Welcome everyone.
To see night's bold ideas in physics or
we apologize for
the delay there's nothing like a technical
problem at Georgia Tech to embarrass us
greatly sorry so
tonight we honor our friend and colleague
David Finkel Sime and David started his
career in Georgia Tech in one thousand
nine hundred seventy six just to put it in
perspective my name is Dr shoemaker and
I have the fortune of being the done
Family Professor of Physics and
the director of the Center for
relativistic astrophysics and
tonight we celebrate David's life and
work through this evening's lecture and
through the displays you might have
seen in the lobby so please take a look
when you have a chance this lecture series
is meant to invite us to be part of
the intersection of creativity beauty and
impact that illustrated David's work and
I have the pleasure tonight of introducing
our speaker for tonight's bold
ideas in physics lecture series professor
by Ashta Carr who was an influential
figure in my own research actually first
met him when I was an undergraduate So
be careful guys will call it twenty
five years ago give or take a few years.
And Professor A by Aster Carr has a long
list of accolades which I won't list all
of them but
he is a member of the National Academy of
Sciences in both the United States and
India he's the president of the
international society on gravitation and
General Timothy I believe Professor of
Physics the director of the Institute for
gravitation and the cosmos just a few.
For this evening however I think
the most important quality about
Professor asked a car is that he is one
of the very few individuals even this is
just that I know of whose work
truly embraces bold ideas so
it's night he brings us
Einstein's cosmos and the quantum
origin of space time and large scale
structure Please join me in welcoming our.
Thank you.
I have known David Finkelstein's work
since I was a graduate student and
I always admired it greatly for as you say
for creativity for regionality and for
Gap So it's a great honor for
me to speak at this occasion so
the title of my talk a director
already told you and
basically the point is that I would
a view of the cosmos is really shaped.
By state and city of generative U.T. and
that is why it says Einstein's cosmos and
the Kontum how they were Einstein's theory
is a classical theory in other words
it is rooted in classical physics and
now we learned that in fact ideas from
quantum con in physics are critical to
understanding the very early stages of
our universe and that is why it is
Einstein Einstein's cosmos and.
The Kontum And then what I'm going to
focus on is this origin of space time and
the large scale structure of the universe
what do we know about it today.
So the organization is in
these parts first I'll tell
you a little bit about general
activity because that's really where.
Our understanding of cosmology today's
contemporary cosmology is based
then I'll tell you about the application
of generally to MITI took a small A-G.
and in particular thing that leads to the
Big Bang which is in general a to Vittie
the book off not only matter but
of space and time itself.
Then I'll tell you a little bit
about inflation which tells about.
Provides provides us with.
With the with the origin of the last
construct of the new worst and
finally I will go beyond
I will speak about.
Quantum Gravity physics beyond
Einstein OK so let us begin.
It's entertaining at least.
So let us begin what would I say
is today of general activity so
it began a really long time ago.
Many most of you probably know about
Einstein's special theory of relativity
which was invented in one thousand or
seven and ninety five and two years later
Einstein was invited to write a review
article on space interactivity and
while doing that he realized that there is
a tension between the Newtonian paradigm
of space and time and
the fact that in special relativity
we do not have a notion of absolute
simultaneity if there are events
in space time event is a point in space
and time space time and if the events in
space time which are separated are widely
then you cannot tell in special relativity
there is no absolute being to them
these events to be simultaneous and
whereas Newtonian theory of gravity is
based on Newtonian ideas of space and
time in which if I move this
microphone a little bit
immediately at the same instant then as
you all know the the Newtonian potential
of the neutron in the infield at the end
of the room changes instantaneously and
but in special relativity signals cannot
really travel faster than light and
therefore the source of the tension that
Einstein started thinking about it and
there is a reason was really a new
theory of space time and gravitation but
I still was was sort of thinking
that if I want to combine.
If I want to have a self-consistent
description of gravity which is compatible
with Newton's ideas of it with which
special relativity idea of space and
time then I would need
a new theory of gravity.
And on the same time as up so
you worked on it for several years and
in one hundred thirteen you're still
working on it had made a lot of progress
by then but Splunk was a founder
of quantum mechanics with.
Here.
He came to visit Einstein in Zurich to
lure I stand back to Berlin Germany and
in fact he did succeed and they made
a very contested offer to Einstein to go
back to Germany and then after the kind
of the administrative matters were
over he asked him What are you working on
so Einstein told him that well I'm trying
to combine I'm trying to find a new theory
of gravity which is beyond Newton and
here is what Max Planck said as an older
friend I must advise you against it for
in the first place you will not succeed.
And even if you decide
no one will believe you.
And this is really coming from the leading
physicists at that time is not some lay
person telling him that so that just
shows how I don't want how I had of time
Einstein was even related to
the leaders in this phase.
Fortunately for us I stand and listen
to Mark's plan to continue to work and
in nine fifteen in Nov thirtieth one
hundred fifty you finally published
a final paper on generative eighteen and
just just the forty just after he sent
the paper to the Journal to the pushing
Academy proceedings you know to our
knowledge I'm a fellow who is on the right
hand side appear Arnolds I'm a fellow was
a leading theoretical physicist in
Germany at that time I think really
many many of his students I forget called
the order of a dozen got Nobel Prizes.
So you know what I stand orders
are much else saying that
during the last month I experienced
one of the most exciting and
most exacting times of my life true
enough also the most successful one and
then he went on to describe how he has a
new T.V. or space and time in gravity that
actually gravity is absorbed into the very
Can very job meeting of space and
time continuum and then in this new
theory he works out Barbe it up but
acutely then there are certain and
normally sudden unexplained future.
This America you are a bit that is
naturally explained in the new T.V. Some
of it was very surprise because Einstein
was never given to sort of such exuberance
it was not quite cork quite a conservative
person in terms of his communications and
so Einstein I'm so
some of it wrote to him.
About well really.
And then I science reply came which
is very uncharacteristic with this
February eighth of nine
hundred sixty two was
of general theory of relativity you'll
be convinced once you're separated
therefore I'm not going to be going
to defend it with a single word.
