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00:00:02,000 --> 00:00:03,760
Where's the reception? Oh, OK...


2
00:00:03,760 --> 00:00:06,760
So nobody knows what this lecture
is going to be about...


3
00:00:06,760 --> 00:00:11,880
I know what it's about.
It'll be about science, and he'll
be promoting that heresy of his.


4
00:00:11,880 --> 00:00:14,400
I hope he's going to unveil
a death ray. I don't know.


5
00:00:16,200 --> 00:00:20,160
I'm going to make one, at least one
unsuspecting celebrity, do sums.


6
00:00:20,160 --> 00:00:23,360
I really am so out of my depth...
LAUGHTER


7
00:00:23,360 --> 00:00:26,720
This is the worst thing
that's happened to me as an adult.


8
00:00:26,720 --> 00:00:29,920
The only thing I do know
is that I've been roped in to go up


9
00:00:29,920 --> 00:00:34,160
on stage - with Simon Pegg,
no less - waving a rope about.


10
00:00:34,160 --> 00:00:36,360
I can see why you've got no hair.


11
00:00:36,360 --> 00:00:37,960
LAUGHTER


12
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I'm so thrilled
to have been asked, to be honest.


13
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I never do clever things.


14
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There's a real buzz in this room,
and it just makes me feel proud to
be a scientist in this day and age.


15
00:00:50,760 --> 00:00:53,120
Perhaps tonight is my chance


16
00:00:53,120 --> 00:00:57,720
to realise what it's all about,
and have a big sort of
Damascene moment.


17
00:00:57,720 --> 00:01:02,840
I'd like to ask
Professor Brian Cox about his hair -
it's a shared interest.


18
00:01:02,840 --> 00:01:06,200
I hope he blows some stuff up.
Whoa... Ow!


19
00:01:06,200 --> 00:01:09,840
I'm hoping it's going to start
simple, for people like me,


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and then get slowly
more complicated.


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Because otherwise, if my brain
starts swelling inside my skull


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it's just going to pop
and I'll distract people.


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Thank you.


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Welcome to the Royal Institution
of Great Britain, established


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in 1799 as "an institution
for diffusing knowledge",


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and perhaps the most iconic
lecture theatre in science.


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Thomas Huxley championed Charles
Darwin's theory of evolution here,


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00:02:04,520 --> 00:02:08,720
Michael Faraday pioneered
our understanding of electricity
and magnetism here,


29
00:02:08,720 --> 00:02:13,720
and on this stage he demonstrated
the first electric motor.


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And the great scientist
and lecturer Sir Humphry Davy,


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who was also the first
director of the Royal Institution


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and one of my heroes,
spoke here many times.


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And he gave the best explanation
of the absolute need to do science
that I know of -


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"Nothing is so fatal
to the progress of the human mind


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"as to suppose that our views
of science are ultimate;


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"that there are no mysteries
in nature;


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"that our triumphs are complete,


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"and that there are no
new worlds to conquer."


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Well, tonight I want to talk about
one of the great mysteries,


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00:02:45,600 --> 00:02:47,640
pillars of our understanding
of nature -


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00:02:47,640 --> 00:02:51,080
the scientific theory that
underpins much of the technology


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00:02:51,080 --> 00:02:53,040
we take for granted
in the 21st century,


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yet retains its reputation
for obscure difficulty
and bizarre predictions.


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Now, by the time I've finished,
I hope that


45
00:03:01,800 --> 00:03:05,160
while your view of reality
might have shifted a little,


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00:03:05,160 --> 00:03:08,800
you'll understand a bit more
about how the universe works.


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00:03:08,800 --> 00:03:13,680
Now, let's start
with the contents of this box.


48
00:03:15,200 --> 00:03:22,320
This is a rough diamond.
It's worth well over £1 million.


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It costs so much because it's rare,
and because it's beautiful.


50
00:03:27,120 --> 00:03:30,600
But there's a different kind
of beauty here, a more profound


51
00:03:30,600 --> 00:03:36,840
kind of beauty - less superficial,
but perhaps far more instructive.


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00:03:36,840 --> 00:03:39,400
A diamond is one of the
hardest known substances -


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which is why diamonds
are widely used industrially -


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00:03:41,960 --> 00:03:46,680
but light can stream through it
relatively unimpeded.


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So there's beauty in a question,
which is,


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00:03:49,040 --> 00:03:52,920
how can something be
so ethereal, and yet be


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00:03:52,920 --> 00:03:55,560
so hard that it can drill through
solid rock?


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00:03:55,560 --> 00:03:58,200
Well, to answer that
we need to know about the


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00:03:58,200 --> 00:04:02,720
structure of the diamond - indeed
the structure of all matter itself.


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And the best theory we have to
describe matter, is quantum theory.


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Now, I understand why quantum theory
can seem a bit odd.


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It makes odd statements.


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It says, for example, that
things can be many places at once -


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in fact, technically it says
things can be in an infinite
number of places at once.


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00:04:22,320 --> 00:04:25,840
It says that subatomic
building blocks of our bodies


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are constantly shifting in response
to events that happened at the edge


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00:04:30,120 --> 00:04:34,400
of the known universe - a billion
light years somewhere over there.


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00:04:34,400 --> 00:04:40,720
Now, this is all true,
but that isn't a licence
to talk utter drivel.


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LAUGHTER


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00:04:42,040 --> 00:04:46,280
See, quantum theory might SEEM weird
and mysterious, but it describes the


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world with higher precision than the
laws of physics laid down by Newton,


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and it's one of the foundations of
our modern understanding of nature.


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It doesn't, therefore,
allow mystical healing,


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00:04:57,360 --> 00:05:01,640
or ESP or any other
manifestation of New Age woo-woo


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00:05:01,640 --> 00:05:03,600
into the pantheon of the possible.


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00:05:03,600 --> 00:05:07,120
Always remember, quantum theory
is physics, and physics is


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00:05:07,120 --> 00:05:11,760
usually done by people without
star signs tattooed on their bottom.


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00:05:11,760 --> 00:05:15,960
What makes quantum theory
a good scientific theory?


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Well, it makes predictions that
can be tested against experiment,


80
00:05:19,440 --> 00:05:24,080
and when we test those predictions
we find that they agree with
observation.


81
00:05:24,080 --> 00:05:29,120
This means quantum theory
is not wrong - it's a survivor,


82
00:05:29,120 --> 00:05:32,360
if you like, because it's been
put to the test over and over again,


83
00:05:32,360 --> 00:05:35,600
and consistently been found
to make correct predictions.


84
00:05:35,600 --> 00:05:38,160
If this changes,
then we'll search for a new theory -


85
00:05:38,160 --> 00:05:40,680
there are NO absolute truths
in science.


86
00:05:40,680 --> 00:05:43,720
This is how we make scientific
progress, and this is how


87
00:05:43,720 --> 00:05:47,200
everything in the world that
you take for granted was delivered.


88
00:05:47,200 --> 00:05:52,080
So, remember that however odd
it might seem, tonight


89
00:05:52,080 --> 00:05:56,400
I'm going to show you, hopefully,
that quantum theory works.


90
00:05:56,400 --> 00:06:01,000
So, I want to explain quantum theory
to you in the simplest way
that I can.


91
00:06:01,000 --> 00:06:03,800
Ultimately, I'll show you how
it gives us insight into the


92
00:06:03,800 --> 00:06:07,480
fundamental building blocks of the
universe, and explains the existence


93
00:06:07,480 --> 00:06:12,160
of some of the most spectacular
phenomena out there in deep space.


94
00:06:12,160 --> 00:06:16,320
And I'm going to do this now because
if I don't point wistfully
at the sky at least once,


95
00:06:16,320 --> 00:06:19,280
some of my viewers will get annoyed,
so there you go.


96
00:06:19,280 --> 00:06:23,240
That's the only mountain-top pose
I'm going to pull...


97
00:06:23,240 --> 00:06:25,160
LAUGHTER
..so, to begin...


98
00:06:29,240 --> 00:06:31,920
No helicopters tonight.


99
00:06:31,920 --> 00:06:36,120
To begin, let's zoom into
the heart of this diamond.


100
00:06:36,120 --> 00:06:39,360
What I've got here is a sequence
of actual photographs of, well,


101
00:06:39,360 --> 00:06:42,560
initially the surface of a diamond,
but these photographs


102
00:06:42,560 --> 00:06:47,160
have been taken by a series of
increasingly powerful microscopes.


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00:06:47,160 --> 00:06:49,840
So as we zoom in you see
that at first you're seeing a more


104
00:06:49,840 --> 00:06:53,240
detailed picture of the structure
of the surface of the diamond.


105
00:06:53,240 --> 00:06:55,760
But as we go right in,
you see that a regular pattern,


106
00:06:55,760 --> 00:06:58,080
a regular structure emerges,


107
00:06:58,080 --> 00:07:02,160
so this is an electron
microscope photograph of diamond.


108
00:07:02,160 --> 00:07:05,200
And what you're looking at here
actually are carbon atoms,


109
00:07:05,200 --> 00:07:07,760
individual atoms.


110
00:07:07,760 --> 00:07:11,520
You see that
they appear to be in a kind of a
dumbbell shape, and there's a space


111
00:07:11,520 --> 00:07:15,000
and another pair, because you're
looking at a two-dimensional image.


112
00:07:15,000 --> 00:07:17,480
But if you take that
to three dimensions


113
00:07:17,480 --> 00:07:21,360
and look at this - this is
the structure of diamond,


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00:07:21,360 --> 00:07:26,960
and what you can see is carbon atoms
surrounded by four other


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00:07:26,960 --> 00:07:30,640
carbon atoms, in a regular,
beautiful crystalline structure.


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00:07:30,640 --> 00:07:35,560
Now, in this diamond, this over-
a-million-pound piece of diamond,


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00:07:35,560 --> 00:07:39,800
there are something like 3 million
billion billion atoms,


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00:07:39,800 --> 00:07:45,400
and they are laid out in precisely
this beautifully simple way.


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00:07:45,400 --> 00:07:48,800
I should say, actually, this diamond
is as it was when it was found,


120
00:07:48,800 --> 00:07:52,840
so this hasn't been cut.
It was found in South Africa
well over 100 years ago,


121
00:07:52,840 --> 00:07:55,280
and it's 3 billion years old.


122
00:07:55,280 --> 00:07:57,720
And that structure,
its diamond shape -


123
00:07:57,720 --> 00:08:01,040
that's how it naturally appeared,
because its structure


124
00:08:01,040 --> 00:08:05,840
is like this, it's built out of
carbon atoms exactly like that.


125
00:08:05,840 --> 00:08:09,600
Carbon atoms can't be packed any
more tightly together than this.


126
00:08:09,600 --> 00:08:12,960
That's what makes diamonds
so tough, and allows them


127
00:08:12,960 --> 00:08:15,280
to cut through virtually anything.


128
00:08:15,280 --> 00:08:17,840
Which makes what I'm about to say
quite remarkable.


129
00:08:17,840 --> 00:08:21,080
See, the atoms that make up
this diamond -


130
00:08:21,080 --> 00:08:24,760
and pretty much everything else for
that matter - are virtually empty.


131
00:08:26,560 --> 00:08:30,960
Now, what do I mean by that?
Well, what is an atom?


