Translator: Tijana Mihajlović Reviewer: Ilze Garda
Is everyone having a good time? All right!
What an amazing set of speakers, ha? TEDxBerkeley go! All right.
(Laughter)
Great to see you all here, hope you're having a great day,
and a wonderful Cal Day outside as well.
I want to tell you today
about the accelerating expansion of the Universe,
a revolutionary discovery that definitely has catalyzed change,
a discovery that was honored with the Nobel Prize in Physics
to the team leaders:
Saul Perlmutter, here at Cal, professor of Physics, in the middle,
Brian Schmidt on the right, at the Australian National University,
and Adam Ries at the left, now at Johns Hopkins University.
He was a postdoctoral scholar working with me at Berkeley
in the mid to late 1990s when we made this discovery.
There were 48 other people associated with the discovery,
but the rules of the Nobel are that at most three can get the prize,
other than a Peace Prize, which can go to organizations.
Fortunately, these gentlemen understand
that without the rest of us working in the trenches,
they wouldn't have been so honored.
So they spent part of their prize money
flying the rest of us out to participate in Nobel Week in Stockholm
in December of 2011.
We went to the most of the parties, and the celebrations,
and lunch and dinner at the embassy,
and all-night things put on by the students;
it was just a wild time.
About the only thing we didn't get
was the gold medal and part of the million bucks,
or the chauffeured limousine.
But, oh well, here we are.
Here's one of the two teams on which I participated.
I had the interesting distinction of being the only person
who was, at one time or another, a member of both teams,
and if you get me sufficiently drunk,
I'll tell you the inside story behind that. (Laughter)
Anyway, the story starts with Edwin Hubble,
who nearly a century ago studied these gigantic collections of stars,
called spiral nebulae,
and their true nature was not yet known.
It was thought by some
that they are clouds of gas in our own galaxy.
Others thought that they are other galaxies.
He studied certain types of stars within them
and showed that these are gigantic systems
far, far away, millions of light years away,
consisting of hundreds of billions of stars;
island universes, if you will.
They come in many shapes and forms, mostly these beautiful spiral ones,
like the one we live in,
and elliptical ones.
He noticed something very interesting: they're all going away from us,
or almost all of them are going away from us.
This had been discovered actually by some other astronomers.
By looking at the spectra, you can tell that they are moving away
because all those dark lines,
which are produced by chemical elements in the atmospheres of stars,
showed the same pattern,
but that pattern was shifted to longer wavelengths, redder wavelengths,
as though the things were moving away from us.
But Hubble noticed
that the nearby galaxies are moving away only pretty fast
and the more distant galaxies,
which generally looked smaller and fainter in the sky,
are moving away faster,
and the more distant galaxies are moving away really fast.
So at a given time, right now, the Universe is expanding,
but the more distant galaxies are moving away from us faster
than the nearby galaxies.
And we now know it is space itself that it's expanding.
Hubble resisted this interpretation for a while,
but we can now tell
that it's not that the galaxies are moving through some pre-existing space,
rather the space itself is expanding,
and the waves of light stretch with it.
This is the cause of the redshift.
It's not that they're moving away, not the classic Doppler effect,
but rather that the waves themselves are stretching.
You're not stretching because you're bound by electromagnetic forces.
You may think you stretch after a big lunch,
but that's your fault, not the Universe's fault.
The Earth isn't stretching because it's bound by gravity.
Our galaxy isn't stretching either,
but it's the space between the galaxies that is stretching.
The Universe is expanding.
So here's, from our perspective, the view:
we're in the middle there,
and all the galaxies are moving away from ours,
and the more distant ones are moving faster than the near-by ones.
Now, it's a bit strange that we're at the center, right?
Do all the other galaxies not like us?
Is it something we said? Do we smell?
(Laughter)
Are all these other galaxies lactose-intolerant?
Get it? Milky Way Galaxy, lactose-intolerant?
(Laughter)
Or, since this is a Cal-friendly crowd, what is it?
Are we from Stanford or something?
(Laughter)
With due apologies to those of you who might be Stanford alumni,
it's an outstanding institution, just not quite as outstanding as Cal.
Anyway, yeah, so…
(Laughter)
No, we're not in any central position.
In fact, we think we would see the same thing
no matter which galaxy we happen to be in.
Imagine a one-dimensional expanding Universe
where you have the galaxies - the ping pong balls,
and the rubber - the space between them.
From the perspective of the orange ball here,
all the others are moving away, so it thinks it's at the center,
but the same can be said from the perspective of any other ball;
all the balls are going away from it.
So there is no unique center,
at least not in the dimensions to which we have physical access.
With today's great telescopes,
we've measured the current expansion rate of the Universe,
and it's just some number; I won't bore you with what it is.
But in fact, the expansion rate should change,
and that's because the Universe isn't empty; it has things in it.
All those things will gravitationally pull on all other things;
the galaxies pull on each other, just as the Earth pulls on the apple,
and so, in its upward journey, the apple slows down;
eventually it stops and comes back.
So, if the Universe is dense,
every little volume will pull on every other volume a lot,
the Universe will slow down in its expansion,
some day stop, and then reverse itself.
