00:04Welcome to Theories of Everything. My name's
Curt Jaimungal, and today we have a special

00:09series, a new series, called Rethinking the
Foundations. This year, the Rethinking the

00:14Foundations of Physics is centered around the
question of what is unification. I'm honored

00:19that I get to bring you an astonishing lecture,
tying together almost every unsolved problem in

00:24physics in a bow. So not only a neat bow, but
a simple one by Professor Neil Turok. Professor

00:30Turok is a cosmologist who holds something called
the Carlo Fidani Roger Penrose Distinguished

00:38Visiting Chair, if I'm not mistaken, at the
Perimeter Institute, and also the Higgs Chair

00:43of Theoretical Physics at the University of
Edinburgh. And to those who are unfamiliar

00:47to physics, if this was the 1800s, those chairs
would be called thrones. So anyway, take it away,

00:54sir.
Thank you very much, Curt. It's a great pleasure

00:57to be with you. Let me just start by saying how
much I appreciate your podcast. I think it's

01:04run in a different way than other ones, more
conversational, and I think that's wonderful.

01:12The more discussion we can have, the better.
And so I'm looking forward to lots

01:17of interaction with the audience.
The issues at stake are very basic to our

01:25understanding of where we sit, why we're here,
how we got to be here, and so on. And I think,

01:33hopefully, the ideas I'll explain are accessible
enough for everyone to engage with. So the

01:46title of my talk is really designed to address
the basic question Curt is asking in this series,

01:55namely, what is unification? And the answer I
would give is that unification, understanding the

02:03laws of physics and the nature of the universe in
a unified way, means understanding the universe.

02:11That the laws of physics and the arena for
physics, namely space and time,

02:16are really a single entity. And
you might think this was obvious,

02:22that our best way of understanding the unified
laws of physics is to look at the universe.

02:29That's the maximum data we have available.
And not to do that is kind of insane,

02:37is that you are trying to invent things about
physics which are outside the universe. And

02:46perhaps unsurprisingly, this has led people to
worry about a multiverse. And this is kind of

02:54the road string theory has gone down. And I feel
that road may well be as likely to be a dead end.

03:02And what we have to do is pay much more attention
to what we actually see and observe in the

03:09universe. And I believe that for some reason, we
don't yet understand what we see and observe in

03:19the universe teaches us about nature at
a very profound level. So we have this

03:27sort of information coming in about the universe
now. And I believe this is an ideal moment,

03:35very opportune moment, to think about unification.
But in doing so, we must take that data very,

03:42very seriously. That doesn't mean believing
every rumor or slight difference between

03:51the basic picture and observations. Many of
those are due to observational problems. These

03:58observations are very difficult in cosmology.
Sometimes they make mistakes, and they eventually

04:03get corrected over many years or even decades. So
don't take the observations absolutely literally,

04:11but do be guided by the broad gist of those
observations. And of course, as in every area

04:21of science, we may always turn out to be wrong.
But I believe this is the best route to progress

04:26is to take our theories very seriously, insist
on logical consistency, but equally insist on

04:37realism that these theories do match and are
consistent with what we see in the universe.

04:43So for me, pursuing unification in its own right
without thinking about the universe is unlikely

04:51to be a successful strategy. Equally thinking
about the universe without thinking about

04:55unification, as you'll see in this talk, doesn't
really make sense because the universe we see

05:02includes logical paradoxes, such as the
emergence of everything from a single point,

05:10namely the Big Bang singularity. And
without thinking about unification,

05:14we really don't know how to begin
to address those logical paradoxes.

05:20So that's the title of my talk. I thought
that since Curt often has a philosophical

05:29flavor to his presentations, which
I find fascinating, by the way.

05:34Well, that's one word for it.

05:36I thought I'd start with a philosophical quote,
which is rather nice and echoes what I'll be

05:42saying in the talk. Life can only be understood
backwards, namely by looking at our past. That's

05:50the only evidence that we have, but it has to
be looked forward to. Namely, the future is, of

05:58course, the most interesting thing about life and
what we make of the future. And as you'll see in

06:05this talk, the past and the future get connected
in very profound ways, and I think we're just

06:13beginning to understand what that means. Now, as
is well known in cosmology, looking out from our

06:24vantage point on Earth, looking out into space,
is also looking back in time. And that's because

06:31light has a finite speed. And so as we look
outwards, we're seeing the universe or the

06:39objects in the universe as they were longer and
longer ago. So as we look outwards, this is what

06:47we see. Of course, our solar system is nearby,
but as we go further, this is a logarithmic scale,

06:54So the distance scale gets very
rapidly longer as you go out in radius.

07:00What is the origin of this picture, by the way?
Is this yours?

07:04Oh, yes.
I mean, the origin, I've given the credit,

07:08Pablo Carles Pagassi.
Yes.

07:10No, it's an artistic picture, but I
think it's a very beautiful picture.

07:16Essentially it's telling us what we
see when we look out in the universe.

07:21So nearby we see the solar system, of course
the most distant planets we're seeing as they

07:25were a few minutes or hours ago, but as we go
further and further out, we're seeing galaxies

07:34and stars as they were forming
up to a billion years ago.

07:41And going further outwards, we see what we
call a cosmic web, which is basically structure

07:47as it was emerging from an initial,
smooth, almost perfectly uniform universe.

07:55That's the cosmic web, the sort of
fringes on the outskirts of the picture.

08:02We go even further out with the red circle here
is what we call the last scattering surface.

08:09It's the hot surface of the radiation coming
out of the Big Bang as it was radiating the

08:17microwaves, which we now receive as the
remnant radiation from the hot Big Bang.

08:24So we're essentially sitting in the middle
of a microwave oven, and as we look outwards,

08:29we're seeing the hot surface that
was emitting those microwaves.

08:34When it was emitting them, incidentally, its
temperature was about 3,000 degrees centigrade,

08:42so only a factor of two different than the Sun.
So essentially we're outside the Sun, but inside

08:49a cavity whose surface looks pretty
much like the surface of the Sun.

08:56And then if we go even further out before
that surface, I imagine we're using a form

09:02of light which can penetrate the
hot radiation of the Big Bang.

09:07For example, gravitational
waves, which would do so.

09:11We reach the white circle, which
is the Big Bang singularity.

09:15And so that seems to be the beginning of the
universe, which we are surrounded by, although

09:23actually it's a point.
Now to see how that works, keep in mind that

09:28this picture I'm showing now is really a cross
section of a four-dimensional universe,

09:34namely time and space.
And we are connected to every point on this

09:42picture by a light ray, so this is what we
actually see.

09:47But if I try to draw the full four-dimensional
picture, I've got to add the time dimension

09:59as well as space.
And you see, if we are sitting on the

10:04right of this picture, in the centre of this patch
of space around us, the green curves here show

10:13the trajectory of light or something
travelling at the speed of light.

