Hello, and welcome to the Physics World Weekly
podcast.
I'm Hamish Johnston.
This episode is sponsored by the Shaw Prize
Foundation.
I'm very pleased to be joined by Richard
Bond and George f Stathieu,
who share the 2025
Shaw Prize in Astronomy.
The award is given for their pioneering research
in cosmology,
and in particular, for their studies of fluctuations
in the cosmic microwave background,
which is a relic of the early universe
that permeates the cosmos.
Their theoretical predictions of the nature of the
cosmic microwave background have been verified
by an armada of ground, balloon, and space
based instruments,
leading to precise determinations
of the age, geometry,
and mass energy content of the universe.
The Shaw prize is an international prize based
in Hong Kong.
It consists of three annual
awards.
The prize in astronomy,
the prize in life science and medicine,
and the prize in mathematical sciences.
Each prize carries a monetary
award of 1,200,000.0
US dollars.
The prize was established by Runrun Shaw, a
media mogul and philanthropist,
and it was first presented
in 02/2004.
Now celebrating
its twenty second anniversary,
the prize has honored over 100
individuals
from across the world.
This year, the Shaw prize is awarded to
four
distinguished
scientists and mathematicians.
They are Wolfgang
Baumeister
for life science and medicine,
Kenji Fukaya
for mathematical
sciences,
and Richard Bond and George f Stathieu
for astronomy.
George f Stathieu is Emeritus Professor of Astrophysics
at the University of Cambridge in The UK,
And Richard Bond is a professor
at the Canadian Institute for Theoretical
Astrophysics
and university professor
at the University of Toronto
in Canada.
They share the award equally.
Richard and George,
welcome to the podcast,
and congratulations
for winning this year's
Shaw prize.
So let's start off by setting the scene
for your research.
George, can you tell us a little bit
about the cosmic microwave background?
What is it?
Okay. Well, our universe
started off in a very hot and dense
state,
and,
it was full of radiation.
And as the universe has expanded,
that radiation has cooled down,
and we now observe it as an all
pervasive,
background radiation
with a low temperature of 2.7
Kelvin.
So it was discovered,
by Penzias and Wilson,
back in,
1965.
And it was a
a very, very significant discovery because,
it confirmed
that, you know, the universe must have started
off in a in a hot and dense
state. And so it excluded the steady state
theory, which, you know,
had a non evolving universe.
So our universe,
has been evolving
and,
has,
evolved from this very hot then state to,
the, you know, cold,
radiation that we see today.
And, Dick, can you just explain
how,
astronomers
observe
the the cosmic microwave background? What what what
sort of instrumentation
are they using, and and what are they
actually seeing?
Well, this has been a,
great development. I mean, you know, we're
honored for the theory in the microwave background,
but,
the the enabler has been the tremendous advances
in technology, in particular, the, methodologies
for detection
and the ability to get
into space, but also
very remote locations on the ground and in
balloons.
The primary technologies that are used right now,
there was a whole series of lower frequency
things called,
HEMPs, which I won't even tell you what
they are. They involve transistors for the microwave,
and they're more coherent,
absorbers of radiation.
But the one that, you know, has really
made a huge difference in our subject
are called the bolometers.
And, essentially, what you're doing is you're measuring
temperatures with bolometers. That is to say the
microwave background comes in, and you are
heating up,
a solid state system,
and then it's,
relaxing back, and that
allows the transform of,
electrons, which you observe as currents.
The reason I'm going into this little bit
of detail
is because there is this remarkable chain from
what is out there on the sky
through to what we actually see and process
in order to be able to,
extract the fundamental physics associated with this tremendous
flow of signals that are, coming at us
all the time carried by the microwave background.
I see. And the radiation itself, it's it's
microwaves.
But am I right in thinking that it
it it didn't start out
as microwaves? We're we're seeing radiation
from a very long time ago, and and
therefore,
it its wavelength has changed?
That that's right. So so,
the the radiation has a very accurate black
body spectrum. In fact,
the COBE satellite back in 09/1992
measured the spectrum of the background,
radiation, and it was,
the most accurate black body that's ever been
seen.
So the temperature of 2.7
Kelvin means that,
it peaks at,
millimeter wavelengths.
And,
but but as if if we go back
in time, the temperature,
is higher in the early universe.
