0:00:02 > 0:00:03Where's the reception? Oh, OK...
0:00:03 > 0:00:06So nobody knows what this lecture is going to be about...
0:00:06 > 0:00:11I know what it's about. It'll be about science, and he'll be promoting that heresy of his.
0:00:11 > 0:00:14I hope he's going to unveil a death ray. I don't know.
0:00:16 > 0:00:20I'm going to make one, at least one unsuspecting celebrity, do sums.
0:00:20 > 0:00:23- I really am so out of my depth... - LAUGHTER
0:00:23 > 0:00:26This is the worst thing that's happened to me as an adult.
0:00:26 > 0:00:29The only thing I do know is that I've been roped in to go up
0:00:29 > 0:00:34on stage - with Simon Pegg, no less - waving a rope about.
0:00:34 > 0:00:36I can see why you've got no hair.
0:00:36 > 0:00:37LAUGHTER
0:00:39 > 0:00:42I'm so thrilled to have been asked, to be honest.
0:00:42 > 0:00:44I never do clever things.
0:00:44 > 0:00:50There's a real buzz in this room, and it just makes me feel proud to be a scientist in this day and age.
0:00:50 > 0:00:53Perhaps tonight is my chance
0:00:53 > 0:00:57to realise what it's all about, and have a big sort of Damascene moment.
0:00:57 > 0:01:02I'd like to ask Professor Brian Cox about his hair - it's a shared interest.
0:01:02 > 0:01:06- I hope he blows some stuff up. - Whoa... Ow!
0:01:06 > 0:01:09I'm hoping it's going to start simple, for people like me,
0:01:09 > 0:01:13and then get slowly more complicated.
0:01:13 > 0:01:17Because otherwise, if my brain starts swelling inside my skull
0:01:17 > 0:01:19it's just going to pop and I'll distract people.
0:01:44 > 0:01:45Thank you.
0:01:46 > 0:01:50Welcome to the Royal Institution of Great Britain, established
0:01:50 > 0:01:54in 1799 as "an institution for diffusing knowledge",
0:01:54 > 0:01:59and perhaps the most iconic lecture theatre in science.
0:01:59 > 0:02:04Thomas Huxley championed Charles Darwin's theory of evolution here,
0:02:04 > 0:02:08Michael Faraday pioneered our understanding of electricity and magnetism here,
0:02:08 > 0:02:13and on this stage he demonstrated the first electric motor.
0:02:13 > 0:02:16And the great scientist and lecturer Sir Humphry Davy,
0:02:16 > 0:02:19who was also the first director of the Royal Institution
0:02:19 > 0:02:22and one of my heroes, spoke here many times.
0:02:22 > 0:02:28And he gave the best explanation of the absolute need to do science that I know of -
0:02:28 > 0:02:31"Nothing is so fatal to the progress of the human mind
0:02:31 > 0:02:34"as to suppose that our views of science are ultimate;
0:02:34 > 0:02:36"that there are no mysteries in nature;
0:02:36 > 0:02:38"that our triumphs are complete,
0:02:38 > 0:02:41"and that there are no new worlds to conquer."
0:02:41 > 0:02:45Well, tonight I want to talk about one of the great mysteries,
0:02:45 > 0:02:47pillars of our understanding of nature -
0:02:47 > 0:02:51the scientific theory that underpins much of the technology
0:02:51 > 0:02:53we take for granted in the 21st century,
0:02:53 > 0:02:59yet retains its reputation for obscure difficulty and bizarre predictions.
0:02:59 > 0:03:01Now, by the time I've finished, I hope that
0:03:01 > 0:03:05while your view of reality might have shifted a little,
0:03:05 > 0:03:08you'll understand a bit more about how the universe works.
0:03:08 > 0:03:13Now, let's start with the contents of this box.
0:03:15 > 0:03:22This is a rough diamond. It's worth well over £1 million.
0:03:22 > 0:03:27It costs so much because it's rare, and because it's beautiful.
0:03:27 > 0:03:30But there's a different kind of beauty here, a more profound
0:03:30 > 0:03:36kind of beauty - less superficial, but perhaps far more instructive.
0:03:36 > 0:03:39A diamond is one of the hardest known substances -
0:03:39 > 0:03:41which is why diamonds are widely used industrially -
0:03:41 > 0:03:46but light can stream through it relatively unimpeded.
0:03:46 > 0:03:49So there's beauty in a question, which is,
0:03:49 > 0:03:52how can something be so ethereal, and yet be
0:03:52 > 0:03:55so hard that it can drill through solid rock?
0:03:55 > 0:03:58Well, to answer that we need to know about the
0:03:58 > 0:04:02structure of the diamond - indeed the structure of all matter itself.
0:04:02 > 0:04:08And the best theory we have to describe matter, is quantum theory.
0:04:08 > 0:04:12Now, I understand why quantum theory can seem a bit odd.
0:04:12 > 0:04:13It makes odd statements.
0:04:13 > 0:04:17It says, for example, that things can be many places at once -
0:04:17 > 0:04:22in fact, technically it says things can be in an infinite number of places at once.
0:04:22 > 0:04:25It says that subatomic building blocks of our bodies
0:04:25 > 0:04:30are constantly shifting in response to events that happened at the edge
0:04:30 > 0:04:34of the known universe - a billion light years somewhere over there.
0:04:34 > 0:04:40Now, this is all true, but that isn't a licence to talk utter drivel.
0:04:40 > 0:04:42LAUGHTER
0:04:42 > 0:04:46See, quantum theory might SEEM weird and mysterious, but it describes the
0:04:46 > 0:04:50world with higher precision than the laws of physics laid down by Newton,
0:04:50 > 0:04:54and it's one of the foundations of our modern understanding of nature.
0:04:54 > 0:04:57It doesn't, therefore, allow mystical healing,
0:04:57 > 0:05:01or ESP or any other manifestation of New Age woo-woo
0:05:01 > 0:05:03into the pantheon of the possible.
0:05:03 > 0:05:07Always remember, quantum theory is physics, and physics is
0:05:07 > 0:05:11usually done by people without star signs tattooed on their bottom.
0:05:11 > 0:05:15What makes quantum theory a good scientific theory?
0:05:15 > 0:05:19Well, it makes predictions that can be tested against experiment,
0:05:19 > 0:05:24and when we test those predictions we find that they agree with observation.
0:05:24 > 0:05:29This means quantum theory is not wrong - it's a survivor,
0:05:29 > 0:05:32if you like, because it's been put to the test over and over again,
0:05:32 > 0:05:35and consistently been found to make correct predictions.
0:05:35 > 0:05:38If this changes, then we'll search for a new theory -
0:05:38 > 0:05:40there are NO absolute truths in science.
0:05:40 > 0:05:43This is how we make scientific progress, and this is how
0:05:43 > 0:05:47everything in the world that you take for granted was delivered.
0:05:47 > 0:05:52So, remember that however odd it might seem, tonight
0:05:52 > 0:05:56I'm going to show you, hopefully, that quantum theory works.
0:05:56 > 0:06:01So, I want to explain quantum theory to you in the simplest way that I can.
0:06:01 > 0:06:03Ultimately, I'll show you how it gives us insight into the
0:06:03 > 0:06:07fundamental building blocks of the universe, and explains the existence
0:06:07 > 0:06:12of some of the most spectacular phenomena out there in deep space.
0:06:12 > 0:06:16And I'm going to do this now because if I don't point wistfully at the sky at least once,
0:06:16 > 0:06:19some of my viewers will get annoyed, so there you go.
0:06:19 > 0:06:23That's the only mountain-top pose I'm going to pull...
0:06:23 > 0:06:25- LAUGHTER - ..so, to begin...
0:06:29 > 0:06:31No helicopters tonight.
0:06:31 > 0:06:36To begin, let's zoom into the heart of this diamond.
0:06:36 > 0:06:39What I've got here is a sequence of actual photographs of, well,
0:06:39 > 0:06:42initially the surface of a diamond, but these photographs
0:06:42 > 0:06:47have been taken by a series of increasingly powerful microscopes.
0:06:47 > 0:06:49So as we zoom in you see that at first you're seeing a more
0:06:49 > 0:06:53detailed picture of the structure of the surface of the diamond.
0:06:53 > 0:06:55But as we go right in, you see that a regular pattern,
0:06:55 > 0:06:58a regular structure emerges,
0:06:58 > 0:07:02so this is an electron microscope photograph of diamond.
0:07:02 > 0:07:05And what you're looking at here actually are carbon atoms,
0:07:05 > 0:07:07individual atoms.
0:07:07 > 0:07:11You see that they appear to be in a kind of a dumbbell shape, and there's a space
0:07:11 > 0:07:15and another pair, because you're looking at a two-dimensional image.
0:07:15 > 0:07:17But if you take that to three dimensions
0:07:17 > 0:07:21and look at this - this is the structure of diamond,
0:07:21 > 0:07:26and what you can see is carbon atoms surrounded by four other
0:07:26 > 0:07:30carbon atoms, in a regular, beautiful crystalline structure.
