back to indexHarry Cliff: Particle Physics and the Large Hadron Collider | Lex Fridman Podcast #92
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The following is a conversation with Harry Cliff,
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a particle physicist at the University of Cambridge,
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working on the Large Hadron Collider beauty experiment
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that specializes in investigating the slight differences
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between matter and antimatter
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by studying a type of particle called the beauty quark
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In this way, he's part of the group of physicists
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who are searching for the evidence of new particles
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that can answer some of the biggest questions
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in modern physics.
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He's also an exceptional communicator of science
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with some of the clearest and most captivating explanations
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of basic concepts in particle physicists
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that I've ever heard.
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So when I visited London, I knew I had to talk to him.
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And we did this conversation
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at the Royal Institute Lecture Theatre,
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which has hosted lectures for over two centuries
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from some of the greatest scientists
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and science communicators in history,
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from Michael Faraday to Carl Sagan.
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This conversation was recorded
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before the outbreak of the pandemic.
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For everyone feeling the medical and psychological
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And now, here's my conversation with Harry Kliff.
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Let's start with probably one of the coolest things
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that human beings have ever created,
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the Large Hadron Collider, OHC.
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Okay, so it's essentially this gigantic
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27 kilometer circumference particle accelerator.
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It's this big ring.
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It's buried about 100 meters underneath the surface
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in the countryside just outside Geneva in Switzerland.
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And really what it's for, ultimately,
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is to try to understand what are the basic building blocks
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So you can think of it in a way
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as like a gigantic microscope,
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and the analogy is actually fairly precise, so.
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Gigantic microscope.
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Effectively, except it's a microscope
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that looks at the structure of the vacuum.
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In order for this kind of thing to study particles,
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which are the microscopic entities, it has to be huge.
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It's a gigantic microscope.
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So what do you mean by studying vacuum?
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Okay, so I mean, so particle physics as a field
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is kind of badly named in a way,
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because particles are not the fundamental ingredients
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They're not fundamental at all.
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So the things that we believe
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are the real building blocks of the universe
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are objects, invisible fluid like objects
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called quantum fields.
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So these are fields like the magnetic field
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around a magnet that exists everywhere in space.
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They're always there.
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In fact, actually, it's funny that we're
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in the Royal Institution,
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because this is where the idea of the field
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was effectively invented by Michael Faraday
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doing experiments with magnets and coils of wire.
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So he noticed that, you know,
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it was a very famous experiment that he did
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where he got a magnet and put on top of it a piece of paper
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and then sprinkled iron filings.
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And he found the iron filings arranged themselves
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into these kind of loops,
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which was actually mapping out the invisible influence
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of this magnetic field, which is a thing, you know,
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we've all experienced, we've all felt, held a magnet
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or two poles of magnet and pushed them together
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and felt this thing, this force pushing back.
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So these are real physical objects.
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And the way we think of particles in modern physics
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is that they are essentially little vibrations,
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little ripples in these otherwise invisible fields
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that are everywhere.
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They fill the whole universe.
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You know, I don't, I apologize perhaps
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for the ridiculous question.
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Are you comfortable with the idea
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of the fundamental nature of our reality being fields?
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Because to me, particles, you know,
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a bunch of different building blocks makes more sense
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sort of intellectually, sort of visually,
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like it seems to, I seem to be able to visualize
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that kind of idea easier.
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Are you comfortable psychologically with the idea
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that the basic building block is not a block, but a field?
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I think it's, I think it's quite a magical idea.
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I find it quite appealing.
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And it's, well, it comes from a misunderstanding
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of what particles are.
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So like when you, when we do science at school
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and we draw a picture of an atom,
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you draw like, you know, a nucleus with some protons
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and neutrons, these little spheres in the middle,
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and then you have some electrons that are like little flies
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flying around the atom.
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And that is a completely misleading picture
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of what an atom is like.
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It's nothing like that.
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The electron is not like a little planet orbiting the atom.
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It's this spread out, wibbly wobbly wave like thing.
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And we know we've known that since, you know,
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the early 20th century, thanks to quantum mechanics.
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So when we, we, we carry on using this word particle
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because sometimes when we do experiments,
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particles do behave like they're little marbles
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or little bullets, you know.
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So in the LHC, when we collide particles together,
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you'll get, you know, you'll get like hundreds of particles
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all flying out through the detector
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and they all take a trajectory and you can see
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from the detector where they've gone
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and they look like they're little bullets.
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So they behave that way, you know, a lot of the time.
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When you really study them carefully,
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you'll see that they are not little spheres.
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They are these ethereal disturbances
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in these underlying fields.
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So this is really how we think nature is,
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which is surprising, but also I think kind of magic.
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So, you know, we are, our bodies are basically made up
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of like little knots of energy
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in these invisible objects that are all around us.
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And what is the story of the vacuum when it comes to LHC?
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So why did you mention the word vacuum?
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Okay, so if we just, if we go back to like the physics,
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So atoms are made of electrons,
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which were discovered a hundred or so years ago.
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And then in the nucleus of the atom,
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you have two other types of particles.
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There's an up, something called an up quark
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And those three particles make up every atom in the universe.
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So we think of these as ripples in fields.
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So there is something called the electron field
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and every electron in the universe is a ripple moving
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about in this electron field.
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So the electron field is all around us, we can't see it,
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but every electron in our body is a little ripple
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in this thing that's there all the time.
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And the quark fields are the same.
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So there's an up quark field and an up quark
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is a little ripple in the up quark field.
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And the down quark is a little ripple
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in something else called the down quark field.
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So these fields are always there.
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Now there are potentially, we know about a certain number
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of fields in what we call the standard model
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of particle physics.
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And the most recent one we discovered was the Higgs field.
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And the way we discovered the Higgs field
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was to make a little ripple in it.
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So what the LHC did, it fired two protons into each other,
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very, very hard with enough energy
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that you could create a disturbance in this Higgs field.
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And that's what shows up as what we call the Higgs boson.
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So this particle that everyone was going on about
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eight or so years ago is proof really,
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the particle in itself is, I mean, it's interesting,
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but the thing that's really interesting is the field.
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Because it's the Higgs field that we believe
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is the reason that electrons and quarks have mass.
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And it's that invisible field that's always there
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that gives mass to the particles.
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The Higgs boson is just our way
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of checking it's there basically.
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And so the Large Hadron Collider,
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in order to get that ripple in the Higgs field,
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it requires a huge amount of energy.
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And so that's why you need this huge,
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that's why size matters here.
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So maybe there's a million questions here,
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but let's backtrack.
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Why does size matter in the context of a particle collider?
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So why does bigger allow you for higher energy collisions?
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Right, so the reason, well, it's kind of simple really,
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which is that there are two types of particle accelerator
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that you can build.
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One is circular, which is like the LHC,
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the other is a great long line.
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So the advantage of a circular machine
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is that you can send particles around a ring
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and you can give them a kick every time they go around.
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So imagine you have a, there's actually a bit of the LHC,
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that's about only 30 meters long,
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where you have a bunch of metal boxes,
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which have oscillating 2 million volt electric fields
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inside them, which are timed so that when a proton
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goes through one of these boxes,
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the field it sees as it approaches is attractive.
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And then as it leaves the box,
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it flips and becomes repulsive
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and the proton gets attracted
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and kicked out the other side, so it gets a bit faster.
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So you send it, and then you send it back round again.
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And it's incredible, like the timing of that,
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the synchronization, wait, really?
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Yeah, yeah, yeah, yeah.
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I think there's going to be a multiplicative effect
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on the questions I have.
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Is, okay, let me just take that attention for a second.
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The orchestration of that, is that fundamentally
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a hardware problem or a software problem?
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Like what, how do you get that?
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I mean, I should first of all say, I'm not an engineer.
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So the guys, I did not build the LHC,
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so they're people much, much better at this stuff than I.
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For sure, but maybe.
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But from your sort of intuition,
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from the echoes of what you understand,
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what you heard of how it's designed, what's your sense?
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What's the engineering aspects of it?
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The acceleration bit is not challenging.
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Okay, I mean, okay, there's always challenges
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with everything, but basically you have these,
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the beams that go around the LHC, the beams of particles
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are divided into little bunches.
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So they're called, they're a bit like swarms of bees,
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if you like, and there are around,
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I think it's something of the order 2000 bunches
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spaced around the ring.
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And they, if you're at a given point on the ring,
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counting bunches, you get 40 million bunches
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passing you every second.
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So they come in like cars going past
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on a very fast motorway.
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So you need to have, if you're an electric field
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that you're using to accelerate the particles,
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that needs to be timed so that as a bunch of protons arrives,
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it's got the right sign to attract them
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and then flips at the right moment.
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But I think the voltage in those boxes
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oscillates at hundreds of megahertz.
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So the beams are like 40 megahertz,
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but it's oscillating much more quickly than the beam.
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So I think it's difficult engineering,
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but in principle, it's not a really serious challenge.
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The bigger problem.
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There's probably engineers like screaming at you right now.
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Probably, but I mean, okay.
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So in terms of coming back to this thing,
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Well, the reason is you wanna get the particles
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through that accelerating element over and over again.
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So you wanna bring them back round.
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So that's why it's round.
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The question is why couldn't you make it smaller?
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Well, the basic answer is that these particles
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are going unbelievably quickly.
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So they travel at 99.9999991% of the speed of light
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And if you think about, say,
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driving your car around a corner at high speed,
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if you go fast, you need a lot of friction in the tires
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to make sure you don't slide off the road.
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So the limiting factor is how powerful a magnet can you make
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because what we do is magnets are used
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to bend the particles around the ring.
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And essentially the LHC, when it was designed,
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was designed with the most powerful magnets
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that could conceivably be built at the time.
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And so that's your kind of limiting factor.
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So if you wanted to make the machine smaller,
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that means a tighter bend,
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you need to have a more powerful magnet.
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So it's this toss up between how strong are your magnets
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versus how big a tunnel can you afford.
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The bigger the tunnel, the weaker the magnets can be.
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The smaller the tunnel, the stronger they've gotta be.
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Okay, so maybe can we backtrack to the Standard Model
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and say what kind of particles there are, period,
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and maybe the history of kind of assembling
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that the Standard Model of physics
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and then how that leads up to the hopes and dreams
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and the accomplishments of the Large Hadron Collider.
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So all of 20th century physics in like five minutes.
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Okay, so, okay, the story really begins properly.
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End of the 19th century, the basic view of matter
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is that matter is made of atoms
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and the atoms are indestructible, immutable little spheres
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like the things we were talking about
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that don't really exist.
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And there's one atom for every chemical element.
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So there's an atom for hydrogen, for helium,
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for carbon, for iron, et cetera, and they're all different.
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Then in 1897, experiments done
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at the Cavendish Laboratory in Cambridge,
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which is where I'm still, where I'm based,
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showed that there are actually smaller particles
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inside the atom, which eventually became known as electrons.
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So these are these negatively charged things
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that go around the outside.
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A few years later, Ernest Rutherford,
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very famous nuclear physicist,
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one of the pioneers of nuclear physics
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shows that the atom has a tiny nugget in the center,
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which we call the nucleus,
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which is a positively charged object.
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So then by like 1910, 11, we have this model of the atom
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that we learn in school,
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which is you've got a nucleus, electrons go around it.
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Fast forward a few years, the nucleus,
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people start doing experiments with radioactivity
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where they use alpha particles
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that are spat out of radioactive elements as bullets,
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and they fire them at other atoms.
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And by banging things into each other,
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they see that they can knock bits out of the nucleus.
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So these things come out called protons, first of all,
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which are positively charged particles
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about 2000 times heavier than the electron.
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And then 10 years later, more or less,
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a neutral particle is discovered called the neutron.
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So those are the three basic building blocks of atoms.