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00:08:30,960 --> 00:08:34,200
Well, about 100 years ago now,
in the greatest city


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00:08:34,200 --> 00:08:38,640
known to civilization -
which is Manchester! -


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00:08:38,640 --> 00:08:39,960
APPLAUSE


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00:08:41,880 --> 00:08:45,680
..Ernest Rutherford discovered
that the atom consists of
an atomic nucleus,


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00:08:45,680 --> 00:08:49,640
which is made of particles
called protons and neutrons
tightly packed together,


137
00:08:49,640 --> 00:08:52,680
and a third kind of particle,


138
00:08:52,680 --> 00:08:57,480
called electrons, orbit somewhere or
exist somewhere around the outside.


139
00:08:57,480 --> 00:08:59,720
The nucleus protons
are positively charged,


140
00:08:59,720 --> 00:09:02,640
the neutrons are neutral,
so it has a positive charge.


141
00:09:02,640 --> 00:09:06,760
The electrons somewhere out here
have a negative charge,


142
00:09:06,760 --> 00:09:10,080
and as Faraday would have
talked about on this very stage


143
00:09:10,080 --> 00:09:12,800
just under 200 years ago,
there is a force that holds


144
00:09:12,800 --> 00:09:14,240
the electron to the nucleus,


145
00:09:14,240 --> 00:09:17,320
because they're both
electrically charged.


146
00:09:17,320 --> 00:09:20,920
So that's kind of a sketch,
a schematic view of the atom.


147
00:09:20,920 --> 00:09:24,040
We've known that now
for around a hundred years.


148
00:09:24,040 --> 00:09:25,920
Protons, neutrons and electrons.


149
00:09:25,920 --> 00:09:29,160
These three particles make up
not only the diamond,


150
00:09:29,160 --> 00:09:33,080
but everything we can touch,
every structure we can see.


151
00:09:33,080 --> 00:09:38,280
Everything is made up of
these same three absolutely
identical particles.


152
00:09:38,280 --> 00:09:41,880
So the richness of the natural
world, everything on planet Earth,


153
00:09:41,880 --> 00:09:45,640
everything we can see beyond
is described by a simple recipe


154
00:09:45,640 --> 00:09:49,600
that determines how these
simple particles combine together.


155
00:09:49,600 --> 00:09:54,640
Now, clearly physicists
don't call it a recipe,
we call that quantum theory.


156
00:09:54,640 --> 00:09:57,480
Now, one of the first great
challenges for quantum theory -


157
00:09:57,480 --> 00:10:01,200
indeed, one of the reasons
it was developed
at the turn of the 20th century,


158
00:10:01,200 --> 00:10:06,600
in Manchester and a few other
places - was to understand
precisely how these particles


159
00:10:06,600 --> 00:10:10,480
come together to create
this diamond, you, me
and everything else.


160
00:10:10,480 --> 00:10:13,800
And a hundred years after
its discovery, it still provides


161
00:10:13,800 --> 00:10:17,520
our best understanding
of the structure of matter.


162
00:10:17,520 --> 00:10:20,840
And admittedly, yes, it is still
a bit strange.


163
00:10:20,840 --> 00:10:27,120
Now, one of the particularly strange
things about it is the behaviour
of electrons inside atoms.


164
00:10:27,120 --> 00:10:29,600
See, these imperceptibly
tiny electrons spend


165
00:10:29,600 --> 00:10:33,120
the overwhelming majority
of their time in far distant clouds.


166
00:10:33,120 --> 00:10:38,120
So between the nucleus and the
electron there is a vast emptiness.


167
00:10:38,120 --> 00:10:42,600
If I were a nucleus,
and I perched on the edge
of the White Cliffs of Dover,


168
00:10:42,600 --> 00:10:45,360
then the fuzzy edge
of the electron cloud would be


169
00:10:45,360 --> 00:10:48,120
somewhere in the farms
of northern France.


170
00:10:48,120 --> 00:10:53,240
Looking out towards the electrons
I'd see nothing but empty,
interatomic space.


171
00:10:53,240 --> 00:10:56,440
So atoms are vast, and
they are empty. Actually about -


172
00:10:56,440 --> 00:10:58,920
I've got to count this
on my fingers -


173
00:10:58,920 --> 00:11:04,880
99.9999999999999% empty.


174
00:11:04,880 --> 00:11:09,120
That's 13 nines.
So, you buy this diamond,


175
00:11:09,120 --> 00:11:13,720
and you're buying about
a million quid's worth
of mainly empty space, and since


176
00:11:13,720 --> 00:11:19,720
everything is made of atoms, that
means you are vast and empty too.


177
00:11:19,720 --> 00:11:21,600
LAUGHTER


178
00:11:21,600 --> 00:11:24,800
Especially you...
No, I can't say that, can I?


179
00:11:24,800 --> 00:11:29,000
Never say that to a stand-up comic -
what am I doing?


180
00:11:29,000 --> 00:11:31,920
Anyway, if I squeezed all the space
out of all the atoms in all


181
00:11:31,920 --> 00:11:35,040
the people on the planet,
then you'd be able to fit the whole


182
00:11:35,040 --> 00:11:40,560
of humanity into that diamond,
and that's how empty matter is.


183
00:11:40,560 --> 00:11:44,440
So, understanding why atoms are
empty and yet so solid,


184
00:11:44,440 --> 00:11:48,120
why light can stream through
that diamond, and yet


185
00:11:48,120 --> 00:11:52,520
it sits nicely on the predominantly
empty cushion and the predominantly
empty floor,


186
00:11:52,520 --> 00:11:58,000
is therefore
a prerequisite to understanding the
structure of everything in nature.


187
00:11:58,000 --> 00:12:00,840
Now, you might have gathered that
the world inside an atom


188
00:12:00,840 --> 00:12:03,240
must be a strange place
where things don't behave


189
00:12:03,240 --> 00:12:07,080
much like they appear to behave
here in the macroscopic world.


190
00:12:07,080 --> 00:12:09,160
Well, there's one
historic experiment


191
00:12:09,160 --> 00:12:12,320
which contains everything you need
to know about the bizarre way


192
00:12:12,320 --> 00:12:17,800
that particles behave, and therefore
why atoms are the way that they are.


193
00:12:17,800 --> 00:12:20,040
I'm going to need
a helping hand for this,


194
00:12:20,040 --> 00:12:25,080
and I know that Sarah Millican
has volunteered kindly to help me.


195
00:12:25,080 --> 00:12:28,680
Where's Sarah? I'm here. Hello.
So Sarah - would you mind...?


196
00:12:38,560 --> 00:12:42,160
Thanks, Sarah. Did you do
a science degree, by the way?


197
00:12:42,160 --> 00:12:45,080
No. I've already been asked
that by somebody in the audience -


198
00:12:45,080 --> 00:12:46,960
"Did you study physics?"


199
00:12:46,960 --> 00:12:50,560
No, I just sort of gave up
after GCSE - is that a problem,


200
00:12:50,560 --> 00:12:53,400
should I go back to me seat?
LAUGHTER


201
00:12:53,400 --> 00:12:56,320
Any other volunteers(?) No...
Only got a C!


202
00:12:56,320 --> 00:13:02,640
So you may or may not have heard of
the double slit experiment, it's
something every physics student...


203
00:13:02,640 --> 00:13:05,560
I've heard of it, but it was
something different. Was it(?)


204
00:13:05,560 --> 00:13:08,600
Well, we're going to...
LAUGHTER


205
00:13:08,600 --> 00:13:13,680
Every physicist is taught this
the moment they step through
the doors of a university.


206
00:13:13,680 --> 00:13:18,040
It's simple, and it demonstrates
the paradoxical world
of quantum particles.


207
00:13:18,040 --> 00:13:22,280
So first of all we're going to
do it - we're going to do it twice,
or even three times.


208
00:13:22,280 --> 00:13:27,360
So I'm going to give you
this bucket of sand,
which is quite heavy actually.


209
00:13:27,360 --> 00:13:32,240
These are particles of sand,
little bits of sand.
They're probably your picture,


210
00:13:32,240 --> 00:13:37,440
I suppose, of what a particle might
be, a little piece of matter.


211
00:13:37,440 --> 00:13:40,000
So what I'm going to ask you to do
is just pour the sand


212
00:13:40,000 --> 00:13:42,880
onto this piece of board,
which has got two slits cut in it,


213
00:13:42,880 --> 00:13:45,200
and I suppose before I do it...


214
00:13:45,200 --> 00:13:47,160
Oh, you bugger!
It's a bit heavy! It is.


215
00:13:47,160 --> 00:13:50,240
You pour it first, then I'll ask
you what you think might happen.


216
00:13:50,240 --> 00:13:54,440
Yeah, let's chat for a while,
while I'm holding the bucket(!)


217
00:13:54,440 --> 00:13:57,960
It weighs a ton, doesn't it?
So just pour it through the slits...


218
00:13:57,960 --> 00:14:00,560
Now, what do you think
is going to happen?


219
00:14:00,560 --> 00:14:05,800
So we're just pouring
particles of sand over the slits.


220
00:14:05,800 --> 00:14:07,120
Just keep going...


221
00:14:09,240 --> 00:14:12,840
So there we are.
That'll do, I think.


222
00:14:12,840 --> 00:14:17,480
So if I remove that...
what does that remind you of?


223
00:14:17,480 --> 00:14:19,880
LAUGHTER


224
00:14:19,880 --> 00:14:22,680
I feel like smacking it -
does that help?


225
00:14:22,680 --> 00:14:27,680
Pour that sand into there.
So that's probably pretty much...


226
00:14:27,680 --> 00:14:30,240
There you go,
you can put it down now. Thank you!


227
00:14:30,240 --> 00:14:34,440
That's probably pretty much,
I suppose, what you expected
would happen.


228
00:14:34,440 --> 00:14:36,560
The sand has just fallen
through the slits,


229
00:14:36,560 --> 00:14:39,240
and beneath each slit
there's a bigger pile of sand.


230
00:14:39,240 --> 00:14:42,200
Particles fall through slits -
pretty obvious.


231
00:14:42,200 --> 00:14:46,640
But...this is a picture
of real data.


232
00:14:46,640 --> 00:14:48,720
So this is real experimental data,


233
00:14:48,720 --> 00:14:52,480
of electrons essentially being
poured through two slits,
so it's electrons


234
00:14:52,480 --> 00:14:57,160
being fired at two slits, and then
there's a screen there, and so what


235
00:14:57,160 --> 00:15:00,200
you're seeing are just piles
of electrons, so the white spots


236
00:15:00,200 --> 00:15:02,560
really are where electrons
hit the screens -


237
00:15:02,560 --> 00:15:04,680
there's a pile,
and then there's nothing,


238
00:15:04,680 --> 00:15:07,760
and then there's a pile,
and then there's nothing...


239
00:15:07,760 --> 00:15:10,920
Looks nothing like that.
But the experiment was the same -


240
00:15:10,920 --> 00:15:14,560
it really is electrons
being poured through two slits


241
00:15:14,560 --> 00:15:17,720
onto a screen,
and you get that strange pattern.


242
00:15:18,880 --> 00:15:24,840
So, let me show you this,
which is a different version of
the same experiment.