10:20As it came out of the Big Bang singularity,
it then travelled outwards at the speed of

10:29light.
But of course, you've got to also take

10:32into account the fact that as you go backwards
in time, the universe is shrinking in size.

10:39So what looks to us in this picture as a big
circle on the outskirts of what we can see

10:48is actually this focal point on the left,
where all those light rays, in fact, came

10:56out of the same point in space.
Professor, is there anything special about

11:01this point where, if you look toward the middle
of this, it initially is going up, it's sloping

11:07up to the right, and then it starts sloping
down to the right?

11:10Is there anything special about
that point where it changes?

11:13No, no, there's nothing special.
This is just, you see, so if I had drawn

11:19the curve for an observer living a billion years
ago, only 12.7 billion years after the Big Bang,

11:29the light would converge a little bit
to the left of where I've drawn it.

11:34And so it would bend downwards a
bit sooner than the curve I show.

11:40This curve is really, if you like, the curve
that we see being where we are in space and

11:51time in the universe.
It's our past horizon, or our past light cone.

12:02So normally, in special relativity, you learn
about light cones, but they're obtained just

12:10by drawing straight lines and then
making them into a surface of revolution.

12:14The difference in an expanding universe is
that the light cones themselves shrink down

12:20to a point at the Big Bang singularity, because
the universe is shrinking as we go back in

12:28time.
So this is what we can see.

12:33We see a slice of the universe, and weirdly
enough, the outskirts of the slice are actually

12:40a single point, which is the Big Bang
singularity, and that's what we want to resolve.

12:46And so everything I'm going to tell you about
today rests on a resolution of that strange

12:54paradox that the whole universe
we see came out of a single point.

13:03Now, as well as the arena for physics, we
need to, of course, think about the laws of

13:08physics, and the laws of physics
we know are shown in this picture.

13:14We have the particles, namely the quarks and
the leptons, and so the quarks make up nuclear

13:22matter, protons and neutrons,
and versions thereof.

13:28There are three families of quark, each of them
containing an uptight quark and a downtight

13:34quark.
Then we have leptons, which are generalizations

13:39of the electrons, which orbit around atoms.
And there are similarly three families of leptons,

13:46each with an electron-like particle.
And each with a neutrino-like particle.

13:53So those are the particles.
And then we have the forces,

13:57which are the electroweak and strong forces.
And those are mediated by gauge bosons.

14:07The particles we describe as fermions.
They're described by Dirac's equation.

14:13So all of these things are very well established.
The Higgs boson somehow connects all of them,

14:20because the Higgs boson is responsible,
or the Higgs field is actually responsible

14:25for breaking the symmetry in the standard model.
And it contributes mass to all of these particles

14:35that you see in this picture.

14:37So those are the laws of particle physics.
And then I've drawn gravity as this blue curve

14:41that sort of couples to everything,
because gravity is really universal.

14:46And gravity feels everything else in the picture.
So we have to somehow combine all of these laws

14:59with this picture of the universe
in order to try to make a coherent picture.

15:08And where it doesn't work,
we have to extend these laws to make it work.

15:17Now, as I mentioned, we live outside the sun.
So this is the hot surface of the sun.

15:25And it's completely remarkable
that the color of the sun

15:30tells us Planck's constant.
I mean, it actually,

15:35the fact that the sun has a single color
and it has a temperature of 6,000 degrees,

15:43one can infer from the color
directly Planck's constant.

15:47And so if there were no quantization of photons,
hot objects like the sun simply could not exist.

15:56It's the quantization of light
which allows hot objects to exist

16:01without radiating an infinite amount of energy.
If you take the Planck's constant to zero,

16:07you find the rate of radiation from the sun
would go to infinity,

16:11and the sun would disappear in a puff of smoke
in no time at all.

16:16So this is an example of how the universe
teaches us its laws.

16:24And this is not how Planck's
law of radiation was discovered

16:30because people didn't really
understand what the sun was

16:32at that point in time.
But it could have been.

16:36And so by taking the observations
as seriously as possible,

16:40trying to make them consistent,
one actually learns all about

16:46the fundamental laws of physics.
And right now we're doing the same

16:50with the other version of the sun, if you like,
which is this cosmic microwave background sphere

16:58within which we live.
It's a hot radiating surface.

17:02By looking at it,
we can see what

17:05happened at the Big Bang singularity.
Why do you call it the other version of the sun?

17:11Well, in this picture,
you see the sun is at the center of the picture

17:14and we orbit around it.
But the red sphere represents,

17:22obviously this is a two-dimensional cross-section
of a sphere.

17:27And the red circle on this picture
represents a sphere which surrounds us,

17:34a two-dimensional sphere on
the sky which surrounds us.

17:38And it's hot.
And it was radiating,

17:42radiation at about 3,000 degrees C,
or Kelvin,

17:51when the radiation decoupled.
It's called the surface of decoupling.

17:55And so the radiation decoupled from the hot plasma

18:00in the Big Bang.
And the radiation

18:02just traveled freely from that surface
to our telescopes at the center of the picture.

18:10So, you know, we're outside the sun.
We're inside the surface of last scattering

18:15or this red surface.
And by staring at the red surface,

18:19we hope to learn the equivalent
of the laws of quantum mechanics,

18:23which we could have learned by staring at the sun.
So, here is the surface.

18:30Here is that surface plotted in much more detail.
So this picture shows a projection onto a plane

18:39of that two-dimensional spherical surface
which surrounds us called the

18:43surface of last scattering.
So this is very much like a map in an atlas,

18:49you know, representing the surface of the earth.
This is a two-dimensional map

18:53representing the sphere that surrounds us.
And what you notice,

18:57what's plotted is the temperature
of the radiation on that surface

19:04as projected forward to the present day.
And that temperature varies

19:11from point to point on that surface.
And these are the fundamental variations

19:16of temperature and density,
which came out of the Big Bang

19:21and which later were responsible
for the creation of structure in the universe.

19:28So these variations are very small in magnitude.
The temperature of the surface,

19:36as I mentioned, was about 3,000 degrees Kelvin
when it emitted the microwave radiation.

19:44But the temperature varied from place to place
by about one part, by a few parts in 100,000.

19:53And so the variations in temperature plotted
on this picture are very modest in size,

19:59just a few parts in 100,000.
But you can see the pattern

20:04of temperature variations.
And this picture, you know,

20:10has been made by a number of beautiful experiments
including the Planck satellite.

20:16So we now have access to it.
The top curve, let's start with the bottom curve.

20:23The bottom curve shows what happens
if I look at this map with a Fourier lens,

20:30namely, I Fourier transform it
with respect to spherical harmonics on the sky.

20:36And then I plot the magnitudes
of those spherical harmonics,

20:40the average magnitude against
L, the harmonic number.