0:07:30 > 0:07:35Now, in this diamond, this over- a-million-pound piece of diamond,
0:07:35 > 0:07:39there are something like 3 million billion billion atoms,
0:07:39 > 0:07:45and they are laid out in precisely this beautifully simple way.
0:07:45 > 0:07:48I should say, actually, this diamond is as it was when it was found,
0:07:48 > 0:07:52so this hasn't been cut. It was found in South Africa well over 100 years ago,
0:07:52 > 0:07:55and it's 3 billion years old.
0:07:55 > 0:07:57And that structure, its diamond shape -
0:07:57 > 0:08:01that's how it naturally appeared, because its structure
0:08:01 > 0:08:05is like this, it's built out of carbon atoms exactly like that.
0:08:05 > 0:08:09Carbon atoms can't be packed any more tightly together than this.
0:08:09 > 0:08:12That's what makes diamonds so tough, and allows them
0:08:12 > 0:08:15to cut through virtually anything.
0:08:15 > 0:08:17Which makes what I'm about to say quite remarkable.
0:08:17 > 0:08:21See, the atoms that make up this diamond -
0:08:21 > 0:08:24and pretty much everything else for that matter - are virtually empty.
0:08:26 > 0:08:30Now, what do I mean by that? Well, what is an atom?
0:08:30 > 0:08:34Well, about 100 years ago now, in the greatest city
0:08:34 > 0:08:38known to civilization - which is Manchester! -
0:08:38 > 0:08:39APPLAUSE
0:08:41 > 0:08:45..Ernest Rutherford discovered that the atom consists of an atomic nucleus,
0:08:45 > 0:08:49which is made of particles called protons and neutrons tightly packed together,
0:08:49 > 0:08:52and a third kind of particle,
0:08:52 > 0:08:57called electrons, orbit somewhere or exist somewhere around the outside.
0:08:57 > 0:08:59The nucleus protons are positively charged,
0:08:59 > 0:09:02the neutrons are neutral, so it has a positive charge.
0:09:02 > 0:09:06The electrons somewhere out here have a negative charge,
0:09:06 > 0:09:10and as Faraday would have talked about on this very stage
0:09:10 > 0:09:12just under 200 years ago, there is a force that holds
0:09:12 > 0:09:14the electron to the nucleus,
0:09:14 > 0:09:17because they're both electrically charged.
0:09:17 > 0:09:20So that's kind of a sketch, a schematic view of the atom.
0:09:20 > 0:09:24We've known that now for around a hundred years.
0:09:24 > 0:09:25Protons, neutrons and electrons.
0:09:25 > 0:09:29These three particles make up not only the diamond,
0:09:29 > 0:09:33but everything we can touch, every structure we can see.
0:09:33 > 0:09:38Everything is made up of these same three absolutely identical particles.
0:09:38 > 0:09:41So the richness of the natural world, everything on planet Earth,
0:09:41 > 0:09:45everything we can see beyond is described by a simple recipe
0:09:45 > 0:09:49that determines how these simple particles combine together.
0:09:49 > 0:09:54Now, clearly physicists don't call it a recipe, we call that quantum theory.
0:09:54 > 0:09:57Now, one of the first great challenges for quantum theory -
0:09:57 > 0:10:01indeed, one of the reasons it was developed at the turn of the 20th century,
0:10:01 > 0:10:06in Manchester and a few other places - was to understand precisely how these particles
0:10:06 > 0:10:10come together to create this diamond, you, me and everything else.
0:10:10 > 0:10:13And a hundred years after its discovery, it still provides
0:10:13 > 0:10:17our best understanding of the structure of matter.
0:10:17 > 0:10:20And admittedly, yes, it is still a bit strange.
0:10:20 > 0:10:27Now, one of the particularly strange things about it is the behaviour of electrons inside atoms.
0:10:27 > 0:10:29See, these imperceptibly tiny electrons spend
0:10:29 > 0:10:33the overwhelming majority of their time in far distant clouds.
0:10:33 > 0:10:38So between the nucleus and the electron there is a vast emptiness.
0:10:38 > 0:10:42If I were a nucleus, and I perched on the edge of the White Cliffs of Dover,
0:10:42 > 0:10:45then the fuzzy edge of the electron cloud would be
0:10:45 > 0:10:48somewhere in the farms of northern France.
0:10:48 > 0:10:53Looking out towards the electrons I'd see nothing but empty, interatomic space.
0:10:53 > 0:10:56So atoms are vast, and they are empty. Actually about -
0:10:56 > 0:10:58I've got to count this on my fingers -
0:10:58 > 0:11:0499.9999999999999% empty.
0:11:04 > 0:11:09That's 13 nines. So, you buy this diamond,
0:11:09 > 0:11:13and you're buying about a million quid's worth of mainly empty space, and since
0:11:13 > 0:11:19everything is made of atoms, that means you are vast and empty too.
0:11:19 > 0:11:21LAUGHTER
0:11:21 > 0:11:24Especially you... No, I can't say that, can I?
0:11:24 > 0:11:29Never say that to a stand-up comic - what am I doing?
0:11:29 > 0:11:31Anyway, if I squeezed all the space out of all the atoms in all
0:11:31 > 0:11:35the people on the planet, then you'd be able to fit the whole
0:11:35 > 0:11:40of humanity into that diamond, and that's how empty matter is.
0:11:40 > 0:11:44So, understanding why atoms are empty and yet so solid,
0:11:44 > 0:11:48why light can stream through that diamond, and yet
0:11:48 > 0:11:52it sits nicely on the predominantly empty cushion and the predominantly empty floor,
0:11:52 > 0:11:58is therefore a prerequisite to understanding the structure of everything in nature.
0:11:58 > 0:12:00Now, you might have gathered that the world inside an atom
0:12:00 > 0:12:03must be a strange place where things don't behave
0:12:03 > 0:12:07much like they appear to behave here in the macroscopic world.
0:12:07 > 0:12:09Well, there's one historic experiment
0:12:09 > 0:12:12which contains everything you need to know about the bizarre way
0:12:12 > 0:12:17that particles behave, and therefore why atoms are the way that they are.
0:12:17 > 0:12:20I'm going to need a helping hand for this,
0:12:20 > 0:12:25and I know that Sarah Millican has volunteered kindly to help me.
0:12:25 > 0:12:28- Where's Sarah?- I'm here. Hello. - So Sarah - would you mind...?
0:12:38 > 0:12:42Thanks, Sarah. Did you do a science degree, by the way?
0:12:42 > 0:12:45No. I've already been asked that by somebody in the audience -
0:12:45 > 0:12:46"Did you study physics?"
0:12:46 > 0:12:50No, I just sort of gave up after GCSE - is that a problem,
0:12:50 > 0:12:53- should I go back to me seat? - LAUGHTER
0:12:53 > 0:12:56- Any other volunteers(?) No... - Only got a C!
0:12:56 > 0:13:02So you may or may not have heard of the double slit experiment, it's something every physics student...
0:13:02 > 0:13:05- I've heard of it, but it was something different.- Was it(?)
0:13:05 > 0:13:08- Well, we're going to... - LAUGHTER
0:13:08 > 0:13:13Every physicist is taught this the moment they step through the doors of a university.
0:13:13 > 0:13:18It's simple, and it demonstrates the paradoxical world of quantum particles.
0:13:18 > 0:13:22So first of all we're going to do it - we're going to do it twice, or even three times.
0:13:22 > 0:13:27So I'm going to give you this bucket of sand, which is quite heavy actually.
0:13:27 > 0:13:32These are particles of sand, little bits of sand. They're probably your picture,
0:13:32 > 0:13:37I suppose, of what a particle might be, a little piece of matter.
0:13:37 > 0:13:40So what I'm going to ask you to do is just pour the sand
0:13:40 > 0:13:42onto this piece of board, which has got two slits cut in it,
0:13:42 > 0:13:45and I suppose before I do it...
0:13:45 > 0:13:47- Oh, you bugger! - It's a bit heavy!- It is.
0:13:47 > 0:13:50You pour it first, then I'll ask you what you think might happen.
0:13:50 > 0:13:54Yeah, let's chat for a while, while I'm holding the bucket(!)
0:13:54 > 0:13:57It weighs a ton, doesn't it? So just pour it through the slits...
0:13:57 > 0:14:00Now, what do you think is going to happen?
0:14:00 > 0:14:05So we're just pouring particles of sand over the slits.
0:14:05 > 0:14:07Just keep going...
0:14:09 > 0:14:12So there we are. That'll do, I think.
0:14:12 > 0:14:17So if I remove that... what does that remind you of?
0:14:17 > 0:14:19LAUGHTER
0:14:19 > 0:14:22I feel like smacking it - does that help?
0:14:22 > 0:14:27Pour that sand into there. So that's probably pretty much...
0:14:27 > 0:14:30- There you go, you can put it down now.- Thank you!
