We are setting off on a journey fraught with dangerous notions
eternity the creation of all things from nothing and
dare I utter a word not to be thrown around with reckless abandon among those of reason
infinity
a case in point of the library of Babel
it is a library that holds every book that has ever been written and
every book that ever will be written now here lies
The madness each book is filled with random strings of letters 26 letters
commas periods
Spaces and each book is different
But every volume in every one of these galleries has four hundred and ten pages
Each page has 40 lines
each line has 80 letters X alias that is to nothing but chance so
for every sensible line of straightforward statement, there are leagues and leagues and leagues of
senseless
Jumbles, and incoherences. For example one volume is made up in its entirety if the letters M
See these perversely repeated from the very first lines to the last
another is mostly filled with gibberish until you reach the next to last page when you see o
Time die
It is
Unbearable knowledge that in some gallery on some shelf a precious
cogent book exists that remains inaccessible
And no one cannot know my belief is the library stretches - dare I say it
the infinitely
Many say I'm mistaken that the possible number of books does have a limit and while that number is beyond my understanding
I
am gladdened by its distant hope
That however improbable I may one day uncover
Something about the library Babel which is an interesting image for the for the universe
But tonight you're going to hear for some people who will give you a much more expansive
Idea of what reality is?
We're going to be talking a lot about the multiverse tonight and the notion of infinity and we're also going to address the question
What is what are the fundamental constituents of nature?
So how did we get to this this point in scientific inquiry into reality?
Let's go back about 117 years to the year 1900 what did reality consist of what was physical reality?
Well, everyone thought it was the Milky Way
Sitting in this otherwise infinite space it was eternal
And didn't wasn't created would last forever
How naive that proved to be
Because in 20 years and 20 years to them about 1920 it was discovered that
The universe couldn't be static. It had to be expanding and we did you know, this could be empirically
Verified you could see the galaxies pulling away from us. So if you extrapolate back in time
You get this or origin to everything the Big Bang. So now we have a completely different view of the universe instead of it being
Eternal and Static it had a finite
Origin in the past and it might end in a finite future and a Big Crunch kind of like human life. You're born
It's the Big Bang you die. It's the Big Crunch. That's so completely different view of the universe
And this was actually exciting to some people a religious sensibility Pope Pius the 12th
When decided when the Big Bang was discovered, you know
this is a scientific proof of creation that the Big Bang Theory was confirmed in the
1960s when the echo of the Big Bang the Cosmic Microwave Background
was
detected by
Almost by accident at first the scientists thought that it was bird guano on the antenna that was causing this
Interference, but it turns out it's the echo of the Big Bang
So now the question is what is this Big Bang event?
and in it by the
1970s some guys that came along two of them are here fortunately. It's really thrilling to have them here
Then they came up with the theory of the Big Bang
Let's see. Do we have images of the two in there in their 70s hair?
There they are not bad for somebody's hair. So they they, you know set out to answer the question
You know, what? Is it that bangs?
Why did it bang and what was going on before it banged and they came up with a theory which is called a theory of
cosmic inflation and
So now once again there's a radical shift in our idea of reality
First it was a static finite universe the Milky Way
Then it was the BIGBANG universe it blows up out of nothing in the seeming creation event
And then goes on its merry history
According to the new theory of inflation. Our universe is just you know one
Member of this vast perhaps infinite ensemble of universe is called the multiverse
So this is where we are right now. So let me tell you who these people are
First of all, where did our universe come from?
Nobody knows but our first guests will tell you
His name was Andrei Linde a he is
Professor of physics at Stanford our next guest is the professor of philosophy at Columbia
He's the Woodbridge professor of philosophy at Columbia. Yeah. Also, he has a PhD in theoretical physics from Rockefeller University
Daivari David Albert
Our next
Guest is a theoretical physicist and a string theorist
She's one of the founding members of the Center for quantum mathematics and physics at the University of California Davis
Veronica
Our next participant is a professor of emeritus of applied mathematics at the University of Capetown
investigates cosmology the nature of time the emergence of complexity George Ellis
Our next guest is is a philosopher of science
He's the only non physicists on stage
But I think if he really had to we could probably calculate the eigenvalues of a harmonic oscillator very lower
I'm finally the
This is the father of inflation the man who really first created in 1979 professor of physics at MIT
Professor Guth is famous for saying the universe is the ultimate free lunch
but on investigation it turns out tax and tip are not included and you'll hear out that so anyway, these are guests and let's
Let's get this thing going
we saw this thing about infinity and
We have somebody on stage the conservative the more conservative with the more conservative view of reality
Which is Professor Ellis and he believes that nothing real can have an infinite number of components. So
first of all
I'm gonna ask you how do you know that and second of all are any of you people who are committed to
You a reality that's infinite in some respect like the multiverse going to take issue with that. So, how do you defend that?