243
00:15:24,840 --> 00:15:29,680
Now, this is a tank of water,
so there's some water in there,


244
00:15:29,680 --> 00:15:33,720
and as you can see there's just
a bar that's vibrating up and down,


245
00:15:33,720 --> 00:15:38,040
and then there's two slits. Yeah.
So you can see the two slits there.


246
00:15:38,040 --> 00:15:44,400
And if you come round here...
you can see the screen here.


247
00:15:44,400 --> 00:15:47,680
So there's the two slits,
and these are the waves of water.


248
00:15:47,680 --> 00:15:50,360
So there's a flat wave of water
hitting the two slits,


249
00:15:50,360 --> 00:15:52,160
and then coming through the slits.


250
00:15:52,160 --> 00:15:54,720
And do you see that
there are waves here,


251
00:15:54,720 --> 00:15:58,440
but here, there's kind of an area
where the water's flat. Yeah.


252
00:15:58,440 --> 00:16:00,080
Then here there are waves,


253
00:16:00,080 --> 00:16:02,280
then here's an area
where the water's flat,


254
00:16:02,280 --> 00:16:05,120
then here are waves, here's
an area where the water's flat.


255
00:16:05,120 --> 00:16:08,480
So if I were to, I could sketch it
actually on the blackboard.


256
00:16:08,480 --> 00:16:10,440
If I draw that...


257
00:16:14,200 --> 00:16:17,200
We've got those two slits, like
that, which you can see there.


258
00:16:17,240 --> 00:16:20,520
and we've got the water wave
coming through


259
00:16:20,520 --> 00:16:22,480
and you can sort of see
that the waves


260
00:16:22,480 --> 00:16:25,960
when they go through the slits
spread out like that.


261
00:16:25,960 --> 00:16:30,080
And I hope you can see that
at the front, you're seeing


262
00:16:30,080 --> 00:16:33,080
a kind of a place where there's no
waves and then some waves


263
00:16:33,080 --> 00:16:35,640
and then there's a place where
there's no waves


264
00:16:35,640 --> 00:16:38,520
and then there's some waves
and a place where there's no waves.


265
00:16:38,520 --> 00:16:40,520
You see that pattern
on the front. Yes.


266
00:16:40,520 --> 00:16:43,960
So if you were to draw kind of
a detector along there,


267
00:16:43,960 --> 00:16:46,480
then you'd see that, right,


268
00:16:46,480 --> 00:16:50,920
because here you'd see nothing,
no waves no electrons.


269
00:16:50,920 --> 00:16:54,080
Here you'd see the electrons, here
no waves, here waves, here no waves.


270
00:16:54,080 --> 00:16:57,760
So what are we to infer
about electrons?


271
00:17:00,000 --> 00:17:03,400
Have you not done your homework
today, is that what it is?


272
00:17:03,400 --> 00:17:06,560
I mean this is just the experimental
data... This was first done,


273
00:17:06,560 --> 00:17:10,720
by the way, in the 1920s
and it was a shock when it was seen,


274
00:17:10,720 --> 00:17:12,200
but the inference is...?


275
00:17:15,280 --> 00:17:18,920
That looks like...that.


276
00:17:18,920 --> 00:17:21,800
This could be a long game.
It's the same pattern!


277
00:17:21,800 --> 00:17:23,240
LAUGHTER


278
00:17:25,040 --> 00:17:27,960
GCSE grade C, remember.


279
00:17:29,960 --> 00:17:31,840
This pattern here...


280
00:17:31,840 --> 00:17:34,720
What do you think...?!


281
00:17:34,720 --> 00:17:36,280
You could just tell us.


282
00:17:38,440 --> 00:17:43,200
So, the electrons are behaving
more like the waves in the tank


283
00:17:43,200 --> 00:17:47,960
on the water waves
and that's a classic pattern you see


284
00:17:47,960 --> 00:17:50,240
when you get waves
passing through slits.


285
00:17:50,240 --> 00:17:53,800
Rather than this, which I suppose
is what you might have expected


286
00:17:53,800 --> 00:17:57,920
electrons to do, because you might
think of electrons as being
little grains of sand.


287
00:17:57,920 --> 00:18:00,160
But actually, they don't behave
like little grains of sand.


288
00:18:00,160 --> 00:18:04,480
That experiment tells us they behave
more like waves and water.


289
00:18:04,480 --> 00:18:05,800
Exactly!


290
00:18:05,800 --> 00:18:07,800
LAUGHTER AND APPLAUSE


291
00:18:09,040 --> 00:18:10,760
Thank you.


292
00:18:17,680 --> 00:18:19,760
Thanks, Sarah!


293
00:18:19,760 --> 00:18:23,960
Thanks, Sarah. That's...
Yeah, physics!


294
00:18:26,480 --> 00:18:27,880
Well...


295
00:18:27,880 --> 00:18:31,640
this might all be a bit confusing,
as you've just seen,


296
00:18:31,640 --> 00:18:37,440
but if you remember nothing else,
remember this - the double slit
experiment reveals something


297
00:18:37,440 --> 00:18:42,720
fundamental about particles like
the electrons inside the diamond.


298
00:18:42,720 --> 00:18:45,000
Sometimes
they behave like particles,


299
00:18:45,000 --> 00:18:50,440
but sometimes experiment says
that they behave like waves.


300
00:18:50,440 --> 00:18:53,040
Now there's a deep explanation
for this


301
00:18:53,040 --> 00:18:55,400
and I'm going to get to that
a little bit later on,


302
00:18:55,400 --> 00:18:59,960
but for now all we need to remember
is that electrons behave like waves,


303
00:18:59,960 --> 00:19:02,960
and this is the key to understanding
the emptiness of atoms.


304
00:19:04,200 --> 00:19:07,480
Simple? I hope so.
So let's clear away the water tank.


305
00:19:14,800 --> 00:19:18,600
So, we've understood that electrons
exhibit wavy behaviour,


306
00:19:18,600 --> 00:19:22,040
but how does that explain
the emptiness of atoms?


307
00:19:22,040 --> 00:19:25,800
Well, I need some volunteers now
and I know that Simon Pegg


308
00:19:25,800 --> 00:19:29,920
and Jim Al-Khalili have kindly
volunteered, so would you both
like to come down?


309
00:19:29,920 --> 00:19:31,200
APPLAUSE


310
00:19:46,960 --> 00:19:48,440
Have you seen him, there?


311
00:19:48,440 --> 00:19:49,720
Hello!


312
00:19:51,080 --> 00:19:55,360
He's got an earpiece in
he's watching really carefully.


313
00:19:55,360 --> 00:20:00,920
So, I've got an experiment for you
both to do involving a spring


314
00:20:00,920 --> 00:20:03,560
and your wrists,


315
00:20:03,560 --> 00:20:06,160
so...


316
00:20:06,160 --> 00:20:07,560
What I'd like you to do


317
00:20:07,560 --> 00:20:13,040
is stretch the string a little bit
as far away as you can.


318
00:20:13,040 --> 00:20:18,560
Now what I want you to do is start
gently oscillating the spring.
Very gently.


319
00:20:18,560 --> 00:20:21,840
Both of us? Yeah.
You'll see what happens.


320
00:20:21,840 --> 00:20:23,840
Up and down, or longitudinally?


321
00:20:23,840 --> 00:20:26,720
ALL: Ooh!


322
00:20:26,720 --> 00:20:28,040
Shall I sit back down?


323
00:20:29,880 --> 00:20:33,080
Up and down is better. Up and down.


324
00:20:33,080 --> 00:20:34,800
So just a bit more...


325
00:20:36,760 --> 00:20:38,920
There you go... And a bit more.


326
00:20:38,920 --> 00:20:42,920
There you go. So what you're doing
is vibrating the spring.


327
00:20:42,920 --> 00:20:44,200
Are you going to jump in?


328
00:20:44,200 --> 00:20:47,080
LAUGHTER


329
00:20:48,080 --> 00:20:50,680
It looks quite painful.


330
00:20:50,680 --> 00:20:54,320
So what you're doing now,
just gently vibrating the string,


331
00:20:54,320 --> 00:20:57,440
you notice that it's vibrating
in a very particular way.


332
00:20:57,440 --> 00:21:00,680
Cos you're holding it still there
and you're holding it still there,


333
00:21:00,680 --> 00:21:03,680
so it's trapped -
it's confined, in a sense.


334
00:21:03,680 --> 00:21:07,360
So what you can see is there's only
one bit which is moving


335
00:21:07,360 --> 00:21:10,440
with the maximum amplitude
if you like, the maximum wave


336
00:21:10,440 --> 00:21:12,560
and it's in the middle there.


337
00:21:12,560 --> 00:21:15,400
So that's called a standing wave.
It's called a standing wave


338
00:21:15,400 --> 00:21:16,680
because it's confined.


339
00:21:16,680 --> 00:21:18,880
It's doing nothing, really -
it's vibrating up and down.


340
00:21:18,880 --> 00:21:22,040
It's not a wave as you might usually
expect it.


341
00:21:22,040 --> 00:21:24,560
Now, if you give it a bit more
wrist action...


342
00:21:24,560 --> 00:21:26,840
GIGGLING


343
00:21:27,640 --> 00:21:30,440
Look at that one - now, that...


344
00:21:30,440 --> 00:21:33,640
THAT is the next standing wave up,


345
00:21:33,640 --> 00:21:37,320
so there is a transition from the
one where we're just moving here -


346
00:21:37,320 --> 00:21:40,480
this one's got three
stationary points.


347
00:21:40,480 --> 00:21:44,840
I lost me stroke...
Don't get carried away.
Sorry, sorry.


348
00:21:45,960 --> 00:21:48,440
Wait, wait, wait -


349
00:21:48,440 --> 00:21:50,880
this has never
happened to me before!


350
00:21:50,880 --> 00:21:54,080
LAUGHTER AND APPLAUSE


351
00:21:55,560 --> 00:21:58,920
There - look at that -
now there's three stationary bits -


352
00:21:58,920 --> 00:22:02,320
there's one stationary there,
one stationary bit there,
one stationary bit there


353
00:22:02,320 --> 00:22:05,320
and the amplitude - the maximum
amplitude is there and there.


354
00:22:05,320 --> 00:22:08,320
Now, you can get another one
going...


355
00:22:08,320 --> 00:22:11,520
if you really try,
which is the third one.


356
00:22:11,520 --> 00:22:12,800
There it is! No!


357
00:22:12,800 --> 00:22:14,280
CHEERING


358
00:22:16,920 --> 00:22:18,920
Look at that.


359
00:22:22,880 --> 00:22:24,680
Yes, yes, yes!


360
00:22:24,680 --> 00:22:27,400
Can you see? That's got two
stationary points -


361
00:22:27,400 --> 00:22:31,040
one there and one there.
That's a brilliant...
Oh, it's gone again!


362
00:22:31,040 --> 00:22:34,240
I can see... Hang on...
There, there, there!


363
00:22:34,240 --> 00:22:37,800
Two stationary points...
1, 2, 3, 4 stationary points.


364
00:22:37,800 --> 00:22:40,480
I can see why you've got no air!
Here it is! There it is!


365
00:22:44,800 --> 00:22:46,960
Ah, that's better now.
There's the fourth one.


