible
to make this happen?
And what are the lessons we should learn
for the future of human civilization
in terms of our scientific progress?
'Cause it seems like this is a great, great illustration
of us working together to do something big.
- Yeah, I think it's possibly the best example,
maybe I can think of, of international collaboration
that isn't for some unpleasant purpose, basically.
I mean, so when I started out in the field in 2008
as a new PhD student, the LHC was basically finished.
So I didn't have to go around asking for money for it
or trying to make the case.
So I have huge admiration for the people
who managed that.
'Cause this was a project that was first imagined
in the 1970s.
In the late '70s was when the first conversations
about the LHC were mooted.
And it took two and a half decades of campaigning
and fundraising and persuasion
until they started breaking ground and building the thing
in the early noughties and 2000.
So, I mean, I think the reason,
just from the point of view of the scientists there,
I think the reason it works ultimately
is that everyone there is there for the same reason,
which is, well, in principle at least,
they're there because they're interested in the world.
They wanna find out what are the basic ingredients
of our universe?
What are the laws of nature?
And so everyone is pulling in the same direction.
Of course, everyone has their own things
they're interested in.
Everyone has their own careers to consider.
And I wouldn't pretend that there isn't also
a lot of competitions.
There's this funny thing in these experiments
where your collaborators, your 800 collaborators in LHCb,
but you're also competitors because your academics
in your various universities,
and you wanna be the one that gets the paper out
on the most exciting new measurements.
So there's this funny thing where you're kind of trying
to stake out your territory while also collaborating
and having to work together to make the experiments work.
And it does work amazingly well, actually,
considering all of that.
And I think there was actually,
I think McKinsey or one of these big management
consultancy firms went into CERN maybe a decade or so ago
to try to understand how these organizations function.
- Did they figure it out?
- I don't think they could.
I mean, I think one of the things that's interesting,
one of the other interesting things about these experiments
is they're big operations.
Like say Atlas has 3000 people.
Now there was a person nominally who is the head of Atlas.
They're called the spokesperson.
And the spokesperson is elected by,
usually by the collaboration,
but they have no actual power, really.
I mean, they can't fire anyone.
They're not anyone's boss.
So, you know, my boss is a professor at Cambridge,
not the head of my experiments.
The head of my experiment can't tell me what to do really.
And there's all these independent academics
who are their own bosses who, you know,
so that somehow it nonetheless,
by kind of consensus and discussion and lots of meetings,
these things do happen and it does get done.
- It's like the queen here in the UK is the spokesperson.
- I guess so.
- No actual power.
- Except we don't elect her, no.
- No, we don't elect her.
But everybody seems to love her.
I don't know, from my outside perspective.
(inhales)
But yeah, giant egos, brilliant people.
And moving forward, do you think there's-
- Actually, I would pick up one thing you said just there,
just the brilliant people thing.
'Cause I'm not saying that people aren't great.
But I think there is this sort of impression
that physicists will have to be brilliant or geniuses,
which is not true actually.
And, you know, you have to be relatively bright for sure.
But, you know, a lot of people,
a lot of the most successful experimental physicists
are not necessarily the people with the biggest brains.
They're the people who, you know,
particularly one of the skills that's most important
in particle physics is the ability to work with others
and to collaborate and exchange ideas and also to work hard.
And it's a sort of, often it's more a determination
or a sort of other set of skills.
It's not just being, you know, kind of some great brain.
(laughs)
- Very true.
So, I mean, there's parallels to that
in the machine learning world.
If you wanna solve any real world problems,
which I see as the particle accelerators,
essentially a real world instantiation
of theoretical physics.
And for that, you have to not necessarily be brilliant,
but be sort of obsessed, systematic, rigorous,
sort of unboreable, stubborn,
all those kind of qualities that make for a great engineer.
So, scientists purely speaking,
that practitioner of the scientific method.
So, you're right.
But nevertheless, to me, that's brilliant.
My dad's a physicist.
I argue with him all the time.
