time
so good evening i'm robert krollwich
no i'm brian green and i'm going to give
a bit of an overture to some of the
ideas in this infinite worlds program
that we're going to be hearing about
tonight
and one way of framing
the discussion the conversation is to
recognize that over the past few
centuries our understanding of the
universe has really increased by leaps
and bounds i mean the festival programs
over the last few days cover a tiny
fraction of the tremendous insights that
we've been fortunate to achieve
but there is one
unexpected
perhaps
implication of the insights that we have
found which is that we have gone through
a kind of demotion our species has kind
of been sequentially demoted through a
variety of the discoveries that we had i
mean you think about it a long time ago
right we we thought the earth was the
center of the universe then people like
copernicus and galileo come along we
recognize no the earth goes around the
sun but we thought the sun was the
center of the universe but then we
realize the sun is one star
out of perhaps hundreds of billions in
our galaxy and then hubble and others
come along and we realize that even our
galaxy is just one of many many galaxies
what we're talking about here tonight is
perhaps one more step in that kind of
demotion from being at the center it's
the idea that perhaps our universe
is not the only universe perhaps there
are many universes we are just one of
them the image to have in mind perhaps
is as if the universe is a big cosmic
bubble bath with all these different
bubbles being different universes our
universe being one bubble in the entire
hole so what i'd like to do in a few
minutes of preamble here is give you a
sense of the essential ideas that lead
up to this kind of notion and then we
will follow it on with a panel
discussion where we explore things in
more detail now the key
physics
the key physics behind all of this
is the physics of gravity
so let's start there so gravity we all
know newton gave us
a way of thinking about gravity way back
in the 1600s he basically wrote down an
interesting formula an equation that
tells us that any object in the universe
attracts any other with a force the
force of gravity that depends on just
two things how big the objects are how
massive they are and how far apart they
are in space very simple equation we
teach the high school students still
today hundreds of years later and we
make use of that same equation when
we're trying to get a rocket ship to
land on the moon or to rendezvous with
some other astrophysical body so it's a
very powerful way of thinking about
gravity
nevertheless
albert einstein realized in the early
part of the 20th century that there was
something deeply missing in newton's
picture of gravity
and it was simply this newton wrote down
a formula that describes the force of
attraction between two objects
but he never explained how it is that
those objects exert that attractive
force how they exert a gravitational
attraction between them and he
deeply einstein deeply wanted to figure
out the mechanism by which gravity
operates and in a famous story he
started on this journey to figure out
the mechanism behind the force of
gravity by going to newton's principia
you know the book that has all the
results in math and physics that newton
discovered in his lifetime and
as you know you all were required to
read it for tonight's discussion
so you're all all familiar with this
in fact i was a little bit surprised
that the the brochure said you had to
read it in the original latin i've never
done that but but you guys so you guys
are a step ahead of me
so you know einstein goes over to the
book
looks under g finds the law of gravity
goes a little further
for subheading m the mechanism by which
gravity operates
and there he finds something surprising
because newton basically says i don't
know how gravity works i can write down
an equation describing its strength but
how it exerts that i don't know in fact
in his own words he said to the answer
of that important question the mechanism
by which gravity operates he said i
leave it to the consideration of the
reader
now most readers would read that and
read on einstein was different and he
spent 10 long years trying to figure out
how gravity works and finally by 1915 he
came to an answer in a theory called the
general theory of relativity and the
answer is is subtle it's beautiful
there's a quick way of sort of thinking
about what he found and it's simply this
einstein said that if you have the sun
here and the earth here
and there's basically empty space in
between them
the force of gravity must somehow be
mediated by empty space space itself
must somehow be the mechanism by which
gravity exerts its influence
and the way of thinking about that first
i'll show you a visual in just a moment
is forget about gravity for a second use
an analogy that physicists love in the
setup imagine you have a rubber sheet
stretched in front of you nice and taut
you take a marble you set it rolling on
the surface it goes in a straight line
easy to picture if i now take a heavy
object i put it in the middle of the
sheet sheet will now curve if i set that
marble rolling it won't go in a straight
line any longer the marble will now roll
on a curved trajectory because it's
rolling on this curved surface of the
rubber sheet
einstein says take that simple idea and
apply it to the universe rather than a
rubber sheet
the fabric of space in fact the fabric
of space and time all around us and he
said when our when object is in space it
causes space to curve and that way it
affects the motion of other objects much
like the curved sheet affects the motion
of the marble so to get an idea of what
that would look like if you just bring
the lights down
if we envision the fabric of space as
sort of this grid like icon this is now
3d space it's a little hard to deal with
visually so rather let's go to a
two-dimensional analog that captures all
the ideas here you see space is nice and
flat when nothing is present but when
the sun appears the fabric curves
similarly if you look in the vicinity of
the earth fabric curves around it now
focus your attention on the moon because
this is the main point
the moon is kept in orbit because it's
rolling along a valley in the curved
environment that the earth creates that
is how gravity is communicated that is
the mechanism for exerting the
gravitational force if we pull back the
earth too is kept in orbit because it is
rolling along a curved portion of the
spatial fabric that the sun creates
that einstein said is how
gravity works
now he wrote down this theory
1915-1916 quickly people
around the world began to think hard
about this general theory of relativity
these ideas and in particular there was
this
interesting physicist a belgian priest a
priest who was also a physicist who got
hold of einstein's work and decided to
apply einstein's ideas not to the sun
not to the earth but to the entire
universe
and when he applied einstein's ideas to
the entire universe he found something
very interesting he found that the
fabric of space should be either
contracting or expanding it could not be
sitting still so he envisioned that
perhaps taking one of those solutions
that the
universe might be growing in time might
be expanding
now he brought this idea to einstein
and einstein said to him
your mathematics is fine but your
physics is abominable
and what he meant by this was he'd
already been through this drill there
was a earlier physicist alexander
friedman who i just as an assignment say
he looks just like my accountant just
before tax day
and and
and and friedman had already found this
idea of an expanding universe and had
told einstein about it einstein at first
thought that friedman had made a
mathematical mistake and in fact said so
in public friedman convinced him that no
there was no mathematical error so when
lemaitre came in with the same idea
einstein would say yes the math is right
but he's saying
your interpretation that the universe
could be expanding that's just nonsense
you look out into the sky clearly the
universe is not expanding so einstein
was very very clear in his own mind
about how he thought the universe should
behave in fact so certain was he that he
went back to the mathematics of general
relativity and tinkered with it in order
to get rid of this possibility that the
universe might be expanding
what happened next is quite wonderful
1929 this gentleman edwin hubble
american-born oxford trained astronomer
examined the motion of various objects
galaxies using this hundred inch
telescope at mount wilson observatory
and found indeed that the distant
galaxies
were all moving away and moving away in
a very particular pattern that was
consistent with the fabric of space
itself stretching it's as if he found
the galaxies are kind of sewn in to the
fabric of space and as the fabric
stretches
the galaxies are all pulled apart from
one another the universe is expanding so
what this gives rise to is what we
conventionally call the big bang this
way of thinking about the universe
starting out small and growing in size
so just pictorially what that would look
like is imagine that the universe begins
really small dense hot nugget it then
expands space expands and as space
expands its hot primordial plasma in the
beginning cools down as things expand
they cool and when it began to cool
structures could begin to coalesce
structures that would ultimately give
rise to the galaxies the stars inside of
the galaxies and give rise to the kinds
of things that you'd see on a nice dark
clear night sky
so this was the picture that ultimately
emerged from this way of thinking about
gravity and the way that the universe
evolves over time
now i don't want to give the impression
that everybody immediately believed this
way of thinking about the universe there
is definitely a need to try to find yet
other experiments other observations
that would convince people that this was
the right way of thinking about the
origin and evolution of the universe and
there was one particular individual
george gamma who played a very important
role in this
george gamma is a very interesting
character he was a six foot four hulking
russian physicist who was as
quick-witted and fun-loving as he was
hard-working and he
and his wife
tried to defect from the soviet union in
a very interesting way they they took a
kayak
filled it only with brandy and fine
chocolate
and set out to cross the black sea
now 36 hours after they started on this
journey they were picked up by the
authorities they were sort of just
drifting around and it was it was really
lucky that the provisions were only
brandy and chocolate because that
corroborated the story that they were
just out sort of for an afternoon paddle
they weren't actually trying to defect
but anyway so gamow
a few years later was successful in
slipping past the iron curtain comes to
america and begins to think about
cosmology einstein's ideas and realizes
the following very simple idea
if the universe began very small and
very hot and then expanded when things
expand they cool off
that means that there should be a little
residual heat today in space all around
us left over from the big bang
and he said we should look out into
space and try to find that residual heat
those residual photons as that will
corroborate this picture that the
universe began very small and very hot
in the beginning
now it's a wonderful paper
he put it out there but he couldn't
convince anyone to actually look for