So,
so what we see on the sky
is the the temperature pattern,
that was imprinted
at the time that the universe had cooled
to the point where,
electrons and protons combined to make neutral hydrogen.
So that happened about,
you know, three hundred thousand years after the
big bang. And so when we,
make a picture of the the fluctuations
over the sky, we're seeing this pattern imprinted
as it was,
when the universe was 300,000
years old.
So, you know, so a
a direct measurement of the, of the very
early universe.
I see. And and so this,
this radiation started off as
light, and it's well, I suppose,
visible light,
and then it's it's been
red shifted as the as the universe gets
older and older?
Yes. I mean, you know, I mean,
you know, at at very early times,
I mean, at the times that the
fluctuations
were generated,
the the
the energy of a photon,
would have been about 11 orders of magnitude
higher
than the
maximum energy achievable in the Large Hadron Collider.
So super high energy.
And, of course, that gives us access to
to physics
to physical mechanisms,
that you just can't,
ever access from accelerators on the ground.
So you can test exotic yeah. You can
test exotic physics in the early universe.
And so so this is giving us, I
suppose, a a picture of what the universe
looked like
very early on in its existence
when it That's right. When it had an
incredible
energy density, a density that we could never
well, I'll never say never.
We could never study,
on Earth.
Yes. And and the observations
fit with the theory
in which,
the
fluctuations
all of the structure in the universe,
that we can see today,
were generated from quantum fluctuations,
that were
expanded in scale as the universe,
expanded faster than the speed of light. And
that imprinted
a a pattern of fluctuations, which we observe
today.
I see. And so these these fluctuations
tell us about the early universe, but do
do they also tell us about
how what what's happened in the universe since
then? How the the universe has expanded
over the last, what is it, thirteen
billion years?
Yeah. Yeah. So,
just to go back to George's point and
your point,
the
energy,
which was,
in basically relativistic particles, this
the current view is that there was a
big
event
called heating or preheating
after the early universe inflation
in which all of the,
basically energy,
in matter
got created as
little fluctuations,
but they were in all sorts of components.
And
as
the universe cooled,
and it's still unimaginably
hot, but as it cooled,
the form of the components changed.
And so the remarkable thing is that the
two main components
that arose
from the big bang
were neutrinos
and also the photons.
But that's like the relic.
And before that, it was in all sorts
of different forms like positrons and electrons,
very
high energies, w mesons, and,
and all of the quarks and gluons before
they
consolidated
into,
the protons and the neutrons, which then
form the helium.
So all of these different transmutations
occurred.
And one of the reasons that we can
handle this story so well
is because there is a conserved quantity,
which I hesitate to bring it up, but
George will at least laugh at me bringing
it up. There's a
a quantity called entropy,
and the thing that was generated in the
transformation
from the early universe expansion,
through this heating epic
is the
entropy, which is huge, really large in the
universe. Some people say it's tiny. It's all
eye of the beholder,
but it's considered to be,
but the main thing is that that is
the conserved quantity more or less
as all of the transmutations
of forms occurred,
which allow us to do the accounting with
high accuracy.
And,
and so,
what happens is that
that entropic
form,
which is changing its nature,
it starts to take different paths towards us.
So prior to,
what we call a redshift of 1,100, but
George referred to it as,
the three hundred and eighty thousand years after
the big bang,
that's when the electrons and protons combined.
And that,
meant that the electrons were not around to
anchor the photons, and the photons, of which
there were so many,
started to stream
freely towards us.
And then they were encoding all of the
information that occurred at that time.
But in particular,
they were,
encoding
the different forms of matter at the time.
And so by,
reading the signals in the cosmic microwave background
fluctuations,
which with these detectors that we talked about,
exquisite work, we've been able to unravel
what the constituents of the universe have been
because of that split into the multiple forms.
And the photons just keep giving,
more light, pardon the expression,
to us because it's revealed.
It's not an exaggeration to say that the
microwave background has revealed more about cosmology than
anything else, including all of our observations of
large scale structure.
So it's very, very rich, and it continues
to be extremely rich subject.
I see. I I wanted to sort sort
of focus in on these fluctuations
with which both of you have studied. Now
are these are these fluctuations, are they fluctuations
in
intensity
or in the the temperature or wavelength of
the cosmic radiation? Is it is it the
polarization
of the radiation
of or is it all of the above?
