if crawling around those caves made you
feel claustrophobic and you might like
space more it’s expanding I’m going to
talk about tell you a little bit about
how observations of exploding stars
called supernovae have revealed that we
live in a universe that is not just
expanding but actually expanding faster
and faster propelled by a mysterious
newly discovered component of the
universe called dark energy so when we
look out at the universe it looks like
it’s expanding around us the universe
acts like it received a big kick that we
call the Big Bang and now the galaxies
are rushing apart you could think of
this like a giant loaf of raisin bread
rising in the oven the galaxies would be
like the raisins and as it gets bigger
there’s more space between more distant
raisins they appear to rush apart even
faster so how do we actually know this
about our universe how do we figure this
out well as you saw in that animation we
would have to measure how far away the
galaxies are around us and we’d have to
measure how fast they appear to be
moving away from us to learn this about
the universe so it turns out the first
of those figuring out how far away
galaxies are is very hard to give you
some understanding of how you measure
distances in space let me first remind
you of how you measure distances here on
earth on earth we use all kinds of tools
for example if you want to know the
distance to a tree
surveyors determine they might look at
that tree compared to a distant mountain
and then they would move their equipment
over and see how the position of that
tree has changed through what angle
relative to the distant mountain by
setting up some triangles some simple
geometry you could determine the
distance to the tree a more natural
means is a lighthouse if you’re a ship
captain you have an understanding of how
luminous a lighthouse is so when you see
one looking very faint you could judge
approximate
how far away you are from that
lighthouse at night now if it were a
foggy night that lighthouse could look
faint and fooling you into thinking it’s
further away than it really is so we
have tools called fog horns that work by
the same principle the attenuation or
reduction of the sound instead of the
light over the distance hearing a
foghorn sound very quiet tells you it’s
far away another tool that we all use
without even thinking is an
understanding of the true physical size
of an object so that when it appears
small we can judge how far away it is so
in the case of these airplanes we
understand that the very small airplanes
are the same thing just in the
background they are not for example baby
airplanes that were birthed by these
larger airplanes that’s just something
that we intuitively understand now all
of these are human-made objects and so
we don’t have the use of those in space
so we have to use telescopes and what
nature provides and what nature provides
to us is something very similar to the
lighthouse naturally-occurring
lighthouses that we call standard
candles and our favorite standard candle
occurs when there’s a galaxy like the
one you see here that might have ten or
a hundred billion stars in it but at
some point in time one of those stars
may explode in what we call a supernova
explosion when it’s as bright as about
four billion times the brightness of the
Sun and provides an excellent standard
candle if you could start the animation
for that I think a supernova is gonna go
off there it is and so as you place that
supernova further away like the
lighthouse we can judge its distance
from its brightness we use what’s called
the inverse square law that the
brightness will decline as one over the
distance squared as the light going out
has to paint the surface of a larger and
larger sphere so if one of these
supernovae is twice as far away it’ll
appear four times as faint if it’s three
times as far away it’ll appear nine
times as faint so we look for the
supernovae and they allow us to measure
the distances to the galaxies in which
they reside so how do we measure that
other aspect of
the the fact that it looks like
everything is moving away from
everything else well we can also
determine that from the light of the
supernova in a different way that light
is emitted at a certain wavelength
these are wavelengths that we can
determine in the laboratory but as that
light travels to our telescopes the
expansion of space stretches the
wavelengths of light it makes that light
longer wavelength that is tilted toward
the red end of the spectrum and so we
see a redshift of the light so this is
what it would look like if you had a
distant supernova emitting some blue
light and while the light is traveling
space expands and it reaches our
observatory it is already stretched or
shifted to the red and so we can measure
that redshift and so every time we see
one of these supernovae these standard
candles we can determine how far away it
is and how fast that galaxy is moving
away from us so you might wonder ok so
the universe is expanding but what
happens after that what’s next in this
story it’s a little bit like asking what
happens to a cannonball when it’s fired
from the top of a tall mountain on the
surface of the earth and the answer is
it depends how fast you fire that
cannonball it depends also relative to
how massive the earth is if the earth is
not very massive or you fire the
