(upbeat music)
(applauding)
- Thank you Roy.
Thank you for that very nice introduction.
Let me see, is this the right volume?
I think, it sounds like it is.
It's a great pleasure to be here.
I am a professor here.
I've been professor for 13 years.
This is rapidly turning
into one of the best days
of a year for me.
A last few days I was felt a
little bit under the pressure
to prepare this talk.
But what fun activity it is to talk about
one of the really great
discoveries of our time in science.
So I'm a cosmologist.
The cosmologist,
essentially astrophysicists
who work on the largest
scales on the universe,
the big bang, dark matter, dark energy,
early universe as opposed
to individual objects
like planets and stars.
We study the universe as a whole.
And I'd like to tell you about
one of the great discoveries
and mysteries of our
present time in cosmology,
but also just in physics
and in science in general,
which is dark energy,
which is the fact that universe
is expanding faster and faster.
But I'm going to go back a little bit
and consider this picture taken
by Hubble Space Telescope.
If I ask you what are these?
Most people will know these are galaxies.
Galaxies are the biggest things
out there in the universe.
They are groups of stars
and each galaxy has
maybe 100 billion stars,
very large number.
You can see a few by AI,
but most of the time you have
to have a good telescope image
in order to see galaxies.
Now, what they are didn't
used to be so well known.
And in fact, exactly
100 years ago in 1920,
there was a so-called great
debate in Washington, D.C
at the Museum of Natural Science
between two astronomers, two
leading astronomers of the day,
Curtis and Shepley.
And this is a so-called
Shapley-Curtis Debate.
The question was,
what is the nature of these
so-called spiral nebulae?
Which we today call galaxies.
These things seen on the sky, for example,
such as Andromeda.
So there a picture of Andromeda.
What is its nature?
Shepley thought they are part
of our galaxy, the Milky Way.
These are just groups of
stars within the Milky Way
and all that there is out there
is Milky Way and it's parts.
And Curtis thought that or
thought that there's evidence
that these are the so
called island universes,
separate objects, which
today we called galaxies.
Well of course Curtis was right.
They are galaxies.
They are not part of the Milky Way.
But if there were,
Saturday morning physics
talk 100 years ago,
this would have been the topic maybe.
What's the nature of island
of these spiral nebulae?
So they are actually much farther away.
They are not part of the Milky Way
and they are, we call them galaxies.
So today of course we know
there are many billions of
galaxies in the universe.
Each one has of worth 100 billion stars
and they are also billions
of light years away.
That is what you are seeing today.
Like this picture is showing them
as they were a few billion years ago
because it took light a
few billion years to get
from them to us.
Okay, so that's the nature of galaxies.
Now, let me go forward a little bit.
In the year 1929,
when American astronomer Edwin Hubble,
makes one of the great
discoveries of all time.
He makes the discovery
that universe is expanding.
Now, Edwin Hubble, he spent
time at university of Chicago
and at Yerkes Observatory first,
which is in Southern Wisconsin.
And then he went to the world's
best telescope at the time,
100-inch, that's to say
two and a half meter,
Hooker Telescope at Mount
Wilson in California.
This is close to Los Angeles.
Today there's light pollution.
It's not the best place to observe.
At the time it was the world's premier
observing site with the best telescope.
So what did Hubble do?
Well, to talk about expanding universe,
let's talk about expanding
space of any kind.
And let's talk about the expanding bread.
So you make, say you make a raisin bread.
Maybe that's not the most
popular kind of thing to make.
But let's say you bake raisin bread.
So you have bread with raisins inside,
that bread is pace.
The space grows as it's in the oven
and as bread grows, these raisins
are moving with the space.
And then it turns out that the
two raisins that are nearby
they're receding from each other.
And two raisins that are far away,
they are also receding from each other,
but they're receding faster.
So the farther they are from each other,
the faster they're
receding from each other.
So I want to point out here,
there is nothing mysterious
about the universe in this story.
This applies to any expanding
space including bread.
Okay?
There's expansion loaf of bread.
It's a space that's expanding.
Well, for the universe,
Hubble, he didn't set out to do this,
but he discovered.
So remember for bread,
the farther away they are,
the faster they are receding.
So the question is, if you
look at galaxies away from us,
imagine you are sitting
at one of the raisins
and you're looking at other raisins
and other raisins are galaxies.
Is it true that the farther away they are,
the faster they're receding,
they're going away from us.
So he set out to measure this relation.
To measure this, you need
to measure two things.
You'd need to measure
distance to other galaxies
and you'd need to measure
their speed or velocity.
It turns out velocity is
easy and distance is hard.
So in the next few slides,
I will explain a little bit
how you measure velocity
and then how you measure distance.
Well, measurement of
velocity is the easier part.
And here it effectively
is equivalent to what
we call Doppler effect.
It's a fancy way named
for absolutely every day,
not quite every day, but common
experience so, to all of us,
which is that if you
here in the ambulance car in the street
or any vehicle that's producing a sound,
you'll hear a higher pitch
as it's approaching to you
and you'll hear lower
pitch as it passes by you.
So you hear that, ah, ah, right.
You hear that everyone, you
can hear just even from cars.
And the reason is as it's approaching you
the sound it's emitting,
it's kind of tends to be bunched up here
because it's moving.
So you'll hear a higher pitches.
It's receding away from
you, here you're behind it,
it's carrying the sound with it.
So you're hearing waves that are
more separated.