Is that how that this wealth of information
is carried in the last say all of
the above, but take over George.
Well,
so the the,
fluctuations in intensity, which translates,
one to one with fluctuations in temperature.
The the,
the pattern of fluctuations
is,
independent of wavelength and,
you know, the physical process is the the
we're,
you know, analyzing.
On on large scales,
we see
the
variations in the gravitational
potential,
as they were created. They haven't evolved and
so on. So it's going right back
to,
the very early universe, maybe 10 to the
minus 32 seconds, you know,
after the origin of the universe, something like
that.
So,
and then on intermediate angular scales, what we
see,
the ripples of the, as Dick said, at
very early times, the electrons and, photons
act as a single fluid.
And so the so you've
the the fluctuations
oscillate like sound waves.
And,
what we can what we,
see on the sky,
tells us about the the,
the sound speed,
you know, at at early times.
And it's the fact that different constituents
can alter the sound speed,
that allows us to infer,
what the universe was made of back in
in those times.
So,
it's, you know, it's quite a rich,
you you in a set of,
you know, observables.
In addition,
the the coupling between,
the photons and
the electrons,
is BDSU by Thompson scattering.
And Thompson scattering is a
anisotropic
process. So if you illuminate the electrons with
the quadripolar
radiation pattern,
then it can generate polarization and net polarization.
And so the polarization has been observed,
and it's been beautifully observed,
now with the,
Azakama Cosmology
Telescope.
And,
the polarization pattern,
tells us additional information,
you know, in addition to the temperature fluctuations.
And, ultimately, we might hope
to find gravitational waves,
by searching for the large angular scale polarization
in the cosmic microwave background. But but just
to jump in there, if I can for
a second,
when George and I were first doing our
theoretical developments on this, which
had a role in the development subject, we
built polarization in from the very beginning. It
was absolutely clear
that it wasn't clear that we would be
observing
it, but it was clear that if you
wanted accurate calculations,
you had to include those anisotropic effects
that George was talking about. So, you know,
theoretically, we were well prepared
for everything that came
ahead.
And not only that,
it stimulated
the experiments
to be
developed in a form that they would be
able to go after this.
Heroic
that we were able to get to the
really tiny levels
of ripples in the sky in the microwave
background radiation
to actually observe it.
But we have with
incredible,
exquisiteness,
modulo that one thing that George talked about,
which was I call the seventh pillar of
the many pillars
that we've,
observed with the microwave background, which is,
the influence of ultra early universe gravity waves
having an effect on the photons,
which can then be,
observed by the same techniques that we're observing,
but it's a very small signal and rather
difficult to go after.
There's a lot of effort right now for
us going after it. There always was, but
we have to go deeper and deeper and
deeper to try and unearth it if we
can unearth it.
So the the the structure,
that existed in the early universe that
was imprinted onto the cosmic microwave background.
Is that something that we can see in
the universe today?
I mean, for example, you know, we've got
distributions of galaxies, and they seem to be
connected in in this sort of web
type thing. Is that is that something that
that
that evolved
along with the
cosmic microwave background?
The microwave background is, basically
giving an earlier image of
what evolved into the current cosmic web of
interconnected structures.
And the emphasis that I like to put
on this is that,
you you know, it used to be that
astronomy was about independent objects, and you'd say,
oh, look at that. There's a galaxy there,
a galaxy there. But the emphasis that grew
partly probably out of the microwave background and
the insight of its relationship to the early
universe is that everything is interconnected with everything
else that's kind of a tautology.
But nonetheless, it's a profound thing that we
have learned that the universe
so if you're dealing with an object somewhere,
it's being, disturbed and affected by all of
the objects around it, and it all sort
of becomes this cosmic web.
So
in effect, we are observing the cosmic web.
It's just at a much earlier time.
So, I mean, the the fluctuations
in the cosmic microwave background,
they they correspond to
irregularities
of about a thousandth of a percent. They're
they're they're tiny.
And,
the the challenge for,
cosmology is to, you know, you start off
with these tiny
fluctuations,
thousandth of a percent in amplitude,
and you want to understand all of the
structure that's formed
since then. Now to put that in context,
the
density contrast
in a typical galaxy is over a million.
So
gravity has taken these tiny fluctuations,
and the action of gravity,
has amplified these fluctuations and produced these very
highly nonlinear,
objects.
