Hello, everyone. My name is Brian
Schmidt, and today I'm going to tell you about
the accelerating universe. Now the accelerating
universe is not a story that is just my own. It really is a story
about cosmology and the 100 years of development
over the past century. And so let's first start
with a tour of the universe. And the first
thing I want to say is that the universe is big. Now to understand
just how big we're going to use the speed of light
as our tour guide and the fact that it travels 300,000
kilometers per second. That's 7 and 1/2 times
around the Earth each second. So for example,
when Neil Armstrong took his "one small
step," well, we found out about it 1 and
1/2 seconds after that event occurred. And the radio waves
from his voice were transported right down the
road here at Honeysuckle Creek and then transported
around the world. You may not realize
it, but the sun is five light seconds
across, so much bigger than the Earth-Moon system. The reason the sun is
so small in the sky is because it's so far away,
about eight light minutes in distance. Now our sun is only one
of many stars in the sky. The nearest of stellar
systems is Alpha Centauri, the brighter of the two pointer
stars to the Southern Cross. Alpha Centauri is a star not
dissimilar to our own sun. And I want you to
imagine it being a pea. If it were a pea and
sitting here in my hand, and we think of the
sun being another pea, where would the sun have to
be to be the right scale? Well, about Sydney,
270 kilometers away. Everything in between
is empty space. And so you can see why
we call space "space." There's a lot of it out there. So if we look out
to our own galaxy, we see our sun is some 30,000
light years from the center. And our sun is made
up of not just one or two stars but a hundred
billion stars like our sun. And so it's a very exciting
part of the universe but only a small part of it. Looking further afield, we
can see the nearest galaxies, the large and small Magellanic
Clouds, right down here, are little satellite
galaxies of the Milky Way. They contain 10 billion and one
billion stars, respectively. But they're tiny little galaxies
that don't amount to much. The first real
galaxy of any size is the Andromeda Spiral,
about two million light years in distance. It's a galaxy that's a little
bigger than our own Milky Way, but just the tip of the iceberg. Here we are looking
only in the nearest part of our own universe. The most distant
image that we have been able to take
of our universe thus far is with the
Hubble Space Telescope. And this is the image we
call the Ultra Deep Field. In this image, there are
about 5,000 galaxies. Each of these galaxies is not
dissimilar to our own Milky Way, containing hundreds
of billions of stars. And so this part of the image--
this part of the universe, very small, is one 32
millionth of the entire sky. And so while the
universe is huge, at least the part we
can see is not infinite. We take 32 million pictures like
this, and we've seen it all. And the reason we
can see it all is because the universe, although
very big and maybe infinite, is not infinitely old. If we look back 13.7
billion years ago, we see a picture of the
sky that looks like this. This is an image taken
in microwaves and shows not stars and galaxies,
but little ripples of sound leftover from the Big Bang. Each one of these
ripples is a sound wave which eventually forms tens
of thousands of galaxies. And before that, of course, we
have the time of the Big Bang. All right, so let's go to
the beginnings of cosmology and figure out how we
learned all of this. I really see the
beginnings of cosmology when we were able to take
the light from stars, spread them out into the
colors of the rainbow, something we call a spectrum. And a spectrum of
a star reveals what the star's made out of
because every element has a fingerprint-- a fingerprint of light and color
which it absorbs and emits. So for example, sodium
has a fingerprint where it emits an orangey-yellow
color, which you can see in, for example, lights
around airports or in other places that
have sodium lights. Neon has a similar fingerprint. That gives you the
fingerprint of a neon sign. Well Vesto Melvin
Slipher, in 1916, took the light of not stars
but galaxies, spread them out into the spectrum, and he saw
that these galaxies looked a lot like stars but
with a difference. And that difference
was that their light was stretched red-ward. And Slipher knew what
that meant from something we call the Doppler shift. So if you look at, for
example, a police car that's coming toward you,
its sound waves are compressed by its motion. And when you
compress sound waves, you raise the pitch of sound. As that star, as that
car, goes past you, well, then you're
seeing the sound waves, which are stretched
rather than compressed. And when you
stretch sound waves, you make the sound lower pitch. Now light is a wave,
and so it is affected by the exact same process. And that process for light
is when you compress light, so an object moving towards
you, the light is made bluer. And when you stretch light,
well, the light is made redder. And so when Slipher went
through and saw that all these galaxies' light was stretched,
he realized that all of the galaxies in the universe
seem to be moving away from us. There are a few
nearby objects which are actually coming towards
us but very, very few, only a handful. And so this was a
big mystery in 1916. Why would all the
