Harry Cliff: Particle Physics and the Large Hadron Collider

00:00:00.000 | The following is a conversation with Harry Cliff,

00:00:03.000 | a particle physicist at the University of Cambridge,

00:00:05.760 | working on the Large Hadron Collider Beauty Experiment

00:00:09.860 | that specializes in investigating the slight differences

00:00:13.020 | between matter and antimatter by studying a type

00:00:16.240 | of particle called the beauty quark or b quark.

00:00:19.900 | In this way, he's part of the group of physicists

00:00:22.320 | who are searching for the evidence of new particles

00:00:25.120 | that can answer some of the biggest questions

00:00:26.940 | in modern physics.

00:00:28.440 | He's also an exceptional communicator of science

00:00:31.820 | with some of the clearest and most captivating explanations

00:00:34.860 | of basic concepts in particle physicists

00:00:37.420 | that I've ever heard.

00:00:39.540 | So when I visited London, I knew I had to talk to him.

00:00:42.940 | And we did this conversation

00:00:44.900 | at the Royal Institute Lecture Theater,

00:00:47.260 | which has hosted lectures for over two centuries

00:00:50.500 | from some of the greatest scientists

00:00:52.100 | and science communicators in history,

00:00:54.140 | from Michael Faraday to Carl Sagan.

00:00:57.660 | This conversation was recorded

00:00:59.080 | before the outbreak of the pandemic.

00:01:01.240 | For everyone feeling the medical and psychological

00:01:03.440 | and financial burden of this crisis,

00:01:05.440 | I'm sending love your way.

00:01:07.360 | Stay strong.

00:01:08.400 | We're in this together.

00:01:09.560 | We'll beat this thing.

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00:03:47.320 | And now, here's my conversation with Harry Cliff.

00:03:50.960 | Let's start with probably one of the coolest things

00:03:54.160 | that human beings have ever created,

00:03:56.120 | the Large Hadron Collider, LHC.

00:03:58.960 | What is it?

00:04:00.920 | How does it work?

00:04:02.160 | - Okay, so it's essentially this gigantic 27 kilometer

00:04:06.480 | circumference particle accelerator.

00:04:08.360 | It's this big ring.

00:04:09.560 | It's buried about a hundred meters underneath the surface

00:04:12.080 | in the countryside just outside Geneva in Switzerland.

00:04:14.680 | And really what it's for ultimately

00:04:17.080 | is to try to understand what are the basic building blocks

00:04:20.360 | of the universe.

00:04:21.640 | So you can think of it in a way

00:04:23.080 | as like a gigantic microscope

00:04:24.520 | and the analogy is actually fairly precise.

00:04:27.520 | So-

00:04:28.480 | - Gigantic microscope.

00:04:30.080 | - Effectively, except it's a microscope

00:04:32.560 | that looks at the structure of the vacuum.

00:04:36.200 | - In order for this kind of thing to study particles,

00:04:39.520 | which are the microscopic entities,

00:04:43.040 | it has to be huge.

00:04:44.400 | - Yes.

00:04:45.240 | - It's a gigantic microscope.

00:04:46.080 | What do you mean by studying vacuum?

00:04:48.560 | - Okay, so I mean, so particle physics as a field

00:04:51.960 | is kind of badly named in a way

00:04:53.440 | because particles are not the fundamental ingredients

00:04:56.600 | of the universe.

00:04:57.760 | They're not fundamental at all.

00:04:58.920 | So the things that we believe

00:05:00.160 | are the real building blocks of the universe

00:05:02.320 | are objects, invisible fluid-like objects

00:05:05.400 | called quantum fields.

00:05:07.440 | So these are fields like the magnetic field

00:05:10.200 | around a magnet that exists everywhere in space.

00:05:12.600 | They're always there.

00:05:13.640 | In fact, actually, it's funny

00:05:14.880 | that we're in the wrong institution

00:05:15.880 | 'cause this is where the idea of the field

00:05:19.000 | was effectively invented by Michael Faraday

00:05:21.240 | doing experiments with magnets and coils of wire.

00:05:23.840 | So he noticed that,

00:05:25.200 | if he was very famous experiment that he did

00:05:28.400 | where he got a magnet and put it on top of it,

00:05:30.280 | a piece of paper and then sprinkled iron filings.

00:05:32.680 | And he found the iron filings arranged themselves

00:05:34.600 | into these kind of loops,

00:05:36.440 | which was actually mapping out

00:05:38.760 | the invisible influence of this magnetic field,

00:05:41.320 | which is the thing,

00:05:42.400 | we've all experienced, we've all felt held a magnet

00:05:44.720 | or two poles of magnet and pushing together

00:05:46.480 | and felt this thing, this force pushing back.

00:05:48.600 | So these are real physical objects.

00:05:51.080 | And the way we think of particles in modern physics

00:05:53.800 | is that they are essentially little vibrations,

00:05:56.640 | little ripples in these otherwise invisible fields

00:06:00.240 | that are everywhere.

00:06:01.400 | They fill the whole universe.

00:06:03.240 | - You know, I don't, I apologize,

00:06:05.440 | perhaps for the ridiculous question.

00:06:07.400 | Are you comfortable with the idea

00:06:10.200 | of the fundamental nature of our reality being fields?

00:06:14.120 | 'Cause to me particles,

00:06:16.160 | you know, a bunch of different building blocks

00:06:19.560 | makes more sense sort of intellectually,

00:06:21.800 | sort of visually, like it seems to,

00:06:24.920 | I seem to be able to visualize that kind of idea easier.

00:06:28.600 | - Yeah. - Are you comfortable

00:06:30.160 | psychologically with the idea

00:06:31.720 | that the basic building block is not a block, but a field?

00:06:35.280 | - I think it's, I think it's quite a magical idea.

00:06:38.200 | I find it quite appealing and it's,

00:06:40.040 | well, it comes from a misunderstanding

00:06:42.000 | of what particles are.

00:06:43.120 | So like when you, when we do science at school

00:06:45.440 | and we draw a picture of an atom,

00:06:46.680 | you draw like, you know, a nucleus

00:06:48.320 | with some protons and neutrons,

00:06:49.680 | these little spheres in the middle,

00:06:50.920 | and then you have some electrons

00:06:51.880 | that are like little flies flying around the atom.

00:06:54.800 | And that is a completely misleading picture

00:06:56.440 | of what an atom is like.

00:06:57.680 | It's nothing like that.

00:06:58.520 | The electron is not like a little planet orbiting the atom.

00:07:01.920 | It's this spread out, wibbly wobbly wave-like thing.

00:07:05.840 | And we know we've known that since, you know,

00:07:07.360 | the early 20th century, thanks to quantum mechanics.

00:07:10.080 | So when we, we carry on using this word particle

00:07:13.160 | because sometimes when we do experiments,

00:07:15.720 | particles do behave like they're little marbles

00:07:17.880 | or little bullets, you know?

00:07:19.160 | So in the LHC, when we collide particles together,

00:07:22.520 | you'll get, you know, you'll get like hundreds of particles

00:07:25.000 | will fly out through the detector

00:07:26.200 | and they all take a trajectory

00:07:27.840 | and you can see from the detector where they've gone

00:07:29.840 | and they look like they're little bullets.

00:07:31.320 | So they behave that way, you know, a lot of the time.

00:07:35.320 | But when you really study them carefully,

00:07:37.560 | you'll see that they are not little spheres.

00:07:40.040 | They are these ethereal disturbances

00:07:43.160 | in these underlying fields.

00:07:44.880 | So this is really how we think nature is,

00:07:48.640 | which is surprising, but also I think kind of magic.

00:07:51.600 | So, you know, we are, our bodies are basically made up of

00:07:54.800 | like little knots of energy in these invisible objects

00:07:59.000 | that are all around us.

00:08:00.240 | - And what is the story of the vacuum when it comes to LHC?

00:08:06.560 | So why did you mention the word vacuum?

00:08:09.880 | - Okay, so if we just, if we go back to like

00:08:12.400 | the physics we do know, so atoms are made of electrons,

00:08:16.280 | which were discovered a hundred or so years ago.

00:08:18.240 | And then in the nucleus of the atom,

00:08:19.960 | you have two other types of particles.

00:08:21.680 | There's an up, something called an up quark

00:08:23.440 | and a down quark.

00:08:24.360 | And those three particles make up every atom

00:08:26.640 | in the universe.

00:08:27.880 | So we think of these as ripples in fields.

00:08:30.640 | So there is something called the electron field

00:08:34.280 | and every electron in the universe is a ripple

00:08:37.080 | moving about in this electron field.

00:08:39.040 | So the electron field is all around us, we can't see it,

00:08:40.760 | but every electron in our body is a little ripple

00:08:42.880 | in this thing that's there all the time.

00:08:45.560 | And the quark field is the same.

00:08:46.920 | So there's an up quark field and an up quark

00:08:48.920 | is a little ripple in the up quark field

00:08:50.240 | and the down quark is a little ripple in something else

00:08:52.280 | called the down quark field.

00:08:53.320 | So these fields are always there.

00:08:54.960 | Now there are potentially, we know about a certain number

00:08:58.840 | of fields in what we call the standard model

00:09:00.400 | of particle physics.

00:09:01.280 | And the most recent one we discovered was the Higgs field.

00:09:04.000 | And the way we discovered the Higgs field

00:09:07.040 | was to make a little ripple in it.

00:09:08.560 | So what the LHC did, it fired two protons into each other

00:09:12.480 | very, very hard with enough energy that you could create

00:09:16.320 | a disturbance in this Higgs field.

00:09:18.400 | And that's what shows up as what we call the Higgs boson.

00:09:20.800 | So this particle that everyone was going on about

00:09:22.920 | eight or so years ago is proof really,

00:09:25.760 | the particle in itself is, I mean, it's interesting,

00:09:28.480 | but the thing that's really interesting is the field

00:09:30.600 | because it's the Higgs field that we believe

00:09:33.880 | is the reason that electrons and quarks have mass.

00:09:38.240 | And it's that invisible field that's always there

00:09:41.000 | that gives mass to the particles.

00:09:42.480 | The Higgs boson is just our way of checking

00:09:45.080 | it's there basically.

00:09:46.360 | - So the Large Hadron Collider,

00:09:49.160 | in order to get that ripple in the Higgs field,

00:09:52.640 | it requires a huge amount of energy, I suppose.

00:09:55.040 | And so that's why you need this huge,

00:09:57.000 | that's why size matters here.

00:09:58.360 | So maybe there's a million questions here,

00:10:01.440 | but let's backtrack.

00:10:02.640 | Why does size matter in the context of a particle?

00:10:07.640 | Of a particle collider.

00:10:09.960 | So why does bigger allow you for higher energy collisions?

00:10:14.960 | - Right, so the reason, well, it's kind of simple really,

00:10:18.500 | which is that there are two types of particle accelerator

00:10:21.080 | that you can build.

00:10:21.920 | One is circular, which is like the LHC,

00:10:23.640 | the other is a great long line.

00:10:25.680 | So the advantage of a circular machine

00:10:28.560 | is that you can send particles around a ring

00:10:30.600 | and you can give them a kick every time they go around.

00:10:32.560 | So imagine you have a, there's actually a bit of the LHC

00:10:34.720 | that's about only 30 meters long,

00:10:36.800 | where you have a bunch of metal boxes,

00:10:38.720 | which have oscillating 2 million volt

00:10:41.120 | electric fields inside them,

00:10:42.700 | which are timed so that when a proton

00:10:44.360 | goes through one of these boxes,

00:10:45.560 | the field it sees as it approaches is attractive.

00:10:48.200 | And then as it leaves the box, it flips and becomes repulsive

00:10:51.240 | and the proton gets attracted and kicked out the other side.

00:10:53.460 | So it gets a bit faster.

00:10:55.060 | So you send it, but then you send it back around again.

00:10:57.160 | - And it's incredible, like the timing of that,

00:10:59.440 | the synchronization, wait, really?

00:11:01.160 | - Yeah, yeah, yeah.

00:11:02.760 | - I think there's going to be a multiplicative effect

00:11:05.520 | on the questions I have.

00:11:06.720 | Okay, let me just take that tangent for a second.

00:11:10.880 | The orchestration of that,

00:11:13.980 | is that a fundamentally a hardware problem

00:11:16.040 | or a software problem?

00:11:17.600 | Like what, how do you get that?

00:11:20.120 | - I mean, I should first of all say, I'm not an engineer.

00:11:22.680 | So the guys, I did not build the LHC.

00:11:24.640 | So there are people much, much better at this stuff

00:11:26.360 | than I could. - For sure, but maybe.

00:11:28.260 | But from your sort of intuition,

00:11:33.680 | from the echoes of what you understand,

00:11:37.440 | what you heard of how it's designed, what's your sense?

00:11:40.560 | What's the engineering aspects of it?

00:11:43.360 | - The acceleration bit is not challenging.

00:11:45.400 | Okay, I mean, okay, there is always challenges

00:11:47.120 | with everything, but basically you have these,

00:11:50.200 | the beams that go around the LHC,

00:11:52.000 | the beams of particles are divided into little bunches.

00:11:55.400 | So they're called, they're a bit like swarms of bees,

00:11:57.680 | if you like.

00:11:58.920 | And there are around, I think it's something of the order

00:12:01.880 | of 2000 bunches spaced around the ring.

00:12:05.200 | And they, if you're at a given point on the ring,

00:12:07.760 | counting bunches, you get 40 million bunches

00:12:10.080 | passing you every second.

00:12:11.200 | So they come in like, you know,

00:12:13.160 | like cars going past in a very fast motorway.

00:12:15.920 | So you need to have, if you're electric fields

00:12:18.240 | that you're using to accelerate the particles,

00:12:20.360 | that needs to be timed so that as a bunch of protons arrives,

00:12:23.760 | it's got the right sign to attract them

00:12:26.040 | and then flips at the right moment.

00:12:27.560 | But I think the voltage in those boxes

00:12:29.560 | oscillates at hundreds of megahertz.

00:12:31.160 | So the beams are like 40 megahertz,

00:12:33.240 | but it's oscillating much more quickly than the beam.

00:12:35.160 | So I think, you know, it's difficult engineering,

00:12:37.600 | but in principle, it's not, you know,

00:12:39.640 | a really serious challenge.

00:12:41.400 | The bigger problem.

00:12:42.240 | - There's probably engineers like screaming at you right now.

00:12:44.520 | - Probably.

00:12:45.360 | - Yeah.

00:12:46.200 | - Well, I mean, okay.

00:12:47.040 | So in terms of coming back to this thing,

00:12:47.880 | why is it so big?

00:12:48.800 | Well, the reason is you want to get the particles

00:12:51.520 | through that accelerating element over and over again.

00:12:54.160 | So you want to bring them back round.

00:12:55.280 | That's why it's round.

00:12:56.320 | The question is why couldn't you make it smaller?

00:12:58.640 | Well, the basic answer is that these particles

00:13:01.360 | are going unbelievably quickly.

00:13:03.120 | So they travel at 99.9999991% of the speed of light

00:13:08.120 | in the LHC.

00:13:11.360 | And if you think about say driving your car

00:13:13.720 | round a corner at high speed,

00:13:16.040 | if you go fast, you need a lot of friction in the tires

00:13:19.520 | to make sure you don't slide off the road.

00:13:21.200 | So the limiting factor is how powerful a magnet can you make

00:13:26.200 | 'cause it's what we do is magnets are used

00:13:28.480 | to bend the particles around the ring.

00:13:30.920 | And essentially the LHC when it was designed

00:13:33.080 | was designed with the most powerful magnets

00:13:35.160 | that could conceivably be built at the time.

00:13:37.880 | And so that's your kind of limiting factor.

00:13:40.360 | So if you want to make the machines smaller,

00:13:41.760 | that means a tighter bend,

00:13:42.840 | you need to have a more powerful magnet.

00:13:44.280 | So it's this toss up between how strong are your magnets

00:13:48.200 | versus how big a tunnel can you afford.

00:13:49.920 | The bigger the tunnel, the weaker the magnets can be.

00:13:51.560 | The smaller the tunnel, the stronger they've got to be.

00:13:54.080 | - Okay, so maybe can we backtrack to the standard model

00:13:57.640 | and say what kind of particles there are period

00:14:00.800 | and maybe the history of kind of assembling

00:14:04.560 | that the standard model of physics

00:14:06.880 | and then how that leads up to the hopes and dreams

00:14:10.360 | and the accomplishments of the Large Hadron Collider.

00:14:12.760 | - Yeah, sure, okay.

00:14:13.960 | So all of 20th century physics in like five minutes.

00:14:16.720 | - Yeah, please.

00:14:17.560 | - Okay, so, okay, the story really begins properly

00:14:21.280 | end of the 19th century,

00:14:23.040 | the basic view of matter is that matter is made of atoms

00:14:26.680 | and the atoms are indestructible, immutable little spheres,

00:14:30.240 | like the things we were talking about

00:14:31.440 | that don't really exist.

00:14:32.560 | And there's one atom for every chemical element.

00:14:35.240 | So there's an atom for hydrogen, for helium,

00:14:36.840 | for carbon, for iron, et cetera, and they're all different.