this radiation this heat left over from
the big bang part of the reason was most
scientists were focused more on quantum
mechanics other aspects of physics not
in cosmology at that particular point
but the other reason why people didn't
really jump on this at least in part was
gamma was kind of a had a reputation as
being kind of a jokester kind of a a
trickster i mean he it was once writing
a paper with a student of his who played
a vital role in this recognition that
there should be heat left over from the
big bang a student named ralph alpher
and
what gamow did was he convinced
this fella over here
not the one on the right the one on the
left he convinced hans beta to put his
name on the paper for the sole reason
that then the authors would be alpha
beta gamma
which is kind of you know passable for a
physics joke because the standards are
not particularly high
but
but it did leave people with this
impression that you know he wasn't to be
taken quite as seriously as his work
actually deserved so the paper that he
wrote with with alpha and also with
robert hermond basically died nobody
nobody really followed up on it
a few years later because you know great
ideas in physics ultimately will be
rediscovered if somebody doesn't follow
it up at the initial time it was you
know thought about this fellow over here
robert dickey at princeton and jim
peebles over here they came upon the
same idea that there should be heat left
over from the big bang they went through
a similar kind of calculation now they
were an interesting pair because dickey
was a great experimentalist so they
started to actually build the equipment
to try to find this heat left over from
the big bang
in the middle of their work they got
a phone call from these guys
arno penzias and robert wilson a phone
call that perhaps is the most famous
phone call in the history of cosmology
i guess it's not that impressive it's
sort of like being the skinniest kid at
fat camp or something like that
but it really i don't want to downplay
this was an incredibly important moment
because
these two guys who were about 30 miles
from princeton working at bell labs
using that
antenna that you see behind them picked
up
a hiss
and it turned out that that hiss they
tried to get rid of it with all the
tried to clean the equipment they
couldn't get rid of the hiss
finally they realized that this hiss
must be
the heat the radiation left over from
the big banks they called up dicky told
them they'd found this and dicky
basically put down the phone and said
we've been scooped these guys have found
it indeed they won the nobel prize for
this particular discovery so this kind
of confirmation of the notion of the big
bang was a very spectacular moment and
it also
was a key watershed because this was
when cosmology entered the realm of a
quantitative science because their
observations as well as others that have
been carried out since has been a second
nobel prize mathers and smoot for these
observations gives rise to a way to test
these ideas and what i'd like to do in
the next
transparency is show you a graph a
theoretical curve it doesn't really
matter if you understand exactly what it
means it's telling us the amount of heat
at every particular frequency the number
of photons at every frequency that
should be all around us left over from
the big bang and then i'll show you the
actual data
so if we take a look here the curve will
start to from the left go up toward the
right
this is theory this is what the big bang
theory says
and now let's see what the observations
say there'll be little red dots
and notice that the little red dots
are following right along the curve a
very impressive match between theory and
experiment allowing people to believe
that this is the right way of thinking
about the universe
now this is great but there were still a
number of unresolved issues and we'll
talk about some of the issues in just a
moment when the panel begins but one of
the biggest was when people look more
closely at the big bang theory they
realized that the big bang really tells
us how the universe evolved after it
started expanding outwards but it
doesn't really tell us what drove the
outward expansion it kind of leaves out
the bang
so the question was what's the bang in
the big bang and it's hard to figure out
what that would be normally you know
gravity pulls things inward so what
would be the outward push that would get
the universe to start expanding in the
first place now there are a lot of ideas
that were put forward on this
you know some some more convincing than
others but there were these two guys
here alan guth and andre linde also
paul steinhardt and uh paul steinhardt
at princeton and andreas albrecht who
actually came up with the answer that we
believe today is probably what happened
and you're going to meet these two
fellows in just a moment but the one
thing i want you to take away from this
slide which is amplified by bringing
friedman back into this
modern cosmologists are really happy
so anyway what did these guys find what
they found is the following going back
to einstein this really comes from
einstein himself
gravity according to einstein is not
only an attractive force newton thought
it was only attractive pulls things
together these guys realized amplifying
einstein's insight that if there's a
kind of energy suffusing space the word
field may come up in the conversation
later on if there's this energy this
field that's suffusing space it can give
rise to a repulsive gravity an outward
pushing gravity that can cause the
universe in some sense to fly apart to
be pushed apart to give the bang in the
big bang so the picture that you come to
in a framework called inflationary
cosmology that we will discuss in just a
moment is there's a little tiny nugget
that little bright area on the left hand
side a little tiny nugget of space gets
filled with this energy gives rise to
this incredible outward push causing the
universe to expand
and carry on in the expansion as we
witness today that's inflationary
cosmology now the one thing that i want
to call out here because the key thing
that i hope that you'll take home
tonight is cosmology is not a bunch of
theoretical ideas that people just posit
and hope that they're right or wrong
it's become a quantitative science so
the most quantitative way of
understanding of convincing yourself
that this is true comes from an
understanding of again heat left over
from the big bang in the following sense
when the universe is very tiny there is
a feature of quantum physics you don't
need to know much about quantum physics
but quantum physics says that there's
always a certain amount of uncertainty
and a certain amount of fluctuating
behavior happening and that would happen
at the far left when the universe is
really tiny but when the universe
expands the jitters of quantum mechanics
get stretched out and when they get
stretched out
they give rise to hot spots and cold
spots in the sky tiny temperature
differences not much one part in the
thousand one part and ten thousand or so
but these tiny temperature differences
in principle can
be measured and let me just focus in if
you see the green and yellow those are
indicating different temperatures i
actually did it in blue and red here but
it's the same thing these are hot spots
and cold spots generated by quantum
fluctuations in the early universe and
the idea is that if you have a device
a satellite over there it can measure
those hot and cold spots the light
travels to the satellite and let me just
show you in a final little convincing
piece of data what you find
here is the theoretical curve coming
from quantum physics and inflationary
cosmology here is the data
and i'll just sit back and let it go
now
this is data
that was set down 13 and a half billion
years ago
this curve
is generated by us humans 13 and a half
billion years later and the data and the
curve match to fantastic precision were
you to ask me
what the most beautiful picture
that our civilization has produced
yeah i mean certain things do come to
mania starry night mona lisa
this would rank for me among those
that's how spectacular this
picture is this agreement between theory
and experiment now the final point i
want to make before i'll be done which
really ties it into our program is this
the discoverers of this inflationary
cosmology
realized a couple of years after the
initial discovery something quite
interesting
this kind of inflationary burst is
likely not to be a one-time event
there can be many of these inflationary
bursts in fact the picture which i like
to have in mind is like a big a big
block of swiss cheese
and what i mean by that is if the swiss
cheese if the cheesy part of the cheese
is this energy that suffusing space the
idea is the cheese expands but in
various locations the energy dissipates
and creates a little opening a little
bubble that then grows over time and the
idea is that all the little bubbles in
the cheese
are different universes our universe
being one of those bubbles
that's the way in which many many
universes come out of this inflationary
cosmology let me show you a visual of
what that would look like final one here
so what we'll see coming into view here
is a misty
gas-like entity which will be like the
cheese that i was describing it's that
energy it's that field suffusing space
so here it is coming into view
the universe is expanding this is
creating a repulsive gravity pushing
everything apart but at various
locations
pockets open up regions where the energy
has dissipated and turns into more
ordinary particles of matter and
radiation so these would all be in this
picture
different universes created within this
vast expanding object we call this
the multiverse now if we go into one of
these
it looks once you penetrate it just like
an ordinary universe like our universe
so here is our universe just one bubble
in this cheese so the fact that it's a
bubble looks small from the outside it's
not it's huge from the inside something
we can talk about in the panel as you
see we've got galaxies all through here
this could be our universe now if we
exit just to take a look at what it
would appear to be in another bubble
let's meander around focus in on one if
we go into another bubble
the world the physics can be a little
bit different
the features do not have to be identical
to ours so all of these different worlds
all these different universes would be
out there embedded in this vast
expanding
gaseous realm with our universe simply
being one of the bubbles
among
many
so the idea is
if this
picture of the universe is correct and
we could
take say the grandest view of the
multiverse we would see
a vast assortment of worlds where
various nuggets of reality would play
themselves out world by world as they
evolve and change as they go forward and
back as they grow in size the universe
in some sense would be
this vast assortment of little bubbles
with our universe
being but
one
melodic line
in this richly textured cosmic score
down
my
music
uh
foreign
down
be
come on
huh
uh
claire chase on flute rebecca heller on
bassoon eric lam on flute and joshua
rubin on clarinet so thank you
uh my i'm robert krollwich the
aforementioned and so
uh i just want to just reset the stage
here because when brian does stuff like
that he does it so well
that you all go oh yeah you know but i
just want to be careful here because
very very recently for most of you
sitting here in front of us here you
thought
as did i that universe meant all that