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You have protons and neutrons in the nucleus
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that are stuck together by something called the strong force,
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the strong nuclear force,
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and you have electrons in orbit around that,
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held in by the electromagnetic force,
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which is one of the forces of nature.
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That's sort of where we get to by like 1932, more or less.
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Then what happens is physics is nice and neat.
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In 1932, everything looks great, got three particles
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and all the atoms are made of, that's fine.
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But then cloud chamber experiments.
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These are devices that can be used to,
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the first device is capable of imaging subatomic particles
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so you can see their tracks.
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And they're used to study cosmic rays,
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particles that come from outer space
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and bang into the atmosphere.
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And in these experiments,
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people start to see a whole load of new particles.
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So they discover for one thing antimatter,
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which is the sort of a mirror image of the particles.
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So we discovered that there's also,
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as well as a negatively charged electron,
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there's something called a positron,
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which is a positively charged version of the electron.
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And there's an antiproton, which is negatively charged.
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And then a whole load of other weird particles
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start to get discovered.
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And no one really knows what they are.
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This is known as the zoo of particles.
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Are these discoveries from the first theoretical discoveries
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or are they discoveries in an experiment?
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So like, yeah, what's the process of discovery
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for these early sets of particles?
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The early stuff around the atom is really
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experimentally driven.
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It's not based on some theory.
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It's exploration in the lab using equipment.
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So it's really people just figuring out,
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getting hands on with the phenomena,
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figuring out what these things are.
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And the theory comes a bit later.
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That's not always the case.
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So in the discovery of the anti electron, the positron,
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that was predicted from quantum mechanics and relativity
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by a very clever theoretical physicist called Paul Dirac,
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who was probably the second brightest physicist
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of the 20th century, apart from Einstein,
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but isn't anywhere near as well known.
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So he predicted the existence of the anti electron
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from basically a combination of the theories
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of quantum mechanics and relativity.
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And it was discovered about a year after
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he made the prediction.
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What happens when an electron meets a positron?
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They annihilate each other.
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So when you bring a particle and its antiparticle together,
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they react, well, they don't react,
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they just wipe each other out and they turn,
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their mass is turned into energy,
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usually in the form of photons, so you get light produced.
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So when you have that kind of situation,
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why does the universe exist at all
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if there's matter in any matter?
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Oh God, now we're getting into the really big questions.
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So, do you wanna go there now?
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Let's, maybe let's go there later.
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Cause that, I mean, that is a very big question.
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Yeah, let's take it slow with the standard model.
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So, okay, so there's matter and antimatter in the 30s.
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So matter and antimatter,
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and then a load of new particles start turning up
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in these cosmic ray experiments, first of all.
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And they don't seem to be particles that make up atoms.
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They're something else.
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They all mostly interact with a strong nuclear force.
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So they're a bit like protons and neutrons.
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And by, in the 1960s in America, particularly,
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but also in Europe and Russia,
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scientists started to build particle accelerators.
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So these are the forerunners of the LHC.
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So big ring shaped machines that were, you know,
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hundreds of meters long, which in those days was enormous.
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You never, you know, most physics up until that point
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had been done in labs, in universities, you know,
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with small bits of kit.
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So this is a big change.
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And when these accelerators are built,
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they start to find they can produce
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even more of these particles.
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So I don't know the exact numbers, but by around 1960,
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there are of order a hundred of these things
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that have been discovered.
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And physicists are kind of tearing their hair out
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because physics is all about simplification.
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And suddenly what was simple has become messy
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and complicated and everyone sort of wants
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to understand what's going on.
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As a quick kind of aside and probably really dumb question,
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but how is it possible to take something like a,
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like a photon or electron and be able to control it enough,
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like to be able to do a controlled experiment
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where you collide it against something else?
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Is that, is that, that seems like an exceptionally difficult
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engineering challenge because you mentioned vacuum too.
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So you basically want to remove every other distraction
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and really focus on this collision.
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How difficult of an engineering challenge is that?
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Just to get a sense.
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And it is very hard.
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I mean, in the early days,
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particularly when the first accelerators are being built
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in like 1932, Ernest Lawrence builds the first,
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what we call a cyclotron,
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which is like a little accelerator, this big or so.
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There's another one.
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Is it really that big?
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There's a tiny little thing.
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So most of the first accelerators
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were what we call fixed target experiments.
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So you had a ring, you accelerate particles around the ring
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and then you fire them out the side into some target.
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So that makes the kind of,
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the colliding bit is relatively straightforward
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because you just fire it,
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whatever it is you want to fire it at.
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The hard bit is the steering the beams
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with the magnetic fields, getting, you know,
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strong enough electric fields to accelerate them,
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all that kind of stuff.
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The first colliders where you have two beams
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colliding head on, that comes later.
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And I don't think it's done until maybe the 1980s.
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I'm not entirely sure, but it's a much harder problem.
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Cause you have to like perfectly get them to hit each other.
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I mean, we're talking about, I mean, what scale it takes,
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what's the, I mean, the temporal thing is a giant mess,
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but the spatially, like the size is tiny.
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Well, to give you a sense of the LHC beams,
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the cross sectional diameter is I think around a dozen
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So, you know, 10 millionths of a meter.
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And a beam, sorry, just to clarify,
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a beam contains how many,
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is it the bunches that you mentioned?
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Is it multiple particles or is it just one particle?
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The bunches contains say a hundred billion protons each.
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So a bunch is, it's not really bunch shaped.
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They're actually quite long.
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They're like 30 centimeters long,
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but thinner than a human hair.
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So like very, very narrow, long sort of objects.
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Those are the things.
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So what happens in the LHC is you steer the beams
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so that they cross in the middle of the detector.
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So they basically have these swarms of protons
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that are flying through each other.
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And most of the, you have to have a hundred billion
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coming one way, a hundred billion another way,
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maybe 10 of them will hit each other.
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So this, okay, that makes a lot more sense.
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But you're trying to use sort of,
link |
it's like probabilistically, you're not.
link |
You can't make a single particle collide
link |
with a single other particle.
link |
That's not an efficient way to do it.
link |
You'd be waiting a very long time to get anything.
link |
So you're basically, right.
link |
You're relying on probability to be that some fraction
link |
of them are gonna collide.
link |
And then you know which,
link |
because it's a swarm of the same kind of particle.
link |
So it doesn't matter which ones hit each other exactly.
link |
I mean, that's not to say it's not hard.
link |
You've got to, one of the challenges
link |
to make the collisions work is you have to squash
link |
these beams to very, very,
link |
basically the narrower they are the better
link |
cause the higher chances of them colliding.
link |
If you think about two flocks of birds
link |
flying through each other,
link |
the birds are all far apart in the flocks.
link |
There's not much chance that they'll collide.
link |
If they're all flying densely together,
link |
then they're much more likely to collide with each other.
link |
So that's the sort of problem.
link |
And it's tuning those magnetic fields,
link |
getting the magnetic fields powerful enough
link |
that you squash the beams and focus them
link |
so that you get enough collisions.
link |
That's super cool.
link |
Do you know how much software is involved here?
link |
I mean, it's sort of,
link |
I come from the software world and it's fascinating.
link |
This seems like software is buggy and messy.
link |
And so like, you almost don't want to rely
link |
on software too much.
link |
Like if you do, it has to be like low level,
link |
like Fortran style programming.
link |
Do you know how much software
link |
is in a large Hadron Collider?
link |
I mean, it depends at which level a lot.
link |
I mean, the whole thing is obviously computer controlled.
link |
So, I mean, I don't know a huge amount
link |
about how the software for the actual accelerator works,
link |
but I've been in the control center.
link |
So at CERN, there's this big control room,
link |
which is like a bit like a NASA mission control
link |
with big banks of desks where the engineers sit
link |
and they monitor the LHC.
link |
Cause you obviously can't be in the tunnel
link |
when it's running.
link |
So everything's remote.
link |
I mean, one sort of anecdote about the software side,
link |
in 2008, when the LHC first switched on,
link |
they had this big launch event
link |
and then big press conference party
link |
to inaugurate the machine.
link |
And about 10 days after that,
link |
they were doing some tests
link |
and this dramatic event happened
link |
where a huge explosion basically took place
link |
in the tunnel that destroyed or damaged, badly damaged
link |
about half a kilometer of the machine.
link |
But the stories, the engineers
link |
are in the control room that day.
link |
One guy told me this story about,
link |
basically all these screens they have in the control room
link |
started going red.
link |
So these alarms like kind of in software going off
link |
and then they assume that there's something wrong
link |
with the software, cause there's no way
link |
something this catastrophic could have happened.
link |
But I mean, when I worked on, when I was a PhD student,
link |
one of my jobs was to help to maintain the software
link |
that's used to control the detector that we work on.
link |
And that was, it's relatively robust,
link |
not such, you don't want it to be too fancy.
link |
You don't want it to sort of fall over too easily.
link |
The more clever stuff comes
link |
when you're talking about analyzing the data
link |
and that's where the sort of, you know.
link |
Are we jumping around too much?
link |
Do we finish with a standard model?
link |
We didn't, so have we even started talking about quarks?
link |
We haven't talked to them yet.
link |
No, we got to the messy zoo of particles.
link |
Let me, let's go back there if it's okay.
link |
Okay, that's fine.
link |
Can you take us to the rest of the history of physics
link |
in the 20th century?
link |
Okay, so circa 1960, you have this,
link |
you have these a hundred or so particles.
link |
It's a bit like the periodic table all over again.
link |
So you've got like having a hundred elements,
link |
it's sort of a bit like that.
link |
And people start to try to impose some order.
link |
So Murray Gellman, he's a theoretical physicist,
link |
American from New York.
link |
He realizes that there are these symmetries
link |
in these particles that if you arrange them in certain ways,
link |
they relate to each other.
link |
And he uses these symmetry principles
link |
to predict the existence of particles
link |
that haven't been discovered,
link |
which are then discovered in accelerators.
link |
So this starts to suggest
link |
there's not just random collections of crap.
link |
There's like, you know, actually some order
link |
to this underlying it.
link |
A little bit later in 1960, again, around the 1960s,
link |
he proposes along with another physicist called George Zweig
link |
that these symmetries arise because
link |
just like the patterns in the periodic table arise
link |
because atoms are made of electrons and protons,
link |
that these patterns are due to the fact
link |
that these particles are made of smaller things.
link |
And they are called quarks.
link |
So these are the particles they're predicted from theory.
link |
For a long time, no one really believes they're real.
link |
A lot of people think that they're a kind of theoretical
link |
convenience that happened to fit the data,
link |
but there's no evidence.
link |
No one's ever seen a quark in any experiment.
link |
And lots of experiments are done to try to find quarks,
link |
to try to knock a quark out of a...
link |
So the idea, if protons and neutrons are made of quarks,
link |
you should be able to knock a quark out and see the quark.
link |
That never happens.
link |
And we still have never actually managed to do that.
link |
So the way that it's done in the end
link |
is this machine that's built in California
link |
at the Stanford Lab, Stanford Linear Accelerator,
link |
which is essentially a gigantic,
link |
three kilometer long electron gun.
link |
It fires electrons, almost the speed of light, at protons.
link |
And when you do these experiments,
link |
what you find is at very high energy,
link |
the electrons bounce off small, hard objects
link |
inside the proton.
link |
So it's a bit like taking an X ray of the proton.
link |
You're firing these very light, high energy particles,
link |
and they're pinging off little things inside the proton
link |
that are like ball bearings, if you like.
link |
So you actually, that way,
link |
they resolve that there are three things
link |
inside the proton, which are quarks,
link |
the quarks that Gellman and Zweig had predicted.
link |
So that's really the evidence that convinces people
link |
that these things are real.
link |
The fact that we've never seen one
link |
in an experiment directly,
link |
they're always stuck inside other particles.
link |
And the reason for that is essentially
link |
to do with a strong force.