00:14:39.760 | Then in 1897, experiments done

00:14:41.840 | at the Cavendish Laboratory in Cambridge,

00:14:43.240 | which is where I'm still, where I'm based,

00:14:45.800 | showed that there are actually smaller particles

00:14:48.680 | inside the atom, which eventually became known as electrons.

00:14:51.640 | These are these negatively charged things

00:14:53.160 | that go around the outside.

00:14:54.800 | A few years later, Ernest Rutherford,

00:14:57.040 | very famous nuclear physicist,

00:14:58.600 | one of the pioneers of nuclear physics,

00:14:59.960 | shows that the atom has a tiny nugget in the center,

00:15:03.440 | which we call the nucleus,

00:15:04.360 | which is a positively charged object.

00:15:05.800 | So then by like 1910, '11,

00:15:07.840 | we have this model of the atom that we learn in school,

00:15:09.920 | which is you've got a nucleus, electrons go around it.

00:15:13.200 | Fast forward, you know, a few years,

00:15:15.520 | the nucleus, people start doing experiments

00:15:17.400 | with radioactivity where they use alpha particles

00:15:20.800 | that are spat out of radioactive elements as bullets.

00:15:24.520 | And they fire them at other atoms.

00:15:26.760 | And by banging things into each other,

00:15:28.560 | they see that they can knock bits out of the nucleus.

00:15:31.200 | So these things come out called protons, first of all,

00:15:33.880 | which are positively charged particles,

00:15:36.040 | about 2000 times heavier than the electron.

00:15:38.800 | And then 10 years later, more or less,

00:15:41.160 | a neutral particle is discovered called the neutron.

00:15:43.880 | So those are the three basic building blocks of atoms.

00:15:47.000 | You have protons and neutrons in the nucleus

00:15:49.400 | that are stuck together by something

00:15:50.680 | called the strong force, the strong nuclear force.

00:15:53.200 | You have electrons in orbit around that

00:15:55.760 | held in by the electromagnetic force,

00:15:57.920 | which is one of the forces of nature.

00:16:00.440 | That's sort of where we get to by like 1932, more or less.

00:16:03.840 | Then what happens is physics is nice and neat.

00:16:07.440 | In 1932, everything looks great.

00:16:08.760 | Got three particles and all the atoms are made of,

00:16:10.380 | that's fine.

00:16:11.220 | But then cloud chamber experiments.

00:16:13.960 | So these are devices that can be used to,

00:16:16.020 | the first device is capable of imaging subatomic particles.

00:16:18.600 | So you can see their tracks

00:16:19.600 | and they're used to study cosmic rays,

00:16:21.760 | particles that come from out of space

00:16:23.760 | and bang into the atmosphere.

00:16:25.640 | And in these experiments,

00:16:28.100 | people start to see a whole lot of new particles.

00:16:29.840 | So they discover for one thing, antimatter,

00:16:31.560 | which is the sort of a mirror image of the particles.

00:16:34.420 | So we discover that there's also,

00:16:35.960 | as well as a negatively charged electron,

00:16:37.440 | there's something called a positron,

00:16:38.520 | which is a positively charged version of the electron.

00:16:40.480 | And there's an antiproton, which is negatively charged.

00:16:43.220 | And then a whole load of other weird particles

00:16:45.600 | start to get discovered

00:16:46.480 | and no one really knows what they are.

00:16:48.800 | This is known as the zoo of particles.

00:16:50.960 | - Are these discoveries

00:16:51.960 | some of the first theoretical discoveries

00:16:55.120 | or are they discoveries in an experiment?

00:16:58.360 | So like, yeah, what's the process of discovery

00:17:01.120 | for these early sets of particles?

00:17:02.840 | - It's a mixture.

00:17:03.840 | I mean, the early stuff around the atom

00:17:05.420 | is really experimentally driven.

00:17:07.120 | It's not based on some theory.

00:17:08.960 | It's exploration in the lab using equipment.

00:17:11.560 | So it's really people just figuring out,

00:17:12.880 | getting hands on with the phenomena,

00:17:14.320 | figuring out what these things are.

00:17:15.920 | And the theory comes a bit later.

00:17:17.520 | That's not always the case.

00:17:18.840 | So in the discovery of the anti-electron, the positron,

00:17:22.440 | that was predicted from quantum mechanics and relativity

00:17:26.120 | by a very clever theoretical physicist called Paul Dirac,

00:17:30.280 | who was probably the second brightest physicist

00:17:33.200 | of the 20th century apart from Einstein,

00:17:34.880 | but isn't anywhere near as well known.

00:17:36.680 | So he predicted the existence of the anti-electron

00:17:39.200 | from basically a combination of the theories

00:17:41.840 | of quantum mechanics and relativity.

00:17:43.200 | And it was discovered about a year

00:17:44.360 | after he made the prediction.

00:17:45.920 | - What happens when an electron meets a positron?

00:17:49.120 | - They annihilate each other.

00:17:50.640 | So when you bring a particle and its antiparticle together,

00:17:54.360 | they react, they just wipe each other out

00:17:57.520 | and their mass is turned into energy,

00:17:59.960 | usually in the form of photons.

00:18:01.520 | So you get light produced.

00:18:03.440 | - So when you have that kind of situation,

00:18:06.920 | why does the universe exist at all

00:18:08.880 | if there's matter in any matter?

00:18:10.320 | - Oh God, now we're getting into the really big questions.

00:18:12.080 | So, depends if you wanna go there now.

00:18:15.440 | - Yeah, maybe let's go there later.

00:18:19.000 | - 'Cause I mean, that is a very big question.

00:18:20.600 | - Yeah, let's take it slow with the standard model.

00:18:23.720 | So, okay, so there's matter and antimatter in the 30s.

00:18:28.240 | So what else?

00:18:29.520 | - So matter, antimatter, and then a load of new particles

00:18:32.240 | start turning up in these cosmic ray experiments,

00:18:35.840 | first of all.

00:18:36.880 | And they don't seem to be particles that make up atoms.

00:18:40.120 | They're something else.

00:18:41.080 | They all mostly interact with a strong nuclear force.

00:18:44.120 | So they're a bit like protons and neutrons.

00:18:46.520 | And by in the 1960s, in America particularly,

00:18:50.280 | but also in Europe and Russia,

00:18:52.320 | scientists started to build particle accelerators.

00:18:54.160 | So these are the forerunners of the LHC.

00:18:55.800 | So big ring-shaped machines that were, you know,

00:18:58.280 | hundreds of meters long,

00:18:59.320 | which in those days was enormous.

00:19:00.720 | You never, you know, most physics up until that point

00:19:02.760 | had been done in labs, in universities, you know,

00:19:04.840 | with small bits of kit.

00:19:06.240 | So this is a big change.

00:19:07.160 | And when these accelerators are built,

00:19:08.920 | they start to find they can produce

00:19:10.680 | even more of these particles.

00:19:12.160 | So I don't know the exact numbers, but by around 1960,

00:19:16.480 | there are of order 100 of these things

00:19:19.320 | that have been discovered.

00:19:20.160 | And physicists are kind of tearing their hair out

00:19:22.720 | because physics is all about simplification.

00:19:25.040 | And suddenly what was simple has become messy

00:19:28.080 | and complicated and everyone sort of wants to understand

00:19:30.240 | what's going on.

00:19:31.640 | - As a quick kind of aside,

00:19:33.000 | and probably a really dumb question,

00:19:34.600 | but how is it possible to take something like a photon

00:19:39.480 | or electron and be able to control it enough,

00:19:44.000 | like to be able to do a controlled experiment

00:19:49.000 | where you collide it against something else?

00:19:51.520 | - Yeah.

00:19:52.360 | - Is that, that seems like an exceptionally difficult

00:19:55.920 | engineering challenge, 'cause you mentioned vacuum too.

00:19:59.560 | So you basically want to remove every other distraction

00:20:03.200 | and really focus on this collision.

00:20:04.800 | How difficult of an engineering challenge is that,

00:20:06.840 | just to get a sense?

00:20:07.680 | - It is very hard.

00:20:09.720 | I mean, in the early days,

00:20:10.960 | particularly when the first accelerators are being built

00:20:12.960 | in like 1932, Ernest Lawrence builds the first,

00:20:17.920 | what we call a cyclotron,

00:20:18.880 | which is like a little accelerator, this big or so.

00:20:21.760 | There's another one. - Literally that big?

00:20:22.920 | - This tiny little thing, yeah.

00:20:24.520 | I mean, so most of the first accelerators

00:20:27.840 | were what we call fixed target experiments.

00:20:31.000 | So you had a ring,

00:20:32.600 | you accelerate particles around the ring

00:20:34.080 | and then you fire them out the side into some target.

00:20:37.480 | So that makes the kind of,

00:20:39.480 | the colliding bit is relatively straightforward

00:20:41.320 | 'cause you just fire it,

00:20:42.360 | whatever it is you want to fire it at.

00:20:43.640 | The hard bit is the steering the beams

00:20:46.200 | with the magnetic fields,

00:20:47.120 | getting strong enough electric fields to accelerate them,

00:20:49.560 | all that kind of stuff.

00:20:50.400 | The first colliders where you have two beams

00:20:53.760 | colliding head on, that comes later.

00:20:56.680 | And I don't think it's done until maybe the 1980s.

00:21:01.680 | I'm not entirely sure, but it takes,

00:21:04.200 | it's a much harder problem.

00:21:05.360 | - That's crazy 'cause you have to like perfectly

00:21:08.680 | get them to hit each other.

00:21:09.840 | I mean, we're talking about, I mean, what scale,

00:21:13.120 | what's the, I mean, the temporal thing is a giant mess,

00:21:18.120 | but the spatially, like the size, it's tiny.

00:21:23.160 | - Well, to give you a sense of the LHC beams,

00:21:26.080 | the cross-sectional diameter is,

00:21:29.120 | I think, around a dozen or so microns.

00:21:32.800 | So, you know, 10 millionths of a meter.

00:21:37.080 | - And a beam, sorry, just to clarify,

00:21:39.880 | a beam contains how many,

00:21:41.320 | is it the bunches that you mentioned?

00:21:43.080 | Is it multiple parts or is it just one part?

00:21:45.080 | - Oh, no, no, the bunches contain,

00:21:46.560 | say, a hundred billion protons each.

00:21:48.920 | So a bunch is, it's not really bunch-shaped.

00:21:51.040 | They're actually quite long.

00:21:51.880 | They're like 30 centimeters long,

00:21:53.680 | but thinner than a human hair.

00:21:54.880 | So like very, very narrow, long sort of objects.

00:21:58.440 | Those are the things.

00:21:59.280 | So what happens in the LHC is you steer the beams

00:22:02.240 | so that they cross in the middle of the detector.

00:22:06.080 | So basically you have these swarms of protons

00:22:08.560 | that are flying through each other.

00:22:10.160 | And most of that, you have, sorry,

00:22:11.520 | a hundred billion coming one way,

00:22:13.080 | a hundred billion another way,

00:22:14.500 | maybe 10 of them will hit each other.

00:22:17.080 | - Oh, okay, so this, okay, that makes a lot more sense.

00:22:19.400 | That's nice.

00:22:20.240 | So you're trying to use sort of,

00:22:21.960 | it's like probabilistically, you're not-

00:22:24.560 | - You can't make a single particle

00:22:25.840 | collide with a single other particle.

00:22:26.680 | - Yeah, so- - That's not an efficient way

00:22:27.800 | to do it.

00:22:28.640 | You'd be waiting a very long time to get anything.

00:22:30.760 | - Yeah, so you're basically, right,

00:22:33.160 | so you're relying on probability to be

00:22:36.520 | that some fraction of them are gonna collide.

00:22:38.800 | And then you know which,

00:22:40.800 | 'cause it's a swarm of the same kind of particle.

00:22:44.320 | - So it doesn't matter which ones hit each other exactly.

00:22:46.440 | I mean, that's not to say it's not hard.

00:22:48.240 | You've got to, one of the challenges

00:22:50.400 | to make the collisions work

00:22:51.480 | is you have to squash these beams to very, very,

00:22:54.520 | basically the narrower they are, the better,

00:22:56.040 | 'cause the higher chances of them colliding.

00:22:58.800 | If you think about two flocks of birds

00:23:00.400 | flying through each other,

00:23:01.600 | the birds are all far apart in the flocks.

00:23:03.680 | There's not much chance that they'll collide.

00:23:04.960 | If they're all flying densely together,

00:23:06.440 | then they're much more likely to collide with each other.

00:23:08.360 | So that's the sort of problem.

00:23:10.040 | And it's tuning those magnetic fields,

00:23:12.040 | getting the magnetic fields powerful enough

00:23:13.400 | that you squash the beams and focus them

00:23:15.240 | so that you get enough collisions.

00:23:16.920 | - That's super cool.

00:23:17.920 | Do you know how much software is involved here?

00:23:20.360 | I mean, so if I come from the software world

00:23:22.400 | and it's fascinating,

00:23:23.600 | this seems like,

00:23:26.240 | it's the software's buggy and messy.

00:23:29.040 | So you almost don't want to rely on software too much.

00:23:31.840 | Like if you do, it has to be low level,

00:23:33.880 | like Fortran style programming.

00:23:36.280 | Do you know how much software

00:23:37.480 | is in a large Hadron Collider?

00:23:39.440 | - I mean, it depends at which level, a lot.

00:23:41.560 | I mean, the whole thing is obviously computer controlled.

00:23:43.600 | So, I mean, I don't know a huge amount

00:23:45.400 | about how the software for the actual accelerator works,

00:23:49.280 | but I've been in the control center.

00:23:51.280 | So at CERN, there's this big control room,

00:23:53.200 | which is a bit like a NASA mission control

00:23:55.400 | with big banks of desks where the engineers sit

00:23:57.680 | and they monitor the LHC

00:23:59.120 | 'cause you obviously can't be in the tunnel

00:24:00.760 | when it's running, so everything's remote.

00:24:03.360 | I mean, one sort of anecdote about the sort of software side

00:24:07.360 | in 2008, when the LHC first switched on,

00:24:10.360 | they had this big launch event

00:24:11.560 | and then, you know, big press conference party

00:24:14.840 | to inaugurate the machine.

00:24:16.200 | And about 10 days after that,

00:24:18.240 | they were doing some tests

00:24:19.520 | and this dramatic event happened

00:24:22.000 | where a huge explosion basically took place in a tunnel

00:24:24.880 | that destroyed or damaged, badly damaged

00:24:26.800 | about half a kilometer of the machine.

00:24:29.800 | But the story is,

00:24:30.840 | the engineers are in the control room that day.

00:24:33.520 | One guy told me this story about, you know,

00:24:35.240 | basically all these screens they have in the control room

00:24:37.640 | started going red.

00:24:38.480 | So all these alarms, like, you know,

00:24:40.080 | kind of in software going off

00:24:42.240 | and then they assumed that there's something wrong

00:24:43.440 | with the software 'cause there's no way

00:24:45.440 | something this catastrophic could have happened.

00:24:48.640 | But I mean, when I worked on,

00:24:51.080 | when I was a PhD student,

00:24:52.280 | one of my jobs was to help to maintain the software

00:24:56.000 | that's used to control the detector that we work on.

00:24:59.080 | And that was, it's relatively robust,

00:25:01.120 | not so, you don't want it to be too fancy.

00:25:02.920 | You don't want it to sort of fall over too easily.

00:25:04.600 | The more clever stuff comes

00:25:07.000 | when you're talking about analyzing the data

00:25:08.440 | and that's where the sort of, you know.

00:25:10.520 | - Are we jumping around too much?

00:25:11.680 | Did we finish with the standard model?

00:25:13.120 | - We didn't, no.

00:25:13.960 | - We didn't.

00:25:14.800 | So have we even started talking about quarks?

00:25:17.000 | - We haven't talked to them yet, no.

00:25:18.000 | We got to the messy zoo of particles.

00:25:20.320 | - Let me, let's go back there if it's okay.

00:25:22.920 | - Okay, that's fine.

00:25:23.760 | - Can you take us to the rest of the history

00:25:25.920 | of physics in the 20th century?

00:25:27.680 | - Okay.

00:25:28.520 | - Sure.

00:25:29.360 | Okay, so circa 1960, you have this,

00:25:31.960 | you have these a hundred or so particles.

00:25:33.640 | It's a bit like the periodic table all over again.

00:25:35.480 | So you've got like having a hundred elements,

00:25:37.840 | sort of a bit like that.

00:25:39.200 | And people start to try to impose some order.

00:25:41.440 | So Murray Gelman,

00:25:43.600 | he's a theoretical physicist American from New York.

00:25:47.640 | He realizes that there are these symmetries

00:25:50.440 | in these particles that if you arrange them

00:25:52.400 | in certain ways, they relate to each other

00:25:54.400 | and he uses these symmetry principles

00:25:56.080 | to predict the existence of particles

00:25:58.240 | that haven't been discovered,

00:25:59.240 | which are then discovered in accelerators.

00:26:01.040 | So this starts to suggest

00:26:02.480 | there's not just random collections of crap.

00:26:04.480 | There's like, you know, actually some order

00:26:06.440 | to this underlying it.

00:26:08.720 | A little bit later in 1960,

00:26:11.120 | again, it's around the 1960s.