20:45And you see this beautiful
red curve on the bottom.

20:47This was actually predicted in the early 1970s
by Jim Peebles and others.

20:53And later, Jim Peebles won
the Nobel Prize for that.

20:58It's a rather clear-cut prediction,
but it rests on a particular assumption

21:04about the cosmological parameters,
which I'll get to in a moment.

21:11So the temperature pattern
shows these oscillatory,

21:17has this oscillatory power spectrum.
Above that is the polarization power spectrum.

21:23And I'm particularly proud of this
because this is a calculation

21:26we did for the first time
when I was a young cosmologist.

21:30So we calculated the red curve.
And then, rather amazingly,

21:35the data points are the blue points.
And you can see they fit perfectly on that curve.

21:41Now, the key point is that this
is with no free parameters.

21:47You fit the free parameters of the cosmology
to the bottom curve and then

21:52just predict the top curve.
And it fits spectacularly well.

21:58That's not because we were particularly clever
with our calculation.

22:01We weren't.
We simply turned the crank

22:04on a way of calculating this,
invented by Chandrasekhar in the 1930s.

22:13But the difference is that we have the data
and we can turn that data into predictions

22:20and they fit beautifully with what we see.
So in other words, for the bottom graph,

22:25that's a temperature graph.
Yes.

22:27You have some knobs that you can fiddle with
and these are called the parameters.

22:30That's right.
How many are there?

22:33So there are five parameters that go into there.
Yeah.

22:35And then you've developed,
when you were a young student,

22:38a function that takes in those five parameters
and outputs that top graph.

22:42Yes.
But those parameters were fixed

22:44by someone else for the bottom graph.
Absolutely.

22:48So there were no new parameters
you had to introduce for the top one.

22:51We had no freedom to introduce parameters.
So all that went into the top curve

22:56are the Einstein equations for gravity
and the equations for the propagation

23:03of radiation,
which were, as I say,

23:06were developed by Chandrasekhar in the 1930s.
And they just used Maxwell's equations

23:10and interactions of light with electrons.
So we didn't do anything.

23:17We were the engineers in this game, okay?
We just took the known laws and applied them.

23:25Nobody had bothered to do the top calculation
because, frankly,

23:28they didn't expect to see it ever measured.
And I had to persuade,

23:33I persuaded the experimentalists
on the Planck satellite

23:37to include detectors to measure the polarization.
You see, the numbers are tiny.

23:42If you look at the units in the top curve,
it's microkelvin squared.

23:47So they had to measure the polarization
with an accuracy of a few microkelvin,

23:54two or three microkelvin.
That's a very big task.

23:59Yes, well, you must not have been
just some whippersnapper then

24:02to have such influence over someone
to develop such a sophisticated tool

24:06by merely suggesting it.
Well, I was lucky.

24:10As I say, all the equations were lying around

24:12in the literature.
Nobody had bothered.

24:14Actually, some people had bothered,
but they'd gotten it wrong.

24:18You can make lots of mistakes
in theoretical calculations.

24:22As far as I know, we were the first people
who actually did it seriously and correctly,

24:26and we got the curve.
And it agrees beautifully.

24:30So this changed, it was a
turning point in my career,

24:37because you look at this curve and you say,
my goodness, the universe is simple, right?

24:42We have five basic parameters,
as I'll explain in a moment.

24:47We fit those to some data set, right?
Could be the temperature in the lower curve,

24:52could be the galaxy distribution,
many other forms of data.

24:56So fit it to some data and
predict everything else.

25:00And the claim is that everything we see
is fit by these five parameters.

25:07And you can measure those five parameters
in multiple ways, right?

25:10And this is called the Lambda CDM model.
And really, it's amazing that it's so simple

25:16and so far fits everything.
And the more and more data

25:21we've got, the better the fit.
It's really quite remarkable.

25:25There are always some tensions.
People claim the Hubble constant

25:29isn't quite consistent,
and so on.

25:31But be very careful about believing those,
because quite often they are

25:35later found to be wrong.
And many of them are only two sigma

25:41or two and a half sigma.
So, so far.

25:45So that's what you were
referring to earlier in the talk

25:47when you said, don't believe every rumor.
Yes, exactly.

25:51So every week or every year,
there's a new tension or anomaly.

25:55Absolutely.
And most of them just, most of them fade away,

26:00and people forget about them.
What has survived is a remarkably simple model,

26:06which as I say, seems to be consistent,
you know, within three sigma or four sigma.

26:15I mean, particle physicists
like to use five sigma.

26:17They never believe anything less than five sigma,
and that's a good rule.

26:21I would say actually in applying it to cosmology,
cosmological measurements are much more difficult

26:26to control than particle physics experiments.
So not in the lab, you know,

26:31you're measuring the natural universe.
And I would say our criterion

26:36for accepting a measurement
should be stronger than five sigma.

26:40If it's five sigma in particle physics,
surely in cosmology, it's gotta

26:43be seven or eight sigma.
If you apply that criterion,

26:47there are no anomalies, okay, with this model.
So here's the model.

26:54It's called Lambda CDM.
It's more or less what Einstein envisaged

27:00in his very first paper on cosmology.
Einstein asked himself,

27:06what is the simplest form of matter or energy?
And he knew they were equivalent,

27:12because E equals mc squared.
So he knew mass and energy are equivalent.

27:17If you just say,
what's the simplest conceivable form of energy?

27:21The answer's very obvious.
It's the cosmological constant,

27:25which is what he invented.
It's a form of energy,

27:29which is absolutely uniform in space, in time,
and furthermore, is what we call

27:35Lorentz invariant.
Namely, if you travel,

27:40with, at some velocity, this stuff doesn't
change at all. No matter how fast you travel,

27:48the cosmological constant is exactly the same
as it was when you, if you're not traveling.

27:55So he invented the cosmological constant, tried
to make a model of cosmology with only that

28:02constant. It didn't work, because he tried to
make a static universe, actually. He didn't

28:10know the universe was expanding. The Lambda
CDM model includes the cosmological constant,

28:16which is 70% of the known energy in the universe.
It includes dark matter. That's a big mystery,

28:27but in this talk, I'm going to resolve that
mystery by explaining what the simplest

28:32candidate is for the dark matter. Actually, I've
already shown it to you on a previous slide.

28:40I'll explain why. The dark matter makes up
about 25% of the energy in the universe,

28:47and the remainder is in nuclear particles and
electrons, just the stuff ordinary matter's made

28:55of, and, of course, photons. So there are five
parameters in the model. One is the density of

29:04the cosmological constant, how much energy there
is in what we call Lambda per cubic meter. The

29:12second one is how much dark matter there is,

29:14again, just how much per
cubic meter in the universe.