To me, engineering is the highest form of science.
And he thinks that's all nonsense,
that the real work is done by the theoretician.
In fact, we have arguments about like people like Elon Musk,
for example, because I think his work is quite brilliant,
but he's fundamentally not coming up
with any serious breakthroughs.
§11Transcript · 1:16:02–1:23:12
He's just creating in this world, implementing,
like making ideas happen that have a huge impact.
To me, that's the Edison.
That to me is a brilliant work,
but to him, it's messy details
that somebody will figure out anyway.
- I mean, I don't know whether you think
there is a actual difference in temperament
between say a physicist and an engineer,
whether it's just what you got interested in.
I don't know.
I mean, 'cause a lot of what experimental physicists do
is to some extent engineering.
I mean, it's not what I do.
I mostly do data stuff, but you know,
a lot of people would be called electrical engineers,
but they trained as physicists,
but they learned electrical engineering, for example,
because they were building detectors.
So there's not such a clear divide, I think.
- Yeah, it's interesting.
I mean, but there does seem to be like,
you work with data.
There does seem to be a certain,
like I love data collection.
There may be an OCD element or something
that you're more naturally predisposed to
as opposed to theory.
Like I'm not afraid of data.
I love data.
And there's a lot of people in machine learning
who are more like,
they're basically afraid of data collection,
afraid of data sets, afraid of all of that.
They just wanna stay in more than theoretical
and they're really good at it space.
So I don't know if that's the genetic,
that's your upbringing, the way you go to school,
but looking into the future of LHC and other colliders.
So there's in America, there's the,
whatever it was called, the super,
there's a lot of super--
- Superconducting super collider.
- Yeah, superconducting--
- The desertron, yeah.
- Desertron.
So that was canceled, the construction of that,
which is a sad thing.
But what do you think is the future of these efforts?
Will a bigger collider be built?
Will LHC be expanded?
What do you think?
- Well, in the near future,
the LHC is gonna get an upgrade.
So that's pretty much confirmed.
I think it is confirmed,
which is, it's not an energy upgrade.
It's what we call a luminosity upgrade.
So it basically means increasing the data collection rates.
So more collisions per second, basically,
because after a few years of data taking,
you get this law of diminishing returns
where each year's worth of data
is a smaller and smaller fraction
of the lot you've already got.
So to get a real improvement in sensitivity,
you need to increase the data rate by an order of magnitude.
So that's what this upgrade is gonna do.
LHC-B at the moment,
the whole detector is basically being rebuilt
to allow it to record data
at a much larger rate than we could before.
So that will make us sensitive
to whole loads of new processes
that we weren't able to study before.
And I mentioned briefly these anomalies that we've seen.
So we've seen a bunch of very intriguing anomalies
in these B quark decays,
which may be hinting at the first signs
of this kind of the elephant,
the signs of some new quantum field
or fields maybe beyond the standard model.
It's not yet at the statistical threshold
where you can say that you've observed something,
but there's lots of anomalies in many measurements
that all seem to be consistent with each other.
So it's quite interesting.
So the upgrade will allow us
to really home in on these things
and see whether these anomalies are real,
because if they are real,
and this kind of connects to your point
about the next generation of machines,
what we would have seen then is,
we would have seen the tail end of some quantum field
in influencing these B quarks.
What we then need to do is to build a bigger collider
to actually make the particle of that field.
So if these things really do exist.
So that would be one argument.
I mean, so at the moment,
Europe has going through this process
of thinking about the strategy for the future.
So there are a number of different proposals on the table.
One is for a sort of higher energy upgrade of the LHC,
where you just build more powerful magnets
and put them in the same tunnel.
That's a sort of cheaper, less ambitious possibility.
Most people don't really like it
because it's sort of a bit of a dead end,
because once you've done that, there's nowhere to go.
There's a machine called CLIC,
which is a compact linear collider,
which is an electron positron collider
that uses a novel type of acceleration technology
to accelerate at shorter distances.