link |
The strong force is the force that holds quarks together.
link |
And it's so strong that it's impossible
link |
to actually liberate a quark.
link |
So if you try and pull a quark out of a proton,
link |
what actually ends up happening
link |
is that you kind of create this spring like bond
link |
in the strong force.
link |
You imagine two quarks that are held together
link |
by a very powerful spring.
link |
You pull and pull and pull,
link |
more and more energy gets stored in that bond,
link |
like stretching a spring,
link |
and eventually the tension gets so great,
link |
the spring snaps, and the energy in that bond
link |
gets turned into two new quarks
link |
that go on the broken ends.
link |
So you started with two quarks,
link |
you end up with four quarks.
link |
So you never actually get to take a quark out.
link |
You just end up making loads more quarks in the process.
link |
So how do we, again, forgive the dumb question,
link |
how do we know quarks are real then?
link |
Well, A, from these experiments where we can scatter,
link |
you fire electrons into the protons.
link |
They can burrow into the proton and knock off,
link |
and they can bounce off these quarks.
link |
So you can see from the angles,
link |
the electrons come out.
link |
I see, you can infer.
link |
You can infer that these things are there.
link |
The quark model can also be used.
link |
It has a lot of successes that you can use it
link |
to predict the existence of new particles
link |
that hadn't been seen.
link |
So, and it basically, there's lots of data
link |
basically showing from, you know,
link |
when we fire protons at each other at the LHC,
link |
a lot of quarks get knocked all over the place.
link |
And every time they try and escape from,
link |
say, one of their protons,
link |
they make a whole jet of quarks that go flying off,
link |
bound up in other sorts of particles made of quarks.
link |
So all the sort of the theoretical predictions
link |
from the basic theory of the strong force and the quarks
link |
all agrees with what we are seeing in experiments.
link |
We've just never seen an actual quark on its own
link |
because unfortunately it's impossible
link |
to get them out on their own.
link |
So quarks, these crazy smaller things
link |
that are hard to imagine are real.
link |
What else is part of the story here?
link |
So the other thing that's going on at the time,
link |
around the 60s, is an attempt to understand the forces
link |
that make these particles interact with each other.
link |
So you have the electromagnetic force,
link |
which is the force that was sort of discovered
link |
to some extent in this room, or at least in this building.
link |
So the first, what we call quantum field theory
link |
of the electromagnetic force is developed
link |
in the 1940s and 50s by Feynman,
link |
Richard Feynman amongst other people,
link |
Julian Schrodinger, Tom Onaga,
link |
who come up with the first,
link |
what we call a quantum field theory
link |
of the electromagnetic force.
link |
And this is where this description of,
link |
which I gave you at the beginning,
link |
that particles are ripples in fields.
link |
Well, in this theory, the photon, the particle of light
link |
is described as a ripple in this quantum field
link |
called the electromagnetic field.
link |
And the attempt then is made to try,
link |
well, can we come up with a quantum field theory
link |
of the other forces, of the strong force and the weak,
link |
the third force, which we haven't discussed,
link |
which is the weak force, which is a nuclear force.
link |
We don't really experience it in our everyday lives,
link |
but it's responsible for radioactive decay.
link |
It's the force that allows, you know,
link |
on a radioactive atom to turn
link |
into a different element, for example.
link |
And I don't know if you've explicitly mentioned,
link |
but so there's technically four forces.
link |
I guess three of them would be in the standard model,
link |
like the weak, the strong, and the electromagnetic,
link |
and then there's gravity.
link |
And there's gravity, which we don't worry about that,
link |
because it's too hard.
link |
Well, no, maybe we bring that up at the end, but yeah.
link |
Gravity, so far, we don't have a quantum theory of,
link |
and if you can solve that problem,
link |
you'll win a Nobel Prize.
link |
Well, we're gonna have to bring up
link |
the graviton at some point, I'm gonna ask you,
link |
but let's leave that to the side for now.
link |
So those three, okay, Feynman, electromagnetic force,
link |
the quantum field, and where does the weak force come in?
link |
So yeah, well, first of all,
link |
I mean, the strong force is the easiest.
link |
The strong force is a little bit
link |
like the electromagnetic force.
link |
It's a force that binds things together.
link |
So that's the force that holds quarks together
link |
inside the proton, for example.
link |
So a quantum field theory of that force
link |
is discovered in the, I think it's in the 60s,
link |
and it predicts the existence
link |
of new force particles called gluons.
link |
So gluons are a bit like the photon.
link |
The photon is the particle of electromagnetism.
link |
Gluons are the particles of the strong force.
link |
So just like there's an electromagnetic field,
link |
there's something called a gluon field,
link |
which is also all around us.
link |
So some of these particles, I guess,
link |
are the force carriers or whatever.
link |
They carry the force.
link |
It depends how you want to think about it.
link |
I mean, really the field, the strong force field,
link |
the gluon field is the thing that binds the quarks together.
link |
The gluons are the little ripples in that field.
link |
So that like, in the same way that the photon is a ripple
link |
in the electromagnetic field.
link |
But the thing that really does the binding is the field.
link |
I mean, you may have heard people talk about things
link |
like you've heard the phrase virtual particle.
link |
So sometimes in some, if you hear people describing
link |
how forces are exchanged between particles,
link |
they quite often talk about the idea
link |
that if you have an electron and another electron, say,
link |
and they're repelling each other
link |
through the electromagnetic force,
link |
you can think of that as if they're exchanging photons.
link |
So they're kind of firing photons
link |
backwards and forwards between each other.
link |
And that causes them to repel.
link |
That photon is then a virtual particle.
link |
Yes, that's what we call a virtual particle.
link |
In other words, it's not a real thing,
link |
it doesn't actually exist.
link |
So it's an artifact of the way theorists do calculations.
link |
So when they do calculations in quantum field theory,
link |
rather than, no one's discovered a way
link |
of just treating the whole field.
link |
You have to break the field down into simpler things.
link |
So you can basically treat the field
link |
as if it's made up of lots of these virtual photons,
link |
but there's no experiment that you can do
link |
that can detect these particles being exchanged.
link |
What's really happening in reality
link |
is that the electromagnetic field is warped
link |
by the charge of the electron and that causes the force.
link |
But the way we do calculations involves particles.
link |
So it's a bit confusing,
link |
but it's really a mathematical technique.
link |
It's not something that corresponds to reality.
link |
I mean, that's part, I guess, of the Feynman diagrams.
link |
Is this these virtual particles, okay.
link |
That's right, yeah.
link |
Some of these have mass, some of them don't.
link |
What does that even mean, not to have mass?
link |
And maybe you can say which one of them have mass
link |
And why is mass important or relevant
link |
in this field view of the universe?
link |
Well, there are actually only two particles
link |
in the standard model that don't have mass,
link |
which are the photon and the gluons.
link |
So they are massless particles,
link |
but the electron, the quarks,
link |
and there are a bunch of other particles
link |
I haven't discussed.
link |
There's something called a muon and a tau,
link |
which are basically heavy versions of the electron
link |
that are unstable.
link |
You can make them in accelerators,
link |
but they don't form atoms or anything.
link |
They don't exist for long enough.
link |
But all the matter particles, there are 12 of them,
link |
six quarks and six, what we call leptons,
link |
which includes the electron and its two heavy versions
link |
and three neutrinos, all of them have mass.
link |
And so do, this is the critical bit.
link |
So the weak force, which is the third of these
link |
quantum forces, which is one of the hardest to understand,
link |
the force particles of that force have very large masses.
link |
And there are three of them.
link |
They're called the W plus, the W minus, and the Z boson.
link |
And they have masses of between 80 and 90 times
link |
that of the protons.
link |
They're very heavy.
link |
They're very heavy things.
link |
So they're what, the heaviest, I guess?
link |
They're not the heaviest.
link |
The heaviest particle is the top quark,
link |
which has a mass of about 175 ish protons.
link |
So that's really massive.
link |
And we don't know why it's so massive,
link |
but coming back to the weak force,
link |
so the problem in the 60s and 70s was that
link |
the reason that the electromagnetic force
link |
is a force that we can experience in our everyday lives.
link |
So if we have a magnet and a piece of metal,
link |
you can hold it, you know, a meter apart
link |
if it's powerful enough and you'll feel a force.
link |
Whereas the weak force only becomes apparent
link |
when you basically have two particles touching
link |
at the scale of a nucleus.
link |
So we just get to very short distances
link |
before this force becomes manifest.
link |
It's not, we don't get weak forces going on in this room.
link |
We don't notice them.
link |
And the reason for that is that the particle,
link |
well, the field that transmits the weak force,
link |
the particle that's associated with that field
link |
has a very large mass,
link |
which means that the field dies off very quickly.
link |
So as you, whereas an electric charge,
link |
if you were to look at the shape of the electromagnetic field,
link |
it would fall off with this,
link |
you have this thing called the inverse square law,
link |
which is the idea that the force halves
link |
every time you double the distance.
link |
No, sorry, it doesn't half.
link |
It quarters every time you double the distance
link |
between say the two particles.
link |
Whereas the weak force kind of,
link |
you move a little bit away from the nucleus
link |
and just disappears.
link |
The reason for that is because these fields,
link |
the particles that go with them have a very large mass.
link |
But the problem that theorists faced in the 60s
link |
was that if you tried to introduce massive force fields,
link |
the theory gave you nonsensical answers.
link |
So you'd end up with infinite results
link |
for a lot of the calculations you tried to do.
link |
So the basically, it seemed that quantum field theory
link |
was incompatible with having massive particles,
link |
not just the force particles actually,
link |
but even the electron was a problem.
link |
So this is where the Higgs
link |
that we sort of alluded to comes in.
link |
And the solution was to say, okay, well,
link |
actually all the particles in the Standard Model are mass.
link |
They have no mass.
link |
So the quarks, the electron, they don't have a mass.
link |
Neither do these weak particles.
link |
They don't have mass either.
link |
What happens is they actually acquire mass
link |
through another process.
link |
They get it from somewhere else.
link |
They don't actually have it intrinsically.
link |
So this idea that was introduced by,
link |
well, Peter Higgs is the most famous,
link |
but actually there are about six people
link |
that came up with the idea more or less at the same time,
link |
is that you introduce a new quantum field,
link |
which is another one of these invisible things
link |
that's everywhere.
link |
And it's through the interaction with this field
link |
that particles get mass.
link |
So you can think of say an electron in the Higgs field,
link |
the Higgs field kind of bunches around the electron.
link |
It's sort of drawn towards the electron.
link |
And that energy that's stored in that field
link |
around the electron is what we see
link |
as the mass of the electron.
link |
But if you could somehow turn off the Higgs field,
link |
then all the particles in nature would become massless
link |
and fly around at the speed of light.
link |
So this idea of the Higgs field allowed other people,
link |
other theorists to come up with a, well,
link |
it was another, basically a unified theory
link |
of the electromagnetic force and the weak force.
link |
So once you bring in the Higgs field,
link |
you can combine two of the forces into one.
link |
So it turns out the electromagnetic force
link |
and the weak force are just two aspects
link |
of the same fundamental force.
link |
And at the LHC, we go to high enough energies
link |
that you see these two forces unifying effectively.
link |
So first of all, it started as a theoretical notion,
link |
like this is some, and then, I mean,
link |
wasn't the Higgs called the God particle at some point?
link |
It was by a guy trying to sell popular science books, yeah.
link |
Yeah, but I mean, I remember because when I was hearing it,
link |
I thought it would, I mean, that would solve a lot of,
link |
that unify a lot of our ideas of physics was my notion.
link |
But maybe you can speak to that.
link |
Is it as big of a leap as a God particle
link |
or is it a Jesus particle, which, you know,
link |
what's the big contribution of Higgs
link |
in terms of this unification power?
link |
Yeah, I mean, to understand that,
link |
it maybe helps know the history a little bit.