The amazing thing is
that
starting off with the tiny fluctuations that we
observe from the CMB,
the we
we could get,
through computer simulations,
really quite good matches to what we observe
today with very highly nonlinear
fluctuations. So it's a remarkable,
you know, it's a remarkable achievement.
And I I just have one
one more question about these fluctuations.
As you mentioned, George, they are really, really
tiny.
And I've often wondered how, you know, how
have these tiny fluctuations survived for
all that time? You know, why are they
still there? Why why weren't they sort of
scrambled
as they you know, as that radiation moved
through the universe, as the universe expanded? Or
are we just lucky that,
that they're still there, or it it it
it is there a a I'm sure there
is a good reason for why the fluctuations
persist to this day.
Well well, they do something that, we call,
collisionless damping. That is
to say, they do diminish. They diminish because
they're flowing around here, there, and everywhere.
But,
it happens to be big enough for us
to see them.
And so
you know?
But they are basically, at some level, trying
to uniformize.
However,
there's a fundamental answer here. I shouldn't go
into it, but I'll put the word out.
Entropy is associated with this. That is to
say,
there's a conservation of the number
of photons,
which is that the
basic patterns are, are effectively conserved,
and that's, you know, we we understand this
extremely well. That's part of the way we
actually calculate what to see on Scott. That
maybe another point to emphasize,
which,
when we have got all of these new
observations with such exquisite detail,
the comparison with the theory
and the observations,
you can't essentially tell the difference.
The lines are essentially exactly the same.
So,
there's something really right about the fundamental
underlying theory
that we have describing this, and then we
take the results from these early times.
And and George is one of the great
pioneers of this subject, which is,
called n body studies, which is describing the
growth into nonlinearity.
And I and I work on it too.
That's the cosmic web whole story.
Everything falls into place. It's just amazing. So
it's essentially like
you you know, the standard story we have
is that,
which which is seems to be the correct
story is that we essentially, the
information
in the universe is encoded in effectively
seven
cosmic parameters
and that everything flows from that. Well, that's
an amazing
simplification.
We're actually hoping for more cosmic parameters so
we can get more information,
but the fact that we've got these exquisitely
determined seven parameters or six parameters
is, been one of the real triumphs, and
it's such a privilege
for us to have been, part of throughout
all of the decades in in the development
of this story.
Yeah. Now I just wanted to add something
about the survival
of,
fluctuations because
because an absolutely key aspect
of,
generating fluctuations
that we, you know, that can grow to
make nonlinear
structure today is the fact that
the universe has,
the the matter content is dominated by cold
dark matter, by dark matter.
Without that, we couldn't make models
that that work and reproduce our universe.
So it's the fact that there's a component
that doesn't interact
with ordinary matter or photons,
that leads to the survivability
of
fluctuations that grow to make structure in the
universe today.
That was the reason George and I,
joined hands and, did the theory of the
microwave background. It was because of the cold
dark the dark matter. We still had the
issue, and we still do, of exactly what
the form of the dark matter is. There
are certain universal forms of which cold dark
matter is one. We actually started in hot
dark matter, which is massive neutrinos.
That's how George and I got together on
a scientific project, and the rest has been
history, of course. But,
a great
pleasure, but the motivation
was the dark matter issue
in order to see how we could
determine the response of the microwave background
essentially to the existence of dark matter
as the main organizing component
for the structure of the universe.
At that time, we weren't talking about the
cosmological
dark energy
that came along a little later, not too
much later, but a little bit later, theoretically.
But we really had the context
even way back when in the, in the
relatively early eighties.
So so, you know, if if people's if
people
express skepticism
about dark matter, you know, the does it
really exist? You know?
And so we would not be able to
we wouldn't come close to making sense of
the cosmic microwave background
without dark
matter. Right. And does that also apply to
to dark energy? Does does does that,
having some sort of concept of dark energy,
is that is that needed when you're trying
to understand Yes.
Yes. When when you get to,
you know,
detailed comparisons,
then you need,
the dark energy
to understand the amplitude
of the fluctuations.
But but the the the
the the actual characteristics,
the pan, the fluctuations,
you wouldn't come close to replicating them without
the cold dark matter. So so, you know,
if you you you can think of the
the
impact of dark energies to change the overall
level, the overall amplitude of the fluctuations,
but the dark matter changes the shape drastically.
