Thank you very much, indeed. Now, I don't know about
you, but personally, watching the previous
talks, seeing all that environmental
destruction, took me from worry,
to abject fury, through to a hint
of hope at the end. So how to follow that
up, except by making us all feel totally
insignificant, which is the aim of the next
half an hour or so. I'm going to ask the question,
what's made our universe? And just to give the game
away right at the start, I'm not really going to
quite answer that question. If I could answer
that question, I'd probably be giving
this talk in Stockholm, receiving my Nobel Prize. But funnily enough, we do
actually know quite a lot about some of the
processes involved in making the universe around
us as we know it today. Now, I'm going to spend
a little more than half the time mainly talking
about actually what's out there in the
universe, setting the stage for some
of these questions about where it's all come from. Because if there's one
world that's familiar to us, it's Earth. I feel like now I should
be redoing this image and putting some
plastic on top of it. But still, from space, the
earth looks something like that. And the earth is, of
course, a big place. What's the radius of the earth? Well, it's something approaching
7,000 kilometres radius. If you wanted to put a ring
of people around the equator, you'd need something like 40
million people, all holding hands around the equator. So it can feel like our own
world is a pretty big place to live, but in
terms of what we're going to see in the
next few minutes, it really is absolutely tiny. In terms of what's
out there in space, the moon has particular
significance for us. It has cultural
significance, of course. But it also has
scientific significance, because it's the furthest
object in the entirety of space that any human has ever visited. So it's something like
400,000 kilometres away. The distances in this image
are not to scale, by the way. The actual relative sizes
are approximately to scale. But obviously, the moon isn't
right there on top of us. But we have-- just to check,
there aren't any conspiracy theorists. We don't have to have
that particular argument. That's good. We have actually
been to the moon. But everything else that I'm
going to talk about in space-- and trust me, space is an
awful lot bigger than that-- we've never been there. So how do we know about it? Well, we know more or
less just by looking. We have fantastic telescopes,
both on the ground and also in space. So this is the famous
Hubble Space Telescope, which has taken many of the
most famous images of space that you'll have no doubt seen. But in terms of its
distance from the Earth, it's actually in
low Earth orbit. It's only a few hundred
kilometres above our heads. And the only reason
it's there is so that it can get a
really clear view of space unobstructed by
Earth's atmosphere, which gets in the way of
taking images from the ground. So its distance from
us is essentially zero, in cosmological terms. But it's able to inform
us about what's out there. Now, if we look slightly
beyond the Earth-Moon system, we come to the other
planets in the solar system. Our nearest neighbour
planet is Mars. And Mars, again, has both
cultural and scientific interest-- scientific interest,
because it may once actually have been a planet
rather like the earth. These days, it seems
to be quite barren. It doesn't seem to
have an atmosphere. But it's possible that
in the distant past, it had an atmosphere not so
dissimilar from the earth's, which has now been lost. And it's even possible that
at some point in the past, it hosted liquid
water on its surface. And so it's really quite a
serious cultural question to ask, is there life on
Mars, or, at least, was there life on Mars at some
point in the past? But all this is still
relatively small scale. Other planets are
an awful lot bigger. So if you put the
earth next to Jupiter, which is the largest planet
in our own solar system-- so in other words, the
largest planet that's orbiting around our sun-- the earth looks pretty tiny. You could fit-- I think if you'd place the earth
along the diameter of Jupiter, you could fit at least 10
of them along the diameter. But all planets are pretty puny
by comparison with the sun. So the sun is 10
times larger still-- something like 1.5
million kilometres across. And it's the most
significant object, I suppose, that's
out there in space, because it governs our
entire life here on Earth. Without the sun, there
would be no life on Earth. So although we
haven't ventured-- individual humans haven't
ventured any further than the moon, all of this
stuff I've been telling you so far within our
own solar system is pretty well known about
through robotic spacecraft. So no human has gone to visit
Jupiter or gone near the sun, but robotic spacecraft
certainly have. In fact, we've sent
robotic spacecraft all over the solar system. And the most distant
robotic spacecraft, and therefore, the most distant