And really for this to happen,
the speed of the ambulance car
has to be not that much smaller
than the speed of sound.
And speed of sound isn't that great.
It's not like the speed of light.
So this happens and
that's why you hear it.
So I'm going to demonstrate here
the Doppler effect.
Just to tell you what I'm talking about.
This is gonna be a little bit loud.
Apologies for that.
Maybe I'll shut off my microphone
and I will whirl this above my head.
It's gonna be producing squeaky sound.
And let's see what we hear.
It's painful to listen to,
but you heard it higher and lower pitch.
I didn't do it too fast,
but you heard the effect.
So this is called the Doppler effect.
And it has to do so by
measuring the pitch.
For example, you can hear,
you could measure how fast
the ambulance is moving.
So that same effect for
sound applies for light.
It's the same as a Doppler effect.
And if some galaxy, let's
say you observe lights,
some spectral lines from
some galaxy or star,
it doesn't matter.
If it's receding away from you,
if it's going away from you,
the light you see would be
shifted to longer wavelength.
That is to say lower frequency.
So this is like an ambulance
car going away from you.
You'll hear lower frequency.
That's called the redshift.
It's shift to the red.
If you think about blue to red spectrum.
If it's coming to you,
then it'd be blue shifted.
Then you would hear a higher pitch
and you'd hear a lower frequency,
lower wavelength, right?
So you can measure,
even now when it's compared
to the speed of light,
speed of light is great,
but galaxy is also much
faster than the ambulance car
moving through space.
So the question is,
what is then the speed of
galaxies relative to us?
And you might guess half of
them are receding away from us,
half of them are coming
toward us, not true.
Almost all of them are
receding away from us.
All the galaxies are running away from us.
One notable exception is in Andromeda,
that I mentioned already.
Now, Andromeda is coming to us.
There's no more going back.
Andromeda is gravitationally
attracted to Milky Way
and Milky Way and Andromeda
are going to collide
very soon in a few billion years.
That's very soon in cosmology.
They're going to collide.
That's too late for Andromeda to escape.
But every other galaxy basically,
is it going away from us?
Is it because we are special somehow?
No, it is because space is expanding.
So that was, remember
velocity part, the easy part.
Now remember that graph I
had velocity and distance.
Distance was hard.
Now distance is the famous hard thing
to measure in astronomy.
And you can imagine that's the case.
You see something on the sky,
maybe it's some star or
galaxy, has a shape, has color,
but how far away is it?
It's really, really hard to know.
So you want the kind of object that
you would almost wish it has
a written distance on it.
So you can read it off.
Well, you don't get that,
but you get a special kinds of objects
like stars that have certain properties
and these stars are called Cepheid stars.
It's a kind of star.
Now you may ask, why are
we talking about stars now?
We talked about galaxies.
Well these stars that live
in galaxies are special.
They pulsate, they light,
brighter, dimmer, brighter dimmer
for a period of few days.
But they pulsate, so that
people found an empirical law.
That is to say they just happens
that the longer the period is
the bigger the luminosity
that is the more light they put out.
So the ones that have
long period take more days
to go bright and dim.
They are intrinsically more luminous.
They're putting out more light
and then the ones that are
faster, shorter period,
they intrinsically have
less light, that luminosity.
Think about, did they have power?
This is the luminosity
is like their power,
the power they put out.
Now this is the only equation
I'm gonna show today,
but I'm gonna show it a couple of times.
It's a relation between flux,
the amount of light you
measure from an object.
Luminosity, which is the
thing I just mentioned,
the intrinsic amount of power
object puts out and distance.
And this is clear.
For example, sun has some luminosity.
So given our distance from the sun,
you can tell how much light do you feel
This is the thing that you measure
if you will lie down on
the beach or anywhere.
So likewise from Cepheid to some object
you can measure the amount of light,
you would love to know the distance.
And this is the sticking point.
How much intrinsic energy is
it putting out per second?
And that luminosity now
you can get from the period
because you can use this
period, luminosity relation,
measure the period, infer the luminosity,
plug it in here, measure
F and get the distance.
So this is a way to get distance.
So this is the hard part in the relation.
Hubble needed to get distances.
So Hubble did all that.
And here's the extra real
plot from Hubble's paper.
It's not a pretty looking plot
because this is a real paper from 1929
but it shows distance on the X-axis
the thing you get from
Cepheids and et cetera.
And velocity the thing you get
from Doppler shift basically.
You'll see a huge sketcher of points.
Points are all over the place here.
It looks like a bunch
of garbage basically.
It looks like all over the place.
And now Hubble heard almost
as if somebody whispered
in his ear, he put the line through it.
Almost like somebody said,
"Hey, put a line through it."
Okay, just trust me,
it's a line.
(laughs)
So Hubble put the line through it
and made one of the great
discoveries of all time.
Because remember, line is
prediction of expanding space.
The farther away you are,
the faster you're receding.
Now, one incredible
thing about this plot is
it is a line and universe is expanding,
but the slope of the line
is the expansion rate.
It's how much faster you're
receding per distance.
It's called the Hubble Constant.
So how many kilometers per second?
Megaparsec is like a million light years.
It's a unit of distance.
So every megaparsec farther your way,
you are receding in our universe
70 kilometers per second more.
For example, galaxy that's
one megaparsec away,
is receding 70 kilometers
per second from us.
One that's two megaparsec away
is receding 140 kilometers
per second from us and so on.
Now one incredible thing is that Hubble
got the relation right, but
he got this slope way off.