there is the whole shebang you know
everything you can imagine and because
the universe is everything there should
be only one everything so most of us
were perfectly happy with the idea that
there was one universe and then along
comes this guy and his pictures and all
and then these other people you're going
to meet very very smart people i should
tell you be sitting here on the stage
who believe there is not one but
strangely as you've just heard many
universes so their universe gets a
plural gets an s
which is a little
odd you know uh
and even more nonsensically really these
people then insist
or propose and insist or at least
artfully describe many many many many
many many perhaps an infinite number of
universes and they don't mean you know
like an idea in your head or a
mathematical equation or an abstraction
or a logical no they they are saying as
you just saw they're saying no this is
the real deal we're proposing that there
are actual physical universes with
energy and matter and maybe atoms and
stars and gases and you know real stuff
actually out there in great perhaps
endless array and collectively they're
calling it the multiverse so that's the
subject tonight
but instead of just insisting that it's
true i'm i'm going to just reset it here
for because i'm going to
i'm going to you'll see so
uh you should know first of all this is
not everybody's view dave gross david
gross a nobel prize winning physicist at
uc santa barbara very respected man
thinks this isn't and these are his
words inelegant unprovable and unlikely
idea
and there's a guy named who many of you
read maybe in scientific american the
mathematician martin gardner who calls
it a frivolous fantasy intellectually
bankrupt paul steinhardt aforementioned
by brian uh the albert einstein
professor at princeton says i'm quoting
him this is a dangerous idea that i am
simply unwilling to come contemplate so
what we're going to talk about tonight
is not a consensus view it is actually
highly debatable but because it's an
idea that is rich and important and i
have to confess very intriguing we
loaded the dice we loaded our stage with
universe pluralists we would call them
the s men because they spell the
universe with an s
and and they'll be here in a moment i
should confess right off though that i
am not a scientist i am not
especially learned about these things
i'm here basically to stand in for most
of you who at least at some point were
going what you know because
it's my job to say to these folks what
do you mean what are you talking about
how do you know this why do you say that
this is a science festival not for
scientists but for curious people like
yourselves who want to spend an hour or
two in the springtime asking what is and
what can be known about our universe
or
our universe says
so we'll get on with that
i will
go to the far seat
and filling in around me will be
nick bostrom who is a flaw i guess they
should just come in as a bunch maybe
uh
they will be smiling as uh as brian
predicted
so i don't know they'll come in
eventually i'll just tell you who
they're going to be oh here they are
okay okay
so
for a purpose this is nick bostrom he's
a philosopher who proposes there's not
only many universes an awful lot of them
may be computer simulations so
everything you see about you right now
just touch your leg if you like and feel
the garment feel the texture there
it's not really
complete
nick bostrom is also director of the
future of humanity institute at oxford
university which should worry you later
in the evening
alan guth is professor of physics at mit
world renowned for his theories of
inflationary cosmology basically because
of alan
the story we tell about the universe has
changed pretty much because he's he of
what he's discovered and what he thinks
so
so that's him and then uh
ryan
brian is professor of physics and
mathematics at columbia university
author of the fabric of the cosmos the
elegant universe made it's rather
significant discoveries in his field
which is super spring theory and his
ability to explain ridiculously
complicated subjects like this one has
irritated me but made him beloved by
many
and andre lin is a cosmologist and
professor of physics at stanford who
believes the universe is endlessly and
forever multiplying into more and more
and more and more universes if you want
someone to blame for this blame that man
sorry so let's begin up with it with
this just to go back over brian's story
just a cup i want to just drop in on a
couple of places the big bang
uh
i just want to visit that one more time
um how do you
you said
that there is and you i was intrigued
that you you can find evidence because
of the microwave radiation and all
um
is is that how you also said the
universe is expanding so how do we know
or just describe it like
what
happened
why they call it a big bang
yeah well that actually began as a
derogatory term i think you can correct
me i think it was fred hoyle
who did not believe in this way of
thinking about things was in a radio
interview and he said oh those guys are
talking about the big bang you know so
it was that kind of a name that he gave
to it
um and the idea simply is if you imagine
something small and getting bigger and
you try to relate it to things that you
see in the world around you when things
explode they get bigger so it's as if
there's a cosmic explosion now that way
of thinking about things is really
awkward because that almost makes it
sound as though there was a surrounding
universe within which this big bang took
place and that's not typically how we
think about it although when we start
the multiverse it begins to become a
little bit more more vague but the
forgetting about the multiverse for a
second just starting simple the
traditional big bang theory envisions
that everything is in this tiny nugget
that you begin with there is no external
space and as it grows it creates the
space all around us and because space
and time says einstein are the same
thing if i ask you as many people would
be what happened just before the big
bang
how do you answer that question well
it's it's there there are many questions
in cosmology that are very awkward uh
and that certainly is one of them and
there's no universal answer to that
question when you get to the multiverse
picture the answer shifts but let's
again start simple in the traditional
big bang one way of thinking about it is
there is no time before the big bang
because time and space come into
existence with that event it's as if i
said to you where
how do you go further north than the
north pole
it doesn't have any meaning right north
is defined and that's where it starts so
you know it's if you say how do you go
before the big bang i'd say it has no
meaning now there are other approaches
and we'll discuss them here tonight
where the big bang is an interesting
event but it's not the creation event
and there can be in a sense events that
take place before so do you all sort of
just you all would rather look past the
what happened before question and just
move on is that uh
because i know by the way there's a
calvin and hobbes that's very cool about
this that uh
calvin says to have what kind of an this
is a cartoon characters you should know
it's about a tiger and a man
and
the boy says to his tiger why didn't
they come up with that name do we have
that do we have the
yeah so
so if you uh if if you look over here in
this panel here there's the alternate
name i think the the horrendous space
kablooey or the
it just might be a better
but uh i'll i will move on
when you when you begin when you have
this moment at the beginning uh now you
you get a dense soup of stuff i guess at
the start very very hot
and then um
then alan i want to ask you i there are
there's some problems that hot soupy
stuff that's at the very first instant
of time then becomes clumpy
and turns into clouds and galaxies like
brian's movie show
the universe keeps extending outwards it
doesn't turn into a circle so it seems
to like something of a plane so it can
expand
and if you look around in all directions
as those radio people did
you find it's sort of the same
everywhere you look
how did you alan explain the unit versus
early initial flatness
clumpiness and sameness and why did you
write in your lab notebook
this idea i just had is a
spectacular realization
right right well that happened one night
when i
put several things together been really
brewing over the past six months or so
but the key idea is this idea of
inflation which really did in the end
get put together in one night
and what i realized is that well put
together there was a good six months of
prelude and a number of lucky pieces of
information fell into my lap during that
time i think it really was a very lucky
find on my part although i think it
certainly would have been discovered by
somebody soon regardless but the key
idea was that uh
i was looking at a phase transition that
we thought took place in the early
universe
and i was
looking at the idea that this phase
transition may have undergone a very
significant amount of super cooling uh
all motivated by studying things called
magnetic monopoles but we won't get into
that that's not going into that ask it
instead no we won't i wasn't going to
just mention the word i threw it away
just like you're supposed to do good
but anyway the super cooling i i
realized uh following through on some
calculations uh would produce this
peculiar field uh essentially what uh
brian has been alluding to uh which
would create this repulsive
gravitational effect uh and it would
have an enormous consequence for the
expansion history of the universe so
enormous consequence if the earth if the
if the universe is very very teeny like
protons or however small
how much does it grow in how short a
time
okay the time that we're talking about
here we still don't know very accurately
by the way but the kind of numbers i was
using then and still seem plausible are
10 to the minus 35 seconds or something
crazy like that 10 to the minus
incredibly decimal point four zero
there's a one that's right much faster
than that's right you can't do it you
could try but you're not gonna be able
to do it okay
i won't even try and during this time it
expands by a factor of like 10 to the 25
or something like that so 10 with 25
zeros that's right and one with 25 so
how big does that make it like uh
it goes from a size that's more than a
billion times smaller than a proton
at the end of this we envision as being
approximately the size of a marble still
very small
a marble a marble right
that's
the whole universe right there
well that's puzzling right well it keeps
expanding after that oh but not
accelerating after that so then it just
grows more grip so why did this push
thing
stop
uh it stopped because this stuff that
was pushing it this field
is unstable
so like a radioactive substance it
decays into other kinds of material
materials that we would consider more
normal that produce attractive gravity
so this
opposite of gravity this instead of come
to me this get out of my way these sharp
elbows for us right if that repulsive
thing uh creates this
this
um
ping-pong ball-sized universe then
how does that solve the problems i just
mentioned how does that make the
universe seem flat so it can expand how
does that create the possibility of
clumpy matter so there's stars over here
how does that create that sense of
sameness all over the place okay let me
take them probably in the exact opposite
order