So for a long time,
at least, you you know, there was the,
discovery of acceleration of the universe with the
supernova data, which I won't get into here.
But the way we got at dark energy
from
it was microwave background plus large scale structure,
that is to say the movement towards the
nonlinear structures that George was talking about. That
it it was the two in combination
that were able for us to show from
that structural point of view
why the cosmological
constant or dark you know, it it may
not be constant, but,
why it's needed.
Then
and we didn't talk about this.
One of the things that happens to the
microwave photons is they're propagating to us. They're
streaming freely,
but they're following what are called geodesics,
which means that they move in and out
depending upon what the,
gravitational field is. This is called,
gravitational
lensing, and in this case, this is the
microwave background.
And so all of the structures that are
in front of us are
the photons are propagating through them, and they're
bending and they're amplifying,
and that
we have been now seeing as a tremendous
signal for us
in order to unravel a lot of information
about
the structures that are in front of what
you would have called the microwave background, which
is released at,
three hundred and eighty thousand years after the
Big Bang. So it's been incredibly rich. And
the reason I brought it up
is because if you use that with the
microwave background, so it's all microwave background, basically,
you can get the cosmological
constant to a high degree
of precision now, actually.
I see. Okay. And the other the other
thing that you can do,
with that is that you can cross correlate
the lensing of the cosmic microwave background
with,
you know, galaxy surveys and any other tracer,
at low redshift.
And that gives you a topographic way of
understanding how structure has evolved as a function
of time. And so, you know, with the
cosmic microwave background, we'd tell you what the
universe was like three hundred and eighty thousand
years
after
the the big bang.
But now you can you can
look at how that structure has evolved,
to to,
to low red shift when the universe was
was, you know,
half its present age.
Okay. So, I mean, it sounds like there's
lots of amazing information that can be gleaned
from the cosmic microwave background. But I I
I wanted to take both of you back
to,
the, you know, the work that you've done,
the the sort of theory and models that
you've developed
that have allowed,
us to interpret the cosmic microwave background. It
sounds, I mean, it sounds like a really
difficult thing to do, you know, just listening
to your description
of of the early universe. It was a
very
violent, very hot place with,
you know, maybe some nuclear physics going on
as well as
electromagnetic and gravitational
interactions.
How how did you begin to to to
look at that,
sort of state of the universe and begin
to understand how it would
create the cosmic microwave background and how that
would evolve
to what we see today. What
where did where did you begin
when you when you started to look at
this?
Well, it's it's it's actually a much simpler
problem than than,
than you described because,
the universe at very early times was in
in thermal equilibrium.
So it was very accurately in thermal equilibrium.
So you don't really have to worry about
all of the
particles that were generated and the interactions and
and so on.
So,
Yeah. So the problem, you know, is is
is much simpler. You break it down into,
the the important constituents. So so radiation and
radicals
is one constituent.
Then,
neutrinos at at late times because neutrinos are
not coupled
to the photons
and and,
baryons.
And then,
you know, baryons,
is an ionized component that's tightly coupled to
to the radiation. So that's so you simplify
the system
down to a small number of components. You
don't worry about, you know, all of the,
you know, very,
the the particles
that have, you know, formed,
at very, very early times.
So, yeah, it's not as complicated as you
might imagine.
It's really complicated.
So,
just to play off of that,
when we were really first getting into the
game,
there was an issue of
what happened at high temperatures,
what the species were, but it was pretty
clear that it, you know, you would always
have the electrons and the protons.
And and, there was a huge subject area
in the, in the sixties, but in particular
in the seventies. It's called big bang nucleosynthesis
in which,
it was shown that,
well, first of all, that's the period when
this huge neutrino sea of particles
decoupled. So what what we're seeing with the
microwave background is when the photons decoupled.
And so that's the three hundred and eighty
thousand years, but the proverbial
number,
which Steven Weinberg wrote a book on, is
first three minutes, but it's more like first
minute. But that's when the decoupling of the
neutrinos occurred. And what that turned out to
allow,
partly because the density is dropping,
is for,
the electrons not to be entirely electron
positron pairs,
but, they were able to undergo nuclear reactions.
And the nuclear reactions only went so far.
They
primarily left
protons,
clearly,
but,
helium particles primarily
as well as the protons
and deuterium
and a few other,
trace particles.