galaxies in the universe be moving away from us? It seemed to
indicate that we were a special place in the
universe, a seemingly very unpopular place in the universe,
which everything else was trying to get away from. So trying to unravel this
mystery took some time, and it took being able
to measure distances. Now measuring distances
in astronomy is not easy. We cannot lay down a ruler
between us and the nearest star or galaxy. Instead, we have to resort
to how things appear. So for example, a candle
or any light source appears fainter the
further away it is. On the other hand,
a ruler, of course, appears smaller the
further away it is. So Edwin Hubble was able to use
a law that Newton had come up with, that is, the
inverse square law, which says that for example,
if you have a light bulb, and you move it to
half the distance, it appears four times brighter. And so by judging how bright
objects are in the universe, one can judge how
far away they are. So Edwin Hubble, in
1929, looked at the stars in Slipher's galaxies,
and he realized that the faster the
galaxy was moving away, the fainter its stars were. Or in other words,
the further the galaxy was, the faster it
was moving away. And to show you his data,
here is his data from 1929. And we have plotted
here brighter stars, meaning nearby
distances, fainter stars, meaning further distances,
and then on this diagram these are-- the bottom part
of the diagram is slow moving objects, fast moving objects. And from this data he said,
wow, there's a relationship. The further away you are,
the faster you're moving. And he said, in 1929, this means
that the universe is expanding. And to give you an idea
why Hubble said that, let's make a little toy
model of the universe. So here we have a
universe full of galaxies which, thanks to the power
of a computer, I can expand. And when I expand
those two images and look what's happened-- I'm going to overlay them from a
reference point in the center-- you can see that nearby objects
have moved a little bit. Distant objects, for example,
have moved a lot, here, here, and here. And so you can see,
the further away you are in an expanding
universe, the faster you move, just what Hubble saw. And furthermore, it
affects all the parts of the universe the same. So if I overlay those
images at a new spot, I see exactly the same thing. We aren't a special
place in the universe. Now it's nice to think
of this toy model, but you really want
to understand things in the universe with a theory. And our theory comes from Albert
Einstein, widely respected as one of the greatest
physicists of all time. In 1907, Albert Einstein
had a revelation that acceleration due to motion
and acceleration due to gravity were indistinguishable. That is, imagine you were in
a box, and you are on earth, and you don't know
where you're at. And you feel yourself
being accelerated by 9.8 meters per second
squared, the gravity of Earth. Albert Einstein's thought was
that you cannot tell using any physical test whether or not
you're on Earth or in a rocket ship that's speeding up at that
acceleration rate of 9.8 meters per second squared. A very simple thought,
but a thought that took him 8 and 1/2 years to
reconcile with mathematics. The result, his field equations. And it predicted many things,
including curved space, and allowed him to do something
for the first time, something that Newton was
never able to do. That is, solve for cosmology--
how the universe behaves on the largest scales. Now he did this in 1917,
and he got a nasty surprise. He found that the solutions
for the universe were dynamic. That meant that the universe
had to be in motion, had to be expanding or contracting. And in 1917, that was
12 years before Hubble made his great discovery. And so Einstein did what
any good theorist does when they have a theory
which they're sure is right but doesn't quite
fit the observations. You come up with a fudge factor. And his fudge factor was
the cosmological constant. This is sort of like
energy that is part of the fabric of space itself. At least that's how
we think of it now. Of course, it was realized later
on in his life, when Hubble discovered the
expanding universe, that the universe
really is in motion, and that Einstein
could have predicted it from the basis of his theories
along with everything else he predicted. But it also turns
out mathematically, the universe wouldn't sit
still, even with the addition of this stuff. So the idea of this stuff
is you'd add some of it to counteract gravity because
this stuff causes gravity to push rather than pull. And we're going to come
back to this later on. So under Einstein's
view of the universe, things are a little different. When we looked at
distant objects, we're looking back into
the past because light takes its time to reach us. But the light, as it
travels to us as a wave, is traveling through
expanding space. And so it's not so much that
the objects are necessarily moving away from us, it's
rather that they're traveling through expanding space. And the further
the object is away, the more it has to travel
through expanding space, so the more it is
red-shifted as it gets to us. So imagine a universe
which is expanding. Let's put it in reverse. Things get closer and closer
and closer until viola, you get to the time of the
Big Bang, the time when everything in the universe
is on top of everything else. And so the Big Bang is sort