0:14:30 > 0:14:34That's probably pretty much, I suppose, what you expected would happen.
0:14:34 > 0:14:36The sand has just fallen through the slits,
0:14:36 > 0:14:39and beneath each slit there's a bigger pile of sand.
0:14:39 > 0:14:42Particles fall through slits - pretty obvious.
0:14:42 > 0:14:46But...this is a picture of real data.
0:14:46 > 0:14:48So this is real experimental data,
0:14:48 > 0:14:52of electrons essentially being poured through two slits, so it's electrons
0:14:52 > 0:14:57being fired at two slits, and then there's a screen there, and so what
0:14:57 > 0:15:00you're seeing are just piles of electrons, so the white spots
0:15:00 > 0:15:02really are where electrons hit the screens -
0:15:02 > 0:15:04there's a pile, and then there's nothing,
0:15:04 > 0:15:07and then there's a pile, and then there's nothing...
0:15:07 > 0:15:10Looks nothing like that. But the experiment was the same -
0:15:10 > 0:15:14it really is electrons being poured through two slits
0:15:14 > 0:15:17onto a screen, and you get that strange pattern.
0:15:18 > 0:15:24So, let me show you this, which is a different version of the same experiment.
0:15:24 > 0:15:29Now, this is a tank of water, so there's some water in there,
0:15:29 > 0:15:33and as you can see there's just a bar that's vibrating up and down,
0:15:33 > 0:15:38- and then there's two slits.- Yeah. - So you can see the two slits there.
0:15:38 > 0:15:44And if you come round here... you can see the screen here.
0:15:44 > 0:15:47So there's the two slits, and these are the waves of water.
0:15:47 > 0:15:50So there's a flat wave of water hitting the two slits,
0:15:50 > 0:15:52and then coming through the slits.
0:15:52 > 0:15:54And do you see that there are waves here,
0:15:54 > 0:15:58- but here, there's kind of an area where the water's flat.- Yeah.
0:15:58 > 0:16:00Then here there are waves,
0:16:00 > 0:16:02then here's an area where the water's flat,
0:16:02 > 0:16:05then here are waves, here's an area where the water's flat.
0:16:05 > 0:16:08So if I were to, I could sketch it actually on the blackboard.
0:16:08 > 0:16:10If I draw that...
0:16:14 > 0:16:17We've got those two slits, like that, which you can see there.
0:16:17 > 0:16:20and we've got the water wave coming through
0:16:20 > 0:16:22and you can sort of see that the waves
0:16:22 > 0:16:25when they go through the slits spread out like that.
0:16:25 > 0:16:30And I hope you can see that at the front, you're seeing
0:16:30 > 0:16:33a kind of a place where there's no waves and then some waves
0:16:33 > 0:16:35and then there's a place where there's no waves
0:16:35 > 0:16:38and then there's some waves and a place where there's no waves.
0:16:38 > 0:16:40- You see that pattern on the front.- Yes.
0:16:40 > 0:16:43So if you were to draw kind of a detector along there,
0:16:43 > 0:16:46then you'd see that, right,
0:16:46 > 0:16:50because here you'd see nothing, no waves no electrons.
0:16:50 > 0:16:54Here you'd see the electrons, here no waves, here waves, here no waves.
0:16:54 > 0:16:57So what are we to infer about electrons?
0:17:00 > 0:17:03Have you not done your homework today, is that what it is?
0:17:03 > 0:17:06I mean this is just the experimental data... This was first done,
0:17:06 > 0:17:10by the way, in the 1920s and it was a shock when it was seen,
0:17:10 > 0:17:12but the inference is...?
0:17:15 > 0:17:18That looks like...that.
0:17:18 > 0:17:21- This could be a long game. - It's the same pattern!
0:17:21 > 0:17:23LAUGHTER
0:17:25 > 0:17:27GCSE grade C, remember.
0:17:29 > 0:17:31This pattern here...
0:17:31 > 0:17:34What do you think...?!
0:17:34 > 0:17:36You could just tell us.
0:17:38 > 0:17:43So, the electrons are behaving more like the waves in the tank
0:17:43 > 0:17:47on the water waves and that's a classic pattern you see
0:17:47 > 0:17:50when you get waves passing through slits.
0:17:50 > 0:17:53Rather than this, which I suppose is what you might have expected
0:17:53 > 0:17:57electrons to do, because you might think of electrons as being little grains of sand.
0:17:57 > 0:18:00But actually, they don't behave like little grains of sand.
0:18:00 > 0:18:04That experiment tells us they behave more like waves and water.
0:18:04 > 0:18:05Exactly!
0:18:05 > 0:18:07LAUGHTER AND APPLAUSE
0:18:09 > 0:18:10Thank you.
0:18:17 > 0:18:19Thanks, Sarah!
0:18:19 > 0:18:23Thanks, Sarah. That's... Yeah, physics!
0:18:26 > 0:18:27Well...
0:18:27 > 0:18:31this might all be a bit confusing, as you've just seen,
0:18:31 > 0:18:37but if you remember nothing else, remember this - the double slit experiment reveals something
0:18:37 > 0:18:42fundamental about particles like the electrons inside the diamond.
0:18:42 > 0:18:45Sometimes they behave like particles,
0:18:45 > 0:18:50but sometimes experiment says that they behave like waves.
0:18:50 > 0:18:53Now there's a deep explanation for this
0:18:53 > 0:18:55and I'm going to get to that a little bit later on,
0:18:55 > 0:18:59but for now all we need to remember is that electrons behave like waves,
0:18:59 > 0:19:02and this is the key to understanding the emptiness of atoms.
0:19:04 > 0:19:07Simple? I hope so. So let's clear away the water tank.
0:19:14 > 0:19:18So, we've understood that electrons exhibit wavy behaviour,
0:19:18 > 0:19:22but how does that explain the emptiness of atoms?
0:19:22 > 0:19:25Well, I need some volunteers now and I know that Simon Pegg
0:19:25 > 0:19:29and Jim Al-Khalili have kindly volunteered, so would you both like to come down?
0:19:29 > 0:19:31APPLAUSE
0:19:46 > 0:19:48Have you seen him, there?
0:19:48 > 0:19:49Hello!
0:19:51 > 0:19:55He's got an earpiece in he's watching really carefully.
0:19:55 > 0:20:00So, I've got an experiment for you both to do involving a spring
0:20:00 > 0:20:03and your wrists,
0:20:03 > 0:20:06so...
0:20:06 > 0:20:07What I'd like you to do
0:20:07 > 0:20:13is stretch the string a little bit as far away as you can.
0:20:13 > 0:20:18Now what I want you to do is start gently oscillating the spring. Very gently.
0:20:18 > 0:20:21- Both of us?- Yeah. You'll see what happens.
0:20:21 > 0:20:23Up and down, or longitudinally?
0:20:23 > 0:20:26ALL: Ooh!
0:20:26 > 0:20:28Shall I sit back down?
0:20:29 > 0:20:33Up and down is better. Up and down.
0:20:33 > 0:20:34So just a bit more...
0:20:36 > 0:20:38There you go... And a bit more.
0:20:38 > 0:20:42There you go. So what you're doing is vibrating the spring.
0:20:42 > 0:20:44Are you going to jump in?
0:20:44 > 0:20:47LAUGHTER
0:20:48 > 0:20:50It looks quite painful.
0:20:50 > 0:20:54So what you're doing now, just gently vibrating the string,
0:20:54 > 0:20:57you notice that it's vibrating in a very particular way.
0:20:57 > 0:21:00Cos you're holding it still there and you're holding it still there,
0:21:00 > 0:21:03so it's trapped - it's confined, in a sense.
0:21:03 > 0:21:07So what you can see is there's only one bit which is moving
0:21:07 > 0:21:10with the maximum amplitude if you like, the maximum wave
0:21:10 > 0:21:12and it's in the middle there.
0:21:12 > 0:21:15So that's called a standing wave. It's called a standing wave
0:21:15 > 0:21:16because it's confined.
0:21:16 > 0:21:18It's doing nothing, really - it's vibrating up and down.
0:21:18 > 0:21:22It's not a wave as you might usually expect it.
0:21:22 > 0:21:24Now, if you give it a bit more wrist action...
0:21:24 > 0:21:26GIGGLING
0:21:27 > 0:21:30Look at that one - now, that...
0:21:30 > 0:21:33THAT is the next standing wave up,
0:21:33 > 0:21:37so there is a transition from the one where we're just moving here -
0:21:37 > 0:21:40this one's got three stationary points.
0:21:40 > 0:21:44- I lost me stroke... - Don't get carried away. - Sorry, sorry.
0:21:45 > 0:21:48Wait, wait, wait -
0:21:48 > 0:21:50this has never happened to me before!
0:21:50 > 0:21:54LAUGHTER AND APPLAUSE
0:21:55 > 0:21:58There - look at that - now there's three stationary bits -
0:21:58 > 0:22:02there's one stationary there, one stationary bit there, one stationary bit there
0:22:02 > 0:22:05and the amplitude - the maximum amplitude is there and there.