And this really is I mean some might
sound arrogant but it really is true
that those of us who continue to study
handstands generally tutti a century later
have the same feeling that it's
just magnificent theory and one for
once one started says one understands
all its beauty and audience step.
So what is generally true so
here is one slide of general activity
explaining the basic ideas
the first thing is that you know
since a historical Stein that people
had interest idea of the space and
time and all of it is space and
time there in the background.
And everything else like
the planets the fields you and
me we all just live in this background
of that girl is necessary space and
time is necessary for
us to to do to function but
the idea is that it is just an arena
it's a stage on which things happen but
in general activity this space and
time and the geometry of space and
time itself becomes a physical entity like
this table like this microphone like all
of us so matter can actually
act on job metry of space and
time and jam it your space and time can
act back on matter so it really becomes
a physical entity in this particular
way in this in this precise sense and
digital feel is that's encoded in
the very geometry of space and time.
And this is very this is possible because
they still force as opposed to mileage
force are the fundamental forces of
nature that weaken the strong force
is in fact has a property
that it is omnipresent
in other words is everywhere in the new
US It doesn't make you know it is not that
you can actually gravity like you can
see like trick and magnetic fields and
it is not discriminating in the sense that
guy would he accept everything in the same
way it could be a cup a ball it could be
a gold ball it could be some other kind
of material gravity will act
exactly in the same way and
therefore job made trees also all around
us and therefore I would be being.
Present and being not
discriminating going to be absorbed
into the very geometry of space and time.
And as I said before that there is
interaction between matter and and
geometry matter tell us how to how to
spacetime how to curve how to bend and
spacetime tears matter how to move and
join me trees here intertwined with matter
the Einstein's equation this picture here
is a standard depiction of how a mass your
body in this case a Sun say is actually
bends space the geometry of spacetime so
actually spacetime is not flat I don't
sun but it is actually bent up there and
that ball that you see up there is for
example a planet like Earth and
that actually actually moves
in the school geometry and
actually in the school geometry it is
trying to do as straight as it can in
a precise mathematical sense geodesics
is really trying to state is it can but
because the job may teach Salafist
this the parts upshot is distance
the state despite sort of say appear to be
curved with respect to our lip tic with
respect to the Newtonian picture of
space and time that was years before.
This idea of encoding Johm it
gravity into Jummy tree is really.
Anybody beautiful is really very
fundamental and therefore for
example had a man while he was a leading
that a magical physicist of the first half
of the twentieth century you wrote
it is as if we generally Timothy It
is as if a wall which separated us from
truth has collapsed why did expanses and
greater Depp's are now exposed to
the searching knowledge regions of
which we have not even a place and demand
things that when you want success Specter
nobody has he wants us to have suspected
and suddenly some do it was some cult and
was and he was drawn and
suddenly the truth was revealed and
here is what a man named John checker when
I was a leap astrophysicist of the last
century has said about gender in the tutti
he actually turned out I was a very
well settled person who was interested
in music literature Scott and therefore
when Henry Moore who has a very fantastic
sculpture as many of you may know on
the campus of University of Chicago
we see Ted in us of Chicago Chandra
asked him how once you just see
sculptures you don't see it from
far from the bar and most response was
that the greatest sculptures can be viewed
and indeed should be viewed from all
distances since new aspects of beauty
are revealed at every scale and
more than cited examples of sculptures of
Michelangelo as example and this is Peter
which is really famous cult sculpture for
which it really is true that at every
angle at every distance that you see you
aspects of beauty are even and that is
really true gender on the T.V. all of
us who work on various different aspects
would be mathematical last this could
be more applied aspects of complication of
relativity looking at the course Maula G.
at the uni was as a whole or a great
addition of ancient black holes colliding
we continue to discover new
aspects of beauty as we
explore the consequences of
gender maturity so these are two.
You know like an evolution
that are good and
indeed since then it has been generally
curiously successful in the whole arena
of new words of our customers as for
physicists astrophysics for example or
here what you see is a black hole in the
center of our galaxy yet is for example.
A creation in of matter into a black hole
and saw that a guy recent lensing or
there there is actually a proof of the
first proof of privations waves which won
the Nobel Prize for Hudson Taylor and so
on so general it is not only beautiful but
it is applicable to a huge other
way of phenomena you know Universe
so this is the first part which is
discovery of generality Vittie how
beautiful it is how deep it is what I want
to do in the second part is or tell you.
What that placation of general
relativity is to a small A-G..
So it was again Einstein's
incredibly bold idea like Newton's
great bold idea was I mean it's There
was a breathless right that you
thought that if I throw a ball appear
that the trajectory of that ball
the that actually meet the description of
that ball is not different from the moon
that is going around the Earth is exactly
the same law that one can extrapolate from
this very strange phenomenon to the Cosmic
to the planetary phenomena Einstein when
he actually had the had the boldness
to really extrapolate it
to all of possible US not just
the planetary system not our galaxy but
all of Cosmos and Einstein just applied
his only creations Einstein's theory of
generative ity to the entire cosmos So
what happens when you do that.
Or what happens is the following that
Einstein to question basically tell us.
How space time curvature Cook is
related to the matter stress and
cancer so because of this it tells us
that geometry is not in the thirty's
not static it is not us but can be
influenced by matter and because we got
matter in the new words the idea is that
geometry is dynamically changes in time
space time that geometry the distances
angles between things that are not fixed
once and for all but they change time and
observations tell us that you
knew was that a sufficiently large scale
is very homogeneous and I saw tropic
there is no preferred place in the any
worse than not a preferred direction and
if you like this the grandest realisation
of the company has principles.
And if you combine these two things
then I started to question tell us
that John metry is the.