of a natural consequence of an expanding universe,
having a time when everything was on
top of everything else, very, very dense. So to think of this
graphically, imagine I have two galaxies separated
by some distance at some time. And if I go through and
I run the universe back with this line-- and this
line is the expansion rate of the universe, what we
call Hubble's Constant. So the steepness of
this line tells you how old the universe is, and
the steepness of this line is the value which
we call the Hubble Constant, the rate that the
universe is expanding today. So by measuring how fast
the universe is expanding, you can figure out how
old the universe is. Now I thought this
was a great thing to know back when I started
my PhD in 1989 at Harvard. And so three years, 11
months, and four days later-- but who's counting?-- here I am, showing my PhD
supervisor, Professor Bob Kirshner at Harvard, my
result for the expansion rate of the universe. And you can see I'm
very excited about it, and because the
answer that I got was that the universe is
about 14 billion years old, or that's a Hubble constant
of 70 in current measurements. Now it turns out, I was
part of a larger discussion throughout the community that
was figuring this number out. The eventual answer was
decided using the Hubble Space Telescope, co-led by Professor
Jeremy Mould, the director of Mount Stromlo
Observatory and the man who brought me here to Australia
back in the end of 1994. So we think the universe is
about 14 billion years old, but there's an
extra complication. When I showed you this
diagram, that line is straight. But what if gravity is
slowing the universe down? We expect, by
Einstein's equations and just common
intuition, that gravity is going to pull on stuff. And so just like a ball
that I throw up in the air and the Earth's gravity
pulls and slows down, I expect all the
gravity in the universe to pull on the universe
and slow it down. And so this universe,
you can see, is not as old as it
might otherwise be. Indeed, if we went through
and added a reasonable amount of gravity to the
universe, the universe, instead of being 14
billion years old, might only be nine or
10 billion years old. And that might be a
problem because we're pretty sure the oldest
stars in the universe are at least 12
billion years old. And we cosmologists
aren't too fussy, but it is useful
for the universe to be older than the
stuff that's in it. Now, when we look at
a diagram like this, we can also project
into the future. So imagine I look at a universe
which isn't slowing down. This is a universe which
is empty and coasting. It just keeps on going
at the same rate, gets bigger, bigger,
and bigger, and bigger. This is a universe
which goes on forever. It is infinite into the future. On the other hand, you
could imagine a universe which is slowing down. Here's the universe. If it's slowing
down quick enough, we'll reach a maximum size,
halt, and then go into reverse, just like the ball that
I throw up into the air. So while both these universes
start with a Big Bang, this second universe, of
course, ends differently. It ends with a gnaB giB. That's a Big Bang backwards. All right, so as a review, the
slowing down of the universe affects how old we think the
universe is from the Hubble Constant. It tells us the ultimate
fate of the universe. And it turns out, it tells
us the shape and weight of the universe. And that's because Einstein's
gravity bends space. So imagine I have
a heavy universe. The weight of the universe
bends space onto itself and makes it finite. This is a universe,
if I start here today, and I head out this
direction, given enough time, I will eventually come
back to where I started. On the other hand, you can
imagine a light universe. Well, space is
naturally hyperbolic, as we would say in geometry. It's the shape of a saddle. It bends away from itself. In this universe, triangles,
when you add up their angles, add up to less than 180 degrees. In the heavy universe, they add
up to more than 180 degrees. And if that doesn't make
sense, go out and try a globe, and make a triangle, a
big triangle on a globe. And add up its angles, and
you will see that on a globe, the angles of a triangle add
up to more than 180 degrees if you string. And finally, we have
the just right universe, the universe
precariously balanced between the finite
and the infinite. A universe which is just right
also because the theorists who study the Big Bang, or
right after the Big Bang-- a period which we
call Inflation, but that's a topic
of another lecture-- they think that
the universe must be right on this precarious
balance between the finite and the infinite for their
theories to make sense. So when I came to Australia
at the end of 1994, I was moving to a new
land, and I decided I wanted to do something big. So measuring the age of
the universe was one thing, but measuring its
ultimate future seemed like the biggest
thing I could think of. And so imagine the plan. You go through and you measure
how fast the universe is expanding now, something I
more or less did for my thesis. And then I look into the past,
and I recreate that experiment. I go and I look at these
objects a long ways in the past. So I'm looking a
far, far way away, and that allows me to see how
the universe changes over time. If the universe
isn't slowing down, well, then it's
going to be coasting. And it will mean that