cannonball very fast the cannonball will
escape the Earth’s gravitational pull it
will go out into space if the cannonball
is not fired very fast or the earth is
very heavy it will fall back down and in
both cases although the cannonball was
slowing down the specific velocity needs
to be determined to know whether it is
what we call the escape velocity that
that knife-edge case between the
cannonball that will go out forever or
the one that will fall down so this is
what we expected after discovering that
the universe was expanding when that was
discovered by Edwin Hubble in 1930 that
although expanding the expansion would
be slowing down now that wasn’t always
the understanding though even before
Hubble observed that the universe was
expanding back in 1916 Einstein was
thinking about the universe he was
thinking about it in the context of a
new
theory he had of gravity called general
relativity and Einstein made one of his
few mistakes he was under the mistaken
impression that the universe was static
that it was immutable that it wasn’t
getting bigger or getting smaller but he
realized that if the universe were in
that state then all the attractive
gravity from all the stuff in the
universe would cause the universe to
start to collapse again so he didn’t
know how to keep the universe in that
static situation and he made an amazing
discovery enabled by his new theory his
amazing discovery was although the
gravity of the objects in the universe
is attractive the gravity of the empty
space between the objects could be
repulsive and this kind of repulsive
gravity could balance the attractive
gravity keep the universe static now he
called that repulsive gravity the
cosmological constant and today we would
call it dark energy now when Einstein
saw that the universe was expanding when
that was shown to him he then called
this the biggest blunder of his career
that he had made that to invent this
idea of this dark energy when it wasn’t
needed so how do we actually measure
then if the expansion is slowing down
and if so by how much well when I told
you how we measure the expansion of the
universe I left one crucial piece of
information out which is that when we
observe these distant supernovae these
exploding stars and when they carry this
information to us how far away they are
how fast or how much redshift has been
caused by the expansion of space there’s
a large delay built-in I like to say
that the universe does not instant
message so when you send an instant
message on your phone you think of it as
getting there right away of course you
know it requires at least the time that
it takes the speed of light to reach
your friend but that’s a trivial amount
it’s not so trivial for the universe
when you are looking at objects that are
billions of light years away it takes
billions of years for the light from
them to reach us which means that we are
learning about the universe as it was
expanding billions of years ago so when
we look at a nearby supernova that might
tell us how fast the universe was
expanding a billion years ago one
further away might tell us how fast the
universe is expanding two billion years
ago further 3 billion years ago so what
seems annoying is actually incredibly
valuable to us these supernovae carry
information about the past by looking
further away and allow us to see how
that expansion rate of the universe has
been changing over time so about 15
years ago when I got involved in this
work when I was a graduate student in a
postdoc the expectation was that the
universe was either slowing down a great
deal like the universe model on the left
a very heavyweight universe full of
matter that was quickly slowing down the
expansion eventually the expansion would
halt and then it would start to contract
and the universe would end any kind of
Big Crunch the inverse of the Big Bang
or we lived in a lightweight universe I
heard some people I don’t know if they
were sounded nervous about this Big
Crunch it’s even in the worst case it
would be about 30 billion years from now
but it could have been that we lived in
a lightweight universe one with very
little matter in it and so the universe
would expand forever that is like the
cannon ball the universe would have
escape velocity from itself and so our
expectation was we can measure this rate
of slowing like we couldn’t measure the
slowing of the Cannonball and figure out
what the ultimate fate was of the
universe now the way we sought to do
this was to look for some of the most
distant supernovae we could find and
generally we can find these only with
the Hubble Space Telescope and these
very distant supernovae give us
information from 10 or 11 billion years
ago when the universe was only one or
two billion years old and so they allow
us to reach way back in the expansion
history of the universe so I think of
the supernovae as sort of natural time
capsules in the universe and after
hearing Kenny’s talk I sort of think of
them almost like the blue holes of our
universe because they’re the places
where we can collect this information
that we can’t get anywhere else that
tells us about the early history of the
universe and so here are a number
pictures showing what a distant galaxy
looks like just before a supernova
explodes and just after a supernova
explodes people usually ask me how do we
find these supernovae and I usually
remarked at if you look at the ends of