00:26:13.240 | He proposes along with another physicist

00:26:16.400 | called George Zweig that these symmetries arise

00:26:19.840 | because just like the patterns in the periodic table arise

00:26:23.360 | because atoms are made of electrons and protons,

00:26:26.400 | that these patterns are due to the fact

00:26:28.120 | that these particles are made of smaller things

00:26:30.240 | and they are called quarks.

00:26:31.880 | So these are the particles that predicted from theory

00:26:34.480 | for a long time, no one really believes they're real.

00:26:36.720 | A lot of people think that they're a kind

00:26:38.400 | of theoretical convenience that happened to fit the data

00:26:41.480 | but there's no evidence.

00:26:42.560 | No one's ever seen a quark in any experiment.

00:26:45.440 | And lots of experiments are done to try to find quarks,

00:26:48.600 | to try to knock a quark out of a...

00:26:50.480 | So the idea, if protons and neutrons are made of quarks,

00:26:52.880 | you should be able to knock a quark out and see the quark.

00:26:55.160 | That never happens.

00:26:56.040 | And we still have never actually managed to do that.

00:26:58.160 | - Wait, really?

00:26:59.280 | - No.

00:27:00.120 | So the way that it's done in the end

00:27:02.240 | is this machine that's built in California

00:27:04.640 | at the Stanford Lab, Stanford Linear Accelerator,

00:27:08.840 | which is essentially a gigantic

00:27:10.520 | three kilometer long electron gun.

00:27:12.480 | It fires electrons almost the speed of light at protons.

00:27:16.280 | And when you do these experiments,

00:27:17.840 | what you find is at very high energy,

00:27:20.120 | the electrons bounce off small hard objects

00:27:24.000 | inside the proton.

00:27:25.400 | So it's a bit like taking an X-ray of the proton.

00:27:28.080 | You're firing these very light, high energy particles

00:27:31.600 | and they're pinging off little things inside the proton

00:27:34.280 | that are like ball bearings, if you like.

00:27:36.240 | So you actually, that way they resolve

00:27:39.040 | that there are three things inside the proton,

00:27:42.040 | which are quarks, the quarks that Gell-Mann

00:27:44.160 | and Zweig had predicted.

00:27:45.440 | So that's really the evidence that convinces people

00:27:47.840 | that these things are real.

00:27:49.360 | The fact that we've never seen one

00:27:50.800 | in an experiment directly,

00:27:51.960 | they're always stuck inside other particles.

00:27:56.200 | And the reason for that is essentially

00:27:58.160 | to do with a strong force.

00:27:59.080 | The strong force is the force that holds quarks together.

00:28:01.680 | And it's so strong, it's impossible

00:28:04.000 | to actually liberate a quark.

00:28:06.440 | So if you try and pull a quark out of a proton,

00:28:08.240 | what actually ends up happening

00:28:09.680 | is that you kind of create this spring-like bond

00:28:14.240 | in the strong force.

00:28:15.080 | You imagine two quarks that are held together

00:28:16.760 | by a very powerful spring.

00:28:18.520 | You pull and pull and pull,

00:28:19.920 | more and more energy gets stored in that bond,

00:28:22.240 | like stretching a spring.

00:28:23.400 | And eventually the tension gets so great,

00:28:25.320 | the spring snaps and the energy in that bond

00:28:28.680 | gets turned into two new quarks

00:28:30.640 | that go on the broken ends.

00:28:32.400 | So you started with two quarks,

00:28:33.440 | you end up with four quarks.

00:28:34.680 | So you never actually get to take a quark out,

00:28:37.160 | you just end up making loads more quarks in the process.

00:28:39.880 | - So how do we, again, forgive the dumb question,

00:28:42.920 | how do we know quarks are real then?

00:28:44.880 | - Well, A, from these experiments where we can scatter,

00:28:48.080 | you fire electrons into the protons,

00:28:49.680 | they can burrow into the proton and knock off,

00:28:52.640 | and they can bounce off these quarks.

00:28:55.120 | So you can see from the angles the electrons come out.

00:28:58.120 | - I see, you can infer.

00:28:59.120 | - You can infer that these things are there.

00:29:02.080 | The quark model can also be used,

00:29:03.640 | it has a lot of success,

00:29:04.880 | so you can use it to predict the existence

00:29:06.600 | of new particles that hadn't been seen.

00:29:08.760 | So, and it basically, there's lots of data

00:29:10.800 | basically showing from, you know,

00:29:12.360 | when we fire protons at each other at the LHC,

00:29:16.440 | a lot of quarks get knocked all over the place,

00:29:18.840 | and every time they try and escape from, say,

00:29:20.880 | one of their protons,

00:29:21.720 | they make a whole jet of quarks that go flying off,

00:29:25.640 | bound up in other sorts of particles made of quarks.

00:29:28.600 | So all the sort of the theoretical predictions

00:29:30.760 | from the basic theory of the strong force and the quarks

00:29:33.800 | all agrees with what we are seeing in experiments.

00:29:35.420 | We've just never seen an actual quark on its own,

00:29:38.040 | because unfortunately it's impossible

00:29:39.320 | to get them out on their own.

00:29:41.180 | - So quarks, these crazy smaller things

00:29:45.160 | that are hard to imagine are real.

00:29:47.200 | So what else?

00:29:48.180 | What else is part of the story here?

00:29:49.820 | - So the other thing that's going on at the time,

00:29:52.120 | around the '60s, is an attempt to understand the forces

00:29:57.120 | that make these particles interact with each other.

00:30:00.240 | So you have the electromagnetic force,

00:30:01.800 | which is the force that was sort of discovered

00:30:03.920 | to some extent in this room, or at least in this building.

00:30:07.160 | So the first, what we call quantum field theory

00:30:10.000 | of the electromagnetic force is developed in the 1940s

00:30:15.000 | and '50s by Feynman, Richard Feynman,

00:30:18.280 | amongst other people, Julian Schwinger, Tomonaga,

00:30:22.000 | who come up with the first, what we call

00:30:23.400 | a quantum field theory of the electromagnetic force.

00:30:25.740 | And this is where this description of,

00:30:27.360 | which I gave you at the beginning,

00:30:28.360 | that particles are ripples in fields.

00:30:30.820 | Well, in this theory, the photon, the particle of light,

00:30:33.920 | is described as a ripple in this quantum field

00:30:36.320 | called the electromagnetic field.

00:30:38.720 | And the attempt then is made to try,

00:30:40.240 | well, can we come up with a quantum field theory

00:30:42.260 | of the other forces, of the strong force

00:30:44.440 | and the weak, the third force, which we haven't discussed,

00:30:47.120 | which is the weak force, which is a nuclear force.

00:30:50.760 | We don't really experience it in our everyday lives,

00:30:52.640 | but it's responsible for radioactive decay.

00:30:54.960 | It's the force that allows, you know,

00:30:56.960 | in a radioactive atom to turn into a different element,

00:31:00.200 | for example.

00:31:01.040 | - And I don't know if you've explicitly mentioned,

00:31:03.360 | but so there's technically four forces.

00:31:06.040 | - Yes.

00:31:06.920 | - I guess three of them would be in the standard model,

00:31:09.880 | like the weak, the strong, and the electromagnetic,

00:31:13.400 | and then there's gravity.

00:31:14.520 | - And there's gravity, which we don't worry about that,

00:31:16.160 | 'cause it's too hard.

00:31:17.000 | - Who cares?

00:31:17.840 | - Maybe we bring that up at the end, but yeah.

00:31:19.920 | Gravity so far, we don't have a quantum theory of,

00:31:22.320 | and if you can solve that problem,

00:31:23.520 | you'll win a Nobel Prize.

00:31:25.080 | - Well, we're gonna have to bring up the graviton

00:31:27.000 | at some point, I'm gonna ask you,

00:31:28.160 | but let's leave that to the side for now.

00:31:31.160 | So those three, okay, Feynman, electromagnetic force,

00:31:36.160 | the quantum field.

00:31:38.440 | - Yeah.

00:31:39.360 | - And where does the weak force come in?

00:31:41.920 | - So yeah, well, first of all,

00:31:43.560 | I mean, the strong force is the easiest.

00:31:44.760 | The strong force is a little bit like

00:31:46.680 | the electromagnetic force.

00:31:47.600 | It's a force that binds things together.

00:31:49.160 | So that's the force that holds quarks together

00:31:51.040 | inside the proton, for example.

00:31:52.860 | So a quantum field theory of that force is discovered

00:31:57.160 | in the, I think it's in the '60s,

00:31:58.900 | and it predicts the existence of new force particles

00:32:03.260 | called gluons.

00:32:04.520 | So gluons are a bit like the photon.

00:32:06.920 | The photon is the particle of electromagnetism.

00:32:09.480 | Gluons are the particles of the strong force.

00:32:13.520 | So there's, just like there's an electromagnetic field,

00:32:15.880 | there's something called a gluon field,

00:32:17.560 | which is also all around us.

00:32:19.480 | - So these, some of these particles, I guess,

00:32:21.760 | are the force carriers or whatever.

00:32:23.640 | They carry the-

00:32:24.480 | - Well, it depends how you wanna think about it.

00:32:25.960 | I mean, really the field, the strong force field,

00:32:28.480 | the gluon field is the thing that binds the quarks together.

00:32:32.880 | The gluons are the little ripples in that field.

00:32:35.440 | So that like, in the same way that the photon

00:32:37.200 | is a ripple in the electromagnetic field.

00:32:39.880 | But the thing that really does the binding is the field.

00:32:43.600 | I mean, you may have heard people talk about things like,

00:32:46.400 | I don't know if you've heard the phrase virtual particle.

00:32:49.840 | So sometimes in some, if you hear people describing

00:32:52.440 | how forces are exchanged between particles,

00:32:54.880 | they quite often talk about the idea that, you know,

00:32:56.600 | if you have an electron and another electron, say,

00:32:59.280 | and they're repelling each other

00:33:00.640 | through the electromagnetic force,

00:33:03.080 | you can think of that as if they're exchanging photons.

00:33:05.800 | So they're kind of firing photons backwards and forwards

00:33:07.680 | between each other and that causes them to repel.

00:33:11.040 | - That photon is then a virtual particle.

00:33:13.080 | - Yes, that's what we call a virtual particle.

00:33:14.440 | In other words, it's not a real thing.

00:33:15.560 | It doesn't actually exist.

00:33:16.840 | So it's an artifact of the way theorists do calculations.

00:33:19.920 | So when they do calculations in quantum field theory,

00:33:22.160 | rather than, no one's discovered a way

00:33:24.440 | of just treating the whole field.

00:33:25.800 | You have to break the field down into simpler things.

00:33:28.200 | So you can basically treat the field

00:33:30.200 | as if it's made up of lots of these virtual photons,

00:33:33.560 | but there's no experiment that you can do

00:33:35.680 | that can detect these particles being exchanged.

00:33:38.440 | What's really happening in reality

00:33:40.480 | is that the electromagnetic field

00:33:42.200 | is warped by the charge of the electron

00:33:44.800 | and that causes the force.

00:33:46.240 | But the way we do calculations involves particles.

00:33:49.320 | So it's a bit confusing,

00:33:50.840 | but it's really a mathematical technique.

00:33:53.300 | It's not something that corresponds to reality.

00:33:55.720 | - I mean, that's part, I guess, of the Feynman diagrams.

00:33:58.240 | - Yes.

00:33:59.080 | - Is this these virtual particles, okay.

00:34:00.080 | - That's right, yeah.

00:34:01.520 | - Some of these have mass, some of them don't.

00:34:04.560 | Is that, what does that even mean, not to have mass?

00:34:09.040 | And maybe you can say,

00:34:10.080 | which one of them have mass and which don't?

00:34:12.840 | - Okay, so--

00:34:14.160 | - And why is mass important or relevant

00:34:17.000 | in this field view of the universe?

00:34:22.000 | - Well, there are actually only two particles

00:34:23.720 | in the standard model that don't have mass,

00:34:25.480 | which are the photon and the gluons.

00:34:28.480 | So they are massless particles,

00:34:30.280 | but the electron, the quarks,

00:34:32.960 | and there are a bunch of other particles

00:34:34.120 | that I haven't discussed.

00:34:34.960 | There's something called a muon and a tau,

00:34:36.400 | which are basically heavy versions of the electron

00:34:39.320 | that are unstable.

00:34:40.160 | You can make them in accelerators,

00:34:41.400 | but they don't form atoms or anything.

00:34:44.240 | They don't exist for long enough.

00:34:45.640 | But all the matter particles, there are 12 of them,

00:34:48.720 | six quarks and six, what we call leptons,

00:34:51.980 | which includes the electron and its two heavy versions

00:34:54.480 | and three neutrinos.

00:34:55.960 | All of them have mass.

00:34:57.440 | And so do, this is the critical bit.

00:34:59.520 | So the weak force,

00:35:00.840 | which is the third of these quantum forces,

00:35:03.840 | which is one of the hardest to understand,

00:35:06.240 | the force particles of that force have very large masses.

00:35:12.840 | And there are three of them.

00:35:14.900 | They're called the W plus, the W minus, and the Z boson.

00:35:19.560 | And they have masses of between 80 and 90 times

00:35:23.000 | that of the protons.

00:35:24.560 | So they're very heavy.

00:35:25.400 | - Wow.

00:35:26.240 | - They're very heavy things.

00:35:27.060 | - So they're what, the heaviest, I guess?

00:35:29.440 | - They're not the heaviest.

00:35:30.280 | The heaviest particle is the top quark,

00:35:32.920 | which has a mass of about 175-ish protons.

00:35:37.920 | So that's really massive.

00:35:39.720 | And we don't know why it's so massive.

00:35:41.680 | But coming back to the weak force,

00:35:43.160 | so the problem in the '60s and '70s was that

00:35:47.380 | the reason that the electromagnetic force

00:35:50.100 | is a force that we can experience in our everyday lives.

00:35:51.920 | So if we have a magnet and a piece of metal,

00:35:53.240 | you can hold it a meter apart if it's powerful enough

00:35:56.160 | and you'll feel a force.

00:35:57.040 | Whereas the weak force only becomes apparent

00:36:00.400 | when you basically have two particles touching

00:36:03.180 | at the scale of a nucleus.

00:36:05.360 | So we get to very short distances

00:36:06.980 | before this force becomes manifest.

00:36:09.600 | It's not, we don't get weak forces going on in this room.

00:36:12.280 | We don't notice them.

00:36:13.600 | And the reason for that is that the particle,

00:36:15.840 | well, the field that transmits the weak force,

00:36:20.160 | the particle that's associated with that field

00:36:22.280 | has a very large mass,

00:36:23.360 | which means that the field dies off very quickly.

00:36:26.240 | So as you, whereas an electric charge,

00:36:28.360 | if you were to look at the shape of the electromagnetic field

00:36:30.640 | it would fall off with this,

00:36:32.160 | you have this thing called the inverse square law,

00:36:33.760 | which is the idea that the force halves

00:36:36.200 | every time you double the distance.

00:36:38.740 | No, sorry, it doesn't half, it quarters

00:36:40.640 | every time you double the distance

00:36:42.560 | between say the two particles.

00:36:44.220 | Whereas the weak force kind of,

00:36:45.760 | you move a little bit away from the nucleus

00:36:47.320 | and it just disappears.

00:36:49.400 | The reason for that is because these fields,

00:36:51.980 | the particles that go with them have a very large mass.

00:36:55.400 | But the problem that theorists faced in the '60s

00:36:59.880 | was that if you tried to introduce massive force fields,

00:37:04.320 | the theory gave you nonsensical answers.

00:37:06.520 | So you'd end up with infinite results

00:37:08.680 | for a lot of the calculations you tried to do.

00:37:11.140 | So the basically, it turned out,

00:37:12.520 | it seemed that quantum field theory was incompatible

00:37:15.220 | with having massive particles.

00:37:17.320 | Not just the force particles actually,

00:37:18.720 | but even the electron was a problem.

00:37:21.920 | So this is where the Higgs

00:37:23.760 | that we sort of alluded to comes in.

00:37:25.640 | And the solution was to say, okay, well,

00:37:28.400 | actually all the particles in the standard model are mass,

00:37:30.480 | they have no mass.

00:37:31.540 | So the quarks, the electron, they don't have a mass.

00:37:33.360 | Neither do these weak particles,

00:37:34.820 | they don't have mass either.

00:37:36.720 | What happens is they actually acquire mass

00:37:38.520 | through another process.

00:37:40.420 | They get it from somewhere else.

00:37:41.660 | They don't actually have it intrinsically.

00:37:43.780 | So this idea that was introduced by,

00:37:46.520 | well, Peter Higgs is the most famous,

00:37:47.760 | but actually there are about six people

00:37:49.400 | that came up with the idea more or less at the same time,

00:37:52.080 | is that you introduce a new quantum field,

00:37:55.200 | which is another one of these invisible things

00:37:56.880 | that's everywhere.

00:37:58.120 | And it's through the interaction with this field

00:38:01.500 | that particles get mass.

00:38:02.640 | So you can think of, say, an electron in the Higgs field,

00:38:07.060 | it kind of Higgs field kind of bunches around the electron.

00:38:10.880 | It's sort of drawn towards the electron.