the universe is infinite. It's empty. It's going to go on forever. On the other hand, if the
universe has got a lot of stuff in it, if it's
heavy, well, there is a trajectory in
which gravity wins. And faster than this, if the
universe is slowing down faster than this line, well,
gravity wins and the universe is heavy and finite. The other side of this
line, gravity loses. The universe is
light and infinite. And so to do this
test, well, we need to be able to measure distances
across the universe's past. And for that, the
universe gave us something, something
called a type Ia supernova, an
incredibly brilliant, exploding star
which to understand, we need to first understand
the life of a star. So the life of a star like
the sun is that it was born. Our sun was born 4.6
billion years ago. And in about 4
billion years, it's going to puff up and
eventually consume the Earth, crash down to a tiny little
star called a white dwarf, a star about the size of the
Earth, but the mass of the sun. Now if our sun was instead
born not as a single star but as a binary, that
same process happens. But when a big star puffs
up next to another one, this other star, the
smaller star, will survive. And it can go through
the same process. And that process
allows this white dwarf to grow in mass as it
siphons off material. And when it reaches 1.38
times the mass of the sun, it becomes a giant
thermonuclear detonation, producing light five billion
times brighter than our sun and synthesizing about 2/3
of the iron in the universe. These objects take
about 20 days to reach their maximum
brightness, and then they fade away into
oblivion over time. So these objects, it
turned out, were first looked at by Fritz Zwicky. Fritz Zwicky used a
Schmidt telescope. Schmidt telescopes
are not named after me or any of my
relatives, but they're a special type of telescope
that allow astronomers to take pictures of large
portions of the night sky at a time. And so by taking photographic
plates one night, and then looking a month later,
Fritz Zwicky and his colleagues could go through and
find things that changed. And they discovered this class
of objects, supernovae, which they named, that were
appearing in the nighttime sky and seemed to be these
powerful explosions. Now over 30 years, they
gathered a lot of data. And by 1968, they
were able to make their version of Hubble's
diagram, shown here by the one that Charlie Kowal did in 1968. And here, bright
supernovae, faint supernovae are plotted against their
redshift, low to high. And you can see the same
thing that Hubble saw. The further away you go,
the faster you're moving or the more you have redshift,
as we would describe it. And the scatter in this
method was relatively large, about a factor of
30% or 40%, but it was consistent with the
uncertainties in the experiment which were very, very large. From this work, supernovae
developed a reputation of being perfect standard
candles, that is, almost all identical. And to test that
a group in Chile formed in the early 1990s, the
Calan-Tololo Supernova Search. And I met Mario Hamuy,
here just above my head, in France in 1990 when I
was just starting my PhD, and they were just starting
this Supernova Search. And so they told me
about their plans to use these objects
as standard candles. And when I visited
Chile in 1991, the group was very depressed. They had been lied to. These supernovae were
not all the same. Three years later, when
I was seeing Mario, he told me that actually there
was a magic formula, a formula developed by his colleague,
and one of my colleagues also, Mark Phillips, which was that
the supernovae, while not all the same, had a very
specific pattern. And that pattern was that
these ones that rise and fall quickly are fainter than the
ones that rise and fall slowly. And we know, from
now, that these things make and synthesize
a little bit of iron. These do a lot of iron. And that process, we
can understand why this pattern happens in nature. So in 1994, when Mario came
and showed me his diagram-- and here is his version
of the Hubble diagram. You can see it looks a little
different than the other ones I've shown you because all
of the dots, each supernova, lie exactly on the line. And that indicates that
these supernovae were giving distances accurate
to 6%, and that is really good by astronomical
standards even today. From this work, this group
eventually found 29 supernovae. And these have provided
the fundamental basis of using type Ia supernovae
as distance indicators. So in 1994, there were
two breakthroughs. There was the one I've
just shown you about how to use these supernovae. But a group at Berkeley, who
had been working since 1988 to discover distant
supernovas in the hope that they could be used to
measure precision distances, had a major breakthrough. They went through and were able
to define, in a period of three months, seven such objects. And the thing that really
contributed to that was a lot of hard work, but
also the idea of technology enabling in the
form of computers and large CCD cameras, which
I'll talk about in a second. So that started a race, a
race between a group that worked on the supernovae,
which was a group that myself and Nick Suntzeff formed
in 1994, who was competing with Saul Perlmutter's group. We did talk about
working together, but the reality is we had very
different ways of approaching the project at this time. And so it became
clear that we needed to do the projects