object that humanity has ever sent out into space, is a
craft known as Voyager 1. It was launched
in, I think, 1977, and it's been
travelling ever since, further and further
away from Earth. And at the present time, it's
something like 22 billion kilometres away. And 22 billion
kilometres is something like 150 times the
distance to the sun, so it seems like we're
finally venturing out. And in fact, Voyager
1 is now considered to be in interstellar space. So it's left the region of space
that's influenced by our sun, and it's entering the
region between stars. But if you're hoping
for a resolution to our environmental problems
by skipping over to the nearest planet, then,
unfortunately, Star Trek is still some way off. Because Voyager 1, if it were
heading towards our nearest neighbour star-- which it isn't-- but
if it were, it, so far, would have got about 0.05%
percent of the way there. The nearest star is 40 trillion
kilometres away from us. And that, of course, is by no
means the end of the story. Because if you look
up at the night sky, it's absolutely
packed with stars, especially you get
away from London so that you can see it without
all this light pollution. And it's packed with stars. The darker site
you go to, the more stars that seem to be there. And in fact, we live in a
galaxy of stars, all of them pretty much like our sun-- maybe a bit bigger,
some of them-- but something like 100 billion,
maybe as many as 400 billion stars in our own galaxy. Our own galaxy might
look something like this. We don't know exactly
what our own galaxy looks like from the outside,
because we haven't been able to send any spacecraft
outside the galaxy to take a look at it. So we see our galaxy
just as a collection of stars in the night sky. And in particular, if you go
somewhere really nice and dark, you see the sort of
band of the Milky Way. And that milky band
you see across the sky is just made up of billions
and billions of stars. So if this were a
view of our own galaxy from outside, then if the
sun was somewhere like there, then we would be-- well, sorry-- if the sun
was somewhere like there, then the nearest star would be
a millimetre away or something. So the galaxy itself
is absolutely huge. But luckily, we have the
tools available to us to learn an awful
lot about what's out there, despite the
vast distances involved. So one of the most
natural questions you might ask about all of
these stars is, are they, like our sun, host
to lots of planets? Or, in fact, are they even
host to planets like the earth? And as a follow-on
question to that, is there life out
there in our galaxy? And in the last 10
years or so, there's been a total transformation
of our knowledge in this area, due to a number of
different projects, but, in particular, the
Kepler Space Telescope, which is another
space telescope that was launched by NASA probably
about 10 years ago, now. And its mission-- unlike
the Hubble Space Telescope, which takes pictures of
lots of different things, the mission of Kepler
was specifically to stare at a handful of
stars and just absolutely stare at them for long periods. And the reason
that's interesting is because if you look at
a star for long enough, you might start to see a hint
that there's a planet there. That hint can take
different forms. But one form is that if
you've got a planet that's orbiting around a star,
then every now and again, it might actually pass
in front of that star, as far as you're concerned. So you're the telescope
looking at the star, and every now and again, a
planet that's going around it actually gets in between
you and the star, and it blocks out some of the
light coming from that star. So although the distances
involved are way too large to be able to see
the planet directly, you can tell it's there
because the star just gets ever so slightly dimmer
because some of the light's been blocked out and
then gets brighter again. That's something called
the transit method. And using that method and
a number of other methods, the Kepler Space
Telescope has been able to identify a very
large number of planets beyond our own solar system-- I think something like 5,000
planets at the last count. So if you take those
kind of numbers, and you factor in how many stars
Kepler is actually looking at, and you also factor in
the fact that you wouldn't see every single planet
using this method, you can come up with
some kind of estimate for how common are planets-- how many of the 100
billion stars in our galaxy might be hosting planets. And you can even narrow
that question down further and say, well, what
fraction of them might be hosting a planet of
the size of the earth, which as I've shown you earlier on, is
actually quite a small planet, but likely, as far
as we can tell, to be the kind of planet
which might give rise to life. And there have been a number
of different estimates, but we think as a lower limit,
something like a sixth of all stars have an Earth-mass