366
00:22:46,960 --> 00:22:48,680
So, you...


367
00:22:48,680 --> 00:22:50,440
You carry on.


368
00:22:50,440 --> 00:22:52,000
Now it feels like someone else!


369
00:22:52,000 --> 00:22:54,280
It's back! Ah, it's gone!


370
00:22:57,240 --> 00:23:00,280
So if I just sketch... Carry on!


371
00:23:00,280 --> 00:23:01,800
There we go - yes!


372
00:23:01,800 --> 00:23:04,200
Brian, Brian, Brian, Brian!
Yeah, yeah, yeah!


373
00:23:04,200 --> 00:23:07,120
APPLAUSE


374
00:23:15,040 --> 00:23:16,520
Perfect.


375
00:23:16,520 --> 00:23:19,200
1, 2, 3, 4, 5 - all right,
you can stop now.


376
00:23:21,080 --> 00:23:23,320
Good practice for later!


377
00:23:25,280 --> 00:23:27,440
Thank you very much! Thanks.


378
00:23:27,440 --> 00:23:28,800
APPLAUSE


379
00:23:33,000 --> 00:23:35,640
I sketched what you saw there.


380
00:23:35,640 --> 00:23:37,600
You saw that one very clearly
which was this wave


381
00:23:37,600 --> 00:23:39,440
where there were just two
stationary points


382
00:23:39,440 --> 00:23:42,080
which were at the ends
and then you saw this one,


383
00:23:42,080 --> 00:23:45,040
where there were three
stationary points.


384
00:23:45,040 --> 00:23:47,760
And then you saw this one where
there were four stationary points


385
00:23:47,760 --> 00:23:51,240
and actually, because you were...
That's the best
I've ever seen it done,


386
00:23:51,240 --> 00:23:53,600
there was one with about five,
I think, or even six. (Yes!)


387
00:23:53,600 --> 00:23:55,880
So, you saw that...


388
00:23:55,880 --> 00:23:58,160
there were only certain waves...


389
00:23:58,160 --> 00:24:01,200
That the spring could vibrate,
certain waves it could vibrate


390
00:24:01,200 --> 00:24:06,680
and the reason it behaved like that
is because it was trapped
at both ends.


391
00:24:06,680 --> 00:24:10,000
So this is what you would call,
physicists would call


392
00:24:10,000 --> 00:24:13,320
standing waves and you saw them
appear on that spring.


393
00:24:14,920 --> 00:24:17,440
Now, what has that got to do
with empty atoms?


394
00:24:17,440 --> 00:24:22,320
Well, just as this wave was
trapped between Jim and Simon,


395
00:24:22,320 --> 00:24:24,320
electrons are trapped inside atoms.


396
00:24:24,320 --> 00:24:29,000
The positive electric charge
of the nucleus effectively traps


397
00:24:29,000 --> 00:24:33,200
the negatively-charged electron
inside an atomic-sized box.


398
00:24:33,200 --> 00:24:34,680
And when an electron is trapped,


399
00:24:34,680 --> 00:24:37,680
just as the spring was trapped
between Jim and Simon,


400
00:24:37,680 --> 00:24:41,960
it exhibits the same kind of
wave-like behaviour as the spring.


401
00:24:41,960 --> 00:24:46,560
So now we're getting closer
to understanding what's happening
inside an atom.


402
00:24:46,560 --> 00:24:52,160
But what do standing electron waves
around a nucleus actually represent?


403
00:24:52,160 --> 00:24:55,560
Well, the clue is that Jim and Simon
had to put more energy in


404
00:24:55,560 --> 00:24:59,040
to switch from one standing wave
to another.


405
00:24:59,040 --> 00:25:03,920
So it's tempting to think of those
electron standing waves


406
00:25:03,920 --> 00:25:08,000
as waves with different energies
inside an atom,


407
00:25:08,000 --> 00:25:11,280
waves that the different energies,
the electron can have, if you like


408
00:25:11,280 --> 00:25:16,240
when it's confined around a nucleus
and this turns out to be correct.


409
00:25:16,240 --> 00:25:19,600
But, just as there were only certain
standing waves on the spring,


410
00:25:19,600 --> 00:25:24,120
inside an atom, there are only
certain energies that electrons
can have.


411
00:25:24,120 --> 00:25:26,600
Now, quantum theory allows
physicists to calculate the shape


412
00:25:26,600 --> 00:25:32,120
of the waves and therefore
the allowed energies the electrons
can have inside the atom.


413
00:25:32,120 --> 00:25:35,560
And when you do the calculations,
you find the lowest energy 'wave',


414
00:25:35,560 --> 00:25:40,360
if you like, so I suppose
this standing wave here


415
00:25:40,360 --> 00:25:42,680
that can fit around the nucleus


416
00:25:42,680 --> 00:25:46,000
has a wavelength of around
3 x 10­-10 metres.


417
00:25:46,000 --> 00:25:49,880
Now, let me just write that down,
because you might not be
familiar with the notation.


418
00:25:49,880 --> 00:25:53,640
It's 1, 2, 3, 4,
5, 6, 7, 8, 9...


419
00:25:53,640 --> 00:25:58,560
0.0000000003 of a metre which sounds


420
00:25:58,560 --> 00:26:03,040
unimaginably small, but it's
enormous compared to the size


421
00:26:03,040 --> 00:26:07,240
of the nucleus. It's actually about
a quarter of a million times larger.


422
00:26:07,240 --> 00:26:11,600
So that is why atoms are so big
and yet so empty.


423
00:26:11,600 --> 00:26:14,000
It's because electrons
trapped around a nucleus


424
00:26:14,000 --> 00:26:17,840
behave like waves - in this case
standing waves - and there has to be


425
00:26:17,840 --> 00:26:22,440
enough room to fit an electron wave
around the atomic nucleus.


426
00:26:22,440 --> 00:26:25,480
But that doesn't answer
a very important question.


427
00:26:25,480 --> 00:26:28,280
Now, we've shown why atoms
are empty,


428
00:26:28,280 --> 00:26:29,960
But we haven't yet explained


429
00:26:29,960 --> 00:26:34,400
how they become so strongly
bound together that they can create
solid objects


430
00:26:34,400 --> 00:26:37,520
like our beautiful
million-pound diamond here.


431
00:26:37,520 --> 00:26:44,120
Answer that, and we explain
the structure of everything
we see in the universe.


432
00:26:49,640 --> 00:26:53,680
The early years of quantum theory
were dominated by boy wonders,


433
00:26:53,680 --> 00:26:56,920
people actually half my age,
believe it or not.


434
00:26:56,920 --> 00:27:00,600
So much so, that it
became nicknamed "Knabenphysik",


435
00:27:00,600 --> 00:27:03,480
which translated from German means
"boy physics".


436
00:27:03,480 --> 00:27:07,280
The key discovery was made by a man
called Wolfgang Pauli.


437
00:27:07,280 --> 00:27:12,600
Pauli published his first paper
on Einstein's Theory of General
Relativity when he was 18.


438
00:27:12,600 --> 00:27:17,000
And his great contribution
to quantum theory was made
when he was only 24.


439
00:27:17,000 --> 00:27:20,120
It's known as
the Exclusion Principle.


440
00:27:20,120 --> 00:27:24,680
We've seen that electrons
can only exist in certain energy
levels around the nucleus.


441
00:27:24,680 --> 00:27:29,600
These energy levels, associated
with the different standing waves.


442
00:27:29,600 --> 00:27:35,400
Those energy levels correspond
to standing waves that can fit
in the atomic size box.


443
00:27:35,400 --> 00:27:37,880
But the key point
that Pauli realised


444
00:27:37,880 --> 00:27:42,480
is that electrons can't all simply
inhabit the lowest energy level.


445
00:27:42,480 --> 00:27:45,720
Now, to a physicist,
this should look a bit odd.


446
00:27:45,720 --> 00:27:48,400
I mean, take this apple,
for example.


447
00:27:48,400 --> 00:27:51,160
If I lift the apple up,
then I have to do work.


448
00:27:51,160 --> 00:27:52,800
I give it energy to lift it up.


449
00:27:52,800 --> 00:27:55,560
And if I let go,
so I don't support it any more,


450
00:27:55,560 --> 00:27:58,280
then it falls to the ground.


451
00:27:58,280 --> 00:28:00,760
Now, the explanation of that,
for a physicist,


452
00:28:00,760 --> 00:28:04,400
is that the apple is falling
into a lower-energy state.


453
00:28:04,400 --> 00:28:07,880
Nature doesn't like to be
in high-energy states.


454
00:28:07,880 --> 00:28:13,000
It wants to cascade down
into the lowest energy
configuration that it can.


455
00:28:13,000 --> 00:28:19,600
But the surprising thing
is that electrons don't all live in
that lowest energy level in an atom.


456
00:28:19,600 --> 00:28:24,640
It turns out they're
forbidden from doing so
by an unbreakable law of nature.


457
00:28:24,640 --> 00:28:28,720
That law is called
the Pauli Exclusion Principle.


458
00:28:28,720 --> 00:28:30,800
It's kind of like all of you
sitting in these rows here.


459
00:28:30,800 --> 00:28:34,840
You aren't allowed to all come down
to the front row.


460
00:28:34,840 --> 00:28:38,760
You can't all squash
into the front seats,
because there isn't room for you.


461
00:28:38,760 --> 00:28:43,520
Electrons don't all occupy the
lowest energy slots around an atom.


462
00:28:43,520 --> 00:28:48,000
Instead, they fill each level up
in order of increasing energy.


463
00:28:48,000 --> 00:28:49,600
This might sound meaningless,


464
00:28:49,600 --> 00:28:51,280
maybe it sounds a bit abstract.


465
00:28:51,280 --> 00:28:52,880
But let me tell you that it isn't.


466
00:28:52,880 --> 00:28:56,800
You see, Pauli's simple quantum rule
is profoundly important.


467
00:28:56,800 --> 00:29:00,240
In fact, it's the key
to understanding chemistry.


468
00:29:00,240 --> 00:29:02,920
But don't take my word for it.
Time for another volunteer.


469
00:29:02,920 --> 00:29:07,360
I know that James May kindly
volunteered to take part in this.


470
00:29:07,360 --> 00:29:11,640
He looks very worried, so maybe he
was never asked! But anyway, James.


471
00:29:22,960 --> 00:29:25,800
Now this is doubly amusing for me,


472
00:29:25,800 --> 00:29:29,200
cos I know that you know exactly
what's going to happen


473
00:29:29,200 --> 00:29:31,360
because there's a canister of
hydrogen gas there


474
00:29:31,360 --> 00:29:34,160
and I know you're a keen aviator,
so...


475
00:29:34,160 --> 00:29:37,400
You think about the story of the
Hindenburg... Mmm! ..while I...


476
00:29:37,400 --> 00:29:42,640
Which was unhappy, wasn't it?
Oh, I get to wear the goggles?
You might have to wear the goggles.


477
00:29:42,640 --> 00:29:47,040
It's only a small safety thing,
because it went wrong in rehearsal.


478
00:29:47,040 --> 00:29:52,280
So what we're going to do is
encourage a small chemical reaction
to happen. What we're doing


479
00:29:52,280 --> 00:29:55,240
is bubbling hydrogen through...
Hydrogen gas through this, um...