We're still talking kilometers long,
but not like a hundred kilometers long.
And then probably the project
that is I think getting the most support,
it'd be interesting to see what happens,
something called the Future Circular Collider,
which is a really ambitious long-term,
multi-decade project to build
a 100 kilometer circumference tunnel
under the Geneva region.
The LHC would become a kind of feeding machine.
It would just feed-
- So the same area, so there would be a feeder for the-
- Yeah, so it would kind of,
the edge of this machine would be where the LHC is,
but it would sort of go under Lake Geneva
and round to the Alps basically,
since up to the edge of the Geneva Basin.
So it's basically the biggest,
it's the biggest tunnel you can fit in the region
based on the geology.
- 100 kilometers, wow. - Yeah, so it's big.
It'd be a long drive if you're,
you know, you make experiments on one side,
you've got to go back to CERN for lunch,
so that would be a pain.
But, you know, so this project is,
in principle, is actually two accelerators.
The first thing you would do
is put an electron positron machine
in the 100 kilometer tunnel to study the Higgs.
So you'd make lots of Higgs bosons,
study it really precisely in the hope
that you see it misbehaving
and doing something it's not supposed to.
And then in the much longer term,
a hundred, that machine gets taken out,
you put in a proton-proton machine.
So it's like the LHC, but much bigger.
And that's the way you start going
and looking for dark matter,
or you're trying to recreate this phase transition
that I talked about in the early universe,
where you can see matter-antimatter being made, for example.
So lots of things you can do with these machines.
The problem is that they will take, you know,
the most optimistic, you're not gonna have any data
from any of these machines until 2040,
or, you know, 'cause they take such a long time to build
and they're so expensive.
So you have, there'll be a process of R&D design,
but also the political case being made.
- So LHC, what cost, a few billion?
- Depends how you count it.
I think most of the sort of more reasonable estimates
that take everything into account properly,
it's around the sort of 10, 11, 12 billion Euro mark.
- What would be the future, sorry, I forgot the name already.
- Future Circular Collider.
- Future Circular Collider.
- Presumably they won't call it that when it's built,
'cause it won't be the future anymore,
but I don't know what they'll call it then.
(both laughing)
Very big Hadron Collider, I don't know.
But that will, I don't know, I should know the numbers,
but I think the whole project is estimated
at about 30 billion Euros,
but that's money spent over between now and 2070 probably,
which is when the last bit of it would be
sort of finishing up, I guess.
So you're talking a half a century of science
coming out of this thing, shared by many countries.
So the actual cost, the arguments that are made
is that you could make this project fit
within the existing budget of CERN,
if you didn't do anything else.
- And CERN, by the way, we didn't mention, what is CERN?
- CERN is the European Organization for Nuclear Research.
It's an international organization
that was established in the 1950s
in the wake of the Second World War as a kind of,
it was sort of like a scientific Marshall Plan for Europe.
The idea was that you bring European science back together
§12Transcript · 1:23:16–1:30:26
for peaceful purposes,
because what happened in the '40s was,
you know, a lot of, particularly a lot of Jewish scientists,
but a lot of scientists from Central Europe
had fled to the United States,
and Europe had sort of seen this brain drain.
So there was a desire to bring the community back together
for a project that wasn't building nasty bombs,
but was doing something that was curiosity-driven.
So, and that has continued since then.
So it's kind of a unique organization.
It's, to be a member as a country,
you sort of sign up as a member,
and then you have to pay a fraction of your GDP
each year as a subscription.
I mean, it's a very small fraction, relatively speaking.
I think it's like, I think the UK's contribution
is 100 or 200 million quid or something like that a year,
which is quite a lot, but not-
- That's fascinating.
I mean, just the whole thing that is possible,
it's beautiful.
It's a beautiful idea,
especially when there's no wars on the line.
It's not like we're freaking out.
It's we're actually legitimately collaborating
to do good science.
One of the things I don't think we really mentioned
is on the final side, that sort of the data analysis side,
is there breakthroughs possible there
in the machine learning side?