starting with sameness that's i think
the easiest to understand uh in
conventional cosmology as it existed
before inflation was added uh the early
universe expanded so fast uh that there
really was not enough time for the
different pieces to communicate with
each other even if they could send
signals to each other at the speed of
light so the conclusion was that the
universe could have started out
perfectly uniform we don't really know
how the universe started out
but if it did not start out perfectly
uniform
in conventional cosmology there was
never enough time for it to smooth out
so it would stay very lumpy it started
out very lumpy
in fact the universe the early universe
was very smooth uh the non-uniformities
are crucially important but they're only
at the level of about one part and a
hundred thousand uh to one part a
hundred thousand the early universe was
just smooth
uh inflation could explain that uh
because with this spurt of
expansion uh it means that before the
spurts
uh the nascent universe uh was vastly
smaller than it would have been in any
previous theory
and while it was vastly smaller uh there
was plenty of time for it to smooth
itself out
by the same way the air in the room
smoothed itself out
so that we don't have lots of pockets of
high pressure and pockets of low
pressure but it takes a little time for
that to happen but there was enough time
on this very small scale
then this tiny speck more than a billion
times smaller than the size of a proton
believe it or not we talk about such
things and think we believe them
expands it's stretched out by the
inflation itself and becomes large
enough to become this marble which then
coasts to become large enough to include
literally everything that we see today
by the way the marble getting to be
literally everything we seem today is
that because there's a lot of energy in
that little marble and the energy
gradually cools into matter and then
everything's in so you get more space
and then more time and more space and
more time and then us that's right
that's right and that latter part is
really just coasting okay
so do you solve the same this problem
you solve the clump okay yeah that's the
finished problem the the the the pumping
problem comes from uh quantum
fluctuations uh on the smaller scale
even in this room we think that you can
measure things on the scale of atoms you
would see large fluctuations in the
electric fields magnetic fields energy
density everything
and what inflation does is it takes
those very small scale fluctuations and
stretches them out to become big enough
so that they can be the galaxies that we
see today and that's something
perservations become galaxies or huge
fields of galaxies
okay that's right what was my other one
then the rest is flatness
uh flatness is a little hard to
understand but let me say that we don't
we don't know what shape the universe
started out but one image which makes it
simple to picture in one possibility
really is the universe could have
started out essentially round uh what we
call closed universe which is the analog
it's a three-dimensional analog of a
sphere
that would be what i'm illustrating with
my hands whatever dimensions you want to
count get a good job that's really good
all right it's a two-dimensional surface
but in a three-dimensional space right
so if the universe goes started out like
that then inflation basically just makes
it vastly larger uh and it ends up
looking flat for exactly the same reason
that the surface of the earth looks flat
to us
even though the earth is really round if
you take something that's round and just
stretch it out enormously uh it looks
flat
well let me then go on to andre to the
next step of this so we have this little
thing that's growing into a bigger thing
it clears up some early problems and
makes the universe a little more
familiar to us but now my question is
called the graceful exit problem
this um
rude form of gravity in reverse that is
pushing everything out
doesn't seem to just you said it sort of
stops growing but it doesn't seem to
stop growing in a
boom way it just keeps on kind of
bothering the universe
and it is from this
flocks of repulsive gravity that we get
this more interesting question so andre
here's my question to you how do you get
from one universe
to
more than one universe's if you if you
pick up where he left off first of all
let's try to understand how to get one
because because what alan did
he
suggested an idea how to make the
universe big and everything etc but then
when these bubbles in his universe when
the universe start this vacuum state
whatever energetic states are decaying
it produces bubbles bubbles start
colliding wait let me stop you there so
there's this energy
and the energy is pushing everything out
and then in in brian's movie
periodically the energy seems to like
take a
it seems to just sigh here and there
right so the energy level goes down here
but not here here but not here here and
every time this repulsive energy thing
sort of gives up a little space that's
where you get a universe yeah well uh
that that's uh how you get an interior
of the universe you see in ellen's
picture you have the universe like this
swiss cheese and then the bubbles appear
and the bubbles collide and after they
collide uh kind of they disappear maybe
but the universe unfortunately after
that became inhomogeneous and then i had
my own nightly lake allen's except for
this was the night when i was
well i brought the phone to my restroom
because this was the only place in in my
home where i could not i would not wake
my son so i would call them some of my
colleagues look i have an idea that's uh
is it stupid or not because what wait so
you had your inspiration rushed to the
bathroom hid your phone
well
this is a good story i i had my
inspiration a little bit before
but what what is important that it did
not stop after i went to the rest
and i went to the restroom
not for the reason you suspect me but
for the reason that i needed to call my
colleague to check with what i'm
thinking is stupid or not okay and he
said no i don't think that it is stupid
and then
and and then i wake up
so to you like do you have to
say something mathematical or you say
i'm going to tell you something do you
think i'm crazy what did you just say no
it was pretty mathematical as
mathematical it goes through the phone
okay so
but
anyway what happens in the end i just
wake up my wife and said look i seem
that i know how the universe was created
is that that's one big trip to the
bathroom
i guess we'll we'll try late anyway so
what
not each time so successful so here
the the idea was this you have many of
these bubbles
but then these bubbles may continue
expand
well internally
and when the
well when you have this whomp when this
energy goes down they still continue
expanding and as a result you do not see
this part this well this wall of the
bubble and that wall of the bubble
colliding with each other because the
interior grows so large that you do not
see the catastrophe here you only get
the benefits of internal part expanding
so then you get smooth ending of
inflation this slower roll and
everything like that small ending of
inflation inside one balloon
okay
in alabama so let me try
i'm sorry i have to translate you back
to myself because i'm this is hard for
me so in my universe there's a certain
logic that takes up and things expand
around me and they seem to be expanding
endlessly and there's a sort of
smoothness to the creation in my
universe but if my universe is over here
and next universe is over there so i
leave
my universe and the space between us
between his universe and myself i'm a
bubble he makes a bubble and the space
between us is growing very very fast so
our universes are getting further and
further and further away mine's okay his
is okay look we're getting is that um is
that what you're saying it was well not
complete story because if this would be
so in the first version of inflationary
theory the new universe would be empty
okay so what happened is that it is not
only that both of your universes is uh
okay but because of this smooth whomp
and expansion of yourself
not only of the distance between your
next universe but what happens around
you then you have a big part of the
universe to occupy for yourself it was
like peaceful kind uh coexistence like i
was in russia allen was in united states
we had kind of problems okay so now
what if our country russia well right
now and u.s
expand exponentially and then u.s expand
exponentially and just not hurt each
other on the boundary but just expand on
all their own resources that's what we
suggested for the universe to do to
peacefully without this crashing okay i
still don't understand why you could
start with one universe
no it's and then get another
and another
and another okay there's a missing logic
here i don't quite okay so a little bit
uh perhaps
a better way to show
something this by the way this is a
picture which we will return a little
bit later but can you show me the golden
universe right now
yeah okay so these are computer
simulations you see when you want to
have high tech cheating you go the
computer you do it so that's what we did
this is x this is y on these two axis c
and this is a laser weapon and
and and here here the height shows you
the energy density level in the universe
all the value of the scale field or
whatever you call it this is something
which is responsible for expansion of
the universe the higher it is the faster
the universe expands now we started the
simulation with nearly homogeneous
universe and then you start expanding
exponentially fast computer cannot
expand exponentially fast so each new
image is actually showing exponentially
larger part of the universe but just
computer shrinks it back and then these
small waves
are the following you see here this in
homogeneity quantum fluctuations they
freeze on top of each other universe
continue expanding new quantum
fluctuations freeze on top of each other
universe continue expanding and then in
some places while the universe goes down
this sorry the energy level in average
goes down okay and we live somewhere in
this corner somewhere around where these
fluctuations are small
and when they are small they launch
satellite they see what happens and they
get this strange interesting looking
curves and they see agreement with
experimental data but there are some
other parts where these fluctuations
add up at each new jump add up and add
up and they produce other parts of the
universe which are so dense they expand
much faster than the original part of
the universe and this is the place where
new parts of the universe are created so
you start with tiny parts of space
and then according to classical theory
which we all love that it would go down
and everything would finish but because
of quantum fluctuations you produce some
regions where this expansion continue
forever by the way this part the part
which shows these small perturbations
this is the one which is well
experimentally tested and going to be
experimentally tested can you show this
planck satellite thing
this movie the uh which shows the recent
launch of the satellite planck satellite
that was launched on 14th of may
it is going to produce data release data
probably in three years from now
and it will show these small
well colored spots on sky
which are the results of these tiny
fluctuations on a small scale
and then in the end of it after all of
these checked and hopefully will be in
agreement with this