29:19And the final one is the proportion of nuclear
matter to photons, and that's a free parameter

29:28in the model. Actually, it will be explained
by the picture I will describe. Not predicted,

29:37but explained. Namely, there are enough free
parameters in the laws of physics to fit the

29:44number of nuclear particles per photon from
what we already know. Now, the fourth and fifth

29:53parameters describe the variations in density
across the universe. This cosmic web, as you

30:02see in the picture, the variations on the
temperature map of the microwave background

30:07radiation, those require a very simple form
of density variations. It's known as random

30:16Gaussian noise, which means it's just like ripples
on the surface of the sea. There are no complex

30:25structures. It's literally a random superposition
of waves where the waves have a particular

30:33strength or power as a function of wavelength.
So, there are two parameters there. One is the

30:42amplitude. This is about the one part in 100,000
that I mentioned before. That's the amplitude of

30:49these primordial density waves. And the second
parameter is what's called a red tilt. It means

30:55that the waves get ever so slightly stronger as
you go to longer wavelengths. In condensed matter

31:05physics, such a phenomenon is very familiar.
It's called a critical exponent. It means that

31:13basically the fluctuations either get a little
bit stronger with scale or a little bit weaker

31:19with scale, but this scales in a certain way. In
the case of cosmology, the red tilt means that

31:26if I go to wavelengths 10 times as long, the
amplitude of the ripples increases by 5%.

31:37That's not much. I think if I go a billion times
longer in length scale, the amplitude doubles.

31:48Can one also interpret that
as it being more numerous?

31:52No. It's just that the strength of the wave gets
a little bit stronger. The waves are all random

31:58Gaussian. It's literally just a random
superposition of waves. When I say the

32:08strength of the waves, I mean the amplitude of
the waves. The fractional change in the density.

32:16Right. What I meant was that
if you were to add two waves,

32:18of course they would have to be directly
on top of one another. Then you can interpret

32:21that as two medium-sized waves giving rise to
something that's one large. You could, but when

32:28you say random Gaussian noise, you're saying that
I just take a bunch of waves of a given

32:35wavelength, point them in random
directions with random phases,

32:40and throw them on top of each other.
Then I pick waves of another wavelength,

32:45need to tell you how strong those waves are,
again make a random superposition of them,

32:50and put them on top of each other. Everything we
see is consistent with that. Random Gaussian noise

32:57with two parameters describing the power spectrum.
One is the amplitude and the other is this slight

33:03tilt. Now, at the end of the talk, I'm
going to tell you that our theory predicts

33:09numbers four and number five almost on the nose.
Based on the laws of physics, we already know.

33:20It's very striking, and we'll see. If this
holds up, essentially it's problem solved,

33:30but we'll see. As you can imagine, I
am really quite excited about this.

33:36Now, dark matter. I used to believe that dark
matter was the one sure indication we had

33:45of physics beyond the physics we know, the laws
of particles and forces which I showed you.

33:53We thought, many people thought, that dark matter
must be made of something else, another particle.

34:02Literally, there are tens of thousands of
suggestions as to what the dark matter might be.

34:11Many, many people have built their careers
inventing and then trying dark matter

34:18particles or other explanations, and
then trying to test those in experiments.

34:25In fact, we can see the dark matter quite
directly now. This is a beautiful picture

34:32from the ACT experiment.
ACT is an Atacama Cosmology Telescope, and

34:39it's actually measuring the microwave radiation.
That's what the picture shows. The surface on

34:45the left is emitting light. What we see
is the map on the right, and as the light

34:52travels through the universe, it gets deflected
by the gravity of the dark matter, just like water

35:01in a glass of water will deflect whatever's
behind the glass of water, so that when you

35:08look through it, you'll see it lensed by the
water. Dark matter does the same thing. You

35:14can use this to literally measure, using the
bending of light, you can measure the density

35:20of dark matter, and you can measure the density
variations in the dark matter. This all fits

35:27beautifully with the Lambda-CDM model.
CW2 Would you, in order to do that,

35:33have to know the leftmost CMB?
MG No, you don't need to know it.

35:37What you need to do is to assume
that the leftmost CMB is random

35:44Gaussian noise with a power spectrum, which has
been measured by the Planck satellite. Just two

35:52numbers specify the spectrum. Then what you do
is, the only thing you measure is on the right,

35:59which, if you can sort of see, they put streaks
on that map. The streaks show the effect of the

36:05lensing. It basically stretches spherical peaks.
If you have random Gaussian noise, the peaks tend

36:11to be quite spherical, but if you lens it, that
tends to shear the pattern. It turns out you can

36:19just measure the shear in the pattern due to
gravitational lensing. From that shear, you can

36:27infer the density of the dark matter. It's really
amazing how all this works. With those five

36:35parameters, you can fit everything and there
is no inconsistency. This has all become rather

36:42precise. I mean, these gravitational lensing
measurements now involve huge amounts of data,

36:49and they're all absolutely compatible. In some
senses, it's very disappointing. People design

36:55these enormous, expensive telescopes that go
through this huge data analysis. They would love

37:02nothing more than to find a contradiction. That
would be super exciting. Well, they haven't found

37:07one. On the contrary, everything fits remarkably
well. So, let's come back to the biggest puzzle of

37:17all. How on Earth did everything we see come
out of a point? The key, I believe, is a certain

37:28symmetry in the laws of physics we already know.
Namely, the laws of those forces of nature, one of

37:37which is electromagnetic forces, the laws of light
and electric and magnetic fields, and the laws of

37:46particle physics we know, which were written
down by Dirac with the Dirac equation. Those two

37:53theories happen to have a symmetry under rescaling
space. This is actually the reason why a light

38:05wave is essentially the same as an X-ray. An X-ray
is just a scaled-down version of a light wave. You

38:13just shrink the wavelength
of light, and you'll get an

38:18X-ray. Expand the wavelength of the light, and
you'll get a radio wave. Light is essentially the

38:27same thing, scaled up and down. It can come in all
forms. They all obey the same equation.

38:37It's uniquely specified by the
wavelength. The reason the theory

38:42behaves like that is it has a symmetry.
The symmetry is scaling symmetry,

38:48rescaling length and time. You
get a shorter or longer wavelength,

38:55higher frequency or lower frequency
light. Now, Dirac's equation has

39:01the same property, as long
as you ignore the masses of

39:05the particles. In other words, when these
equations are taken to the massless limit,

39:13the Big Bang is exactly such
a place, because the plasma is

39:17extremely hot, so masses are irrelevant there.
It's very tempting to believe that at the Big Bang

39:28singularity, essentially there was
nothing but light and light-like

39:31particles. They all have this scaling
symmetry. Now, that scaling symmetry is

39:40very deep, very profound. What it's
telling us in colloquial terms is

39:48that the matter did not know about the
size of the universe. It evolves in such

39:55a way that it doesn't care that the
universe is shrinking as we go back

40:00in time. So the matter is evolving
as if the universe were in fact not

40:06shrinking to a point, or can be
described mathematically with

40:14ignoring the shrinking away of the
universe. This is what we noticed

40:20about the Einstein equations and
the laws of radiation. The Big Bang

40:27singularity is a very particular type of
singularity called a conformal singularity.