0:22:05 > 0:22:08Now, you can get another one going...
0:22:08 > 0:22:11if you really try, which is the third one.
0:22:11 > 0:22:12There it is! No!
0:22:12 > 0:22:14CHEERING
0:22:16 > 0:22:18Look at that.
0:22:22 > 0:22:24Yes, yes, yes!
0:22:24 > 0:22:27Can you see? That's got two stationary points -
0:22:27 > 0:22:31- one there and one there. That's a brilliant... - Oh, it's gone again!
0:22:31 > 0:22:34I can see... Hang on... There, there, there!
0:22:34 > 0:22:37Two stationary points... 1, 2, 3, 4 stationary points.
0:22:37 > 0:22:40- I can see why you've got no air! - Here it is! There it is!
0:22:44 > 0:22:46Ah, that's better now. There's the fourth one.
0:22:46 > 0:22:48So, you...
0:22:48 > 0:22:50You carry on.
0:22:50 > 0:22:52Now it feels like someone else!
0:22:52 > 0:22:54It's back! Ah, it's gone!
0:22:57 > 0:23:00So if I just sketch... Carry on!
0:23:00 > 0:23:01There we go - yes!
0:23:01 > 0:23:04- Brian, Brian, Brian, Brian! - Yeah, yeah, yeah!
0:23:04 > 0:23:07APPLAUSE
0:23:15 > 0:23:16Perfect.
0:23:16 > 0:23:191, 2, 3, 4, 5 - all right, you can stop now.
0:23:21 > 0:23:23Good practice for later!
0:23:25 > 0:23:27- Thank you very much!- Thanks.
0:23:27 > 0:23:28APPLAUSE
0:23:33 > 0:23:35I sketched what you saw there.
0:23:35 > 0:23:37You saw that one very clearly which was this wave
0:23:37 > 0:23:39where there were just two stationary points
0:23:39 > 0:23:42which were at the ends and then you saw this one,
0:23:42 > 0:23:45where there were three stationary points.
0:23:45 > 0:23:47And then you saw this one where there were four stationary points
0:23:47 > 0:23:51and actually, because you were... That's the best I've ever seen it done,
0:23:51 > 0:23:53- there was one with about five, I think, or even six.- (Yes!)
0:23:53 > 0:23:55So, you saw that...
0:23:55 > 0:23:58there were only certain waves...
0:23:58 > 0:24:01That the spring could vibrate, certain waves it could vibrate
0:24:01 > 0:24:06and the reason it behaved like that is because it was trapped at both ends.
0:24:06 > 0:24:10So this is what you would call, physicists would call
0:24:10 > 0:24:13standing waves and you saw them appear on that spring.
0:24:14 > 0:24:17Now, what has that got to do with empty atoms?
0:24:17 > 0:24:22Well, just as this wave was trapped between Jim and Simon,
0:24:22 > 0:24:24electrons are trapped inside atoms.
0:24:24 > 0:24:29The positive electric charge of the nucleus effectively traps
0:24:29 > 0:24:33the negatively-charged electron inside an atomic-sized box.
0:24:33 > 0:24:34And when an electron is trapped,
0:24:34 > 0:24:37just as the spring was trapped between Jim and Simon,
0:24:37 > 0:24:41it exhibits the same kind of wave-like behaviour as the spring.
0:24:41 > 0:24:46So now we're getting closer to understanding what's happening inside an atom.
0:24:46 > 0:24:52But what do standing electron waves around a nucleus actually represent?
0:24:52 > 0:24:55Well, the clue is that Jim and Simon had to put more energy in
0:24:55 > 0:24:59to switch from one standing wave to another.
0:24:59 > 0:25:03So it's tempting to think of those electron standing waves
0:25:03 > 0:25:08as waves with different energies inside an atom,
0:25:08 > 0:25:11waves that the different energies, the electron can have, if you like
0:25:11 > 0:25:16when it's confined around a nucleus and this turns out to be correct.
0:25:16 > 0:25:19But, just as there were only certain standing waves on the spring,
0:25:19 > 0:25:24inside an atom, there are only certain energies that electrons can have.
0:25:24 > 0:25:26Now, quantum theory allows physicists to calculate the shape
0:25:26 > 0:25:32of the waves and therefore the allowed energies the electrons can have inside the atom.
0:25:32 > 0:25:35And when you do the calculations, you find the lowest energy 'wave',
0:25:35 > 0:25:40if you like, so I suppose this standing wave here
0:25:40 > 0:25:42that can fit around the nucleus
0:25:42 > 0:25:46has a wavelength of around 3 x 10-10 metres.
0:25:46 > 0:25:49Now, let me just write that down, because you might not be familiar with the notation.
0:25:49 > 0:25:53It's 1, 2, 3, 4, 5, 6, 7, 8, 9...
0:25:53 > 0:25:580.0000000003 of a metre which sounds
0:25:58 > 0:26:03unimaginably small, but it's enormous compared to the size
0:26:03 > 0:26:07of the nucleus. It's actually about a quarter of a million times larger.
0:26:07 > 0:26:11So that is why atoms are so big and yet so empty.
0:26:11 > 0:26:14It's because electrons trapped around a nucleus
0:26:14 > 0:26:17behave like waves - in this case standing waves - and there has to be
0:26:17 > 0:26:22enough room to fit an electron wave around the atomic nucleus.
0:26:22 > 0:26:25But that doesn't answer a very important question.
0:26:25 > 0:26:28Now, we've shown why atoms are empty,
0:26:28 > 0:26:29But we haven't yet explained
0:26:29 > 0:26:34how they become so strongly bound together that they can create solid objects
0:26:34 > 0:26:37like our beautiful million-pound diamond here.
0:26:37 > 0:26:44Answer that, and we explain the structure of everything we see in the universe.
0:26:49 > 0:26:53The early years of quantum theory were dominated by boy wonders,
0:26:53 > 0:26:56people actually half my age, believe it or not.
0:26:56 > 0:27:00So much so, that it became nicknamed "Knabenphysik",
0:27:00 > 0:27:03which translated from German means "boy physics".
0:27:03 > 0:27:07The key discovery was made by a man called Wolfgang Pauli.
0:27:07 > 0:27:12Pauli published his first paper on Einstein's Theory of General Relativity when he was 18.
0:27:12 > 0:27:17And his great contribution to quantum theory was made when he was only 24.
0:27:17 > 0:27:20It's known as the Exclusion Principle.
0:27:20 > 0:27:24We've seen that electrons can only exist in certain energy levels around the nucleus.
0:27:24 > 0:27:29These energy levels, associated with the different standing waves.
0:27:29 > 0:27:35Those energy levels correspond to standing waves that can fit in the atomic size box.
0:27:35 > 0:27:37But the key point that Pauli realised
0:27:37 > 0:27:42is that electrons can't all simply inhabit the lowest energy level.
0:27:42 > 0:27:45Now, to a physicist, this should look a bit odd.
0:27:45 > 0:27:48I mean, take this apple, for example.
0:27:48 > 0:27:51If I lift the apple up, then I have to do work.
0:27:51 > 0:27:52I give it energy to lift it up.
0:27:52 > 0:27:55And if I let go, so I don't support it any more,
0:27:55 > 0:27:58then it falls to the ground.
0:27:58 > 0:28:00Now, the explanation of that, for a physicist,
0:28:00 > 0:28:04is that the apple is falling into a lower-energy state.
0:28:04 > 0:28:07Nature doesn't like to be in high-energy states.
0:28:07 > 0:28:13It wants to cascade down into the lowest energy configuration that it can.
0:28:13 > 0:28:19But the surprising thing is that electrons don't all live in that lowest energy level in an atom.
0:28:19 > 0:28:24It turns out they're forbidden from doing so by an unbreakable law of nature.
0:28:24 > 0:28:28That law is called the Pauli Exclusion Principle.
0:28:28 > 0:28:30It's kind of like all of you sitting in these rows here.
0:28:30 > 0:28:34You aren't allowed to all come down to the front row.
0:28:34 > 0:28:38You can't all squash into the front seats, because there isn't room for you.
0:28:38 > 0:28:43Electrons don't all occupy the lowest energy slots around an atom.
0:28:43 > 0:28:48Instead, they fill each level up in order of increasing energy.
0:28:48 > 0:28:49This might sound meaningless,
0:28:49 > 0:28:51maybe it sounds a bit abstract.
0:28:51 > 0:28:52But let me tell you that it isn't.
0:28:52 > 0:28:56You see, Pauli's simple quantum rule is profoundly important.
0:28:56 > 0:29:00In fact, it's the key to understanding chemistry.
0:29:00 > 0:29:02But don't take my word for it. Time for another volunteer.
0:29:02 > 0:29:07I know that James May kindly volunteered to take part in this.
0:29:07 > 0:29:11He looks very worried, so maybe he was never asked! But anyway, James.
