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)