Hubble got 500 for this number.
So he was way, way, way, way
off from the Hubble Constant,
even though he discovered the law.
And it took decades for us
to convert to this value.
Now this will become a very important
just near the end of my talk.
So remember this Hubble Constant
is ballpark 70 kilometers per
second for each megaparsec.
So this was discovery of the
expanding universe in 1929
it's really one of the great discoveries,
the universe is expanding.
Why is it expanding?
Into what is expanding?
I didn't say that yet.
Hubble didn't know that.
The fact is that things
are receding away from us
and in fact they are receding
from every other object.
So I have a couple of
demos here to demonstrate.
In expanding universe,
I'm gonna have expanding,
what is it though?
Square on the wall.
And as the square as this
space, being this board,
this pattern on the world is expanding.
Every point is expanding
from every other point.
So not only does the
bright point in the middle
recede away from its neighboring.
But if you take any two points,
they are becoming farther and
farther away from each other.
That's a very basic demo.
A little bit more sophisticated
demo just a little bit,
is given by this balloon.
So I'm going to blow up this balloon here.
This is gonna be my universe, so to speak.
I'm gonna turn it on.
Leave it like that.
And we'll give it a few moments.
As it starts to
expand or not.
(laughs)
Oh I see.
It was already on.
Thank you.
So we gonna start expanding this universe.
There are some galaxies on it,
actually they look like stars,
but there are galaxies on it.
So galaxies in this
universe and it's expanding.
So what happens is that
it gets bigger and bigger and bigger.
I'll leave it here for awhile.
Every galaxy is receding
from every other galaxy.
If you pick any one of them,
none of them is special, it's receding.
And the father away its neighbor is
the faster it's receding.
Okay, so some more nearby
is receding at some speed,
one far away is receding faster.
So this is a pretty good
model of expanding space.
There are some limitations to this model.
One limitation is that
this is of course two dimensional,
we live in three dimensional spaces,
this is two dimensional.
Another limitation is that each
galaxy seems to be growing.
In real life, galaxies themselves
are not expanding with the universe.
Just like this room is not
stretching with the universe,
nor is this table.
You really need two separate galaxies
to be receding away from each other.
But the biggest limitation of this model
is that this universe here,
the surface is expanding into something.
I'm here, very comfortable
in three dimensional space
and I'm looking at this two,
this space expand into my,
the space I live in.
For the real universe,
the real universe is not
expanding into anything.
It's all there is.
So it's just growing.
But people often ask into what?
There is no fourth dimension
into which it's expanding.
That's it.
It's a little bit hard for
our minds to come around that
because we are used to space
expanding into another space.
Like we are looking at this
and this is still within our 3-D.
Oh, no.
But the real universe is
not expanding into anything.
It is all there is.
So that's a good model
of expanding space demonstrating
yet another Hubble law.
So there's a Hubble law for this balloon.
There's Hubble law for
the expanding universe.
Okay, so having talked
about this discovery
of the expanding universe,
let me now briefly go through
the history of the universe,
kind of maybe step back
and this will include
some other discoveries
we in cosmology have made
over the past 100 years.
So this is a time-axis,
this is a big bang.
This is the present day.
Time is running down and
this is a very rough chart.
Space is getting bigger as you see,
and I'm just gonna review it quickly.
From time equal to zero,
from the big bang to 13.8
billion years after the big bang,
which is today.
So big bang is time equal to zero.
That's when we start counting.
Expansion starts.
Did it happened here?
Did it happen there?
It happened everywhere.
Okay, it happened everywhere.
Details are really not very well known.
People talk about it,
but there's no way to probe T equal zero.
That time of the big bang itself
is currently beyond
the reach of any probe.
And don't ask please what
happened before the big bang?
We don't know.
Time started at the big bang weak thing.
What does it even mean?
We are not sure.
Was there a time before?
It's actually possible.
There are some speculations
how there could have been,
this could be the debut
universe out of other universes.
That speculation exists.
We hope to have a way to probe this
in the near future, but not just yet.
However, one of the great
triumphs of cosmologists
that we know is something
about incredibly tiny
moments after the big bang.
At about 0.00003001
seconds after the big bang.
So unimaginably.
So trillions of a trillion of
something like that, whatever.
Seconds after the big bang.
These are high energies
and exotic potential new physics,
but we particularly know
that something called inflation
happened during that time.
This is not increasing prices of products.
This is a rapid increase of
the size of the universe.
Now inflation would be a great subject
for another Saturday morning physics talk.
It's a fascinating topic
and it's been confirmed by data by large,
but I won't have a chance
to talk about it today.
Then about less than a
second after the big bang,
we have a quark soup, super particle.
It's called quarks.
They have funny names like up and down
and charm and strange and they
make up protons and neutrons
that we are very familiar with.
But this was very early time.
And in fact, only about a
minute after the big bang
did nuclei form.
Now nuclei elements like
hydrogen and helium.
So they formed, so these
quarks finally had the mercy
to combine together
and then protons and neutrons
combined into nuclei only
about the minute.
And this process is very
well understood in cosmology,
very, very well understood
for about 50 years.
Hydrogen and helium and
lightest elements formed then
and heavier elements like iron
formed in stars much later.
About 300,000 years.
So this is not going
second by second obviously,
this is jumping in a little bit,
300,000 years, something called
Cosmic Microwave Background was generated.
The CMB is the radiation
leftover from the big bang.
It's the photons the light
left from the big bang.