link |
So when the, what we call electroweak theory
link |
was put together, which is where you unify electromagnetism
link |
with the weak force and Higgs is involved in all of that.
link |
So that theory, which was written in the mid 70s,
link |
predicted the existence of four new particles,
link |
the W plus boson, the W minus boson,
link |
the Z boson and the Higgs boson.
link |
So there were these four particles
link |
that came with the theory,
link |
that were predicted by the theory.
link |
In 1983, 84, the W's and the Z particles
link |
were discovered at an accelerator at CERN
link |
called the super proton synchrotron,
link |
which was a seven kilometer particle collider.
link |
So three of the bits of this theory had already been found.
link |
So people were pretty confident from the 80s
link |
that the Higgs must exist
link |
because it was a part of this family of particles
link |
that this theoretical structure only works
link |
if the Higgs is there.
link |
So what then happens,
link |
and so you've got this question about
link |
why is the LHC the size it is?
link |
Well, actually the tunnel that the LHC is in
link |
was not built for the LHC.
link |
It was built for a previous accelerator
link |
called the large electron positron collider.
link |
So that began operation in the late 80s, early 90s.
link |
They basically, that's when they dug
link |
the 27 kilometer tunnel.
link |
They put this accelerator into it,
link |
the collider that fires electrons
link |
and anti electrons at each other, electrons and positrons.
link |
So the purpose of that machine was,
link |
well, it was actually to look for the Higgs.
link |
That was one of the things it was trying to do.
link |
It didn't have enough energy to do it in the end.
link |
But the main thing it achieved was it studied
link |
the W and the Z particles at very high precision.
link |
So it made loads of these things.
link |
Previously, you can only make a few of them
link |
at the previous accelerator.
link |
So you could study these really, really precisely.
link |
And by studying their properties,
link |
you could really test this electroweak theory
link |
that had been invented in the 70s
link |
and really make sure that it worked.
link |
So actually by 1999, when this machine turned off,
link |
people knew, well, okay, you never know
link |
until you find the thing.
link |
But people were really confident
link |
this electroweak theory was right.
link |
And that the Higgs almost,
link |
the Higgs or something very like the Higgs had to exist
link |
because otherwise the whole thing doesn't work.
link |
It'd be really weird if you could discover
link |
and these particles, they all behave exactly
link |
as your theory tells you they should.
link |
But somehow this key piece of the picture is not there.
link |
So in a way, it depends how you look at it.
link |
The discovery of the Higgs on its own
link |
is obviously a huge achievement in many,
link |
both experimentally and theoretically.
link |
On the other hand, it's like having a jigsaw puzzle
link |
where every piece has been filled in.
link |
You have this beautiful image, there's one gap
link |
and you kind of know that piece must be there somewhere.
link |
So the discovery in itself, although it's important,
link |
is not so interesting.
link |
It's like a confirmation of the obvious at that point.
link |
But what makes it interesting
link |
is not that it just completes the standard model,
link |
which is a theory that we've known
link |
had the basic layout offs for 40 years or more now.
link |
It's that the Higgs actually is a unique particle.
link |
It's very different to any of the other particles
link |
in the standard model.
link |
And it's a theoretically very troublesome particle.
link |
There are a lot of nasty things to do with the Higgs,
link |
but also opportunities.
link |
So that we basically, we don't really understand
link |
how such an object can exist in the form that it does.
link |
So there are lots of reasons for thinking
link |
that the Higgs must come with a bunch of other particles
link |
or that it's perhaps made of other things.
link |
So it's not a fundamental particle,
link |
that it's made of smaller things.
link |
I can talk about that if you like a bit.
link |
That's still a notion, so the Higgs
link |
might not be a fundamental particle,
link |
that there might be some, it might, oh man.
link |
So that is an idea, it's not been demonstrated to be true.
link |
But I mean, all of these ideas basically come
link |
from the fact that this is a problem
link |
that motivated a lot of development in physics
link |
in the last 30 years or so.
link |
And it's this basic fact that the Higgs field,
link |
which is this field that's everywhere in the universe,
link |
this is the thing that gives mass to the particles.
link |
And the Higgs field is different from all the other fields
link |
in that, let's say you take the electromagnetic field,
link |
which is, if we actually were to measure
link |
the electromagnetic field in this room,
link |
we would measure all kinds of stuff going on
link |
because there's light, there's gonna be microwaves
link |
and radio waves and stuff.
link |
But let's say we could go to a really, really remote part
link |
of empty space and shield it and put a big box around it
link |
and then measure the electromagnetic field in that box.
link |
The field would be almost zero,
link |
apart from some little quantum fluctuations,
link |
but basically it goes to naught.
link |
The Higgs field has a value everywhere.
link |
So it's a bit like the whole,
link |
it's like the entire space has got this energy
link |
stored in the Higgs field, which is not zero,
link |
it's finite, it's a bit like having the temperature
link |
of space raised to some background temperature.
link |
And it's that energy that gives mass to the particles.
link |
So the reason that electrons and quarks have mass
link |
is through the interaction with this energy
link |
that's stored in the Higgs field.
link |
Now, it turns out that the precise value this energy has
link |
has to be very carefully tuned if you want a universe
link |
where interesting stuff can happen.
link |
So if you push the Higgs field down,
link |
it has a tendency to collapse to,
link |
well, there's a tendency,
link |
if you do your sort of naive calculations,
link |
there are basically two possible likely configurations
link |
for the Higgs field, which is either it's zero everywhere,
link |
in which case you have a universe
link |
which is just particles with no mass that can't form atoms
link |
and just fly about at the speed of light,
link |
or it explodes to an enormous value,
link |
what we call the Planck scale,
link |
which is the scale of quantum gravity.
link |
And at that point, if the Higgs field was that strong,
link |
even an electron would become so massive
link |
that it would collapse into a black hole.
link |
And then you have a universe made of black holes
link |
and nothing like us.
link |
So it seems that the strength of the Higgs field
link |
is to achieve the value that we see
link |
requires what we call fine tuning of the laws of physics.
link |
You have to fiddle around with the other fields
link |
in the Standard Model and their properties
link |
to just get it to this right sort of Goldilocks value
link |
that allows atoms to exist.
link |
This is deeply fishy.
link |
People really dislike this.
link |
Well, yeah, I guess, so what would be,
link |
so two explanations.
link |
One, there's a god that designed this perfectly,
link |
and two is there's an infinite number
link |
of alternate universes,
link |
and we just happen to be in the one in which life
link |
is possible, complexity.
link |
So when you say, I mean, life, any kind of complexity,
link |
that's not either complete chaos or black holes.
link |
I mean, how does that make you feel?
link |
What do you make of that?
link |
That's such a fascinating notion
link |
that this perfectly tuned field
link |
that's the same everywhere is there.
link |
What do you make of that?
link |
Yeah, what do you make of that?
link |
I mean, yeah, so you laid out
link |
two of the possible explanations.
link |
Some, well, yeah, I mean, well,
link |
someone, some cosmic creator went,
link |
yeah, let's fix that to be at the right level.
link |
That's one possibility, I guess.
link |
It's not a scientifically testable one,
link |
but theoretically, I guess, it's possible.
link |
Sorry to interrupt, but there could also be
link |
not a designer, but couldn't there be just,
link |
I guess I'm not sure what that would be,
link |
but some kind of force that,
link |
that some kind of mechanism
link |
by which this kind of field is enforced
link |
in order to create complexity,
link |
basically forces that pull the universe
link |
towards an interesting complexity.
link |
I mean, yeah, I mean, there are people
link |
who have those ideas.
link |
I don't really subscribe to them.
link |
As I'm saying, it sounds really stupid.
link |
No, I mean, there are definitely people
link |
that make those kind of arguments.
link |
There's ideas that, I think it's Lee Smolin's idea,
link |
or one, I think, that universes are born inside black holes.
link |
And so, universes, they basically have
link |
like Darwinian evolution of the universe,
link |
where universes give birth to other universes.
link |
And if universes where black holes can form
link |
are more likely to give birth to more universes,
link |
so you end up with universes which have similar laws.
link |
I mean, I don't know, whatever.
link |
Well, I talked to Lee recently on this podcast,
link |
and he's a reminder to me that the physics community
link |
has like so many interesting characters in it.
link |
Anyway, sorry, so.
link |
I mean, as an experimentalist, I tend to sort of think,
link |
these are interesting ideas, but they're not really testable,
link |
so I tend not to think about them very much.
link |
So, I mean, going back to the science of this,
link |
there is an explanation.
link |
There is a possible solution to this problem of the Higgs,
link |
which doesn't involve multiverses or creators fiddling about
link |
with the laws of physics.
link |
If the most popular solution
link |
was something called supersymmetry,
link |
which is a theory which involves a new type of symmetry
link |
In fact, it's one of the last types of symmetries
link |
that it's possible to have
link |
that we haven't already seen in nature,
link |
which is a symmetry between force particles
link |
and matter particles.
link |
So what we call fermions, which are the matter particles
link |
and bosons, which are force particles.
link |
And if you have supersymmetry, then there is a super partner
link |
for every particle in the standard model.
link |
And without going into the details,
link |
the effect of this basically is that you have
link |
a whole bunch of other fields,
link |
and these fields cancel out the effect
link |
of the standard model fields,
link |
and they stabilize the Higgs field at a nice sensible value.
link |
So in supersymmetry, you naturally,
link |
without any tinkering about with the constants of nature
link |
or anything, you get a Higgs field with a nice value,
link |
which is the one we see.
link |
So this is one of the,
link |
and supersymmetry's also got lots of other things
link |
It predicts the existence of a dark matter particle,
link |
which would be great.
link |
It potentially suggests that the strong force
link |
and the electroweak force unify at high energy.
link |
So lots of reasons people thought this was a productive idea.
link |
And when the LHC was, just before it was turned on,
link |
there was a lot of hype, I guess,
link |
a lot of an expectation that we would discover
link |
these super partners because,
link |
and particularly the main reason was
link |
that if supersymmetry stabilizes the Higgs field
link |
at this nice Goldilocks value,
link |
these super particles should have a mass
link |
around the energy that we're probing at the LHC,
link |
around the energy of the Higgs.
link |
So it was kind of thought, you discover the Higgs,
link |
you probably discover super partners as well.
link |
So once you start creating ripples in this Higgs field,
link |
you should be able to see these kinds of,
link |
you should be, yeah.
link |
So the super fields would be there.
link |
When I, at the very beginning I said,
link |
we're probing the vacuum.
link |
What I mean is really that, you know,
link |
okay, let's say these super fields exist.
link |
The vacuum contains super fields.
link |
They're there, these supersymmetric fields.
link |
If we hit them hard enough, we can make them vibrate.
link |
We see super particles come flying out.
link |
That's the sort of, that's the idea.
link |
That's the whole, okay.
link |
That's the whole point.
link |
So, so far at least, I mean,
link |
we've had now a decade of data taking at the LHC.
link |
No signs of super partners have,
link |
supersymmetric particles have been found.
link |
In fact, no signs of any physics, any new particles
link |
beyond the Standard Model have been found.
link |
So supersymmetry is not the only thing that can do this.
link |
There are other theories that involve
link |
additional dimensions of space
link |
or potentially involve the Higgs boson
link |
being made of smaller things,
link |
being made of other particles.
link |
Yeah, that's an interesting, you know,
link |
I haven't heard that before.
link |
That's really, that's an interesting,
link |
but can you maybe linger on that?
link |
Like what, what could be,
link |
what could the Higgs particle be made of?
link |
Well, so the oldest, I think the original ideas about this
link |
was these theories called technicolor,
link |
which were basically like an analogy with the strong force.
link |
So the idea was the Higgs boson was a bound state
link |
of two very strongly interacting particles
link |
that were a bit like quarks.