Like, is there a lot more signal to be mined
in more effective ways from the actual raw data?
- Yeah, a lot of people are looking into that.
I mean, so I use machine learning in my data analysis,
but pretty naughty, basic stuff,
'cause I'm not a machine learning expert.
I'm just a physicist who had to learn to do this stuff
for my day job.
So what a lot of people do is they use
kind of off the shelf packages that you can train
to do signal noise-
- Just clean up all the data.
- Yeah, but one of the big challenges is,
the big challenge of the data is A, it's volume.
There's huge amounts of data.
So the LHC generates, now, okay,
I try to remember what the actual numbers are,
but if we don't record all our data,
we record a tiny fraction of the data.
It's like of order one 10,000th or something, I think.
Is that right?
Around that.
So most of it gets thrown away.
You couldn't record all the LHC data
'cause it would fill up every computer in the world
in a matter of days, basically.
So there's this process that happens on live
on the detector, something called a trigger,
which in real time, 40 million times every second,
has to make a decision about whether this collision
is likely to contain an interesting object
like a Higgs boson or a dark matter particle.
And it has to do that very fast.
And the software algorithms in the past
were quite relatively basic.
You know, they did things like measure momentas
and energies of particles and put some requirements.
So you would say, if there's a particle
with an energy above some threshold,
then record this collision.
But if there isn't, don't.
Whereas now the attempt is to get more
and more machine learning in at the earliest possible stage.
- That's cool, at the stage of deciding
whether we wanna keep this data or not.
- But also even maybe even lower down than that,
which is the point where there's this,
so generally how the data is reconstructed
is you start off with a set of digital hits
in your detector.
So channels saying, did you see something?
Did you not see something?
That has to be then turned into tracks,
particles going in different directions.
And that's done by using fits
that fit through the data points.
And then that's passed to the algorithms that then go,
is this interesting or not?
What'd be better is you could train in machine learning
to just look at the raw hits,
the basic, real base level information,
not have any of the reconstruction done.
And it just goes,
and it can learn to do pattern recognition
on this strange three-dimensional image that you get.
And potentially that's where you could get really big gains
because our triggers tend to be quite inefficient
because they don't have time
to do the full whiz bang processing
to get all the information out that we would like
because you have to do the decision very quickly.
So if you can come up
with some clever machine learning technique,
then potentially you can massively increase
the amount of useful data you record
and get rid of more of the background earlier in the process.
- Yeah, to me, that's an exciting possibility
'cause then you don't have to build a,
sort of you can get a gain without having to,
without having to build any hardware, I suppose.
- Hardware, yeah.
- Although you need lots of new GPU farms, I guess.
- So hardware still helps.
But the, you know, I got to talk to you.
Sort of, I'm not sure how to ask,
but you're clearly an incredible science communicator.
I don't know if that's the right term,
but you're basically a younger Neil deGrasse Tyson
with a British accent.
So, and you've, I mean, can you say where we are today?
Actually?
- Yeah, so today we're in the Royal Institution in London,
which is an old, a very old organization.
It's been around for about 200 years now, I think.
Maybe even I should know when it was founded,
but sort of early 19th century.
It was set up to basically communicate science to the public.
So it was one of the first places in the world
where scientists, famous scientists would come
and give talks.
So very famously, Humphry Davy, who you may know of,
who was the person who discovered nitrous oxide,
he was a very famous chemist and scientist,
also discovered electrolysis.
So he used to do these fantastic,
he was a very charismatic speaker.
So he used to appear here, there's a big desk
that they usually have in the theater,
and he would do demonstrations to the sort of the folk
of London back in the early 19th century.
And Michael Faraday, who I talked about,
who was the person who did so much work on electromagnetism,
he lectured here.
He also did experiments in the basement.
So this place has got a long history
of both scientific research, but also-
- And the communication. - Communication
of scientific research.
- So you gave a few lectures here, how many, two?