480
00:29:55,240 --> 00:29:59,360
LAUGHTER
..through this soap, here. Mmm.


481
00:29:59,360 --> 00:30:04,120
What I'd like you to do...
Actually, just wet your hands first.
Just because it's a safety thing.


482
00:30:04,120 --> 00:30:05,760
It stops your hands catching fire.


483
00:30:05,760 --> 00:30:09,200
It actually... Perhaps
roll your sleeves up a little bit.


484
00:30:09,200 --> 00:30:11,920
You'll be all right.
I'm sure you'll be fine.


485
00:30:11,920 --> 00:30:16,600
So I'd like you to get - grab -
some of that of that hydrogen
in the soap bubbles.


486
00:30:17,640 --> 00:30:19,440
Um...


487
00:30:20,920 --> 00:30:23,560
How's that? Don't look...


488
00:30:23,560 --> 00:30:25,400
at what I'm doing.


489
00:30:25,400 --> 00:30:33,240
What I'm going to do
is I'm going to encourage
a chemical reaction to happen...


490
00:30:33,240 --> 00:30:34,920
from over here.


491
00:30:34,920 --> 00:30:36,200
LAUGHTER


492
00:30:38,960 --> 00:30:40,480
Whoa!


493
00:30:40,480 --> 00:30:41,960
Ow! You all right?


494
00:30:41,960 --> 00:30:45,160
LAUGHTER AND APPLAUSE


495
00:30:45,160 --> 00:30:47,160
LAUGHTER AND APPLAUSE DROWNS SPEECH


496
00:30:50,960 --> 00:30:54,200
Thank you very much for putting
yourself at great risk!


497
00:31:01,800 --> 00:31:06,560
Thanks, James. That actually was a
lot more fire than I was expecting!
Sorry about that.


498
00:31:06,560 --> 00:31:08,200
So what happened there?


499
00:31:08,200 --> 00:31:12,800
What we did was we bubbled
hydrogen gas into these bubbles.


500
00:31:12,800 --> 00:31:17,080
James held them, and then I just
gave them a little kick of energy


501
00:31:17,080 --> 00:31:20,760
which encouraged them
to react with oxygen in the air.


502
00:31:20,760 --> 00:31:23,680
Now if draw the energy levels
of oxygen,


503
00:31:23,680 --> 00:31:25,920
then they look something like that.


504
00:31:25,920 --> 00:31:30,080
They don't quite look as neat as
when I drew the standing waves on
the spring.


505
00:31:30,080 --> 00:31:33,160
That's really because of the shape
of the atomic box,


506
00:31:33,160 --> 00:31:36,720
the shape of the box
surrounding the oxygen nucleus.


507
00:31:36,720 --> 00:31:41,520
Now oxygen has eight protons
and eight neutrons in its nucleus,


508
00:31:41,520 --> 00:31:45,520
which means it needs eight electrons
filling up its energy levels.


509
00:31:45,520 --> 00:31:49,160
And the electrons fill up
the energy levels like that.


510
00:31:51,080 --> 00:31:53,560
So you get three full energy levels


511
00:31:53,560 --> 00:31:57,680
and two energy levels
with a single electron in them.


512
00:31:57,680 --> 00:32:04,280
Now that kind of makes oxygen
a voracious consumer of electrons.


513
00:32:04,280 --> 00:32:06,080
It would like, if it can -


514
00:32:06,080 --> 00:32:09,760
it's energetically favourable for it
to fill up those missing gaps.


515
00:32:09,760 --> 00:32:13,640
Hydrogen has one proton,


516
00:32:13,640 --> 00:32:17,400
and so it has one electron sat
there in its lowest energy level.


517
00:32:17,400 --> 00:32:21,720
Again, it has a space there.
It would also like to fill that up.


518
00:32:21,720 --> 00:32:26,040
So what happens, when I give it
a little kick with this splint,


519
00:32:26,040 --> 00:32:31,240
is that the hydrogen is encouraged
to react with the with the oxygen.


520
00:32:31,240 --> 00:32:35,000
It's energetically favourable for it
to share its electron.


521
00:32:35,000 --> 00:32:36,600
So the oxygen shares
with the hydrogen,


522
00:32:36,600 --> 00:32:38,400
the hydrogen shares with the oxygen.


523
00:32:38,400 --> 00:32:43,320
There are two gaps, so you get two
hydrogens which would like to react.


524
00:32:43,320 --> 00:32:47,840
In doing so,
the rearrangement of those electrons
in the energy levels


525
00:32:47,840 --> 00:32:50,760
is such a great giver of energy
that you saw a flash.


526
00:32:50,760 --> 00:32:55,360
All that flash that you saw,
the little explosion,
was energy being released


527
00:32:55,360 --> 00:33:00,200
when the electrons in the hydrogen
and the oxygen reconfigure -


528
00:33:00,200 --> 00:33:02,520
just like the apple reconfigured
itself


529
00:33:02,520 --> 00:33:06,040
by dropping to the ground
to get into the lowest energy state.


530
00:33:06,040 --> 00:33:10,480
Two hydrogens, one oxygen.
What does that make?


531
00:33:10,480 --> 00:33:11,560
MAN: Water.


532
00:33:11,560 --> 00:33:14,240
ALL: Water! Right!


533
00:33:14,240 --> 00:33:17,640
H2O.


534
00:33:17,640 --> 00:33:22,560
So that is essentially the reason
why we get chemistry.


535
00:33:22,560 --> 00:33:24,560
Without Pauli's Exclusion Principle,


536
00:33:24,560 --> 00:33:30,400
all the electrons would crowd down
into the lowest energy level
and there'd be no chemistry.


537
00:33:30,400 --> 00:33:32,680
Which is worse than it sounds...


538
00:33:32,680 --> 00:33:34,040
LAUGHTER


539
00:33:37,800 --> 00:33:42,520
..because without chemistry,
we'd have no magnificent structures
in the universe,


540
00:33:42,520 --> 00:33:47,000
like water, diamonds, or indeed,
any of you.


541
00:33:47,000 --> 00:33:51,000
Now, there's another consequence
of the exclusion principle


542
00:33:51,000 --> 00:33:53,360
that wasn't proved until 1967,


543
00:33:53,360 --> 00:33:55,360
just one year before I was born.


544
00:33:55,360 --> 00:33:59,560
Pauli's principle says
that identical electrons


545
00:33:59,560 --> 00:34:01,240
can't occupy the same energy level.


546
00:34:01,240 --> 00:34:03,480
This is an absolute requirement.


547
00:34:03,480 --> 00:34:07,880
So it also means that electrons
will avoid each other at all costs.


548
00:34:07,880 --> 00:34:11,120
And that, it was proved,
is the actual reason


549
00:34:11,120 --> 00:34:15,000
that I don't fall through the empty
atoms that make up the floor.


550
00:34:15,000 --> 00:34:21,320
That's ultimately what gives
the illusion of solidity
to the empty world of atoms.


551
00:34:21,320 --> 00:34:24,480
And if you think a little bit more
deeply about it,


552
00:34:24,480 --> 00:34:27,880
then this throws up a bewildering
conclusion, and it's this.


553
00:34:27,880 --> 00:34:33,080
The Pauli Exclusion Principle
applies to EVERY electron
in the universe.


554
00:34:33,080 --> 00:34:36,880
Not just every electron in
a single atom, or a single molecule.


555
00:34:36,880 --> 00:34:39,040
And this leads to a bizarre
conclusion.


556
00:34:39,040 --> 00:34:41,000
The particles that make up
this diamond


557
00:34:41,000 --> 00:34:43,680
are in communication
with particles everywhere.


558
00:34:45,280 --> 00:34:46,520
Inside all of you,


559
00:34:46,520 --> 00:34:50,840
and inside the atoms in the furthest
corners of the universe.


560
00:34:50,840 --> 00:34:54,200
Let me explain that a little bit
more. The Pauli Exclusion Principle


561
00:34:54,200 --> 00:34:58,640
says no identical electrons can be
in precisely the same energy level.


562
00:34:58,640 --> 00:35:00,920
What if you have more than one atom?


563
00:35:00,920 --> 00:35:03,200
For example, in this diamond


564
00:35:03,200 --> 00:35:07,160
there are 3 million billion billion
carbon atoms.


565
00:35:07,160 --> 00:35:10,720
So this is a diamond-size box
of carbon atoms.


566
00:35:10,720 --> 00:35:14,080
And the Pauli Exclusion Principle
still applies.


567
00:35:14,080 --> 00:35:16,040
So all the energy levels


568
00:35:16,040 --> 00:35:18,280
in all those 3 million
billion billion atoms


569
00:35:18,280 --> 00:35:21,400
have to be slightly different
in order to ensure that


570
00:35:21,400 --> 00:35:25,680
none of the electrons sit in
precisely the same energy level.


571
00:35:25,680 --> 00:35:30,920
Pauli's principle holds fast. But
it doesn't stop with the diamond.


572
00:35:30,920 --> 00:35:35,720
See, you can think of the whole
universe as a vast box of atoms,


573
00:35:35,720 --> 00:35:38,360
with countless numbers
of energy levels


574
00:35:38,360 --> 00:35:42,080
all filled by countless numbers
of electrons.


575
00:35:42,080 --> 00:35:46,480
So here's the amazing thing - the
exclusion principle still applies,


576
00:35:46,480 --> 00:35:50,680
so none of the electrons in the
universe can sit in precisely


577
00:35:50,680 --> 00:35:52,920
the same energy level.


578
00:35:52,920 --> 00:35:54,960
But that must mean
something very odd.


579
00:35:54,960 --> 00:35:57,320
See, let me take this diamond,
and let me just


580
00:35:57,320 --> 00:35:59,680
heat it up a little bit
between my hands.


581
00:35:59,680 --> 00:36:01,280
Just gently warming it up,


582
00:36:01,280 --> 00:36:04,800
putting a bit of energy into it, so
I'm shifting the electrons around,


583
00:36:04,800 --> 00:36:08,480
some of the electrons are jumping
into different energy levels.


584
00:36:08,480 --> 00:36:11,520
But this shift in the configuration
of the electrons


585
00:36:11,520 --> 00:36:14,520
inside the diamond has consequences,
because the sum total


586
00:36:14,520 --> 00:36:19,000
of all the electrons in the universe
must respect Pauli.


587
00:36:19,000 --> 00:36:22,080
Therefore,
every electron, around every atom


588
00:36:22,080 --> 00:36:26,760
in the universe, must be shifting
as I heat the diamond up,


589
00:36:26,760 --> 00:36:30,280
to make sure that none of them
end up in the same energy level.


590
00:36:30,280 --> 00:36:34,400
When I heat this diamond up, all
the electrons across the universe


591
00:36:34,400 --> 00:36:38,320
instantly but imperceptibly
change their energy levels.


592
00:36:38,320 --> 00:36:43,840
So everything is connected
to everything else.


593
00:36:50,560 --> 00:36:54,120
At the beginning, I promised I'd
explain everything in the universe,


594
00:36:54,120 --> 00:36:58,440
which I have in some way,
but also I said that I'd give you


595
00:36:58,440 --> 00:37:03,080
a deeper explanation of that wavy
behaviour of the subatomic world.