What you couldn't do,
you could have done if the universe had
been different, you could have broken through and
produced all of the elements. But that that
occurred in the stars.
But, anyway, that subject was being,
well probed
and well computed,
and that was, like, one minute after.
But
going back to milliseconds
and earlier,
nobody knew what the degrees of freedom were
in the universe. You said, okay. It's gonna
be mesons and all of that.
And it took a really big theoretical
step
to be able to have the audacity
to think that we could take the constituents
and understand that what they were gonna be
like in these ultra early moments in which
these fluctuations are generated.
And that was a major breakthrough.
In the jargon of the time, it was
called asymptotic
freedom, but what it meant
is that,
instead of having all of the complexity
of mesons like pions, etcetera,
it became simple. It became a simple gas
of quarks,
like simple gas of gluons, which have a
lot of similarity to photons,
except they interact more.
And these,
these species were around, but they were free
of each other more or less.
And that was a remarkable
development,
and it allowed us to take the great
leap
towards the ultra earliest moments of the universe.
And so,
but at some level,
what George and I did, we didn't need
any of that because
we could just propagate
the state from, let's say,
a little bit later than a minute all
the way through
to now,
with the basic constituents
without knowing what happened in the ultra early
moments,
but we always built that in.
The way I used to have to present
it
is that there was at the beginning of
time a Greek dragon that was breathing
breathing a fire.
Our theory is not that more sophisticated
than that now,
but that was the key development
that we were able to relate
what happened now to something that was there
built in from the earliest moments,
but the key thing is that it remained
basically invariant for almost all of the history
of the universe, and then it got modified
as we went through three hundred and eighty
thousand years.
And so it's it's really an amazing story,
and it's the reason we have been able
to now learn
all these precious details about the ultra early
universe
and could even say it without,
you know, with without
nudge, nudge, wink, wake, what a joke it
is.
It's an amazing accomplishment of human beings that
we can even think that we can think
about those eras
with precision.
And so I'd say that's maybe the greatest
thing that came out of all of the
work.
I see. And, I mean, my understanding of
of your of your early work is that,
you know, you you developed the theories and
the models,
to such a point that you you could
tell
the observational
community what to look for
and,
and sort of help them,
I suppose, design their experiments,
design their
observatories. And and lo and behold,
they they saw
essentially what you
predicted.
I mean, that must have been a very
satisfying
experience for you. I mean, I I don't
think a lot of theorists get that
in their careers, do they?
I mean, I think
did you think that we'd ever observe these
things,
that position? But The
the concept
concept of, of seeing some of them seem
to be far fetched, but that's because we
weren't,
I would say, ambitious enough. No. I mean,
the the, you know, technology improved. We didn't
think the technology could do this. But, you
know, I mean, I have, you know, I
mean, back then when we were doing these
calculations,
we made
pictures
from the calculations
instead of just summarizing the calculations to statistical,
quantities that people could measure.
We generated simulated pictures of what the CMB
sky would look like.
And this is nowadays,
it would be considered trivial. But when I
first showed these pictures,
people didn't know what it was. What what
have we actually done? We've just generated
random realizations of a two dimensional random field,
which is, you know, really simple thing to
do. But,
initially, the audience members of the audience didn't
really know what what we were doing.
But these were these were picked up by
observers.
And
and lo and behold, you know, now we
we have measurements of actual maps, beautiful maps,
high resolution
that show all these blobs.
And you can test whether,
the statistical properties,
of these fluctuations match,
the expectations of inflationary
cosmology,
and it's just remarkable.
May maybe I could add on to that
and something I'm very proud of. But, you
know, George was there fundamentally.
We, held a meeting not too long after
I arrived in Toronto from California.
It was called delta t over t. Delta
t meaning
small changes of temperature
over t is usually the average temperature, but
here it was over t e a because
it was
Canada, Britain joined together, and we all like
T.
But the key thing about the expect, about
the meeting,
it was the first time
that the,
experimental community
was brought together with the theory community
as a collective group.
And that had a big impact on the
subject
because at that time,
the experimentalists
were all buried in their labs,
like in MIT or at Berkeley or something,
and they were all totally into their devices
because the devices were fascinating.
But they weren't really tuning
in to the,
context,
cosmological.
And then, George and I did this work.