link |
So like quarks, but I guess higher energy things
link |
with a super strong force.
link |
So not the strong force, but a new force
link |
that was very strong.
link |
And the Higgs was a bound state of these, these objects.
link |
And the Higgs would in principle, if that was right,
link |
would be the first in a series of technicolor particles.
link |
Technicolor, I think not being a theorist,
link |
but it's not, it's basically not done very well,
link |
particularly since the LHC found the Higgs,
link |
that kind of, it rules out, you know,
link |
a lot of these technicolor theories,
link |
but there are other things that are a bit like technicolor.
link |
So there's a theory called partial composite,
link |
which is an idea that some of my colleagues
link |
at Cambridge have worked on,
link |
which is a similar sort of idea that the Higgs
link |
is a bound state of some strongly interacting particles,
link |
and that the standard model particles themselves,
link |
the more exotic ones like the top quark
link |
are also sort of mixtures of these composite particles.
link |
So it's a kind of an extension to the standard model,
link |
which explains this problem
link |
with the Higgs bosons, Goldilocks value,
link |
but also helps us understand we have,
link |
we're in a situation now, again,
link |
a bit like the periodic table,
link |
where we have six quarks, six leptons in this kind of,
link |
you can arrange in this nice table
link |
and you can see these columns where the patterns repeat
link |
and you go, okay, maybe there's something deeper
link |
going on here, you know,
link |
and so this would potentially be something,
link |
this partial composite theory could explain,
link |
a sort of enlarge this picture
link |
that allows us to see the whole symmetrical pattern
link |
and understand what the ingredients, why do we have,
link |
so one of the big questions in particle physics is,
link |
why are there three copies of the matter particles?
link |
So in what we call the first generation,
link |
which is what we're made of,
link |
there's the electron, the electron neutrino,
link |
the up quark and the down quark,
link |
they're the most common matter particles in the universe,
link |
but then there are copies of these four particles
link |
in the second and the third generations,
link |
so things like nuons and top quarks and other stuff,
link |
we don't know why, we see these patterns,
link |
we have no idea where it comes from,
link |
so that's another big question, you know,
link |
can we find out the deeper order that explains
link |
this particular periodic table of particles that we see?
link |
Is it possible that the deeper order includes
link |
like almost a single entity,
link |
so like something that I guess like string theory
link |
dreams about, is this essentially the dream,
link |
is to discover something simple, beautiful and unifying?
link |
Yeah, I mean, that is the dream,
link |
and I think for some people, for a lot of people,
link |
it still is the dream,
link |
so there's a great book by Steven Weinberg,
link |
who is one of the theoretical physicists
link |
who was instrumental in building the Standard Model,
link |
so he came up with some others with the electroweak theory,
link |
the theory that unified electromagnetism and the weak force,
link |
and he wrote this book,
link |
I think it was towards the end of the 80s, early 90s,
link |
called Dreams of a Final Theory,
link |
which is a very lovely, quite short book
link |
about this idea of a final unifying theory
link |
that brings everything together,
link |
and I think you get a sense reading his book
link |
written at the end of the 80s, early 90s,
link |
that there was this feeling that such a theory was coming,
link |
and that was the time when string theory
link |
was very exciting, so string theory,
link |
there's been this thing called the superstring revolution,
link |
and theoretical physicists were very excited,
link |
they discovered these theoretical objects,
link |
these little vibrating loops of string
link |
that in principle not only was a quantum theory of gravity
link |
but could explain all the particles in the Standard Model
link |
and bring it all together,
link |
and as you say, you have one object, the string,
link |
and you can pluck it, and the way it vibrates
link |
gives you these different notes,
link |
each of which is a different particle,
link |
so it's a very lovely idea,
link |
but the problem is that, well, there's a few,
link |
people discover that mathematics is very difficult,
link |
so people have spent three decades or more
link |
trying to understand string theory,
link |
and I think if you spoke to most string theorists,
link |
they would probably freely admit
link |
that no one really knows what string theory is yet,
link |
I mean, there's been a lot of work,
link |
but it's not really understood,
link |
and the other problem is that string theory
link |
mostly makes predictions about physics
link |
that occurs at energies far beyond
link |
what we will ever be able to probe in the laboratory.
link |
Yeah, probably ever.
link |
By the way, so sorry to take a million tangents,
link |
but is there room for complete innovation
link |
of how to build a particle collider
link |
that could give us an order of magnitude increase
link |
in the kind of energies,
link |
or do we need to keep just increasing the size of things?
link |
I mean, maybe, yeah, I mean, there are ideas,
link |
to give you a sense of the gulf that has to be bridged.
link |
So the LHC collides particles at an energy
link |
of what we call 14 tera electron volts,
link |
so that's basically the equivalent
link |
if you've accelerated a proton through 14 trillion volts.
link |
That gets us to the energies
link |
where the Higgs and these weak particles live.
link |
They're very massive.
link |
The scale where strings become manifest
link |
is something called the Planck scale,
link |
which I think is of the order 10 to the,
link |
hang on, get this right,
link |
it's 10 to the 18 giga electron volts,
link |
so about 10 to the 15 tera electron volts.
link |
So you're talking trillions of times more energy.
link |
Yeah, 10 to the 15th or 10 to the 14th larger, I don't even.
link |
It's of that order.
link |
It's a very big number.
link |
So we're not talking just an order
link |
of magnitude increase in energy,
link |
we're talking 14 orders of magnitude energy increase.
link |
So to give you a sense of what that would look like,
link |
were you to build a particle accelerator
link |
with today's technology.
link |
Bigger or smaller than our solar system?
link |
The size of the galaxy.
link |
So you'd need to put a particle accelerator
link |
that circled the Milky Way to get to the energies
link |
where you would see strings if they exist.
link |
So that is a fundamental problem,
link |
which is that most of the predictions
link |
of these unified theories, quantum theories of gravity,
link |
only make statements that are testable at energies
link |
that we will not be able to probe,
link |
and barring some unbelievable,
link |
completely unexpected technological
link |
or scientific breakthrough,
link |
which is almost impossible to imagine.
link |
You never say never, but it seems very unlikely.
link |
Yeah, I can just see the news story.
link |
Elon Musk decides to build a particle collider
link |
the size of our galaxy.
link |
We'd have to get together
link |
with all our galactic neighbors to pay for it, I think.
link |
What is the exciting possibilities
link |
of the Large Hadron Collider?
link |
What is there to be discovered
link |
in this order of magnitude of scale?
link |
Is there other bigger efforts on the horizon in this space?
link |
What are the open problems, the exciting possibilities?
link |
You mentioned supersymmetry.
link |
Yeah, so, well, there are lots of new ideas.
link |
Well, there are lots of problems that we're facing.
link |
So there's a problem with the Higgs field,
link |
which supersymmetry was supposed to solve.
link |
There's the fact that 95% of the universe
link |
we know from cosmology, astrophysics, is invisible,
link |
that it's made of dark matter and dark energy,
link |
which are really just words
link |
for things that we don't know what they are.
link |
It's what Donald Rumsfeld called a known unknown.
link |
So we know we don't know what they are.
link |
Well, that's better than unknown unknown.
link |
Yeah, well, there may be some unknown unknowns,
link |
but by definition we don't know what those are, so, yeah.
link |
But the hope is a particle accelerator
link |
could help us make sense of dark energy, dark matter.
link |
There's still, there's some hope for that?
link |
There's hope for that, yeah.
link |
So one of the hopes is the LHC could produce
link |
a dark matter particle in its collisions.
link |
And it may be that the LHC
link |
will still discover new particles,
link |
that it might still, supersymmetry could still be there.
link |
It's just maybe more difficult to find
link |
than we thought originally.
link |
And dark matter particles might be being produced,
link |
but we're just not looking in the right part of the data
link |
for them, that's possible.
link |
It might be that we need more data,
link |
that these processes are very rare
link |
and we need to collect lots and lots of data
link |
before we see them.
link |
But I think a lot of people would say now
link |
that the chances of the LHC
link |
directly discovering new particles
link |
in the near future is quite slim.
link |
It may be that we need a decade more data
link |
before we can see something, or we may not see anything.
link |
That's the, that's where we are.
link |
So, I mean, the physics, the experiments that I work on,
link |
so I work on a detector called LHCb,
link |
which is one of these four big detectors
link |
that are spaced around the ring.
link |
And we do slightly different stuff to the big guys.
link |
There's two big experiments called Atlas and CMS,
link |
3000 physicists and scientists
link |
and computer scientists on them each.
link |
They are the ones that discovered the Higgs
link |
and they look for supersymmetry and dark matter and so on.
link |
What we look at are standard model particles
link |
called bequarks, which depending on your preferences,
link |
either bottom or beauty,
link |
we tend to say beauty because it sounds sexier.
link |
But these particles are interesting
link |
because they have, we can make lots of them.
link |
We make billions or hundreds of billions of these things.
link |
You can therefore measure their properties very precisely.
link |
So you can make these really lovely precision measurements.
link |
And what we are doing really is a sort of complimentary thing
link |
to the other big experiments, which is they,
link |
if you think of the sort of analogy they often use is,
link |
if you imagine you're looking in, you're in the jungle
link |
and you're looking for an elephant, say,
link |
and you are a hunter and you're kind of like,
link |
let's say there's the relevance, very rare.
link |
You don't know where in the jungle, the jungle's big.
link |
So there's two ways you go about this.
link |
Either you can go wandering around the jungle
link |
and try and find the elephant.
link |
The problem is if the elephant,
link |
if there's only one elephant and the jungle's big,
link |
the chances of running into it are very small.
link |
Or you could look on the ground
link |
and see if you see footprints left by the elephant.
link |
And if the elephant's moving around, you've got a chance,
link |
that you're better chance maybe
link |
of seeing the elephant's footprints.
link |
If you see the footprints, you go, okay, there's an elephant.
link |
I maybe don't know what kind of elephant it is,
link |
but I got a sense there's something out there.
link |
So that's sort of what we do.
link |
We are the footprint people.
link |
We are, we're looking for the footprints,
link |
the impressions that quantum fields
link |
that we haven't managed to directly create the particle of,
link |
the effects these quantum fields have
link |
on the ordinary standard model fields
link |
that we already know about.
link |
So these B particles, the way they behave
link |
can be influenced by the presence of say,
link |
super fields or dark matter fields or whatever you like.
link |
And the way they decay and behave can be altered slightly
link |
from what our theory tells us they ought to behave.
link |
And it's easier to collect huge amounts of data
link |
We get billions and billions of these things.
link |
You can make very precise measurements.
link |
And the only place really at the LHC
link |
or really in high energy physics at the moment
link |
where there's fairly compelling evidence
link |
that there might be something beyond the standard model
link |
is in these B, these beauty quarks decays.
link |
Just to clarify, which is the difference
link |
between the different, the four experiments,
link |
for example, that you mentioned,
link |
is it the kind of particles that are being collided?
link |
Is it the energies which they're collided?
link |
What's the fundamental difference
link |
between the different experiments?
link |
The collisions are the same.
link |
What's different is the design of the detectors.
link |
So Atlas and CMS are called,
link |
they're called what are called general purpose detectors.
link |
And they are basically barrel shaped machines
link |
and the collisions happen in the middle of the barrel
link |
and the barrel captures all the particles
link |
that go flying out in every direction.
link |
So in a sphere effectively that can fly out
link |
and it can record all of those particles.
link |
And what's the, sorry to be interrupting,
link |
but what's the mechanism of the recording?
link |
Oh, so these detectors, if you've seen pictures of them,
link |
they're huge, like Atlas is 25 meters high
link |
and 45 meters long, they're vast machines,
link |
instruments, I guess you should call them really.
link |
They are, they're kind of like onions.
link |
So they have layers, concentric layers of detectors,
link |
different sorts of detectors.