It's hard to see with the lights here, but it goes -
it starts with the Big Bang, ends with a Big Crunch,
or you could say Big Bang, Gnab Gib, which is Big Bang backwards.
In a similar way, though the Universe is expanding now,
you could be lying on your back, looking at all these galaxies, saying,
"Tam-ta-ram, the Universe is expanding."
Then you notice something strange,
and right around now, you start getting a little bit nervous,
then it's sort of "Goodbye, cruel world!", and the Universe implodes in on you.
But there's another possibility.
If the Universe isn't very dense,
then, although the galaxies are pulling on one another,
slowing down the expansion,
that expansion should never stop
if the Universe has sufficiently low density.
That would be like an apple that I heave up or above Earth's escape speed;
it keeps on going away from the Earth forever.
So in that case, the Universe would expand eternally,
becoming ever colder, darker, more dilute,
and you're sitting there on your back,
looking at the galaxies living for billions of years,
and all is fine, except that the Universe
is going to become a very cold, and dark, and lonely place eventually.
We would like to know the fate of the Universe.
It's a central question of cosmology,
and we can figure it out
by examining the past history of the expansion.
After all, if I measure the speed of the apple
at many different times during its trajectory
and I notice it's been slowing down a lot,
then I can figure out that it'll some day recollapse,
whereas if I measure it and it hasn't been slowing down very much,
then it'll keep on expanding forever.
So in a similar way, we examine the past history of the expansion,
and we can determine the future, at least in principle.
Well, we have to look far back in time in order to examine the history,
and that means look far away.
The farther away you look, the farther back in time you're seeing,
because light doesn't travel infinitely fast;
it takes some time to travel.
You're seeing typical stars
as they were maybe tens, hundreds, maybe a thousand years ago,
because they're tens, hundreds or thousands of light years away.
Well, these galaxies might be one billion light years away, 4 billion,
those little tiny specks might be 9 billion light years away,
and encoded in their light is information about the expansion of the Universe
one, four, nine billion years ago,
that is during the time that the light has been traveling.
The redshift keeps on increasing.
So measuring the redshift as a function of look-back time
tells you the expansion history of the Universe.
To get distances of galaxies,
we need to see individual stars whose properties we recognize.
We know how powerful they are, we see how bright they appear to be,
and that tells us the distance.
But you can't see individual stars in those galaxies unless they blow up.
The individual stars are too faint, but some stars blow up.
They are supernovae,
they become millions or even billions of times the power of our Sun.
And they can been seen in very distant galaxies
and distinguished from their neighbors.
If we know the true peak power
because we've measured them in nearby galaxies,
- we measure how bright they appear to be -
we know how far away they are,
and hence, how far back in time we are looking.
Now, our Sun won't do this.
If it were to do this,
then sun blocker of 50 just wouldn't cut it, folks;
you'd need sun blocker, supernova blocker of a few billion to protect yourself.
But don't worry, be happy:
our Sun isn't going to end its life this way.
What we do is we find galaxies like this that are nearby.
We can measure their distances using relatively normal stars.
We find a supernova, measure how bright it gets.
If we know the distance to the galaxy, we then calibrate the true power.
This is how you judge the distance of an oncoming car;
you look at how bright the headlights appear to be,
you know how bright the headlights of a nearby car are,
and so you almost intuitively,
almost instinctively make this calculation.
If you're not very good at doing this, you shouldn't be driving at night.
We find nearby ones, and we've calibrated them
- that has been done -
so now we want to go
and find distant examples in faint, fuzzy, distant galaxies,
find the supernovae,
measure how bright they appear to be.
You know how powerful they really are,
that then tells you the distance.
By measuring the redshift - I don't know if we can see,
you can see it, I can't see it on my screen -
you can measure the redshift;
you can see how much space has expanded during the time of flight.
That's the idea.
We find them in these distant galaxies,
and we measure their brightness, we calculate the distance,
we compare with the redshift,
we reconstruct the expansion history of the Universe, and here's the punchline:
the Universe is accelerating in its expansion.
These supernovae are all fainter than they were expected to be.
The implied distances are so great
that no decelerating Universe could have expanded that much.
Even in the Universe that expands at a constant rate,
you can't get the galaxies, the supernovae, the apples far enough away
to make them look that faint.
Instead, the Universe had to have accelerated
in the past 4 or 5 billion years,
as though there is a cosmic anti-gravity force at work.
Here's the headline that came out in February of 1998,
after I had the privilege of announcing this result for Brian Schmidt's team.
We use this term anti-gravity hesitantly because people ask us,
"Can we attach this stuff, whatever it is, to our cars,
and levitate over Bay Area traffic jams?"
And the answer is no.
It's either a property of space itself,
or there's so little of it
that you can't harness it and attach it to your car.
By the end of 1998,
the editors of science magazine proclaimed this
to be the single, most important discovery in science that year.
Obviously, we were very pleased.
You might wonder why the caricature of Einstein looks surprised here.
It's because he's blowing universes out of this pipe.
You might not have known that universes exist in multiple forms
and come from the pipes of theoretical physicists.
Well, maybe not, but we do think there may be multiple universes.