Well, what happened to that light?
Before 300,000 years it was there,
but it was bouncing
off of other particles.
If you imagine particles
of like they were bouncing
like ping pong.
And then finally they were
able to not bounce anymore.
The universe rarefied
enough they were able to go.
And that microwave
background we observe today.
So one of the great
discoveries in cosmology
now in the 1960s, so long time ago,
was two engineers, Penzias and Wilson.
They were Bell Labs engineers.
And for the younger in the audience,
Bell Labs at the time
was like Google today.
It was a dominant company.
It was absolutely dominant company
with most brilliant people, engineers
and others are working for it though.
So they were Bell Labs engineers
and they had antenna in
Crawford Hill, New Jersey.
So this is American discovery.
And they found strange noise.
What is this noise coming from?
It's messing things up.
It turns out the noise was this radiation,
Fein's radiation from the early universe.
I drew a picture here.
It's not literal picture, but
it's uni-former radiation.
It's the same thing in
all directions in space.
It's about, you can quote
it's a corrective temperature
three Kelvin about that point zero.
So it's like very low energy radiation.
You're not gonna get sent in out of it.
Very low energy, barely
discovered with this huge antenna
in the 1960s they won Nobel Prize.
Then another Nobel Prize was discovered
for another great discovery.
That radiation actually
isn't perfectly uniform.
And there are fluctuations
we call them anisotropies,
of about one part in 100,000.
So one part in 100,000 is
like going to a deep ocean
that's a kilometer deep.
And seeing waves that are
I think a centimeter,
a centimeter high like
1/2 an inch high, right?
So it's a small fluctuations but non-zero.
So this map, it's a real
actual map of the sky.
This is old sky.
And you can see these fluctuations,
we subjected the temperature
and then just looking
at that fluctuations.
So here I have another map.
This is a beach ball.
It's a very nice beach ball.
It's actual map of the CMB.
It's the same as that map, similar.
It just has this extra red thing around
that's a galactic kind of dust,
it's got noise that's in the way.
But to imagine you are
sitting in the middle.
So you're sitting anywhere on earth
and you're observing the sky.
So this is like the sky.
If you are sitting in
the middle of this ball
and looking out, you'd see the sky
and you'd see three Kelvin,
but slightly hotter, slightly colder,
slightly hotter, slightly colder.
And that's the same if you
unroll that map of the sky.
That's the one you see on the screen.
So this is also called the
Rosetta Stone of cosmology
by some people because by measuring
the statistical distribution
of these hot and cold spots,
using sophisticated statistical
techniques, lots of math,
lots of theory, that was
developed over decades.
You can discover wonderful things.
Now, some of you may have
heard of Rosetta Stone,
this basalt stone dug up
by Napoleon groups in Egypt
where they were able to read three scripts
and decipher hieroglyphic script
using this one piece of stone
that's now in the
British museum in London.
There's one incredible piece
that can tell you wonderful things.
We in cosmology feel like a
microwave background is like,
it's a one map that tells us
many things among other things.
when we say universe is
14 billion years old,
that information comes from this map.
The structure of hot and cold spots,
the statistical distribution
is sensitive to that.
Another thing that this measures
is the Hubble Constant the expansion rate.
And I'm going to come back
to that in a little bit.
Okay, but anyway, this is a CMB.
It's been released 300,000
years after the big bang.
We observe it today.
It's some radiation
from the early universe.
Moving on, we enter the Dark Ages.
Now let's say in Europe, Dark
Ages were 12, 13, 14 hundreds.
Poor times, dark, lots of disease
and dying and unhappiness,
not much going on.
Likewise for the universe, the Dark Ages,
dark and cold, and not much going on.
But eventually during these dark,
after the Dark Ages, for
stars, start to form.
Stars and then galaxies.
And then of course the
present day universe
we are pretty well familiar with.
There are stars and galaxies everywhere.
There's dark matter,
which I won't have a
chance to talk about much,
but it's certain kind of matter
that is dark that people
are trying to find.
And then there's a big
surprise in the store
called dark energy.
That's a subject of this talk.
Now I'm going to run,
this is not like a movie.
This is a simulation.
So this is gonna run
for a couple of minutes.
I'm going to talk during this.
This is a starting at the big bang
and it's showing you billions
of years after the big bang.
It's a numerical
simulation on the computer.
So it's not like a movie
people would make for
a film on television, right?
Where somebody makes
up some fancy graphics.
At each step here, there are equations,
let me just try to get rid of.
Oh, sorry.
Let me run it again.
Okay.
At each step in this movie,
there are physical equations
that are being solved.
There are billions of
particles that are being moved
by the laws of physics,
in this simulation.
This simulation takes
millions of CPU hours.
You run it on a supercomputer,
it takes several months
to just produce one of these simulations.
So it's a really incredible
effort by cosmologists.
And so all the things
you see in them are real
to the extent that we understand physics.
So what you are seeing here
is formation of structure in the universe.
The camera so to speak
is also penning around.
As you see it's kind of
zooming around this box
and it's also zooming in.
It's also zooming in slowly.
So you're gonna see more and more detail.
This is not the whole universe,
this is only a chunk of it.
But what you see, the
blueish stuff you see
is by enlarged dark matter.
And then the explosions
and reddish things you see
are mostly normal matter like
hydrogen, helium, carbon
and other elements.
And you can even see some
supernova explosions.
There are black coals maybe even
that are hiding somewhere
in these regions.