00:38:12.840 | And that energy that's stored in that field

00:38:15.560 | around the electron is what we see

00:38:17.680 | as the mass of the electron.

00:38:19.280 | But if you could somehow turn off the Higgs field,

00:38:21.700 | then all the particles in nature would become massless

00:38:23.840 | and fly around at the speed of light.

00:38:26.500 | So this idea of the Higgs field allowed other people,

00:38:31.500 | other theorists to come up with a, well,

00:38:36.120 | it was another, basically a unified theory

00:38:39.480 | of the electromagnetic force and the weak force.

00:38:41.520 | So once you bring in the Higgs field,

00:38:43.040 | you can combine two of the forces into one.

00:38:45.600 | So it turns out the electromagnetic force

00:38:47.860 | and the weak force are just two aspects

00:38:49.600 | of the same fundamental force.

00:38:52.380 | And at the LHC, we go to high enough energies

00:38:54.720 | that you see these two forces unifying effectively.

00:38:59.440 | - So first of all, it started as a theoretical notion,

00:39:04.200 | like this is something, and then,

00:39:07.080 | I mean, wasn't the Higgs called the god particle

00:39:09.880 | at some point?

00:39:10.720 | - It was by a guy trying to sell popular science books, yeah.

00:39:13.640 | - Yeah, but I mean, I remember,

00:39:16.400 | 'cause when I was hearing it,

00:39:17.880 | I thought it would, I mean, that would solve a lot of,

00:39:22.040 | that unify a lot of our ideas of physics,

00:39:24.400 | is what was my notion.

00:39:26.320 | But maybe you can speak to that.

00:39:29.040 | Is it as big of a leap?

00:39:30.800 | Is it a god particle, or is it a Jesus particle?

00:39:34.160 | (laughing)

00:39:36.280 | Which, you know, what's the big contribution of Higgs

00:39:39.000 | in terms of this unification power?

00:39:40.800 | - Yeah, I mean, to understand that,

00:39:42.560 | it maybe helps to know the history a little bit.

00:39:45.080 | So when the, what we call electroweak theory

00:39:47.760 | is put together, which is where you unify electromagnetism

00:39:50.600 | with the weak force, and Higgs is involved in all of that.

00:39:53.280 | So that theory, which was written in the mid '70s,

00:39:55.440 | predicted the existence of four new particles,

00:39:59.360 | the W plus boson, the W minus boson,

00:40:01.760 | the Z boson, and the Higgs boson.

00:40:03.480 | So there were these four particles

00:40:04.760 | that came with the theory,

00:40:06.000 | that were predicted by the theory.

00:40:07.440 | In 1983, '84, the Ws and the Z particles were discovered

00:40:12.360 | at an accelerator at CERN,

00:40:14.280 | called the super proton synchrotron,

00:40:15.960 | which was a seven kilometer particle collider.

00:40:19.200 | So three of the bits of this theory had already been found.

00:40:22.760 | So people were pretty confident from the '80s

00:40:25.520 | that the Higgs must exist,

00:40:27.000 | because it was a part of this family of particles

00:40:30.760 | that this theoretical structure only works

00:40:33.000 | if the Higgs is there.

00:40:34.440 | So what then happens,

00:40:36.560 | and so you have this question about why is the LHC

00:40:38.120 | the size it is? - Yes.

00:40:39.400 | - Well, actually the tunnel that the LHC is in

00:40:41.480 | was not built for the LHC.

00:40:42.800 | It was built for a previous accelerator

00:40:45.120 | called the large electron positron collider.

00:40:48.720 | So that began operation in the late '80s, early '90s.

00:40:53.720 | They basically, that's when they dug

00:40:55.240 | the 27 kilometer tunnel.

00:40:56.440 | They put this accelerator into it,

00:40:58.000 | the collider that fires electrons and anti electrons

00:41:00.720 | at each other, electrons and positrons.

00:41:02.640 | So the purpose of that machine was,

00:41:05.160 | well, it was actually to look for the Higgs.

00:41:06.680 | That was one of the things it was trying to do.

00:41:08.680 | It didn't have enough energy to do it in the end.

00:41:11.400 | But the main thing it achieved was it studied

00:41:13.840 | the W and the Z particles at very high precision.

00:41:17.560 | So it made loads of these things.

00:41:19.280 | Previously you could only make a few of them

00:41:20.560 | at the previous accelerator.

00:41:21.440 | So you could study these really, really precisely.

00:41:24.480 | And by studying their properties,

00:41:25.680 | you could really test this electroweak theory

00:41:28.200 | that had been invented in the '70s

00:41:29.800 | and really make sure that it worked.

00:41:31.280 | So actually by 1999, when this machine turned off,

00:41:36.280 | people knew, well, okay, you never know

00:41:39.480 | until you find the thing.

00:41:41.400 | But people were really confident

00:41:43.000 | that this electroweak theory was right.

00:41:44.840 | And that the Higgs almost,

00:41:46.840 | the Higgs or something very like the Higgs had to exist

00:41:49.880 | because otherwise the whole thing doesn't work.

00:41:52.280 | It'd be really weird if you could discover

00:41:54.040 | and these particles, they all behave exactly

00:41:55.920 | as your theory tells you they should.

00:41:57.360 | But somehow this key piece of the picture is not there.

00:42:00.920 | So in a way, it depends how you look at it.

00:42:03.960 | The discovery of the Higgs on its own

00:42:05.840 | is obviously a huge achievement in many,

00:42:10.040 | both experimentally and theoretically.

00:42:12.360 | On the other hand, it's like having a jigsaw puzzle

00:42:15.240 | where every piece has been filled in.

00:42:17.080 | You have this beautiful image, there's one gap

00:42:19.000 | and you kind of know that piece must be there somewhere.

00:42:22.240 | - Yeah. - Right.

00:42:23.080 | So the discovery in itself, although it's important,

00:42:27.960 | is not so interesting.

00:42:30.400 | - It's like a confirmation of the obvious at that point.

00:42:34.360 | - But what makes it interesting

00:42:36.040 | is not that it just completes the standard model,

00:42:38.080 | which is a theory that we've known

00:42:39.960 | had the basic layout of for 40 years or more now.

00:42:44.760 | It's that the Higgs actually is a unique particle.

00:42:48.400 | It's very different to any of the other particles

00:42:50.520 | in the standard model.

00:42:51.840 | And it's a theoretically very troublesome particle.

00:42:55.240 | There are a lot of nasty things to do with the Higgs,

00:42:59.200 | but also opportunities.

00:43:00.800 | So that we basically, we don't really understand

00:43:02.520 | how such an object can exist in the form that it does.

00:43:06.200 | So there are lots of reasons for thinking

00:43:08.440 | that the Higgs must come with a bunch of other particles

00:43:12.520 | or that it's perhaps made of other things.

00:43:15.000 | So it's not a fundamental particle

00:43:16.400 | that it's made of smaller things.

00:43:17.880 | I can talk about that if you like a bit.

00:43:19.520 | - That's still a notion.

00:43:20.920 | So the Higgs might not be a fundamental particle,

00:43:24.760 | that there might be some, oh man.

00:43:27.160 | - So that is an idea.

00:43:28.360 | It's not been demonstrated to be true.

00:43:31.040 | But I mean, all of these ideas basically come

00:43:33.800 | from the fact that this is a problem that motivated

00:43:38.520 | a lot of development in physics in the last 30 years or so.

00:43:42.320 | And it's this basic fact that the Higgs field,

00:43:44.720 | which is this field that's everywhere in the universe,

00:43:47.240 | this is the thing that gives mass to the particles.

00:43:49.000 | And the Higgs field is different

00:43:50.160 | from all the other fields in that,

00:43:52.080 | let's say you take the electromagnetic field,

00:43:54.360 | which is, if we actually were to measure

00:43:56.040 | the electromagnetic field in this room,

00:43:57.360 | we would measure all kinds of stuff going on

00:43:58.840 | 'cause there's light, there's gonna be microwaves

00:44:00.920 | and radio waves and stuff.

00:44:02.120 | But let's say we could go to a really, really remote part

00:44:04.920 | of empty space and shield it and put a big box around it

00:44:07.680 | and then measure the electromagnetic field in that box.

00:44:10.080 | The field would be almost zero,

00:44:12.200 | apart from some little quantum fluctuations,

00:44:14.800 | but basically it goes to naught.

00:44:16.960 | The Higgs field has a value everywhere.

00:44:19.160 | So it's a bit like the whole,

00:44:20.680 | it's like the entire space has got this energy

00:44:23.440 | stored in the Higgs field, which is not zero,

00:44:25.440 | it's finite, it's got some,

00:44:26.960 | it's a bit like having the temperature of space raised

00:44:29.920 | to some background temperature.

00:44:32.360 | And it's that energy that gives mass to the particles.

00:44:36.880 | So the reason that electrons and quarks have mass

00:44:40.440 | is through the interaction with this energy

00:44:42.440 | that's stored in the Higgs field.

00:44:44.800 | Now, it turns out that the precise value this energy has

00:44:49.800 | has to be very carefully tuned if you want a universe

00:44:55.600 | where interesting stuff can happen.

00:44:58.140 | So if you push the Higgs field down,

00:45:00.660 | it has a tendency to collapse to,

00:45:03.040 | well, there's a tendency,

00:45:04.000 | if you do your sort of naive calculations,

00:45:05.640 | there are basically two possible likely configurations

00:45:08.280 | for the Higgs field, which is either it's zero everywhere,

00:45:11.320 | in which case you have a universe

00:45:12.480 | which is just particles with no mass that can't form atoms

00:45:15.840 | and just fly about at the speed of light,

00:45:18.040 | or it explodes to an enormous value,

00:45:20.700 | what we call the Planck scale,

00:45:21.800 | which is the scale of quantum gravity.

00:45:24.160 | And at that point, if the Higgs field was that strong,

00:45:27.060 | even an electron would become so massive

00:45:28.900 | that it would collapse into a black hole.

00:45:31.200 | And then you have a universe made of black holes

00:45:33.080 | and nothing like us.

00:45:34.940 | So it seems that the strength of the Higgs field

00:45:37.640 | is to achieve the value that we see

00:45:40.160 | requires what we call fine tuning of the laws of physics.

00:45:42.920 | You have to fiddle around with the other fields

00:45:45.340 | in the standard model and their properties

00:45:47.320 | to just get it to this right sort of Goldilocks value

00:45:50.760 | that allows atoms to exist.

00:45:53.120 | This is deeply fishy.

00:45:54.580 | People really dislike this.

00:45:57.400 | - Well, yeah, I guess, so what would be,

00:45:59.400 | so two explanations.

00:46:00.840 | One, there's a God that designed this perfectly,

00:46:03.040 | and two is there's an infinite number

00:46:05.560 | of alternate universes, and we just happen

00:46:08.680 | to be in the one in which life is possible.

00:46:11.120 | - Yeah, yeah. - Complexity.

00:46:12.360 | So when you say, I mean, life, any kind of complexity,

00:46:15.540 | that's not either complete chaos or black holes.

00:46:19.920 | - Yeah, yeah.

00:46:21.520 | - I mean, how does that make you feel?

00:46:22.760 | What do you make of that?

00:46:23.600 | That's such a fascinating notion

00:46:25.280 | that this perfectly tuned field

00:46:28.360 | that's the same everywhere is there.

00:46:31.120 | What do you make of that?

00:46:33.160 | Yeah, what do you make of that?

00:46:34.200 | - I mean, yeah, so you laid out

00:46:35.320 | two of the possible explanations.

00:46:36.680 | - Really? - Somewhat.

00:46:37.920 | Yeah, I mean, well, someone,

00:46:39.520 | some cosmic creator went, yeah, let's fix that

00:46:42.160 | to be at the right level.

00:46:43.160 | That's one possibility, I guess.

00:46:44.420 | It's not a scientifically testable one,

00:46:45.880 | but theoretically, I guess it's possible.

00:46:48.720 | - Sorry to interrupt, but there could also be

00:46:50.880 | not a designer, but couldn't there be just,

00:46:53.480 | I guess I'm not sure what that would be,

00:46:55.960 | but some kind of force that,

00:46:58.220 | some kind of mechanism by which

00:47:04.240 | this kind of field is enforced

00:47:09.880 | in order to create complexity,

00:47:11.960 | basically forces that pull the universe

00:47:16.320 | towards an interesting complexity.

00:47:19.800 | - I mean, yeah, I mean, there are people

00:47:21.400 | who have those ideas.

00:47:22.320 | I don't really subscribe to them.

00:47:23.640 | - As I'm saying, it sounds really stupid.

00:47:25.560 | - No, I mean, there are definitely people

00:47:27.160 | that make those kind of arguments.

00:47:29.440 | There's ideas that, I think it's Lee Smolin's idea,

00:47:33.040 | one, I think, that universes are born inside black holes.

00:47:38.040 | And so universes, they basically have

00:47:40.320 | like Darwinian evolution of the universe

00:47:42.520 | where universes give birth to other universes.

00:47:44.840 | And if universes where black holes can form

00:47:46.760 | are more likely to give birth to more universes,

00:47:48.800 | so you end up with universes which have similar laws.

00:47:51.280 | I mean, I don't know, whatever.

00:47:52.480 | - But I talked to Lee recently on this podcast

00:47:57.080 | and he's a reminder to me that the physics community

00:48:02.080 | has like so many interesting characters.

00:48:05.600 | It's fascinating.

00:48:06.960 | Anyway, sorry, so.

00:48:07.800 | - I mean, as an experimentalist,

00:48:09.040 | I tend to sort of think, these are interesting ideas,

00:48:11.200 | but they're not really testable.

00:48:12.760 | So I tend not to think about them very much.

00:48:14.720 | So, I mean, going back to the science of this,

00:48:17.580 | there is an explanation.

00:48:19.120 | There is a possible solution to this problem of the Higgs,

00:48:21.240 | which doesn't involve multiverses

00:48:23.160 | or creators fiddling about with the laws of physics.

00:48:26.560 | If the most popular solution

00:48:28.400 | was something called supersymmetry,

00:48:30.440 | which is a theory which involves

00:48:33.760 | a new type of symmetry of the universe.

00:48:35.720 | In fact, it's one of the last types of symmetries

00:48:37.680 | that is possible to have

00:48:38.560 | that we haven't already seen in nature,

00:48:40.400 | which is a symmetry between force particles

00:48:43.600 | and matter particles.

00:48:44.760 | So what we call fermions,

00:48:46.480 | which are the matter particles

00:48:47.880 | and bosons, which are force particles.

00:48:49.920 | And if you have supersymmetry,

00:48:51.120 | then there is a super partner for every particle

00:48:54.520 | in the standard model.

00:48:55.920 | And without going into the details,

00:48:57.520 | the effect of this basically is that

00:48:58.980 | you have a whole bunch of other fields,

00:49:01.320 | and these fields cancel out

00:49:03.760 | the effect of the standard model fields,

00:49:05.680 | and they stabilize the Higgs field

00:49:07.840 | at a nice sensible value.

00:49:09.000 | So in supersymmetry, you naturally,

00:49:11.360 | without any tinkering about

00:49:12.880 | with the constants of nature or anything,

00:49:15.160 | you get a Higgs field with a nice value,

00:49:17.360 | which is the one we see.

00:49:18.960 | So this is one of the reasons,

00:49:20.200 | and supersymmetry has also got lots

00:49:21.600 | of other things going for it.

00:49:22.600 | It predicts the existence of a dark matter particle,

00:49:25.360 | which would be great.

00:49:27.000 | It potentially suggests that the strong force

00:49:30.120 | and the electroweak force unify at high energy.

00:49:32.740 | So lots of reasons people thought

00:49:33.800 | this was a productive idea.

00:49:35.320 | And when the LHC was, just before it was turned on,

00:49:37.800 | there was a lot of hype, I guess,

00:49:39.600 | a lot of an expectation that we would discover

00:49:42.440 | these super partners, because,

00:49:44.280 | and particularly the main reason was

00:49:46.080 | that if supersymmetry stabilizes the Higgs field

00:49:50.240 | at this nice Goldilocks value,

00:49:52.960 | these super particles should have a mass

00:49:55.760 | around the energy that we're probing at the LHC,

00:49:58.520 | around the energy of the Higgs.

00:49:59.920 | So it was kind of thought, you discover the Higgs,

00:50:01.520 | you probably discover super partners as well.

00:50:03.640 | - So once you start creating ripples in this Higgs field,

00:50:06.200 | you should be able to see these kinds of,

00:50:08.680 | you should be, yeah.

00:50:09.520 | - So these super fields would be there.

00:50:11.000 | When at the very beginning I said

00:50:12.320 | we're probing the vacuum,

00:50:13.720 | what I mean is really that,

00:50:15.280 | okay, let's say these super fields exist.

00:50:16.680 | The vacuum contains super fields,

00:50:18.200 | they're there, these supersymmetric fields.

00:50:20.160 | If we hit them hard enough, we can make them vibrate.

00:50:22.640 | We see super particles come flying out.

00:50:24.840 | That's the sort of, that's the idea.

00:50:26.280 | - That's the whole, okay.

00:50:27.120 | - That's the whole point.

00:50:28.160 | - But we haven't.