How do you know that?
I'll take a double stand on this first it for me. It's a philosophical principle and philosophical principles underlying
Science and I'm going with David
Hilbert who said the infinity never occurs in physical reality and that's because infinity is beyond what we can ever attain
Doesn't matter how many things you've done how much stuff you've counted how far you've gone?
You haven't taken the first step on the road to infinity and I think people forget that when they talk about
Infinity in loose ways but more specifically if you claim there's an infinite number of anything in the universe galaxies people
so it's an
Scientifically unprovable because firstly you can't see them
but secondly
If you could see them you could never prove they were infinite because no matter how many hundred thousand
Million million million million, you have proved you haven't taken the first step on the way to proving. There's infinite
But I believe a scientific statement should be provable
So I think any statement about science that involves the word infinity is not provable therefore. It's not science
What if space were infinite and it were uniform than they were galaxies uniformly distributed throughout space?
Do you think that's metaphysically impossible surely that someone's going to object to that that was a what if statement so what if statement?
Yeah, well that might be true, but we can see up to 42 million light years away. We can't see anything further
So you might say it's infinite time. I say to you
No
it isn't it closes up in itself and a finite radius or I can say that it's bounded by a
Singularity of the finite distance. You can't prove you're right. I can't prove. I'm right
You can say anything you like I can say anything. I'll ah
By the way, that's a very controversial statement because there are many cosmologists now who believe that
Our part of the universe is infinite. It's flat and it's uniformly filled with with matter including a Brian green
I think who's the father of this whole thing but you know, we have to we have to proponents of the multiverse here
Surely you're going to take issue with this, you know, rather metaphysical claim that he's making or maybe not
I'd like to make an important distinction between what we view is space and what we view is time space
I think we have no way of knowing directly whether it's inferred or not
As you say we can only see a certain distance and only speculate beyond that
Same thing is true about time except for time evolution. We kind of have a theory the Schrodinger equation of quantum mechanics and
Quantum mechanics does not seem to have any natural way of ending time
Therefore I think the reasonable assumption to pursue is that time is infinite
Time is
The correct statement is not the time is infinite the correct step into the time will be infinite in the far future
Which we will never reach because no matter how far time has gone. You haven't reached the far future where it is infinite
So it's always in the future. So it isn't true that it isn't
Well
IIIi don't think distinction has any real importance -
I mean space-time exists we talk about space-time and and if we know it will exist. That's as good as I don't know
What the tenths now means in the context of a space-time we need to floss reality. We need to
It's very one of the first just a one remark from theosophy
Is that Aristotle that guy a long time ago made a distinction between the actual infinite and the potential infinite I think?
George's view is that
There's a may be a potential infinity unless there's no boundary
Allan's view might be there's an actual infinite as far as I can
See, there's nothing contradictory about space or time actually being infinite. We know there are models in
Mathematics and which are consistent in which they're actually in infinitely many abstract entities at any rate numbers
Whether any scientific theory needs to posit the existence
Of an actual infinite is a open question, I think
Get to which is that given what we call them physics coma DeLucie tunneling
Technical word. If you have an infinity of time you automatically get an infinity of space
Coming along with it space and time were more or less interchangeable in the context of general relativity
Pick up on that. I mean science is full of claims
You know current science is committed to all kinds of claims about what sorts of laws things are obeying
in the Centers of distant stars
That we're never going to be able to witness, but we take it to be a natural
extrapolation of things that we take ourselves to have good reason for believing
So the observation which is surely true that there's never going to be a direct empirical proof
That the world is infinite or that the world is finite
It doesn't seem to me to be equivalent to a claim like we couldn't imagine ourselves
Having what?
