[Applause]
there are few things in the world that
seem more constant than the stars in the
night sky
if you look up the milky way you will
see the same thing that people have
looked at for thousands and thousands of
years but as professor schmidt found out
the universe is a much more dynamic
place than we give it credit for
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 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 slifer saw that all of
the galaxies in the sky were moving away
from the milky way and so that was a
real funny measurement back then and
actually was indicating the motion of
the universe but how did slifer know
that the galaxies were moving away from
us
well he saw that their light was
red-shifted if an object is moving away
from us its light appears more red if
it's moving towards us its light appears
more blue and virtually all of the
galaxies slifer looked at were
red-shifted 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 slifer 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 stars were now stars become
fainter when they're further away so i
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 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 an 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 supernovae so type
1a supernovae
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 million
years
the center of it will collapse down to
something that is
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 the mass of our sun
so our sun will never do that it doesn't
have anyone to provide that mass 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
that cause it to grow
at some point the star ignites
and the whole thing in a period of
second goes kaboom
with the power of about five billion
times what our son 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 percent
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're going to measure
how fast they were moving away from us
or their redshift 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
it'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 give
that's the big bag backwards
so at the end of 1997 um
adam reese
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 it 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 figured out that'll be an easy mistake
we'll find it
and i have to say there's 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 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 the mistake
but after a while you know like well
there's no mistake going away and then
you start getting perplexed because
you're saying god we're gonna 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
[Laughter]