00:50:30.680 | - But we haven't.

00:50:31.520 | So, so far at least, I mean, we've had now

00:50:35.040 | a decade of data taking at the LHC.

00:50:37.920 | No signs of super partners,

00:50:41.440 | have supersymmetric particles have been found.

00:50:43.320 | In fact, no signs of any physics,

00:50:45.120 | any new particles beyond the standard model

00:50:46.680 | have been found.

00:50:47.520 | So supersymmetry is not the only thing that can do this.

00:50:49.480 | There are other theories that involve

00:50:51.400 | additional dimensions of space

00:50:53.120 | or potentially involve the Higgs boson

00:50:55.640 | being made of smaller things,

00:50:56.880 | being made of other particles.

00:50:58.320 | - Yeah, that's an interesting,

00:50:59.400 | I haven't heard that before.

00:51:00.520 | That's really, that's an interesting point.

00:51:02.440 | Could you maybe linger on that?

00:51:03.600 | Like what, what could be,

00:51:06.360 | what could the Higgs particle be made of?

00:51:08.840 | - Well, so the oldest,

00:51:10.120 | I think the original ideas about this

00:51:11.520 | was these theories called technicolor,

00:51:14.040 | which were basically like an analogy

00:51:16.320 | with the strong force.

00:51:17.280 | So the idea was the Higgs boson

00:51:19.560 | was a bound state of two

00:51:22.480 | very strongly interacting particles

00:51:24.440 | that were a bit like quarks.

00:51:25.520 | So like quarks, but I guess higher energy things

00:51:29.160 | with a super strong force.

00:51:30.360 | So not the strong force,

00:51:31.200 | but a new force that was very strong.

00:51:32.960 | And the Higgs was a bound state of these, these objects.

00:51:36.440 | And the Higgs would in principle, if that was right,

00:51:38.400 | would be the first in a series of

00:51:40.760 | technicolor particles.

00:51:42.360 | Technicolor, I think, not being a theorist,

00:51:45.520 | but it's not, it's basically not done very well,

00:51:48.080 | particularly since the LHC found the Higgs,

00:51:49.560 | that kind of, it rules out, you know,

00:51:52.320 | a lot of these technicolor theories.

00:51:53.440 | But there are other things

00:51:54.280 | that are a bit like technicolor.

00:51:55.400 | So there's a theory called partial compositeness,

00:52:00.400 | which is an idea that some of my colleagues

00:52:02.520 | at Cambridge have worked on,

00:52:04.320 | which is a similar sort of idea

00:52:06.360 | that the Higgs is a bound state

00:52:08.160 | of some strongly interacting particles.

00:52:10.400 | And that the standard model particles themselves,

00:52:12.960 | the more exotic ones like the top quark

00:52:15.080 | are also sort of mixtures of these composite particles.

00:52:20.440 | So it's a kind of an extension to the standard model,

00:52:23.280 | which explains this problem with the Higgs bosons,

00:52:27.000 | Goldilocks value, but also helps us understand.

00:52:30.720 | We have, we're in a situation now, again,

00:52:32.800 | a bit like the periodic table where we have six quarks,

00:52:36.680 | six leptons in this kind of,

00:52:38.600 | you can arrange in this nice table

00:52:39.960 | and there you can see these columns

00:52:41.320 | where the patterns repeat and you go,

00:52:43.640 | "Okay, maybe there's something deeper going on here."

00:52:47.600 | And so this would potentially be something

00:52:49.560 | this partial compositeness theory could explain,

00:52:52.800 | sort of enlarge this picture

00:52:54.280 | that allows us to see the whole symmetrical pattern

00:52:56.400 | and understand what the ingredients, why do we have,

00:52:59.040 | so one of the big questions in particle physics is,

00:53:02.080 | why are there three copies of the matter particles?

00:53:06.160 | So in what we call the first generation,

00:53:07.880 | which is what we're made of,

00:53:08.840 | there's the electron, the electron neutrino,

00:53:11.680 | the up quark and the down quark,

00:53:13.080 | they're the most common matter particles in the universe,

00:53:15.560 | but then there are copies of these four particles

00:53:18.680 | in the second and the third generations.

00:53:20.280 | So things like muons and top quarks and other stuff,

00:53:23.040 | we don't know why, we see these patterns,

00:53:25.160 | we have no idea where it comes from.

00:53:26.360 | So that's another big question,

00:53:28.800 | can we find out the deeper order

00:53:31.920 | that explains this particular periodic table

00:53:35.160 | of particles that we see?

00:53:36.400 | - Is it possible that the deeper order

00:53:39.280 | includes like almost a single entity?

00:53:42.360 | So like something that I guess like string theory

00:53:44.920 | dreams about, is this essentially the dream?

00:53:49.920 | Is to discover something simple, beautiful and unifying?

00:53:54.120 | - Yeah, I mean, that is the dream.

00:53:55.600 | And I think for some people, for a lot of people,

00:53:59.480 | it still is the dream.

00:54:00.400 | So there's a great book by Steven Weinberg,

00:54:03.800 | who is one of the theoretical physicists

00:54:05.760 | who was instrumental in building the standard model.

00:54:08.360 | So he came up with some others with the electroweak theory,

00:54:12.000 | the theory that unified electromagnetism

00:54:13.920 | and the weak force.

00:54:14.760 | And he wrote this book,

00:54:15.680 | I think it was towards the end of the 80s, early 90s,

00:54:18.080 | called "Dreams of a Final Theory,"

00:54:20.000 | which is a very lovely, quite short book

00:54:22.920 | about this idea of a final unifying theory

00:54:26.200 | that brings everything together.

00:54:27.560 | And I think you get a sense reading his book

00:54:29.440 | written at the end of the 80s, early 90s,

00:54:31.760 | that there was this feeling that such a theory was coming.

00:54:35.600 | And that was the time when string theory

00:54:39.160 | had been, was very exciting.

00:54:41.200 | So string theory, there's been this thing

00:54:42.680 | called the super string revolution

00:54:44.080 | and theoretical physics getting very excited.

00:54:46.120 | They discovered these theoretical objects,

00:54:47.960 | these little vibrating loops of string that in principle,

00:54:50.480 | not only was a quantum theory of gravity,

00:54:52.440 | but could explain all the particles in the standard model

00:54:54.840 | and bring it all together.

00:54:55.760 | And as you say, you have one object, the string,

00:54:59.520 | and you can pluck it and the way it vibrates

00:55:02.560 | gives you these different notes,

00:55:03.840 | each of which is a different particle.

00:55:05.960 | So it's a very lovely idea.

00:55:08.160 | But the problem is that, well, there's a few,

00:55:11.920 | people discover that mathematics is very difficult.

00:55:14.680 | So people have spent three decades or more

00:55:17.640 | trying to understand string theory.

00:55:19.120 | And I think, you know,

00:55:20.400 | if you spoke to most string theorists,

00:55:21.520 | they would probably freely admit

00:55:22.640 | that no one really knows what string theory is yet.

00:55:24.920 | I mean, there's been a lot of work,

00:55:26.000 | but it's not really understood.

00:55:27.320 | And the other problem is that string theory

00:55:31.240 | mostly makes predictions about physics

00:55:34.040 | that occurs at energies far beyond

00:55:36.560 | what we will ever be able to probe in the laboratory.

00:55:40.600 | Yeah, probably ever.

00:55:42.200 | - By the way, so sorry, take a million tangents,

00:55:44.840 | but is there room for complete innovation

00:55:48.080 | of how to build a particle collider

00:55:50.200 | that could give us an order of magnitude increase

00:55:52.760 | in the kind of energies,

00:55:55.200 | or do we need to keep just increasing the size of things?

00:55:58.520 | - I mean, maybe, yeah.

00:55:59.440 | I mean, there are ideas,

00:56:00.920 | to give you a sense of the gulf that has to be bridged.

00:56:03.920 | So the LHC collides particles at an energy

00:56:08.920 | of what we call 14 tera electron volts.

00:56:13.440 | So that's basically the equivalent

00:56:15.040 | of you've accelerated a proton through 14 trillion volts.

00:56:19.200 | That gets us to the energies where the Higgs

00:56:21.160 | and these weak particles live.

00:56:23.240 | They're very massive.

00:56:24.480 | The scale where strings become manifest

00:56:27.760 | is something called the Planck scale,

00:56:29.320 | which I think is of the order 10 to the,

00:56:31.960 | hang on, get this right,

00:56:33.700 | is 10 to the 18 giga electron volts.

00:56:35.840 | So about 10 to the 15 tera electron volts.

00:56:40.840 | So you're talking trillions of times more energy.

00:56:44.800 | - Yeah, 10 to the 15, or 10 to the 14th larger.

00:56:48.760 | - I may be wrong, but it's of that order.

00:56:50.880 | It's a very big number.

00:56:52.720 | So we're not talking just an order

00:56:54.440 | of magnitude increase in energy.

00:56:55.640 | We're talking 14 orders of magnitude energy increase.

00:56:58.640 | So to give you a sense of what that would look like,

00:57:01.200 | were you to build a particle accelerator

00:57:03.000 | with today's technology.

00:57:04.780 | - Bigger or smaller than our solar system.

00:57:07.520 | - As the size of the galaxy.

00:57:09.160 | - The galaxy.

00:57:10.080 | - So you need to put a particle accelerator

00:57:11.520 | that circled the Milky Way to get to the energies

00:57:14.600 | where you would see strings if they exist.

00:57:17.640 | So that is a fundamental problem,

00:57:20.400 | which is that most of the predictions of the unified,

00:57:23.480 | these unified theories, quantum theories of gravity,

00:57:26.080 | only make statements that are testable

00:57:28.680 | at energies that we will not be able to probe.

00:57:31.200 | And barring some unbelievable,

00:57:35.240 | completely unexpected technological

00:57:37.200 | or scientific breakthrough,

00:57:38.120 | which is almost impossible to imagine.

00:57:40.000 | You never say never, but it seems very unlikely.

00:57:42.840 | - Yeah, I can just see the news story.

00:57:45.160 | Elon Musk decides to build a particle collider

00:57:48.880 | the size of our--

00:57:50.600 | - It would have to be, we'd have to get together

00:57:51.840 | with all our galactic neighbors to pay for it, I think.

00:57:55.160 | - What is the exciting possibilities

00:57:56.760 | of the Large Hadron Collider?

00:57:59.000 | What is there to be discovered

00:58:00.680 | in this order of magnitude of scale?

00:58:04.200 | Is there other bigger efforts on the horizon?

00:58:07.920 | In this space, what are the open problems,

00:58:11.600 | exciting possibilities?

00:58:12.760 | You mentioned supersymmetry.

00:58:14.600 | - Yeah, so well, there are lots of new ideas.

00:58:17.600 | Well, there are lots of problems that we're facing.

00:58:18.960 | So there's a problem with the Higgs field,

00:58:20.160 | which supersymmetry was supposed to solve.

00:58:23.320 | There's the fact that 95% of the universe

00:58:25.720 | we know from cosmology, astrophysics is invisible,

00:58:29.360 | that it's made of dark matter and dark energy,

00:58:31.840 | which are really just words for things

00:58:34.040 | that we don't know what they are.

00:58:35.360 | It's what Donald Rumsfeld called a known unknown.

00:58:37.920 | So we know we don't know what they are.

00:58:39.880 | - Well, that's better than unknown unknown.

00:58:42.480 | - Yeah, well, there may be some unknown unknowns,

00:58:43.800 | but by definition, we don't know what those are.

00:58:46.200 | So yeah.

00:58:47.360 | - But the hope is a particle accelerator

00:58:52.360 | could help us make sense of dark energy, dark matter.

00:58:55.560 | There's still some hope for that?

00:58:57.680 | - There's hope for that, yeah.

00:58:58.760 | So one of the hopes is the LHC could produce

00:59:01.400 | a dark matter particle in its collisions.

00:59:03.800 | And it may be that the LHC will still discover new particles,

00:59:08.800 | that supersymmetry could still be there.

00:59:12.320 | It's just maybe more difficult to find

00:59:14.360 | than we thought originally.

00:59:15.680 | And dark matter particles might be being produced,

00:59:18.560 | but we're just not looking

00:59:19.400 | in the right part of the data for them.

00:59:21.200 | That's possible.

00:59:22.160 | It might be that we need more data,

00:59:23.360 | that these processes are very rare

00:59:24.840 | and we need to collect lots and lots of data

00:59:26.640 | before we see them.

00:59:27.640 | But I think a lot of people would say now

00:59:29.880 | that the chances of the LHC

00:59:33.760 | directly discovering new particles

00:59:36.040 | in the near future is quite slim.

00:59:37.840 | It may be that we need a decade more data

00:59:40.840 | before we can see something, or we may not see anything.

00:59:43.960 | That's where we are.

00:59:45.520 | So I mean, the physics, the experiments that I work on,

00:59:49.040 | so I work on a detector called LHCb,

00:59:50.840 | which is one of these four big detectors

00:59:52.840 | that are spaced around the ring.

00:59:54.440 | And we do slightly different stuff to the big guys.

00:59:57.600 | There's two big experiments called Atlas and CMS,

01:00:00.680 | 3,000 physicists and scientists

01:00:02.800 | and computer scientists on them each.

01:00:04.840 | They are the ones that discovered the Higgs

01:00:06.160 | and they look for supersymmetry in dark matter and so on.

01:00:08.640 | What we look at are standard model particles

01:00:11.240 | called bquarks, which depending on your preferences,

01:00:14.920 | either bottom or beauty, we tend to say beauty

01:00:17.640 | 'cause it sounds sexier.

01:00:18.880 | - Yeah, for sure.

01:00:20.520 | - But these particles are interesting

01:00:22.760 | because we can make lots of them.

01:00:25.880 | We make billions or hundreds of billions of these things.

01:00:28.920 | You can therefore measure their properties very precisely.

01:00:31.600 | So you can make these really lovely precision measurements.

01:00:34.440 | And what we are doing really is a sort of complimentary thing

01:00:39.440 | to the other big experiments, which is,

01:00:41.960 | if you think of the sort of analogy they often use is,

01:00:44.160 | if you imagine you're in the jungle

01:00:45.840 | and you're looking for an elephant, say,

01:00:48.720 | and you are a hunter and you're kind of like,

01:00:52.080 | let's say there's the elephant's very rare,

01:00:53.560 | you don't know where in the jungle, the jungle's big.

01:00:55.480 | So there's two ways you go about this.

01:00:56.800 | Either you can go wandering around the jungle

01:00:58.760 | and try and find the elephant.

01:01:00.240 | The problem is if there's only one elephant

01:01:02.120 | and the jungle's big,

01:01:02.960 | the chances of running into it are very small.

01:01:04.760 | Or you could look on the ground

01:01:07.200 | and see if you see footprints left by the elephant.

01:01:09.200 | And if the elephant's moving around,

01:01:10.840 | you've got a chance,

01:01:11.680 | you've got a chance maybe of seeing the elephant's footprints

01:01:13.880 | if you see the footprints, you go, okay, there's an elephant.

01:01:16.080 | I maybe don't know what kind of elephant it is,

01:01:18.320 | but I got a sense there's something out there.

01:01:20.000 | So that's sort of what we do.

01:01:21.600 | We are the footprint people.

01:01:23.040 | We are, we're looking for the footprints,

01:01:25.800 | the impressions that quantum fields

01:01:28.800 | that we haven't managed to directly create the particle of,

01:01:32.600 | the effects these quantum fields have

01:01:33.960 | on the ordinary standard model fields

01:01:35.560 | that we already know about.

01:01:36.480 | So these B particles,

01:01:39.000 | the way they behave can be influenced by the presence

01:01:41.280 | of say super fields or dark matter fields

01:01:43.840 | or whatever you like.

01:01:45.160 | And the way they decay and behave can be altered slightly

01:01:48.600 | from what our theory tells us they ought to behave.

01:01:51.920 | - Gotcha.

01:01:52.760 | And it's easier to collect huge amounts of data

01:01:54.600 | on B quarks.

01:01:56.560 | - We get billions and billions of these things.

01:01:58.440 | You can make very precise measurements.

01:02:00.280 | And the only place really at the LHC

01:02:03.160 | or in really in high energy physics at the moment

01:02:05.160 | where there's fairly compelling evidence

01:02:08.880 | that there might be something beyond the standard model

01:02:10.920 | is in these B, these beauty quarks decays.

01:02:15.320 | - Just to clarify,

01:02:17.040 | which is the difference between the different,

01:02:19.440 | the four experiments, for example, that you mentioned,

01:02:21.600 | is it the kind of particles that are being collided?

01:02:24.760 | Is it the energies of which they're collided?

01:02:27.160 | What's the fundamental difference

01:02:28.960 | between the different experiments?

01:02:30.440 | - The collisions are the same.

01:02:32.280 | What's different is the design of the detectors.

01:02:34.480 | So Atlas and CMS are called,

01:02:37.040 | they're called what are called general purpose detectors.

01:02:39.760 | And they are basically barrel shaped machines.

01:02:42.400 | And the collisions happen in the middle of the barrel.

01:02:44.440 | And the barrel captures all the particles

01:02:46.600 | that go flying out in every direction.

01:02:48.040 | So in a sphere effectively, they come flying out

01:02:49.840 | and it can record all of those particles.