theory that we have right now we will
have pictures like the one which i i
would like to show right now it's a
colored universe can you show me
so this is the picture which okay so
here is the universe which is similar to
the first picture x and y and here is a
density but here are different colors
different colors show that in some part
of the universe you have
space with some kind of properties let's
call it red and in some other part it's
different type of property let's call it
green and by historical reasons because
i was from russia i started with
simulations with red well square
and
and and then you see everything ends up
with the universe which is multi-colored
so what does it mean multicolored like
you have water okay yeah i actually have
water okay so water can be solid water
it can be liquid water and can be gas
okay this is the same water the same
chemistry in it the same physics in it
same can be with theory you can have one
fundamental theory for everything but it
can represent
different parts of the universe with
different properties you can still have
red universe you can have green
universe here blue universe but because
of exponential expansion of the universe
the distance between red and blue will
be exponentially large and if you decide
to cross the border okay you just start
moving from the red universe to the blue
universe there will be boundary here
like the main wall no policeman is
necessary very very difficult to cross
and if you are stupid enough and young
enough brave enough and cross the
boundary you must probably instantly die
because
let me stop you before you
i don't want you to die in the
exposition here
uh
because this is uh
can i interrupt you just a second
because we happen to have a carnival we
just look we're very well endowed on
this panel we have this version and
you're now moving into a chapter a
little bit one step past where i want to
go just yet okay can you hold on
you have one too right you have a i
don't know if you brought it but do you
have a i need to have a second version
of
of just building the universe could you
have one well i mean this this visual
that you see here is a more scientific
version of the visual that i showed at
the end of the remarks that i was making
where each of these different colors is
really a different universe it's a
different bubble in this vast expanding
substrate within which all the bubbles
are sitting so the idea is that this is
the more technical way of indicating
that there can be many many different
kinds of universes inside the different
bubbles so i just do want to get back
because i'm still i want to get back to
the underlying notion the underlying
notion is that at the bottom of the
existence is this
fluxing fluxy thing and the fluxy thing
is either a robust get out of here get
out of my way or a relaxed sort of less
version of and that
in some places the robustness
bursts out and you get separation from
one university you get lots and lots of
distance as it moves very fast one
universe from the other
and then the universes themselves come
popping out of this underlying repulsive
energy that is always there sometimes up
sometimes now sometimes is that the
general idea
you know how odd and weird that is
i mean couldn't you have thought of
something simpler
well one thing i think is really
important to bear in mind these ideas
when framed in ordinary language do
sound complicated do sound strange
they're unfamiliar
but if you look at the mathematics
behind the versions of these theories
that these two gentlemen came up with
it's actually the simplest mathematics
that we encounter in many of our
physical theories of this sort it's very
very straightforward and it does imply
when you look at the math that indeed if
these theories are correct that we're
embedded in this vast expanding
substrate and that these openings can
happen and what we consider to be the
universe is simply one opening of many
possible openings in this vast expanding
substrate and the properties can differ
from opening to opening so every
universe is
is a sigh of this flux and every
in-between is a robust separation
doesn't that mean that the universe
between nick's universe and my universe
is the distance between us growing and
is it going fast really fast
so
the universe that is his universe and my
universe are getting further and further
at beyond the speed of light if they're
far enough apart it would be faster than
the speed of light yes
i thought you couldn't go faster than
einstein only told us that nothing can
travel through space faster than the
speed of light he didn't say anything
about objects that are being pulled
apart by the expansion of space itself
so if objects are sufficiently far apart
and space is expanding their motion
relative to one another will in a sense
be faster than the speed of light which
means that they will be permanently
beyond your ability to talk to
to communicate with so they are out
there but they are permanently beyond
your ability to see or for them to see
you
before we get to that so you've just
increased
you've just increased the what i would
have used to call the universe which was
you've just increased it enormously
it's
you're doubling at the speed i mean it's
in
no when these guys came on the scene the
picture of the vastness of the universe
changed dramatically there was one time
you know the universe is like 14 billion
years old it was roughly 14 billion
light years across more or less a few
factors of three here and there but
these guys changed it by factors like 10
to 100. and
or infinite we
we should add that it's not a precisely
well complete picture what we're
discussing and sometimes the universe
can crash into another so sometimes
sometimes
well you see that the main wall coming
on you and crush you and you actually do
not see it because it moves with the
speed uh approaching speed of light so
at the moment when it crashes to you you
start seeing it and you stop seeing it
and
well well audrey let me let me just
re-address it but that's quite probable
why do you think that this is going you
added the notion that it's going to go
on and on and on and on so do you think
there's a beginning to the multiverse
and do you think there's an end to it
like in any one of these universes i
think you could get exhausted and die
and the universe could collapse but this
big thing doesn't seem to be have a
collapse in it
so is it is it an eternal universe you
are proposing to the future uh if we can
show
again this bubbly universe and the
picture okay so as for the beginning as
alan together with several other people
have shown we still need this something
which we are screening probably by our
chairs this first bubble appearing here
there probably must be something which
started the whole tree growing
maybe however
it did not start simultaneously in the
whole universe but what happens once
this process of producing new and new
universes start it never ends so the
universe is eternal in the future so
what does it mean for us well uh some
things like for example previously we
thought that this first bubble which is
partially screened by the chairs first
bubble is the whole thing what we wanted
to explain cosmology wanted to explain
we see a universe around us it's more or
less homogeneous in more or less uniform
in all directions in fact albert
einstein had the idea that the universe
must be uniform and homogeneous he
called it
some other people who called it
cosmological principle you can still see
it in the books of astrophysics perfect
technology cosmological principle means
that the universe must be uniform so if
it is yellow balloon this is yellow
balloon and sometimes i used to make a
joke that some people who do not have
good ideas they have principles so
but i stopped making this joke after i
learned that this cosmological principle
was
invented by albert einstein
well so what what happens here
greeks had this idea of perfect sphere
we wanted to have some mechanism which
explains why our universe is a perfect
sphere
and then inflation came and inflation
explained why our universe locally looks
like a perfect sphere but then inflation
told you that the universe globally
looks like a fractal eternally growing
fractal so what was the leading idea of
greek's perfect sphere what was the
beauty concept of 20th century is a
fractal and that's exactly what
inflationary theory brought to you the
multiverse as a fractal and fractal
having all possible colors
why won't it stop
i would not it is continue growing
producing you and you like look but what
support is this because that why yeah
why i don't know
maybe i'll just try it i'm sure you can
do it better but just uh you know uh one
way of thinking about it is
as we said when the energy goes
then that part of it stops undergoing
this inflation but the thing is you've
got two competing effects it drops it
falls down but the part that hasn't
fallen down continues to grow so you've
got a growing effect you get more and
more of the stuff that's pushing
outwards created every moment and only
some of it is falling down so some falls
down but some gets larger and the amount
that it grows larger always in these
models beats out the amount that falls
down so there's always some place out
there filled with this
stuff that does that so it just goes on
now wait if it reproduces i live in this
universe and this universe this one here
let's say it's ours so it has you know
the physics of ours it has gravity it
has atoms and it has forces and then i
think about this universe does this
universe have the same gravity that we
have and the same atoms we have do you
know do you have a theory no that's why
it is blue okay
oh you're a mean man
so so therefore there are not only many
many many universes but there are many
many many kinds of universes so yeah and
uh you
you know how many
okay well things
like
uh in 80
something 86 87 people working in
stringy community speculated how many
and they said it's probably 10 to the
degree 1 000 different universes
different kinds yes but but nobody took
them seriously okay because they did not
have any one demonstrably well whatever
probably existing which would be well
stable kind of you see string theory is
based on the idea that our space
fundamentally is 10 dimensional maybe
and then six of these ten dimensions are
squeezed into something very very small
and four a large like three space and
one time okay but nobody was able to
actually keep these six dimensions from
being starting expanding the universe
wanted to be ten dimensional and what
something happened in well 2003 uh
several people from stanford well i was
a cosmology consultant there but there
was katrina kalash and trivedi from
india
they've suggested some mechanism how to
stabilize these six dimensions can you
show calabial
picture
here well this is well some
mathematician actually produced an image
of how this six dimensional space looks
like okay so six dimensional space is
compactified but it can be compactified
in so many different ways it has so many
different holes and it because there are
lots of combinatorical freedom there the
total number of ways it can compactify
is exponentially large and for each type
of these ways you have different
properties of our universe living there
different properties of elementary
particle physics different energy of
empty space different everything and
when people calculated the number of
these stable compactifications they came
to the number 10 to the degree 500.