the arrows and the pictures usually you
can find them without too much trouble
now we had those arrows that afterwards
actually but anyway so this was one of
those really exciting times where both
of the prevailing theories were ruled
out and we ended up with a very
surprising picture for the universe that
the universe was actually accelerating
and this was the breakthrough of the
year for science magazine in 1998
because you know poor Einstein it’s been
yanked back and forth along this whole
story you know the universe is static no
now we need spark energy no that was a
big blunder no now we think it exists
after all but that’s sometimes the way
science goes so we now think the
universe is actually dominated by this
dark energy component the energy of
empty space which causes this repulsive
gravity which causes the universe to
accelerate so after about a decade
decade in half of working hard on this
we have arrived at what is on the one
hand the glasses have full story you
know we’ve made tremendous progress we
now have labeled every part of the
universe about 0.05 percent of it is in
the form of planets another point 5% in
the form of stars another 4% in the form
of gas gas which is made of the elements
that you see in the periodic table of
elements so about the whole universe
made of normal stuff the stuff we’re
made of is only about 4 and 1/2 percent
of the universe so it’s really quite
striking that the the stuff we’re
familiar with is really just sort of the
frosting on the cake the majority is 23%
in the form of another type of matter
that has attracted gravity but we don’t
understand the kind of particle that it
is made out of but it is not what I
would call normal physics or the kinds
of particles that we’re already familiar
with and then there’s the even more
mysterious component to dark energy that
makes up now we think about 73% of the
universe and so the I said
glass-is-half-full part of the story is
we have finally come to terms with the
pie chart of the universe
and the part that’s a little frustrating
is we don’t understand ninety-six
percent of it so but that as Kenny said
in this case this is our job security is
you know our vast ignorance but anyway
so I think what we are looking forward
to over the next decade is experiments
and measurements that will help us
understand both the nature of the dark
matter the nature of the dark energy and
in all likelihood from this will come a
deeper understanding of gravity and the
fundamental laws of physics and in the
past when we have learned more about the
fundamental laws of physics
we’ve always learned a great deal in the
realms of science and technology so I
will end there thank you
you
feel claustrophobic and you might like
space more it’s expanding I’m going to
talk about tell you a little bit about
how observations of exploding stars
called supernovae have revealed that we
live in a universe that is not just
expanding but actually expanding faster
and faster propelled by a mysterious
newly discovered component of the
universe called dark energy so when we
look out at the universe it looks like
it’s expanding around us the universe
acts like it received a big kick that we
call the Big Bang and now the galaxies
are rushing apart you could think of
this like a giant loaf of raisin bread
rising in the oven the galaxies would be
like the raisins and as it gets bigger
there’s more space between more distant
raisins they appear to rush apart even
faster so how do we actually know this
about our universe how do we figure this
out well as you saw in that animation we
would have to measure how far away the
galaxies are around us and we’d have to
measure how fast they appear to be
moving away from us to learn this about
the universe so it turns out the first
of those figuring out how far away
galaxies are is very hard to give you
some understanding of how you measure
distances in space let me first remind
you of how you measure distances here on
earth on earth we use all kinds of tools
for example if you want to know the
distance to a tree
surveyors determine they might look at
that tree compared to a distant mountain
and then they would move their equipment
over and see how the position of that
tree has changed through what angle
relative to the distant mountain by
setting up some triangles some simple
geometry you could determine the
distance to the tree a more natural
means is a lighthouse if you’re a ship
captain you have an understanding of how
luminous a lighthouse is so when you see
one looking very faint you could judge
approximate
how far away you are from that
lighthouse at night now if it were a
foggy night that lighthouse could look
faint and fooling you into thinking it’s
further away than it really is so we
have tools called fog horns that work by
the same principle the attenuation or
reduction of the sound instead of the
light over the distance hearing a
foghorn sound very quiet tells you it’s
far away another tool that we all use
without even thinking is an
understanding of the true physical size
of an object so that when it appears
small we can judge how far away it is so
in the case of these airplanes we
understand that the very small airplanes
are the same thing just in the
background they are not for example baby
airplanes that were birthed by these
larger airplanes that’s just something
that we intuitively understand now all