So the epiphany
I had was to get
Dave Wilkinson,
who was the great experimentalist in the microwave
background at the time after the
originator of of much of what we were
have been able to do,
Dickie who is Princeton, but Wilkinson was great.
They launched what was called
the microwave anisotropy probe
map
designed to make maps of the universe, and
this was
the major
satellite after the COBE satellite.
And then,
sadly, Dave Wilkinson died, but just before he
died,
they added Wilkinson in the front. It became
the WMAP
telescope.
In fact, there's a Shaw prize for
WMAP.
And,
and by bringing him,
he drew in the experimental community. I drew
in the theory community.
George
George's talk there was to unveil
all of our calculations
in the primary what we call the primary
microwave background,
including where to look,
you know, that there is this mountain,
which is called the first acoustic peak, which
is really where it's easier to make the
detection.
It wasn't where the first detection was actually
made. It was made at larger angular scales
by the COBE satellite,
but,
it it was basically a blueprint.
And
there was
a little bit of skepticism
that who are these young Turks that seem
to know
what the whole subject could do.
But it was embraced. People took it seriously
and a lot focused on that region,
and that's where the second
detections occurred. And when you brought the two
together,
you started to piece that it was the
full story.
And every step along the way, there were
major theoretical results that came out of it.
In particular,
that there was this huge
acoustic
mountain
of,
anisotropy
that could be detected
meant that
the first stars that formed in the universe
couldn't have formed at redshift or,
you know, maybe within a million years of
the big bang. It had to be later
because otherwise, it would have been all wiped
out. Well, that was an amazing accomplishment.
I'd you know, it's like a yes or
no thing
that was determined, and that was determined really
very early, very, very early nineties.
And so one thing after another, everything locked
in place.
It didn't have to be that way. It
could have been another theory. There were other
theories floating around.
But now the theory is unassailable.
It's called the
standard model of cosmology.
It has the dark energy associated with it,
but our goal
is beyond the standard model of cosmology.
We want the newer physics
that's
associated with something that's not just
dark energy, dark matter,
and then the baryons electrons.
And it does say the protons,
neutrons, electrons,
you know, the usual constituents. We wanna
see more physics from it. Right.
Hopefully, with glimpses
early universe.
And that's that that's how I wanted to
to sort of end this discussion on what
what's next,
in
research,
involving the cosmic microwave background?
Are there are there new observatories
that are coming online that you're very excited
about? Or
are is the community working on new ways
to interpret
data that we have already to maybe get
a handle on the nature of dark matter
or dark energy? So what what what are
you most excited about? Maybe, George, can I
start with you on that question?
The great
thing about the the cosmic microwave background is
that because
the
we're making these measurements
when the fluctuations
with small amplitude
that the theory is simple.
So,
so if you can improve the measurements,
then
you
get clean
interpretation
of what's going on from the physics because
there there aren't the complicated
nonlinear processes when you're dealing with astrophysical objects
like galaxies or supernovae or whatever.
So,
so and there's a lot of information to
be extracted from the cosmic microwave background.
Now the the at the moment, I think
the the premier new facility
is going to be the Simons Observatory,
and that will,
you it's you know, it's just a fantastic
science case because,
it'll
do a wide range of things. But
primary
thing that it will do
is improve the polarization
measurements
of the CMB, get,
more accurate polarization measurements.
It also has,
a series of,
small aperture telescopes that is designed to try
and go,
to high sensitivity to search for the signatures
of gravitational waves
from,
an inflationary era. I mean, if if if,
if a signal like that were were detected
that you could unambiguously
say came from the very early universe gravitational
waves. It'd be the first time that a
quantum gravitational effect would have been detected, which
so it's a you know, it would be
a big deal. See, I would disagree with
that. Well.
Because,
I think that the fluctuations themselves that we
observe
are quantum.
Everything's quantum. Yeah. You could But in particular,
I'm not exaggerating with that. They're essentially phonons,
which is what we observe, the impact of
of phonons from the ultra early universe.
But just like
you can have,
transverse elastic waves as well as longitudinal elastic
waves, so you can have
gravity waves as well
as phonons.
And they're all occurring at that Yeah. I
know you agree with that. It's just that
some skeptics
might say, well, you know, maybe the fluctuations
were generated by topological defects or something else,
you know, whatever.