I am Mickle and is related to matter and
that in fact the universe began
with a big explosion was a primordial
exports explosion about thirteen point
eight billion years ago so
this idea that geometry is not static but
is act upon by matter you know precise
of a cover instance a question and
the symmetries that we observe of them you
need the worst to tell us that Big Bang is
inevitable so here is a picture of the Big
Bang on the on the right hand side up here
OK but now I'm going on in Iraq myself
because this is something that we know now
but this is not something that was
known in the early days after Einstein
discovered general Nativity and he applied
general maturity to all of course most
in fact thought that the it was
a static it was not dynamic and
that therefore he introduce a so-called
cosmological constant which creates
the repulsive force which is supposed to
balance that attractive force of gravity
and thus make a universe which is static
at the same time there is another
that's physicist mathematical and
physicist in the center you also have
a more than a few words in which there
are no big bang in us us no beginning nor
end no singularity but then US or sort of.
Was always finite and went on to
all the time appear in both these
models the US are sort of his specially
compact interrupt having like a U.
plane Euclidean plane it was more like
a sphere like a surface of a ball but
in two dimensions three dimensional
sphere but then that changed so this
was in nineteen seventeen that changed
with the with the Russian mathematics and
I asked an astronomical
freedom Friedman and all and
a Belgian physicist Metra the matter
was actually Jesuit priest but
he was really very very well trained and
very astute and
very deep with respect to
his discoveries in physics.
He really understood the idea of
Einstein's equations and applying them
to the universe very very well from
the point of view of an astrophysicist and
then they what they found was that
the universe in fact isn't so they found
a solution of my stance a question this
also solution of my stance equation but
as we'll see in a minute that it has
some problems whereas this solution of
Einstein's The question was was was
then found and this origin of my
stance a question is such that this
is a depiction time is running for
the future this if you like a little
circle here is like the you worse and
this in you is expanding very rapidly and
therefore if you go back in time you were
sort of said begins here with a big bang
saw these solutions have
a Big Bang singularity.
So this is what happened and
then the statement is that for
a number of years which is surprising to
most stories but for a number of years for
several decades people actually
continued to believe that either
to work with either Einstein's model which
is static Einstein model had a matter but
it was time independent because he thought
the real universe was like that and
aging and this it a model there was no
matter and the US was still dynamical and
therefore after Eddington who was
the president of the British Royal Society
of astronomy he in January in nineteen
thirty had a meeting in which I asked
well why do some thing neither of those
two models are actually satisfactory so we
put a little bit of motion into Einstein's
the world up in the earth matter or
shall we put a little matter into
this it does premium or by you know
like a premium abide because no matter and
yet he was also first contracting and
then expand these are genuine solutions
of Einstein's equations but the state
is that they don't really describe the
world as we know it at this time limit or
wrote a letter to the Addington
saying that well but
you know this problem was already
solved by means while ago and I went.
Sent you a paper explaining what happens
that in fact the US begins the Big Bang
it is dynamical etc and then Edington took
it seriously and after that the people
started paying attention to this big
bang there's also the big discovery of.
Hubble who found that he knew
what is actually expanding and
with does discovery then Einstein dropped
his idea of a static universe and
embraced this dynamic and
universe of freedom and matter.
Now but the point is that what exactly
does the new US look like whether in fact
there is a big bang or there is no Big
Bang is part of the fact that these things
were very well I know lies that continue
to be a debate for several decades.
Jargon got more ought to pop up by George
Gamow as a physicist Russian physicist but
working in the United States and
you know what to do to Pope Pius saying
that well you know Einstein's equations
General Electric game of modern physics
is telling us that the US has a finite
beginning or Piestewa was very excited
because he thought it really confront
Bible and but then again Edington.
Metro had the great grace to go and
tell the pope saying that no we
should not mix science and religion let's
get them started separately and after that
incredibly the pope actually there were
repeated this and the Pope actually said
that the two things are coming together
in a big conference of scientists but
after that there are other conferences the
Pope and there were repeated so limited
has the distinction that he corrected
the pope and he characterized time.
That there are also Soviet program
much later in the late fifty's led by
the leading physicist land lived his in
the land and left his cities left his
Kalashnikov and others to say that in fact
the Big Bang is a something which is very.
Spatial and he said so
listen up by science a question but
in the real universe it is
really because of symmetries
that you get something which is
a infinity the big the big big bang and
that would actually go away in a general
solution of my stance a question and
similarly the British School really that
big bang was not really satisfactory and
in fact the US should I be
a steady state universe and so so
they were all these ideas
that were floating around but
really what changed from physics and
ice to takes and
philosophical can so what change from
mathematics and I stood next to physics
is really the following two
things The first is that.
Nucleosynthesis you see how one of the how
we are made up of items all atoms and
nuclear So there are these nuclei come
from where does this atoms come from so
the idea was that well.
That in fact these atoms are in stars
the stars are like over in Star extremely
hot because actually fusion as you
probably heard of it because fusion of so
you can a simple hydrogen atom and sun is
kind of what into our heavier Hellyeah
matter and then that and this nucleus
process actually keeps continuing and
more and more heavier atoms are bought.
But then when people get precise
measurement they found that while there
are enough stops to actually account for
the observed abundance of heavy
elements like iron gold copper etc If but
the lighter elements of the hydrogen.
Lithium etc There are but most could
not be expected about could not be X.
explained by just looking at the stars
those all once are not enough to create as
much highly Hey Liam and lithium and so on
the universe as it was actually observed
and therefore the idea came that maybe
there are another over and in the universe
a hot phase of the new words which
are very very early on and then
this was really the big bang where in fact
the U.S. was supposed to be very hard.
And this is the first idea that came from
physics and the second idea was that there
had to be a cosmic microwave background so
the idea that the only you knew was in.
The matter and radiation were kind of in
equilibrium as the new was expanded it
cooled and then they've matter and
radiation fell out of equilibrium and then
at that time the radiation could travel
freely and that is what is called a cross
make microwave background and it surrounds
us and it destroys something that was the.
Actually did and
from nine hundred sixty five onwards
Dickey people are all in Wilkinson really.
