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This is, this is Hubble's original data
from 1929
And this is one of the reasons he was such a great scientist
cause he knew to draw a straight line through this dataset
which itself is already
not so clear
It’s not obvious to see the right answer
and he, but what he found was in fact that velocity
is proportional to distance
And the great thing is he got the answer wrong by a factor of ten
which, uhm...
which was an embarrassment at the time
Again, I'll throw a little commentary in it
because if the universe were expanding this fast you could calculate its age and its age would be
1.5 billion years old
That was in 1929
Now, as anyone knows if you read any of Richard's books you would know that well by 1929
we already knew the Earth
was older than 1.5 billion years old
And so it was embarrassing
that the universe was younger than the Earth
One of the many embarrassments in cosmology that's happened over the years...
and, in fact, taken by some people to, once again, argue that science didn't know what it was doing
But the problem was, of course, that he wasn't a bad astronomer, a bad scientist, the problem was
trying to measure distance Because he didn't have good standard candles
and that, as I say, had been
the Holy Grail, if you wish, of cosmology over the last century
And we now have standard candles – here's one - I wish there was better resolution
on this...
projector, it's a beautiful picture from the Hubble Space Telescope
of a distant galaxy
far, far away
and long, long ago
And, uh...
and there's a whole galaxy, it’s about a billion light years away
We're looking at it as it looked a billion years ago
so many of those stars no longer exist
And here's an object that's just uh... as bright as the whole center the galaxy, you’d think it's a star
that's near in our galaxy that just got caught in the picture frame - it's not!
It's a star on the edge of that galaxy that has exploded
And exploding stars shine with the brightness of ten billion stars, they're the brightest fireworks
in the universe – supernovae.
They're remarkable, and again, I keep having asides, maybe I'll get to my point eventually
but uh...
the, the uh... This is something that I wrote a whole book about
And someone asked me yesterday why I wrote that book
because it is the most poetic thing I know about the universe
Richard wrote a great book called... what's it called, 'Our ancestors...', what's it called...
'The Ancestor's Tale’ yes, I wanted to make sure I got that right
And I wrote a book that was a different ancestor's tale, called 'Atom'.
But the amazing thing is that every atom in your body
came from a star that exploded
And the atoms in your left hand probably came from a different star than in your right hand
It really is the most poetic thing I know about physics -
you are all star dust!
You couldn't be here if stars hadn't exploded because the elements, the carbon, nitrogen, oxygen and iron
and all the things that matter
for evolution
weren’t created at the beginning of time they're were created in the nuclear furnaces of stars
And the only way they can get into your body
is if the stars were kind enough to explode
So forget Jesus! The stars died so that you could be here
today! Okay?!
Anyway...
the point is, the real point, the reason why I showed this picture, is that these objects,
these exploding stars
are great standard candles. We can actually observe them
Amazingly! Even though only one occurs every hundred years per galaxy,
there’re enough galaxies
that if you put your hand up, in the night
away from LA
and looked at a dark spot in the sky and made a hole the size of a dime,
with a large enough telescope you could see a hundred thousand galaxies
And that means that even though stars explode once every hundred years per galaxy,
in that little region with a hundred thousand galaxies
on a given night, you'll see ten stars explode
The universe is huge and old and rare things happen all the time... including life!
And so it's an amazing thing and here's what, we can observe stars exploding,
we can measure their brightness
we can measure their colors, and that has allowed us to produce a great standard candle
And after
75 years we now can determine the expansion rate of the universe. This is a new...
Hubble diagram
much better than Hubble's
It was made after the discovery that in a long log everything was a straight line and uh... and
uh... but even still, we now know the rate of expansion the universe to ten percent
not a factor of ten
and we, therefore, in fact, we now know the age of the universe
or other things, extremely accurately
to almost four decimal places
13.72 billion years
is the age of the universe
It's amazing that we can
say that with a straight face
and have scientific reasons to support that
Okay, great,
so let's go back to Einstein
Einstein had this Cosmological Term, he said: 'That was my biggest blunder, I wanna throw it out
... get rid of it', but the problem is you can’t get rid of it so easily
Because using the miracle of modern mathematics you can rewrite that equation
and, um...
now, this is a small step for a mathematician but a giant leap
for a physicist
not because it's that hard to put
this term over there, most of us could do that
but because it now represents something very different when it's on this side of the equations
Here, it was somehow a geometric quantity
When it’s here, it looks like a new contribution to the energy and the momentum of the universe
What could contribute a term like this?