- I've given, yeah, I've given a couple of lectures
in this theater before, so.
- I mean, that's, so people should definitely
go watch online.
It's just the explanation of particle physics,
so all the, I mean, it's incredible.
Like your lectures are just incredible.
I can't sing it enough praise.
So it was awesome.
But maybe, can you say, what did that feel like?
What does it feel like to lecture here, to talk about that?
And maybe from a different perspective,
more kind of like how the sausage is made,
is how do you prepare for that kind of thing?
How do you think about communication,
the process of communicating these ideas
in a way that's inspiring to what I would say
your talks are inspiring to, like, the general audience.
You don't actually have to be a scientist.
You can still be inspired without really knowing much.
You start from the very basics.
So what's the preparation process?
And then the romantic question is,
what did that feel like to perform here?
- I mean, the profession, yeah.
I mean, the process, I mean, the talk,
my favorite talk that I gave here
was one called "Beyond the Higgs,"
which you can find on the Royal Institution's
YouTube channel, which you should go and check out.
I mean, and their channel's got loads of great talks
from loads of great people as well.
I mean, that one, I'd sort of given a version of it
many times, so part of it is just practice, right?
And actually, I don't have some great theory
of how to communicate with people.
It's more just that I'm really interested
and excited by those ideas, and I like talking about them.
And through the process of doing that,
I guess I figured out stories that work
and explanations that work.
- When you say practice, you mean legitimately
just giving- - Just giving talks.
- Just giving talks. - I started off, you know,
when I was a PhD student, doing talks in schools,
and I still do that as well some of the time,
and doing things, I've even done a bit of stand-up comedy,
which was sort of, went reasonably well,
even if it was terrifying.
- That's on YouTube as well.
§13Transcript · 1:30:27–1:38:13
- That's also on, I wouldn't necessarily recommend
you check that out.
(laughing)
I'm gonna post the links several places
to make sure people click on it.
- Yeah, but it's basically, I kind of have a story
in my head, and I kind of, I have to think about
what I wanna say, usually have some images
to support what I'm saying, and I get up and do it.
And it's not really, I wish there was some kind of,
I probably should have some proper process.
This probably sounds like I'm just making it up
as I go along, and I sort of am.
- Oh, I think the fundamental thing that you said,
I think, it's like, I don't know if you know
who a guy named Joe Rogan is.
- Yes, I do, yeah.
- So he's also kind of sounds like you in a sense
that he's not very introspective about his process,
but he's an incredibly engaging conversationalist.
And I think one of the things that you and him share
that I could see is like a genuine curiosity
and passion for the topic.
I think that could be systematically cultivated.
I'm sure there's a process to it,
but you come to it naturally somehow.
I think maybe there's something else as well,
which is to understand something.
There's this quote by Feynman, which I really like,
which is, "What I cannot create, I do not understand."
So like, I'm not particularly super bright.
So for me to understand something,
I have to break it down into its simplest elements.
And if I can then tell people about that,
that helps me understand it as well.
So I've actually, I've learned to understand physics
a lot more from the process of communicating,
'cause it forces you to really scrutinize the ideas
that you're communicating.
And it quite often makes you realize
you don't really understand the ideas you're talking about.
And I'm writing a book at the moment.
I had this experience yesterday where I realized
I didn't really understand a pretty fundamental
theoretical aspect of my own subject.
And I had to go and I had to sort of spend a couple of days
reading textbooks and thinking about it
in order to make sure that the explanation I gave
captured the, got as close to what is actually happening
in the theory.
And to do that, you have to really understand it properly.
- Yeah, and there's layers to understanding.
Like it seems like the more,
there must be some kind of Feynman law.
I mean, the more you understand sort of the simply,
you're able to really convey the essence of the idea, right?
So it's like this reverse effect that it's like,
the more you understand the simpler the final thing
that you actually convey.
And so the more accessible somehow it becomes.
That's why Feynman's lectures are really accessible.
It was just counterintuitive.