Worked out this theory about and
and observations about this nucleus
about this quest make micro back up so
these two physical facts change our view
of the universe was Universe was
not in a steady state it really had
a hard beginning it was was really
dynamic it is the ruling and so.
So now what we look at what what what
I want to now look at is the following
something spectacular happens so
this decoupling between matter and
radiation occurred when the you were so
this is again time and this is space so
this decoupling occurred very early on
in the US becomes transparent that is
when the new was about three hundred and
eighty thousand years old.
Now the US is fourteen point four billion
years old so this is really happening
a very very early it was when the US was
very young but this four times I've been
traveling all this time and they can
actually be detected our earth and
that is what actually has been seen with
this cosmic microwave background and
there's been a spectacular success or
the past two decades and
there's a powerful interplay between
theory and high precision observations
especially through the space missions and
this space missions are called.
Planck.
Map and blank so these were satellites
which were sent out which actually
studied the cosmic microwave
background and its properties so
these are just pictures about
the first satellite the micro egg of
the globe in the Mike cosmic
microwave background Explorer and
the second one is called
Wilkens Wilkinson Microwave and
I sort of be probably map and
then more recently
that has been the Planck satellite which
was launched in two thousand and nine and
it releases first data in two thousand and
thirteen and then this is the head.
Lines from New York Times which say
the astronomers release the letters on
the most exquisite baby picture yet
of the U.S. on Thursday and songs of and
then the the last data release was
done in two thousand and fifteen and
that is due to us not the most accurate
picture observations about the universe
so what is happening with
cosmic microwave background so
the cosmic microwave background what we
learned was that the you knew was was
extraordinary homogeneous in the early
phase so it was really as the better had
any sage is extraordinary homogeneous
except for some tiny fluctuations and
these fluctuations are you know one part
in ten to the fired one hundred thousand.
So when they knew was Austrian
eighty thousand years all
they knew was an extremely homogeneous as
limited ice and decision and in fact that
it isn't was really perfect blackbody what
temperature I seen today after the cooling
of about two point seven to three
degrees Kelvin and keep this explorers
of course the satellites that I showed you
were tied they actually if plotted what is
the distribution of intensity what's
its frequency and they really had this
beautiful plot which is really foremost
a black body very very accurately.
So.
So now that one more interesting thing
to me this is kind of makes life so
fantastic I mean I mean we start
when you knew was only three hundred
eighty thousand years old it was
almost homogeneous except for
this tiny homogeneity of one part in
ten to the five very very small and
then what you can do is we can use our
known physics and astrophysics that
the laws of that who are very established
to say that well if in fact early on
there were these tiny fluctuations
what would happen to them today and
basically you know wherever the universe
is little more dense more matter flows
in doing that ever it is less little
less dense matter lose that area and
goes to places where that matter is more
dense and their force structure is forming
and this is kind of the picture of
the kind of structure that we get and
the point is that really our known
physics us and with computers and
simulations with starting from these
initial conditions we arrive at a picture
where the new Was looks like back and
this picture is something that is then
a five observationally
these are essentially this
picture that we actually see and in fact
we know how to go from here to here so
it's fantastic right the large scale
start of the universe is traced back
to the time when the union was quite young
This is today this is when the new muscles
quite young and these are to triumph are
generally pretty and all of not physics
again I like it does our knowledge if
you're here in a thousand years and
you have you why did by the get
an eight just fourteen point four
billion years you get a number and that
ration number is the same as a one day you
wanted to hundred years so this means
that in human terms if you Alice
knocked out of a baby one day after
the birth supporting We had our
science you know our food your knowledge
of microbiology by chemistry understood so
deeply that I could just
put in this picture and
outcomes become computer systems spits
out what the person would look like when
the person is a hundred years old imagine
a home no need to know and that is what
we know of any worse is the baby any worse
this is the hundred year old he was.
That I think is something spectacular We
are very lucky to live in such a time that
we understand so much but of course
physicists astronomers astrophysicists
I'm never satisfied we understand so much
but then down ask Well yeah that's nice
very beautiful that we can come from year
to year but they did this come probably
So this is what people I didn't know
what about in the last few decades and
this is what I would like to tell you and
this is the inflation which is the origin
of the lot skin structure of the US so
they did this they did this.
We want to know where did how did this for
two nations find the kitchen's or
the can it how did they come about.
So.
Now is the first time then
quantum physics becomes essential
in what I talked to talked about
before kind of physics is used but
it's not going to be essential but
now it becomes essential.
So.
So far we apply generally
to your cosmology but
ignore the fundamental counter physics and
this is justified because we focused
only on the Alaskan structure and
you can order what happened
in the early era before the new US was
three hundred eighty thousand years or.
But it does provide a real understanding
with but but this does not
provide any idealized standing of the tiny
home which it is in the cosmic microwave
background itself and we just have to
accept that these students existed and
use observation to tell us their
properties and we made subsequent
calculations as to what happened to
the US So the issue of the beginning and
the origin was pushed back but only to
three hundred eighty thousand years old or
go everybody in the universe was the end
eighty thousand years or but what
we're not going to do is what we want to
push the issue of origin even further and
here we did quantum physics and
this is the idea of inflation the idea
of inflation in the following.
That soon after the Big Bang they
knew was so the idea is that soon
after the Big Bang they knew most of the
extremely homogeneous and isotropic and
it went underwent a phase
of private expansion.
And the point is that at the onset of
this phase they knew was completely
homogeneous completely
homogeneous except for
quantum effects you see
the mechanics is fundamental and
what car mechanics introduces is so called
Heisenberg Uncertainty is you cannot
measure all of us to arbitrary accuracy in
the beginning for example if you take the.