in our own ways. And this set up a competition
between two teams, the High-Z Team and the Supernova
Cosmology Project. And here you can see Saul
Perlmutter, the leader of the Supernova
Cosmology Project, and myself trying to
punch each other out. We had a spirited competition. But I think most of the time,
we were very well-behaved. And certainly one
thing is clear. Science benefited
from the competition. Now I told you in 1994, we
had these two breakthroughs, and the one breakthrough
that's implicit was technology. In 1994, the Keck
telescopes came online. These were the new
10-meter size telescopes, bigger than the four- and
five-meter size telescopes we had before. These were necessary to go
through and take the redshifts and spectra of the
supernovae that we needed for this experiment. The other thing
that came along were these large-format, CCD cameras. These CCD cameras you know
in your digital cameras and video cameras, but they
came through the military, through astronomy, and were
dispersed into civilian life by astronomers more than anyone. And in 1994, we had the first
4 million pixel detectors, or 2K by 2K detectors
as we call them. And these things are about
100 times more sensitive than the ones, for
example, in your iPhone. And although 4 million pixels
doesn't sound very big compared to your iPhone, which typically
has an 8 megapixel camera now, you have to realize
in 1994, we were dealing with computers that
were Pentium II, 150 megahertz. And we were dealing with
one gigabyte hard drives. And so we were usually taking
20 gigabytes worth of data a night, and so the
technological challenge of sifting through this data
and finding the supernovae was very hard. Now just to make you think
that we here at the ANU are not sitting
still in technology, the ANU, through the Australian
government for Australia, has invested in the next
generation of telescopes. And these are called-- this new telescope that we've
invested in is called the Giant Magellan Telescope, a telescope
that is made up of seven 8.36-meter mirrors. And you can see these
mirrors all work together to give us both a
deeper and sharper view of the distant universe. The scale of this is
represented by the semitrailer at the bottom. And you see, this
huge telescope has to be aligned to an incredibly
precise accuracy of better than a micron, or a
millionth of a meter, and it's a very technologically
challenging project that we expect to reach
fruition over the next decade. It is a project we are doing
in concert with the Carnegie Institution, the country of
Korea, Harvard-Smithsonian, Texas A&M, University of Texas,
and the University of Chicago, and the University of Arizona. So it's a great
project for the future. And to show you that
is really happening, I was at the
University of Arizona, where I was a undergraduate,
which is making the mirrors. And here is the first
mirror, 8.36 meters, polished to 19 nanometers--
so a nanometer, a billionth of a meter-- across the whole surface. And that's mirror one. It's done. Mirror two, well, it
came out of the oven, and here it is sitting there. And mirror three goes in
to be melting in the oven early next year. And so this project is
really coming online. So technology is the secret
enabler to astronomy. And so I think astronomy,
with investments like this, has a great future in the
future here in Australia. So the technology
of 1994, as I said, was very challenging
to go through and sift through data like this to
find the exploding stars. There's 5,000 galaxies
in this image, and the key is to find the
needle in the haystack, the exploding star. And that exploding star is
this little smudge right here. And the way we find this
is not by taking one image, but by taking two and
separating them in time. So for example, if
we take an image, and we compare it to an
image taken, in this case, 24 days earlier, we can see that
nothing has become something here. This something, a supernova 5
billion years in the universe's past, a supernova which exploded
before the Earth was formed. That is the power of cosmology,
being able to look in the past. Fortunately, we can't
look into the future. We can only speculate
about the future. To give you an idea about
how one of these trips works, I'm going to take you to
Chile, to the CTIO four-meter telescope, where we are getting
ready for a night's observing. Here we see Greg Aldering from
the Supernova Cosmology Project silhouetted against
the background because he's the bad guy. Nick Suntzeff here is
leading the observations. Nick is a incredibly
finicky astronomer. He wants everything
to be perfect. And well so, because we
only get six nights a year because we have to
share this telescope, of course, with all the other
astronomers in the world. Nick makes sure that every image
is precisely pointed and is of perfect quality so that
my software can run on it. And then a team of
people can go through and look for the candidates
my software puts up and see if we are finding
things that we can use for measuring distances. My software is OK. It's not perfect. There's a lot of junk,
and time is of the essence because we have to go
and look at these things across the globe at the Keck
telescopes 36 hours later. So we have to process all
that data as fast as we can, so we can get onto it with
these large telescopes. Here we have Alex Filippenko
and Adam Riess making sure that they get spectra. And of course there, we're