- Yeah, although there are some ideas
that are very difficult to explain
no matter how well or badly you understand them.
Like I still can't really properly explain
the Higgs mechanism.
Because some of these ideas only exist in mathematics,
really, and the only way to really develop an understanding
is to go unfortunately into a graduate degree in physics.
But you can get kind of a flavor of what's happening,
I think, and it's trying to do that in a way
that isn't misleading, but also intelligible.
- So let me ask them the romantic question of what to you
is the most, perhaps an unfair question.
What is the most beautiful idea in physics?
One that fills you with awe, is the most surprising,
the strangest, the weirdest.
There's a lot of different definitions of beauty.
And I'm sure there's several for you,
but is there something that just jumps to mind
that you think is just especially beautiful?
- There's a specific thing and a more general thing.
So maybe the specific thing first,
which when I first came across this as an undergraduate,
I found this amazing.
So this idea that the forces of nature,
electromagnetism's strong force, the weak force,
they arise in our theories as a consequence of symmetries.
So symmetries in the laws of nature,
in the equations essentially,
that used to describe these ideas.
The process whereby theories come up
with these sorts of models is they say,
imagine the universe obeys this particular type of symmetry.
It's a symmetry that isn't so far removed
from a geometrical symmetry, like the rotations of a cube.
It's not, you can't think of it quite that way,
but it's sort of a similar sort of idea.
And you say, okay, if the universe respects this symmetry,
you find that you have to introduce a force
which has the properties of electromagnetism.
Or a different symmetry, you get the strong force,
or a different symmetry, you get the weak force.
So these interactions seem to come from some deeper,
it suggests that they come
from some deeper symmetry principle.
I mean, depends a bit how you look at it,
'cause it could be that we're actually
just recognizing symmetries in the things that we see,
but there's something rather lovely about that.
But I mean, I suppose a bigger thing
that makes me wonder is actually,
if you look at the laws of nature,
how particles interact when you get really close down,
they're basically pretty simple things.
They bounce off each other by exchanging
through force fields, and they move around
in very simple ways.
And somehow, these basic ingredients,
these few particles that we know about in the forces,
creates this universe which is unbelievably complicated
and has things like you and me in it,
and the Earth and stars that make matter in their cores
from the gravitational energy of their own bulk
that then gets sprayed into the universe
that forms other things.
I mean, the fact that there's this incredibly long story
that goes right back to the beginning,
we can take this story right back
to a trillionth of a second after the Big Bang,
and we can trace the origins of the stuff
that we're made from.
And it all ultimately comes from these simple ingredients
with these simple rules.
And the fact you can generate such complexity from that
is really mysterious, I think, and strange.
And it's not even a question that physicists
can really tackle, because we are sort of trying
to find these really elementary laws.
But it turns out that going from elementary laws
in a few particles to something even as complicated
as a molecule becomes very difficult.
So going from a molecule to a human being
is a problem that just can't be tackled,
at least not at the moment.
So-- - Yeah, the emergence
of complexity from simple rules is so beautiful
and so mysterious.
And we don't have good mathematics
to even try to approach that emergent phenomena.
- That's why we have chemistry and biology
in all the other subjects.
Yeah, I guess.
- I don't think there's a better way to end it, Harry.
I can't, I mean, I think I speak for a lot of people
that can't wait to see what happens
in the next five, 10, 20 years with you.
I think you're one of the great communicators of our time.
So I hope you continue that, and I hope that grows.
And I'm definitely a huge fan.
So it was an honor to talk to you today.
Thanks so much, man. - It was really fun.
Thanks very much.
- Thanks for listening to this conversation
with Harry Cliff, and thank you to our sponsors,
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And now let me leave you with some words from Harry Cliff.
You and I are leftovers.
Every particle in our bodies is a survivor
from an almighty shootout between matter and antimatter
that happened a little after the Big Bang.
In fact, only one in a billion particles created
at the beginning of time have survived to the present day.
Thank you for listening and hope to see you next time.
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