10 to the degree 500. this means 10
and okay so it is like one one and five
hundred zeros there all right okay
approximately
it's plus minus plus plus minus
something that i wake and at the moment
they start saying actually maybe there
will be infinitely many but then they
cut back to the standard all right stop
for a second stop for a second you have
to take a breath with you all right so
let me i haven't asked you anything yet
hi
um
does it strike you as a little difficult
to hear a theory of everything
that is
open to everything
i mean wouldn't a theory be a good
theory let me just i have a line here
somewhere
um a good theory that would be a good
line yeah i hope so
well i don't remember where it is but um
yeah you see you have nothing against it
after all it seems to me that a theory
that says that anything is possible
doesn't explain anything
i mean a good theory says why this is so
but this guy has just said and these
guys are all nodding that
this multiverse contains just about
every conceivable including that weirdly
shaped thing that was behind you every
conceivable organization of matter every
conceivable number of dimensions every
conceivable possibility and i say well
okay if that's your idea of science then
go ahead and conceive in the bathroom
again because that's not
how i mean if it's too much but i'm just
interested in your opinion
well now so
you get a similar problem even if you
just have one universe if it's big
enough
say it's infinite you will have all
possible types of observers existing
somewhere
and having all possible types of
illusions
so whatever measurements you make
even in a single infinite universe you
will have some observer somewhere
you know imagining that they are making
exactly that observation
the question then become how can you
test theories if all the theories you
are comparing each predict that for any
possible observation you make there will
be some observer making that observation
it seems that the theories are
consistent with all possible
observations
so this is the problem
and
the solution must be
to consider not just whether a theory
says that a given observation will be
made
but
what the theory says about the frequency
with which these types of observations
will be made
so
it has to be you have to think about
if there are all possible types of
observers making all possible types of
observations
the interesting thing is
what will most observers see
in a given type of universe
so you think about the fraction of
observers who will make
particularly let me ask that question in
a different way to you to all of you
actually
this universe that we're in
seems to have a very very sensitive sort
of set of circumstances so
our
the gravity is just so the forces that
bind atoms are just so
and if you changed any of those
variables and i think there's six or ten
or some very important ones then the
universe as we know it would collapse
and we wouldn't be here
so people sometimes ask
as you i guess just did like how many of
them of all of the universes are like
our universes where life is possible and
intelligent life is possible and how
many of them are and how come we're in
ours are we in ours because we just are
here at the end result of a set of
circumstances or are we in ours because
somehow
our universe expected us
well i mean one way of thinking about
this that comes out of these pictures i
mean if you have you know andre's image
of all the different universes with the
different colors
if we can only exist in a red universe
then if you ask yourself why are we in a
red universe we're there because we can
live there i mean this is a kind of
reasoning that we accept in other
circumstances you know if i said to you
why do we live on the surface of a
planet why don't we live in interstellar
space
the answer is pretty clear we couldn't
survive an interstellar space we're on a
planet where the conditions are
hospitable to life as we know it and
that's why we're here similarly why are
we in this universe well we're here
because we simply can't exist in the
other ones and this may feel somewhat
circular tautological but what gives
this power is when you really start to
realize that if that picture's true and
there really are these other universes
out there it's not just mathematics it's
real then of course we're going to be in
the one that we can live in and that is
a reasonable explanation if indeed this
picture is correct how do you guys know
that andre's
probably right how do you know the
answer to your question like how many
how do we know
that we can't see them they're receding
further and further away faster than the
speed of light so how do we how do we
answer the question there's no crow that
can fly over the whole thing
i i think it would be too strong to say
that we can know at this point that
andre is right but one of the reasons
for taking this type of model seriously
is exactly this problem that you
mentioned the fine tuning problem
so we see that there are a number of
these
physical constants that appear to be
fine-tuned for life
it's possible why should i have exactly
the right values that enable
you know human beings or detenable any
kind of complex chemistry at all and i
wasn't even i wasn't even cool enough to
i should have told that story much more
dramatically that's really really it's
really precise finding and there are
sort of four different possible
approaches you could take to this it
could be just a coincidence but by
definition it would be very unlikely
that the values would just turn out
right by chance
of course if you're religious you could
think that god designed it to be like
this but that explanation has all sorts
of other problems that are well known
okay
you could search
you could search for some simple you may
be hit by lightning okay well
you could search for some further simple
theory that nobody has thought of some
simple equation that is itself very
simple but
from which all these specific values of
the constants just pop out
problem is nobody has any idea for what
that simple thing could be and the
fourth path which is the one that
lind and gothital are exploring
is that there is this big ensemble of
universes
and the values of constants in these
universes vary randomly so that you have
all all or almost all possible different
constellations of values of these
constances are
implemented or instantiated in some
universe or another
but most of these possible universes
will be void of
observers the observers will only live
in those universes where the values are
exactly right for the
evolution and existence of life complex
chemistry
so all observers
will find themselves living in these
universes where the values look like
they are just fine-tuned because they
only see the universes where they are
fine-tuned all the others are void of
observers or at least they're much fewer
observers than others and so that would
then explain the appearance of
fine-tuning and the fact that you could
explain that through this kind of
multiverse theory is one of the
underlying rationales for taking
so you're just there for you you've
created a a vast array of different
kinds of universes you've conveniently
gotten rid of god and it can just be a
random
upsurge but you haven't gotten rid of
the mysterious
fact that you all hold on to which is
underlying this whole system
is still this flux this gravity that is
that is pushing out and sighing and
pushing out this gravity has an
omnipresence a godlike on the present
like we why do you all think that this
is to be assumed that's an assumption
just like any first assumption and
you're stuck with it
oh no no
you see the thing that we are reporting
is just the simplest model and that's
why the gravity is here of course we can
do much better than that but this will
be well preserved for the next i guess
well meeting here but right right now we
are trying to do the simplest job so
what we have shown you assuming some
fundamental law of physics including
gravity and what happens there and you
already have 10 to the 500 different
possibilities so that's just a simple
scenario so you're not worried that you
have to assume a kind of underlying but
universal graph set of gravitational
waves it's
uh well
it is
self-constraining rule it's well you
know uh
probably probably i should say something
psychological here okay
like
when i was living in russia okay we had
one particular rule and we knew that
this is right and the only possible okay
and eventually we will spread okay
something like that right okay and
therefore when we have freedom having 10
to the 500 different possibilities we're
ecstatic and i'm coming to the country
which has freedom and suddenly oh it's
too much of it this is 10 to the 500. we
need one rule i say my god
so he's comfortable with freedom what
about you brian
well
the criticism that you make i think can
be made always you're always when you're
a theorist putting forward ideas and
even if they're successful you could say
well why those ideas so i think that
that's an issue that can always be
raised and i don't think it's one that
we can really deal with but speaking
from my perspective as a strengthers let
me just say why i find these ideas
compelling and it was really what andre
was describing i mean these guys had
developed these interesting cosmological
theories where there'd be all these
different bubble universes out there and
that was a very interesting cosmology
put that to the side for a moment we're
working on string theory for all these
years and indeed there's this feature
string theory that you have more than
three dimensions of space you have six
possibly seven other dimensions of space
that as andre was saying we saw a
picture can be curled up into these
little tiny spaces and our hope in the
80s was that there'd be one particular
shape for the extra dimensions
that if we knew it we'd be able to then
explain all of the observed features of
the world around us because it turns out
that the size and shape of those extra
dimensions determines things like the
electrons mass or the mass of the quarks
or the strength of the forces so we have
this image that one day we're going to
understand which shape there is for the
extra dimensions we'll calculate
everything and it will all agree and
we'll be done
the more we went on we found more and
more shapes for the extra dimensions we
had a catalog of a few hundred in the
80s it like went up to a few thousand in
the 90s then it just blossomed into as
andre was saying 10 to the 500 different
possible shapes for the extra dimensions
you're like wow this is turning out not
to be the way that we thought it was
going to go but then when you put it
together with this cosmological picture
it becomes very interesting you have
these 10 to the 500 shapes they're
realized in all of these different
bubbles