planet orbiting around them-- so a very, very large fraction. Now, that doesn't mean, of
course, that all of those are suitable for
life and certainly doesn't mean that all of them
have any form of life on them. But it certainly gives
you some kind of hope. The only slight issue is that
we'll probably never actually be able to get there ourselves. But it'd be nice to know that
life is out there, nonetheless. Well, learning about all of
these planets is by no means the end of the story. We're trying to understand where
our entire galaxy came from. And many different tools
exist to help us with that. But one that's having
a huge amount of impact on the scientific
community at the moment is something called the
Gaia Space Telescope. It's, again, a specialised
space telescope that's designed
just to catalogue the stars in our galaxy and
find out, first of all, very accurately where
they are in 3D space and also how fast they're
moving in 3D space. And the aim is that if you can
put all of that information together, you start to
get some kind of hint of how our galaxy
may have formed, and where did all of
these stars actually come from in the first place. That's what we're aiming,
ultimately, to answer. But it turns out
that if you want to answer that
question, unfortunately, you can't just
stop at our galaxy. You need to broaden your sights
a little bit further still, because our galaxy
is not by any means the only galaxy in the universe. So even just to account for
the formation of our galaxy, you need to understand
what's around it in space. And to do that, you start by
making some kind of census of what else is out there. So beyond our own galaxy,
we find other galaxies. The nearest neighbour galaxy
is the Andromeda Galaxy. It's 22 quintillion
kilometres away. I had to look up
what the correct name for that number of zeros is. That like 22 million, million,
million kilometres away. And it's this swirling
mass of stars, and gas, and dust, much like
our own Milky Way, we think. But of course, now, we get
the genuine external view of what Andromeda looks like. And in fact, you can get this
with a pair of binoculars if you know where to look
on a nice, dark night. You can see this galaxy,
which is pretty amazing. It's this huge space in
between us and this galaxy, and yet the combined power of
hundreds of billions of stars is enough to shine
out as a beacon that you can actually
see with your eyes. But that's not the end of
the story either, of course. It is not just us
and one other galaxy. If you look out
further into space, you'll find a
smorgasbord of galaxies. They come in all sorts of
different shapes and sizes. And we've made estimates of
just how many galaxies are there out there. And one way to do that
estimate is to go back to the Hubble Space Telescope. This is a famous picture
taken with the Hubble Space Telescope, known as the
Hubble Ultra-Deep Field. And it has its origins
in work done shortly after the launch of the
Hubble Space Telescope, actually, where they took the
most expensive telescope ever built-- by then, luckily, it had
optical correctors put in it. Because I don't know
whether you remember, but when it was launched,
there was actually a giant mistake in the way that
mirror had been fabricated. So They were able to put
in optical connectors, take this hugely
expensive piece of kit, and somehow, somebody
persuaded NASA to then point it at an area of the sky which,
to everyone's knowledge, was completely blank. Nobody had ever seen anything
in that little patch of the sky before. And to give you a sense
of the size of it, it's something like a tenth
of the diameter of the moon-- so really tiny, little
patch of the night sky. And they took Hubble,
and they pointed it at that little patch of
the sky for about 10 days. I think it was over
Christmas 1995, the first time this was done. And it's been done again since
then to get a sharper image. But essentially, that
first time it was done, an image very much
like the one you're seeing before you today came
back from the telescope. So in that tiny little
patch of the sky where no object was
known to exist, you saw all of these
sources of light. And in fact, pretty
much every dot of light you're looking at here
is a galaxy beyond our own. Now, if you scale up from
that tiny patch of the sky up to the size that we
can see in the universe today-- so if you could
somehow point the Hubble Space Telescope at all of the
different patches of sky, which, of course,
nobody is going to do because you want to point
it at more interesting things. But if you could
somehow replicate this across the entire
sky, then you come to an estimate of the
number of galaxies around about 200 billion
galaxies or maybe 400. So not only do all
of these galaxies have hundreds of
billions of stars, but there are hundreds of
billions of the galaxies. And perhaps a very
large fraction of all of those stars
in the entire universe have planets around
them, as well. So there's an awful lot of