link |
So close into the beam pipe,
link |
you have what are called usually made of silicon,
link |
they're tracking detectors.
link |
So they're little made of strips of silicon
link |
or pixels of silicon.
link |
And when a particle goes through the silicon,
link |
it gives a little electrical signal
link |
and you get these dots, electrical dots
link |
through your detector, which allows you
link |
to reconstruct the trajectory of the particle.
link |
So that's the middle
link |
and then the outsides of these detectors,
link |
you have things called calorimeters,
link |
which measure the energies of the particles
link |
and the very edge you have things called muon chambers,
link |
which basically these muon particles,
link |
which are the heavy version of the electron,
link |
they're like high velocity bullets
link |
and they can get right to the edge of the detectors.
link |
If you see something at the edge, that's a muon.
link |
So that's broadly how they work.
link |
And all of that is being recorded.
link |
That's all being fed out to, you know, computers.
link |
Data must be awesome, okay.
link |
So LHCb is different.
link |
So we, because we're looking for these be quarks,
link |
be quarks tend to be produced along the beam line.
link |
So in a collision, the be quark tend to fly
link |
sort of close to the beam pipe.
link |
So we built a detector that sort of pyramid cone shaped
link |
basically, that just looks in one direction.
link |
So we ignore, if you have your collision,
link |
stuff goes everywhere.
link |
We ignore all the stuff over here and going off sideways.
link |
We're just looking in this little region
link |
close to the beam pipe
link |
where most of these be quarks are made.
link |
So is there a different aspect of the sensors involved
link |
in the collection of the be quark trajectories?
link |
There are some differences.
link |
So one of the differences is that,
link |
one of the ways you know you've seen a be quark
link |
is that be quarks are actually quite long lived
link |
by particle standards.
link |
So they live for 1.5 trillionths of a second,
link |
which is if you're a fundamental particle
link |
is a very long time.
link |
Cause the Higgs boson, I think lives for about
link |
a trillionth of a trillionth of a second,
link |
or maybe even less than that.
link |
So these are quite long lived things
link |
and they will actually fly a little distance
link |
before they decay.
link |
So they will fly a few centimeters maybe if you're lucky,
link |
then they'll decay into other stuff.
link |
So what we need to do in the middle of the detector,
link |
you wanna be able to see,
link |
you have your place where the protons crash into each other
link |
and that produces loads of particles that come flying out.
link |
So you have loads of lines, loads of tracks
link |
that point back to that proton collision.
link |
And then you're looking for a couple of other tracks,
link |
maybe two or three that point back to a different place
link |
that's maybe a few centimeters away
link |
from the proton collision.
link |
And that's the sign that a little B particle has flown
link |
a few centimeters and decayed somewhere else.
link |
So we need to be able to very accurately resolve
link |
the proton collision from the B particle decay.
link |
So the middle of our detector is very sensitive
link |
and it gets very close to the collision.
link |
So you have this really beautiful delicate
link |
silicon detector that sits,
link |
I think it's seven millimeters from the beam.
link |
And the LHC beam has as much energy
link |
as a jumbo jet at takeoff.
link |
So it's enough to melt a ton of copper.
link |
So you have this furiously powerful thing sitting next
link |
to this tiny delicate silicon sensor.
link |
So those aspects of our detector that are specialized
link |
to measure these particular B quarks
link |
that we're interested in.
link |
And is there, I mean, I remember seeing somewhere
link |
that there's some mention of matter and antimatter
link |
connected to the B, these beautiful quarks.
link |
Is that, what's the connection?
link |
Yeah, what's the connection there?
link |
Yeah, so there is a connection, which is that
link |
when you produce these B particles,
link |
these particles, because you don't see the B quark,
link |
you see the thing that B quark is inside.
link |
So they're bound up inside what we call beauty particles,
link |
where the B quark is joined together with another quark
link |
or two, maybe two other quarks, depending on what it is.
link |
They're a particular set of these B particles
link |
that exhibit this property called oscillation.
link |
So if you make a, for the sake of argument,
link |
a matter version of one of these B particles,
link |
as it travels, because of the magic of quantum mechanics,
link |
it oscillates backwards and forwards
link |
between its matter and antimatter versions.
link |
So it does this weird flipping about backwards and forwards.
link |
And what we can use this for is a laboratory
link |
for testing the symmetry between matter and antimatter.
link |
So if the symmetry between antimatter is precise,
link |
it's exact, then we should see these B particles decaying
link |
as often as matter, as they do as antimatter,
link |
because this oscillation should be even.
link |
It should spend as much time in each state.
link |
But what we actually see is that one of the states,
link |
it spends more time and it's more likely to decay
link |
in one state than the other.
link |
So this gives us a way of testing this fundamental symmetry
link |
between matter and antimatter.
link |
So what can you, sort of returning to the question
link |
before about this fundamental symmetry,
link |
it seems like if there's perfect symmetry
link |
between matter and antimatter,
link |
if we have the equal amount of each in our universe,
link |
it would just destroy itself.
link |
And just like you mentioned,
link |
we seem to live in a very unlikely universe
link |
where it doesn't destroy itself.
link |
So do you have some intuition about why that is?
link |
I mean, well, I'm not a theorist.
link |
I don't have any particular ideas myself.
link |
I mean, I sort of do measurements
link |
to try and test these things,
link |
but I mean, so the terms of the basic problem
link |
is that in the Big Bang,
link |
if you use the standard model to figure out
link |
what ought to have happened,
link |
you should have got equal amounts of matter
link |
and antimatter made,
link |
because whenever you make a particle
link |
in our collisions, for example,
link |
when we collide stuff together,
link |
you make a particle, you make an antiparticle.
link |
They always come together.
link |
They always annihilate together.
link |
So there's no way of making more matter than antimatter
link |
that we've discovered so far.
link |
So that means in the Big Bang,
link |
you get equal amounts of matter and antimatter.
link |
As the universe expands and cools down during the Big Bang,
link |
not very long after the Big Bang,
link |
I think a few seconds after the Big Bang,
link |
you have this event called the Great Annihilation,
link |
which is where all the particles and antiparticles
link |
smack into each other, annihilate, turn into light mostly,
link |
and you end up with a universe later on.
link |
If that was what happened,
link |
then the universe we live in today would be black and empty,
link |
apart from some photons, that would be it.
link |
So there is stuff in the universe.
link |
It appears to be just made of matter.
link |
So there's this big mystery as to how did this happen?
link |
And there are various ideas,
link |
which all involve sort of physics going on
link |
in the first trillionth of a second or so of the Big Bang.
link |
So it could be that one possibility
link |
is that the Higgs field is somehow implicated in this,
link |
that there was this event that took place
link |
in the early universe where the Higgs field
link |
basically switched on, it acquired its modern value.
link |
And when that happened,
link |
this caused all the particles to acquire mass
link |
and the universe basically went through a phase transition
link |
where you had a hot plasma of massless particles.
link |
And then in that plasma,
link |
it's almost like a gas turning into droplets of water.
link |
You get kind of these little bubbles forming in the universe
link |
where the Higgs field has acquired its modern value,
link |
the particles have got mass.
link |
And this phase transition in some models
link |
can cause more matter than antimatter to be produced,
link |
depending on how matter bounces off these bubbles
link |
in the early universe.
link |
So that's one idea.
link |
There's other ideas to do with neutrinos,
link |
that there are exotic types of neutrinos
link |
that can decay in a biased way to just matter
link |
and not to antimatter.
link |
So, and people are trying to test these ideas.
link |
That's what we're trying to do at LHCb.
link |
There's neutrino experiments planned
link |
that are trying to do these sorts of things as well.
link |
So yeah, there are ideas, but at the moment,
link |
no clear evidence for which of these ideas might be right.
link |
So we're talking about some incredible ideas.
link |
By the way, never heard anyone be so eloquent
link |
about describing even just the standard model.
link |
So I'm in awe just listening.
link |
Yeah, just having fun enjoying it.
link |
So the, yes, the theoretical,
link |
the particle physics is fascinating here.
link |
To me, one of the most fascinating things
link |
about the Large Hadron Collider is the human side of it.
link |
That a bunch of sort of brilliant people
link |
that probably have egos got together
link |
and were collaborate together and countries,
link |
I guess, collaborate together for the funds
link |
and everything's just collaboration everywhere.
link |
Cause you may be, I don't know what the right question here
link |
to ask, but almost what's your intuition
link |
about how it was possible to make this happen
link |
and what are the lessons we should learn
link |
for the future of human civilization
link |
in terms of our scientific progress?
link |
Cause it seems like this is a great, great illustration
link |
of us working together to do something big.
link |
Yeah, I think it's possibly the best example.
link |
Maybe I can think of international collaboration
link |
that isn't for some unpleasant purpose, basically.
link |
You know, I mean, so when I started out in the field
link |
in 2008 as a new PhD student,
link |
the LHC was basically finished.
link |
So I didn't have to go around asking for money for it
link |
or trying to make the case.
link |
So I have huge admiration for the people who managed that.
link |
Cause this was a project that was first imagined
link |
in the 1970s, in the late 70s
link |
was when the first conversations about the LHC were mooted
link |
and it took two and a half decades of campaigning
link |
and fundraising and persuasion
link |
until they started breaking ground
link |
and building the thing in the early noughties in 2000.
link |
So, I mean, I think the reason just from a sort of,
link |
from the point of view of the sort of science,
link |
the scientists there,
link |
I think the reason it works ultimately
link |
is that everywhere, everyone there is there
link |
for the same reason, which is, well, in principle, at least
link |
they're there because they're interested in the world.
link |
They want to find out, you know,
link |
what are the basic ingredients of our universe?
link |
What are the laws of nature?
link |
And so everyone is pulling in the same direction.
link |
Now, of course, everyone has their own
link |
things they're interested in.
link |
Everyone has their own careers to consider.
link |
And, you know, I wouldn't pretend that
link |
there isn't also a lot of competition.
link |
So there's this funny thing in these experiments
link |
where your collaborators,
link |
your 800 collaborators in LHCb,
link |
but you're also competitors
link |
because your academics in your various universities
link |
and you want to be the one that gets the paper out
link |
on the most exciting, you know, new measurements.
link |
So there's this funny thing where you're kind of trying
link |
to stake out your territory while also collaborating
link |
and having to work together to make the experiments work.
link |
And it does work amazingly well,
link |
actually considering all of that.
link |
And I think there was actually,
link |
I think McKinsey or one of these big management
link |
consultancy firms went into CERN maybe a decade or so ago
link |
to try to understand how these organizations function.
link |
Did they figure it out?
link |
I don't think they could.
link |
I mean, I think one of the things that's interesting,
link |
one of the other interesting things
link |
about these experiments is, you know,
link |
they're big operations like say Atlas has 3000 people.
link |
Now there was a person nominally
link |
who was the head of Atlas, they're called the spokesperson.
link |
And the spokesperson is elected by,
link |
usually by the collaboration,
link |
but they have no actual power really.
link |
I mean, they can't fire anyone.
link |
They're not anyone's boss.
link |
So, you know, my boss is a professor at Cambridge,
link |
not the head of my experiments.
link |
The head of my experiment can't tell me what to do really.
link |
And there's all these independent academics
link |
who are their own bosses who, you know,
link |
so that somehow it, nonetheless,
link |
by kind of consensus and discussion and lots of meetings,
link |
these things do happen and it does get done, but.
link |
It's like the queen here in the UK is the spokesperson.
link |
No actual power. Except we don't elect her, no.
link |
No, we don't elect her.
link |
But everybody seems to love her.
link |
I don't know, from my outside perspective.
link |
But yeah, giant egos, brilliant people.
link |
And moving forward, do you think there's.
link |
Actually, I would pick up one thing you said just there,
link |
just the brilliant people thing.
link |
Cause I'm not saying that people aren't great.