Now we've zoomed in quite a bit,
so we are looking at really
small chunk of the universe.
But you see one defining fact
of the universe we live in
is a filamentary structure.
It looks like a sponge, right?
The structure.
That's the kind of think.
Why is there such structure?
Because gravity does it, right?
As the law of gravity apply
Newton's second law of gravity,
basically, to particles,
you'll get this filamentary structure.
You'll see the filamentary
structure in a few moments
when the color of this changes
because it's showing both gas
and dark matter particles.
But now we are, let's see,
9 billion years after the big bang
so we are past the Dark Ages,
I think, and into the modern era.
It's going to run up to
until 14 billion years.
And now it's zoomed in quite a bit.
So you're not really seeing
those filaments as much anymore
but you are seeing individual structures.
And these greenish reddish
things may be galaxies.
Actually, they may be dark matter clumps
that surround galaxies.
Real galaxies you'll also see,
you can actually now in
this contrast you can see,
so the reddish things
and yellowish in the
middle there are galaxies.
And then the bluish case is a
dark matter that concentrated.
So I didn't talk about dark matter.
It's some kind of particle that
isn't in the periodic table
that's out there and dominates
all of the other matter.
So this illustrates simulation,
it's state of the earth numerical,
we call it N-body
because there are N-bodies
where N is very large simulation
that's being done by cosmologists.
Well okay, so that's how
the universe looks today.
Now question is
what kind of space
does mathematics, the law that we live in?
Well, space in mathematics
as well as in real life.
It can be three kinds.
It can be flat.
You know curvature, positively
curved and negativity curved.
Flat space is the most familiar kind.
If you have a triangle,
angles add to 180 degrees.
And two lines that are parallel continue
to be parallel forever.
Positively curved space
is where you have a triangle angles
add to more than 180 degrees
and two parallel lines converge.
Now everybody is actually
familiar with curved space.
Surface of the earth is curved.
And so you know that there are some
slightly strange things that happened.
For example, if you
walk in a straight line
for a long, long time or fly
an airplane for a long time,
you'll come back where
you came from, right?
You may come back to an (murmurs)
if you go around the poles.
Because in curved space,
in flat space you'll never come back
if you're going in a straight line,
but in curved space you do.
You also can do in curved space,
follow the straight line three
times go along the equator,
go to the North Pole,
come back to the equator
and you'll kind of can
close the funny triangle.
So geometry is a little
funny in curved space.
We also know when airplanes
fly from here to Europe,
trajectory you follow may
not be the one you imagined.
It's kind of looks a little weird,
to do the shortest.
We are familiar with closed space
with positively curved.
We are not so familiar
with negativity curved
because surface of the earth
or anything we know about,
isn't negativity curve.
But it's like surface of the saddle
where angles in a triangle add
up to less than 180 degrees.
Well, the first person to
seriously set out to us,
okay, so what is our universe, our world?
Is it flat, positively
curved, negativity curved?
We don't know it's flat for a fact.
It was Carl Friedrich
Gauss, German mathematician.
He actually climbed peaks
in Bavaria, three peaks.
And from each peak he measured the angle
to the other two peaks
and measured the angle.
So he summed the three
angles and he tried to see
if they add to 180 degrees.
I think he found they do,
but he never had the chance to find this.
Because to ask it for universe,
you have to climb to each galaxy
and look at the angles to galaxies,
you have to go much further
than peaks in Bavaria.
So of course you can't
go to another galaxy
and ask that question.
But it turns out in cosmology
that you can measure that same relation
I talked about earlier,
where remember distance under one axis
and velocity or redshift on the other,
except, before I had distance
here and velocity there
and I have them in the axis.
And remember we talked about
the slope of this line,
the fact that it's a line,
this is the relation
I talked about before,
the linear relation between distance
and velocity or redshift.
Well, it turns out if you
continue with those curves,
you just have to trust me on this.
I haven't really motivated
it, I haven't explained it,
that you get a different
behavior between distance
and say velocity or redshift.
Whether geometry of space
is flat, open and close.
That is to say negatively
curved or positively curved.
So if you just go out and measure,
do the same thing as Hubble did,
but do it at the larger distance.
Then you can select
between these three curves.
And to do that,
you use that same relation
I talked about before,
but now the Cepheid
stars are too far away.
So you need a new object.
And this kind of object is
called type 1a supernova.
It's an exploding star.
It's a case of wide dwarf,
accreting matter from a
companion, undergoing explosions.
What does type 1a mean?
It's a certain type.
Not every type of supernova works.
There's a certain type that works.
Don't worry why.
They're very bright when
these explosions happen.
Here's a galaxy far away.
Remember it has 100 billion stars
and one of those stars that exploded
is actually comparable
to the whole galaxy.
It's that bright.
It's a tremendous explosion.
If it happened in our
galaxy, it'd be a disaster.
But it happens in other
galaxies, not very often.
And it is bright, but it
has a special property
that the luminosity is almost the same
every time it happens.
Now remember, this is the
same for similar for Cepheid.
It's a so called standard candle.
It's a thing you can trust to know
how much light it put out.
It only works for these objects.
For type 2 supernova doesn't work.
For other kinds of
explosions it doesn't work.
It's a similar luminosity only
for these special objects.
So here's an example.
You can see light going up and down
and the supernova happened here.
I'm gonna run this movie again.
This is the real data.
So here's the galaxy, the
supernova is gonna be right here.
Take another look.
It goes up and it goes down.
That takes about a month.