the universe to go around. And if we want to
start putting together some picture of where on
Earth it all came from, we actually have to broaden our
horizons even further, still, to look at not just the
individual galaxies, but the way that the
individual galaxies are spread across space. Because when you look in
a relatively small patch, like this image from the
Hubble Space Telescope, they appear to be more or
less just randomly scattered through space like somebody's
just thrown them in at random. But actually, if you're able
to use specialised telescopes to get an even
broader view, you can start to understand that
the galaxies are not spread at random. They have some
structure to them. And this is a picture, actually,
of a computer-generated universe, but it
gives what we think is a pretty good representation
of the way galaxies are spread out in our universe. So every dot of light
you're looking at here is an individual galaxy. And you're now looking
at it on such vast scales that the individual
galaxies themselves are joining up to form
long chains through space, in something that we
call the cosmic web. The fact that the galaxies are
not spread at random tells you that there's some kind
of organisation behind the universe, as a whole. And it is that organisation that
we're seeking to understand. In fact, we think the same
organisation that gives rise to this cosmic web also
gives rise to the individual galaxies. And in fact, by
extension, it gives rise to the stars and the planets. Because as far as we can
tell, the story of the cosmos is that early on, there
were no stars and planets. And over time, things get
built within our cosmos. So the universe
started something like 14 billion years ago,
and since then, structure has been building. And only by building
galaxies can you actually create the conditions
to form stars and then planets within that. So how is it that I'm able
to make statements like, well, the universe is
14 billion years old, and things have been being
built ever since then. Well, I'm not making
it up on the spot. We do actually
have some evidence that this is what's going on. We're trying to gather
more evidence about exactly how the universe has evolved. But one of the most important
things we have on our side is that when it comes
to these cosmic scales, light travels pretty slowly. So when we're on human scales,
it seems like light travels instantaneously. Pretty much to all
intents and purposes, as I wave my arms around now,
you can see me instantly, even at the back of
the lecture theatre. But if you scale that up
to enormous cosmological distances, that's just
no longer the case. Although light is
moving very fast, like anything, if it has
to travel a large distance, it takes a long
time to get there. So if you look out
into the cosmos over sufficiently
large distances, you're actually
looking back in time. So when we look
at the sun-- well, actually, don't look at the sun. That was really a
bad thing to say. But if you were
to look at the sun through the correct
visual apparatus, then you would be seeing
the sun as it was something like eight minutes ago. And that's just literally
because of the time it takes for the light to
get from the sun to us. And when you go out to
stars, it can take years for the light to reach
you, or even tens of years, or hundreds of years, up
to thousands of years. But if you go to
distant galaxies, you're talking about
millions of years, or to the really
distant galaxies where you need powerful professional
telescopes to find them, you're suddenly talking
about billions of years. So we can actually
see what the universe was like when it was younger. And by taking that
information, we're able to build up a story
of how the universe got to be like it is today. And one of the
most famous things that's been established
about the universe is it's actually expanding. So not only is it vast,
but in fact, the space itself is getting
bigger every single day. It's doing that at a
relatively slow rate, but over billions of years,
it's extremely significant. In fact, when we look
at galaxies around us today, we see that they're
streaming away from us. So if we reverse the tape--
if we imagine-- all right, so we've got evidence
that the galaxies are flying away from us today. If we imagine
going back in time, then all the galaxies must
have been closer and closer together. And if you extrapolate that
far enough back in time, then all the
galaxies must surely have been on top of each other. That might seem like quite a
leap from where the universe is expanding today to
the universe therefore once had everything on
top of everything else. But in fact, by building
specialised telescopes, we're able to find very
direct evidence for that. And this is a telescope
called the Planck Satellite. It was launched by ESA, again,
probably about 10 years ago, now. And it was specially designed
to pick up the oldest light in the universe. So light exists at a range
of different wavelengths. That's what gives rise