01:02:51.840 | And-

01:02:52.800 | - What's the, sorry to be interrupting,

01:02:54.720 | but what's the mechanism of the recording?

01:02:57.480 | - Oh, so these detectors,

01:02:58.680 | if you've seen pictures of them, they're huge.

01:03:00.160 | Like Atlas is 25 meters high and 45 meters long.

01:03:04.200 | They're vast machines,

01:03:06.460 | instruments, I guess you should call them really.

01:03:09.640 | They are, they're kind of like onions.

01:03:11.800 | So they have layers, concentric layers of detectors,

01:03:15.400 | different sorts of detectors.

01:03:16.520 | So close into the beam pipe,

01:03:18.200 | you have what are called usually made of silicon,

01:03:20.640 | they're tracking detectors.

01:03:21.760 | So they're little, made of strips of silicon

01:03:23.640 | or pixels of silicon.

01:03:25.000 | And when a particle goes through the silicon,

01:03:26.800 | it gives a little electrical signal

01:03:28.520 | and you get these dots, you know,

01:03:29.480 | electrical dots through your detector,

01:03:31.000 | which allows you to reconstruct

01:03:32.160 | the trajectory of the particle.

01:03:34.120 | So that's the middle.

01:03:34.960 | And then the outsides of these detectors,

01:03:36.280 | you have things called calorimeters,

01:03:37.720 | which measure the energies of the particles.

01:03:39.600 | And then very edge,

01:03:40.440 | you have things called muon chambers,

01:03:42.640 | which basically these muon particles,

01:03:44.680 | which are the heavy version of the electron,

01:03:46.720 | they are like high velocity bullets

01:03:48.440 | and they can get right to the edge of the detectors.

01:03:50.120 | If you see something at the edge, that's a muon.

01:03:52.480 | So that's broadly how they work.

01:03:54.000 | - And all of that is being recorded.

01:03:55.720 | - That's all being fed out to, you know, computers.

01:03:58.280 | - Data must be awesome.

01:03:59.840 | Okay.

01:04:00.800 | - So LHCb is different.

01:04:02.000 | So we, because we're looking for these b-quarks,

01:04:04.680 | b-quarks tend to be produced along the beam line.

01:04:07.960 | So in a collision,

01:04:09.160 | the b-quark tend to fly sort of close to the beam pipe.

01:04:12.840 | So we built a detector that sort of pyramid,

01:04:14.800 | cone shaped basically, that just looks in one direction.

01:04:18.120 | So we ignore, if you have your collision,

01:04:20.280 | stuff goes everywhere.

01:04:21.120 | We ignore all the stuff over here and going off sideways.

01:04:23.400 | We're just looking in this little region

01:04:26.200 | close to the beam pipe

01:04:27.080 | where most of these b-quarks are made.

01:04:28.720 | So.

01:04:29.720 | - Is there a different aspect of the sensors involved

01:04:34.160 | in the collection of the b-quark trajectories?

01:04:37.600 | - There are some differences.

01:04:38.720 | So one of the differences is that

01:04:40.840 | one of the ways you know you've seen a b-quark

01:04:42.600 | is that b-quarks are actually quite long lived

01:04:44.880 | by particle standards.

01:04:45.960 | So they live for 1.5 trillionths of a second,

01:04:49.120 | which is if you're a fundamental particle

01:04:50.600 | is a very long time.

01:04:51.640 | 'Cause you know, the Higgs boson,

01:04:53.480 | I think lives for about a trillionth of a trillionth

01:04:56.720 | of a second, or maybe even less than that.

01:04:58.520 | So these are quite long lived things

01:05:00.840 | and they will actually fly a little distance

01:05:02.680 | before they decay.

01:05:03.520 | So they will fly, you know, a few centimeters,

01:05:05.200 | maybe if you're lucky, then they'll decay into other stuff.

01:05:08.000 | So what we need to do in the middle of the detector,

01:05:10.440 | you wanna be able to see,

01:05:12.240 | you have your place where the protons crash into each other

01:05:14.640 | and that produces loads of particles that come flying out.

01:05:16.960 | So you have loads of lines,

01:05:18.160 | loads of tracks that point back to that proton collision.

01:05:21.360 | And then you're looking for a couple of other tracks,

01:05:23.440 | maybe two or three that point back to a different place

01:05:25.920 | that's maybe a few centimeters away

01:05:27.400 | from the proton collision.

01:05:28.440 | And that's the sign that little b particle

01:05:30.880 | has flown a few centimeters and decayed somewhere else.

01:05:33.280 | So we need to be able to very accurately resolve

01:05:36.800 | the proton collision from the b particle decay.

01:05:39.520 | So we are, the middle of our detector is very sensitive

01:05:42.400 | and it gets very close to the collision.

01:05:44.200 | So you have this really beautiful, delicate silicon detector

01:05:47.480 | that sits, I think it's seven mil millimeters from the beam.

01:05:52.400 | And the LHC beam has as much energy as a jumbo jet

01:05:54.680 | at takeoff.

01:05:55.520 | So it's enough to melt a ton of copper.

01:05:57.320 | So you have this furiously powerful thing sitting next

01:05:59.880 | to this tiny, delicate, you know, silicon sensor.

01:06:03.360 | So those aspects of our detector that are specialized

01:06:07.160 | to measure these particular b quarks

01:06:09.840 | that we're interested in.

01:06:10.880 | - And is there, I mean, I remember seeing somewhere

01:06:12.960 | that there's some mention of matter and antimatter

01:06:15.360 | connected to the b, these beautiful quarks.

01:06:18.280 | Is that, what's the connection?

01:06:21.640 | Yeah, what's the connection there?

01:06:25.880 | - Yeah, so there is a connection,

01:06:27.200 | which is that when you produce these b particles,

01:06:31.840 | these particles, 'cause you don't see the b quark,

01:06:33.760 | you see the thing that b quark is inside.

01:06:35.440 | So they're bound up inside what we call beauty particles,

01:06:38.000 | where the b quark is joined together with another quark

01:06:40.640 | or two, maybe two other quarks, depending on what it is.

01:06:43.400 | There are a particular set of these b particles

01:06:46.200 | that exhibit this property called oscillation.

01:06:49.520 | So if you make a, for the sake of argument,

01:06:52.320 | a matter version of one of these b particles,

01:06:55.480 | as it travels, because of the magic of quantum mechanics,

01:06:58.880 | it oscillates backwards and forwards

01:07:01.040 | between its matter and antimatter versions.

01:07:03.880 | So it does this weird flipping about backwards and forwards.

01:07:06.760 | And what we can use this for is a laboratory

01:07:09.200 | for testing the symmetry between matter and antimatter.

01:07:12.920 | So if the symmetry between antimatter is precise,

01:07:15.720 | it's exact, then we should see these b particles decaying

01:07:20.080 | as often as matter as they do as antimatter,

01:07:21.880 | 'cause this oscillation should be even.

01:07:23.360 | It should spend as much time in each state.

01:07:26.040 | But what we actually see is that one of the states

01:07:29.000 | it spends more time in,

01:07:30.240 | it's more likely to decay in one state than the other.

01:07:32.840 | So this gives us a way of testing this fundamental symmetry

01:07:37.000 | between matter and antimatter.

01:07:39.200 | - So what can you, sort of returning to the question

01:07:42.120 | we were before about this fundamental symmetry,

01:07:44.480 | it seems like if there's perfect symmetry

01:07:46.520 | between matter and antimatter,

01:07:50.560 | if we have the equal amount of each in our universe,

01:07:54.600 | it would just destroy itself.

01:07:57.000 | And just like you mentioned,

01:07:58.760 | we seem to live in a very unlikely universe

01:08:00.920 | where it doesn't destroy itself.

01:08:03.520 | So do you have some intuition about why that is?

01:08:07.280 | - I mean, well, I'm not a theorist.

01:08:10.160 | I don't have any particular ideas myself.

01:08:11.720 | I mean, I sort of do measurements

01:08:13.160 | to try and test these things.

01:08:14.200 | But I mean, so in terms of the basic problem

01:08:16.040 | is that in the Big Bang,

01:08:17.840 | if you use the standard model

01:08:18.800 | to figure out what ought to have happened,

01:08:20.160 | you should have got equal amounts of matter

01:08:21.720 | and antimatter made.

01:08:22.560 | 'Cause whenever you make a particle,

01:08:23.920 | in our collisions, for example,

01:08:25.440 | when we collide stuff together,

01:08:26.840 | you make a particle, you make an antiparticle.

01:08:28.440 | They always come together.

01:08:29.480 | They always annihilate together.

01:08:30.920 | So there's no way of making more matter than antimatter

01:08:33.480 | that we've discovered so far.

01:08:35.040 | So that means in the Big Bang,

01:08:36.080 | you get equal amounts of matter and antimatter.

01:08:38.240 | As the universe expands and cools down

01:08:40.400 | during the Big Bang,

01:08:41.760 | not very long after the Big Bang,

01:08:43.240 | I think a few seconds after the Big Bang,

01:08:45.040 | you have this event called the Great Annihilation,

01:08:47.280 | which is where all the particles and antiparticles

01:08:49.840 | smack into each other,

01:08:51.040 | annihilate, turn into light mostly,

01:08:53.520 | and you end up with a universe later on.

01:08:55.000 | If that was what happened,

01:08:55.960 | then the universe we live in today

01:08:57.080 | would be black and empty,

01:08:58.800 | apart from some photons, that would be it.

01:09:01.600 | So there's stuff in the,

01:09:02.520 | there is stuff in the universe.

01:09:03.560 | It appears to be just made of matter.

01:09:04.960 | So there's this big mystery as to where the,

01:09:06.920 | how did this happen?

01:09:08.200 | And there are various ideas

01:09:09.640 | which all involve sort of physics going on

01:09:13.520 | in the first trillionth of a second or so of the Big Bang.

01:09:17.040 | So it could be that one possibility

01:09:20.080 | is that the Higgs field is somehow implicated in this,

01:09:22.600 | that there was this event that took place

01:09:25.320 | in the early universe

01:09:26.360 | where the Higgs field basically switched on.

01:09:28.640 | It acquired its modern value.

01:09:31.400 | And when that happened,

01:09:33.480 | this caused all the particles to acquire mass.

01:09:35.600 | And the universe basically went through a phase transition

01:09:37.880 | where you had a hot plasma of massless particles.

01:09:41.000 | And then in that plasma,

01:09:42.040 | it's almost like a gas turning into droplets of water.

01:09:44.800 | You get kind of these little bubbles forming in the universe

01:09:47.960 | where the Higgs field has acquired its modern value.

01:09:50.800 | The particles have got mass.

01:09:52.280 | And this phase transition in some models

01:09:55.200 | can cause more matter than antimatter to be produced

01:09:57.920 | depending on how matter bounces off these bubbles

01:10:00.600 | in the early universe.

01:10:01.720 | So that's one idea.

01:10:02.760 | There's other ideas to do with neutrinos,

01:10:04.640 | that there are exotic types of neutrinos

01:10:06.360 | that can decay in a biased way to just matter

01:10:09.280 | and not to antimatter.

01:10:10.160 | So people are trying to test these ideas.

01:10:12.600 | That's what we're trying to do at LHCb.

01:10:14.280 | There's neutrino experiments planned

01:10:15.720 | that are trying to do these sorts of things as well.

01:10:17.520 | So yeah, there are ideas,

01:10:18.960 | but at the moment no clear evidence

01:10:20.920 | for which of these ideas might be right.

01:10:22.880 | - So we're talking about some incredible ideas.

01:10:25.480 | By the way, never heard anyone be so eloquent

01:10:28.280 | about describing even just the standard model.

01:10:31.680 | So I'm in awe just listening.

01:10:34.520 | - Oh, thank you.

01:10:35.360 | - Interesting, just having fun enjoying it.

01:10:38.060 | So yes, the theoretical,

01:10:40.240 | the particle physics is fascinating here.

01:10:42.480 | To me, one of the most fascinating things

01:10:44.640 | about the Large Hadron Collider is the human side of it,

01:10:47.840 | that a bunch of sort of brilliant people

01:10:51.480 | that probably have egos got together

01:10:54.320 | and were collaborating together.

01:10:56.260 | And countries, I guess, collaborated together

01:10:59.120 | for the funds and everything.

01:11:01.160 | Just collaboration everywhere.

01:11:02.960 | 'Cause you may be,

01:11:03.980 | I don't know what the right question here to ask,

01:11:07.820 | but what's your intuition about how it's possible

01:11:10.720 | to make this happen?

01:11:11.800 | And what are the lessons we should learn

01:11:14.320 | for the future of human civilization

01:11:16.040 | in terms of our scientific progress?

01:11:17.820 | 'Cause it seems like this is a great, great illustration

01:11:21.580 | of us working together to do something big.

01:11:24.620 | - Yeah, I think it's possibly the best example,

01:11:27.020 | maybe I can think of, of international collaboration

01:11:30.260 | that isn't for some unpleasant purpose, basically.

01:11:33.500 | I mean, so when I started out in the field in 2008

01:11:38.460 | as a new PhD student, the LHC was basically finished.

01:11:41.420 | So I didn't have to go around asking for money for it

01:11:44.540 | or trying to make the case.

01:11:45.460 | So I have huge admiration for the people

01:11:47.620 | who managed that.

01:11:48.700 | 'Cause this was a project that was first imagined

01:11:51.100 | in the 1970s.

01:11:51.940 | In the late '70s was when the first conversations

01:11:54.700 | about the LHC were mooted.

01:11:56.380 | And it took two and a half decades of campaigning

01:12:00.740 | and fundraising and persuasion

01:12:03.540 | until they started breaking ground and building the thing

01:12:05.940 | in the early noughties and 2000.

01:12:07.980 | So, I mean, I think the reason,

01:12:10.540 | just from the point of view of the scientists there,

01:12:14.060 | I think the reason it works ultimately

01:12:16.660 | is that everyone there is there for the same reason,

01:12:20.380 | which is, well, in principle at least,

01:12:23.660 | they're there because they're interested in the world.

01:12:25.500 | They wanna find out what are the basic ingredients

01:12:28.660 | of our universe?

01:12:29.500 | What are the laws of nature?

01:12:31.020 | And so everyone is pulling in the same direction.

01:12:32.940 | Of course, everyone has their own things

01:12:35.020 | they're interested in.

01:12:35.860 | Everyone has their own careers to consider.

01:12:37.380 | And I wouldn't pretend that there isn't also

01:12:39.580 | a lot of competitions.

01:12:40.860 | There's this funny thing in these experiments

01:12:42.900 | where your collaborators, your 800 collaborators in LHCb,

01:12:46.140 | but you're also competitors because your academics

01:12:48.860 | in your various universities,

01:12:49.940 | and you wanna be the one that gets the paper out

01:12:51.500 | on the most exciting new measurements.

01:12:53.420 | So there's this funny thing where you're kind of trying

01:12:55.700 | to stake out your territory while also collaborating

01:12:58.460 | and having to work together to make the experiments work.

01:13:00.900 | And it does work amazingly well, actually,

01:13:04.060 | considering all of that.

01:13:05.140 | And I think there was actually,

01:13:06.780 | I think McKinsey or one of these big management

01:13:08.660 | consultancy firms went into CERN maybe a decade or so ago

01:13:11.820 | to try to understand how these organizations function.

01:13:15.020 | - Did they figure it out?

01:13:16.100 | - I don't think they could.

01:13:16.940 | I mean, I think one of the things that's interesting,

01:13:18.780 | one of the other interesting things about these experiments

01:13:20.740 | is they're big operations.

01:13:22.500 | Like say Atlas has 3000 people.

01:13:24.980 | Now there was a person nominally who is the head of Atlas.

01:13:27.340 | They're called the spokesperson.

01:13:29.700 | And the spokesperson is elected by,

01:13:32.380 | usually by the collaboration,

01:13:34.260 | but they have no actual power, really.

01:13:36.420 | I mean, they can't fire anyone.

01:13:38.540 | They're not anyone's boss.

01:13:39.700 | So, you know, my boss is a professor at Cambridge,

01:13:43.340 | not the head of my experiments.

01:13:45.140 | The head of my experiment can't tell me what to do really.

01:13:47.540 | And there's all these independent academics

01:13:50.220 | who are their own bosses who, you know,

01:13:52.420 | so that somehow it nonetheless,

01:13:54.580 | by kind of consensus and discussion and lots of meetings,

01:13:58.540 | these things do happen and it does get done.

01:14:01.660 | - It's like the queen here in the UK is the spokesperson.

01:14:04.940 | - I guess so.

01:14:05.780 | - No actual power.

01:14:06.620 | - Except we don't elect her, no.

01:14:07.460 | - No, we don't elect her.

01:14:08.900 | But everybody seems to love her.

01:14:10.500 | I don't know, from my outside perspective.

01:14:13.300 | (inhales)

01:14:16.300 | But yeah, giant egos, brilliant people.

01:14:19.900 | And moving forward, do you think there's-

01:14:22.980 | - Actually, I would pick up one thing you said just there,

01:14:24.860 | just the brilliant people thing.

01:14:25.900 | 'Cause I'm not saying that people aren't great.