40:36I'll tell you a little bit more
about conformal. Conformal symmetry

40:41is a picture which illustrates this.
Light and particles are described as

40:47gauge fields and fermions in the standard
model, a la Maxwell and Dirac. So conformal

40:57symmetry is a symmetry of light
and massless particles. Conformal

41:02symmetry means that you can actually
rescale space and time locally, and the

41:10equations are invariant. So here's an example.
Imagine I was solving Maxwell's equations inside a

41:20cylinder. So the boundary of the cylinder was a
circle, as the left picture shows. Alternatively,

41:27imagine I was solving Maxwell's equation.
inside a square pipe. Okay, so the cross

41:35section was a square. Conformal symmetry tells
you those two situations are actually identical

41:42as far as the light is concerned. And often, so
the grid you see on the right, you know, that's

41:49just a coordinate grid. It's useful for writing
down equations or putting them on a computer, but

41:55has no particular physical significance. Now if I
distort this square on the right into the disc

42:05on the left, with a conformal transformation,
that means a local change of scale, which does

42:13not change angles, it only changes lengths, I get
the picture on the left. So that's another grid,

42:19I could solve the Maxwell's equations
on that grid. And then the statement

42:23of conformal symmetry is that these two
things give exactly the same result. So

42:30these funny points where you see this pile
up of grid points in the left hand picture,

42:36they're a little bit like
the Big Bang singularity,

42:39right? There's a sort of pile up of space
into a point. And what it's saying is you

42:45just have to blow that up with
a conformal transformation,

42:48just expand your grid. And the equations
are just the same in the new picture.

42:58So we actually use this picture to
make sense of the Big Bang singularity.

43:06So we go back to the Big Bang singularity.
Now imagine blowing up that singularity,

43:12I don't mean in the sense of explosion, I mean
in a mathematical sense, like changing the scale

43:18of space. So one can do this mathematically, and
then the singularity actually becomes a finite,

43:25it's not a point, it's now a finite patch. And
then we impose a boundary condition on that patch

43:33which implements mirror symmetry. So
that initial patch at the Big Bang,

43:44we treat as if it were a mirror. So normally
when we deal with, let's say, Maxwell's equations

43:54in a mirror, the propagation of light in the
presence of a mirror, there are two ways to do it.

44:00Either you impose a boundary condition at
the mirror, you say that the electric field

44:07parallel to the mirror has to be zero, and you
literally solve the equations showing how the

44:13light travels to the mirror, bounces off the
mirror, and comes back. That's one way of doing

44:19it. It's actually a rather tedious way of doing
it. There's a much nicer way of doing it, which

44:25is to say, look, I'm looking at myself in the
mirror. If I'm right-handed, let me make a

44:33left-handed version of myself, put that behind
the mirror, okay? So it's a fictitious person,

44:41that's literally a mirror image of me. Put it
behind the mirror, an equal distance from the

44:46mirror, throw the mirror away, and just solve
Maxwell's equations for the light coming from that

44:53person to me. That's called the method of images
in physics. It's a very elegant way of solving

45:02boundary value problems. And what we're
claiming is that you can apply the same method

45:10to describe the Big Bang.
The Big Bang is a mirror,

45:13so I literally take the post-Bang universe,
make an image of it before the Big Bang, and then

45:21I would just propagate light and particles from
that pre-Bang universe through the Big Bang

45:27singularity. Because of conformal symmetry,
that propagation is completely smooth and regular

45:34and predictable, and I propagate that forward to
see what we see. So we claim that this extended or

45:42mirror universe picture is absolutely compatible
with everything we see in the universe. So in a

45:48certain sense, when we look back towards the Big
Bang, we are seeing our own image. The Big Bang

46:00is a boundary condition. You see, the conventional
thinking about the Big Bang, which I think leads

46:09to terrible paradoxes, is that somebody input all
the stuff in the universe at the Big Bang and

46:19sort of threw it apart. What
we're doing is the opposite

46:24of that. We say, no, all that happens at the Big
Bang is a boundary condition which the matter has

46:30to respect. If you look at this, the traditional
way is that someone or something just spurred

46:37everything into existence from that single point,
but then you're saying that this is an improved

46:41picture. However, it just looks like someone or
something spurred all from all points at once,

46:47so it doesn't seem like much of an improvement.
So tell me why this is different. Right. No,

46:52good question. You might say, our picture looks
like somebody made two universes, so surely it's

47:00twice as difficult. Yes. No, good point.
What we're saying is that there is a...yeah,

47:08in fact, the answer is this.
LWR Great, natural lead-up.

47:14MG Yes, the answer is this. So the most
fundamental law of physics we know,

47:21which is a direct consequence of quantum
mechanics and relativity, is called CPT symmetry.

47:30CPT symmetry was discovered in the 30s and 40s
as an inevitable consequence of bringing quantum

47:39mechanics and relativity together. So it underlies
quantum field theory. Now, what is CPT symmetry?

47:48CPT symmetry says the following, that
if I look at some physical process

47:56and I try to make another physical process
using a law of symmetry. Okay, so take some

48:04physical process, turn every particle into
its antiparticle. That's what the C does.

48:13P inverts space, so literally just send any
space coordinate in three-dimensional space

48:24to its inverse.
X goes to minus

48:26X. Okay, that's an inversion of space.
That's a very dramatic thing to do,

48:32but the laws, you know, you can do this with
the laws of physics. T is time reversal,

48:38so whatever's going forward in time make
it go backwards in time. The CPT theorem

48:44in relativistic quantum physics tells you
that the rate for any process and its CPT

48:52conjugate process is identical. Okay, so this is
kind of analogous to time reversal in Newtonian

49:00mechanics. You know, in Newtonian mechanics you
can take the laws of motion and reverse time,

49:07and because they're second-order equations
in time, you know, they are invariant. So

49:13Newtonian mechanics has no arrow of time,
and in relativity the generalization is CPT.

49:21So we take our observed universe,
the right-hand part of this picture.