to different colours in our everyday lives. But there are colours of light
that we can't see directly, and one of those is microwaves. So the thing that your microwave
cooker uses to heat stuff up is, in fact, a type of light. And it's exactly
the type of light that you would expect to be able
to find from the earliest time in the history of the universe. Because if the universe was
once very small with everything on top of everything
else, then it must also have been
really quite hot. This is the same physics where
if you pump up a bicycle tyre, you'll find that it
actually gets quite hot. That same physics means that
as you cram more and more stuff together as you go further and
further back into the universe, it must actually have been
at a higher temperature. So the early universe
was a very hot place. Since then, it's been
expanding and cooling down. Now, if that is
true, there should be remnant microwaves left
over from that early time in the universe's past. The Planck Satellite was
not the first telescope to go after these microwaves. In fact, there'd been a
bunch of experiments starting as early as the 1960s that had
already found these microwaves. So the first piece
of evidence that really showed that
the universe was once absolutely tiny, and
very hot, and dense was found in the 1960s. And it was just the existence
of these microwaves-- just the fact that you can
find the microwaves at all. But in the last 20
years or so, the story has been not so
much the existence of the microwaves, but measuring
the detailed properties of the microwaves-- in some sense, putting
together a picture of what the early universe
actually looked like. So the picture that Planck
put together looks like this. And it sort of looks a bit like
somebody got a bit carried away in the early universe with
painting the nursery bright colours. That's not what's
going on, of course. What's going on is you're
seeing a false colour image of the actual picture
that was taken. Because what we're
trying to show here is the fact that some
parts of the early universe were ever so slightly
hotter than other parts of the universe,
which you pick up just by pointing the telescope
in different directions. And the fact that
it's a big oval just reflects that this is actually
a map of the entire sky. So it's a bit like making
a map of the entire Earth and then projecting it
onto a circle on the page. You can do the same with the
sky, project it onto the page, and this is what you get. So the red spots are regions
of the early universe that were just ever so slightly hotter. And the blue parts of
regions of the early universe that were ever so
slightly colder. And the differences from the
blue to the red in this image are absolutely minute. They're at the level of
something like one part in 10 to the fives-- one part in 100,000 or so. And what that tells you is
that unlike today's universe where things are very different
from one place to another-- here, we are on Earth. If we teleport to a
random part of space, we'll just find it's pretty
much completely empty, and we'll suffocate. So one part of
the universe today doesn't really look like another
part of the universe today. Back in these early times, there
was very little distinction between one part of the
universe and another. You could barely
tell the difference about which part of the
universe you were living in. And in particular,
there's no evidence that there were any
galaxies, or stars, or planets there at this time. So how do we fit all
of this together? Well, we've come up with quite
a remarkable story about how this can be made to work. And the idea is that
although the differences in the early universe were
very slight from one place to another, they were
enough that gravity is a factor you have to include. So if you have a part of
the early universe which has slightly more stuff in
it than its neighbours, then there will actually be a
net force of gravity towards that part of the universe. And that will have
the effect of sucking in material from the surrounding
regions of the universe. So over time, something
which starts out just having a little bit
more stuff in it will get more, and more,
and more stuff in it. And this is a kind of runaway
process that, in the end, is able, we think, to
build galaxies, and stars, and planets, and the universe
that we know and love. There's just a small price to
pay for this beautiful picture of how the universe has got to
its current state of affairs, which is that it works, but
only if 95% of the universe is invisible. So on the one hand,
it's an amazing success. But on the other hand,
it does invoke a lot of unknown quantities, which-- really, the goal of
cosmologists at the moment is to understand some
of these unknowns. But let me show
you how it works. I'm going to do this with
some computer simulations that we ran. A lot of what we do in cosmology
involves computer simulations. Essentially, we programme the