01:14:28.300 | But I think there is this sort of impression

01:14:30.620 | that physicists will have to be brilliant or geniuses,

01:14:33.020 | which is not true actually.

01:14:34.100 | And, you know, you have to be relatively bright for sure.

01:14:37.580 | But, you know, a lot of people,

01:14:39.220 | a lot of the most successful experimental physicists

01:14:41.620 | are not necessarily the people with the biggest brains.

01:14:44.020 | They're the people who, you know,

01:14:45.700 | particularly one of the skills that's most important

01:14:47.460 | in particle physics is the ability to work with others

01:14:50.100 | and to collaborate and exchange ideas and also to work hard.

01:14:52.420 | And it's a sort of, often it's more a determination

01:14:55.620 | or a sort of other set of skills.

01:14:57.580 | It's not just being, you know, kind of some great brain.

01:15:00.220 | (laughs)

01:15:01.500 | - Very true.

01:15:02.340 | So, I mean, there's parallels to that

01:15:04.220 | in the machine learning world.

01:15:05.220 | If you wanna solve any real world problems,

01:15:08.300 | which I see as the particle accelerators,

01:15:11.220 | essentially a real world instantiation

01:15:14.980 | of theoretical physics.

01:15:16.820 | And for that, you have to not necessarily be brilliant,

01:15:20.340 | but be sort of obsessed, systematic, rigorous,

01:15:25.340 | sort of unboreable, stubborn,

01:15:28.740 | all those kind of qualities that make for a great engineer.

01:15:31.200 | So, scientists purely speaking,

01:15:34.260 | that practitioner of the scientific method.

01:15:36.260 | So, you're right.

01:15:37.460 | But nevertheless, to me, that's brilliant.

01:15:39.860 | My dad's a physicist.

01:15:41.700 | I argue with him all the time.

01:15:43.080 | To me, engineering is the highest form of science.

01:15:46.060 | And he thinks that's all nonsense,

01:15:48.420 | that the real work is done by the theoretician.

01:15:50.820 | In fact, we have arguments about like people like Elon Musk,

01:15:55.100 | for example, because I think his work is quite brilliant,

01:15:58.700 | but he's fundamentally not coming up

01:16:00.560 | with any serious breakthroughs.

01:16:02.500 | He's just creating in this world, implementing,

01:16:07.140 | like making ideas happen that have a huge impact.

01:16:09.700 | To me, that's the Edison.

01:16:12.260 | That to me is a brilliant work,

01:16:17.460 | but to him, it's messy details

01:16:22.460 | that somebody will figure out anyway.

01:16:24.660 | - I mean, I don't know whether you think

01:16:26.700 | there is a actual difference in temperament

01:16:29.060 | between say a physicist and an engineer,

01:16:31.220 | whether it's just what you got interested in.

01:16:33.060 | I don't know.

01:16:34.260 | I mean, 'cause a lot of what experimental physicists do

01:16:37.940 | is to some extent engineering.

01:16:40.060 | I mean, it's not what I do.

01:16:40.900 | I mostly do data stuff, but you know,

01:16:43.180 | a lot of people would be called electrical engineers,

01:16:45.540 | but they trained as physicists,

01:16:46.980 | but they learned electrical engineering, for example,

01:16:48.900 | because they were building detectors.

01:16:50.980 | So there's not such a clear divide, I think.

01:16:52.940 | - Yeah, it's interesting.

01:16:53.780 | I mean, but there does seem to be like,

01:16:56.260 | you work with data.

01:16:57.140 | There does seem to be a certain,

01:16:59.940 | like I love data collection.

01:17:01.700 | There may be an OCD element or something

01:17:03.740 | that you're more naturally predisposed to

01:17:06.620 | as opposed to theory.

01:17:07.660 | Like I'm not afraid of data.

01:17:08.940 | I love data.

01:17:10.220 | And there's a lot of people in machine learning

01:17:11.740 | who are more like,

01:17:14.420 | they're basically afraid of data collection,

01:17:16.980 | afraid of data sets, afraid of all of that.

01:17:18.940 | They just wanna stay in more than theoretical

01:17:20.780 | and they're really good at it space.

01:17:22.820 | So I don't know if that's the genetic,

01:17:24.100 | that's your upbringing, the way you go to school,

01:17:28.340 | but looking into the future of LHC and other colliders.

01:17:33.340 | So there's in America, there's the,

01:17:35.820 | whatever it was called, the super,

01:17:37.580 | there's a lot of super--

01:17:38.420 | - Superconducting super collider.

01:17:39.860 | - Yeah, superconducting--

01:17:40.700 | - The desertron, yeah.

01:17:41.900 | - Desertron.

01:17:43.020 | So that was canceled, the construction of that,

01:17:45.980 | which is a sad thing.

01:17:50.900 | But what do you think is the future of these efforts?

01:17:54.180 | Will a bigger collider be built?

01:17:56.500 | Will LHC be expanded?

01:17:58.580 | What do you think?

01:17:59.980 | - Well, in the near future,

01:18:01.980 | the LHC is gonna get an upgrade.

01:18:03.380 | So that's pretty much confirmed.

01:18:04.860 | I think it is confirmed,

01:18:06.340 | which is, it's not an energy upgrade.

01:18:08.180 | It's what we call a luminosity upgrade.

01:18:10.220 | So it basically means increasing the data collection rates.

01:18:13.380 | So more collisions per second, basically,

01:18:15.900 | because after a few years of data taking,

01:18:18.180 | you get this law of diminishing returns

01:18:19.580 | where each year's worth of data

01:18:20.700 | is a smaller and smaller fraction

01:18:21.980 | of the lot you've already got.

01:18:23.460 | So to get a real improvement in sensitivity,

01:18:25.820 | you need to increase the data rate by an order of magnitude.

01:18:28.300 | So that's what this upgrade is gonna do.

01:18:30.500 | LHC-B at the moment,

01:18:31.980 | the whole detector is basically being rebuilt

01:18:34.620 | to allow it to record data

01:18:36.180 | at a much larger rate than we could before.

01:18:37.940 | So that will make us sensitive

01:18:39.220 | to whole loads of new processes

01:18:40.620 | that we weren't able to study before.

01:18:42.140 | And I mentioned briefly these anomalies that we've seen.

01:18:45.700 | So we've seen a bunch of very intriguing anomalies

01:18:49.020 | in these B quark decays,

01:18:51.380 | which may be hinting at the first signs

01:18:55.460 | of this kind of the elephant,

01:18:56.900 | the signs of some new quantum field

01:18:59.580 | or fields maybe beyond the standard model.

01:19:01.140 | It's not yet at the statistical threshold

01:19:02.900 | where you can say that you've observed something,

01:19:06.180 | but there's lots of anomalies in many measurements

01:19:08.820 | that all seem to be consistent with each other.

01:19:11.020 | So it's quite interesting.

01:19:11.980 | So the upgrade will allow us

01:19:13.580 | to really home in on these things

01:19:15.820 | and see whether these anomalies are real,

01:19:17.340 | because if they are real,

01:19:19.460 | and this kind of connects to your point

01:19:20.860 | about the next generation of machines,

01:19:23.700 | what we would have seen then is,

01:19:26.300 | we would have seen the tail end of some quantum field

01:19:29.260 | in influencing these B quarks.

01:19:31.780 | What we then need to do is to build a bigger collider

01:19:34.540 | to actually make the particle of that field.

01:19:37.500 | So if these things really do exist.

01:19:40.260 | So that would be one argument.

01:19:41.260 | I mean, so at the moment,

01:19:42.380 | Europe has going through this process

01:19:44.020 | of thinking about the strategy for the future.

01:19:47.780 | So there are a number of different proposals on the table.

01:19:49.700 | One is for a sort of higher energy upgrade of the LHC,

01:19:53.620 | where you just build more powerful magnets

01:19:55.300 | and put them in the same tunnel.

01:19:56.220 | That's a sort of cheaper, less ambitious possibility.

01:19:59.660 | Most people don't really like it

01:20:00.820 | because it's sort of a bit of a dead end,

01:20:02.580 | because once you've done that, there's nowhere to go.

01:20:05.580 | There's a machine called CLIC,

01:20:06.860 | which is a compact linear collider,

01:20:08.980 | which is an electron positron collider

01:20:10.740 | that uses a novel type of acceleration technology

01:20:13.460 | to accelerate at shorter distances.

01:20:15.540 | We're still talking kilometers long,

01:20:17.020 | but not like a hundred kilometers long.

01:20:19.900 | And then probably the project

01:20:21.820 | that is I think getting the most support,

01:20:23.900 | it'd be interesting to see what happens,

01:20:25.420 | something called the Future Circular Collider,

01:20:28.060 | which is a really ambitious long-term,

01:20:30.780 | multi-decade project to build

01:20:32.580 | a 100 kilometer circumference tunnel

01:20:35.980 | under the Geneva region.

01:20:38.180 | The LHC would become a kind of feeding machine.

01:20:40.740 | It would just feed-

01:20:41.580 | - So the same area, so there would be a feeder for the-

01:20:44.060 | - Yeah, so it would kind of,

01:20:45.580 | the edge of this machine would be where the LHC is,

01:20:47.660 | but it would sort of go under Lake Geneva

01:20:49.140 | and round to the Alps basically,

01:20:50.940 | since up to the edge of the Geneva Basin.

01:20:52.940 | So it's basically the biggest,

01:20:54.100 | it's the biggest tunnel you can fit in the region

01:20:56.380 | based on the geology.

01:20:57.220 | - 100 kilometers, wow. - Yeah, so it's big.

01:20:58.900 | It'd be a long drive if you're,

01:21:00.580 | you know, you make experiments on one side,

01:21:01.860 | you've got to go back to CERN for lunch,

01:21:03.100 | so that would be a pain.

01:21:04.140 | But, you know, so this project is,

01:21:07.580 | in principle, is actually two accelerators.

01:21:09.140 | The first thing you would do

01:21:09.940 | is put an electron positron machine

01:21:11.740 | in the 100 kilometer tunnel to study the Higgs.

01:21:14.340 | So you'd make lots of Higgs bosons,

01:21:15.580 | study it really precisely in the hope

01:21:17.420 | that you see it misbehaving

01:21:18.620 | and doing something it's not supposed to.

01:21:20.500 | And then in the much longer term,

01:21:22.860 | a hundred, that machine gets taken out,

01:21:24.820 | you put in a proton-proton machine.

01:21:26.500 | So it's like the LHC, but much bigger.

01:21:29.060 | And that's the way you start going

01:21:30.460 | and looking for dark matter,

01:21:32.420 | or you're trying to recreate this phase transition

01:21:35.940 | that I talked about in the early universe,

01:21:37.100 | where you can see matter-antimatter being made, for example.

01:21:39.740 | So lots of things you can do with these machines.

01:21:41.100 | The problem is that they will take, you know,

01:21:44.460 | the most optimistic, you're not gonna have any data

01:21:46.700 | from any of these machines until 2040,

01:21:49.060 | or, you know, 'cause they take such a long time to build

01:21:51.820 | and they're so expensive.

01:21:52.900 | So you have, there'll be a process of R&D design,

01:21:55.940 | but also the political case being made.

01:21:57.940 | - So LHC, what cost, a few billion?

01:22:01.260 | - Depends how you count it.

01:22:03.180 | I think most of the sort of more reasonable estimates

01:22:05.420 | that take everything into account properly,

01:22:06.980 | it's around the sort of 10, 11, 12 billion Euro mark.

01:22:10.380 | - What would be the future, sorry, I forgot the name already.

01:22:13.180 | - Future Circular Collider.

01:22:14.700 | - Future Circular Collider.

01:22:15.540 | - Presumably they won't call it that when it's built,

01:22:16.900 | 'cause it won't be the future anymore,

01:22:18.260 | but I don't know what they'll call it then.

01:22:20.620 | (both laughing)

01:22:23.420 | Very big Hadron Collider, I don't know.

01:22:25.060 | But that will, I don't know, I should know the numbers,

01:22:28.780 | but I think the whole project is estimated

01:22:31.100 | at about 30 billion Euros,

01:22:32.820 | but that's money spent over between now and 2070 probably,

01:22:37.780 | which is when the last bit of it would be

01:22:40.540 | sort of finishing up, I guess.

01:22:42.300 | So you're talking a half a century of science

01:22:46.500 | coming out of this thing, shared by many countries.

01:22:48.660 | So the actual cost, the arguments that are made

01:22:51.140 | is that you could make this project fit

01:22:53.060 | within the existing budget of CERN,

01:22:56.100 | if you didn't do anything else.

01:22:57.420 | - And CERN, by the way, we didn't mention, what is CERN?

01:23:00.500 | - CERN is the European Organization for Nuclear Research.

01:23:03.260 | It's an international organization

01:23:05.220 | that was established in the 1950s

01:23:07.060 | in the wake of the Second World War as a kind of,

01:23:10.260 | it was sort of like a scientific Marshall Plan for Europe.

01:23:12.460 | The idea was that you bring European science back together

01:23:16.060 | for peaceful purposes,

01:23:17.300 | because what happened in the '40s was,

01:23:19.740 | you know, a lot of, particularly a lot of Jewish scientists,

01:23:21.220 | but a lot of scientists from Central Europe

01:23:22.580 | had fled to the United States,

01:23:24.940 | and Europe had sort of seen this brain drain.

01:23:27.220 | So there was a desire to bring the community back together

01:23:29.860 | for a project that wasn't building nasty bombs,

01:23:32.220 | but was doing something that was curiosity-driven.

01:23:34.220 | So, and that has continued since then.

01:23:37.260 | So it's kind of a unique organization.

01:23:38.780 | It's, to be a member as a country,

01:23:41.420 | you sort of sign up as a member,

01:23:42.980 | and then you have to pay a fraction of your GDP

01:23:45.900 | each year as a subscription.

01:23:47.260 | I mean, it's a very small fraction, relatively speaking.

01:23:49.460 | I think it's like, I think the UK's contribution

01:23:51.420 | is 100 or 200 million quid or something like that a year,

01:23:54.980 | which is quite a lot, but not-

01:23:57.380 | - That's fascinating.

01:23:58.300 | I mean, just the whole thing that is possible,

01:23:59.980 | it's beautiful.

01:24:01.140 | It's a beautiful idea,

01:24:02.140 | especially when there's no wars on the line.

01:24:05.220 | It's not like we're freaking out.

01:24:06.460 | It's we're actually legitimately collaborating

01:24:08.780 | to do good science.

01:24:09.780 | One of the things I don't think we really mentioned

01:24:11.780 | is on the final side, that sort of the data analysis side,

01:24:15.260 | is there breakthroughs possible there

01:24:17.020 | in the machine learning side?

01:24:18.060 | Like, is there a lot more signal to be mined

01:24:22.620 | in more effective ways from the actual raw data?

01:24:25.340 | - Yeah, a lot of people are looking into that.

01:24:27.260 | I mean, so I use machine learning in my data analysis,

01:24:31.540 | but pretty naughty, basic stuff,

01:24:33.780 | 'cause I'm not a machine learning expert.

01:24:35.380 | I'm just a physicist who had to learn to do this stuff

01:24:37.900 | for my day job.

01:24:38.740 | So what a lot of people do is they use

01:24:40.540 | kind of off the shelf packages that you can train

01:24:43.620 | to do signal noise-

01:24:46.140 | - Just clean up all the data.

01:24:47.780 | - Yeah, but one of the big challenges is,

01:24:49.940 | the big challenge of the data is A, it's volume.

01:24:52.620 | There's huge amounts of data.

01:24:53.780 | So the LHC generates, now, okay,

01:24:56.420 | I try to remember what the actual numbers are,

01:24:57.860 | but if we don't record all our data,

01:24:59.420 | we record a tiny fraction of the data.

01:25:02.180 | It's like of order one 10,000th or something, I think.

01:25:05.220 | Is that right?

01:25:06.060 | Around that.

01:25:06.980 | So most of it gets thrown away.

01:25:08.540 | You couldn't record all the LHC data

01:25:10.060 | 'cause it would fill up every computer in the world

01:25:11.460 | in a matter of days, basically.

01:25:13.620 | So there's this process that happens on live

01:25:16.940 | on the detector, something called a trigger,

01:25:18.820 | which in real time, 40 million times every second,

01:25:21.300 | has to make a decision about whether this collision

01:25:23.660 | is likely to contain an interesting object

01:25:26.380 | like a Higgs boson or a dark matter particle.

01:25:28.540 | And it has to do that very fast.

01:25:29.780 | And the software algorithms in the past

01:25:33.220 | were quite relatively basic.

01:25:35.820 | You know, they did things like measure momentas

01:25:37.820 | and energies of particles and put some requirements.

01:25:40.300 | So you would say, if there's a particle

01:25:42.180 | with an energy above some threshold,

01:25:43.620 | then record this collision.

01:25:44.820 | But if there isn't, don't.

01:25:46.220 | Whereas now the attempt is to get more

01:25:47.740 | and more machine learning in at the earliest possible stage.

01:25:51.060 | - That's cool, at the stage of deciding

01:25:53.140 | whether we wanna keep this data or not.