So it happens over about one month.
So if you find such objects
you can measure their, you
know where their luminosity is.
Because remember, I go
back to the same equation.
You can measure the amount of light
and you know the intrinsic
amount of light, the luminosity.
This is the standard candle.
That's the golden information you'll get.
You can measure light
easily through a telescope.
You'd like to know the distance,
but the key part is that you get L.
I can make analogy with cars.
Imagine you have a car at night,
with just a pitch black,
you just see lights.
Is it Fiat Uno nearby or
is it the truck far away?
You don't know, you just see
like this light here it's,
I see a light.
I see some of you so I have
a scale of what's happening.
If it was pitch black,
I just saw that light.
I wouldn't know if it's a
really bright light far away
or dim light nearby.
But if I have additional information,
"Hey this is a light that
output this much power,"
then immediately like,
"Hey, this is a standard car light,"
then immediately my brain can
calculate how far away it is.
So that's the key information
about what we call luminosity.
What in real life we could call
the intrinsic amount of
light at some car, right?
So your brain already does this.
It sees lights in pitch black.
As soon as you know, it's
some kind of regular car,
it calculates the distance.
And you can do the same thing.
So with this information now,
this is the same thing.
So you measure flux,
that's you can get
distance to see supernova
and then remember
redshift you can get also.
So now it turns out, okay, great.
I just need this some supernovae
and I can measure that relation.
I can find geometry of space.
Problem is if you write the
proposal to NASA and say,
"Hey NASA, please,
"I would like to use Hubble
Space Telescope to do this."
It turns out it takes
about 500 years on average
for one supernova to go off in a galaxy.
So if you wrote proposal to say,
"I'm gonna wait 500 years
"with Hubble Space Telescope
"and wait for supernova to go off one,"
that wouldn't go so well.
So a key challenge for
the cosmology community
was to develop techniques
to get enough supernovae
in half a year, not in million years.
And this was
dirty hard work
made by two groups
of cosmologists,
International Collaborations
to manage, to observe enough galaxies
to be able to guarantee
that you will be getting
enough supernovae.
And those people in fact
won Nobel Prize in 2011
for the discovery that I'm
gonna talk about in a moment.
These two folks Riess and
Schmidt were part of one team,
Paul, Monroe of another.
And I would say in my
personal biased opinion,
even among the Nobel
Prizes, this was a big one.
This was a really big one
because this was discovery for all time,
that our universe is
doing something weird.
But what did they find?
Well, they plotted the same kind of thing.
This is kind of a distance
except I took a log in now,
and this is kind of velocity.
The same kind of graph.
I'm using slightly different scaling here,
so it's not the line anymore.
But remember they set out to see
if universe is open, flat or closed.
Remember now, they're going much farther.
Edwin Hubble looked right
here, really nearby.
And now they are looking way out,
billions of light years away.
And it turns out that
neither one of these cases,
neither open nor flat nor
closed, fits the data.
This is real data that
I massage a little bit
to put it in the form
that is a little visible.
In fact, their data favored another model,
that is the universe that's
not made up only on matter,
but it's a universe
that decided to speed up
its expansion today.
So matter only universe never speeds up.
But this is expansion
that very recently in cosmological
terms start to speed up.
And you can see that the data don't like
either one of these three curves.
So this new thing, we
don't know what it is.
We call it dark energy.
It was named by my PhD advisor
at university of Chicago, Michael Turner.
Universe has dominated something,
but other than dark matter.
This new component is dark energy.
It makes universe expand
faster and faster.
That component is smooth
and we don't know all that much.
Now, in the early days
people said,
"Hey, you guys, I know
the two teams agreed,
"but you made some kind of error.
"Please go back and check.
"Oh, you forgot about
this in your analysis."
Not only have many teams
re-check these results,
but completely independent
methods unrelated to supernova
or anything like not even distances
have done separate
measurements in cosmology
and found that there's dark energy.
Now it's amusing.
I was asked by a journal,
by a magazine recently
to comment on a paper
that brings some of this into question,
but it's incorrect in my view,
and I was quoted by
saying, "I bet my life,
"the dark energy is there."
Then I was thinking later,
betting your life on anything
is not maybe the greatest idea.
Just out of principle.
Don't bet your life, bet
your house or something.
But we are that sure that
something's going on.
Now, what is dark energy?
We don't know,
but that none of those regular
models with matter only,
they just don't fit the data at all.
We are completely sure of it now.
And here's just a very crude movie
showing galaxies expanding
and now check it out.
Just now they start to
expand faster and faster.
So they were slowing.
And then recently, in cosmological terms,
that's to say a few billion years ago,
they start to expand faster.
So that's a very crude movie.
This is not a real simulation,
but it's showing you the kind of thing
the dark energy does.
There's very unusual out
of the blue acceleration
of galaxies running away from each other
faster and faster at late times.
Well now remember, dark matter
is not equal to dark energy.
This is one of common confusions
because they have similar names.
They're totally different.
Dark matter, this is a very crude picture.
Anytime you see a galaxy,
imagine a bluish halo of dark matter.
We've seen some of them
in a simulation I ran.
Dark energy in contrast is, doesn't clump.
It's perfectly smooth.
At gravitationally, it
actually pushes away,
it doesn't attract.
So it's doing all the opposite
things of dark matter.
The only similar thing is the name.
Well, here are some basic
facts about dark energy.
It's smooth, it pushes things apart.
Now, it has funny property
that it's density is constant.