of these are human-made objects and so
we don’t have the use of those in space
so we have to use telescopes and what
nature provides and what nature provides
to us is something very similar to the
lighthouse naturally-occurring
lighthouses that we call standard
candles and our favorite standard candle
occurs when there’s a galaxy like the
one you see here that might have ten or
a hundred billion stars in it but at
some point in time one of those stars
may explode in what we call a supernova
explosion when it’s as bright as about
four billion times the brightness of the
Sun and provides an excellent standard
candle if you could start the animation
for that I think a supernova is gonna go
off there it is and so as you place that
supernova further away like the
lighthouse we can judge its distance
from its brightness we use what’s called
the inverse square law that the
brightness will decline as one over the
distance squared as the light going out
has to paint the surface of a larger and
larger sphere so if one of these
supernovae is twice as far away it’ll
appear four times as faint if it’s three
times as far away it’ll appear nine
times as faint so we look for the
supernovae and they allow us to measure
the distances to the galaxies in which
they reside so how do we measure that
other aspect of
the the fact that it looks like
everything is moving away from
everything else well we can also
determine that from the light of the
supernova in a different way that light
is emitted at a certain wavelength
these are wavelengths that we can
determine in the laboratory but as that
light travels to our telescopes the
expansion of space stretches the
wavelengths of light it makes that light
longer wavelength that is tilted toward
the red end of the spectrum and so we
see a redshift of the light so this is
what it would look like if you had a
distant supernova emitting some blue
light and while the light is traveling
space expands and it reaches our
observatory it is already stretched or
shifted to the red and so we can measure
that redshift and so every time we see
one of these supernovae these standard
candles we can determine how far away it
is and how fast that galaxy is moving
away from us so you might wonder ok so
the universe is expanding but what
happens after that what’s next in this
story it’s a little bit like asking what
happens to a cannonball when it’s fired
from the top of a tall mountain on the
surface of the earth and the answer is
it depends how fast you fire that
cannonball it depends also relative to
how massive the earth is if the earth is
not very massive or you fire the
cannonball very fast the cannonball will
escape the Earth’s gravitational pull it
will go out into space if the cannonball
is not fired very fast or the earth is
very heavy it will fall back down and in
both cases although the cannonball was
slowing down the specific velocity needs
to be determined to know whether it is
what we call the escape velocity that
that knife-edge case between the
cannonball that will go out forever or
the one that will fall down so this is
what we expected after discovering that
the universe was expanding when that was
discovered by Edwin Hubble in 1930 that
although expanding the expansion would
be slowing down now that wasn’t always
the understanding though even before
Hubble observed that the universe was
expanding back in 1916 Einstein was
thinking about the universe he was
thinking about it in the context of a
new
theory he had of gravity called general
relativity and Einstein made one of his
few mistakes he was under the mistaken
impression that the universe was static
that it was immutable that it wasn’t
getting bigger or getting smaller but he
realized that if the universe were in
that state then all the attractive
gravity from all the stuff in the
universe would cause the universe to
start to collapse again so he didn’t
know how to keep the universe in that
static situation and he made an amazing
discovery enabled by his new theory his
amazing discovery was although the
gravity of the objects in the universe
is attractive the gravity of the empty
space between the objects could be
repulsive and this kind of repulsive
gravity could balance the attractive
gravity keep the universe static now he
called that repulsive gravity the
cosmological constant and today we would
call it dark energy now when Einstein
saw that the universe was expanding when
that was shown to him he then called
this the biggest blunder of his career
that he had made that to invent this
idea of this dark energy when it wasn’t
needed so how do we actually measure
then if the expansion is slowing down
and if so by how much well when I told
you how we measure the expansion of the
universe I left one crucial piece of
information out which is that when we
observe these distant supernovae these
exploding stars and when they carry this
information to us how far away they are
how fast or how much redshift has been
caused by the expansion of space there’s
a large delay built-in I like to say
that the universe does not instant
message so when you send an instant
message on your phone you think of it as
getting there right away of course you
know it requires at least the time that
it takes the speed of light to reach
your friend but that’s a trivial amount
it’s not so trivial for the universe