49:27It has more matter than antimatter.
Okay, so it is not invariant under C,

49:36and it's not invariant under T. It's going one
way in time, and so the right-hand side of this

49:42picture violates CPT. But if you apply CPT to the
right-hand side of the universe, what you get is

49:52the left-hand side. Namely, every particle goes to
its antiparticle. What was going forwards in time

50:00moving to the right in the right-hand part of the
picture is now going forwards in time moving to

50:05the left in the left-hand part of the picture.
And so the statement is that if you want the

50:11universe to respect the laws of physics in the
most obvious way, namely that it is invariant

50:20under CPT, then you are led to this doubled
picture. And in the doubled picture,

50:30there is then a very natural boundary
condition which is symmetrical under CPT,

50:38and the boundary condition is the one that we
use. So we're saying the Big Bang is a CPT mirror,

50:47and this resolves the fundamental puzzle of

50:50why the universe appears to
us to violate its own laws.

50:55We say more matter than antimatter, and that
looks like the universe is not invariant under

51:06C. Likewise, we see time going one way, and
that's incompatible with the fact that the laws of

51:14physics are invariant under reversing time and
changing matter to antimatter. So what we're

51:21doing here is an extremely minimal application
of CPT to the universe, and the consequence is

51:32this mirror universe hypothesis. So to put it
differently, anyone who makes any other hypothesis

51:39is going to have to violate CPT, and that's
a losing battle. So we were very surprised.

51:53So in Newtonian mechanics, if you
take a ball and there's no friction,

51:56and you drop it, it hits, and
then it comes right back up.

52:00Exactly.
Okay, now if you were to look locally,

52:02if you were to just look at half a second,
you would say, well, look, there is a difference

52:07between the future and the past, because in the
past it starts to go down, but in the future it

52:12starts to go up. But you're saying, well,
you have to look at the whole picture.

52:15Of course.
So let's take the full movie.

52:17Of course.
So now, philosophically speaking,

52:20we used that word earlier.
Sure.

52:21What is someone who's watching this supposed
to feel? There's some religions that say

52:26something or someone or the universe started
itself, and you experienced this world once.

52:31Right.
Then there are some other traditions that

52:34say you experience it cyclically, infinitely.
Right.

52:36And then there's here, which seems to suggest,
well, you experience everything twice.

52:41No, because you see, when I say we're using
the method of images to impose a boundary

52:49condition at the Big Bang. So this picture
is a mathematical picture, a device, which

52:57is useful in order to impose a particular
boundary at the Big Bang. So in this picture,

53:04the universe in a certain sense creates
itself. Okay. It's extremely minimal.

53:11Everything I described could be described
by just taking the right half of the picture

53:17with this boundary condition, which
is in effect the result of doubling it

53:24and imposing the symmetry. You see,
if I double it and impose a symmetry,

53:29the doubling goes away because the
left and right halves are identical.

53:34So then to be specific, is it correct
to say the Big Bang is a mirror?

53:41For mathematical convenience, it's useful
to model the Big Bang as a mirror. Like,

53:46is that the more elaborate correct statement?
No.

53:48Or the Big Bang is a mirror
is the correct statement?

53:50Correct statement is the Big Bang is a mirror.
And for any mirror, it is useful to double

53:58the universe.
I see.

53:59Yeah. The doubling is just a mathematical
trick, which you can use for any mirror.

54:05And we're saying that literally
the Big Bang is a mirror.

54:10So I would say that this, I mean, certainly in my
experience, and I've worked with Stephen Hawking,

54:16and I've worked with a number of other
such people on scenarios for cosmology,

54:22there is no doubt this is the most
economical hypothesis you can make.

54:29Because it's compatible with the laws
of physics and extremely minimal.

54:35So, you know, either it's right or it's wrong.
We'll see. That's the attractive feature of this

54:40whole setup, is that it is eminently
disprovable. And that makes it interesting.

54:49So, yeah, as I mentioned,
these laws, the particles

54:53and forces actually do have this symmetry
under local changes of scale. And that

55:00allows us to resolve the Big Bang singularity,
to blow up the point everything came from into a

55:07patch. And then that patch is the mirror
at the Big Bang. This is

55:15actually all the particles we know.
Now, notice something funny about this picture.

55:22All right, so the neutrinos in the bottom
left have a superscript L, okay, meaning that

55:31they are left-handed. If they are traveling
along in the direction of the thumb of your

55:38left hand, the spin follows the fingers of
your left hand. So it's rather strange that

55:45the light neutrinos we see only come in the
left-handed variety. All the other particles

55:54have a right-handed and a left-handed version.
Now, so that is, you know, what we see in

56:00laboratory experiments. We only ever
see left-handed neutrinos. However,

56:11if we were to imagine the simplest or the
most minimal conceivable extension of the

56:20standard laws of physics, what would it be?
And I just made it, right? I went from this

56:26slide to that slide by removing the L, okay?
Now, all the particles have both left and

56:35right-handed versions, okay? And my claim, our
claim, this is with Latham-Boyle, our claim

56:45is that removing that L, in other words, giving
the neutrinos a right-handed as well as a

56:51left-handed version, allows you to solve the
problem of dark matter, okay, in an extremely

56:57minimal way with the mirror hypothesis. So
now imagine these are the laws of physics.

57:05There's no L anymore on any particle.
Every particle has left and right versions.

57:12Now what happens is I take my left-handed
neutrino, it's coming in from the left,

57:18it then, what we call, we say that it can
oscillate into a right-handed neutrino,

57:26the new right in the middle, and oscillate
back into a left-handed neutrino on the right.

57:33Now the left-handed neutrinos are very
light. Neutrinos are very light particles,

57:39they don't have much mass. If the right-handed
neutrino is very heavy, then this process can

57:47only be a virtual process. You had a certain
amount of energy, you can't stay as a right-handed

57:54neutrino, you just don't have enough energy to
account for its mass. So you've got to go back

58:00to being a left-handed neutrino. So this is what
we call neutrino oscillations. The left-handed

58:06neutrinos can oscillate briefly
into a right-handed neutrino,

58:11and then they find themselves in,
if you like, they've got more mass than they can

58:16account for with their energy, and so they go back
into being a left-handed neutrino. This mechanism

58:22is a mechanism for giving
the left-handed neutrinos

58:25a small mass. Neutrino masses started to be
measured in the 1970s, and this mechanism was

58:36quickly realized as the simplest explanation for
those masses. Namely, if there are right-handed

58:42neutrinos which are very heavy, this would explain
why the left-handed neutrinos are very light.