And we know the answer
Nothing!
By nothing I don't mean nothing, I mean Nothing
If you take empty space and that means get rid of all the particles
all the radiation,
absolutely everything,
so there's nothing there,
if that nothing
weighs something
then it contributes a term like this
That sounds ridiculous. Why should nothing weigh something?
Nothing is nothing!
The answer is Nothing isn’t nothing anymore
in physics, because of the laws of quantum mechanics and special relativity,
on extremely small scales,
Nothing is really a boiling, bubbling brew of virtual particles that are popping in and out
of existence
in time scale so short you can’t see them
Now again that sounds like philosophy like counting the number of angels on the head of a pin,
or religion or something
useless! I shouldn’t say, uh...
Dan Dennet is here, I shouldn’t say philosophy is useless. Anyway...
He’s also a friend
but uh...
The point is, we can't measure virtual particles directly
but we can measure their effects indirectly
and, in fact, they're responsible for the best predictions in physics
Here, by the way, is actually, uh
uh... an animation that was shown at the Nobel Prize ceremony about five years ago by a friend of mine
who happened to win the Nobel prize for...
for developing the theory that produced this
This is the space inside of a proton
The empty space inside of a proton
not where the quarks are, but the empty space between the quarks
And this is not, uh, this is an animation but it's an exact
animation coming from physical calculations
This is what the space looks like
Now, how do we know that? Well there are a lot of reasons but one of the things are, it turns out most of the mass
of the proton
comes not from the quarks within a proton but from the empty space between the quarks
These fields
popping in and out of existence
produced about 90% of the mass
of a proton
And since protons and neutrons
are the dominant stuff in your body,
the empty space is responsible for 90% your mass
So these empty spaces are vital
to science, and these calculations are vital to understanding
not just protons but electrons and atoms and produce the best
comparisons the, and I will repeat this, the best comparisons between theory and experiment
in all of science
to ten decimal places in quantum electrodynamics
Using these calculations,
we can get the right answer
It's amazing!
So if that's the case let's calculate the energy of nothing
where there's nothing else
And when we do that
we come up with the calculation
which is pretty bad it's the worst prediction in all of physics
We calculate, you can’t even see, I think there's a 1 at the end of that
we calculate that the energy of the empty space
is a gazillion times the energy of everything we see
That, as I say, is the worst prediction in all of physics which is why we didn't talk about it for
a long time
We calculate that empty space should have an energy of a hundred and twenty orders of magnitude
more
than galaxies and stars, and people, and aliens an all the rest
And if that were the case, we just wouldn't be here
so we knew something was wrong with this calculation which has been around since I was a graduate student
And we knew what the answer was
Theorists always know the answers, they're just sometimes right
uh...
the, uh...
We knew the answer was zero
because it's the only sensible answer
Cause, you know, you can't cancel a big number like this
Let's say the energy of the empty space was comparable to the energy of everything we see. Well, we’d have to
cancel this big number to a hundred and twenty decimal places
and leave a finite answer in the hundred and twenty first decimal place
No one knows how to do that in science
But 0 was a number we can get beautifully in science. We use mathematical symmetries
things cancel, equal
and opposite things cancel all the time in science because of symmetries of nature
So we knew the answer
We didn’t know what the symmetry was but we knew the answer was 0
And we could go to bed at night and that was fine
But, you know, the neat thing about cosmology,
is that it’s really a science
And science is empirical
Knowing the answer means nothing
Testing your knowledge means everything
And so the question is we should test what the energy of the empty space is
and how can we do that, well we weigh the universe
How do we do that? We stand on the shoulders of giants
This is a picture I took on an island off Sweden
which used to be an island, no, an island off Denmark which used to be an island off Sweden
It’s The Island of Hven I think I said that right
And this guy, if you look carefully he doesn’t have the end of his nose
uh... His name is Tycho Brahe
And he, as many of you know,
laid the basis for Newton's law of gravity
by doing nothing other than spending twenty years on his back uh... a noble tradition uh...
... look, in this case, looking up at the sky,
without a telescope,
measuring the positions of the planets around the sun. And then, he was a crummy feudal lord,
got kicked off that island, he gave the data, he went to Prague
gave the data to hapless assistant named Johannes Kepler
Who, again, spent twenty years without a macintosh trying to interpret the data and uh...
and fudged it, we now know,
uh... And came up with, of course, Kepler’s laws which led to Newtonian gravity, and the point is -
we can use gravity to weigh the universe, including
the weight of empty space
Now why do we care?
The reason I got into cosmology
General relativity tells us that space is curved, and therefore the universe can be one of three different
geometries -
open, closed or flat
Now, I can't draw a picture of three-dimensional curved universes very well
so here are pictures of two-dimensional curved universes
This is a closed universe – a surface of a sphere in two dimensions
But, if we had a closed three-dimensional universe it’s very simple, it would be very similar
If we, if our universe was closed
we would look, if you looked far enough in that direction
we would see the back of our heads
Light would go around the universe
And an open universe would be infinite in spatial extents as would a flat universe - that sounds really nice
but it’s irrelevant
The really important thing is in a universe full of matter a closed universe will expand
and stop and then re-collapse in a big ****, in a Big Crunch – the reverse to the Big ***
An open universe will expand forever and a flat universe will expand and slow down but never quite stop
And that's why we wanted to know which universe we live in and, as I say, that's why I wanted to
to learn about it because once I knew which universe we lived in
I would know how the universe ended
Okay? And so...
weighing the universe tells us what the curvature of the universe is. And that’s why we wanna weigh it
so here, I wanted to show you in the next few minutes how, in fact, some of the most remarkable developments
in cosmology
And then tell you, how they completely changed our picture of the universe
so that we understand
that the universe we live in
is the worst of all possible universes to live
Okay? Just so you know where we’re headed
This is a cluster of galaxies
Each dot in this picture
is a galaxy
Again, amazing to think about it
Remarkable!
Every one of these galaxies contains hundreds of billions of stars
and pehaps civilizations
some civilizations that admire the religious gunk other civilizations that have moved beyond
And other civilizations that are long dead
Cause this is about three billion light years away
Three billion years ago was when that picture was taken, basically
Now, clusters of galaxies are the biggest bound objects in the universe. So if we can weigh them,
we can weigh all the mass of the universe and we can weigh them now
We can weigh them by using general relativity
Because in this picture
is a remarkable
phenomenon that Einstein first predicted in 1937 though he said it would never be observed
He underestimated observers
If you look at this picture you’ll see these blue things, these weird blue things
That is a phenomenon
that we now understand as gravitational lensing
Einstein told us that a mass will curve space around it
And he realized, therefore, if you have a big enough mass,
and you have a source of light behind that mass - the light can bend around that object
and come back
And be magnified - just like my glasses magnify things
Or like a cut glass goblet, if you looked through it, you’d see many, I’d see many images of this room
Mass can act like a lens and can magnify things
and split images,
and that's precisely what we're seeing. All of these blue things
are different images of a single galaxy located about three billion light years behind this cluster
Gravity
is magnifying the image -
it’s distorting it and bending it
Remarkable...
Truly remarkable! But because we understand general relativity we could work backwards
and figure out how much mass must be in that system and where it is in order to produce that image
We can weigh the system
using general relativity
And when we do that...
Here's an inversion by Tony Tyson, who’s now up in Davis
These are, this is the system and the spikes are where, well, this is where the mass is
in the system
The spikes are where the galaxies are
but you notice most of the mass
in this whole system of clusters of galaxies,
is not where the galaxies are
It's between the galaxies,
it's where nothing is shining
About fifty times as much mass
in this system and in all systems we can measure
comes from stuff that doesn't shine
And physicist with their
linguistic perspicacity, have called it:
dark matter
And we now understand that 90% of the mass
of galaxies and clusters,
including our own Milky Way galaxy,
is made of stuff that doesn't shine
And that isn't, maybe, that exciting cause there’s lots of things that don't shine: you don't shine.
If I turned the lights out, well those of you who are from Los Alamos might but the rest of you
don't... but, uh... the, uh...