To manage the creel classically I can
measure the electric field a magnetic
field arbitrarily accuracy but in quantum
electrodynamics if you bring in quantum
mechanics into it then the statement is
that there is a fundamental uncertainty
I cannot simultaneously measure bought
the uncertainties are small therefore in
everyday life we can ignore it but in fact
there are fundamental and seventy's which
really prevent us from measuring electric
and magnetic fields identically so
the idea here is that you have some
quantum describing so to say these
fluctuations in the microwave background
they were really in a vacuum state so
vacuum is has as good as you can get to
perfect what you need and I saw probably
but it was a quantum vacuum and condom
vacuum always has any fluctuations which
you cannot remove just not possible and so
this tiny fluctuations where there so if
you like then you also I should probably
get homogeneous as much as it could.
As much as Heisenberg would allow it
to be and that is what happened so
we just assumed that and then the
statement is that the end at the end of
inflation with this idea that there
are only vacuum fluctuations we produce
a spectrum which looks exactly like
this so thus there is a new course for
Genesis and the new origin of
the structure of the universe and
the new origin of the core structure
of the universe is quantum nothingness
the quantum vacuum the fluctuation
the condom vacuum produced all the Alaskan
structure in the universe this
sighting is again pretty boring pretty
amazing and the important thing of
course is that this is something that
works in detail in detail calculations
people are still debating whether
it inflation is the only possibility but
that inflation a calculation give us
a structure is not something that
is that is that that is debated.
OK But now again we might say that's
great you know you we understand
what has happened because inflation
really the answer up inflation or
soon after the Big Bang and so
that is good but the point is the.
Or knowing that we would still want to go
beyond inflation we're still ambitious and
the idea is that.
The cosmic microwave background in which
it is a rose just from the inevitable
fundamental has and
by the uncertainties is all inspiring but
there is a fundamental problem
namely inflation I should stick so
it continues to shew me that
the space time is described still
by classical general activity and
in classical generally T.V.
If you go back in time this
Big Bang Big Bang is a time is a place and
it is a configuration in which
physics just breaks down
because I just infinities and
you cannot calculate anything so
physics just stops at the big bang and
everything i do we know in physics
today is that there were this happens it
is a signature it's a side it's a signal
that we are using a T.V. which is not
sufficiently deep which is not applicable
we are pushing the theory beyond its
domain of applicability So the big bang
is really particular generally to Vittie
in a domain where it is not applicable
because it just ignores condom physics and
we need to bring in quantum physics so
we need a complete union and
that complete union is going to gravity.
So here is a picture here's a picture
Let us first look at Explain what it
is and run the simulation once again so
in flesh in this sort of scalar field and
if you go back in time
the scalar field also rolls down a certain
potential and then I think probes
are the sort of potentials what
happens is I don't know it stop.
So I did roll down the potential
energy density in in fact on
solar increases it's very very low
in the beginning increases but
then the wall of the newer shrinks
becomes all about zero and energy and
then city becomes infinite So basically it
is the prediction of general relativity
that is infinite and rolls down in fact
the energy density becomes infinity
the wallet of the US goes to zero and
then therefore
the statement is that the predictability
of physics just completely breaks down.
So the general expectation is that it
just were pushed a little bit in a domain
where it was not it is not applicable and
we need to incorporate corner physics
also for gravity but gravity geometry
therefore also pajama tree so
the big bang is a predicts generality of
the precise in the domain of bad it is not
applicable classical singularities
classical infinities that are predicted by
Big Bang by General a Timothy out of the
three the gates to physics beyond Einstein
any Bible condom theory should answer the
question what really happened the Planck
regime what happened near the singularity
in the Standard Model cosmic microwave
background occurs three hundred eighty
thousand years after the Big Bang so
often you think that people say that about
a spectacular background is a proof that
the Big Bang occurred just not
because it occurred to you
It thousand years after the Big Bang many
things could have happened before that
we could also give Rice this
cosmic microwave background so
the question is does the content
his Does ponder physics really stop
if we went further back are you
are is there really if I if so
then there will be a finite beginning but
if the fun of physics does not stop if you
can go beyond then in fact generally
tippity is not a good theory.
And in that case we can ask what was
there before the general if you dare not
want to emphasize that this is not some
crazy idea or anything like that Einstein.
Self was quite aware of this in nineteen
forty five in his book meaning of
a relativity he said explicitly
that one man are assuming the value
of field equations Einstein's equations
at very high density a field that is just
a high curvature of space and time and
high density of matter and when
men are conclude that at the beginning
of the expansion should be a singularity
in the sense that everything becomes
infinite in the mathematical sense so
really neither the cosmic microwave
background presence nard of No I'm
not an idea that inflation works
very well really proves that in fact
the Big Bang is correct something
else could well happen and yet but
I stoop to observe the universe
as the observations tell us so
this being later last part which
is physics beyond Einstein so
we want to unify Concord mechanics and
joy and
general maturity and want to see what
really replaces the Big Bang and
can we then observationally find out
if his ideas are on the right track
part so this is the if occasion
of general nature of D.
and quantum physics is
called quantum gravity and
there are conceptual difficulties.
As I told you in the beginning in general
a typically the fundamental lesson is
that gravity is encoded in
the very Jameco of space time.
So if you're exploring the quantum nature
of gravity we have to explore the quantum
nature of geometry and then you say that
you would say What the hell does it mean
you know in this room I can
measure distances like I mean.
How can it be called a mechanic and
what's happening up here but
that's exactly what we need to do we
need to understand quantum gravity for
other students who may have taken some
advance at the graduate courses generative
it is something that is based on
sort of a specific job Mickey Kaus
that he money in Job metry and the idea
is now we need to look to build condom
gravity we need to generalize the money
John metric accountably money in geometry.
So John it is a physical entity
as we saw in general activity and
therefore in quantum Riemannian
geometry the geometry will have basic
constituents you see the table looks to
me a very smooth continuous surface but
you all know that if I put it in the
electron microscope I will see it that is
really made of atoms it has a very
discrete structure it just that our light
that I use in this room does not have
very well and which is short enough for
my eyes our eyes are not so good enough so
we need specialised moment to really see
that there is a discrete structure
to just continuous continuum
can be a very good approximation even the
underlying structure is very discrete and
just like this table is atoms
because it's a physical entity John
matter is a physical entity so Richard
has some atoms so what are these items
what equations do they obey how do
we describe and how do they fit
together to give us a continuum picture
this table that we know how that will fit
together that crystalline the interactions
between them and then we get large
objects which can be described by
smooth surfaces What can we do for
it for space and time itself.