58:49You see, the heavier the right-handed neutrino,
the shorter the time you're going to spend

58:56as a right-handed neutrino. And so basically,
the heavier you make it, the less and less

59:03probable it is that the neutrino oscillates in
this way. And so it's called the seesaw mechanism

59:11because the heavier you make the right-handed
neutrino, the lighter the mass of the left-handed

59:17neutrino. So this was understood in the 70s.
And at that time, people could have said,

59:25oh well, maybe the dark matter is a right-handed
neutrino. You see, the right-handed neutrino is

59:30a very obvious candidate because it has no
electromagnetic charge. It doesn't couple to

59:37the strong or the weak force at all. So the
only thing the right-handed neutrino couples to

59:44is the Higgs field, this thing noted by H, and
gravity. So for the right-handed neutrino to be

59:53the dark matter, all you need to do is switch off
this coupling. Actually, this is the important

01:00:04one. So for the right-handed
neutrino to be the dark matter,

01:00:08the only problem is that it can decay.
This diagram shows a right-handed neutrino

01:00:15decaying into a Higgs and a left-handed neutrino.
So if you want the dark matter to be stable,

01:00:23it has to have survived for
at least 14 billion years,

01:00:27you've got to switch off this vertex. And if you
switch off that vertex, you must switch off this

01:00:32vertex because they're the same vertex. And if you
do that, it means the left-handed neutrino cannot

01:00:39oscillate into the right-handed neutrino. And
this actually means the left-handed guy must be

01:00:44massless. So just from this picture, you can see
that if the dark matter is stable and consists of

01:00:53right-handed neutrinos, then it's plausible that
one of the left-handed neutrinos is massless.

01:01:00And that's actually our prediction, which is
going to be tested in the next five years.

01:01:07The second thing you've got to do is you've
actually got to make these right-handed neutrinos.

01:01:12How do they get made? And the way
they get made is rather beautiful.

01:01:17You see, if I switch off this vertex, there are
actually three of these right-handed neutrinos

01:01:25and three vertices, so I'm somewhat simplifying
the story. But if I take one of them and I switch

01:01:32off its vertex, then it actually doesn't couple to
anything except gravity. So this poor right-handed

01:01:39neutrino is sitting there in the universe. It
doesn't see the hot plasma at all. And the mystery

01:01:45is, how did it get created? What determines its
abundance? And so this was actually our first

01:01:53starting point with this whole picture. We
realized the right-handed neutrinos are produced

01:01:58as Hawking radiation from the Big Bang, that it
is simply the time dependence of the universe

01:02:08that creates these right-handed particles.
It literally pulls them out of a vacuum,

01:02:14which is a process called Hawking radiation.
It's due to gravity, it's due to their coupling

01:02:20to gravity, and due to the fact that the universe
is expanding.

01:02:25So what we showed is that if their mass was
500 million times the mass of a proton, then

01:02:34they account for all the dark matter we see.
And this is the simplest yet

01:02:40explanation for the dark matter.
It's just right-handed neutrinos.

01:02:44They were created by the
expansion of the universe.

01:02:47To calculate that creation, we had to assume a
particular quantum state for the right-handed

01:02:55And what we did is to use the state defined
by CPT symmetry and the mirror hypothesis.

01:03:05So all of this is kind of self-consistent.
And is that a bound on the mass of the

01:03:11right-handed neutrino, or
is that an actual prediction

01:03:14for it?
It's an exact prediction.

01:03:18That has to be its mass.
Now it's very hard to measure indirectly.

01:03:25You would have to literally have a little
gravimeter and go through space and wait until

01:03:31a right-handed neutrino traveled past you
and measure the deflection due to its mass.

01:03:39One day that will be possible.
It's not possible today.

01:03:43But no, this is a very precise
prediction of its mass.

01:03:47There are no free parameters in that prediction.
So if it's stable, the lightest neutrino is

01:03:55Because to make it stable, I
had to switch off this vertex.

01:03:59And if I switch off this vertex,
I have to switch off that one.

01:04:03And that means this left-handed neutrino cannot
acquire a mass by becoming a virtual right-handed

01:04:09neutrino for a little while.
So the prediction is that the lightest neutrino,

01:04:16namely one of these left-handed neutrinos,
is exactly massless.

01:04:21Amazingly, this is now possible using the
Euclid satellite telescope survey now underway.

01:04:32And basically what you do is measure the strength
and clustering of galaxies on a certain scale,

01:04:44which corresponds to the,
well, yeah, let me start again.

01:04:55The way you measure neutrino masses using
galaxy surveys, and it's quite extraordinary

01:04:59that you can do this, is by measuring
the strength of the clustering of matter.

01:05:05Now if the neutrinos are massless, they
do not clump with the rest of the matter.

01:05:14If they have a mass, then as the universe
expands, they actually slow down relative

01:05:21to the expansion, because the mass kind of
becomes important and they no longer are moving

01:05:27at the speed of light.
They slow down and

01:05:30they clump with the other matter.
And that effect turns out to be large enough

01:05:35that by measuring the clustering of galaxies,
you can measure the mass of the neutrino.

01:05:40And so they claim they will be able to check
that the lightest neutrino is massless within

01:05:47about five sigma, quite accurately, using
these forthcoming galaxy surveys within the

01:05:54next five years.
So should this prediction be confirmed?

01:05:59My claim is that this will be easily the most
compelling explanation for the dark matter.

01:06:07There are other predictions.
We can predict the decay rate of atomic nuclei,

01:06:13a process called neutrino-less double beta
decay, but that process is very, very slow

01:06:20and may take one or two decades to measure.
It's a very, very tough experimental test.

01:06:26But if this one works out, there will be very
strong motivation for doing nuclear physics

01:06:32experiments to check this idea that the
dark matter is a right-handed neutrino.

01:06:41So where do we get to?
Well, the Big Bang was a

01:06:43special type of singularity.
The size of the universe is

01:06:49governed by what we call the scale factor.
This comes into the metric on space-time.

01:06:56And what happens is that as time goes to zero,
this scale factor, the size of the universe,

01:07:02shrinks to zero in a very simple
way, just linearly in time.

01:07:08When it hits zero, we call that a conformal
zero, meaning that the scale shrinks to zero,

01:07:19the overall scale shrinks to zero.
So colloquially, the universe is at a point.

01:07:25But as I mentioned, you can always blow up
the scale, essentially by dividing by this

01:07:32quantity that goes to zero.
You can blow it up, and that becomes the mirror.

01:07:36So this conformal zero in this picture of
the Big Bang becomes, in fact, an extended

01:07:44three-dimensional mirror in what
we call the conformal frame.

01:07:52So one way of saying it is that the conformal
four geometry is actually regular at the Big

01:08:00is a resolution of the Big Bang singularity.
The Big Bang is, in a sense, a shrinking away

01:08:09of space, but the thing is that the particles
and forces are not affected by that shrinking.

01:08:20They're still obeying equations as if they
were an extended three-dimensional space.

01:08:29So this is a way of resolving the Big Bang
singularity and turning it into a mirror.

01:08:35So I was going to tell you about explaining
the geometry of the universe, but I think

01:08:40that's too long.
I want to talk a little bit about the most

01:08:46exciting and most recent development in this
hypothesis.

01:08:52And so this is addressing the very fundamental
dilemma which occurs in coupling quantum fields

01:09:05to gravity.
So we know that in order to describe the laws

01:09:09of fundamental physics, we have to use quantum
fields.