sharing the telescope time also with the Supernova
Cosmology Project. Saul Perlmutter there. And they are too, of course,
using the same facility. We were both using
the same facilities, the best facilities that were
on offer to do this work. So in 1997, Adam
Riess contacted me. He was reducing and
analyzing the data that we were taking for our next paper. And he said, well, what
do you think of this? And what I saw
was the following. Each supernova here
is a point, and it has an error bar because the
supernovae have an uncertainty. And these error bars
essentially tell you where 68.3% of the time,
the correct answer lies. So one in three chances,
it's out of here. But two out of three is it
lies within that error bar. And when I looked at
these nearby objects-- these are the objects of
the Calan-Tololo survey, the Chilean group,
who are actually part of our team as well. And you can see that compared
to this trajectory, on average, you can't tell what's going on. That's why we had to
look a long ways away. These objects, the
distant objects, though, not a single
one of them is consistent with the
universe which is finite. But on average, you
can also see that they don't lie in the yellow
part of the diagram, the part of the diagram where
the universe is slowing down. Instead, they seem to lie up
in the top part of the diagram, the part of the diagram
which says the universe is being accelerated
by something unknown. In this case the question then
was, hmm, what's going on? People ask, did you say eureka? And the answer is no. I think we really thought,
jeez, what have we done possibly wrong? So here we have Adam
Riess's lab notebook where he first wrote down
what this meant to him. And what he found, when
he did the calculations by the traditional method, is
the universe had negative mass, or effectively gravity was
pushing rather than pulling. So I'm afraid there
was no eureka. There was a great
deal of hard work to figure out what was
going possibly wrong. After the end of that
period, we decided nothing seemed to be going wrong. It was a crazy result, but
as scientists, we ultimately have to report what we
see, not what we like. And so in 1998, we
put a paper out. And it turns out that the
Supernova Cosmology Project was getting the exact same
crazy result at the same time. And so it wasn't one,
it was two papers that came out pointing
towards an acceleration of the universe. And so these two papers
are what eventually led to the discovery of
the accelerating universe, and to what became the
Nobel Prize of 2011. And because this work is really
done not by three individuals who won the Nobel
Prize, but by two teams, I think it's very important
to point out the teams. Here's the Supernova Cosmology
Project and our own High Redshift Supernova team, dressed
as we like to normally dress, in white bow ties
and tails, here for the first time ever
together at the Nobel Prize ceremony in Stockholm. So that sort of gives you
an insight of team dynamics. This team had never all
been together in one place until the Nobel Prize ceremony. We all knew each other. We had all worked
with each other. But because we were dispersed
across five continents, we were never able all to be in
the one place at the one time. We had a great
time in Stockholm. And to give you a
sense of what Stockholm is like, when you got off the
plane, if you're a Nobel Prize winner, first
thing is they don't have you go through
security in the normal way. Instead, they give you a
driver, and they whisk you off the airplane. And in my case, I
came up, and my driver said, hello, my name is Steig. And I said Steig? Hmm. And I thought, I
think he's going to get us around the streets of
Stockholm just fine, thank you. The other thing you get to do
is you get to meet the king. So here the king is
presenting me the award. And the Swedes really wanted
to know, more than anything, not, what came
before the Big Bang? What is the universe
expanding into? No. They want to know, what
did the king say to you? So in my case, the king
said, congratulations on behalf of the Swedish Academy
for the Nobel Prize in physics, and thank you very much
for the bottle of wine. Because I'm a winemaker,
among other things, and I presented him a bottle of
wine before the ceremony. So I hope he liked it. And the final thing that they
give you, in my case at least, was a princess. And here I am escorting Princess
Victoria at the banquet. And when I look at this
photograph, when I first saw it, I said to
my wife, I said, jeez, I look so glamorous
with a princess on my arm. And turned out she
didn't appreciate that as much as I had hoped. Turns out she also had the
Swedish prime minister, a tall handsome guy, so she
didn't completely miss out. All right, so what is
pushing on the universe? Well, we only have to look
to Einstein for the answer. His cosmological
constant, the energy that is part of space
itself, well, that turns out can actually provide us a
way to make gravity push rather than pull. This stuff, if it exists,
makes gravity push as the fundamental way that
gravity works in his theory rather than pull. So by adding some of
this stuff to space, we can go through and get
the universe to speed up. Now, we're not sure that
Einstein's version of this is correct. And so we give it another name,
and that name is dark energy. Now, whenever astronomers
use the word dark, it's because we can't see it. And that means, since
astronomers look at things, we don't understand