As a universe grows,
you double the volume,
you double the energy.
Now, if you imagine regular matter,
if I have 20 particles in a box,
if I increase that box, so
that's my universe that grow,
the density goes down
because the density,
I have 20 per volume
and volume go went up.
So the density of energy
of number is lower.
Here, the density is
constant approximately.
So that the total energy in the universe,
because the volume grows, increases,
and this is actually allowed
by the laws of physics.
So total energy increases.
You can't do that in physics,
contrary to maybe some basic intuition.
So that's what dark energy does.
And actually verifying
whether it's exactly true
that this double or
is it exactly doubling or some other.
Law is at the forefront of research,
exactly what the behavior is with time.
Dark energy is noticeable
only at recent times.
If you go back to the early universe,
we think it goes away.
We don't see any evidence for it.
It's slows down the growth of structure.
And maybe most importantly,
the universe is apparently
more complicated
than needed to be.
This is a bit of a philosophical point.
You and I could have this
very nice conversation,
exact same Saturday morning physics
and the rest of our lives
with our dark energy.
Because we barely discovered it, right?
It's kind of hard to find.
So why is it there?
Their method to the madness,
we don't know what
principle is rolling it.
But there are lots of
ideas for dark energy
and some of them involve things like,
theoretical predictions for example,
in quantum mechanics, particles
pop in and out of air.
This is kind of a more technical thing.
I'm only describing it here in a slide.
Turns out that this
popping up in particles,
which has been known for
many years, this has allowed,
it creates something like dark energy.
So you may say, "Oh, okay,
known physical principle
"can create the effect."
The only problem is if you calculate,
you find that the amount you predict
is unimaginably larger
than what you observed.
So this is probably
the biggest discrepancy
I think any of you have seen ever
between what you predict,
what you observe.
It's number of 10 to the 120.
Now remember there are, what?
10 billion people on earth.
That's 10 to the 10.
How many particles are
there in the universe?
That's 10 to the 80.
This is 10 to the 120.
So it's completely unimaginably
off, this prediction.
So this has created a great
mystery in physics of why,
this one model that could
work is obviously wrong.
It's way off.
So this is really putting a
lot of interest into studying.
What's going on with theoretical
prediction for dark energy?
The other mystery of dark energy is,
if you look at the time
and if you look at how
matter, as universe grows,
time is running to the right.
Matter dilutes
dark energy.
Remember, density is constant,
so dark energy was
sub-dominant in the past.
It will be dominant to the future.
Blue is greater than red in the future.
And we just happen to live in an era
when dark energy is about 70%
and the regular matter is about 30%.
It's about three to one
is about ballpark equal.
It's not one to billion or billion to one.
It's like one to one.
So here's another picture.
We live in an era.
Here's us today.
Pie chart is 70% dark energy.
The red part is dark matter,
the yellow part is
periodic table of elements.
If you look in the future,
it's gonna be all dark energy.
If you look in the past
it was all different kinds of matter.
So why are we just born?
It's like you wake up someday
and you find something special.
Three birds are chirping at the same time
in your window or something.
Some kind of unusual situation
you ask yourself in this.
So this may or may not be a coincidence,
but it's something that
cosmologists are working on.
Okay, so I mentioned two big conundrums,
the prediction and why.
What is dark energy?
Well, we don't know.
Obviously this is one
of the great mysteries
of cosmology today.
Is it vacuum energy?
Well, the prediction is way off.
Is it modifications of
Einstein's theory of relativity?
Maybe.
A lot of people are working with that.
Is it some kind of funny
fluid that fills the universe?
Maybe.
Or most likely it's something else.
Well, that of course would be
wonderful thing to find out.
There are some consequences of dark energy
that are really kind of bizarre.
One of them is a sure thing.
In the accelerating universe,
galaxies are leading
what we call horizon.
So imagine some galaxy far away.
We see it because it's
light can get to us,
but now it's accelerating from us.
And because it's far away,
it's accelerating a lot.
Like a few billion years in the future
we will not gonna be able to see it
because it will be so
far away that even light
won't be able to get to us.
It'll be receding so,
at such a rate.
So in fact, in 100 billion years or so,
the sky will be empty.
Except for Andromeda,
that's gonna hit us in
a few billion years.
But after that Andromeda
and we will settle and
much, much future generations,
100 billion years from now.
This is a sure thing by the way,
if dark energy is doing
what we think is doing.
And the thing that's even more bizarre,
that's not a sure thing because
under certain circumstances,
which we are not sure if
they are satisfied or not.
The dark energy is creating
so much acceleration that
the first, the houses and
the planets and the houses
and smaller things and moments
later of fabric of space
will rip itself apart,
in a process called Big Rip.
And for those of you who
are studying some math,
I can say this is where
the size of the universe,
the distances become
infinite in finite time.
So not anything time in finite
time, they become infinite.
I don't even understand
what this means intuitively,
but equations show it.
We don't know whether these
conditions are satisfied.
So this is a maybe depending
on uncertain conditions,
which we are still trying to measure.
This here is a sure thing.
Okay.
So these are some bizarre,
Big Rip is a maybe,
I think it's maybe.
So where are we?
We have a worldwide effort.
This is again, this beach ball
and we are in the middle of the beach ball
and I'm showing some galaxies
that we measured, galaxies measured.
We are sitting at the center.
This is kind of the observable universe.
There are some galaxies.
The first survey was smaller
than this red triangle,
the 1980, it's called Harvard CFA Survey.