But I don't think that's plausible. You see,
we can still have our lively conversations about
it. But just to amplify on,
I'm still well, actually, George too, but I'm
still engaged with these experiments
in my dotage.
So I'm a member of the Simons Observatory,
but that was a basically, a direct outgrowth
with a huge amount of money from,
the great Jim Simons,
of the Atacama Cosmology Telescope, which George
alluded to already.
So, you know, Planck is unbelievable.
And then what just
was released
was,
information from the Atacama Cosmology Telescope.
That mission is over.
It was really high up in the Andes
because you're trying to get
above as much,
as much water vapor as you can.
And it just has given exquisite results, and
Simons Observatory is gonna be so much better
than that. And it's going to have legs
into around
2035
to 2037.
Then there may be other experiments that'll be
taking over, one in space called Lightbird,
another,
on the ground that has
big support from the Department of Energy in
The United States.
It's called,
CMB stage four, and I'm part of that,
but it's kind of beyond my
working time horizon
because it's probably 2036
before it really starts We're getting old.
Well, for every young George and even for
you, for every young, you will learn that
that's the mantra to sing to the world,
because it's an extremely exciting period.
But
what I think is as fundamental
as,
the experimental
advances and, you know, cleaning up the story
is that the theorists keep working away on
trying to find
new signatures
to look for in the data
that will deliver new information to us to
shape the physical theories of cosmology.
And so that's this beyond the standard model
of cosmology
thing that I referred to. And it's a,
you know, a goal which,
should be informing the theory side as well
as the tremendous experimental advances, which are absolutely
astounding,
that we are seeing happening.
And then it's all completely
connected
to
the thing that we haven't talked about, which
is the cosmic web and the large scale
structure and all of that, of which there
are huge, huge experiments.
We've always gotten a huge amount of data
from that,
but we're
you know, it's like a discontinuous
step upward in terms of the amount of
data
coming in. And so
we're getting these exquisite
mappings
of
the universe and all of its epics, and
putting them all together
will make this incredibly
precise,
we think, cosmic story of evolution from the
ultra early moments right to now. I mean,
the the here and now. Development of
the
Lambda CDM model that that that, you know,
fits the data beautifully.
You know, it's a big success story.
However,
if we actually analyze the key ingredients,
an inflationary year at very early times, we
don't understand the physics behind that.
The the cold, dark matter that's necessary to
make the model work, We don't know what
it is.
And
the dark energy, we haven't a clue. And
and, I mean, you know, dark energy is
just deeply mysterious from the theoretical point of
view. So the key ingredients, we don't really
understand
from the point of view of fundamental physics.
So,
you know, the hope is
that if we make more detailed observations
that the model will break, and it will
break in some way
that tells us
something about the physics
of,
of these, components.
So to give you an ex an example,
the the,
in inflation,
the
interactions
between fields involved in inflation can introduce
statistical
correlations
that can in principle be detected. They haven't
been detected yet. But then that would tell
us, you know,
a lot about the nature
of, the fields that were responsible for an
inflationary
epoch.
So
so,
you know, the
the hope is that the model would break,
but nobody can tell you
how it might break, you know, what to
what to look for. We just have to
keep trying
and hope that nature is kind to us,
and we see something
radically new.
So it sounds like there might be another
sharp rise in the future
related to the cosmic microwave background.
Well, that's great. Thanks thanks to both of
you. I'm afraid that's that's all the time
we've got for this discussion. Thanks for such
a fascinating discussion, and
congratulations,
for winning the 2025
Shaw prize in astronomy.
Thank you.
Okay. Thank you. And, George, see you in
Hong Kong.
Yeah.
This episode is sponsored by the Shaw Prize
Foundation.
The Shaw Prize honors individuals
regardless of race,
nationality,
gender,
and religious belief,
who are currently
active in their respective
fields and who have recently achieved
distinguished and significant
advances,
who have made
outstanding
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in academic
and scientific
research or applications,
or who in other domains
have achieved excellence.
The Shaw prize is dedicated
to furthering
societal
progress,
enhancing
quality of life, and enriching humanity's
spiritual
civilization.
I'm afraid that's all the time we have
for this week's podcast.
Thanks to Richard Bond and George F. Stathieu
for joining me today. And a special thanks
to our producer, Fred Ailes.
We'll be back again next week.