Can condemn gravity
provide us with a quick.
Since that still holds at and
beyond the Big Bang where this continuum
picture actually test the Continuum
test and the classical ideas fail.
So these are the questions
that we need to answer.
And then we can ask the question of
when that's on them John McCrea become
important so
the geometry is kind of mechanical
then are those effects important and
then can I ignore them just like for the
stable I can ignore them but for example
if I looked at the electron microscope
I cannot so we are the same question so
there are fundamental constants of nature
which go into the guy we did he and
quantum mechanics GNC you
don't cause of gravity and
see the speed of light that go in
general a T.V. G.'s a guy with T.
and see if you like from space have
a devotee and Planck's constant edge and
go into quantum mechanics edge body just
as you are but apart from this constants
we can actually construct a unique length
which is given by G.H. by a poncy cube but
when it is only about ten to the minus
thirty three centimeters and
that sets the scale at which on them
effects are going to be important so
if we had then I like the electron
microscope which is probing the geometry
in this room I can see distances up to
ten to minus thirty three centimeters
then I would be able to see that
our mix truck or the discreteness.
Now usually when you see these numbers
they sort of don't mean much to people who
are not used to them so let's do
the following let's take the elementary
particle proton proton is a fundamental
new component of a nucleus
which we did not meeting as being
a tiny tiny seed use it in Exodus and
sun so how large the proton
compared to the Planck length
then areas of the program is about
ten to the minus thirteen centimeter
that is what if I think the ratio I
get into the twenty so the proton is
a huge astronomical object if I were
to think of Planck length with this.
It ought to be huge just a logical object
this is really a blank slate is really
tiny ten to twenty is a huge number so
so in the twenty years the US budget for
ten million years at the night
two thousand and seventeen level
is two thousand seven hundred or
one thousand trillion dollars So
we need that you know two to two to
make it so this tells us how tiny
Planck length case that you can
compare to a profit on it is so tiny.
But it comes to forefront at extremely
high when the space time is curved very
very much for that matter density really
is very very high then the statement
is that generally today phases and this
kind of geometry effect become important
it does not matter density is only a Plank
Length simulate is a plan density and
it is about ten to the ninety four
grams per cubic centimeter and
just to tell you the nuclear density you
know there are these neutron stars that
you might have heard about with the like
a discovery that's the densest matter that
we know there's about ten to fifteen
grams per second per cubic centimeter so
that is really a standard the eighty eight
and the seventy nine factor between these
two densities so we don't encounter these
densities and this kind of excess usually
even in the highest energy experiments and
that is why would I safely ignore
quantum gravity effects but near
the Big Bang and inside the black hole
singularities go to which it does
become so large and therefore there we
can already know already we have to
take into account condom job Miter and
change Einstein's equations or use them
on the motion of by stanch equations and
then explore what really
happened near the Big Bang and
one approach to this problem of quantum
gravity is called Loop Quantum Gravity
it is really you know followed by by
several groups all over the world.
There are about two hundred fifty
three hundred searchers about two
hundred fifty gather to two hundred to two
hundred fifty gather every two years for
international media OK so.
The.
What what is the hallmarks of look on
the gravity it retains the Einstein
fusion of geometry and gravity but
uses quantum geometry instead of
classical geometry that is used for
Einstein So
the idea here is that continuous
spacetime is only an approximation.
And at a fundamental level not only
is a matter quantum mechanical but
spacetime condom Xpress time job metry is
also on a mechanical right from the books
of the same continuum is an approximation
that you marriages later and
bad new mathematical and
conceptual tools are therefore needed
because if you want to deal with the
spacetime continuum this is what was done.
And the idea here if you like
the atoms of geometry or of the fabric
of space that constants out and these
are very detailed that you people and
yesterday all of this mathematical
theories will build what is required so
these are very detailed theories
that the fabric of space time is all
one by one dimensional contacts so
the fundamental constituents of Jamey tree
are really one dimensional and really
give this example yesterday which is that
it really is like my shirt right if you
look at my shirt it looks like a two
dimensional surface space looks like
a three dimensional continuum appear but
the space but should is really all
one by one dimensional threads
that are just old closely packed
together that for all practical purposes
it looks like a two dimensional continuum
Similarly the job meter in this room looks
like a three dimensional continuum because
we're not looking at the microscopic
structure of the microscopic structure
the fundamental accelerations according to
look quantum gravity one dimensional but
they are just packed in a coherent way and
very very dense way to give us this
continuum picture which works very well so
long as you don't probe what is happening.
At the very high covered but of course
if you want to know what happened near
the Big Bang then if you like that
knowledge of this fabric is the fabric
chaos we cannot describe anymore
what is going on in spacetime
geometry using Einstein's continuum we
have to look at these building blocks and
these building blocks are these
one dimensional fibers and so
the question of blue quantum guy would
you did not break down because they
refer to this fundamental
building blocks and
major departures from Einstein's
equations near the Big Bang but
what is the matter density is only about
ten to the fourteen to the transplant
density generally Judy starts becoming
an excellent approximation so spacetime
continuum of generality of details but
the contents have a precise well defined
behavior that is given by the equations of
blood quantum gravity and Condor physics
does not stop the condom gravity questions
tell us that there was no big bang
all physical quantities remain finite
space time curvature for example is.
She's about ten to the seventy eight
times what it is on the surface of
a solar mass black hole but is finite that
thing becomes infinite eclipses I mean
predictable there is no problem so here
was a cover story in The New Scientist
basically the idea is that there is a
previous branch of the universe which then
bounces up become big singular
it actually bounces back and
becomes and I walk around
the branch of the universe so
here is a picture again look around
I'm gravity what happens again
when I got this scalar field which is
going down just like in the other case and
now however the matter density as of now
are going from like the left instrument so
you like to left from left to right but
the matter density however becomes
immense finite so matter density of the
world as you can see European It actually
remains finite it doesn't blow up
it's a maximum power point for
the one planck length preplan density and
then again it becomes very very low yet
again you know what is going back in time
and it does not does not stop the volume
does not become zero it really
becomes some finite volume up here and
then the universe actually bounces.