link |
But I think there is this sort of impression
link |
that physicists all have to be brilliant or geniuses,
link |
which is not true actually.
link |
And you know, you have to be relatively bright for sure.
link |
But you know, a lot of people,
link |
a lot of the most successful experimental physicists
link |
are not necessarily the people with the biggest brains.
link |
They're the people who, you know,
link |
particularly one of the skills that's most important
link |
in particle physics is the ability to work
link |
with others and to collaborate and exchange ideas
link |
and also to work hard.
link |
And it's a sort of, often it's more a determination
link |
or a sort of other set of skills.
link |
It's not just being, you know, kind of some great brain.
link |
So, I mean, there's parallels to that
link |
in the machine learning world.
link |
If you wanna solve any real world problems,
link |
which I see as the particle accelerators,
link |
essentially a real world instantiation
link |
of theoretical physics.
link |
And for that, you have to not necessarily be brilliant,
link |
but be sort of obsessed, systematic, rigorous,
link |
sort of unborable, stubborn, all those kind of qualities
link |
that make for a great engineer.
link |
So, scientists purely speaking,
link |
that practitioner of the scientific method.
link |
But nevertheless, to me that's brilliant.
link |
My dad's a physicist.
link |
I argue with him all the time.
link |
To me, engineering is the highest form of science.
link |
And he thinks that's all nonsense,
link |
that the real work is done by the theoretician.
link |
So, in fact, we have arguments about like people
link |
like Elon Musk, for example,
link |
because I think his work is quite brilliant,
link |
but he's fundamentally not coming up
link |
with any serious breakthroughs.
link |
He's just creating in this world, implementing,
link |
like making ideas happen that have a huge impact.
link |
To me, that's the Edison.
link |
That to me is a brilliant work,
link |
but to him, it's messy details
link |
that somebody will figure out anyway.
link |
I mean, I don't know whether you think
link |
there is a actual difference in temperament
link |
between say a physicist and an engineer,
link |
whether it's just what you got interested in.
link |
I mean, a lot of what experimental physicists do
link |
is to some extent engineering.
link |
I mean, it's not what I do.
link |
I mostly do data stuff,
link |
but a lot of people would be called electrical engineers,
link |
but they trained as physicists,
link |
but they learned electrical engineering, for example,
link |
because they were building detectors.
link |
So, there's not such a clear divide, I think.
link |
Yeah, it's interesting.
link |
I mean, but there does seem to be,
link |
like you work with data.
link |
There does seem to be a certain,
link |
like I love data collection.
link |
There might be an OCD element or something
link |
that you're more naturally predisposed to
link |
as opposed to theory.
link |
Like I'm not afraid of data.
link |
And there's a lot of people in machine learning
link |
who are more like,
link |
they're basically afraid of data collection,
link |
afraid of data sets, afraid of all of that.
link |
They just want to stay in more than theoretical
link |
and they're really good at it, space.
link |
So, I don't know if that's the genetic,
link |
that's your upbringing, the way you go to school,
link |
but looking into the future of LHC and other colliders.
link |
So, there's in America,
link |
there's whatever it was called, the super,
link |
there's a lot of super.
link |
Superconducting super colliders.
link |
Yeah, superconducting.
link |
The desertron, yeah.
link |
So, that was canceled, the construction of that.
link |
Which is a sad thing,
link |
but what do you think is the future of these efforts?
link |
Will a bigger collider be built?
link |
Will LHC be expanded?
link |
What do you think?
link |
Well, in the near future, the LHC is gonna get an upgrade.
link |
So, that's pretty much confirmed.
link |
I think it is confirmed, which is,
link |
it's not an energy upgrade.
link |
It's what we call a luminosity upgrade.
link |
So, it basically means increasing
link |
the data collection rates.
link |
So, more collisions per second, basically,
link |
because after a few years of data taking,
link |
you get this law of diminishing returns
link |
where each year's worth of data
link |
is a smaller and smaller fraction
link |
of the lot you've already got.
link |
So, to get a real improvement in sensitivity,
link |
you need to increase the data rate
link |
by an order of magnitude.
link |
So, that's what this upgrade is gonna do.
link |
LHCb, at the moment, the whole detector
link |
is basically being rebuilt to allow it to record data
link |
at a much larger rate than we could before.
link |
So, that will make us sensitive
link |
to whole loads of new processes
link |
that we weren't able to study before.
link |
And I mentioned briefly these anomalies that we've seen.
link |
So, we've seen a bunch of very intriguing anomalies
link |
in these b quark decays,
link |
which may be hinting at the first signs
link |
of this kind of the elephant,
link |
the signs of some new quantum field
link |
or fields maybe beyond the standard model.
link |
It's not yet at the statistical threshold
link |
where you can say that you've observed something,
link |
but there's lots of anomalies in many measurements
link |
that all seem to be consistent with each other.
link |
So, it's quite interesting.
link |
So, the upgrade will allow us
link |
to really home in on these things
link |
and see whether these anomalies are real,
link |
because if they are real,
link |
and this kind of connects to your point
link |
about the next generation of machines,
link |
what we would have seen then is,
link |
we would have seen the tail end of some quantum field
link |
in influencing these b quarks.
link |
What we then need to do is to build a bigger collider
link |
to actually make the particle of that field.
link |
So, if these things really do exist.
link |
So, that would be one argument.
link |
I mean, so at the moment,
link |
Europe is going through this process
link |
of thinking about the strategy for the future.
link |
So, there are a number of different proposals on the table.
link |
One is for a sort of higher energy upgrade of the LHC,
link |
where you just build more powerful magnets
link |
and put them in the same tunnel.
link |
That's a sort of cheaper, less ambitious possibility.
link |
Most people don't really like it
link |
because it's sort of a bit of a dead end,
link |
because once you've done that, there's nowhere to go.
link |
There's a machine called Click,
link |
which is a compact linear collider,
link |
which is a electron positron collider
link |
that uses a novel type of acceleration technology
link |
to accelerate at shorter distances.
link |
We're still talking kilometers long,
link |
but not like 100 kilometers long.
link |
And then probably the project that is,
link |
I think getting the most support,
link |
it'd be interesting to see what happens,
link |
something called the Future Circular Collider,
link |
which is a really ambitious longterm multi decade project
link |
to build a 100 kilometer circumference tunnel
link |
under the Geneva region.
link |
The LHC would become a kind of feeding machine.
link |
It would just feed.
link |
So the same area, so it would be a feeder for the.
link |
So it would kind of, the edge of this machine
link |
would be where the LHC is,
link |
but it would sort of go under Lake Geneva
link |
and round to the Alps, basically,
link |
up to the edge of the Geneva basin.
link |
So it's basically the biggest tunnel you can fit
link |
in the region based on the geology.
link |
Yeah, so it's big.
link |
It'd be a long drive if your experiment's on one side.
link |
You've got to go back to CERN for lunch,
link |
so that would be a pain.
link |
But you know, so this project is,
link |
in principle, it's actually two accelerators.
link |
The first thing you would do
link |
is put an electron positron machine
link |
in the 100 kilometer tunnel to study the Higgs.
link |
So you'd make lots of Higgs bows
link |
and study it really precisely
link |
in the hope that you see it misbehaving
link |
and doing something it's not supposed to.
link |
And then in the much longer term,
link |
100, that machine gets taken out,
link |
you put in a proton proton machine.
link |
So it's like the LHC, but much bigger.
link |
And that's the way you start going
link |
and looking for dark matter,
link |
or you're trying to recreate this phase transition
link |
that I talked about in the early universe,
link |
where you can see matter anti matter being made,
link |
There's lots of things you can do with these machines.
link |
The problem is that they will take,
link |
you know, the most optimistic,
link |
you're not gonna have any data
link |
from any of these machines until 2040,
link |
or, you know, because they take such a long time to build
link |
and they're so expensive.
link |
So you have, there'll be a process of R&D design,
link |
but also the political case being made.
link |
So LHC, what costs a few billion?
link |
Depends how you count it.
link |
I think most of the sort of more reasonable estimates
link |
that take everything into account properly,
link |
it's around the sort of 10, 11, 12 billion euro mark.
link |
What would be the future, sorry,
link |
I forgot the name already.
link |
Future Circular Collider.
link |
Future Circular Collider.
link |
Presumably they won't call it that when it's built,
link |
cause it won't be the future anymore.
link |
But I don't know, I don't know what they'll call it then.
link |
The very big Hadron Collider, I don't know.
link |
But that will, now I should know the numbers,
link |
but I think the whole project is estimated
link |
at about 30 billion euros,
link |
but that's money spent over between now and 2070 probably,
link |
which is when the last bit of it
link |
would be sort of finishing up, I guess.
link |
So you're talking a half a century of science
link |
coming out of this thing, shared by many countries.
link |
So the actual cost, the arguments that are made
link |
is that you could make this project fit
link |
within the existing budget of CERN,
link |
if you didn't do anything else.
link |
And CERN, by the way, we didn't mention, what is CERN?
link |
CERN is the European Organization for Nuclear Research.
link |
It's an international organization
link |
that was established in the 1950s
link |
in the wake of the second world war as a kind of,
link |
it was sort of like a scientific Marshall plan for Europe.
link |
The idea was that you bring European science back together
link |
for peaceful purposes,
link |
because what happened in the forties was,
link |
a lot of particular Jewish scientists,
link |
but a lot of scientists from central Europe
link |
had fled to the United States
link |
and Europe had sort of seen this brain drain.
link |
So there was a desire to bring the community back together
link |
for a project that wasn't building nasty bombs,
link |
but was doing something that was curiosity driven.
link |
So, and that has continued since then.
link |
So it's kind of a unique organization.
link |
It's you, to be a member as a country,
link |
you sort of sign up as a member
link |
and then you have to pay a fraction of your GDP
link |
each year as a subscription.
link |
I mean, it's a very small fraction, relatively speaking.
link |
I think it's like, I think the UK's contribution
link |
is a hundred or 200 million quid or something like that.
link |
Yeah, which is quite a lot, but not so.
link |
That's fascinating.
link |
I mean, just the whole thing that is possible,
link |
It's a beautiful idea,
link |
especially when there's no wars on the line,
link |
it's not like we're freaking out,
link |
as we're actually legitimately collaborating
link |
to do good science.
link |
One of the things I don't think we really mentioned
link |
is on the final side, that sort of the data analysis side,
link |
is there breakthroughs possible there
link |
and the machine learning side,
link |
like is there a lot more signal to be mined
link |
in more effective ways from the actual raw data?
link |
Yeah, a lot of people are looking into that.
link |
I mean, so I use machine learning in my data analysis,
link |
but pretty naughty, basic stuff,
link |
cause I'm not a machine learning expert.
link |
I'm just a physicist who had to learn to do this stuff
link |
So what a lot of people do is they use
link |
kind of off the shelf packages
link |
that you can train to do signal noise.
link |
Just clean up all the data.
link |
But one of the big challenges,
link |
the big challenge of the data is A, it's volume,
link |
there's huge amounts of data.
link |
So the LHC generates, now, okay,
link |
I try to remember what the actual numbers are,
link |
but if you, we don't record all our data,
link |
we record a tiny fraction of the data.
link |
It's like of order one 10,000th or something, I think.
link |
So most of it gets thrown away.
link |
You couldn't record all the LHC data
link |
cause it would fill up every computer in the world
link |
in a matter of days, basically.
link |
So there's this process that happens on live,
link |
on the detector, something called a trigger,
link |
which in real time, 40 million times every second
link |
has to make a decision about whether this collision
link |
is likely to contain an interesting object,
link |
like a Higgs boson or a dark matter particle.
link |
And it has to do that very fast.
link |
And the software algorithms in the past
link |
were quite relatively basic.
link |
They did things like measure mementos
link |
and energies of particles and put some requirements.
link |
So you would say, if there's a particle
link |
with an energy above some threshold,
link |
then record this collision.
link |
But if there isn't, don't.
link |
Whereas now the attempt is get more and more
link |
machine learning in at the earliest possible stage.
link |
That's cool, at the stage of deciding
link |
whether we want to keep this data or not.
link |
But also maybe even lower down than that,
link |
which is the point where there's this,
link |
so generally how the data is reconstructed
link |
is you start off with a set of digital hits
link |
So channels saying, did you see something?
link |
Did you not see something?
link |
That has to be then turned into tracks,
link |
particles going in different directions.
link |
And that's done by using fits
link |
that fit through the data points.
link |
And then that's passed to the algorithms
link |
that then go, is this interesting or not?
link |
What'd be better is you could train machine learning
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to just look at the raw hits,
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the basic real base level information,
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not have any of the reconstruction done.
link |
And it just goes, and it can learn to do pattern recognition
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on this strange three dimensional image that you get.