01:09:12And so we're going to look at
the laws of quantum fields.

01:09:12This is an extremely successful technique,
and it's the basis for the Standard Model.

01:09:19Everything is described by quantum
fields in the Standard Model.

01:09:24However, these quantum fields look like
the right-hand picture in the vacuum.

01:09:30And this is just a consequence of
the Heisenberg uncertainty principle.

01:09:35You might want to set a field to zero and just say
there's no electric or magnetic field in space,

01:09:44but this is inconsistent with quantum
mechanics. Why? Because the magnetic field

01:09:50is like a coordinate of a particle, x, and the
electric field is like the velocity of a particle

01:09:57or its momentum. And the Heisenberg uncertainty
principle says that either you measure x

01:10:03or you measure p. You can't measure both. You
can't set the position of a particle to zero

01:10:10and its momentum to zero at the same
time. You can do one or the other.

01:10:15And so what happens in the quantum vacuum, you
might say, okay, let's have zero electric field,

01:10:21but then you've got infinite magnetic field.
You might say, okay, zero magnetic field,

01:10:26but then you've got infinite electric field.
So the compromise which happens in the vacuum

01:10:32is that neither the electric nor the
magnetic fields are zero. They're both

01:10:36oscillating with what is called zero-point
fluctuations. So the vacuum is full of

01:10:44these fluctuations, which are pictured in the
right-hand side. And these are all the fields

01:10:50in the standard model. The electron fields, the
photon fields, the strong force, the weak force,

01:10:56everything is sort of going crazy in the vacuum.
I say going crazy advisedly because there's

01:11:02infinite energy in these oscillations. This is a
very deep paradox about trying to couple quantum

01:11:09fields to gravity. Now, not only do you get
infinite energy in the vacuum, as I mentioned,

01:11:16gravity detects all energy. And in particular,
it's very hard to stop gravity feeling all this

01:11:24energy in the vacuum. So you're led to this
immediate paradox that gravity is coupling to

01:11:31an infinity, and cosmology doesn't really make
any sense. So people cheat in various ways. They

01:11:38subtract that infinity in certain ways. But
there's a further problem, which is that these

01:11:44zero-point fluctuations in the vacuum spoil this
beautiful local scale symmetry of the Maxwell

01:11:51and Dirac theory, which we needed in order
to make sense of the Big Bang singularity.

01:11:59So these vacuum fluctuations seem to prevent us
describing the Big Bang singularity as a mirror.

01:12:10So what we have done recently, very recently,
is we discovered an entirely new mechanism,

01:12:18A, for cancelling the energy in the vacuum, B,
for restoring the symmetry of Maxwell and Dirac,

01:12:28the local scale symmetry. And we found
we could do that in a very unique way.

01:12:37We call them dimension zero fields. They're rather
peculiar fields. They do not have any particles.

01:12:43They merely exist, if you like, in the vacuum.
So all they do is sit there and cancel out these

01:12:52various diseases in the vacuum. So it's, again,
extremely minimal addition to the standard model.

01:12:58It's very unique. Their properties are uniquely
defined. And then, rather miraculously,

01:13:05these same extra ingredient, the same extra
ingredient in the vacuum, turns out to explain

01:13:13the origin of the density variations. And so this
is now rather technical. I'm going to leak to a

01:13:20formula, which I'm not going to justify. But this
formula is a direct consequence of the assumptions

01:13:28I've laid out. It says that the power spectrum
in the early universe, that's this curly P thing,

01:13:36as a function of wavelength, is given by these
numerical factors, which are just a consequence

01:13:43of relativity, quantum mechanics, quantum field
theory. Various numbers here, C beta, this alpha

01:13:52y, alpha 2, and alpha 3, are the strong, weak,
and electromagnetic coupling constants as measured

01:14:00in the laboratory. So roughly speaking, you
could say that this is given by defined structure

01:14:06constant, but it's for the strong, weak, and
electromagnetic forces. So these numbers are all

01:14:13a consequence of the standard model, all these
funny fractions, a direct consequence of the

01:14:18number of particles of various charges and types
in the standard model. So these are all standard

01:14:25models. There's a number of effective degrees of
freedom. This is basically the number of particles

01:14:30in the standard model. So these numbers are just
inescapable consequences of the standard model.

01:14:39This is the red tilt. You see, this power of
the fluctuations as a function of wavelength

01:14:45is growing with wavelength, like lambda to this
small power. And this small power turns out to be

01:14:520.04, which is what we observe in the cosmic
microwave sky. Okay, so there is this rather

01:15:00magical formula that comes out of
those assumptions. It turns out,

01:15:06and this may be a coincidence, but

01:15:07it's a very tempting one, turns out that this
formula matches both the amplitude and the red

01:15:14tilt. So this number gives you roughly 10 to
the minus 5. Within a factor of two, it matches

01:15:21the observations. The red tilt it predicts is
0.042, using the CERN measurements of the strong

01:15:28coupling constant, and the observed number from
the Planck satellite is 0.041. So this is very

01:15:36tantalizing. All I would say at this point is
that I think very few cosmologists are, except us,

01:15:45are convinced by this yet. I'm going around,
Latham's going around giving talks, people are

01:15:52challenging us in various ways. If only you could
do the calculation this way or that way or check

01:15:57this or check that, we might believe you. That's
very important that we are checked and that we

01:16:05really present a full-blown calculation that
would satisfy everyone. There are various

01:16:12assumptions we've made. They are always the
simplest conceivable assumption, but there

01:16:17are some assumptions in this result. If this
turns out to be theoretically safe, no one points

01:16:27out a problem with it. If the observations,
as they improve, confirm this scaling extends

01:16:36to even smaller wavelengths, then this will
be the explanation. Cosmology will be unified.

01:16:48Just to close on this, what I've put forward
here is the prospect, at least, of an extremely

01:16:56unified picture. There is just the standard
model and gravity, perhaps with a few little

01:17:03additions in the vacuum, but no extra particles,
no extra forces. Maybe we are actually very

01:17:12close to understand all the physical laws
governing the universe and how they describe

01:17:21the Big Bang itself. If this is true, there
are many, many other consequences. It leads

01:17:27to a new picture of black holes, which resolves
the black hole information paradox. It will

01:17:33lead to many other predictions because it's
so constrained, this picture, and there's

01:17:40no wiggle room. Either this picture
is right or it's wrong, so we'll see.

01:17:47Here are some references of papers on this.
There are other papers on the archive, and

01:17:54there are new papers in preparation. Thank
you very much for listening, and I welcome

01:18:00any questions.
Thank you so much,

01:18:03Professor. The question and answer
session is on Theories of Everything.

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01:18:12this lecture. Neil Turok was also interviewed
solo for two hours here on TOE, and this is

01:18:17the most-watched interview with Neil
Turok ever. Check that out as well.

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