So if you like this is going back in time
if you are going forward in time the U.S.
is contracting it contacts to
a minimum radius not zero and
then expands out to infinity so this are
the predictions of new quantum gravity and
the quantum cosmology yet again I have
written those predictions on them
John metric what happens is that basically
coming from past to future in general
a T.V. if they knew was of contracting
bitter collapse and make a singularity but
now there's a new repulsive force which
is of quantum mechanical origin which
actually makes us bumps in the standard
condom a car in the standard
gas mask a marvelous us bounces and
the pretty big the people Big Bang
branch is joined to the post
Big Bang branch So this is the.
This is the P.-P. Big Bang bike
that it was big like a branch and
here the quantum tunnelling like
which actually joins them so
cosmic microwave background and the
inflation is an effect we can reproduce
the ideas the results of that are up and
then you look one of the smaller G.
and therefore the statement is that to
assume that Einstein's theory is correct
all the way to the singularity it just
not tenable and if you do there is
that expected placement which does not
contradict any observations that we know.
OK so now all our models done so on one
of the examples of that So this is not a.
I mean one might say well this is
something weird really what this or
the mechanical force being so strong but
in fact all of you who know about neutron
stars the due to exist because of
a quantum mechanical repulsive force
in classical generative they are classical
radio was neutron stars would never exist
because I return pull is too strong
they will collapse to a single but
when the mechanics come into picture in
that case because the neutrons are from
yards there is a sort of in the pulse
of forces going to mechanical logon and
that creates these objects so these are
these used in our objects in sky which can
exist because of quantum mechanics and
we're seeing similar thing repeat
at the level of the Big Bang OK
now what we have done is
a condom drive to completion information
the Big Bang singularity of the early T.V.
state in the look of the smaller and
is replaced by the big bows they're
all physical countries are finite and
there are certain observational
consequences I would NOT going to too many
details about it but the observations from
plant mission shows certain anomalies
which are not explained naturally by
standard inflation and now the work is in
progress to show that in fact these can
be naturally explained starting for
the front from the Big Bounce of quantum
look out of gravity as opposed to.
Just assuming that there is a big.
Back OK.
To summarize.
So gender maturity is a deep in matter
of the city conception of compact and
supremely beautiful and it accounts for
many many astrophysical phenomena so
this combination of aesthetic
beauty mathematical elegance and
such huge applicability makes it
very attractive very beautiful.
In cosmology we apply
just permittivity and
then the statement is that a given Dobbs
or tiny intimate unity is the cause
microwave background of the younger
new words generally typically and
known successfully predict the scale
structure we are observing some thirteen
point eight billion years later I'm adding
to the end in a thousand years or so.
However generally duty is incomplete
because it ignores Karna physics
that is crucial in the early universe
is predictions that the Big Bang
is the beginning cannot be trusted so
I hold to the topic of the start
is really our original space time and last
can structure and the statement is that
there are Judy says that the origin is in
the Big Bang but that cannot be trusted.
Furthermore the last year structure is
something that we can in we can understand
using quantum physics the Impreza
says over the past two decades
how could by taking into account
on the physics of course tickle
classical spacetime inflation leads to
a successful paradigm to account for
the tiny fluctuations that are in
the cosmic microwave background
that generated the needs a seed would
lead to the large scale structure but
because spacetime is Classical the big
banks in Europe could still persist and
physics just not does not stop there for
conceptual coherence of fundamental laws
we need and even grander deeper
theory from which generally tutti and
not quantum physics emerge
as limiting cases and
this would be the theory of quantum
gravity not have a complete and satisfied.
The theory of quantum gravity but
there are very very and there are some
candidates and I use the subs described to
you when I approach which has had a lot of
success look or no gravity if you look
at them gravity quantum matter as
well our job metry sorry matters but
our job our economy conical from start and
Einstein's continuum is an approximation
that works in everyday physics but
breaks down near the Big Bang but
look what I would get does not break down
there is no initial singularity the Big
Bang is replaced by Big Brown big bones.
Brand new physics in the Planck regime
appears which is can you worked out in
detail and provides or even completion
of the inflationary paradigm and
there is a writing radical change in
the issue on the issue of origin and
as a matter said scientific
progress is discovery of more and
more comprehensive simplicity and if you
go back to these three transferences
then you see that Bohr and
more comprehensive call reading more and
more phenomenon and
also increasing simplicity.
Those of students and so on what
interested many semi-popular articles and
also videos at this website is for
these two different
collaboration across most and their
website is guy with dark P.S.U. Doc edu.
And it has concluded with a quote
from Heisenberg who started work on
quantum mechanics.
And this course of all.
A really new field of experience
will always lead to crystallization of
a new system of scientific concepts and
laws that is what happened in each of the
epics that I told you about prospects and
like you do generally duty to
inflation to quantum gravity
then faced with essentially new
intellectual challenges we continually
follow the example of Columbus who possess
the courage to leave the normal world
in an almost insane hope
of finding land your again
beyond the sea and this is what I
stand did and you wonder we are No but
none of us are in any way comparable to
a strain that is a goal that we have.
Thanks
no because this really is something that
becomes important only when the space
time coverage is very large as soon as the
space time code which is a matter density
is less than about ten to the fourth it
can do the minus fourteen to minus five so
about a hundred thousand of the plant
density ten days out of these four to
become negligible is not a postulate it
is a piece of something that comes out of
the theory whereas in this bigger tractor
and so on the matter densities are nowhere
around there and therefore this conduct
is it is not really that important for
that that there could be other
classical explanations of that.