it very well. So dark energy is really "stuff
we don't understand very well" energy. So if you do a detailed
analysis of our work, you come to the conclusion
that the universe is a 30% mixture of normal stuff
pulling on the universe and 70% pushing on the universe. So we really need a little bit
of pull, a fair bit of push, to make our
observations make sense. Now, when we released
these in 1998, the community was
justifiably skeptical. I was skeptical. I couldn't believe the
universe could be so crazy. But I knew that our measurements
were fundamentally correct, that the supernovae were
too faint to make sense, except for if something
crazy were going on. So a series of
experiments were made. And the first one was done-- or one of the first ones
was done here in Australia, where a group using the
Anglo-Australian telescope, an Anglo-Australian group, made
a map of the nearby universe out to about a billion
light years, making a map of 221,000 galaxies. And you can see
that the galaxies aren't smoothly distributed. They sort of show
this cosmic foam, and that foam is caused
as a signature of gravity. And so it turns out by
looking at this foam and how galaxies are moving
and the nature of this foam, they were able to
very precisely measure the weight of the universe
in gravity as it attracts. So they actually essentially to
weigh attractive gravity here. And so the amount of gravity
pulling on the universe, by their measurement,
was 27% of the amount of stuff necessary to
make the universe flat. So astronomers weigh
the universe, typically, relative to the amount
of stuff necessary to make the universe
just right, to bring it to that precarious position
between finite and infinite. The amount of stuff
in the universe was 27% of the way
there, at least the stuff that makes gravity pull. The other experiment that came-- sorry. But the other thing
I need to mention is that this, while not enough
to make the universe flat, was still five times
stronger than the gravity we could account for by
the number of atoms that were in the universe. And so this stuff, of
course, the shortfall is what we call dark
matter, or in the vernacular before, "I don't really
understand" matter. This is stuff which
we're hopefully going to get an insight into
over the next couple of years. But we think it's some
undiscovered particle that, like a neutrino, can pass
right through the Earth. So it has gravity,
just like atoms, but is essentially invisible. That's at least our hope
what this stuff might be. So the other experiment
that was able to be done was using the cosmic
microwave background, this image of the universe
taken right after the Big Bang, 380,000 years back
to the Big Bang. So these sound waves
splashing around the universe have physics which is very
similar to what we can do here on Earth very accurately. And so the physics tells
us exactly how long these sound waves are. So for example, one
of these sound waves right here is about
450,000 light years long. And if you remember, how
big something appears depends on how far away it is. But it turns out,
it also depends on the shape of the universe. If you look at things
in a curved space, the light waves get bent. And so not dissimilar to a
car, objects, for example, in curved space
that's finite appear larger than in a flat universe. So we can use that to
make a precise measurement of the geometry of space. And when you do this, you find
that those little bumps add up to being exactly what you
expect for a universe which is geometrically flat,
that is, has 100% of all the stuff necessary to be flat. Now, the geometry
of space doesn't care if it's made
up of stuff that makes gravity pull or push. It's sensitive to everything. And that allows us to do a
little bit of subtraction. So if we add up
everything, we have 100%. We subtract off the stuff
which is attracting, 27%. And that leaves us with
73% mystery matter, the same mysterious stuff
that the supernovae found, is pushing the universe apart. So what does that leave us? Well, it really leaves us
with a mess, a universe where 4 and 1/2% of the universe
are atoms, the stuff we know and love and are made out of. We represent a
very small minority of what's in the universe. The rest of the stuff is
dark matter and dark energy, dark matter pulling,
dark energy pushing. Dark matter pulls
along with the atoms in almost exactly the same way. Now you might think,
well, if we only understand 4% of
the universe, and we have to make up 95 and
1/2% of the universe, we just don't know
what we're doing. And that may be a good call. But this model of the
universe has been asked to predict many, many things. And over the last
13 years, everything it has been able
to predict, we have been able to go out and
measure and show to be true. And that is how science works. Reality is what the
theory predicts. You know, when a theory
predicts something to be true, that is the reality of the day. Now, it may be that
there is something wrong with this model,
and we're getting lucky being able to predict things. But the things we predict
are sufficiently complicated now that I think
most people think that this model
has, essentially, the truth embodied in it. And while it's probably not a
perfect model of the universe, it is a model like
Newton's gravity, which works very, very
well at describing the universe we live in. Crazy? Yes. Messy? Yes. But it seems to be the way