But anyway, he's surprised because this one Universe
is expanding faster and faster with time, rather than more and more slowly,
as it would have been expected under the influence of normal gravity.
That was really surprising.
It's even more surprising because he has a sheet of papers under his arm
where there's an equation,
the Greek letter lambda equals 8πG, Newton's constant,
times the density of the vacuum.
And you say, "Density of the vacuum. Boy, Berkeley really has become Berserkeley."
Who is this bozo telling you about the density of the vacuum?
You were taught on your mother's knee that vacuum is nothing, zilch, nada.
How can it have a non-zero energy density?
Well, I'm just the messenger here. This was Einstein's idea, OK?
He came up with this idea in order to explain in 1917
the apparently static nature of the Universe.
The sky didn't appear to be falling,
it didn't look the Universe was expanding either;
it looked static.
It's like this apple.
If gravity pulls down on it,
but I'm pulling up with the same force upward,
the net force is zero, the apple doesn't accelerate.
You know, they say, "May the force be with you."
Lucas got it wrong: may the net force be with you.
(Laughter)
The force may be with you,
but if some other forces are against you, you're going to lose,
so here, Einstein came up with
(Applause) - thank you -
he came up with an anti-gravity, so to speak,
that cosmological constant that would make the Universe static.
Twelve years later, Hubble discovered that the Universe isn't static after all;
it's expanding, there was a Big Bang.
We don't know why that happened,
but given that there was a Big Bang, nothing needs to keep it going;
it keeps going on its own.
So Einstein renounced the cosmological constant
as having been the biggest blunder of his career,
because had he not introduced it,
he could have predicted that the Universe is expanding, not static.
He could have been famous had he not introduced this;
So here he is, sad that he ever introduced the idea.
I don't know if that's what he's thinking, but he might be thinking that.
What have we done the better part of the century later?
We've reincarnated the idea not to have a static Universe,
but one which, on the larger scales,
is expanding progressively faster with time.
So here, in this room, the down arrow dominates.
In our Solar System, down.
In our galaxy, down.
In our local group of galaxies, down.
But as you get to tens or hundreds of millions of light years,
the up arrow begins to dominate
and the Universe accelerates in its expansion.
If Einstein were around right now, his reaction might be something like this,
because what he thought was his biggest blunder
may well have been his greatest intellectual triumph.
Alright, well, you might say, you know,
"What is this stuff? Is it the visible matter?"
No, because that all pulls.
"Is it dark matter that holds galaxies and clusters of galaxies?"
No, that all pulls as well.
"Is it anti-matter?"
No, anti-matter has a normal gravity.
It has to be something new: dark energy.
As a consolation prize to the rest of us,
my wife Noelle came up with this T-shirt, "Dark energy is the new black."
Dark energy is the term we give to this mysterious invisible stuff
that's accelerating the expansion of the Universe,
and it's dark because we don't see it.
It's also dark in the sense that it's mysterious;
we don't know what it is.
You could say maybe the supernova technique is wrong,
maybe we're flawed somehow,
but it turns out
there are now other techniques that give exactly the same result
and most recently splattered
all over The New York Times and other newspapers
with the results from the Planck satellite,
a satellite that takes a baby picture of the Universe,
a picture of the Universe as it was when it was only 380,000 years old.
And analysis of that baby picture supports what we have done.
And indeed, though this is very recent,
it is just the latest in a set of a number of observations and experiments
that lead to the same conclusion,
that the Universe appears to be accelerating in its expansion.
It's not just the supernova result.
And those little fluctuations you saw were fluctuations in the temperature
and hence the density of the baby Universe.
Those tiny little variations,
set up by quantum fluctuations at the very beginning,
grew under the influence of gravity, that great sculptor of the Universe,
and the dense regions became denser
by stealing material from their surroundings.
It's like global economics:
the rich get richer at the expense of the poor.
So here you can see, in front of your very eyes,
the growth of what we call large-scale structure,
galaxies and clusters of galaxies under the influence of gravity,
but thwarted to some degree by this repulsive negative effect,
this anti-gravity.
The dark energy is thought to constitute
something like 70% of the contents of the Universe as a whole.
Not in this room,
but averaged over spheres of like a billion light years.
And we don't know what it is.
It has really catalyzed change in physics.
Dark matter, mostly remaining pie.
We don't know what that is either.
What we know of are the atoms; they are a small sliver in the cosmic pie.
So, because of the importance of this dark energy,
the recognition of the accelerating expansion of the Universe
was honored with the Nobel prize.
It has truly revolutionized our view of the Universe,
it is changing physics as we speak.
Many physicists think
that the physical origin and nature of the dark energy
is certainly among the most important problems in physics,
and some say the single most important problem in physics.
It's 70% of the Universe.
Moreover, it perhaps provides a clue to a quantum theory of gravity,
a unification of the two great pillars of modern physics,
quantum physics of the very small, and the physics of the very large.
No single observation has eclipsed
the magnitude of the change
that has occurred in the physics and astrophysics community
over the past 10 years,
and I feel incredibly privileged to have played a role in this discovery.
Thank you very much.
(Applause)
Thank you.
(Applause)