we take to be good scientific reasons for
Supposing that the world is infinite or finite in this or that respect. I'm
Barry just mentioned one the the you know, we have the Schrodinger equation
It's you know
We we have all sorts of good empirical reasons
For having faith in the Schrodinger equation and the Schrodinger equation doesn't present this with a natural opportunity for the time
Parameter to come to an end. So it seems like a plausible thing to say that it's infinite
You're absolutely right in pointing out that that's going to be one among
you know uncountable numbers of
claims about the world that our science is committed to which we're never going to be able to directly
Empirically confirm or refute you seem to be equated that with a claim that we couldn't have anything that counts as a good scientific
reason to believe one way or another
About such claims and I guess I don't see how that follows
You are the father of the theory of eternal inflation and eternity has a kind of intimate
relationship to infinity
Give us your take on this and make it funny
Be stopped and that actually is similar to what actually happens in our universe
Most probably now right now. Our universe tends to be well at least started up about 5 billion years ago
Exponentially expanding. And if this continues then our part of the universe eventually will become empty and
We will found ourselves
in
Something which is called de sitter space and the sitter space has largest distance
From which we can ever get any information and this is called de sitter horizon
So the whole universe the whole digital universe may be infinite
But only part of it will be accessible to us. So in a sense, you'll say ok
So what is then the unit multiverse if you have just a finite patch of everything to explore?
on the other hand if we study it a little bit deeper and
Study what happens in string theory?
for example in string theory
a lot of different working states in our working state may decay in the future and when it decays our
Horizon may expand and expand and become infinite or we may all collapse and die instantly, so there are some possibilities
Which right now we cannot even fully first
see all of this picture of the universe didn't exist in the sense, which we
Perceive it right now. It didn't exist about 35 years ago. So
To come and stay I would forbid this picture being discussed because it well
Against my general principle. This would probably be
well
III would warn us against following the lead of those who want to forbid us something but I don't think that George want to forbid
He want to put a question mark here be careful because there is something we should be taken into account
Seriously, and I absolutely agree with this position. I
Particularly want to put a question mark against statements coming out in the popular journals saying how far away is your next self?
And I just think to talk about yourself having infinite replications is kind of really stretching beyond
This notion of the universe. There are exact replicas 10 to the 10 to the 100, you know angstroms or light-years
It doesn't matter that scale away careful with words because multiverse is used
like a slogan by many and if you try to Google the multiverse who studies it how the
tendency then she grows up all the time and then you will do more careful search who actually
Will dialing on Google the multiverse. It appears that most of the people who do it are from Peru and
Then next
Position is from France
And then you will fine-tune
The search and it appears that people in Peru. They playing the game dragon multiverse
So
What kind of game do we play and this is actually very very simple
Just think about our own earth. There are many many countries on earth
Each country has its own laws. Okay, China
Russia us and then imagine that the size of the universe blows up to incredible ball
size and that the main idea of inflation so we have China so large that
anybody living in China would have no idea about
United States in the United States would not have any trade war with China
because it will be not infinitely but practically infinite distance and there will be no internet connection or
whatever
so then the this is a very simple very
practical idea and then somebody comes and say oh
I live in the place where these set of laws and this set of laws is unique and other laws are impossible
and if I water than its liquid water and the captain of the ship just
Take the ship and then suddenly in night
He crashes into solid water and Titanic goes down
So the fact that we have seen something
experienced something
it does not necessarily prove that something else is not possible and broad a set of possibilities as a
Larger set of rules is more natural from my perspective than forbidding something beforehand
I'm trying to bring Veronica into this but I do want to bring you in prematurely
Would you as a string theorist and of course the string theory?