and when you have that picture then the
explanation for why things are the way
they are becomes far simpler we see
things to be the way they are because we
can exist in that particular bubble with
that shape for the extra dimensions
that's compatible with our biology and
our chemistry what you don't describe
the biggest bribe that we gave you the
biggest what the biggest bribe oh what
was that oh okay okay so
so here what happened
uh in 98 people have found cosmologists
cosmologists have found that there is
vacuum energy empty space is not
entirely empty there is something which
is called dark energy cosmological
constant vacuum energy not empty and it
shows in exponential expansion of the
universe right now the universe 5
billion years ago start exponentially
expanding okay so it exponentially
expand very very slowly don't worry you
will still have some time to finish the
logic
but the fact is that when string
theories have learned about it ed
whitten who is well the head of uh
strings
not there is no head okay but
one of the
very very very esteemed okay
one of the major leaders in string
theory mentioned in his talk in india
that i do not know how string theory can
explain this exponential expansion of
the universe and when he said so
ed does not know and well i also don't
know nobody knows and then what is going
on string theory does not know how to
describe our universe so that that was
bad and then everybody start being
nervous and i start checking how to
describe it and then finally we have
found a way how to describe it and then
we found this 10 of the 500 different
ways to describe it but
but then
but then the thing was that the value of
vacuum energy which people
experimentally found was absolutely
incredibly minuscule
it was 10 to the okay so 10 to the
degree minus 120 of expected value you
see theorists are calculated if it is
non-zero what will be the next
number okay so the next number was huge
and people experimentally found
something which is 10 to the minus 120
of this which means
zero point and then 120 zeros and then
one standing there and it looked
absolutely ridiculous okay
so however now we have this 10 to the
500 states okay so now watch me here
this is theoretically expected value
okay
this is zero
and this is another well negative
theoretically expected volume now let's
slice it by this slices ten to the five
hundred different slices okay
and then you come to close to zero you
come to the place where it is 10 to the
minus 120 see okay
so it is still you continue slicing
because there are 10 to the 500 slices
so in this tiny place 10 to the minus
120 you have 10 to the plus 380 slices
different types of the universes with
the cosmological constant which just
fits experimental data okay so first i
don't know what you just said but it
came out good in the end didn't it okay
okay so so
string theory allows first allows to
describe the universe with this tiny
tiny value of vacuum energy but then the
second step e vacuum energy was just 100
times larger okay or if it is negative
and 100 times larger but negative we
would not be able to live there that's
what anthropic principle says okay
because why if we're here then the
galaxies would be torn apart if we're
here down below then the universe will
collapse too quickly for this well
discussion to take place okay so
so what we have found that string theory
allows to explain
this value of vacuum energy and so far
no other explanation was
proposed oh here we go so your ultimate
defense is that the only explanation
that just might cover the situation is
this one which we can't test but it's
the one maybe left standing because just
so in the middle of the code of your
dream theory plus inflationary theory
together give you the only explanation
of the experiment which was happening
happened 10 years ago so far nobody
suggested anything better but see if if
that's your defense that we've got the
best explanation
here's a review of that explanation by
somebody named bryce dewitt you know who
he's important apparently
bryce dewitt
i go or i must for these quotes i don't
even know who i'm quoting
i still recall vividly the vividly the
shock i experienced first encountering
the multi-world concept the idea of 10
to 100 plus slightly imperfect copies of
oneself all splitting into more and more
copies is not easy to reconcile with
common sense this is schizophrenia with
a vengeance
blind brian's bryce dewitt martin
gardner the mathematician
in my layman's opinion these are
frivolous fantasies surely the
conjecture that just one universe with
one creator is infinitely simpler and
easier to believe that there are
countless billions upon billions of
worlds constantly increasing in number
and created by nobody john wheeler
mr uno whom we all bow down to
apparently says i don't know i'm turning
again says it contains too much physical
badge baggage and john s bell a
physicist from ireland
says this is just plain silly
so robert i should just jump in
um one thing that we haven't emphasized
too much tonight is that there are many
flavors of parallel universes we've been
focusing on the one that comes out of
inflationary cosmology
most of the comments that you're
referring to there are coming
at the version of many worlds from
quantum mechanics the quantum mechanical
version of the many worlds
interpretation which um is another
flavor of the way that you can get
parallel universe but rather different
from the one that we've been talking
about here today okay that maybe i've
been unfair no um but but there is a
criticism that that certainly can be
launched it does feel uneconomical when
you hear about all these other universes
but i have to agree with andre i i
certainly had the perspective in the 80s
and 90s that there's one universe we're
going to work out the laws we'll have
some unique predictions and we'll be
kind of done that was certainly my
perspective and when this experiment in
1998 took place that andre was referring
to which found that the universe is
accelerating in its expansion which
means there's some more of that pushing
out stuff out there today and the amount
of that dark energy as we call it was
this fantastically small number about 10
to the minus 120
we say to ourselves can we envision ever
doing a calculation starting with some
interesting equations and pies and e's
and square roots of two the kinds of
things that appear in a natural
calculation and by the end of the
calculation the answer to be point zero
zero zero zero zero zero hundred and
twenty zeros and a one and none of us
can imagine that we'll ever do a
calculation where that is the answer so
we look for other ways of getting to
that result and one of the other ways is
if there are many many universes where
this amount of dark energy varies from
one to another then there's going to be
at least one if there are enough
universes out there where it has a small
value that we see and it's as if if i
have a deck of cards and i randomly take
one and i throw a few cards out it's
unlikely that someone's going to get the
ace of spades if i just throw a few
cards but if i have you know this is a
room about 900 people if i have 900
cards take many decks and i just throw
them all out there
i'm sure someone's going to have an ace
of spades because it's somewhere in fact
there are a few aces spades if it got
900. so you've just described say the
the event of us the reason we're here
we're just one of those many we're just
the ace of spades out there yeah and and
and it's hard for us to envision doing a
calculation
in a unique universe where we get that
crazy small number that has but you're
supposed to be scientists
so
as scientists aren't you supposed to try
to find some way to examine your theory
oh yeah
if the universe that you want to check
ours against is rushing at more than the
speed of light in some other direction
how will you ever that that's a great
question but one thing that is worth
emphasizing too we did describe this
that's a great question you never mean
it no no i really do
i really do so we've been describing
these different universes are rushing
apart really quickly and that's sort of
the generic case but if two of these
bubbles are really close when they're
created they can slam into each other
and if they do slam into each other this
could leave little ripples on this
radiation that we've been talking about
this microwave background radiation so
there are people looking for these
ripples and that could really give
evidence that we were slammed into by
one of these other bubble universes so
it's not that it's completely beyond the
ability to test these ideas
let me stick with one more idea here um
people are sort of used to the idea that
there ought to be one universe so if
we're talking about many it seems like
we're being very fanciful but let's
think about it really if we think of all
the nouns in the english language all
the nouns you can find in the dictionary
how many of them are there just one of
or does anybody anticipate the idea that
there might be just one of i know of
only two nouns that could fit that bill
and that is god and universe uh so if
you want to have a scientific
concept oh i think i'm so wishing i
could come up with something if you want
to have a scientific concept of the
universe do you want to put it in the
same category as god or the same
category as planet galaxy
uh cluster of galaxies
if you want to be unsettled then let's
turn to the silent one here to nick
because his idea has got to be the most
bizarre in the house
and i don't know how comfortable you'll
be i'm not sure i want to claim that
honorable
the thing is called
the problem of um the what is called the
simulation argument
so
i'll sum up and you explain what that is
you believe that it would be possible
for a universe to be a simply a
staggeringly successful computer
that imagines a universe so perfectly
that
anyone in the simulation
like a character in the matrix like that
that in that little blobby brain
would have an experience that seemed
utterly real
so i could go
and
i would feel my skin and i'd feel the
texture of your and and this would all
be a computer simulation so you you
propose that might be they might one
some civilization could build a machine
right right so a lot of people have
proposed that there's a possibility in
the whole premise of the matrix or
anything like that is that
just as we can build simple virtual
realities today with simple simulated
creatures living inside them
maybe in the future with vastly more
powerful computers you could build more
complex virtual realities with more
complex simulated creatures inside them
maybe these creatures could be complex
enough that they would actually have
brains like ours simulated down to the
level of individual neurons and synapses
such that the inhabitants of these