0:29:22 > 0:29:25Now this is doubly amusing for me,
0:29:25 > 0:29:29cos I know that you know exactly what's going to happen
0:29:29 > 0:29:31because there's a canister of hydrogen gas there
0:29:31 > 0:29:34and I know you're a keen aviator, so...
0:29:34 > 0:29:37- You think about the story of the Hindenburg...- Mmm!- ..while I...
0:29:37 > 0:29:42- Which was unhappy, wasn't it? - Oh, I get to wear the goggles? - You might have to wear the goggles.
0:29:42 > 0:29:47It's only a small safety thing, because it went wrong in rehearsal.
0:29:47 > 0:29:52So what we're going to do is encourage a small chemical reaction to happen. What we're doing
0:29:52 > 0:29:55is bubbling hydrogen through... Hydrogen gas through this, um...
0:29:55 > 0:29:59- LAUGHTER - ..through this soap, here.- Mmm.
0:29:59 > 0:30:04What I'd like you to do... Actually, just wet your hands first. Just because it's a safety thing.
0:30:04 > 0:30:05It stops your hands catching fire.
0:30:05 > 0:30:09It actually... Perhaps roll your sleeves up a little bit.
0:30:09 > 0:30:11You'll be all right. I'm sure you'll be fine.
0:30:11 > 0:30:16So I'd like you to get - grab - some of that of that hydrogen in the soap bubbles.
0:30:17 > 0:30:19Um...
0:30:20 > 0:30:23- How's that?- Don't look...
0:30:23 > 0:30:25at what I'm doing.
0:30:25 > 0:30:33What I'm going to do is I'm going to encourage a chemical reaction to happen...
0:30:33 > 0:30:34from over here.
0:30:34 > 0:30:36LAUGHTER
0:30:38 > 0:30:40Whoa!
0:30:40 > 0:30:41- Ow!- You all right?
0:30:41 > 0:30:45LAUGHTER AND APPLAUSE
0:30:45 > 0:30:47LAUGHTER AND APPLAUSE DROWNS SPEECH
0:30:50 > 0:30:54Thank you very much for putting yourself at great risk!
0:31:01 > 0:31:06Thanks, James. That actually was a lot more fire than I was expecting! Sorry about that.
0:31:06 > 0:31:08So what happened there?
0:31:08 > 0:31:12What we did was we bubbled hydrogen gas into these bubbles.
0:31:12 > 0:31:17James held them, and then I just gave them a little kick of energy
0:31:17 > 0:31:20which encouraged them to react with oxygen in the air.
0:31:20 > 0:31:23Now if draw the energy levels of oxygen,
0:31:23 > 0:31:25then they look something like that.
0:31:25 > 0:31:30They don't quite look as neat as when I drew the standing waves on the spring.
0:31:30 > 0:31:33That's really because of the shape of the atomic box,
0:31:33 > 0:31:36the shape of the box surrounding the oxygen nucleus.
0:31:36 > 0:31:41Now oxygen has eight protons and eight neutrons in its nucleus,
0:31:41 > 0:31:45which means it needs eight electrons filling up its energy levels.
0:31:45 > 0:31:49And the electrons fill up the energy levels like that.
0:31:51 > 0:31:53So you get three full energy levels
0:31:53 > 0:31:57and two energy levels with a single electron in them.
0:31:57 > 0:32:04Now that kind of makes oxygen a voracious consumer of electrons.
0:32:04 > 0:32:06It would like, if it can -
0:32:06 > 0:32:09it's energetically favourable for it to fill up those missing gaps.
0:32:09 > 0:32:13Hydrogen has one proton,
0:32:13 > 0:32:17and so it has one electron sat there in its lowest energy level.
0:32:17 > 0:32:21Again, it has a space there. It would also like to fill that up.
0:32:21 > 0:32:26So what happens, when I give it a little kick with this splint,
0:32:26 > 0:32:31is that the hydrogen is encouraged to react with the with the oxygen.
0:32:31 > 0:32:35It's energetically favourable for it to share its electron.
0:32:35 > 0:32:36So the oxygen shares with the hydrogen,
0:32:36 > 0:32:38the hydrogen shares with the oxygen.
0:32:38 > 0:32:43There are two gaps, so you get two hydrogens which would like to react.
0:32:43 > 0:32:47In doing so, the rearrangement of those electrons in the energy levels
0:32:47 > 0:32:50is such a great giver of energy that you saw a flash.
0:32:50 > 0:32:55All that flash that you saw, the little explosion, was energy being released
0:32:55 > 0:33:00when the electrons in the hydrogen and the oxygen reconfigure -
0:33:00 > 0:33:02just like the apple reconfigured itself
0:33:02 > 0:33:06by dropping to the ground to get into the lowest energy state.
0:33:06 > 0:33:10Two hydrogens, one oxygen. What does that make?
0:33:10 > 0:33:11MAN: Water.
0:33:11 > 0:33:14- ALL: Water!- Right!
0:33:14 > 0:33:17H2O.
0:33:17 > 0:33:22So that is essentially the reason why we get chemistry.
0:33:22 > 0:33:24Without Pauli's Exclusion Principle,
0:33:24 > 0:33:30all the electrons would crowd down into the lowest energy level and there'd be no chemistry.
0:33:30 > 0:33:32Which is worse than it sounds...
0:33:32 > 0:33:34LAUGHTER
0:33:37 > 0:33:42..because without chemistry, we'd have no magnificent structures in the universe,
0:33:42 > 0:33:47like water, diamonds, or indeed, any of you.
0:33:47 > 0:33:51Now, there's another consequence of the exclusion principle
0:33:51 > 0:33:53that wasn't proved until 1967,
0:33:53 > 0:33:55just one year before I was born.
0:33:55 > 0:33:59Pauli's principle says that identical electrons
0:33:59 > 0:34:01can't occupy the same energy level.
0:34:01 > 0:34:03This is an absolute requirement.
0:34:03 > 0:34:07So it also means that electrons will avoid each other at all costs.
0:34:07 > 0:34:11And that, it was proved, is the actual reason
0:34:11 > 0:34:15that I don't fall through the empty atoms that make up the floor.
0:34:15 > 0:34:21That's ultimately what gives the illusion of solidity to the empty world of atoms.
0:34:21 > 0:34:24And if you think a little bit more deeply about it,
0:34:24 > 0:34:27then this throws up a bewildering conclusion, and it's this.
0:34:27 > 0:34:33The Pauli Exclusion Principle applies to EVERY electron in the universe.
0:34:33 > 0:34:36Not just every electron in a single atom, or a single molecule.
0:34:36 > 0:34:39And this leads to a bizarre conclusion.
0:34:39 > 0:34:41The particles that make up this diamond
0:34:41 > 0:34:43are in communication with particles everywhere.
0:34:45 > 0:34:46Inside all of you,
0:34:46 > 0:34:50and inside the atoms in the furthest corners of the universe.
0:34:50 > 0:34:54Let me explain that a little bit more. The Pauli Exclusion Principle
0:34:54 > 0:34:58says no identical electrons can be in precisely the same energy level.
0:34:58 > 0:35:00What if you have more than one atom?
0:35:00 > 0:35:03For example, in this diamond
0:35:03 > 0:35:07there are 3 million billion billion carbon atoms.
0:35:07 > 0:35:10So this is a diamond-size box of carbon atoms.
0:35:10 > 0:35:14And the Pauli Exclusion Principle still applies.
0:35:14 > 0:35:16So all the energy levels
0:35:16 > 0:35:18in all those 3 million billion billion atoms
0:35:18 > 0:35:21have to be slightly different in order to ensure that
0:35:21 > 0:35:25none of the electrons sit in precisely the same energy level.
0:35:25 > 0:35:30Pauli's principle holds fast. But it doesn't stop with the diamond.
0:35:30 > 0:35:35See, you can think of the whole universe as a vast box of atoms,
0:35:35 > 0:35:38with countless numbers of energy levels
0:35:38 > 0:35:42all filled by countless numbers of electrons.
0:35:42 > 0:35:46So here's the amazing thing - the exclusion principle still applies,
0:35:46 > 0:35:50so none of the electrons in the universe can sit in precisely
0:35:50 > 0:35:52the same energy level.
0:35:52 > 0:35:54But that must mean something very odd.
0:35:54 > 0:35:57See, let me take this diamond, and let me just
0:35:57 > 0:35:59heat it up a little bit between my hands.
0:35:59 > 0:36:01Just gently warming it up,
0:36:01 > 0:36:04putting a bit of energy into it, so I'm shifting the electrons around,
0:36:04 > 0:36:08some of the electrons are jumping into different energy levels.
0:36:08 > 0:36:11But this shift in the configuration of the electrons
0:36:11 > 0:36:14inside the diamond has consequences, because the sum total
0:36:14 > 0:36:19of all the electrons in the universe must respect Pauli.
0:36:19 > 0:36:22Therefore, every electron, around every atom
0:36:22 > 0:36:26in the universe, must be shifting as I heat the diamond up,
0:36:26 > 0:36:30to make sure that none of them end up in the same energy level.