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And potentially that's where you could get really big gains
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because our triggers tend to be quite inefficient
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because they don't have time to do
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the full whiz bang processing
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to get all the information out that we would like,
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because you have to do the decision very quickly.
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So if you can come up with some clever
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machine learning technique,
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then potentially you can massively increase
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the amount of useful data you record
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and get rid of more of the background
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earlier in the process.
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Yeah, to me, that's an exciting possibility
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because then you don't have to build a sort of,
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you can get a gain without having to.
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Without having to build any hardware, I suppose.
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Although you need lots of new GPU farms, I guess.
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So hardware still helps.
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But I got to talk to you,
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sort of I'm not sure how to ask,
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but you're clearly an incredible science communicator.
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I don't know if that's the right term,
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but you're basically a younger Neil deGrasse Tyson
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with a British accent.
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So, and you've, I mean,
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can you say where we are today, actually?
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Yeah, so today we're in the Royal Institution in London,
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which is a very old organization.
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It's been around for about 200 years now, I think.
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Maybe even I should know when it was founded.
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Sort of early 19th century,
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it was set up to basically communicate science to the public.
link |
So it was one of the first places in the world
link |
where famous scientists would come and give talks.
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So very famously Humphrey Davy, who you may know of,
link |
who was the person who discovered nitrous oxide.
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He was a very famous chemist and scientist.
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Also discovered electrolysis.
link |
So he used to do these fantastic,
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he was a very charismatic speaker.
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So he used to appear here.
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There's a big desk that they usually have in the theater
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and he would do demonstrations to the sort of the,
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the folk of London back in the early 19th century.
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And Michael Faraday, who I talked about,
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who is the person who did so much work on electromagnetism,
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he used, he lectured here.
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He also did experiments in the basement.
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So this place has got a long history
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of both scientific research,
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but also communication of scientific research.
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So you gave a few lectures here.
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I've given, yeah, I've given a couple of lectures
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in this theater before, so.
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I mean, that's, so people should definitely go watch online.
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It's just the explanation of particle physics.
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So all the, I mean, it's incredible.
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Like your lectures are just incredible.
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I can't sing it enough praise.
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So it was awesome.
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But maybe can you say, what did that feel like?
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What does it feel like to lecture here, to talk about that?
link |
And maybe from a different perspective,
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more kind of like how the sausage is made is,
link |
how do you prepare for that kind of thing?
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How do you think about communication,
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the process of communicating these ideas
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in a way that's inspiring to,
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what I would say your talks are inspiring
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to like the general audience.
link |
You don't actually have to be a scientist.
link |
You can still be inspired without really knowing much of the,
link |
you start from the very basics.
link |
So what's the preparation process?
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And then the romantic question is,
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what did that feel like to perform here?
link |
I mean, profession, yeah.
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I mean, the process, I mean, the talk,
link |
my favorite talk that I gave here
link |
was one called Beyond the Higgs,
link |
which you can find on the Royal Institute's YouTube channel,
link |
which you should go and check out.
link |
I mean, and their channel's got loads of great talks
link |
with loads of great people as well.
link |
I mean, that one, I'd sort of given a version of it
link |
many times, so part of it is just practice, right?
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And actually, I don't have some great theory
link |
of how to communicate with people.
link |
It's more just that I'm really interested
link |
and excited by those ideas and I like talking about them.
link |
And through the process of doing that,
link |
I guess I figured out stories that work
link |
and explanations that work.
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When you say practice, you mean legitimately
link |
just giving talks? Just giving talks, yeah.
link |
I started off when I was a PhD student
link |
doing talks in schools and I still do that as well
link |
some of the time and doing things,
link |
I've even done a bit of standup comedy,
link |
which sort of went reasonably well,
link |
even if it was terrifying.
link |
And that's on YouTube as well.
link |
That's also on, I wouldn't necessarily recommend
link |
you check that out.
link |
I'm gonna post the links several places
link |
to make sure people click on it.
link |
But it's basically, I kind of have a story in my head
link |
and I kind of, I have to think about what I wanna say.
link |
I usually have some images to support what I'm saying
link |
and I get up and do it.
link |
And it's not really, I wish there was some kind of,
link |
I probably should have some proper process.
link |
This is very sounds like I'm just making up as I go along
link |
Well, I think the fundamental thing that you said,
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I think it's like, I don't know if you know
link |
who a guy named Joe Rogan is.
link |
So he's also kind of sounds like you in a sense
link |
that he's not very introspective about his process,
link |
but he's an incredibly engaging conversationalist.
link |
And I think one of the things that you and him share
link |
that I could see is like a genuine curiosity
link |
and passion for the topic.
link |
I think that could be systematically cultivated.
link |
I'm sure there's a process to it,
link |
but you come to it naturally somehow.
link |
I think maybe there's something else as well,
link |
which is to understand something.
link |
There's this quote by Feynman, which I really like,
link |
which is what I cannot create, I do not understand.
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So I'm not particularly super bright.
link |
So for me to understand something,
link |
I have to break it down into its simplest elements.
link |
And if I can then tell people about that,
link |
that helps me understand it as well.
link |
So I've learned to understand physics a lot more
link |
from the process of communicating,
link |
because it forces you to really scrutinize the ideas
link |
that you're communicating and it often makes you realize
link |
you don't really understand the ideas you're talking about.
link |
And I'm writing a book at the moment,
link |
and I had this experience yesterday where I realized
link |
I didn't really understand a pretty fundamental
link |
theoretical aspect of my own subject.
link |
And I had to go and I had to sort of spend
link |
a couple of days reading textbooks and thinking about it
link |
in order to make sure that the explanation I gave
link |
captured the, got as close to what is actually happening
link |
And to do that, you have to really understand it properly.
link |
Yeah, and there's layers to understanding.
link |
It seems like the more,
link |
there must be some kind of Feynman law.
link |
I mean, the more you understand sort of the simpler
link |
you're able to really convey the essence of the idea, right?
link |
So it's like this reverse effect that it's like
link |
the more you understand, the simpler the final thing
link |
that you actually convey.
link |
And so the more accessible somehow it becomes.
link |
That's why Feynman's lectures are really accessible.
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It was just counterintuitive.
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Yeah, although there are some ideas
link |
that are very difficult to explain
link |
no matter how well or badly you understand them.
link |
Like I still can't really properly explain
link |
the Higgs mechanism.
link |
Because some of these ideas only exist
link |
in mathematics really.
link |
And the only way to really develop an understanding
link |
is to go unfortunately to a graduate degree in physics.
link |
But you can get kind of a flavor of what's happening,
link |
I think, and it's trying to do that in a way
link |
that isn't misleading, but always also intelligible.
link |
So let me ask them the romantic question of
link |
what to you is the most, perhaps an unfair question,
link |
what is the most beautiful idea in physics?
link |
One that fills you with awe is the most surprising,
link |
the strangest, the weirdest.
link |
There's a lot of different definitions of beauty.
link |
And I'm sure there's several for you,
link |
but is there something that just jumps to mind
link |
that you think is just especially beautiful?
link |
There's a specific thing and a more general thing.
link |
So maybe the specific thing first,
link |
which I can now first came across as an undergraduate.
link |
I found this amazing.
link |
So this idea that the forces of nature,
link |
electromagnetism, strong force, the weak force,
link |
they arise in our theories as a consequence of symmetries.
link |
So symmetries in the laws of nature,
link |
in the equations essentially
link |
that used to describe these ideas,
link |
the process whereby theories come up
link |
with these sorts of models is they say,
link |
imagine the universe obeys this particular type of symmetry.
link |
It's a symmetry that isn't so far removed
link |
from a geometrical symmetry, like the rotations of a cube.
link |
It's not, you can't think of it quite that way,
link |
but it's sort of a similar sort of idea.
link |
And you say, okay, if the universe respects the symmetry,
link |
you find that you have to introduce a force
link |
which has the properties of electromagnetism
link |
or a different symmetry, you get the strong force
link |
or a different symmetry, you get the weak force.
link |
So these interactions seem to come from some deeper,
link |
it suggests that they come
link |
from some deeper symmetry principle.
link |
I mean, it depends a bit how you look at it
link |
because it could be that we're actually
link |
just recognizing symmetries in the things that we see,
link |
but there's something rather lovely about that.
link |
But I mean, I suppose a bigger thing that makes me wonder
link |
is actually, if you look at the laws of nature,
link |
how particles interact when you get really close down,
link |
they're basically pretty simple things.
link |
They bounce off each other by exchanging
link |
through force fields and they move around
link |
in very simple ways.
link |
And somehow these basic ingredients,
link |
these few particles that we know about in the forces
link |
creates this universe, which is unbelievably complicated
link |
and has things like you and me in it,
link |
and the earth and stars that make matter in their cores
link |
from the gravitational energy of their own bulk
link |
that then gets sprayed into the universe
link |
that forms other things.
link |
I mean, the fact that there's this incredibly long story
link |
that goes right back to the beginning,
link |
and we can take this story right back to a trillionth
link |
of a second after the Big Bang,
link |
and we can trace the origins of the stuff
link |
that we're made from.
link |
And it all ultimately comes from these simple ingredients
link |
with these simple rules.
link |
And the fact you can generate such complexity from that
link |
is really mysterious, I think, and strange.
link |
And it's not even a question that physicists
link |
can really tackle because we are sort of trying
link |
to find these really elementary laws.
link |
But it turns out that going from elementary laws
link |
and a few particles to something even as complicated
link |
as a molecule becomes very difficult.
link |
So going from a molecule to a human being
link |
is a problem that just can't be tackled,
link |
at least not at the moment, so.
link |
Yeah, the emergence of complexity from simple rules
link |
is so beautiful and so mysterious.
link |
And we don't have good mathematics
link |
to even try to approach that emergent phenomena.
link |
That's why we have chemistry and biology
link |
and all the other subjects, yeah, okay.
link |
I don't think there's a better way to end it, Harry.
link |
I can't, I mean, I think I speak for a lot of people
link |
that can't wait to see what happens
link |
in the next five, 10, 20 years with you.
link |
I think you're one of the great communicators of our time.
link |
So I hope you continue that and I hope that grows.
link |
And I'm definitely a huge fan.
link |
So it was an honor to talk to you today.
link |
Thanks so much, man.
link |
It was really fun, thanks very much.
link |
Thanks for listening to this conversation with Harry Kliff.
link |
And thank you to our sponsors, ExpressVPN
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Please consider supporting the podcast
link |
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If you enjoy this podcast, subscribe on YouTube,
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link |
on Twitter at lexfreedman.
link |
And now let me leave you with some words from Harry Kliff.
link |
You and I are leftovers.
link |
Every particle in our bodies is a survivor
link |
from an almighty shootout between matter and antimatter
link |
that happened a little after the Big Bang.
link |
In fact, only one in a billion particles created
link |
at the beginning of time have survived to the present day.
link |
Thank you for listening and hope to see you next time.