universe with some of the laws of physics that we think
are relevant, in particular, things like gravity. We tell the computer
what the early universe was like using things like
the evidence from the Planck Satellite. And then we more or less
hit Go and say, OK, show us how the universe unfolds. So if I hit Go now,
you'll see the Big Bang. This big ball of stuff
is expanding towards you. We don't think that the universe
has an edge to it like this. But when we put it
into a computer, we can only run some finite
little portion of the universe, so our computer
model, of course, has to have some
kind of edge to it. And you saw it
expanding towards you, and now here we are, approaching
2 billion years after the Big Bang. That expansion is just
the overall expansion of the universe. And what you'll
have seen so far is something that
originally just looked like a green ball has turned
into a green web of structure. And that structure is what I
was showing you earlier on. That's the cosmic web. Now, nothing much
in space is green, so you might wonder why
on Earth this looks green. It's because we've
asked the computer to project this in green
for the simple reason that you could never
see this view yourself. It just reminds you that this is
actually not something that you could see with a telescope. Because what you're
actually looking at is what we think the dark matter
does at those early times. If I switch to a view that would
be more like something that you could take with a
telescope, the universe at 1.7 billion years old
looks something like this. So you can see a lot of
the features I showed you earlier on already exist. There are these big filaments. They've got gas in them,
and they've also got little forming protogalaxies
along them, which already have millions
or billions of stars living in them. So you can take a flight
through our little portion of the early universe here-- take a look through what
the various bits and bobs look like. And they just look
like blobs, really. A lot of the galaxies
that we think were there in the early
universe are a bit blobby-- not all of them. Some of them are also
beautiful spirals, like the ones that
we're more used to seeing in images from
the modern universe. You saw, there, the
scaffolding of dark matter that surrounds these galaxies. So that's really the
need for dark matter-- is to give the galaxy
some kind of scaffolding. And it's actually a lot of the
impetus that's drawing material into the little
forming protogalaxies that we see here on the screen. And if I restart time, you see
what happens as time goes on. It's this process I was
talking about a moment ago that one small galaxy
has the effect of pulling in all the neighbouring
galaxies because it's just got that slight extra
gravitational tug towards it. So surrounding little
galaxies tend to get attracted into their slightly
more massive neighbour. And if you watch
what happens next, those galaxies
progressively merge together and build larger, and
larger, and larger galaxies. All the while, as
this is happening, the raw materials,
like gas and dust, within these
individual galaxies are being able to form more stars. And so the total number of
stars in our little portion of the universe is
rapidly going up. And they would also be
forming planets around them. We don't have computer models
that are yet powerful enough to see planets form around
the individual stars. Hopefully, one day, we'll
be able to get there. But at the moment,
all we can really say is that some stars
are forming within our computerised universe. If I skip all the way forward
to near the present day, you end up with this big
swirling mass of gas, stars, and dust that, if
you fly into it and go all the way
to about halfway out to some
insignificant spiral arm, you find somewhere that our own
star, the sun, might reside. And then you can
take a look at what the night sky in this computer
universe actually looks like. And it looks at least a little
bit like what our own night sky looks like. And all of that
comes from starting with what seems to be
quite an alien beginning to the universe-- very small,
very hot, and only very small ripples going
through the universe. So we do actually understand
quite a bit about, at least, what made what's
inside our universe. And if you want to really
answer the question of what made our universe as
a whole, of course, you have to answer
the question that's one layer deeper than
that, which is, well, where did these ripples come from? And that's a very
interesting topic that we'll have to
postpone for the next time you vote for a
cosmological topic. So for now, I just wanted to
conclude by saying even though all this can make you
feel insignificant-- or it certainly makes
me feel insignificant-- I think it is really
a great privilege to be part of a human race
that has taken the time and energy to actually
look into all of this and piece together
our own cosmic history and our part in it. So thanks very
much for listening. [APPLAUSE]