when you are looking at objects that are
billions of light years away it takes
billions of years for the light from
them to reach us which means that we are
learning about the universe as it was
expanding billions of years ago so when
we look at a nearby supernova that might
tell us how fast the universe was
expanding a billion years ago one
further away might tell us how fast the
universe is expanding two billion years
ago further 3 billion years ago so what
seems annoying is actually incredibly
valuable to us these supernovae carry
information about the past by looking
further away and allow us to see how
that expansion rate of the universe has
been changing over time so about 15
years ago when I got involved in this
work when I was a graduate student in a
postdoc the expectation was that the
universe was either slowing down a great
deal like the universe model on the left
a very heavyweight universe full of
matter that was quickly slowing down the
expansion eventually the expansion would
halt and then it would start to contract
and the universe would end any kind of
Big Crunch the inverse of the Big Bang
or we lived in a lightweight universe I
heard some people I don’t know if they
were sounded nervous about this Big
Crunch it’s even in the worst case it
would be about 30 billion years from now
but it could have been that we lived in
a lightweight universe one with very
little matter in it and so the universe
would expand forever that is like the
cannon ball the universe would have
escape velocity from itself and so our
expectation was we can measure this rate
of slowing like we couldn’t measure the
slowing of the Cannonball and figure out
what the ultimate fate was of the
universe now the way we sought to do
this was to look for some of the most
distant supernovae we could find and
generally we can find these only with
the Hubble Space Telescope and these
very distant supernovae give us
information from 10 or 11 billion years
ago when the universe was only one or
two billion years old and so they allow
us to reach way back in the expansion
history of the universe so I think of
the supernovae as sort of natural time
capsules in the universe and after
hearing Kenny’s talk I sort of think of
them almost like the blue holes of our
universe because they’re the places
where we can collect this information
that we can’t get anywhere else that
tells us about the early history of the
universe and so here are a number
pictures showing what a distant galaxy
looks like just before a supernova
explodes and just after a supernova
explodes people usually ask me how do we
find these supernovae and I usually
remarked at if you look at the ends of
the arrows and the pictures usually you
can find them without too much trouble
now we had those arrows that afterwards
actually but anyway so this was one of
those really exciting times where both
of the prevailing theories were ruled
out and we ended up with a very
surprising picture for the universe that
the universe was actually accelerating
and this was the breakthrough of the
year for science magazine in 1998
because you know poor Einstein it’s been
yanked back and forth along this whole
story you know the universe is static no
now we need spark energy no that was a
big blunder no now we think it exists
after all but that’s sometimes the way
science goes so we now think the
universe is actually dominated by this
dark energy component the energy of
empty space which causes this repulsive
gravity which causes the universe to
accelerate so after about a decade
decade in half of working hard on this
we have arrived at what is on the one
hand the glasses have full story you
know we’ve made tremendous progress we
now have labeled every part of the
universe about 0.05 percent of it is in
the form of planets another point 5% in
the form of stars another 4% in the form
of gas gas which is made of the elements
that you see in the periodic table of
elements so about the whole universe
made of normal stuff the stuff we’re
made of is only about 4 and 1/2 percent
of the universe so it’s really quite
striking that the the stuff we’re
familiar with is really just sort of the
frosting on the cake the majority is 23%
in the form of another type of matter
that has attracted gravity but we don’t
understand the kind of particle that it
is made out of but it is not what I
would call normal physics or the kinds
of particles that we’re already familiar
with and then there’s the even more
mysterious component to dark energy that
makes up now we think about 73% of the
universe and so the I said
glass-is-half-full part of the story is
we have finally come to terms with the
pie chart of the universe
and the part that’s a little frustrating
is we don’t understand ninety-six
percent of it so but that as Kenny said
in this case this is our job security is
you know our vast ignorance but anyway
so I think what we are looking forward
to over the next decade is experiments
and measurements that will help us
understand both the nature of the dark
matter the nature of the dark energy and
in all likelihood from this will come a
deeper understanding of gravity and the
fundamental laws of physics and in the
past when we have learned more about the
fundamental laws of physics
we’ve always learned a great deal in the
realms of science and technology so I
will end there thank you
you
Please follow and like us: