Hello everyone! I hope you are all
healthy well and safe.
Thanks for joining us
for the first talk of our 'Golden Week of
Webinars and Astrophysics' series.
My name is Thomas Puzia and I'm a
faculty member at the Institute of
Astrophysics of Pontificia Universidad Católica
and I'm the head of outreach activities
at the institute,
and together with Evelyn Johnston, one of
our postdoctoral fellows at the
institute we have organized this week for you.
We're very excited to bring you talks
from scientists who have significantly
contributed
to astronomy, astrophysics, and cosmology
and thereby expanded our understanding
of the nature and the inner workings of
the universe.
It will be hopefully an exciting and
instructive journey for you
as we move from the largest scales of
the universe
over structure and galaxy formation to
planet formation
and the fabric of reality itself during
this webinar series.
We're looking forward to bringing you
these talks in the original English
language
and the Spanish simultaneous translation
to your screens without any registration
fees.
This is made possible by the generous
support of the vice rectorate for
investigation of our university
and the center for astrophysics and
related technologies
also known as CATA for its Spanish acronym.
Our first talk this week will be given
by professor Jim Peebles 
of Princeton University, but we
will start with some words of welcome
from
Gaspar Galaz, the director of the Institute
of Astrophysics
then followed by Max Bañados the dean of
the faculty of physics of our university
and Ignacio Sanchez the rector of our
university.
Gaspar would you please tell us some
words of welcome.
Sure Thomas, thanks. I am Gaspar Galaz
the chair of the
Institute of Astrophysics. I will opening
this uh ... I have the honor to open this uh
webinar with our friend Jim Peebles
and I will talk in Spanish, because I
have prepared this also for other people
and
in principle it's easier for me too.
So Max would you like to say some words?
Yes, thank you, can you hear me? Yes?
very well
Good thing! Um, well, thank you Thomas
for the invitation and thank you Gaspar
for giving this
very complete introduction. I will
I've been invited to this panel as
dean of the school of physics at the
Universidad of Catolica, but I also happen
to work on relativity, so I will not miss
this chance to say
two quick words about gravity, it would be
rather quick; but my first comment is
that I fully agree with James Peebles
when he says that the big bang theory is
a very bad name for modern cosmology.
I fully agree with you. It gives the impression
that an explosion happens somewhere in
the past
and this is not what equations are
really telling us.
My second comment is that I have
full admiration for people like James Peebles
who in the 60s and 70s
were working on the evolution of
fluctuations in relativistic cosmology.
Einstein's equations are very complicated
I can tell you that with knowledge.
They're very complicated. Today when I
had to do a calculation myself I opened
a mathematical notebook
and press enter. That's pretty much all I
do with relativity
these days. But what they did in the 70s
all by hand without knowing
exactly where they were
where they're going to, is really
incredible. I can tell you with knowledge that
what James Peebles faced was
seriously complicated
and yet he managed to get it so right.
it's really impressive the work they did,
he did, and well, and his collaborators.
So, welcome James to the school of physics at catholic university
it's wonderful to have you here, and
thanks Thomas
for organizing this amazing week of webinars
at Católica. Thank you very much.
Thank you Max. Ignacio would you like to say some words
Thank you Thomas, and my first words are
for
professor Peebles. It is a real, an honor for us
to have you here. I'm seeing that
we have more than two thousand
participants, actually it's 2012 by now
which is a really impressing
and I would like to give a more welcome
to everyone that is connected to this web seminar.
Our Institute of Astrophysics has done
a tremendous work
putting this this agenda
during this week. So I'm completely
happy and honored to to have this
program, and to have you professor Peebles
as a first speaker.
This crisis, this pandemia show us the importance of science.
In Chile we have a really new
minister of science and he's
working very
close together with the minister of
health,
analyzing the data,
analyzing what are the projections of the
pandemia and I think that
to discuss about science to discuss
about the new
era after the pandemia
is so important. That's why I really
appreciate the effort of
the Institute of Astrophysics, and
particularly Thomas and the team
I most welcome the words of Gaspar
and the dean that has recently done.
I guess everyone is waiting for your presentation
and welcome to the catholic
university, welcome to chile and welcome
to these 2031 participants right now.
Thank you professor Peebles.
So we are looking forward to bringing
you these talks in two languages.
For this talk series we have arranged a
simultaneous language interpretation
provided by Mr. Patricio Gonzalez,
director of Serendipia Soluciones, who
will be simultaneously translating for us, in both
english to spanish and spanish to
English directions. So on your device you
can switch between the English and spanish channels
using the language or interpretation
option that you can see at the bottom of
your zoom window
if you have any questions during the
talk please type them into the Q&A
window. To open the Q&A window please
just click on the Q&A button
at the bottom of the zoom page.
All viewers will be able to upvote
or downvote questions and comment on them
and we have a team of astronomers and
journalists behind the scenes, who will
be monitoring your questions and select
the best questions for the discussion after the talk.
so the talk is expected to last around
45 minutes and we will have time for
questions at the end, so these questions
from the audience will be selected only
from the Q&A window.
So before we begin, we have now 2055
people in the audience,
I would
like to also briefly say a few words
about the panel members that
are with us today. So my colleagues at
the Institute of Astrophysics Alejandro
Clocchiatti,
Nelson Padilla, Ezequiel Treister, Felipe Barrientos, and professor emeritus Hernan Quintana
are with us today as well,
and we have also an honor to have with us
another Nobel prize laureate from 2011
Adam Riess from the Johns Hopkins university
and also the Space Telescope Science
Institute. We have also with us
Giuseppe D'Ago who is postdoc at our
institute
and three graduate students Ernesto
Camacho, Simon Angel,
and Cristobal Moya. Also with us today,
managing the Q&A section of this talk
will be Daniela Fernandez,
Carl Rojas, and Ricardo Acevedo.
So let's begin! So it is a great great
pleasure to introduce professor James
Peebles as our first speaker this week.
Jim has started his career as an
undergraduate at the University of
Manitoba in Canada in 1958
before moving on then to Princeton
University for his PhD thesis, which he
completed in 1962;
since then he has remained at Princeton
where he became an assistant professor in 1965
and a full professor in 1972
he then became an Albert Einstein
professor of science in '84, and 
has been professor emeritus since 2000 at Princeton.
So during his career Jim has had
received many awards including the
Gruber prize in cosmology back in 2000
and the Nobel prize in physics in 2019.
So Jim works on physical cosmology and
has made important theoretical
contributions to primordial nucleosynthesis,
dark matter, the cosmic microwave background,
and structure formation.
He continues to work on physical
cosmology with a preference for
underappreciated issues
such as isolated galaxies, pure disk
galaxies and the internal dynamics of galaxies.
So, as you can see, Jim has worked at all
scales of astrophysics from the
hierarchical structure formation to
processes related to galaxy and star formation,
and so today Jim will tell us about his
work towards the discovery and evidence
of the expanding universe.
So over to you Jim.
Are we ready? Yeah we're ready. Yeah
please go ahead and share the screen.
then, come on. Here it is
so, I now got this thing ... share
ah ... perfect ... ah
good
whoops
So, it is a pleasure to speak to you all
about notions of the large-scale nature
of the universe.
I think a good introduction to this is
to consider
looking around you at what you see.
Then imagine taking a step back and
looking at still larger
pictures, then another step back still a
broader view
and keep going as follows.
So I begin with this image of
our planet Earth among the first
to be obtained from far enough away that
you can see that the planet is a sphere
quite isolated far from anything else.
We all knew that prior to these
photographs, but yet
seeing it is a different matter.
This photograph
impressed a lot of people, among others
Stewart Brand,
who edited this catalog
of means of obtaining hand tools of all
sorts from carpentry to gardening
to, well, you name it. But all in the name of
what we would now term sustainability
of this very limited surface, on which we live.
You might notice the streams of clouds
they're a result of the rotation of the Earth
stringing out.
Here is an image, a modern one now,
of the largest planet in our solar
system Jupiter.
It has a composition very different from
Earth more like that of the Sun,
mostly hydrogen and helium. It's not a
star, because it's not heavy enough
not massive enough, but it is cooling off
from the original heat of formation
cooling by currents of gas flowing up
and radiating and the currents
are twisted by the rotation of the
planet to make these remarkable patterns
in particular for several hundred years
has been this tropical storm
known as the eh ... as the great red spot.
Here is the Sun, a star.
Here is an image of the surface of the star
again heat is being conducted through
the upper layers
by streams of plasma.
You may have seen the same effect if
you're warming, uhm
well in my native land, porridge
or a thick soup and you see these convective
cells rising and falling. Here is a sunspot
as here and here, where the magnetic
field is strong enough
whoops, to have a stopped the circulation
and to produce a cool spot.
Here are the stars in our neighborhood.
The sun is here.
The sizes of these spheres are in
proportion to the real sizes of these stars,
but of course, the distance between stars
is immensely large compared to the sizes
of stars.
The big star in our neighborhood
Sirius A
is twice the mass of the Sun. That makes
it much more luminous in the Sun, in fact
25 times as luminous. The high luminosity
comes with a hot surface.
Hot is blue. Small stars nearby 
are much less luminous.
Cooler surfaces, that's red. Sirius uh
being much more luminous is going to
exhaust its supply of nuclear fuel
far before the Sun, when it does it will
shed some mass
the rest will contract to form a white
dwarf.
Sirius B right here is ...
was a still more massive star than
Sirius A.
It exhausted its fuel already, has
contracted to a white dwarf. Uhm
Anything else to say? Well yes, down here:
Proxima Centauri uh is now known
to have a star up to have a planet,
but just the right distance from this
faint star
that water on the surface of the planet
would neither freeze
nor boil. Wouldn't you just love to see
what's happening on the surface of that
planet? Many would.
It's four light years away. So it's just
possible to imagine sending a fleet of
robots
one or two of which may be close enough
to pass near the surface
send us back a photograph; it takes four
light years to get back.
It'll take a lot longer to get there, but
people can dream.
Here is the distribution of stars on a
larger scale.
We see that we live in a galaxy of stars.
It's a flattened disc right along this
direction, because we're looking through
the disc.
You notice the bands of dark. That's not
absence of stars but rather presence of
dust between the stars
that absorbs light.
We get a better feeling for
the nature of our galaxy of stars
by looking at a nearby
galaxy rather similar to the Milky Way,
similar spiral arms.
You see perhaps streams of dark
those are streams of dust. You see 
blue spots.
That's where stars have formed fairly
recently.
Among the recent stars there are massive
stars still burning.
Their surfaces are hot blue. You see
these blue patches.
You see red patches. That's where
interstellar gas
has been ionized and in that plasma
hydrogen produces a strong line
in the red. You see also toward the
center a sheen of
yellow that continues out through all
the whole affair, but is
less prominent on the outer parts.
It's the light of some thousand million
stars like the Sun.
Astronomers tell us that at least in our
neighborhood
there are as many planets around stars
as there are stars.
Here we can is a very good bet there are
some
thousands of millions of planets
on which
all sorts of interesting things
are happening, that we can be very sure that we,
the human race, will never see.
An important lesson, I think.
Some galaxies look like this they're just
balls of stars
not very interesting perhaps. Here is our
neighborhood of galaxies.
You see the red dot. Those are the 15
most massive galaxies in our
neighborhood.
Our milky way galaxy is one of them.
You see lots of black dots. They are
fainter dwarf galaxies
You see vast empty regions and a strong
concentration, and I should have
mentioned that these are two
perpendicular views
of the distribution. In either view you
see the flattened band across the center
for reasons best known not to us
the galaxies large and small tend to be
in that plane
but of course there are some that stick
out here quite close to the void,
here and here, in two perpendicular views.
Down below you see photographs of four
of the large galaxies in our
neighborhood. You've seen already a
picture of M101.
Here are two more, other disc galaxies.
Here is
an elliptical galaxy. And why do I keep
hitting that?
Uhm
And ... charmingly enough in this great
empty region there is just a few
galaxies including this
very tantalizing looking extreme dwarf
galaxy.
What is it doing in there? There are lots
of things to consider,
but we should move on.
Here is the distribution of galaxies across
about 50 degrees of the sky
to a distance six that as i'll
discuss.
These galaxies are moving away from us.
It's something like seven percent of the
speed of light.
You see a great concentration of
galaxies here
in the coma
in the coma region of the sky.
It is a galaxy of galaxies.
You see clumps of galaxies and streams of
galaxies all over the place.
You may notice you're seeing also
something, something new:
this part this guy looks a lot like this
part.
We see this in most detail if we look at
galaxies
that, on occasion, suffer vast explosions
in their central parts.
An explosion that sends out relativistic
jets of plasma
that piles up in these plumes that are
very strong radio sources.
This is a rare phenomenon.
It can be seen at enormous distance.
And so, when we look at the distribution
across the sky
of these exploding galaxies, we see
a long way out. Now this picture this map
of the distribution of positions of
these exploding galaxies across the sky
requires a few words of explanation. You
must ignore the hole in the center.
The telescope couldn't reach that part
of the sky.
You must now ignore this
patch right here. That's Cygnus A,
that very bright,
relatively nearby exploding galaxy. It's
so bright that it confuses the telescope.
I don't quite know, why there's a hole here
but there's got to be some
explanation, another
bright radio galaxy. You note it's a band
across here.
That's faint galaxy radio sources in the
plane of our Milky Way galaxy.
And this part didn't get mapped. Anyway, whoop.
You look at this and you see something
quite new. Nothing! 
You pause to consider
that in natural science we tend to study
layers in a hierarchy of structure.
You may study atoms or you may study
concentrations of atoms, molecules,
or you may just study the way those
molecules form together
in cells and the cells form together to
form you and me
and how we get together to form a city
and how cities form on the Earth and
how the Earth is part of the Solar System
and there are many others; layer upon
layer of structure,
both to large scales and the small. And on
each of those scales we see something
new as you've seen, except here we stop
seeing something new. This is why
we can pretend to have a theory of the
universe
rather than a theory of one or another
part of the universe. Because on this scale
the universe is the same everywhere
and we may talk about the evolution of
this universe of sameness. Fair enough.
Now I mentioned that the universe is
expanding. There's an illustration.
Imagine for a moment you live in
two spatial dimensions rather than three.
And imagine that this two-dimensional
space is curved into the surface of a
balloon.
You must not ask me what you live on the
surface of the balloon.
You must not ask me about this space
outside the surface ... why do i keep doing that?
The space outside the surface is not
accessible. You can't see it
and you can't see what's inside. You can
only see what's on the surface of the
balloon.
You must also imagine that the balloon
is being blown up.
I will explain later this curious stick
figure and this
and these words. At the moment just consider 
that as the balloon is being blown up
you are not
expanding. The galaxies are not expanding,
but the distance between galaxies is
increasing.
So you sit on a galaxy, you look around
you
and you see the other galaxies moving
away from you,
and you may say, wow! The universe is
expanding and it's expanding away from me.
But everyone else can say the same thing.
That galaxy
has observers who also see the universe
is expanding away from them.
That's the way it has to be if the
universe is the same everywhere.
You might also notice that objects
further away are moving away faster, 
known as Hubble's law and
whoop
Here is Hubble's law. Horizontal axis
distance, vertical axis rate at which the
galaxies are moving away.
Here was the discovery in 1929, here
the astronomers Edwin Hubble and Milton
Humason 1936
reported measurements of
recession velocities of galaxies,
I should remark,
you measure the
recession velocity by the doppler effect.
You've all seen the Doppler effect or
heard it as you've watched a car roar by,
aaaarrrroooom.
The tone emitted by the car isn't
changing, but as the car rushes toward
you, the sound waves get compressed,
shorter wavelength higher frequency,
same for light.
And the car rushing away, the lower tone,
the analog here, the galaxies rushing
away from us,
have longer wavelengths.
And impressive to consider
that back in 1936, when I was one year old,
the astronomers were observing galaxies
so far away
that they're moving away at 10 percent
of the velocity of light.
Well, I can't resist showing you
some of the people involved in these
great discoveries.
And uh, well what amuses me to reflect
the one person responsible for a lot of
these early discoveries,
Percival Lowell of the very prominent,
socially most acceptable, very wealthy
Lowell family. He conceived of the idea
that there may be an advanced
civilization on the planet Mars, and the
civilization may have built canals to
carry water around.
He used his fortune to build an
observatory
to look for those canals.
Although astronomers, in general, were
rather embarrassed by this,
they celebrate his memory for choosing a
good place to build his observatory,
where observing is good, and for hiring
excellent people
to instrument and use the telescope
including, Melvin Slipher,
who developed the technology to measure
wavelengths
of light from galaxies and to
demonstrate the galaxies rotate
and that their wavelengths are shifted
toward the red,
as if galaxies were moving away from us.
Henrietta Leavitt showed astronomers how
to measure distances to some stars,
Cepeheid variables. Here in a
moment Einstein is visiting, so the suits
come out,
but in particular Edwin Hubble, who at
the time
late 1920s, early 1930s,
had the best instincts for developing
new aspects of extra-galactic astronomy.
He had the best telescope in the world
and he had Milt Humason
who I reckon must be one of the best
people at the technical
job of measuring galaxies
Here we see photographs of the
interpretation
whoops, why do I keep doing this? ...
interpretation
The German Hermann Weyl, who fled the
country
in the late 30s, as the nazis got into
power
seems to have been the first to have
come across the idea
that in general relativity theory,
Einstein's new theory of gravity physics,
you might expect this sort of expansion.
But although he was an excellent
mathematician, he didn't have the
physical theory down pat.
The Russian Alexsander Friedman had
the theory
but the misfortune to die young and not
to notice the phenomenology,
these redshifts of the galaxies. 
The Belgian
Georges Lemaître was just on the spot at
the right time. He knew the phenomena,
he knew the theory, and he put the two
together
to give us the theory of the expanding
universe.
That that expanding balloon you saw
earlier, was inspired by Georges Lemaître.
I'll discuss a little more of that later on.
So now we come to the starting
development of our
current theory of the hot expanding
universe
It was mentioned that I dislike the
term big bang.
It's quite inappropriate, but everyone
uses it; I've given up trying to remedy that.
So I'm going to say
the hot big bang theory.
We can't change everything. 
Four people
um ... yeah, there we are.
Post war, after the second world war
there was a burst of activity,
released in technology and science
and four people coming out of that war
were particularly active in giving us
the starting ideas
of the big bang, the hot big bang universe.
Bob Dicke on the far, on our left,
far left and Yakov Zel'dovich far right,
both worked in war research during world war II.
Zel'dovich on a Soviet program of nuclear
weapons.
Bob Dicke the USA program in
in radar and other electronics.
Fred Hoyle in the United Kingdom,
Cambridge University and George Gamow,
Ukrainian
refusenik, ended up in the USA.
Gamow is to my mind the person
with the deepest physical intuition of
anyone I've come across.
Just gorgeous! It's unfortunate, I guess,
that it must be that someone deeply
intuitive is not going to care about
details.
And that was Gamow's fate. He did
great things, but was underappreciated.
So we'll begin with him, and uh, I will
begin
by a post of Gamow, 
a comment, please do not panic at these equations,
they will not be on the exam.
I only mean to indicate that in the
late 1930s, early 1940s, people were
wondering
where did the chemical elements come
from.
It was thought at the time that stars
are not hot enough
to have triggered thermonuclear
reactions, that would've produced
the heavy elements.
It was known, at that time, a lot about
the statistical mechanics
of thermal reactions that could produce,
for example,
or convert ... to make for example ammonia.
The equations are of this form
and it was proposed we will use these
equations
to discover what would be the abundance
ratios of isotopes of heavy elements
under the assumption
that they reach statistical equilibrium
under very high temperature in the early universe.
This paper was by Chandrasekhar, a deeply
impressive physicist, very knowledgeable.
He surely knew
that implicit in this equation is the
idea that the
elements are in a sea of thermal
radiation
at a high temperature to be sure.
That sea of radiation, he surely knew,
would not go away
as the universe expanded and cooled.
There's no place for it to go.
The universe is everywhere. Instead it
would cool, it would
retain its thermal spectrum and it would
still be present.
These people had the notion of radiation
left over from an early universe, but
they didn't
grasp it. Gamow did.
He realized that you must be careful
with this ... Oh, and I should have
remembered
to say, astronomers also had
the sea of thermal radiation in their
grasp.
There is in interstellar space molecules,
including the cyanogen molecule, carbon
and a nitrogen atom
stuck together, cyanogen. You might recall
that in quantum mechanics,
and in the real world, these molecules
can have energy levels that are discrete.
A ground level,
the first level of excitement, second, and
so on.
Astronomers observed absorption from the
ground
of starlight passing through
interstellar space.
Absorption by the trans ... absorption by
cyanogen in the ground level
causes a notch in the spectrum. They also
saw absorption from the first excited
level of cyanogen.
They wondered why are these cyanogen
molecules in the excited level.
It was a puzzle.
If these were excited by a sea of
radiation
the radiation would be at a temperature
of around 2.3 Kelvin.
It's pretty close to what's now
observed.
Again, these astronomers had in their
grasp
of the notion of a hot big bang that
cooled,
but didn't quite grasp it. Gamow did.
In these two marvelous papers in 1948,
he developed much of the
current ideas about our hot big bang.
In particular, he noted
that as the universe expands and cools
the thermonuclear reactions would very
naturally produce helium,
in an amount about 30% by mass.
That was sketched out by him in 1948.
Soon after that by Enrico Fermi
and Turkevich at the University of Chicago,
you've got a little deuterium, the stable
heavy isotope of hydrogen,
traces of heavier elements. What you get
out of this hot big bang is helium
and of course thermal radiation.
This helium is a fascinating story.
Here is a discussion in 1957
on the origin of the elements. 
By that time
people have come to the view that indeed
the heavy elements could be synthesized
in stars
and scattered about and placed in new
stars and planets,
as stars evolve and die and explode.
In particular, it was noticed that the
oldest stars
have little abundance or abundances of
the heavy elements.
Younger stars have higher abundances.
What you'd expect if the stars were
making the elements,
so that as you increase, the younger stars
have had a chance to accumulate more
heavy elements. The difficulty was helium.
It's hard to ...  it's not readily made and
scattered about interstellar space.
Helium is not likely to be produced.
It's a difficulty. How does it do so much?
Martin Schwarzschild pointed out Gamow's
old theory
and saying that helium production up to
mass 4,
that's helium, could work
by production in the early hot big bang.
Fred Hoyle: "that is why a knowledge of
the helium concentration in extreme
population II is so important."
Extreme population II is the oldest stars
that can be observed.
They're old, so they have low abundances
of the heavier elements.
The question is: do they have a lot of
helium or only a little?
Well, I was asking seven years later in 1964,
the helium, the evidence of astronomers had
become clear,
and Hoyle knew it. Oldest stars
have low abundances of the heavy
elements, but they have about a third of
their mass in helium. 
Where did that helium come from?
Hoyle seriously disliked the hot big bang,
he preferred the steady-state model.
I didn't know Hoyle well,
but from conversations I got the clear
impression
he felt that the scales of time and
space
in cosmology are so vast, that you're not
going to be able to empirically
construct a cosmology. 
You're going to have to do it
by philosophy and I must say his
steady-state philosophy is really elegant.
But as time went on, he found himself
incapable of accepting that we were
discuss constructing
a phenomenologically based cosmology.
Anyway,
I point this out, because I admire his
fact that
in '64, although he disliked intensely
Gamow's ideas,
he felt he had to publish a paper
pointing out
that that high helium abundance could be
from Gamow's hot big bang.
Here I go briefly to Bob Dicke's
research
on electronics during world war II. Here
is Rai Weiss, center.
You might remember his name. In
this building, which was
constructed during world war II, a
temporary structure that stood
until very recently for war research.
Rai Weiss took over and developed much
of the technology
for LIGO and the great detection of
gravitational waves, some merging
massive stars, for which he shared the Nobel prize.
During world war II, Bob Dicke was
working here
developing the technology
that could detect radiation at
microwaves, millimeters to centimeters,
that could have been left over from the
early universe.
Here is a photograph of an experiment in
1959
at the Bell telephone laboratories on
communication by microwave
radiation, centimeter to millimeter
wavelengths.
This was a progenitor of the cell phones,
which I think is not an entirely good
thing. I'm distressed at
the sight of our students, wandering
around campus,
looking at their cell phones, instead of
where they're going.
But there it is. Now this experiment
revealed a curious anomaly.
Again, the technology is to be ignored
the point is,
that the engineers, who built these
microwave receivers, were very careful
to check all of the little insertion
noise that accompanies any measurement.
And to make the books balance they had
to postulate
the ground radiation was sneaking in
over the antenna
and into this cone reflected back into
the receiver, a monitor around two
degrees
above absolute zero. It's getting to be a
familiar number.
This antenna was picking up radiation
from the hot big bang.
But the engineers didn't pause to ask
themselves such a question.
Their job was to make the lowest-noise
system possible.
So here we come to 1964,
when Bob Dicke, remember he of the
microwave radiation,
the radiation lab at MIT,
decided on his own, for reasons, 
we needn't get into,
that a hot big bang would be elegant. He
saw some problems, he felt were interesting.
He, uh, in 1964 told two of his young
postdocs in his group,
David Wilkinson, and
not present here alas Peter Roll, why
don't you guys build a radiometer
technically known as Dicke radiometers,
because he invented them
to see if you might be able to detect
this radiation from the early universe.
I remember so well his turning to me and
saying casually
why don't you think about the
theoretical implications.
So Peter Roll went off into education,
David Wilkinson and I spent the rest of
our careers following Bob's suggestion.
That was, because of course this
radiation was detected.
We come now to the faithful year 1964 in summary.
Here is Yakov Zel'dovich
in the Soviet union, a few years after
the discovery of this radiation.
In 1964 and I, we should pause to remember that
the scientists in the Soviet Union had
great problems doing
original research, because they could not
communicate readily with the outside world.
Zel'dovich, important and instrumentally
important in developing nuclear weapons
in the Soviet Union,
had lots of influence in the Soviet Union.
He was four times decorated socialist
worker hero.
I'm told that when he wanted something
from the bureaucracy, he would put on his
medals
social worker hero medals and get all
kinds of
reactions from ... attention from the
bureaucracy,
but he could never leave the country.
He could not access readily journalists
from outside the country. They passed
slowly through censors.
He could not publish his articles
in the journals that people outside the
Soviet Union read,
because the censors slowed them down.
In 1964 he knew Gamow's hot big bang theory.
He thought it must be wrong, because he
thought the helium abundance of stars is low.
Unfortunately, he couldn't communicate
with astronomers who could have
straightened them out.
In that year, here are
Arnold Penzias and Bob Wilson
with one of the
Bell Labs receivers, trying very hard to
understand the origin of that anomaly.
Why were there a few degrees Kelvin
extra radiation creeping into the system?
They deserve great credit for trying
every possible interpretation:
radiation of the ground, no, radiation
from nearby
transmitters, no, radiation leaking into
cracks in the sides of the antenna,
no ... uh deeply frustrated.
They're owed great credit for not giving up
on this anomaly
and for complaining about it until
someone heard
and directed their attention to this
experiment,
uh ... at Princeton. Here is David Wilkinson
again.
You may just be able to see Peter Roll's
plaid shirt; a dickey radiometer
built to look for this radiation.
Fred Hoyle in the U.K.
realizing that there's a high helium
abundance
and that it could be from a hot big bang.
He at one time knew
about that cyanogen temperature. 
He wrote papers on it,
but in 1964 he forgot. So here we have
this delicious scene:
Fred Hoyle knew about helium that could
come from a hot big bang.
He used to know about the
cyanogen temperature, but forgot.
In the Soviet Union, Zel'dovich
didn't know that the helium abundance is high.
If he had, it would have been a
different story.
In Bell Labs, this is only 30 miles from Princeton,
these people are trying to understand
the origin of that excess noise.
In Princeton, unbeknownst to anyone else,
these guys are working through a detection.
I was invited to give a colloquium
at the Johns Hopkins University.
In that colloquium, I talked about
this work, I remember David's work ...
rewards ... you can talk about this
experiment as well as your theories,
because
no one can catch up with us now. In the
audience was a friend from high school
days, Ken Turner.
He talked to Bernie Burke, who told
Arnold Penzias: "You ought to talk to
these guys at Princeton."
It all came together. By 1964 we had it.
So we had this. So this is '66, pretty close.
Penzias and Wilson were observing
using an antenna at wavelength 
around seven centimeters.
At Princeton they were using around
three centimeters.
If this is thermal radiation left over
from a hot big bang,
then the intensity at every wavelength
is determined by one quantity: the temperature.
Here is what it should look like.
The temperature's a touch high here, but
all right, it's a basic idea.
These are two points.
Looks good!
To convince people that this is really
thermal radiation, and that, therefore,
it surely came from the hot big bang, you
need to measure this spectrum up over the peak.
I now would take great pleasure in showing you
two groups who worked on this.
Here is one group COBE cosmic background explorer
science working group, supported largely at NASA.
Much of the building being done at Princeton.
Here is David Wilkinson once again.
This tall guy in the back John Mather,
won a Nobel prize for this work.
But here is Rai Weiss again, although his Nobel prize was with gravitational wave detection,
and a group of others.
Here's a second group
in the University of British Columbia,
Western Canada.
Herb Gush
Excellent physicist with great
experience in microwave radiation technology.
Here are his two associates Mark Halpern
on the left, and Wishnow above.
This is one of my favorite all-time photographs
of scientists at work.
I cannot resist inviting you to ask
yourself
if all you knew about these two, was what
you could deduce from this photograph,
if you didn't know that they were part
of something truly great
would this image inspire confidence?
So, here are the results.
It impresses me so to consider that 
each of these groups took about 15 years from the
start of the project
to completion with these measurements.
The results were obtained within a few
months of each other.
Either measurement would have told the story.
This radiation has a thermal spectrum.
That is so significant, because the
universe as it is now
is transparent at these wavelengths.
It cannot cause
radiation therefore to relax to this
equilibrium form.
This surely was produced when the universe 
was very different from now,
hot and dense enough to have relaxed 
due to thermal equilibrium
These are in effect
tangible pieces of evidence of cosmic evolution.
John Mather was received ... awarded the
Nobel prize for his work in obtaining this spectrum.
Herb Gush was awarded deep respect by
all colleagues for this measurement.
A point for all of you, particularly younger
people to bear in mind
Nobel prizes are wonderful things, but
they depend on all sorts of contingencies.
Don't judge your career by prizes and awards,
judge your career by how well you've done.
End of that lesson: the prizes and awards
must be capricious.
Not that I'm complaining about mine, 
but there it is.
Now this is cosmological constant.
Here again this professor doctor Willem de Sitter.
Director of the observatory in Leiden, The Netherlands.
One of the first people to appreciate
Einstein's general relativity theory
to write influential articles on it.
Impressive, because
de Sitter is an astronomer,
and in particular,
on Einstein's cosmological constant.
Now Einstein took it for granted that
the universe is static.
Diamonds may not be forever, but surely
the universe is.
To make his theory allow and expand ...
to allow a universe that is the same everywhere
and by the way,
it's an interesting reflection, Einstein
had no idea that we live in a galaxy, 
as far as I can tell,
much less that the galaxies are, on average,
uniformly distributed.
He just guessed on philosophical grounds
that the only reasonable universe is
uniform one. Somehow he was right.
We still debate whether he was right for
the right reason.
But anyway, here's a uniform universe.
It was Georges Lemaître
who pointed out that this universe is, 
if it's stable
is ... if it's stationary, is unstable.
Einstein's cosmological constant serves
as a repulsion
that can balance the force of gravity
and try to pull the universe together.
Lambda pushing it apart; you can have a balance.
That balance unfortunately is unstable.
A slight perturbation and the universe will either
expand or contract. Einstein's
cosmological constant, he wrote it
as a lowercase greek lambda.
The artist wrote it as a backwards lambda.
Well, poetic license.
Until recently, we've all used an
uppercase lambda
I don't know why the change.
And very recently it's become dark energy.
This is all public relations. We know no more
about Einstein's cosmological constant
than when he introduced it. Well we know,
we have lots of ideas but
we still don't understand it. Anyway,
this in Dutch is whoever ... who however
blows up the ball
what makes the universe expand or swell
up that is done by the lambda.
Another off ... another
something rather cannot be given.
That was Lemaître's original idea that
the universe started out in
in Einstein's stationary
world picture and then it started
expanding, because of this instability.
The makers soon recognized that 
you don't need
to start from stability in an unstable
equilibrium.
You can start from a hot big bang, 
what he called a
primeval Adam.
As soon as Einstein recognized the
evidence there might be an expanding
universe, he decided
that his cosmological constant really
spoils the elegance of his theory. 
Here is Einstein
with George Lemaître. Here is a letter
Einstein wrote to Lemaître. It's dated 1947.
Isn't it September? Einstein was then at
the Princeton Institute for Advanced Study.
He is writing to Lemaître in Belgium.
Uh, Brussels.
You may be able to read this
writing that about,
I give you the bottom line, I cannot...
Lemaître had written to Einstein trying
to persuade him over the merits
of the cosmological constant. Einstein's
pleasant response, I thank you very much
for your kind letter etc.,
but the bottom line, "I cannot help to
feel it strongly
and I'm unable to believe that such an
ugly thing should be realized in nature."
Philosophy sometimes is great. Einstein
guessed at the homogeneous
universe. Philosophy sometimes can be
misleading. Uhm.
He may be right that
the cosmological constant is ugly.
Many people share that view,
but we're going to have to ... we have to
live with it.
Although Einstein disliked the
cosmological constant,
astronomers tried to look for its effect.
Here is Alan Sandage at
the great 200-inch telescope at the
Palomar range in Southern California.
Here is a paper on how he may be able to
detect the effect of the cosmological constant.
Just the bottom line
here are...
whoops!
here are...
Well, here's Brian Schmidt, here Adam Riess
Uhm, Hi Adam! And uh, Saul Perlmutter,
receiving the very influential Shaw prize.
This was in happier days for Hong Kong.
...there, less troubled times, the chief
executive of Hong Kong at the time.
Here, Sir Run Run Shaw, after which his
prize is named,
made his fortune in entertainment, I
believe including kung fu movies.
well known and respected in Hong Kong
and in the mainland for his support for
education.
On the left other winners of Shaw
prizes in other fields mathematics and
other fields. I just like to pause and admire this photograph
because these guys
are as spiffy looking as I've ever seen them.
Though you'll notice Sir Run Run's
suit is bespoke. It fits him to the millimeter.
These guys look good, but I don't think
these suits were bespoke.
Well let's carry on.
Dark matter, already in the 30s,
the Swiss-American astronomer Fritz Zwicky
recognized a real puzzle. Remember I
showed you that galaxy of galaxies in
the sky map?
Here it is again. Each of these dots is a
galaxy.
They're swarming about in this ... in this
uh galaxy of galaxies.
What we notice is that they're
swarming about quickly.
Too quickly for gravity to hold this thing
together
if gravity is produced only by the mass
you see in the
galaxies; a deep puzzle
that for a long time
was not really treated with much respect.
It was an anomaly but what are you going
to do with it.
Here's our nearest galaxy and another
large galaxy
similar to the Milky Way. And the dots
are regions where you see blue light,
red light...
sorry, red light, that strong
recombination
of line from hydrogen,
ionized hydrogen converting to atomic hydrogen.
At each of these spots you can measure
the doppler shift of the lines
and what you discover is an anomaly.
These other parts are rotating
far more quickly than you'd expect if
all of the mass that you see is in all
of the starlight.
This next figure again will not be on
the exam.
Don't get ... don't get too ... read the
captions if you're interested, but the
basic point, already in 1939
Horace Babcock measured redshifts
for four of these ... the little black dots
are four measurements of redshifts
that were surprisingly large. We all know
that in the Solar System the mass is
concentrated in the Sun.
The planets further away from the Sun
are moving more slowly,
because gravity is weaker. So surely the
same is true of a galaxy.
The bits of material that are out in the
outer parts are well away from this
mass concentration in the galaxy. Sure
that they're moving more slowly. 
But then ... may all light...
There is good evidence of the decrease
in rotational velocity with increasing
distance from the center of the galaxy.
Do you see it? I don't. It's a fascinating
example of the power
of standard and accepted ideas.
These guys knew the velocity should
decrease, because the mass is surely
where the light is.
But it's not. Here is technology of
21 centimeter radiation.
Here is Vera Rubin's great contribution
thanks to Kent Ford's image intensifier,
a first example over photographic
emulsions and quantum efficiency;
a clear demonstration the rotation
velocity isn't decreasing with
increasing
distance from the center. An example of many.
There's something wrong. There's mass in
the outskirts of galaxies
and concentration of galaxies that we
can't see.
Of course, from an astronomical point of
view, it could be just
planets, it could be a lot of Jupiters or
very low mass stars.
They're very faint. You put a lot of them
in and not be able to see them.
But the ... it was another deep
puzzle at the time. Here I remind you
again, well, here's that galaxy of
galaxies; here's the distribution of
galaxies. It's clumpy,
distinctly so. Down below...
Can we see this? Well, this thing is
always getting in the way.
oh well, never mind. This is a map of the
microwave background radiation as a
function of position across the sky. 
Hot spots, cold spots. But you must
understand that in this map
the mean has been taken out. These are
the departures from the mean.
There are departures of parts in a million.
This is very smooth. This is distinctly clumpy.
It was in the early 1980s,
a deep problem ... a crisis in many a few of
people's views:
how could gravity have gathered the
galaxies together
without more seriously disturbing the radiation?
Some felt ... but this is an indication
that we don't have the right cosmology,
that something's wrong;
maybe wrong physics. 
I didn't like that and so I pointed out
a way to get around it.
Namely, let's imagine that that dark
subliminal matter,
again equations which you can ignore, um
I only want to boast a bit. We need to
unexplain how the radiation could
remain so smooth, when the matter 
grew so clumpy.
The trick, that I introduced, was to imagine
that the mass that is dark around the
outskirts of galaxies
is not of the court of material that you
and I are made of.
We're made of, well the technicians say,
baryonic matter.
This stuff would be non-baryonic matter.
It wouldn't interact with matter
of sort were made of, and it
wouldn't interact with radiation,
except through gravity.
So a little calculation
showed that if
this dark matter were non-baryonic
interacted only with with gravity,
then the effect of gravity would
produce an anisotropy across the sky
of about three and a half parts per million.
That was 1982. Now...
2003, two decades later, it was measured,
well, five parts in a million.
I could get pretty close to the right
answer, because
I guessed the right physics and I spent
a lot of time,
we might just look back, measuring this.
What are the statistical measures
of this distribution.
I had good measures and I could show
that they're good,
because they scale well,
reproducible. So, good! I had the
distribution of mass.
I had the simple theory of how mass
affects this radiation
if plasma is non-interacting with
radiation.
And uhm, so, there we were. I come now
to oscillations. The universe
began hot. So hot that it ionized all the
baryonic matter.
The baryonic matter has ... consists of
plasma; it's free electrons that scatter
well off radiation and free electrons also
scatter well off ions through the
electric interaction. The result was that
in the early universe
baryonic matter and radiation
act like a fluid with pressure. Now I
want to discuss
the effect of boundary conditions on an
oscillating fluid.
So I have here from my youth, uh,
a game we used to play.
[lower pitch flute sound]
[higher pitch flute sound]
The shorter one, matches wavelengths 
that are shorter
and so it's a higher pitch.
[higher pitch flute sound]
[lower pitch flute sound]
Isn't that neat? 
Here, I took a photograph of a plastic dish,
containing a little bit of water.
I hit the dish and then with my cell
phone took that photograph.
Do you see the pattern aligned with the
boundary?
Again an effect of boundary conditions.
In the universe
the boundary conditions are that the
plasma is present and interacting
strongly with the radiation, so you have
a fluid,
until the temperature drops to around
3000 degrees Kelvin. The 
plasma combines to neutral atomic hydrogen;
that frees the radiation.
It's a boundary condition in time, but it
has the same effect.
It produces resonances, characteristic
wavelengths.
Again, ignore all the details and uh
groove on the
phenom... the facts
that the theory predicts waves
in the distribution of matter. 
These are galaxies and radiation.
Those of you who care about should think ...
should be informed that this is a power
spectrum, the square of Fourier
amplitudes of the Fourier decomposition
of the large field distribution of
galaxies.
This is the analog on the sky, spherical
harmonics rather than
Fourier components. Basic point: there are
favored wavelengths
either in spatial distribution or
angular distribution.
You can see a line through these points
not very precise measurement. It's a very
difficult measurement.
Here an easier measurement done with a
spectacular precision. The same
theory is deep inside these lines.
A wonderful agreement between theory and
observation,
which convinces most of us, certainly me,
that we have a good approximation to
what actually happened
as the universe expanded and cooled.
Uhm, I'll just take a moment to tell you
about some of the problems with this
wonderful picture.
Back when I was starting looking into
cosmology,
when it was very poorly established,
I was uneasy. In fact, I was reluctant to get
into cosmology, because the experimental
basis was so
much ... so modest. But I could see a few
things to do
that led to other things and so on. But
one thing I could consider
back then, is that in cosmology we have
this constant of proportionality
recession velocity proportional to the
distance. Its reciprocal is a
characteristic time.
In gravitational physics we have
Newton's constant G.
From Planck's constant and Newton's
constant, we have a mass density.
Even then we knew that this is a pretty good
characteristic time for the ages of the
older stars,
and this is a rough approximation to the
mass density in galaxies.
The fact that both
are in the same ballpark,
as what's observed
showed me that the theory can't be
entirely without merit.
But the horrible thing is
quantum mechanics gives us Planck's
constant, from Planck's constant we get
another mass density
which is absurd, just absurd.
What is going on? It is a deep barrier to
our attempts to bring together
quantum mechanics and cosmology and
gravity physics.
Don't despair. Lots of people are working
on this,
but I wish to make the point: all of our
physics is incomplete which is to say
it ... physics applied to the wrong
situation, will give you wrong answers.
That's not to say that physics is wrong,
it's to say
that all of our physics is
approximations.
That is certainly true of cosmology.
Among the other approximations 
we have this postulate
of, um, non-baryonic dark matter. 
We don't know what it is.
We have the postulate of Einstein ... of
Einstein's cosmological constant,
we don't know what is,
but we have an abundance of evidence
that the theory we put together with
those postulates works very well.
It means, we are leaving to the next
generations
many far fascinating problems to work on.
Congratulations. I cannot resist a brief,
uh
brief commercial moment, uh, you can read
all about what I've been talking about
and much more 
in this book. I think this is now available.
On how we got to where we are now from
where we were
a century ago, when Einstein introduced
the startling ideas of all of this.
I conclude now
with a statement ... from ...
a deeply respected U.S. expert on
philosophy
and the game of baseball, Yogi Berra, 
who said many
fascinating things, among others
you can see a lot
just by looking. I offer here some of the
images
of the many people, 
who looked at our universe
and who saw many things,
that put together, gave us
a theory of the evolving universe that
we could be pretty confident is a good
approximation
to reality, though by no means the
complete story.
But I will thank you there, pause there
and thank you for your attention.
Shall I stop showing?
Beautiful. Thank you very much Jim.
Wonderful talk!
We have many many many questions in the Q&A.
Uhm, but I would like to leave first the
stage here to our panel members to ask
maybe the first questions.
Are there any?
Ezequiel!
Yes, uhm, and actually I'm going to repeat one 
that came in the Q&A
and I'm going to take advantage that we have the honor of having you Jim
and Adam Riess as well, and one of the
fascinating questions we have now
is the this tension now within the
values of H0, which is now I think at
about the five sigma level, right? So we
should start taking it seriously.
It raised from about two sigma 
and now it's about five sigma.
So, we're wondering, may be asking you 
and Adam as well
what's...what's your take on that.
Do you
think it's real first,
and what does it mean?
You know Adam is heavily involved 
in this very controversy.
He should speak first.
[Laughter]
Uhm, I had the honor of
seeing Jim very recently, when we could
all actually meet about six months ago,
and we talked a fair bit about this.
I think that, you know, as Jim described 
we have this
wonderful model
and I think there's no doubt that the
basic strokes are right,
but, you know, we continue to press it
with more and more precise measurements,
and we're seeing one very interesting
anomaly we don't know where it will go
that when you measure very precisely the
state of the universe shortly after the
big bang and use this
the most basic version of this model to
turn that into a prediction or an
extrapolation
really of how fast the universe ought to
be expanding today,
then you get an answer that's different
than what we actually measure by about
nine percent; and we think the
uncertainty in that
nine percent has gotten down to under
two percent.
Uh, by a number of different sort of
cross-checking methods and so
right now it looks like a tension
between
what the early universe says should be
happening now and what we see.
And it might be telling us something
interesting about the model, maybe some
extra feature
or wrinkle. We need to continue to improve
the measurements of course
and we'll see where it goes.
Wonderful. May I make some 
comments now?
Please, go ahead.
Okay, uhm
You will see in the community two lines
of thought
sometimes entertained by the same person
both
both lines of thought. First, we are
conditioned
to worry about systematic error 
and it is...
our conditioning demands that we
consider the possibility
that something is wrong with these
measurements.
Adam, I totally respect you and but there it
is
I have this conditioned response, I
wonder about systematic errors,
but at the same time, 
I'm hoping you're right
because if this is a true discrepancy
then it is telling us something about
the nature of
the physics.
We're pretty sure we have about the
right model. I emphasize though
that our hot big bang model is only an
approximation. It has this dark matter
which properties we don't understand fully.
That stupid cosmological constant and
an anomaly may point us to something new.
It will be wonderful. There are no
shortage of ideas floating through the
internet. I have no favorites.
I do though, hope we find more anomalies. 
These days you know
I'm fascinated by the properties of galaxies
and I'm particularly fascinated by
anomalies I think
I see there in these galaxies that have
very small bulges
charming ... charming phenomenology. 
Let's hope you're right
and let's hope people find more of these
anomalies that will guide us to a better theory.
So why not actually pick up on this.
So uhm, there was recently, like
speaking of anomalies, the other anomaly
that was the spin alignment of
elliptical gala ... uh sorry, uhm
disc galaxies along the filaments in
a quadrupole alignment are reported and
what do you think of that?
You know, I don't think I know about this
by that are you talking about the dwarfs
around
large galaxies? Yeah not only, not only
giants
uh spirals or disc galaxies, but all kinds of galaxies.
standard all-star galaxy spiral,
one for years people have been talking
about the distribution of dwarfs around
them
and whether there is an anisotropy, if so
what it tells us, uhm
I don't know the current status of that.
It's ... It's fascinating
It was more ... it was more a cosmological
effect, right? So yeah people ... people
looked at the large scale distribution
and
it changed actually, the effect became
stronger as a function of redshift.
I don't have the paper on top of my head
here.
That group photograph had Diego Garcia Lombus.
He and I worked on this a similar effect
the tendency for spiral galaxies to
point toward the nearest large mass
concentration.
These are dynamical effects that I'm not
sure you'll be able to turn into a very
precise test,
because the dynamics is complicated but
of course we can always hope for the best.
Uhm, there are lots of
it should be understood, well, at the one
on the one side
I'm persuaded that we have the right
general theory
I surely cannot believe that it is the
final theory
there's going to be corrections and uh
they're going to be fascinating to find.
So do you see anywhere the weight of
evidence being so completely
overwhelming that it would force any new
developments in cosmology?
In any direction? Do I see any evidence
yeah where shall we look?
That's a question to you. Well,
wherever it's best to focus on...
Well, if you can ... if you can measure reliably
and if you can compute predictions
reliably then you have something interesting.
Galaxies are so complicated that it's
rather difficult to make many
predictions
and that's why there's a lack of
enthusiasm, I think,
about tests of cosmology based on
properties of galaxies.
But if you are careful, I think there are
possibilities
at least in my opinion, uhm,
a good ... there is a good chance that we
will be able to
uh test our cosmology by the properties
of galaxies
as we consider them in greater detail.
That's what ... it's a line of research I'm
pursuing now.
Certainly uhm, we have Adam Riess's approach
let us compare such quantities
as Hubble's constant, derived in different ways
and it's a worthwhile to pause to notice
that these constraints are derived from
observations of the nearby universe
from observations that happened
back when the temperature of the
universe was a thousand times greater
uh when matter and radiation separated.
And from observations back when the
temperature of the universe was 10 to
the ninth Kelvin
and helium and deuterium are being
formed.
There are lots of checks on cosmological
parameters from these three epochs.
By and large they are all consistent. The best test, the most precise test, is Adam's and uh
it's showing an anomaly.
There are other parameters that are also
constrained multiply
by different epochs of observation
and it will be fascinating to see if
more of them
show anomalies as the precision of the
tests increases.
I see there are a few more questions,
Nelson had his hand raised. Nelson go ahead.
Jim, thanks very much for the talk. It was
really great to see how
these ideas came together.
It's very impressive. So, I was wondering
about one thing, I mean the anomaly
in H0 is actually very interesting
but there's, uhm, there are other things that
we sort of take before...
take for granted now, like dark matter
and dark energy. So, uhm I guess dark
matter there's
there are very interesting theories
um there may be a particle that
could be that matter, but do you have
any
I don't know ... I don't want to say
prediction, but
do you have any hunches of on what could
dark energy be.
You know, I emphasized all those
planets around stars
in each of the galaxies that we will
never ever be able to observe for a reason.
We are issued no guarantee that we can
answer all questions in science.
We have not been issued a guarantee in
particular
that we can detect the dark matter.
I'm quite...
I deeply respect the immense effort that
has gone into
searching for direct and indirect
detection of dark matter,
I am waiting to hear that wonderful news
of a convincing detection of a
significant new component of the dark matter.
Bbut we have to face the fact that it's
perfectly possible
that the dark matter is not detectable
it's totally isolated from
our matter, baryonic matter, except for gravity.
It's a horrible thought, but it may be
that way.
If it's that way, I don't think it argues
against the hot big bang.
It's just the way it is.
So, ...
I deeply admire and I encourage
the hard work going into dark matter
detection, but you never know.
Let's face it, you have to be a strong
person to go into that
field, because it takes decades to
construct these detectors
they will look for a very specific kind
of dark matter
and that may not be the way it is.
So, luckily, humans are persistent and
you will ... the search will continue.
The one thing, I would warn you 
and everyone is
when you hear breathless announcement
that the dark matter has been detected
be sure to look for whether or not this
is a dark matter that is an appreciable
component of the total.
I think it's truly inevitable that the
dark matter isn't a simple gas of
particles
it surely got some complexity and it
surely means, therefore,
that when you detect a dark matter
component it may be only a subdominant
component,
maybe not, but uhm, and it'll be exciting
we'll learn about ... we'll learn new things
from it, but
uh it's going to be a long road to
convincing ourselves
that we have a detection of a dominant
component of the dark matter.
But what it will be, I ...
and you know it's also worth pausing to
consider that the first searches for
dark matter were
detection were were done in the early
to mid nineteen eighteen ... 1985,
about 40 years, 45 years ago.
It's been a long road.
Do continue.
Alejandro had a question.
Yeah, I mean, hi there.
Nelson partially focused on my question, 
but I would like to take
benefit of the opportunity to exp, I mean, 
to ask about the
the other possibility, I mean, we have
been so far, or you have been so far,
trying to analyze the universe using a
theory
and what we call an anomaly comes
out of things that that theory somehow
doesn't completely take care of or
parameters that are needed to enter
in order to match the theory or the
predictions with
the observations. But what about the
possibility that the theory needs some
reshaping, some ... some part of it that
is, I mean, failing to match a reality.
Absolutely, uh, reshaping is a good word.
Reconstruction perhaps less appropriate.
Surely our present theory is not
the whole story. For example, uhm
when I introduced this cold dark matter
hypothesis,
I assumed that the universe ... that the
energy fluctuation spectrum is so-called
scale invariant.
I did that for pure simplicity. I didn't
know for sure
that that's the way it would be, and in
fact we have learned that the
fluctuation spectrum is not quite scale
invariant it must be tilted a bit
that's an adjustment parameters must be
adjusted to fit the phenomena. 
That was an adjustment.
We don't have a free parameter that will
eliminate this tension
Adam discussed, it's going to have to be
an adjustment of either the physics of
gravity or the physics of the dark sector.
It will be an adjustment of the theory
but the question you might ask is would
that adjustment so ... be so big
as to reconfigure the whole theory.
I think the odds on that are very low, 
I think
almost certainly the story will be
in outline the same but the details will
be adjusted
for example the dark matter components
may contain one that is relativistic
so it's evolving in a different way.
I just saw on the web
the notion that neutrinos of different
species interact.
Neutrinos are a substantial contribution
to the mass density back in the very
early universe.
It has computable effects there surely
will be such adjustments
but an adjustment for example that
eliminates the need for dark matter
I think, does not seem at all likely.
And, regarding the cosmological constant
the dark
energy, yes, what about it? Any hunch?
Well, what is it? [Laughter]
It's a deep anomaly.
We could discuss for example the ... uhm
the anthropic argument. The anthropic
argument.
Life appeared on Earth rather than
on the planet Mercury for a very good
reason.
The surface of Mercury is far too hot
for an interesting chemistry.
That is to say, life formed in a place
where it's convenient to
for complexity to develop. If you imagine
there are many universes
with many different properties each
universe having its own physics
then among all those universes, 
the multiverse so-called,
there will be some that have the
properties needed for life such as us
and that's where we'll find ourselves
and if among other things
a universe that uh allows complexity
like us
to arise, can allow a cosmological
constant but it has to be very small
then we would live in situ universe
the notion is then that there are many
universes each with their own value of
the cosmological constant.
The natural value of the cosmological
constant in within quantum physics is
some 100 orders of magnitude
bigger than what's needed for cosmology.
So all those universes are no good to us
the expansion would be too rapid or else
the expansion
would stop too soon to allow us to form.
Our universe has to be one in which, uhm,
the cosmological constant is just about
as big as it is allowed. 
You may be familiar with
the notion of just so
storage and how the leopard got its spots.
The anthropic arguments strike me as
similar to that
uh the cosmological constant is what it
is because it's the largest of value
that we could get away with and still
allow complexity.
Maybe that's the way it is, 
but I really dislike the thought.
For that matter I can't get at all
excited and interested in
multiverses. 
They're an elegant notion, but
since we can't ever go there, 
the wonderful aspect of
physical science, the interaction of
theory and observation,
theory and practice, 
that has been so fruitful
just can't happen. We can't go to another
universe and check things out.
So, to me that's fascinating, but not
real interesting science.
Thank you.
I see that Gaspar has a raised hand.
Okay thanks, uh, thanks James for your
talk, it was really amazing.
I have, I will pick, I have many questions
for my own, but
I will provide the time to ask
a question from the public, we have a
more than 2000 people
waiting for something, so apart from
your talk of course,
and uh, there is uh, there are many good
questions and I will pick up one of them.
There is Savannah Goods, who asks
What do you consider
to be the most intriguing mystery of
primordial nucleosynthesis
yet not solved, if there is one?
Because when we saw things 
about nucleosynthesis, it
seems that
everything is already settled, you have
hydrogen, you have helium, lithium
and that's it.
And then there's no more mysteries about
nucleosynthesis
are there other mysteries to solve?
Well until recently, the so-called
r-process in which
in which neutrons are captured
by atomic nuclei,
beta decay you build up the heaviest
elements.
That r-process through my career has
been a mystery.
Where did this happen? It is Gamow's
original idea about how the heavy
elements formed he wanted to build up
beyond
helium to heavy elements by rapid
captures of neutrons;
beta decay to give you the chemical
elements.
Passages of that idea appear now in the
standard theory for
where gold and the heavy elements came
from until recently there was no
evidence of where that process happened.
We then saw a merging pair of neutron stars.
Neutrons lots of them and production of
heavy elements. It was beautiful.
Whether there are mysteries with the
production in the early universe
is to be known is to be discovered.
Remember, I mentioned these cross checks.
One has an estimate of the
the helium abundance from the theory of
nucleosynthesis in the very early
universe.
It is checked by the abundance of the
light element of the heavier 
stable isotope of hydrogen, deuterium.
With that abundance, one can infer the
abundance of helium,
which can be checked against what is
observed recently
and one can ask is the abundance of
helium then
consistent with the abundance of helium
now or is there a chance for an anomaly.
Uh, it's the same sort of game as what
Adam is playing, except with the
abundance of helium
it can be inferred from what's happening
in high redshift
which can be measured in nearby objects.
It's difficult because ... because helium is
produced and destroyed by stars, in small
amounts to be sure,
but a complicated correction.
But still you could ask is the abundance
of deuterium and helium consistent with
what you'd expect
coming out of the hot big bang, and you
know, if you adjusted the theory
so as to fit the expansion rate
that Adam Riess needs back at when the
universe was a thousand times
hotter than it is now, with that
adjusted theory
give us a theory of nucleosynthesis
that is consistent with the observations.
You're going to have to be
clever enough to adjust the theory
to fit both. And indeed, we will
be paying attention both to
the theories that reconcile Adam
Riess's problem
with what's required by the theory
and, uh, at the same time, the increasing
knowledge and the abundances of the
light elements,
including particularly, deuterium and
helium.
Maybe an anomaly will reappear
Thank you.
So I have a few questions I've picked
out from all the
hundreds of questions that the
audience has given us.
So, if spacetime is expanding and it
means that the space
expands and distances grow what happens
to time during the expansion. I mean
does time intervals between the events somehow change?
Let us consider a time interval
my pulse rate no that's not a good example.
Look there are those people who have perfect pitch.
They can hum the C ... uhm.
That perfect pitch isn't changing as the
universe expands.
uh there are
We have atomic clocks, very stable,
they're running at a constant rate.
As we measure them time is not being
stretched
I already emphasized and I hope you
remember, as the universe expands, we're
not expanding.
We feel no effect of the expanding
universe. Our galaxy may be expanding
a bit because it's
losing matter.
It's not expanding either. It's a
complicated business.
Observers in each galaxy will have their
own clocks
that will run at a steady rate as far as
they're concerned,
but of course when you compare clocks
you have to send signals
they take time and you can see
differences in rates
due to that effect. But, uh, really it's
pretty simple,
you and I are not affected by the
expanding universe. We're fascinated by
it
but time doesn't get affected.
So I don't know whether that's answered
the question. Maybe, maybe, you could
reinterpret what I said
Not sure, I'm quite qualified to, uhm, 
I mean for me at least this is something
that's so mind-boggling big,
I can't physic... I can't
imagine the distances between these objects
and how time would interact between them, as the universe expands so that that
question jumped out at me; it triggered
 questions of my own. I was curious as
to your own interpretation.
Yes, but you know again
let's be very local to begin with
and consider, oh a tuning fork.
It has a constant period and that period
doesn't change.
In fact you could carry, if you could, you
could carry a few...
You can't carry a tuning fork back in time,
but you can carry it forward in time.
You should live so long,
the universe will expand, become less and
less dense, on average,
but the tuning fork won't care. It'll
still sound its pitch and you will recognize...
If I could add one thing to it; 
we do, of course, see
uhm, the stretching or dilation of time
intervals, when we look at far away
objects in the universe,
because of cosmic expansion and one of
the most remarkable things we see, uhm,
Alejandro Clocchiatti, who's on the call,
myself,
we observe distant exploding stars,
supernovae and they have a certain
time scale,
on which their explosions decay and we
see that time scale
is elongated. It can be up to doubled or
tripled
by the expansion of the universe; and
so we see these distant clocks running
slow,
just in a way like Einstein talked about
not of course due to
motion, but due to the expansion of space.
Right, we should be careful again
about the expansion of space, because
you're not saying
that these these supernovae
are affected by the expansion of the
universe. It's only our observations of
them. Correct.
And indeed this is observed
it's observed in the frequencies of
lines of emission
from the spectra of stars,
observed to be stretched toward
the red,
but of course an observer on the star
would not see any stretching.
So we have, we also had a few people
asking us
about your disagreement with the name or
with the term the 'hot big bang'. Why do
you think it's such a bad name for the
expanding universe and what would you
call it instead?
I've tried many alternatives, none has stuck.
Let's just remember that a bang
denotes an event in space-time.
It happened here at this time a
firecracker went off,
a supernova exploded, but that's not a
good description of our cosmology.
There is no specific place.
The expansion of the universe is
happening everywhere.
There's no specific time. You might ask
what was the universe doing before it
was expanding.
There are ideas, maybe only
loosely tested and more or less
substantiated, but they're not
very convincing.
The well-established part of
our cosmology
has nothing to do with a specific time.
It is the evolution of the universe
from the very early stages of expansion,
when the temperature was very high
to the present. We have well tested
theories of this evolution
because the evolution left behind
fossils, such as helium
and the thermal radiation and later on
the supernovae
that Adam observes.
Yeah, I got a few more questions, well about one more question, so during your
career the field of cosmology and our
understanding of the universe has
changed
very dramatically. What do you feel has
been the most impressive
and significant change.
Uh, you know um, I have been working on
cosmology for over half a century,
and I have continually
been startled by what
can be done, what can be measured. 
Time and again,
I've asked myself, could they really
measure that well?
[Laughter]
Time and again. So it's pretty difficult
to uh ... it is difficult
to pick out any one event, but I can tell
you the one that most startled me,
I think, uhm
Could I show again my slides?
Sure, go ahead.
Is this it? No wait.
Where is it?
Well, I mentioned this spectrum
It would be fun to show it, but I don't
know where it is.
Is this it? No, what is that?
That's a phone booth.
Oh oh oh, let's look at this.
It's here. What do I do now? I've lost you. Hihi.
Good, uhm share.
aahhh
There we go. Now we go back.
Now we see your presentation.
What is this thing doing? Oh there's,
the other way.
Uhm, so, these measurements.
Bef .. in the ... in the... through ... from the beginning
until the early 1980s
until the late 1980s, sure,
the measurement of the spectrum
had shown
very significant anomalies,
departures from
a pure statistical equilibrium.
Those departures, if real, would mean
that the universe is not as simple as
we thought. They could be the result
of large temperature variations in
different parts of
space-time that would cause anomalies
over here.
They could be the result of advanced
explosions
Any such anomaly would quite
mess up the primeval distribution of
radiation.
And so quite vitiate the possibility
of using the angular distribution of
radiation
to test the cosmology.
Those anomalies were so annoying that in
the 1970s, I stepped away from
the microwave radiation studies and
instead
spent my time studying the distribution
of galaxies,
because I could check them and see that
we could measure them reliably.
I remember well the, and of course,
as these data were coming in
the groups carefully guarded their
results. You don't release
evidence ahead of time, because you may
have to correct, and you don't want to
cause the confusion.
You want to wait until you're quite
ready to release your data
and then show it and be able to answer
all questions about it.
During that time of waiting to make sure
they can answer all the questions, 
David Wilkinson took me aside
and showed me this,
although in an earlier view version.
I was so startled. It is simple.
The universe then can be analyzed. There
weren't big explosions.
There weren't large inhomogeneities.
It it caused me to change my
line of research. Wow! I said.
Now where do, where am I?
I think you have to hit escape, yeah oh
well actually
just close close the keynote.
Should I try pressing this button?
oh there we go
presentation, oh no, oh well, hihi
yeah, that's it, okay.
Ah! There you are! Okay we're all back.
So uhm, are there any other questions from
the panelists?
You should reflect that in the 50 years
I've gone through
layer upon layer of technology, much of
my career was spent with a slide rule
Do you know what a slide rule is? Have
you ever seen one? I still know, yes.
Layers of technology, this is just the
latest and I can no longer absorb them.
Thomas? Max go ahead please.
Thank you. There's some people who
have said in the past that
we might be close to find a theory of
everything. What's your opinion
about that?
you seem to and you said that at that
point at some point that
our models cannot be the final answer or
not near
the final answer. So, in a more, in a
broader context,
do you believe that if such a thing like
a theory if everything could ever exist?
We would ever find it or what's your
opinion about that?
Stephen Weinberg, a brilliant physicist,
uh, wrote a book "Dreams of a Final Theory",
in which he persuasively argues that we
may be approaching
the final fundamental theory.
Carefully argued, but I just cannot buy it,
because I don't know, how we will know
that we have the final theory,
rather than
the best approximation
that money will buy.
How do we know that it's not successive
approximations
all the way down?
Of course, we'll never know, we'll only
have the best approximation we can establish.
It doesn't bother me to think that we'll
never have the final theory.
Uhm, I'm so impressed we've got this far
and from all evidence we're going to get further.
What better could it be?
Thank you.
On that note, I think we have to
come to an end. Thank you all
for joining us for Jim's talk today, and
thank you especially and very much
for Jim, for his time, to tell us about
his work and the career and the
discoveries.
Uhm we would like to welcome everyone
back again tomorrow morning
for the second talk in the series in
which Volker Springel will be telling us
about
hydrodynamical simulations of structure
and galaxy formation.
And remember you should register in
advance for each talk
and they all will be streamed on our
YouTube channel
and also via Zoom of course, and
recordings will be made up available
then later on on our youtube channel as
as an edited capsule.
And so there is uh nothing left to say
except to thank all of you again all the
panelists
and see you all tomorrow. 
Thank you very much.
Okay it's been a pleasure.
Good bye all.