0:36:30 > 0:36:34When I heat this diamond up, all the electrons across the universe
0:36:34 > 0:36:38instantly but imperceptibly change their energy levels.
0:36:38 > 0:36:43So everything is connected to everything else.
0:36:50 > 0:36:54At the beginning, I promised I'd explain everything in the universe,
0:36:54 > 0:36:58which I have in some way, but also I said that I'd give you
0:36:58 > 0:37:03a deeper explanation of that wavy behaviour of the subatomic world.
0:37:03 > 0:37:06So here it is. In my view, this is the deepest explanation we have,
0:37:06 > 0:37:09and it's down to the Nobel Prize-winning physicist
0:37:09 > 0:37:12Richard Feynman who, his colleague Freeman Dyson once described
0:37:12 > 0:37:15as half genius, half buffoon but he subsequently, after having
0:37:15 > 0:37:19worked with him for a while, changed that to all genius, all buffoon.
0:37:19 > 0:37:22Let's go back to the double slit experiment, but now,
0:37:22 > 0:37:24instead of just showing you the pattern...
0:37:24 > 0:37:26This is Richard Feynman.
0:37:26 > 0:37:28Instead of just showing you the pattern,
0:37:28 > 0:37:30I want to show you how that pattern builds up.
0:37:30 > 0:37:32Remember, we're firing electrons at two slits,
0:37:32 > 0:37:34almost pouring them through two slits
0:37:34 > 0:37:38and seeing what happened when they were detected on the other side.
0:37:38 > 0:37:43Well, this is one electron at a time being fired through the slits
0:37:43 > 0:37:46and hitting the screen, and building up in a pile.
0:37:46 > 0:37:49Only when the one electron has gone through, was another one fired
0:37:49 > 0:37:54and this is real data, again, a real movie of that happening
0:37:54 > 0:37:56and you see the interference pattern.
0:37:56 > 0:37:59Electrons, no electrons, electrons, no electrons.
0:37:59 > 0:38:03The wavy-type interference pattern building up.
0:38:03 > 0:38:05What could be happening there?
0:38:05 > 0:38:07So, here it is again. Just electrons
0:38:07 > 0:38:10and you see that what emerges is that wave-like behaviour.
0:38:10 > 0:38:13So, you might have thought, "Well, I kind of understand
0:38:13 > 0:38:16"what's going on with the double slits, there's loads of electrons
0:38:16 > 0:38:19"piling through the slits and somehow there's some interference
0:38:19 > 0:38:23"just like a big water wave and you build up the interference pattern."
0:38:23 > 0:38:27Well, no, because this is one electron at a time,
0:38:27 > 0:38:29so, what could possibly be happening?
0:38:29 > 0:38:34Well, Feynman was a wonderfully intuitive, logical physicist.
0:38:34 > 0:38:37No ordinary genius, he was often described as.
0:38:37 > 0:38:40And he said this.
0:38:40 > 0:38:43Here are the slits.
0:38:43 > 0:38:45Here's the screen.
0:38:45 > 0:38:48The electrons starts off here. What happens?
0:38:48 > 0:38:51Well, obviously, the particle - electron - must go through a slit
0:38:51 > 0:38:54and it must appear somewhere on the screen,
0:38:54 > 0:38:57but it needs to be able to interfere with itself -
0:38:57 > 0:39:01there've got to be regions on the screen where there are no electrons,
0:39:01 > 0:39:02it's prevented from landing there,
0:39:02 > 0:39:06so it must, at least, go through the other slit, as well,
0:39:06 > 0:39:09and get to that point, and there must be some mechanism
0:39:09 > 0:39:14for these paths interfering with each other, but why stop there?
0:39:14 > 0:39:16See, that wouldn't be particularly logical.
0:39:16 > 0:39:18Why only let it go through two paths?
0:39:18 > 0:39:21Why not let it go through that path or maybe
0:39:21 > 0:39:26some sort of path like that, or maybe like or maybe, indeed,
0:39:26 > 0:39:29off here, out of this lecture theatre
0:39:29 > 0:39:33and then maybe through Jonathan's head on its way...
0:39:33 > 0:39:36I've got to say through Paul's foot, haven't I? Cos I just have to.
0:39:36 > 0:39:40Paul Foot. I don't know - what a rubbish thing to say.
0:39:40 > 0:39:43But, anyway, it could go through you, through Jonathan,
0:39:43 > 0:39:46off up Oxford Street, up to Newcastle
0:39:46 > 0:39:48indeed on to the Andromeda Galaxy
0:39:48 > 0:39:51and back again, and land at this point on the screen.
0:39:51 > 0:39:54Why not?
0:39:54 > 0:39:57Why not allow the particle to travel along every possible path it can,
0:39:57 > 0:40:02from one point to the other? And that is indeed what happens,
0:40:02 > 0:40:06in the sense that's the way Feynman's theory works.
0:40:06 > 0:40:08In principle, it's not too difficult.
0:40:08 > 0:40:10You just have to calculate some quantity
0:40:10 > 0:40:14associated with each path and find some mathematical machinery
0:40:14 > 0:40:18from adding all those things up, and seeing whether or not they all
0:40:18 > 0:40:22interfere together and disappear or appear when they land on the screen.
0:40:22 > 0:40:24There is a formula that does that
0:40:24 > 0:40:27and this is all I really need to say.
0:40:27 > 0:40:30Let me turn it around. There it is.
0:40:30 > 0:40:32Thank you and good... No, no, I won't say that!
0:40:32 > 0:40:35This is called the Feynman path integral,
0:40:35 > 0:40:36and this just says,
0:40:36 > 0:40:40sum up over all the paths and calculate something
0:40:40 > 0:40:42that will tell you the probability
0:40:42 > 0:40:44of an electron going from one place to another.
0:40:44 > 0:40:47Now, that might look a tremendous mess,
0:40:47 > 0:40:50or it might look very simple and illuminating -
0:40:50 > 0:40:52I suppose it depends on your point of view.
0:40:52 > 0:40:55Probably a tremendous mess, granted.
0:40:55 > 0:40:57But this formula is just a little machine,
0:40:57 > 0:40:59I think that's a good way to think about it.
0:40:59 > 0:41:02It that takes all the possible paths a particle can have,
0:41:02 > 0:41:05it adds them up and it spits out the probability
0:41:05 > 0:41:08that it'll end up at some particular place.
0:41:08 > 0:41:13And that includes the particles that make up the diamond.
0:41:13 > 0:41:17Now, for the moment, it's sat on its little cushion there.
0:41:17 > 0:41:19Let me put it back in its box.
0:41:21 > 0:41:24Now, Feynman's version of quantum theory tells us
0:41:24 > 0:41:26something rather shocking.
0:41:26 > 0:41:28This diamond is made up of atoms,
0:41:28 > 0:41:31and the atoms are behaving according to quantum theory -
0:41:31 > 0:41:33according to Feynman's equation.
0:41:33 > 0:41:36In other words, they are all currently exploring the universe,
0:41:36 > 0:41:41hopping around everywhere, exploring every possible path they can.
0:41:41 > 0:41:43And that means this diamond is doing the same thing,
0:41:43 > 0:41:46because it's made of atoms.
0:41:46 > 0:41:48That means there is a finite chance that it will not
0:41:48 > 0:41:54be inside this box at a later time - you can see where I'm going -
0:41:54 > 0:41:59but it'll jump, completely out of its own accord,
0:41:59 > 0:42:03without me touching it...and that's what I'm going to tell the judge!
0:42:05 > 0:42:09But what's remarkable, is that I can calculate what the chance is
0:42:09 > 0:42:15by using a simplified version of Feynman's formula.
0:42:15 > 0:42:17And this is it.
0:42:17 > 0:42:21See, just by doing a bit of maths, you can work that, simplify it,
0:42:21 > 0:42:23and turn it into this...
0:42:23 > 0:42:27which is an expression for the time you would have to wait,
0:42:27 > 0:42:30on the average, to have a reasonable chance of it hopping
0:42:30 > 0:42:34out of its box, and it goes like this.
0:42:37 > 0:42:42OK, so, that is the distance we want it to hop,
0:42:42 > 0:42:44that is the size of the box,
0:42:44 > 0:42:46that's the mass of the diamond
0:42:46 > 0:42:48and that's something called Planck's constant.
0:42:48 > 0:42:50I'm going to need another volunteer here
0:42:50 > 0:42:53because I'm going to actually do the maths
0:42:53 > 0:42:55because I want to show you that you can do the sum quite simply
0:42:55 > 0:42:58and I believe that Jonathan has kindly agreed
0:42:58 > 0:43:01to do some sums, so, thank you.
0:43:12 > 0:43:17- How's your maths?- Well, you know, you know that's easy for me.
0:43:17 > 0:43:20I do. That's why I asked you, actually.
0:43:20 > 0:43:21We're going to do it,
0:43:21 > 0:43:24so x - that's the distance we want the diamond to jump.