the universe is constructed. So dark matter. As the universe expands, the
amount of matter and atoms stays the same, so
dark matter's density and gravitational
effect gets smaller as the universe expands. On the other hand, dark energy
is tied to space itself. As the universe
expands, the dark energy gets created with
the created space, and so it becomes
stronger relative to dark matter over time. So this sets up a battle for
domination of the universe, dark energy versus dark matter. After the Big Bang, the
universe was expanding. Dark matter would have been
very dense and very strong. It would have been
slowing the universe down. As the universe gets
bigger and bigger, dark matter's
domination is dropping. And at some point about
5 or 6 billion years ago, it turns out the universe
got sufficiently big, before dark matter
could slow it down, that dark energy took over. And so the future of
the universe-- well, the future of the universe
seems to be dark energy. The more space expands,
the more dark energy can push against
gravity, creating even more space and
even more dark energy, leading to a runaway process. Eventually, the
creation of space can happen even more quickly
than light can travel. And so galaxies we see
today will literally be lost as their light
goes through and is stranded in the
expansion of space between us and those galaxies. In the first-- in the oldest
picture of the universe I showed you, taken with the
Hubble Space Telescope, those galaxies that we see back
10 to 12 billion years ago-- the light they emit today
will never reach us. Those photons will be
stranded in the creation of space between us. Now, just to allay
some of your fears, attractive gravity has
defeated dark energy in our part of the universe. You are not expanding. The Earth is not expanding. The Milky Way is not expanding. And that's because our part
of the universe, dark matter and atoms overwhelmed the
expansion of the universe 13 billion years ago. And so our part of the universe
quit expanding and collapsed. And there's a little
sphere or ball of material where there was enough
mass to do that, and that's what formed our
own part of the universe. However that part of the
ball, of the universe, is gravitationally bound
and will eventually merge into what we will
call a super galaxy. And so we believe the
Andromeda Galaxy, which is one of the few
galaxies in the sky that's coming towards us,
will eventually merge with the Milky Way 3 or
4 billion years in the future. And we're going to have
this spectacular change in the nighttime sky,
from first two Milky Ways, effectively, in the
sky, finally merging into a big ball of
stars, into something that would look more like
an elliptical galaxy, as we call them. But the rest of the universe
beyond that bound ball will be accelerated
out of sight. We will look out onto
stars and nothing else. The rest of the
universe will be empty. And that will leave
cosmologists such as myself, who study the distant
universe and galaxies, out of a job because there'll be
nothing left for us to look at. But the reality is
until we understand what is accelerating the
cosmos, anything is possible. One of the most
speculative ideas involves how dark
energy might be a little different than Einstein's view. You know, when
anything's possible, this dark energy
can change over time and potentially even accelerate
the cosmos at a faster rate than Einstein's version. And this leads to
the potential-- and I should say, this is very
speculative-- of something called the Big Rip
if dark energy gets created more quickly than
the creation of space. That is, if I have a box, and
I double the size of the box by the expanding universe, I
get more than double the amount of dark energy. Then that leads
to a runaway that is able to penetrate to
every part of the universe, including your own
body, and your atoms, and even down to breaking
the universe down into essentially
subatomic particles. And this point, as the universe
expands more and more quickly, the density of this dark energy
rises and eventually approaches infinity, allowing
the dark energy to eat in to where the
universe has already collapsed. And so this really has almost
a human timescale to it. As the galaxies disappear--
that happened a long time ago. Suddenly, the stars in the Milky
Way will start disappearing. Eventually, the sun
would disappear. And then some time later, poof,
every atom in your body taken far enough away that light
cannot be transported between any of the atoms, and even the
atoms themselves broken apart into quarks and electrons. So a very exciting
end of the universe. And that leaves nothing. Well, it leaves something. It leaves an infinitely
dense universe which is expanding very quickly. And that has a certain synergy,
I think, with Big Bang. So I kind of like
it at some level, but it doesn't mean it's true. So this is one of the things
we can go out and try to see if the universe is doing. At this point, there is no
evidence, unfortunately, that this is going to happen. And I should say, as far as
a theory of the universe, it has some real messiness
associated with it, having this energy
getting created more quickly with space. However, that aside, really
unless dark energy suddenly disappears, the universe will,
at an ever increasing rate, expand and fade away
in front of our eyes so that people like me, 50
billion years in the future, have nothing left to do. Thank you very much.