simulations would be conscious
but
what the simulation argument adds to
that is that
instead of just stopping at the question
of how could you ever prove with
certainty that we're not in a simulation
ourselves the simulation argument
tries to establish a constraint
about what we can believe and it tries
to show that one of three possibilities
is true although it doesn't tell us
which one of them it is
okay um now in a sense this sounds more
radical even perhaps than some of the
multiverse theories that we've heard but
in another sense it's less because it
doesn't presuppose any unknown physics
so we're just assuming that it would be
possible to build
computers that are much more powerful in
the future i mean i think they could be
very powerful but i if i thought i was
in a computer simulation i would watch
your face really closely because maybe
they'd be a skipped frame and you go
and i noticed that okay
um so we can come back to that i mean i
get these people
writing to me and anyway
um so what the simulation argument tries
to show is that one of three
possibilities is true the first one is
that
almost all civilizations at our stage of
technological development
go extinct before they become
technologically mature
technologically mature meaning having
developed all those technologies we can
currently show our physically possible
given only uncontroversially obtainable
physics so they make a radio they make a
rocket ship they make a bomb yeah you
can build big computers the size of
planets and stuff we can calculate what
performance they would have we can't
build them now but maybe a thousand
years from now people will build it so
first possibility is
people at our stage they just fail to
get through to that level of
technological maturity maybe they
destroy themselves on the way
second possibility is that almost all
civilizations that do reach
technological maturity lose interest in
creating
these kinds of ancestor simulations as i
call them these would be detailed
computer simulations of people like
their historical predecessors
so they have these
powerful computers they have the ability
to program them but they have better
things to do with their computers and
their time okay here comes three right
and the third possibility is that we are
almost certainly living in a computer
simulation
and the argument in its full version it
requires some probability theory but the
gist of it can be grasped
quite simply and intuitively so if you
imagine that the first two possibilities
do not obtain
that means
some non-negligible fraction of
civilizations at our stage do reach
technological maturity and some
non-negligible fraction of those
you know are interested in creating
these ancestor simulations they devote
some non-trivial fraction of the
resources to this end
you can then show
that there would be many many more
ancestor simulations than that would be
original courses of history because
it might be more because because if you
calculate the computing power
that a technologically mature
civilization would have
and the computing power that would be
required to simulate all human brains
it turns out that the latter quantity is
a tiny tiny fraction of the former so
in other words by devoting a tiny
fraction of their computational
resources to this end they could create
astronomical numbers billions and
billions
so you're saying that if the assignment
in mrs magetti's class and the planet
xantar in another universe is all right
everybody i want you to make a universe
with extraordinary accuracy and you
might create a billion people with every
neuron in place so they all think
they're alive everybody go and then
johnny says can i do it with real matter
can i can i make it with like energy and
math and i said no johnny that would
require 50 tons of stuff we're just
going to do this with bits and bytes so
everybody in the class does it with bits
and bytes and then in the next year
people just keep hitting the repeat
button
right so the cost of making a pretend
universe is just infinitely smaller than
making a real one
what maybe not infinitely but a lot
smaller i mean to the point where if you
have the ability to use some advanced
form of nano technology to transform
planets into computational systems
by using just one planetary computer
just the millionth of its computing
power for a tiny fraction of one second
you could run many many courses of you
know simulations of human history so if
somebody goes
that means that
that creates the likelihood that we're
in one of those universes well or maybe
johnny just does one but maybe there are
other people
millions of years later that repeat it
over time that would be more similar how
do you wake up in the morning
well
so so
to conclude the little arc of the
argument so if you assume that the first
you have to that's the if the first two
are false the first two assumptions you
then reach this
conclusion that there would be many more
simulations than
originals
and if almost all people with our types
of experiences
were simulated rather than implemented
you know in basic level reality we
should think that we are probably one of
the typical people the simulated ones
rather than the very exceptional ones
that
that were
part of the original history so now this
doesn't show that we already know what
you saw this idea and you proposed to
yourself it may be more likely that
we're all simulated well except that i
don't believe we don't believe if not
okay so i think that i believe the
simulation argument which shows that one
of those three is true but it doesn't
tell us which one
so i think we should distribute our
credence over each of these three
possibilities we just don't have enough
evidence to pick one
so
that's what i believe
so as to why i you know
if we assume for the sake of the
argument that it's the third possibility
the simulation hypothesis that's true
then a lot of people's first reaction is
well you know it might just as well go
crazy anything can happen
but once you start reflect on it for a
little while you realize that even if we
are in a simulation you know the best
way to
predict what will happen next
to decide what to do are still the
methods that we would use anyway we
observe patterns in our simulated
reality we extrapolate them
and act accordingly
so the implications are not quite as
radical as they might at first seem
well i i don't i have a feeling do we
how much time do we have left we are
getting up on it
okay because i don't know whether i
don't see anybody going like stop so
good uh
then collectively it's the morning in
china
do you do you guys feel that a a
multiverse concept in which there are is
this array of possibilities including
his rather doer possibility that if that
if you align if you think of the
universe or the many universes in this
way
do you feel
that it's beautiful or do you feel that
it's
oh it's uh to use the copernican
principle notion that it makes us much
smaller
perhaps not even real
uh oh well i mean yeah i mean it's a
very diminished state you have left us
in i think this idea that there's so
many i liked it better with one because
you know you you stood taller in that
concept
oh i mean there are many ways of looking
at it but i've always felt that every
time we get diminished the universe does
become more beautiful
and what i mean by that is
it's spectacular to me
that we little creatures
that are not special to the universe
we're not central to the universe we
might actually just be a simulation yet
can figure so much out so to me the
disparity between sort of how we are and
the grandeur of what there is the more
space there is between the two the more
spectacular our understanding becomes
so i don't really feel diminished by it
i really feel energized by all of these
things so
you know and also i think our aesthetics
really is developed and and progresses
along what we find to be true there are
many things today that i think if you
asked you know people 500 years ago what
do you think about this idea would be
foreign and strange and off-putting but
yet now we've become used to it and our
aesthetics have come along for the ride
and we now think that these theories are
beautiful so the bottom line is i think
we just have to wait and see if there's
evidence for this or if we can come up
with better explanations for the things
that currently only have a good
explanation in this framework well let
me ask the question in reverse people
sometimes who leave manhattan and go to
shanghai find shanghai is so big and so
bustly and so overwhelming that when
they come back to times square it looks
a little bit petite to them and they
feel that new york has somehow shrunk
around them let's do it by the universe
since you guys have all imagined a
multiverse so grand and so shanghai-ish
does the universe that you live in seem
a little bit petite
well okay we're getting towards the back
end of the show so i'm just throwing
them all out here
i mean so to me
i mean
even if you have a single universe if
it's infinite you already have you know
as much vastness as you could possibly
hope for and more now if you then add
other universes it has perhaps
interesting observational consequences
but if they if it's the mere size that
you're interested in you already get
that with standard big cosmology if you
have an open universe
you know
oh my god
i i didn't think that i will come to it
okay
well did you
no
one of the famous books of
mahabharata okay
and there
well there is a story how
of some
um
okay
famous
warrior
he actually um
he speaks with krishna
and he asked krishna can you show me
your universal form
and no no no i don't know that but
please or please show me your universal
form and then at some moment krishna
tells okay
so he suddenly shown his universal form
and that is the god who eats everything
and destroys everything and gives gifts
everything and he is also a lion and he
is also a tiger and he is also an
elephant and he is everything and the
waves involved
and then
the arjuna was speaking with him oh no
please now please show me your normal
face okay so this is right now the
situation just nature is much richer
than what we previously
thought about it but each step when we
will learn more it is more beautiful
it's actually absolutely exciting it's
exhilarating you're trying to find it
all and then yes when you look at it
it's some kind of dangerous you look at
the face of it you do not understand
what it is
oh no no let me do something else let me
do something so many people go to
finance
but that didn't work out for them
see
that's why inflation
in our theory is much better
i can't think of a better way to end
this thing than right there i i want to
thank all of you for for participating
if you have a final word feel free but i
think that was pretty good i think
so thank you all for coming and thank
you
so
you