596
00:37:03,080 --> 00:37:06,920
So here it is. In my view, this is
the deepest explanation we have,


597
00:37:06,920 --> 00:37:09,480
and it's down to
the Nobel Prize-winning physicist


598
00:37:09,480 --> 00:37:12,840
Richard Feynman who, his colleague
Freeman Dyson once described


599
00:37:12,840 --> 00:37:15,920
as half genius, half buffoon
but he subsequently, after having


600
00:37:15,920 --> 00:37:19,520
worked with him for a while, changed
that to all genius, all buffoon.


601
00:37:19,520 --> 00:37:22,520
Let's go back to the double slit
experiment, but now,


602
00:37:22,520 --> 00:37:24,720
instead of just showing you the
pattern...


603
00:37:24,720 --> 00:37:26,280
This is Richard Feynman.


604
00:37:26,280 --> 00:37:28,320
Instead of just showing you
the pattern,


605
00:37:28,320 --> 00:37:30,680
I want to show you how
that pattern builds up.


606
00:37:30,680 --> 00:37:32,880
Remember, we're firing electrons
at two slits,


607
00:37:32,880 --> 00:37:34,960
almost pouring them
through two slits


608
00:37:34,960 --> 00:37:38,640
and seeing what happened when they
were detected on the other side.


609
00:37:38,640 --> 00:37:43,400
Well, this is one electron at a time
being fired through the slits


610
00:37:43,400 --> 00:37:46,000
and hitting the screen,
and building up in a pile.


611
00:37:46,000 --> 00:37:49,720
Only when the one electron has gone
through, was another one fired


612
00:37:49,720 --> 00:37:54,280
and this is real data, again,
a real movie of that happening


613
00:37:54,280 --> 00:37:56,440
and you see
the interference pattern.


614
00:37:56,440 --> 00:37:59,840
Electrons, no electrons,
electrons, no electrons.


615
00:37:59,840 --> 00:38:03,000
The wavy-type interference
pattern building up.


616
00:38:03,000 --> 00:38:05,080
What could be happening there?


617
00:38:05,080 --> 00:38:07,320
So, here it is again. Just electrons


618
00:38:07,320 --> 00:38:10,760
and you see that what emerges
is that wave-like behaviour.


619
00:38:10,760 --> 00:38:13,520
So, you might have thought,
"Well, I kind of understand


620
00:38:13,520 --> 00:38:16,400
"what's going on with the double
slits, there's loads of electrons


621
00:38:16,400 --> 00:38:19,160
"piling through the slits and
somehow there's some interference


622
00:38:19,160 --> 00:38:23,680
"just like a big water wave and you
build up the interference pattern."


623
00:38:23,680 --> 00:38:27,040
Well, no, because this is
one electron at a time,


624
00:38:27,040 --> 00:38:29,440
so, what could possibly
be happening?


625
00:38:29,440 --> 00:38:34,600
Well, Feynman was a wonderfully
intuitive, logical physicist.


626
00:38:34,600 --> 00:38:37,760
No ordinary genius,
he was often described as.


627
00:38:37,760 --> 00:38:40,520
And he said this.


628
00:38:40,520 --> 00:38:43,440
Here are the slits.


629
00:38:43,440 --> 00:38:45,360
Here's the screen.


630
00:38:45,360 --> 00:38:48,080
The electrons starts off here.
What happens?


631
00:38:48,080 --> 00:38:51,600
Well, obviously, the particle -
electron - must go through a slit


632
00:38:51,600 --> 00:38:54,760
and it must appear
somewhere on the screen,


633
00:38:54,760 --> 00:38:57,600
but it needs to be able
to interfere with itself -


634
00:38:57,600 --> 00:39:01,240
there've got to be regions on the
screen where there are no electrons,


635
00:39:01,240 --> 00:39:02,880
it's prevented from landing there,


636
00:39:02,880 --> 00:39:06,200
so it must, at least, go through
the other slit, as well,


637
00:39:06,200 --> 00:39:09,720
and get to that point,
and there must be some mechanism


638
00:39:09,720 --> 00:39:14,160
for these paths interfering with
each other, but why stop there?


639
00:39:14,160 --> 00:39:16,400
See, that wouldn't
be particularly logical.


640
00:39:16,400 --> 00:39:18,200
Why only let it go
through two paths?


641
00:39:18,200 --> 00:39:21,480
Why not let it go through
that path or maybe


642
00:39:21,480 --> 00:39:26,120
some sort of path like that, or
maybe like or maybe, indeed,


643
00:39:26,120 --> 00:39:29,480
off here,
out of this lecture theatre


644
00:39:29,480 --> 00:39:33,520
and then maybe through
Jonathan's head on its way...


645
00:39:33,520 --> 00:39:36,840
I've got to say through Paul's foot,
haven't I? Cos I just have to.


646
00:39:36,840 --> 00:39:40,560
Paul Foot. I don't know -
what a rubbish thing to say.


647
00:39:40,560 --> 00:39:43,960
But, anyway, it could go through
you, through Jonathan,


648
00:39:43,960 --> 00:39:46,120
off up Oxford Street,
up to Newcastle


649
00:39:46,120 --> 00:39:48,080
indeed on to the Andromeda Galaxy


650
00:39:48,080 --> 00:39:51,960
and back again, and land
at this point on the screen.


651
00:39:51,960 --> 00:39:54,000
Why not?


652
00:39:54,000 --> 00:39:57,760
Why not allow the particle to travel
along every possible path it can,


653
00:39:57,760 --> 00:40:02,920
from one point to the other?
And that is indeed what happens,


654
00:40:02,920 --> 00:40:06,040
in the sense that's the way
Feynman's theory works.


655
00:40:06,040 --> 00:40:08,320
In principle,
it's not too difficult.


656
00:40:08,320 --> 00:40:10,840
You just have to
calculate some quantity


657
00:40:10,840 --> 00:40:14,880
associated with each path
and find some mathematical machinery


658
00:40:14,880 --> 00:40:18,480
from adding all those things up,
and seeing whether or not they all


659
00:40:18,480 --> 00:40:22,480
interfere together and disappear or
appear when they land on the screen.


660
00:40:22,480 --> 00:40:24,280
There is a formula that does that


661
00:40:24,280 --> 00:40:27,320
and this is all
I really need to say.


662
00:40:27,320 --> 00:40:30,400
Let me turn it around.
There it is.


663
00:40:30,400 --> 00:40:32,720
Thank you and good...
No, no, I won't say that!


664
00:40:32,720 --> 00:40:35,280
This is called the Feynman path
integral,


665
00:40:35,280 --> 00:40:36,560
and this just says,


666
00:40:36,560 --> 00:40:40,040
sum up over all the paths and
calculate something


667
00:40:40,040 --> 00:40:42,040
that will tell you the probability


668
00:40:42,040 --> 00:40:44,760
of an electron going
from one place to another.


669
00:40:44,760 --> 00:40:47,840
Now, that might look
a tremendous mess,


670
00:40:47,840 --> 00:40:50,280
or it might look very
simple and illuminating -


671
00:40:50,280 --> 00:40:52,480
I suppose it depends
on your point of view.


672
00:40:52,480 --> 00:40:55,240
Probably a tremendous mess, granted.


673
00:40:55,240 --> 00:40:57,400
But this formula is just
a little machine,


674
00:40:57,400 --> 00:40:59,680
I think that's a good way
to think about it.


675
00:40:59,680 --> 00:41:02,760
It that takes all the possible paths
a particle can have,


676
00:41:02,760 --> 00:41:05,480
it adds them up and it
spits out the probability


677
00:41:05,480 --> 00:41:08,160
that it'll end up
at some particular place.


678
00:41:08,160 --> 00:41:13,360
And that includes the particles
that make up the diamond.


679
00:41:13,360 --> 00:41:17,200
Now, for the moment, it's sat
on its little cushion there.


680
00:41:17,200 --> 00:41:19,520
Let me put it back in its box.


681
00:41:21,680 --> 00:41:24,720
Now, Feynman's version
of quantum theory tells us


682
00:41:24,720 --> 00:41:26,640
something rather shocking.


683
00:41:26,640 --> 00:41:28,880
This diamond is made up of atoms,


684
00:41:28,880 --> 00:41:31,800
and the atoms are behaving
according to quantum theory -


685
00:41:31,800 --> 00:41:33,720
according to Feynman's equation.


686
00:41:33,720 --> 00:41:36,760
In other words, they are all
currently exploring the universe,


687
00:41:36,760 --> 00:41:41,040
hopping around everywhere, exploring
every possible path they can.


688
00:41:41,040 --> 00:41:43,960
And that means this diamond
is doing the same thing,


689
00:41:43,960 --> 00:41:46,200
because it's made of atoms.


690
00:41:46,200 --> 00:41:48,720
That means there is a finite
chance that it will not


691
00:41:48,720 --> 00:41:54,480
be inside this box at a later time -
you can see where I'm going -


692
00:41:54,480 --> 00:41:59,640
but it'll jump,
completely out of its own accord,


693
00:41:59,640 --> 00:42:03,920
without me touching it...and that's
what I'm going to tell the judge!


694
00:42:05,440 --> 00:42:09,920
But what's remarkable, is that
I can calculate what the chance is


695
00:42:09,920 --> 00:42:15,320
by using a simplified version
of Feynman's formula.


696
00:42:15,320 --> 00:42:17,360
And this is it.


697
00:42:17,360 --> 00:42:21,760
See, just by doing a bit of maths,
you can work that, simplify it,


698
00:42:21,760 --> 00:42:23,480
and turn it into this...


699
00:42:23,480 --> 00:42:27,200
which is an expression for the time
you would have to wait,


700
00:42:27,200 --> 00:42:30,840
on the average, to have a
reasonable chance of it hopping


701
00:42:30,840 --> 00:42:34,880
out of its box,
and it goes like this.


702
00:42:37,680 --> 00:42:42,360
OK, so, that is the distance
we want it to hop,


703
00:42:42,360 --> 00:42:44,440
that is the size of the box,


704
00:42:44,440 --> 00:42:46,160
that's the mass of the diamond


705
00:42:46,160 --> 00:42:48,600
and that's something called
Planck's constant.


706
00:42:48,600 --> 00:42:50,640
I'm going to need
another volunteer here


707
00:42:50,640 --> 00:42:53,000
because I'm going to
actually do the maths


708
00:42:53,000 --> 00:42:55,800
because I want to show you that you
can do the sum quite simply


709
00:42:55,800 --> 00:42:58,600
and I believe that Jonathan
has kindly agreed


710
00:42:58,600 --> 00:43:01,880
to do some sums, so, thank you.


711
00:43:12,360 --> 00:43:17,320
How's your maths? Well, you know,
you know that's easy for me.


712
00:43:17,320 --> 00:43:20,040
I do. That's why
I asked you, actually.


713
00:43:20,040 --> 00:43:21,360
We're going to do it,


714
00:43:21,360 --> 00:43:24,520
so x - that's the distance
we want the diamond to jump.


715
00:43:24,520 --> 00:43:27,640
So let's say the box is about 5cm.


716
00:43:27,640 --> 00:43:31,480
Let's say 6cm for x


717
00:43:31,480 --> 00:43:36,120
and the mass of the diamond is
290-something carats -


718
00:43:36,120 --> 00:43:41,480
it's about 60g. Roughly, yes.
An expert on diamonds, are you?