0:43:24 > 0:43:27So let's say the box is about 5cm.
0:43:27 > 0:43:31Let's say 6cm for x
0:43:31 > 0:43:36and the mass of the diamond is 290-something carats -
0:43:36 > 0:43:41- it's about 60g.- Roughly, yes. - An expert on diamonds, are you?
0:43:41 > 0:43:45So, first of all, we just have to multiply those 3 numbers together.
0:43:45 > 0:43:486cm x 5cm x 60g.
0:43:48 > 0:43:49Yeah. 6 x 5 x 6.
0:43:49 > 0:43:53So 30 x 60. You just said 6!
0:43:53 > 0:43:5460. 60g.
0:43:54 > 0:43:57OK, 30 x 6 = 1,800.
0:43:57 > 0:43:59Is that right? 60?
0:43:59 > 0:44:03- It's heavy.- It is. The BBC used to pay me in these.
0:44:03 > 0:44:07LAUGHTER AND APPLAUSE
0:44:12 > 0:44:17- I better take it back. I'm going to get... - HE LAUGHS NERVOUSLY
0:44:17 > 0:44:19- Then, though we get to this. - Over the thing.
0:44:19 > 0:44:276.6 x 10-34 kgm2/s.
0:44:27 > 0:44:29That is Planck's constant -
0:44:29 > 0:44:32this is a fundamental constant of nature.
0:44:32 > 0:44:35It's intrinsic to the way the universe is put together.
0:44:35 > 0:44:39It's like the speed of light, like the strength of gravity.
0:44:39 > 0:44:40It is THE fundamental THING -
0:44:40 > 0:44:43constant, if you like - that sets the scale for quantum phenomena.
0:44:43 > 0:44:46So, there's a slight issue here
0:44:46 > 0:44:48because you see... You'll have noticed it.
0:44:48 > 0:44:50The unit's are kilograms metres squared per second
0:44:50 > 0:44:53and we calculated the 1,800 in cm and grams.
0:44:53 > 0:44:56Which, by the way, I'm amazed I got that right!
0:44:56 > 0:45:01So, first of all, we better another 10-2 and a 10-2 and a 10-3 on,
0:45:01 > 0:45:04- so it's 10-7.- Yeah.
0:45:05 > 0:45:08So all you've got to do is divide that by that.
0:45:08 > 0:45:11- All of that with that? - Divide that by that roughly.
0:45:11 > 0:45:15Roughly I don't even know if I can do...
0:45:20 > 0:45:25That, for me... That's a kilogram? I don't even know. I do pounds!
0:45:25 > 0:45:30- No, I've done the unit conversion for you - you've just got to divide. - Where's the unit conversion?
0:45:30 > 0:45:331,800 x 10-7 x 6.6 x 10...
0:45:33 > 0:45:36I have no idea what you're doing and why you would want to do this to me!
0:45:36 > 0:45:38Help him out, Jim.
0:45:38 > 0:45:40Well you've got 10-34 downstairs. Bring it upstairs
0:45:40 > 0:45:43- and it becomes 1034. - Where do I put it? Up here?
0:45:43 > 0:45:46Yeah, put it next to the 10...
0:45:46 > 0:45:50- So then you've got 34 - 7. - OK 34-7?- Yeah.- Yes, OK.
0:45:50 > 0:45:52So that's 1027.
0:45:52 > 0:45:57- You've got about 103. - I really... I'm so out of my depth.
0:45:58 > 0:46:01This is the worst thing that's happened to me as an adult.
0:46:02 > 0:46:04- You've got 1027.- OK.
0:46:04 > 0:46:10Just for any children watching, I should say,
0:46:10 > 0:46:1234 - 7 = 27
0:46:12 > 0:46:16So you've got 1027 and then we've got 6 and we've got 1,800,
0:46:16 > 0:46:22so we've got to divide those things so we get about a 3 and another 100.
0:46:22 > 0:46:24If you say so!
0:46:24 > 0:46:273 x 1029...ish.
0:46:27 > 0:46:31Once again, I am none the wiser. LAUGHTER
0:46:31 > 0:46:36Why couldn't I have done James May's job where you just set fire to me?
0:46:36 > 0:46:41And everyone went "Oooh!" And he's so happy he did that
0:46:41 > 0:46:44and I'm now sweating.
0:46:44 > 0:46:49- We're done.- We've done it? - Yeah, you see, this is what that number is you calculated.
0:46:49 > 0:46:53See, we just put in the numbers divided by Planck's constant? What this number is
0:46:53 > 0:46:57is the number of seconds you would have to wait on the average to have
0:46:57 > 0:47:00a reasonable chance of the diamond hopping out of the box on its own.
0:47:00 > 0:47:03I could have told you that's not going to happen without any of this.
0:47:03 > 0:47:05LAUGHTER
0:47:05 > 0:47:08I didn't need the sums. The diamond is safe in the box,
0:47:08 > 0:47:11unless it's turned into a dead cat. That's the theory, isn't it?
0:47:11 > 0:47:14I'll tell you what this is. Do you know roughly what that is?
0:47:14 > 0:47:18- A nine?- 3 x 1029? - Why would I know? I'm an idiot!
0:47:18 > 0:47:23- In years?- That's about... - Well, I'll tell you what it is. It is 600 billion times
0:47:23 > 0:47:26the current age of the universe.
0:47:26 > 0:47:29I don't know what to do. I'm just going to keep smiling at you.
0:47:29 > 0:47:33- LAUGHTER Thank you for sharing that. - Thank you.
0:47:35 > 0:47:38Thanks.
0:47:43 > 0:47:45Thanks, Jon.
0:47:46 > 0:47:52The point of that... The point of that is to show that quantum theory doesn't just
0:47:52 > 0:47:55apply to the inconceivably small world of the atom.
0:47:55 > 0:47:59The same rules apply to you, to me, and the diamond.
0:47:59 > 0:48:03It's just that for objects out here in the familiar world,
0:48:03 > 0:48:06like the diamond, we don't usually see quantum effects.
0:48:06 > 0:48:11The reason for that is the smallness of Planck's constant. We had quite a big number here,
0:48:11 > 0:48:15but we had to divide it by an extremely small number in order
0:48:15 > 0:48:19to work out the time we'd have to wait and that's why that's big.
0:48:19 > 0:48:23See, if that was one or something like that, then we wouldn't have had to wait many seconds -
0:48:23 > 0:48:27about 1,800 seconds or something like that, for the diamond to hop out of the box.
0:48:27 > 0:48:30So it's Planck's constant, this fundamental constant of nature
0:48:30 > 0:48:34that means that quantum theory is rather unfamiliar
0:48:34 > 0:48:39because it applies to small things, because Planck's constant is small.
0:48:39 > 0:48:43Now you could theoretically make the diamond jump sooner.
0:48:43 > 0:48:45Look again at this equation.
0:48:45 > 0:48:49One way to do it, as I've said, would be to make Planck's constant very big,
0:48:49 > 0:48:53but you can't do that. It's a fundamental constant of nature. What you could do, though,
0:48:53 > 0:48:57is you could shrink the size of the box, this delta x here.
0:48:57 > 0:49:01If I made the box smaller and smaller and smaller,
0:49:01 > 0:49:07I'd make the time I had to wait for it to jump out of the box smaller and smaller and smaller.
0:49:07 > 0:49:11So this equation says that the more we know the position
0:49:11 > 0:49:15of something, the position of this diamond in the box, let's say,
0:49:15 > 0:49:19then the more likely it is for the diamond to jump out of the box.
0:49:19 > 0:49:23Now this is known as Heisenberg's Uncertainty Principle -
0:49:23 > 0:49:27the more you try to pin down a particle's position by trapping it
0:49:27 > 0:49:31in a smaller and smaller box, the more likely it is to jump around.
0:49:31 > 0:49:35You might have come across Heisenberg's Uncertainty Principle.
0:49:35 > 0:49:37It's one of the most famously misunderstood
0:49:37 > 0:49:40and misrepresented parts of quantum theory.
0:49:40 > 0:49:44It says, precisely, that the more precisely you know
0:49:44 > 0:49:49a particle's position, the less certain you can be of its momentum.
0:49:49 > 0:49:54And you can see that it emerged... I derived it from a fundamental equation.
0:49:54 > 0:49:57It's not complete nonsense. I didn't make it up.
0:49:57 > 0:50:01It's often misrepresented by what I would call "mischievous hippies"
0:50:01 > 0:50:04to mean that physicists are rubbish at their job
0:50:04 > 0:50:07or that the equipment is no good and we're unable to measure
0:50:07 > 0:50:10two things about a particle with any accuracy.
0:50:10 > 0:50:13But Heisenberg's Uncertainty Principle is a consequence
0:50:13 > 0:50:15of the laws of quantum theory. It emerges
0:50:15 > 0:50:21from Feynman's equation. It has nothing to do with any of that wishy-washy, drivelly nonsense.