And then as you look
at the new experiments,
Dark Energy Survey, something called DESI,
LSST,
Euclid, WFIRST and even new methods,
which I won't have a chance to explain.
They're like explore
bigger and bigger chunk
of the space we live in to find out
what dark energy is.
So if you look at the biggest telescopes
that was built for cosmology,
many of them have dark energy
or letter, the E in their title.
That's really the number one motivation.
At least as far as
cosmology is concerned is
to find out what dark energy is.
And in my personal and
possibly biased opinion
in all of astronomy and astrophysics,
the only thing in my mind that comes close
to how at least I'm excited
about it is extrasolar planets.
So extrasolar planets are very cool
finding these planets around other stars.
And this dark energy is
right up there with it
to try to understand
what's our universe doing?
Why is it speeding up the expansion?
So the idea is to measure
galaxies and supernovae
and measure a lot of
different things better
in order to find out what's going on.
That's the idea.
And that's what we work on.
Now, one of these surveys
is Dark Energy Survey.
I and David Gerdes our chairman
and many of us in Michigan
are involved in it.
It's
at Cerro Blanco Telescope
on a peak called Cerro Tololo in Chile.
It's in Chile, it's a sky survey.
It's this big building.
As 700 scientists worldwide,
we are working on the analysis now,
observations are actually finished.
But we are working on the analysis
and I have a few pictures.
I am a theorist.
So I've never in my life,
I'd never gone observing in my
life up until like a year ago
when I went to Chile to observe.
And here I'm sitting in
front of this screens
I'm pretending I know what I'm doing.
Actually I had no idea what I'm doing.
(laughs)
But everything was automated,
so it was very nice and very civilized.
So I was a complete
outsider at observation
and I came away very impressed.
I can tell you it's a beautiful site,
completely quiet, gorgeous site.
It's a huge building.
This door is the size of
a large, very large truck.
So this is like a seven
story or 10 story building.
It's a huge building.
The size of a person is much smaller.
You climb there, you
have this big telescope
with fancy instrumentation
and very nice software.
In fact, by the time I was there,
you can set software to observe
and you can read the book
the rest of the night.
It's just automated.
It's almost like artificial intelligence.
I was completely blown away.
But these are the kinds of
observations we are doing
to try to find out what dark energy is.
Now, that's basically the main,
that's my main story.
Okay.
Now I have some breaking
news, breaking news cycle.
A breaking news is news that happened
in a just couple of years,
last couple of years
and this is the latest
and greatest excitement.
What are we excited about today?
This year in cosmology.
It's something called Hubble tension.
What kind of tension is it?
Well, there are two kinds of measurements
of the Hubble Constant.
This method I talked about
from type 1a supernova in Cepheids,
remember you do the same as Hubble did.
You measure Hubble constant,
the same as Hubble did,
you get 74 kilometers per
second per megaparsec.
Remember the structure
of the hot and cold spots
also tells you this expansion
rate of the universe,
you get 67.
Now you may say, "Well, excellent."
You told us it's about, one number is 74
the other number is 67, perfect.
Except, take a look at the error bars.
This is plus minus 1.4,
this is plus minus 0.4,
these are the margins of error, right?
This is how you report the error.
The errors are very small.
The CMB error is tiny and the
first error is still small.
So, in fact, if you
look at the difference,
which is seven, 74 minus 67 is seven.
Even in units of the loss
of this larger error bars,
it's five, five margins of errors
because it's five times 1.4,
is the difference between
these two numbers.
So in cosmology in statistics,
we call this five Sigma.
Five margins error, five Sigma,
any physicist will tell you is margin,
it's a threshold for excitement.
For real excitement,
something doesn't fit.
Because formally it corresponds
to a 99.99997% confidence
that these two numbers don't match.
Now of course you may say,
"Look, come on, you're messed up.
"This was really a bigger error bar,
"but you forgot to include something."
Multiple teams around the
world have redone the analysis,
have looked at this, have
checked and rechecked.
There was, I think last year
there was something like 10
conferences devoted to this.
So many people have looked at this
and kind of agree that's about right
and this is why we are excited,
not just because one person,
went out and is claiming something.
So in my personal opinion,
this is the cutting
edge kind of development
is this discrepancy that won't go away.
These two numbers should be the same
unless if something in
our assumptions is wrong.
And what in our
assumptions could be wrong?
Well, new physics,
new behavior or dark
matter and dark energy,
they won't go away.
But is it new behavior of dark energy?
Is it some kind of new?
Is it not negligible at
early times in the universe?
Some other new effect that
we haven't thought of.
So many people are working on this,
writing papers about this.
This is the kind of cutting edge.
I don't have a resolution to this.
This is the current excitement.
But the exciting thing about it
is a very solid, two very,
very solid measurements.
These are not just two random,
they don't agree to a margin.
And the difference is such that it's five,
it's what we call five Sigma.
Okay, so that's the latest
from the cosmology front
going on around the world,
is this Hubble tension.
And there are many conferences
and workshops right now being devoted.
In conclusion, I said that
universe is expanding.
It was smaller in the past.
This start through the big bang.
Dark energy is for sure there.
I'm guaranteeing it
with my life apparently,
and universities accelerating.
And there's a worldwide
effort to understand why.
And I talked about Hubble tension,
which is discrepancy in modern
measurements of each node
by two trusted methods and teams
that may indicate
a new effect or new major discovery.
Thank you.
(applauding)
(upbeat music)
