Kind: captions
Language: en
There are few things in the world that
seem more constant than the stars in the
night sky. If you look up at the Milky
Way, you will see the same thing that
people have looked at for thousands
[music] and thousands of years. But as
Professor Schmidt found out, the
universe is a much more dynamic place
than we give it credit for. [music] When
Albert Einstein was doing his theory of
gravity, his theory of gravity said the
universe should be in motion. He didn't
know if it was getting bigger or getting
smaller. [music] but his uh universe
should have been in motion. And yet he
looked around and said, "Well, the
astronomers tell me that the universe is
pretty static." Now, there were hints.
In 1916, a guy by the name of Vesto
Sliper saw that all of the galaxies in
the sky were moving away from the Milky
Way. [music] And so, that was a real
funny measurement back then and actually
was indicating the motion of the
universe. But how did Sifer know that
the galaxies were [music] moving away
from us? Well, he saw that their light
was redshifted. If an object is moving
away from us, its light [music] appears
more red. If it's moving towards us, its
light appears more blue. And virtually
all of the galaxies Sliper looked at
were redshifted. But it took till Hubble
in 1929 really to put it all together.
And he went out and he measured
distances to the nearest galaxies. Now,
Sliper knew that these galaxies were
moving away. Hubble looked at the stars
in them. And what he noticed was that
the faster that the object was moving
away from us, the fainter the [music]
stars were. Now, stars become fainter
when they're further away. So, he said,
"Well, let's just assume all those stars
are about the same." Hubble relied on
what's called a standard candle. A
standard candle is an object in space
that always gives off the same amount of
light. But as that light spreads out
through space, it becomes less intense.
So, by looking at the intensity of the
light, you can determine how far away
the candle is. So, if I walk out through
this field behind me, you'll be able to
tell how far away I am [music] by how
bright the candle light looks. By seeing
that the stars were fainter, he could
infer that the galaxies were further
away. So, the idea that the further away
an object was, the faster it was moving,
he said that means the universe is
expanding. And you can think of it as if
you put little dots on a balloon. You
blow the balloon up. Every dot moves
away from every other dot. And the
further the two dots are away, the
faster they're actually moving away from
each other when you blow the balloon up.
It's just like the expanding balloon.
The expanding universe does the same
thing. I wanted to do an experiment
which I thought I could explain to my
grandmother and measuring the ultimate
fate of the universe struck me as being
a good experiment to do that. So when we
started this experiment in 1994, we
wanted to measure the ultimate fate of
the universe by measuring how fast the
universe was slowing down over time.
That allowed us to see how much gravity
there was in the universe.
For his standard candle, Professor
Schmidt used type 1A supernova.
So type 1a supernovi are explosions of
white dwarf stars. So, a white dwarf
star is the thing that the center of our
sun will become once it uses all of its
nuclear fuel. So, it turns out that the
outer parts of the sun will blow off in
about 5 billion years. The center of it
will collapse down to something that is
uh about the size of the earth. And so
that star is a ticking nuclear bomb if
it can be made to grow to about 1.4
times [music] the mass of our sun. So
our sun will never do that. It doesn't
have anyone to provide that mass.
[music]
But if our sun was born as a binary
star, then when our sun would become the
white dwarf, this star could put
material onto [music] that, cause it to
grow. At some point the star ignites and
the whole thing [music] in a period of
second goes kaboom
with the power of about five billion
times what our sun puts out. When one of
these things explode they go from being
something that's very very faint. Over
the course of about 20 days they rise to
5 billion times the brightness of the
sun and then they slowly fade into
oblivion. We can measure how bright they
are to about 7%. And that is very
precise. That's better than a light
bulb. So we have these light bulbs, but
these are light bulbs that are, you
know, roughly 43 orders of magnitude
brighter than a light bulb here on
Earth. And so they are really, really
bright and we can see them all the way
across the universe. So by measuring how
bright these objects are, we can measure
distance like Hubble tried to with
stars, but we do it much, much more
accurately. We were going to go through
and measure a bunch of these exploding
stars. We were going to measure how fast
they were moving away from us or their
red shift as we call it. And we were
going to put that together and we're
going to do Hubble's experiment nearby.
And then we're going to do it a long
ways away. And of course, we're looking
into the universe's past when we look a
long ways away. So, we're going to
measure how fast the universe was
expanding in the past and in the present
and see how that's changing. And we're
going to see how fast it was slowing
down. then therefore weigh the universe
and that would tell us its ultimate
fate. The universe going to expand
forever or is it going to slow down
enough, reach a maximum size and then
collapse and go into the ganab gibb
that's the big bag backwards. So at the
end of 1997 um Adam Ree uh co-winners
one of the members of the team was
showing me the results he was getting
and they were strange. They were showing
that the universe was not slowing down
at all. was speeding up. So, of course,
we kind of figured that we had made a
mistake as one does. Initially, it
wasn't too bad. I just figured out
that'll be an easy mistake. We'll find
it. And I have to say there was a
context that the other team, the
supernova cosmology project, had put out
a paper
um in 1997 saying that the universe was
slowing down and it it was slowing down
pretty quickly. And then when we get
this measurement saying the universe is
speeding up, you're saying going, "Oh,
geez. Okay, we'll just find the m the
the mistake. But after a while, you're
like, well, there's no mistake going
away. And then you start getting
perplexed because you're saying, God,
we're going to have to go out and not
only tell the world something crazy, the
universe is speeding up. But that we are
getting a completely different answer
than the other team is getting something
completely sensible. So I was concerned,
definitely concerned.
We think the solution to this is that
the universe is made up of 73% of
something that causes gravity to work in
reverse. Something Einstein called the
cosmological constant and what we now
call dark energy. So, how is the
universe going to end? Well, it seems
it's going to go a little something like
this.
[panting]
[laughter]
[sighs]