719
00:43:41,480 --> 00:43:45,320
So, first of all, we just have to
multiply those 3 numbers together.


720
00:43:45,320 --> 00:43:48,240
6cm x 5cm x 60g.


721
00:43:48,240 --> 00:43:49,640
Yeah. 6 x 5 x 6.


722
00:43:49,640 --> 00:43:53,200
So 30 x 60. You just said 6!


723
00:43:53,200 --> 00:43:54,880
60. 60g.


724
00:43:54,880 --> 00:43:57,840
OK, 30 x 6 = 1,800.


725
00:43:57,840 --> 00:43:59,560
Is that right? 60?


726
00:43:59,560 --> 00:44:03,320
It's heavy. It is.
The BBC used to pay me in these.


727
00:44:03,320 --> 00:44:07,200
LAUGHTER AND APPLAUSE


728
00:44:12,280 --> 00:44:17,200
I better take it back.
I'm going to get...
HE LAUGHS NERVOUSLY


729
00:44:17,200 --> 00:44:19,920
Then, though we get to this.
Over the thing.


730
00:44:19,920 --> 00:44:27,240
6.6 x 10­-34 kgm­2/s.


731
00:44:27,240 --> 00:44:29,160
That is Planck's constant -


732
00:44:29,160 --> 00:44:32,040
this is a fundamental
constant of nature.


733
00:44:32,040 --> 00:44:35,880
It's intrinsic to the way
the universe is put together.


734
00:44:35,880 --> 00:44:39,040
It's like the speed of light,
like the strength of gravity.


735
00:44:39,040 --> 00:44:40,560
It is THE fundamental THING -


736
00:44:40,560 --> 00:44:43,960
constant, if you like - that sets
the scale for quantum phenomena.


737
00:44:43,960 --> 00:44:46,000
So, there's a slight issue here


738
00:44:46,000 --> 00:44:48,240
because you see...
You'll have noticed it.


739
00:44:48,240 --> 00:44:50,960
The unit's are kilograms
metres squared per second


740
00:44:50,960 --> 00:44:53,480
and we calculated the 1,800
in cm and grams.


741
00:44:53,480 --> 00:44:56,800
Which, by the way, I'm amazed
I got that right!


742
00:44:56,800 --> 00:45:01,440
So, first of all, we better another
10­-2 and a 10­-2 and a 10­-3 on,


743
00:45:01,440 --> 00:45:04,520
so it's 10­-7. Yeah.


744
00:45:05,680 --> 00:45:08,800
So all you've got to do
is divide that by that.


745
00:45:08,800 --> 00:45:11,400
All of that with that?
Divide that by that roughly.


746
00:45:11,400 --> 00:45:15,280
Roughly I don't even know
if I can do...


747
00:45:20,480 --> 00:45:25,200
That, for me... That's a kilogram?
I don't even know. I do pounds!


748
00:45:25,200 --> 00:45:30,040
No, I've done the unit conversion
for you - you've just got to divide.
Where's the unit conversion?


749
00:45:30,040 --> 00:45:33,160
1,800 x 10­-7 x 6.6 x 10...


750
00:45:33,160 --> 00:45:36,680
I have no idea what you're doing and
why you would want to do this to me!


751
00:45:36,680 --> 00:45:38,080
Help him out, Jim.


752
00:45:38,080 --> 00:45:40,880
Well you've got 10­-34 downstairs.
Bring it upstairs


753
00:45:40,880 --> 00:45:43,840
and it becomes 10­34.
Where do I put it? Up here?


754
00:45:43,840 --> 00:45:46,520
Yeah, put it next to the 10...


755
00:45:46,520 --> 00:45:50,840
So then you've got 34 - 7.
OK 34-7? Yeah. Yes, OK.


756
00:45:50,840 --> 00:45:52,880
So that's 10­27.


757
00:45:52,880 --> 00:45:57,160
You've got about 10­3.
I really... I'm so out of my depth.


758
00:45:58,520 --> 00:46:01,400
This is the worst thing that's
happened to me as an adult.


759
00:46:02,720 --> 00:46:04,880
You've got 10­27. OK.


760
00:46:04,880 --> 00:46:10,640
Just for any children watching,
I should say,


761
00:46:10,640 --> 00:46:12,880
34 - 7 = 27


762
00:46:12,880 --> 00:46:16,800
So you've got 10­27 and then
we've got 6 and we've got 1,800,


763
00:46:16,800 --> 00:46:22,640
so we've got to divide those things
so we get about a 3 and another 100.


764
00:46:22,640 --> 00:46:24,840
If you say so!


765
00:46:24,840 --> 00:46:27,920
3 x 10­29...ish.


766
00:46:27,920 --> 00:46:31,320
Once again, I am none the wiser.
LAUGHTER


767
00:46:31,320 --> 00:46:36,880
Why couldn't I have done James May's
job where you just set fire to me?


768
00:46:36,880 --> 00:46:41,960
And everyone went "Oooh!"
And he's so happy he did that


769
00:46:41,960 --> 00:46:44,080
and I'm now sweating.


770
00:46:44,080 --> 00:46:49,200
We're done. We've done it?
Yeah, you see, this is
what that number is you calculated.


771
00:46:49,200 --> 00:46:53,640
See, we just put in the numbers
divided by Planck's constant?
What this number is


772
00:46:53,640 --> 00:46:57,360
is the number of seconds you would
have to wait on the average to have


773
00:46:57,360 --> 00:47:00,920
a reasonable chance of the diamond
hopping out of the box on its own.


774
00:47:00,920 --> 00:47:03,200
I could have told you that's not
going to happen without any of this.


775
00:47:03,200 --> 00:47:05,360
LAUGHTER


776
00:47:05,360 --> 00:47:08,800
I didn't need the sums.
The diamond is safe in the box,


777
00:47:08,800 --> 00:47:11,800
unless it's turned into a dead cat.
That's the theory, isn't it?


778
00:47:11,800 --> 00:47:14,880
I'll tell you what this is.
Do you know roughly what that is?


779
00:47:14,880 --> 00:47:18,000
A nine? 3 x 10­29?
Why would I know? I'm an idiot!


780
00:47:18,000 --> 00:47:23,520
In years? That's about...
Well, I'll tell you what it is.
It is 600 billion times


781
00:47:23,520 --> 00:47:26,560
the current age of the universe.


782
00:47:26,560 --> 00:47:29,520
I don't know what to do. I'm just
going to keep smiling at you.


783
00:47:29,520 --> 00:47:33,320
LAUGHTER
Thank you for sharing that.
Thank you.


784
00:47:35,880 --> 00:47:38,040
Thanks.


785
00:47:43,920 --> 00:47:45,280
Thanks, Jon.


786
00:47:46,720 --> 00:47:52,080
The point of that...
The point of that is to show
that quantum theory doesn't just


787
00:47:52,080 --> 00:47:55,560
apply to the inconceivably
small world of the atom.


788
00:47:55,560 --> 00:47:59,480
The same rules apply to you,
to me, and the diamond.


789
00:47:59,480 --> 00:48:03,520
It's just that for objects
out here in the familiar world,


790
00:48:03,520 --> 00:48:06,600
like the diamond, we don't
usually see quantum effects.


791
00:48:06,600 --> 00:48:11,200
The reason for that is
the smallness of Planck's constant.
We had quite a big number here,


792
00:48:11,200 --> 00:48:15,120
but we had to divide it by
an extremely small number in order


793
00:48:15,120 --> 00:48:19,080
to work out the time we'd have to
wait and that's why that's big.


794
00:48:19,080 --> 00:48:23,280
See, if that was one or something
like that, then we wouldn't have
had to wait many seconds -


795
00:48:23,280 --> 00:48:27,280
about 1,800 seconds or something
like that, for the diamond
to hop out of the box.


796
00:48:27,280 --> 00:48:30,800
So it's Planck's constant, this
fundamental constant of nature


797
00:48:30,800 --> 00:48:34,920
that means that quantum theory
is rather unfamiliar


798
00:48:34,920 --> 00:48:39,680
because it applies to small things,
because Planck's constant is small.


799
00:48:39,680 --> 00:48:43,800
Now you could theoretically make
the diamond jump sooner.


800
00:48:43,800 --> 00:48:45,800
Look again at this equation.


801
00:48:45,800 --> 00:48:49,560
One way to do it, as I've said,
would be to make Planck's constant
very big,


802
00:48:49,560 --> 00:48:53,880
but you can't do that. It's
a fundamental constant of nature.
What you could do, though,


803
00:48:53,880 --> 00:48:57,720
is you could shrink the size
of the box, this delta x here.


804
00:48:57,720 --> 00:49:01,000
If I made the box
smaller and smaller and smaller,


805
00:49:01,000 --> 00:49:07,800
I'd make the time I had to wait
for it to jump out of the box
smaller and smaller and smaller.


806
00:49:07,800 --> 00:49:11,760
So this equation says that
the more we know the position


807
00:49:11,760 --> 00:49:15,240
of something, the position of this
diamond in the box, let's say,


808
00:49:15,240 --> 00:49:19,680
then the more likely it is for
the diamond to jump out of the box.


809
00:49:19,680 --> 00:49:23,320
Now this is known as Heisenberg's
Uncertainty Principle -


810
00:49:23,320 --> 00:49:27,480
the more you try to pin down a
particle's position by trapping it


811
00:49:27,480 --> 00:49:31,800
in a smaller and smaller box, the
more likely it is to jump around.


812
00:49:31,800 --> 00:49:35,120
You might have come across
Heisenberg's Uncertainty Principle.


813
00:49:35,120 --> 00:49:37,640
It's one of
the most famously misunderstood


814
00:49:37,640 --> 00:49:40,800
and misrepresented parts
of quantum theory.


815
00:49:40,800 --> 00:49:44,480
It says, precisely,
that the more precisely you know


816
00:49:44,480 --> 00:49:49,800
a particle's position, the less
certain you can be of its momentum.


817
00:49:49,800 --> 00:49:54,840
And you can see that it emerged...
I derived it
from a fundamental equation.


818
00:49:54,840 --> 00:49:57,680
It's not complete nonsense.
I didn't make it up.


819
00:49:57,680 --> 00:50:01,760
It's often misrepresented by what
I would call "mischievous hippies"


820
00:50:01,760 --> 00:50:04,800
to mean that physicists
are rubbish at their job


821
00:50:04,800 --> 00:50:07,680
or that the equipment is no good
and we're unable to measure


822
00:50:07,680 --> 00:50:10,160
two things about a particle
with any accuracy.


823
00:50:10,160 --> 00:50:13,200
But Heisenberg's Uncertainty
Principle is a consequence


824
00:50:13,200 --> 00:50:15,360
of the laws of quantum theory.
It emerges


825
00:50:15,360 --> 00:50:21,040
from Feynman's equation. It has
nothing to do with any of that
wishy-washy, drivelly nonsense.


826
00:50:21,040 --> 00:50:26,960
In that spirit, I want to show you
that rather than restricting
our knowledge of the natural world,


827
00:50:26,960 --> 00:50:30,000
Heisenberg can actually widen it.