01:25:55.260 | - But also even maybe even lower down than that,

01:25:57.580 | which is the point where there's this,

01:26:01.140 | so generally how the data is reconstructed

01:26:02.780 | is you start off with a set of digital hits

01:26:06.220 | in your detector.

01:26:07.060 | So channels saying, did you see something?

01:26:08.780 | Did you not see something?

01:26:10.100 | That has to be then turned into tracks,

01:26:12.540 | particles going in different directions.

01:26:14.060 | And that's done by using fits

01:26:15.540 | that fit through the data points.

01:26:17.180 | And then that's passed to the algorithms that then go,

01:26:19.140 | is this interesting or not?

01:26:20.500 | What'd be better is you could train in machine learning

01:26:22.540 | to just look at the raw hits,

01:26:24.140 | the basic, real base level information,

01:26:26.380 | not have any of the reconstruction done.

01:26:28.420 | And it just goes,

01:26:29.660 | and it can learn to do pattern recognition

01:26:31.060 | on this strange three-dimensional image that you get.

01:26:34.260 | And potentially that's where you could get really big gains

01:26:36.780 | because our triggers tend to be quite inefficient

01:26:38.740 | because they don't have time

01:26:41.220 | to do the full whiz bang processing

01:26:43.380 | to get all the information out that we would like

01:26:45.380 | because you have to do the decision very quickly.

01:26:46.740 | So if you can come up

01:26:47.580 | with some clever machine learning technique,

01:26:50.060 | then potentially you can massively increase

01:26:52.020 | the amount of useful data you record

01:26:54.980 | and get rid of more of the background earlier in the process.

01:26:59.820 | - Yeah, to me, that's an exciting possibility

01:27:01.420 | 'cause then you don't have to build a,

01:27:03.660 | sort of you can get a gain without having to,

01:27:08.660 | without having to build any hardware, I suppose.

01:27:10.340 | - Hardware, yeah.

01:27:11.180 | - Although you need lots of new GPU farms, I guess.

01:27:13.980 | - So hardware still helps.

01:27:15.300 | But the, you know, I got to talk to you.

01:27:20.300 | Sort of, I'm not sure how to ask,

01:27:22.860 | but you're clearly an incredible science communicator.

01:27:27.500 | I don't know if that's the right term,

01:27:29.580 | but you're basically a younger Neil deGrasse Tyson

01:27:32.580 | with a British accent.

01:27:34.220 | So, and you've, I mean, can you say where we are today?

01:27:38.580 | Actually?

01:27:39.420 | - Yeah, so today we're in the Royal Institution in London,

01:27:42.620 | which is an old, a very old organization.

01:27:45.900 | It's been around for about 200 years now, I think.

01:27:47.780 | Maybe even I should know when it was founded,

01:27:49.620 | but sort of early 19th century.

01:27:51.500 | It was set up to basically communicate science to the public.

01:27:55.900 | So it was one of the first places in the world

01:27:57.620 | where scientists, famous scientists would come

01:28:00.060 | and give talks.

01:28:01.260 | So very famously, Humphry Davy, who you may know of,

01:28:05.460 | who was the person who discovered nitrous oxide,

01:28:07.580 | he was a very famous chemist and scientist,

01:28:11.220 | also discovered electrolysis.

01:28:12.740 | So he used to do these fantastic,

01:28:13.940 | he was a very charismatic speaker.

01:28:15.060 | So he used to appear here, there's a big desk

01:28:16.860 | that they usually have in the theater,

01:28:18.460 | and he would do demonstrations to the sort of the folk

01:28:21.660 | of London back in the early 19th century.

01:28:23.780 | And Michael Faraday, who I talked about,

01:28:25.220 | who was the person who did so much work on electromagnetism,

01:28:27.300 | he lectured here.

01:28:28.420 | He also did experiments in the basement.

01:28:29.900 | So this place has got a long history

01:28:31.260 | of both scientific research, but also-

01:28:33.940 | - And the communication. - Communication

01:28:34.940 | of scientific research.

01:28:35.780 | - So you gave a few lectures here, how many, two?

01:28:39.340 | - I've given, yeah, I've given a couple of lectures

01:28:41.100 | in this theater before, so.

01:28:42.300 | - I mean, that's, so people should definitely

01:28:43.860 | go watch online.

01:28:45.160 | It's just the explanation of particle physics,

01:28:48.660 | so all the, I mean, it's incredible.

01:28:50.500 | Like your lectures are just incredible.

01:28:53.380 | I can't sing it enough praise.

01:28:54.540 | So it was awesome.

01:28:55.500 | But maybe, can you say, what did that feel like?

01:29:00.340 | What does it feel like to lecture here, to talk about that?

01:29:03.620 | And maybe from a different perspective,

01:29:06.460 | more kind of like how the sausage is made,

01:29:08.900 | is how do you prepare for that kind of thing?

01:29:12.140 | How do you think about communication,

01:29:14.360 | the process of communicating these ideas

01:29:16.500 | in a way that's inspiring to what I would say

01:29:19.780 | your talks are inspiring to, like, the general audience.

01:29:22.600 | You don't actually have to be a scientist.

01:29:25.140 | You can still be inspired without really knowing much.

01:29:28.100 | You start from the very basics.

01:29:30.760 | So what's the preparation process?

01:29:33.380 | And then the romantic question is,

01:29:34.860 | what did that feel like to perform here?

01:29:38.020 | - I mean, the profession, yeah.

01:29:39.620 | I mean, the process, I mean, the talk,

01:29:42.260 | my favorite talk that I gave here

01:29:43.340 | was one called "Beyond the Higgs,"

01:29:44.540 | which you can find on the Royal Institution's

01:29:46.300 | YouTube channel, which you should go and check out.

01:29:48.300 | I mean, and their channel's got loads of great talks

01:29:50.020 | from loads of great people as well.

01:29:51.740 | I mean, that one, I'd sort of given a version of it

01:29:55.180 | many times, so part of it is just practice, right?

01:29:57.380 | And actually, I don't have some great theory

01:29:59.040 | of how to communicate with people.

01:30:00.420 | It's more just that I'm really interested

01:30:02.660 | and excited by those ideas, and I like talking about them.

01:30:05.300 | And through the process of doing that,

01:30:07.340 | I guess I figured out stories that work

01:30:09.700 | and explanations that work.

01:30:10.540 | - When you say practice, you mean legitimately

01:30:12.940 | just giving- - Just giving talks.

01:30:14.340 | - Just giving talks. - I started off, you know,

01:30:16.020 | when I was a PhD student, doing talks in schools,

01:30:18.460 | and I still do that as well some of the time,

01:30:20.660 | and doing things, I've even done a bit of stand-up comedy,

01:30:23.220 | which was sort of, went reasonably well,

01:30:25.260 | even if it was terrifying.

01:30:26.300 | - That's on YouTube as well.

01:30:27.540 | - That's also on, I wouldn't necessarily recommend

01:30:29.260 | you check that out.

01:30:30.100 | (laughing)

01:30:31.220 | I'm gonna post the links several places

01:30:33.220 | to make sure people click on it.

01:30:35.020 | - Yeah, but it's basically, I kind of have a story

01:30:37.380 | in my head, and I kind of, I have to think about

01:30:41.140 | what I wanna say, usually have some images

01:30:42.540 | to support what I'm saying, and I get up and do it.

01:30:44.420 | And it's not really, I wish there was some kind of,

01:30:47.220 | I probably should have some proper process.

01:30:48.660 | This probably sounds like I'm just making it up

01:30:50.060 | as I go along, and I sort of am.

01:30:52.220 | - Oh, I think the fundamental thing that you said,

01:30:54.260 | I think, it's like, I don't know if you know

01:30:58.300 | who a guy named Joe Rogan is.

01:31:01.100 | - Yes, I do, yeah.

01:31:02.220 | - So he's also kind of sounds like you in a sense

01:31:05.020 | that he's not very introspective about his process,

01:31:08.620 | but he's an incredibly engaging conversationalist.

01:31:13.020 | And I think one of the things that you and him share

01:31:15.820 | that I could see is like a genuine curiosity

01:31:19.940 | and passion for the topic.

01:31:22.340 | I think that could be systematically cultivated.

01:31:26.860 | I'm sure there's a process to it,

01:31:28.220 | but you come to it naturally somehow.

01:31:30.540 | I think maybe there's something else as well,

01:31:31.940 | which is to understand something.

01:31:34.260 | There's this quote by Feynman, which I really like,

01:31:35.940 | which is, "What I cannot create, I do not understand."

01:31:38.260 | So like, I'm not particularly super bright.

01:31:43.260 | So for me to understand something,

01:31:44.740 | I have to break it down into its simplest elements.

01:31:47.260 | And if I can then tell people about that,

01:31:49.820 | that helps me understand it as well.

01:31:51.140 | So I've actually, I've learned to understand physics

01:31:54.580 | a lot more from the process of communicating,

01:31:57.180 | 'cause it forces you to really scrutinize the ideas

01:32:00.660 | that you're communicating.

01:32:01.500 | And it quite often makes you realize

01:32:02.620 | you don't really understand the ideas you're talking about.

01:32:06.020 | And I'm writing a book at the moment.

01:32:08.140 | I had this experience yesterday where I realized

01:32:09.980 | I didn't really understand a pretty fundamental

01:32:12.620 | theoretical aspect of my own subject.

01:32:14.500 | And I had to go and I had to sort of spend a couple of days

01:32:16.620 | reading textbooks and thinking about it

01:32:18.860 | in order to make sure that the explanation I gave

01:32:21.780 | captured the, got as close to what is actually happening

01:32:24.860 | in the theory.

01:32:26.060 | And to do that, you have to really understand it properly.

01:32:29.060 | - Yeah, and there's layers to understanding.

01:32:30.780 | Like it seems like the more,

01:32:33.740 | there must be some kind of Feynman law.

01:32:35.940 | I mean, the more you understand sort of the simply,

01:32:39.700 | you're able to really convey the essence of the idea, right?

01:32:44.700 | So it's like this reverse effect that it's like,

01:32:51.100 | the more you understand the simpler the final thing

01:32:54.900 | that you actually convey.

01:32:56.300 | And so the more accessible somehow it becomes.

01:32:58.820 | That's why Feynman's lectures are really accessible.

01:33:01.960 | It was just counterintuitive.

01:33:04.900 | - Yeah, although there are some ideas

01:33:06.740 | that are very difficult to explain

01:33:09.460 | no matter how well or badly you understand them.

01:33:12.260 | Like I still can't really properly explain

01:33:15.300 | the Higgs mechanism.

01:33:17.420 | Because some of these ideas only exist in mathematics,

01:33:19.900 | really, and the only way to really develop an understanding

01:33:24.340 | is to go unfortunately into a graduate degree in physics.

01:33:29.100 | But you can get kind of a flavor of what's happening,

01:33:31.920 | I think, and it's trying to do that in a way

01:33:33.540 | that isn't misleading, but also intelligible.

01:33:36.820 | - So let me ask them the romantic question of what to you

01:33:41.220 | is the most, perhaps an unfair question.

01:33:44.500 | What is the most beautiful idea in physics?

01:33:47.580 | One that fills you with awe, is the most surprising,

01:33:52.660 | the strangest, the weirdest.

01:33:54.740 | There's a lot of different definitions of beauty.

01:33:57.580 | And I'm sure there's several for you,

01:33:59.340 | but is there something that just jumps to mind

01:34:01.100 | that you think is just especially beautiful?

01:34:06.100 | - There's a specific thing and a more general thing.

01:34:08.780 | So maybe the specific thing first,

01:34:10.060 | which when I first came across this as an undergraduate,

01:34:12.380 | I found this amazing.

01:34:13.460 | So this idea that the forces of nature,

01:34:17.140 | electromagnetism's strong force, the weak force,

01:34:19.980 | they arise in our theories as a consequence of symmetries.

01:34:24.740 | So symmetries in the laws of nature,

01:34:27.460 | in the equations essentially,

01:34:28.980 | that used to describe these ideas.

01:34:31.020 | The process whereby theories come up

01:34:34.420 | with these sorts of models is they say,

01:34:36.580 | imagine the universe obeys this particular type of symmetry.

01:34:39.940 | It's a symmetry that isn't so far removed

01:34:42.240 | from a geometrical symmetry, like the rotations of a cube.

01:34:44.860 | It's not, you can't think of it quite that way,

01:34:46.380 | but it's sort of a similar sort of idea.

01:34:49.020 | And you say, okay, if the universe respects this symmetry,

01:34:51.860 | you find that you have to introduce a force

01:34:54.700 | which has the properties of electromagnetism.

01:34:57.940 | Or a different symmetry, you get the strong force,

01:35:00.020 | or a different symmetry, you get the weak force.

01:35:01.780 | So these interactions seem to come from some deeper,

01:35:05.100 | it suggests that they come

01:35:06.240 | from some deeper symmetry principle.

01:35:07.940 | I mean, depends a bit how you look at it,

01:35:09.640 | 'cause it could be that we're actually

01:35:10.700 | just recognizing symmetries in the things that we see,

01:35:12.780 | but there's something rather lovely about that.

01:35:15.100 | But I mean, I suppose a bigger thing

01:35:16.340 | that makes me wonder is actually,

01:35:18.720 | if you look at the laws of nature,

01:35:20.180 | how particles interact when you get really close down,

01:35:22.660 | they're basically pretty simple things.

01:35:24.220 | They bounce off each other by exchanging

01:35:26.340 | through force fields, and they move around

01:35:27.840 | in very simple ways.

01:35:29.300 | And somehow, these basic ingredients,

01:35:31.900 | these few particles that we know about in the forces,

01:35:34.540 | creates this universe which is unbelievably complicated

01:35:37.380 | and has things like you and me in it,

01:35:39.500 | and the Earth and stars that make matter in their cores

01:35:43.420 | from the gravitational energy of their own bulk

01:35:46.140 | that then gets sprayed into the universe

01:35:47.580 | that forms other things.

01:35:48.480 | I mean, the fact that there's this incredibly long story

01:35:52.900 | that goes right back to the beginning,

01:35:55.900 | we can take this story right back

01:35:57.340 | to a trillionth of a second after the Big Bang,

01:35:59.420 | and we can trace the origins of the stuff

01:36:01.260 | that we're made from.

01:36:02.420 | And it all ultimately comes from these simple ingredients

01:36:05.020 | with these simple rules.

01:36:06.540 | And the fact you can generate such complexity from that

01:36:08.700 | is really mysterious, I think, and strange.

01:36:11.060 | And it's not even a question that physicists

01:36:12.900 | can really tackle, because we are sort of trying

01:36:15.740 | to find these really elementary laws.

01:36:19.080 | But it turns out that going from elementary laws

01:36:21.920 | in a few particles to something even as complicated

01:36:24.080 | as a molecule becomes very difficult.

01:36:26.640 | So going from a molecule to a human being

01:36:28.680 | is a problem that just can't be tackled,

01:36:32.000 | at least not at the moment.

01:36:33.480 | So-- - Yeah, the emergence

01:36:34.960 | of complexity from simple rules is so beautiful

01:36:39.640 | and so mysterious.

01:36:40.640 | And we don't have good mathematics

01:36:43.640 | to even try to approach that emergent phenomena.

01:36:47.320 | - That's why we have chemistry and biology

01:36:48.800 | in all the other subjects.

01:36:50.280 | Yeah, I guess.

01:36:51.120 | - I don't think there's a better way to end it, Harry.

01:36:55.880 | I can't, I mean, I think I speak for a lot of people

01:36:59.040 | that can't wait to see what happens

01:37:01.880 | in the next five, 10, 20 years with you.

01:37:03.820 | I think you're one of the great communicators of our time.

01:37:06.100 | So I hope you continue that, and I hope that grows.

01:37:09.840 | And I'm definitely a huge fan.

01:37:12.280 | So it was an honor to talk to you today.

01:37:13.920 | Thanks so much, man. - It was really fun.

01:37:14.760 | Thanks very much.

01:37:16.360 | - Thanks for listening to this conversation

01:37:17.960 | with Harry Cliff, and thank you to our sponsors,

01:37:21.000 | ExpressVPN and Cash App.

01:37:23.240 | Please consider supporting the podcast

01:37:25.000 | by getting ExpressVPN at expressvpn.com/lexpod

01:37:29.880 | and downloading Cash App and using code LEXPODCAST.

01:37:34.160 | If you enjoy this podcast, subscribe on YouTube,

01:37:36.760 | review it with Five Stars on Apple Podcast,

01:37:39.280 | support it on Patreon,

01:37:40.720 | or simply connect with me on Twitter @LexFriedman.

01:37:44.360 | And now let me leave you with some words from Harry Cliff.

01:37:48.540 | You and I are leftovers.

01:37:52.080 | Every particle in our bodies is a survivor

01:37:54.560 | from an almighty shootout between matter and antimatter

01:37:57.920 | that happened a little after the Big Bang.

01:38:00.160 | In fact, only one in a billion particles created

01:38:03.560 | at the beginning of time have survived to the present day.

01:38:07.760 | Thank you for listening and hope to see you next time.

01:38:11.240 | (upbeat music)

01:38:13.820 | (upbeat music)

01:38:16.400 | [BLANK_AUDIO]

Harry Cliff: Particle Physics and the Large Hadron Collider | Lex Fridman Podcast #92

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