0:50:21 > 0:50:26In that spirit, I want to show you that rather than restricting our knowledge of the natural world,
0:50:26 > 0:50:30Heisenberg can actually widen it.
0:50:30 > 0:50:34In fact, this rule about the unimaginably small particles
0:50:34 > 0:50:39can explain some of the most massive and spectacular objects in the universe.
0:50:42 > 0:50:44I'm going to end
0:50:44 > 0:50:47by explaining how everything I've told you this evening
0:50:47 > 0:50:51predicts the existence of diamonds bigger than this -
0:50:51 > 0:50:53in fact, bigger than this lecture theatre.
0:50:53 > 0:50:59In fact, diamonds as big as a planet and as massive as a star.
0:50:59 > 0:51:03Now to understand how this can be, we need to understand something
0:51:03 > 0:51:06about the life cycles of the stars themselves.
0:51:06 > 0:51:09Stars are big clumps of matter collapsing under their own gravity.
0:51:09 > 0:51:12As they collapse, they heat up and they set off a chain reaction
0:51:12 > 0:51:16of nuclear fusion reactions where the nuclei of hydrogen
0:51:16 > 0:51:21fuse together, initially to form helium, and eventually they fuse
0:51:21 > 0:51:26to form carbon and oxygen and all the heavy elements up to and including iron.
0:51:26 > 0:51:30That's where the heavy elements come from in the universe.
0:51:30 > 0:51:33In this process, vast amounts of energy are released.
0:51:33 > 0:51:36That energy creates a pressure that holds the star up
0:51:36 > 0:51:38and prevents it from collapsing.
0:51:38 > 0:51:41The stars don't have infinite amounts of fuel
0:51:41 > 0:51:44and eventually those fusion reactions must cease.
0:51:44 > 0:51:47In five billion years, this will happen to our sun.
0:51:47 > 0:51:50It'll stop generating enough energy to prevent its own collapse
0:51:50 > 0:51:53and so it will collapse.
0:51:53 > 0:51:58By the end of their lives, stars like our sun have converted all the hydrogen in their cores
0:51:58 > 0:52:03and mainly they've converted it into oxygen and carbon.
0:52:03 > 0:52:06Now remember that those carbon atoms,
0:52:06 > 0:52:10just like those in our diamond, are almost entirely empty space,
0:52:10 > 0:52:15so you might expect that the space can be squashed and compressed almost out of existence
0:52:15 > 0:52:17as the dying star collapses.
0:52:17 > 0:52:20But as the star collapses and becomes denser,
0:52:20 > 0:52:24its electrons get closer and closer together.
0:52:24 > 0:52:30Finally, they're so close that they try to occupy the same volume of space as each other.
0:52:30 > 0:52:33Then Pauli's Exclusion Principle steps in,
0:52:33 > 0:52:37because the electrons cannot occupy the same bit of space -
0:52:37 > 0:52:43they are unable to overlap, so they try to arrange themselves
0:52:43 > 0:52:45such that they have as much space as they possibly can.
0:52:45 > 0:52:49And you might imagine them as being alone inside little boxes like this
0:52:49 > 0:52:55and the boxes shrink and shrink and shrink as the star collapses.
0:52:55 > 0:52:58But then, as the electrons become more and more confined,
0:52:58 > 0:53:04Heisenberg's Uncertainty Principle comes into play. As the electrons' boxes get smaller and smaller,
0:53:04 > 0:53:08their tendency to hop out of the box becomes greater and greater,
0:53:08 > 0:53:11so you can think of it that they are frantically vibrating
0:53:11 > 0:53:16around faster and faster inside these boxes of ever-decreasing size.
0:53:16 > 0:53:20This quantum jiggling exerts a pressure, which stops
0:53:20 > 0:53:23the star from collapsing any further, leaving something called
0:53:23 > 0:53:28a white dwarf star, which is a densely-packed dead star the size of the Earth
0:53:28 > 0:53:33but the mass of our sun, and a million times more dense than water.
0:53:33 > 0:53:37White dwarfs are so dense that if I were to stand on their surface
0:53:37 > 0:53:43the gravitational pull would make me weigh something like 30,000 tonnes.
0:53:43 > 0:53:45White dwarfs are strange objects indeed.
0:53:45 > 0:53:49But here is the final triumph, I think, of quantum theory.
0:53:49 > 0:53:55It is the most powerful example I know of its power to predict how the natural world behaves.
0:53:55 > 0:54:01See, it predicts the existence of these strange stars of white dwarfs.
0:54:01 > 0:54:03But it does more than that.
0:54:03 > 0:54:06In the 1930s, the physicist Subrahmanyan Chandrasekhar
0:54:06 > 0:54:09used quantum theory to predict the maximum mass
0:54:09 > 0:54:14of a lump of matter that can be held up by the exclusion pressure of electrons
0:54:14 > 0:54:18to form a white dwarf. He just used the uncertainty principle, essentially,
0:54:18 > 0:54:20and the exclusion principle.
0:54:20 > 0:54:23He found that there should be no stars of this type
0:54:23 > 0:54:26with masses greater than 1.4 times the mass of our sun.
0:54:26 > 0:54:32Now to date, astronomers have found tens of thousands of white dwarf stars
0:54:32 > 0:54:38and they have found that not one in the sky exceeds the maximum mass
0:54:38 > 0:54:43calculated by Chandrasekhar using the simple laws of quantum theory.
0:54:43 > 0:54:48And in amongst those stars, astronomers have found something that I think is quite extraordinary.
0:54:48 > 0:54:51Now that diamond is 296 carats.
0:54:51 > 0:54:57In the heart of this constellation, Centaurus, which is a few tens of light years away,
0:54:57 > 0:55:03they've detected a white dwarf star with the wonderful name BPM 37093(!)
0:55:03 > 0:55:09- LAUGHTER - As it died and cooled, the carbon within the core crystallised.
0:55:09 > 0:55:18So BPM 37093, which is somewhere around there, became a diamond,
0:55:18 > 0:55:21just like this, but of ten billion trillion trillion carats.
0:55:21 > 0:55:23LAUGHTER
0:55:23 > 0:55:27We understand in detail why such a thing can exist.
0:55:27 > 0:55:33That's a diamond, light years away, intimately connected to this diamond,
0:55:33 > 0:55:35and indeed, intimately connected to everything else
0:55:35 > 0:55:38in the universe, by the laws of quantum physics.
0:55:38 > 0:55:43What a remarkable testament to the power of the wavy behaviour of electrons,
0:55:43 > 0:55:47and what a spectacular demonstration of the effectiveness of quantum theory.
0:55:47 > 0:55:51Quantum theory is a uniquely potent tool that gives us
0:55:51 > 0:55:55our best understanding of how the inconceivably small
0:55:55 > 0:55:57can give rise to the inconceivably large.
0:55:57 > 0:56:01It is THE most accurate way that we currently possess
0:56:01 > 0:56:03to understand our universe.
0:56:03 > 0:56:06It explains how atoms are empty yet solid,
0:56:06 > 0:56:11how the wave-like behaviour of electrons creates the hardest known substances,
0:56:11 > 0:56:15and how the real world emerges from subatomic particles
0:56:15 > 0:56:20that explore the universe, the entire universe, in an instant.
0:56:20 > 0:56:25There's nothing strange, there's nothing weird, there's no woo-woo.
0:56:25 > 0:56:28It is just beautiful physics. Thank you.
0:56:28 > 0:56:32APPLAUSE
0:56:49 > 0:56:51It was mind-blowing.
0:56:51 > 0:56:55I couldn't... Some of it I could understand,
0:56:55 > 0:56:58other parts I could not understand. It was so exciting. I loved it.
0:56:58 > 0:57:02I love listening to him because he does makes things clear.
0:57:02 > 0:57:04He speaks at just the right pace for me to absorb it
0:57:04 > 0:57:07and also he's got that very winning smile, so even though
0:57:07 > 0:57:11he does insist on telling us how soon it is that the sun's going to die out
0:57:11 > 0:57:15and we will all die screaming and flying off into the inky void of space,
0:57:15 > 0:57:18you don't mind it because he looks so sweet when he tells you.
0:57:18 > 0:57:20What do you now think of quantum physics?
0:57:20 > 0:57:24I feel like I maybe should have stuck in at school a little bit more,
0:57:24 > 0:57:29but you know, the career that I've chosen is going well, so...
0:57:29 > 0:57:34But I have learnt a lot - mainly "don't volunteer for things"!
0:57:34 > 0:57:36How are your hands now?
0:57:36 > 0:57:41My hands are fine. All it does is singe the very fine hairs on the back.
0:57:41 > 0:57:46But I was getting a bit, you know, gorilla-ish anyway, so he's probably done me a favour.
0:57:46 > 0:57:50It was great. I loved it. It was fantastic. It was almost exactly about everything
0:57:50 > 0:57:51I think about all the time.
0:58:13 > 0:58:15Subtitles by Red Bee Media Ltd
0:58:15 > 0:58:17E-mail subtitling@bbc.co.uk