828
00:50:30,000 --> 00:50:34,600
In fact, this rule about
the unimaginably small particles


829
00:50:34,600 --> 00:50:39,040
can explain some of the most massive
and spectacular objects
in the universe.


830
00:50:42,000 --> 00:50:44,160
I'm going to end


831
00:50:44,160 --> 00:50:47,640
by explaining how everything
I've told you this evening


832
00:50:47,640 --> 00:50:51,360
predicts the existence
of diamonds bigger than this -


833
00:50:51,360 --> 00:50:53,760
in fact, bigger than
this lecture theatre.


834
00:50:53,760 --> 00:50:59,400
In fact, diamonds as big as a planet
and as massive as a star.


835
00:50:59,400 --> 00:51:03,080
Now to understand how this can be,
we need to understand something


836
00:51:03,080 --> 00:51:06,200
about the life cycles
of the stars themselves.


837
00:51:06,200 --> 00:51:09,720
Stars are big clumps of matter
collapsing under their own gravity.


838
00:51:09,720 --> 00:51:12,960
As they collapse, they heat up
and they set off a chain reaction


839
00:51:12,960 --> 00:51:16,640
of nuclear fusion reactions
where the nuclei of hydrogen


840
00:51:16,640 --> 00:51:21,080
fuse together, initially to form
helium, and eventually they fuse


841
00:51:21,080 --> 00:51:26,720
to form carbon and oxygen
and all the heavy elements
up to and including iron.


842
00:51:26,720 --> 00:51:30,400
That's where the heavy elements
come from in the universe.


843
00:51:30,400 --> 00:51:33,760
In this process, vast amounts
of energy are released.


844
00:51:33,760 --> 00:51:36,840
That energy creates a pressure
that holds the star up


845
00:51:36,840 --> 00:51:38,840
and prevents it from collapsing.


846
00:51:38,840 --> 00:51:41,560
The stars don't have
infinite amounts of fuel


847
00:51:41,560 --> 00:51:44,800
and eventually those
fusion reactions must cease.


848
00:51:44,800 --> 00:51:47,520
In five billion years,
this will happen to our sun.


849
00:51:47,520 --> 00:51:50,800
It'll stop generating enough
energy to prevent its own collapse


850
00:51:50,800 --> 00:51:53,080
and so it will collapse.


851
00:51:53,080 --> 00:51:58,520
By the end of their lives,
stars like our sun have converted
all the hydrogen in their cores


852
00:51:58,520 --> 00:52:03,440
and mainly they've converted
it into oxygen and carbon.


853
00:52:03,440 --> 00:52:06,320
Now remember that
those carbon atoms,


854
00:52:06,320 --> 00:52:10,200
just like those in our diamond,
are almost entirely empty space,


855
00:52:10,200 --> 00:52:15,760
so you might expect that the space
can be squashed and compressed
almost out of existence


856
00:52:15,760 --> 00:52:17,920
as the dying star collapses.


857
00:52:17,920 --> 00:52:20,920
But as the star collapses
and becomes denser,


858
00:52:20,920 --> 00:52:24,320
its electrons get closer
and closer together.


859
00:52:24,320 --> 00:52:30,960
Finally, they're so close
that they try to occupy the same
volume of space as each other.


860
00:52:30,960 --> 00:52:33,800
Then Pauli's Exclusion
Principle steps in,


861
00:52:33,800 --> 00:52:37,920
because the electrons cannot occupy
the same bit of space -


862
00:52:37,920 --> 00:52:43,040
they are unable to overlap,
so they try to arrange themselves


863
00:52:43,040 --> 00:52:45,640
such that they have as much
space as they possibly can.


864
00:52:45,640 --> 00:52:49,080
And you might imagine them as being
alone inside little boxes like this


865
00:52:49,080 --> 00:52:55,040
and the boxes shrink and shrink
and shrink as the star collapses.


866
00:52:55,040 --> 00:52:58,640
But then, as the electrons become
more and more confined,


867
00:52:58,640 --> 00:53:04,160
Heisenberg's Uncertainty Principle
comes into play. As the electrons'
boxes get smaller and smaller,


868
00:53:04,160 --> 00:53:08,160
their tendency to hop out of the box
becomes greater and greater,


869
00:53:08,160 --> 00:53:11,240
so you can think of it
that they are frantically vibrating


870
00:53:11,240 --> 00:53:16,280
around faster and faster inside
these boxes of ever-decreasing size.


871
00:53:16,280 --> 00:53:20,840
This quantum jiggling
exerts a pressure, which stops


872
00:53:20,840 --> 00:53:23,760
the star from collapsing any
further, leaving something called


873
00:53:23,760 --> 00:53:28,080
a white dwarf star,
which is a densely-packed dead star
the size of the Earth


874
00:53:28,080 --> 00:53:33,800
but the mass of our sun, and a
million times more dense than water.


875
00:53:33,800 --> 00:53:37,840
White dwarfs are so dense that
if I were to stand on their surface


876
00:53:37,840 --> 00:53:43,000
the gravitational pull would make me
weigh something like 30,000 tonnes.


877
00:53:43,000 --> 00:53:45,840
White dwarfs
are strange objects indeed.


878
00:53:45,840 --> 00:53:49,680
But here is the final triumph,
I think, of quantum theory.


879
00:53:49,680 --> 00:53:55,640
It is the most powerful example I
know of its power to predict
how the natural world behaves.


880
00:53:55,640 --> 00:54:01,400
See, it predicts the existence of
these strange stars of white dwarfs.


881
00:54:01,400 --> 00:54:03,400
But it does more than that.


882
00:54:03,400 --> 00:54:06,440
In the 1930s, the physicist
Subrahmanyan Chandrasekhar


883
00:54:06,440 --> 00:54:09,640
used quantum theory
to predict the maximum mass


884
00:54:09,640 --> 00:54:14,480
of a lump of matter
that can be held up by
the exclusion pressure of electrons


885
00:54:14,480 --> 00:54:18,720
to form a white dwarf.
He just used the uncertainty
principle, essentially,


886
00:54:18,720 --> 00:54:20,280
and the exclusion principle.


887
00:54:20,280 --> 00:54:23,200
He found that there should be
no stars of this type


888
00:54:23,200 --> 00:54:26,720
with masses greater than 1.4 times
the mass of our sun.


889
00:54:26,720 --> 00:54:32,600
Now to date,
astronomers have found tens of
thousands of white dwarf stars


890
00:54:32,600 --> 00:54:38,600
and they have found that not one
in the sky exceeds the maximum mass


891
00:54:38,600 --> 00:54:43,000
calculated by Chandrasekhar using
the simple laws of quantum theory.


892
00:54:43,000 --> 00:54:48,240
And in amongst those stars,
astronomers have found something
that I think is quite extraordinary.


893
00:54:48,240 --> 00:54:51,800
Now that diamond is 296 carats.


894
00:54:51,800 --> 00:54:57,320
In the heart of this constellation,
Centaurus, which is a few tens
of light years away,


895
00:54:57,320 --> 00:55:03,600
they've detected a white dwarf star
with the wonderful name BPM 37093(!)


896
00:55:03,600 --> 00:55:09,920
LAUGHTER
As it died and cooled, the carbon
within the core crystallised.


897
00:55:09,920 --> 00:55:18,040
So BPM 37093, which is somewhere
around there, became a diamond,


898
00:55:18,040 --> 00:55:21,720
just like this, but of ten billion
trillion trillion carats.


899
00:55:21,720 --> 00:55:23,320
LAUGHTER


900
00:55:23,320 --> 00:55:27,400
We understand in detail why such
a thing can exist.


901
00:55:27,400 --> 00:55:33,040
That's a diamond, light years away,
intimately connected
to this diamond,


902
00:55:33,040 --> 00:55:35,240
and indeed, intimately
connected to everything else


903
00:55:35,240 --> 00:55:38,560
in the universe,
by the laws of quantum physics.


904
00:55:38,560 --> 00:55:43,280
What a remarkable testament
to the power of the wavy behaviour
of electrons,


905
00:55:43,280 --> 00:55:47,840
and what a spectacular demonstration
of the effectiveness
of quantum theory.


906
00:55:47,840 --> 00:55:51,440
Quantum theory is a uniquely
potent tool that gives us


907
00:55:51,440 --> 00:55:55,280
our best understanding
of how the inconceivably small


908
00:55:55,280 --> 00:55:57,680
can give rise
to the inconceivably large.


909
00:55:57,680 --> 00:56:01,600
It is THE most accurate way
that we currently possess


910
00:56:01,600 --> 00:56:03,920
to understand our universe.


911
00:56:03,920 --> 00:56:06,160
It explains how
atoms are empty yet solid,


912
00:56:06,160 --> 00:56:11,280
how the wave-like behaviour
of electrons creates
the hardest known substances,


913
00:56:11,280 --> 00:56:15,440
and how the real world
emerges from subatomic particles


914
00:56:15,440 --> 00:56:20,320
that explore the universe,
the entire universe, in an instant.


915
00:56:20,320 --> 00:56:25,040
There's nothing strange, there's
nothing weird, there's no woo-woo.


916
00:56:25,040 --> 00:56:28,560
It is just beautiful physics.
Thank you.


917
00:56:28,560 --> 00:56:32,000
APPLAUSE


918
00:56:49,480 --> 00:56:51,640
It was mind-blowing.


919
00:56:51,640 --> 00:56:55,280
I couldn't...
Some of it I could understand,


920
00:56:55,280 --> 00:56:58,720
other parts I could not understand.
It was so exciting. I loved it.


921
00:56:58,720 --> 00:57:02,200
I love listening to him
because he does makes things clear.


922
00:57:02,200 --> 00:57:04,680
He speaks at just
the right pace for me to absorb it


923
00:57:04,680 --> 00:57:07,720
and also he's got that
very winning smile, so even though


924
00:57:07,720 --> 00:57:11,480
he does insist on telling us
how soon it is that
the sun's going to die out


925
00:57:11,480 --> 00:57:15,400
and we will all die screaming
and flying off into
the inky void of space,


926
00:57:15,400 --> 00:57:18,280
you don't mind it because
he looks so sweet when he tells you.


927
00:57:18,280 --> 00:57:20,720
What do you now
think of quantum physics?


928
00:57:20,720 --> 00:57:24,240
I feel like I maybe should have
stuck in at school
a little bit more,


929
00:57:24,240 --> 00:57:29,000
but you know, the career that I've
chosen is going well, so...


930
00:57:29,000 --> 00:57:34,320
But I have learnt a lot -
mainly "don't volunteer for things"!


931
00:57:34,320 --> 00:57:36,000
How are your hands now?


932
00:57:36,000 --> 00:57:41,200
My hands are fine. All it does
is singe the very fine hairs
on the back.


933
00:57:41,200 --> 00:57:46,200
But I was getting a bit,
you know, gorilla-ish anyway,
so he's probably done me a favour.


934
00:57:46,200 --> 00:57:50,080
It was great. I loved it.
It was fantastic. It was
almost exactly about everything


935
00:57:50,080 --> 00:57:51,600
I think about all the time.


936
00:58:13,560 --> 00:58:15,600
Subtitles by Red Bee Media Ltd


937
00:58:15,600 --> 00:58:17,720
E-mail subtitling@bbc.co.uk