Well thank you for that wonderful talk
my question is What role do you think
information plays and Loop Quantum Gravity
I'm thinking of thinking starts papers
about the universe being a natural
Quantum Brain slash quantum computer.
They information is playing a role mainly
in understanding the following question
at the fundamental level the part
of John McCain is very discrete and
it doesn't look anything
like this continuum so
the question is one of the stage in look
when I'm driving which correspond to this
continuum up here and their ideas of
entropy and entanglement entropy and so
on coming to the forefront and the idea is
that this is not something that is proof
but a lot of progress has been done the
country that was put forward by Eugenio be
Anky and other people are working on
it now is really that if you have
states in which there entanglement Entropy
goes like area so in other words and
entanglement probably is that you're going
to some system and you need a subsystem so
you take a subsystem and area in which
is that subsystem is cloying closed
I study the entropy of this subsystem and
take a minute probably goes like the area
which separates the two then those states
of the seven classical and there is quite
a bit of a you know support for this idea
and that is what people are falling so
that is one very very concrete thing is
one of the leading things that people
are doing now.
Professor I have a question you
know you said something about
explaining I mean basically can
quantum fluctuations in the mak you
be considered a quantum
fluctuation in space time and B.
and then you know that is
actually gravity which G.R.
actually says that it's the curvature
of the questions so I'm like OK so
the question is whether contemplate
your sense and matter can somehow.
Intervene to pray to discourage other
spacetime and therefore their religion
is really manifestation of constant
quantum fluctuations of matter
that's a question and the answer to
that question is No that's the quantum
fluctuations due to matter really
don't curve the spacetime very much so
very very little except in the very early
universe that is that's very different but
in the everyday you know
like like around the sun
in the space time is actually curve on
the fluctuations cannot really account for
that I guess you had another question
which was what which was that
I am saying that in the detail so
the question is that
the magic of space time according
to Einstein theory and do for
you is just a matter that for the quantum
fluctuations of matter can account for
the Go To reach of spacetime which
then gives rise to gravity and
I'm saying that no those effects
are calculated and that extremely small
they cannot account for the gravity for
example on the sun the bending of.
Sun So this garden fluctuations
are really important in extremely
extremely Jeems and not in not even our
own neutron stars that anybody's way
could you try and how this relates
to the idea of a multiverse.
So it's a little bit difficult because I
don't understand the idea of multiverse
this in the sense of but I'll try so
the idea of a multiverse is really that.
That they can exist diseases of space of
space time which really don't communicate
with each other and therefore they are.
They can each of them can be thought
of as a universe in its own right.
But in this pictures that we have you know
with the initial conditions we gave and so
on we don't find that OK So
very often people say that during during
inflation and so on somebody could
inflate the region could inflate then
they would draw proper spacetime diagrams
that all the risks are cool diagrams in
which one has a nearly a bubble growing
up here and like a tree like structure or
bubbles and balloons so what I would
like to know causally disconnected me is
that one should write a lead role proper
spacetime diagram technically called
Penrose diagrams and really find out who
they communicated in our communicate and
I don't see any really.
You know that expect because of that.
Another way of looking at multiverse
is that it is a fact that if there is
a positive causality a constant as we seem
to have then there are regions of space
normal There are reasons as some some
observers will never be able to see even
if you live forever you know to be able to
see some other part of the spacetime so
you could call that is my new worse it is
another you observe what here there is
that person to new worlds and then then
the goal communicate with each other and
you can call that might be worse but then
such things going to be easily put in one
space time and we just say it's a fact
of life that one spacetime one observer
even if it waits for ever there's
a sea of any worse and there's nothing
fundamentally wrong with Jack So this
really does not tie in with my divorcing
So I think this would be naive but
maybe related to the multiverse
question if you if you go deep into
deeper time before the Big Bounce What
are the equations predict.
A billion years five hundred
thousand years what is happening.
So the way that we can do this is
really take the data say at the onset
of inflation and he wandered back in time
and the statement is that we don't see
anybody worse we actually have a signal in
the same sense that I was saying before
there are regions which causally
do not talk to each other but
they are all part of the same OK
they're not OK good good good so
what we say in this case is that
in the past the union was not
really how much of a structure so
it really does bounce is a post bonds.
Phase is what is really creating this
large structure before that everything was
very dilute and there is no fluctuations
but they're very small they were there
they don't go into some structure and
the like that and it's really these bonds
which does something to this I mean we
know what but are difficult to translate.
Since simple words it is bounce
which creates this this more
now this is a statement about particular
states I'm not saying that the theory
does not have some states in which in the
past it would be something different but
what we have done is well I mean stopped
they kidding about what that could be
would take the state we know to be
correct today and we've got it in for
Howard I mean you all week from back all
of this time we come to inflation and
we further back the questions
around break down and
therefore we just see what happens so it
is something I mean a lot of work on this
because somehow How does this I mean
that I simply time are symmetry that is
the past branches very different from
future Brown is a property of this
particular state it is not you know it's
not sort of fundamental property of the so
this is the universe we happen to
believe it so that is a prediction.
Thank you for the question
because people are really place
so the statement is that the.
Is really like Initial
the loss of the I mean.
The statement is that so the question was
in the classical general actually forget
about quantum effect there is a big bang
and then you will start from there and
expects pours out and the question is
Where did the energy come from and
the point is that it is very difficult to
answer that question because we started
the singularity events everything
is infinite sort of say so
if you like Soon after
the Big Bang then this is Galaxy
these elementary matter if
in classical physics terms
you get huge velocities they're
bored with this huge losses and
so that is the initial
condition of the universe so
it's there's no explanation for
the initial condition of the universe and
then the big bang because it really you
can't even properly give the initial
conditions at the Big Bang Big Bang the
big bounce again because it's finite but
the big bang because it's really
everything is really infinite there so
you just think of it as a you know I.
I saw some awesome water filling
the balloon or something and
I just loitered the balloon burst and
the water just split
comes out of here now where the energy
come from well I mean is the initial
kinetic energy is what is in any
propelling it that is what is happening
thank.
You.