Feeds into the idea of the inflationary multiverse because it produces something called a landscape multiverse
But you have a slightly coy and cagey relationship to string theory
because you see it more as a tool rather than as a
fun a real description of reality
But I'm I'll let you talk. I mean, I view it as a framework which allows all these possibilities
Depending on what you put in so it doesn't really bother me that the framework allows
all these possibilities and
Whether or not there's infinitely many of them
You know doesn't threaten our our notion of reality and and and so forth
But let me put in a word for infinity in a context of dust can infinity be useful in physics
So so far we have been talking about
You know is our universe infinite or something like that and I I sympathize with all that have been sort of said on stage here
that
You know if you count
Physical objects, let's say then, of course, you can never get infinitely many of them
But you know
If you it might still be mathematically useful notion in the sense that if you allow me that that can be say
Zero number of a certain types of objects then I can just say well, let me talk about one over that
okay, that's that's a bit silly example, but it
It goes to sort of it's meant to illustrate
That there could be different
descriptions of
the same physical
Reality and those different descriptions could be useful for various different things and it could be that in one of these descriptions
The thing that's most natural is the one over the what end that ends up being zero
I think this is a very important point I think just as
Infinity doesn't exist in physics zero doesn't exist in physics either and that's what the quantum vacuum tells us. So I don't believe that
I don't believe that between my fingers. There's an infinite number
Uncountably infinite number of physically different points and that's equivalent to saying that those points have zero size
in fact in in in the real universe
I believe that space time must be quantized will have a little finite size and then there won't be an infinite number of points between
my fingers
two things
I wanted to add to this conversation one was about what Veronica just said in this discussion with George and that is if
You can count to infinity if it took half as long to count
The next thing is it did the previous thing then of course, that would be a series that converges to infinity
Sure, though George thinks that that's an impossibility
the other thing that I
Count to infinity you say it takes you one second to say 1 1/2 a second
Say to a quarter of a second say 3 and so you've run through all the numbers in 2 seconds that way
Other thing I noticed was the different attitudes that Andrei and George have to what exists
Andrei's idea if it said if it's not forbidden
It's there George is you got to show me. It's there that it's it's there only if it's and
demonstrated to be their
Position minds of physics
Given what I know about Andres background in physics is shorthand for waste of time
Two years from Russia and one of my friends there
well expressed his attitude of the difference between
How things work in different countries and he say in Russia everything that it is not explicitly
Allowed is forbidden
In the United States everything that it is not explicitly forbidden is allowed
And I much prefer this was possibility
So, I think that's really very good in politics maybe not so good in epistemology
So we've done infinity and eternity now, so let's move on to something I mean, how about creation now
Andre and
Allan but had both
Years ago had a kind of really clever
Creation ex nihilo scheme and I understood it and I thought I don't know whether it's true or not
But it's a an alternative to you know
The God bringing the world into existence and all of that and the idea was that out of sheer
nothing a little nugget of false vacuum could quantum tunnel into existence that
White sure nothing. They need something very particular. It's a closed space time of zero radius
So it's like taking a balloon and shrinking down to a point and that's the closest you can get mathematically speaking to defining nothingness
So out of this beginning of nothing a little nugget of false vacuum
quantum tunnels into existence and then by the magic of inflation this blows up into the multiverse, but now everyone has
Stopped believing in it and you believe that the universe the multiverse didn't have a an origin in a finite time in the past
It's eternal
Looking back into the past and eternal looking into the future and you know, I frankly don't understand this
Why were you wrong about saying it had a finite past in the first place?
Allan you had a proof of mathematical proof that the universe had a finite beginning in the in the past
And now yet what was wrong with proof?
Listen why should we bleed you on global warming if you okay kidding?
Nothing was wrong with the proof with what's wrong is your summary of the argument
The statement was never that the universe
Necessarily had a beginning the statement is that we followed the era of inflation backwards
The era of inflation had to have a beginning that we still think is true
And it's certainly also but I think you exaggerated tremendously when you said that now all of you people
Don't believe that the universe had a beginning as far as I know. I'm really just speaking here for myself and Sean Carroll
we've been working together on a model of the universe that would be eternal and
In this model that Sean and I are working on it will was originally proposed by Sean to give credit where credit is due
We'd be living in an era where time is going forward and entropy that is disorder
Which we think of as almost a proxy for what the finds the arrow of time?
Disorder is growing towards the future and getting smaller towards the past
And then these models with a definite beginning the universe would have begun at some finite time in the past with essentially zero entropy
Zero disorder and that's still a possibility. I don't mean to say that that's not possible
What appeals to Sean me about this alternative approach?
has to do with the symmetry in physics
symmetry of time reversal invariance
all the laws of physics that we know of our time reversal invariant that is
we here can be sitting on the stage and talking and time has gone forward if
There's also a quantum state wherever all that is reversed
then everything is happening exactly the same but in the opposite order the laws of physics don't care about distinctions between future and past and
One puts in a beginning of this sort you're putting in a distinction between the future in the past
We have a beginning in the past
The goal is to produce a picture of the universe or multiverse
Where know where those when put in anything that violates this symmetry between future and past so the way the model works
There's an intermediate period which you might think of is the logical starting point
Where the arrow of time is not well-defined
Disorder might be growing might be shrinking doing one thing one place
One thing a different place just chaos basically, but then if you follow that forward in time
there are laws that we think we understand which say that
Disorder will start to grow
Entropy will grow an hour of time will develop
Going that way and we also have in mind that all this is going to be undergoing in inflation and in fact eternal inflation
If you follow the same thing backwards in time the same thing happens
but in the opposite order of this the laws of physics as I mentioned don't care about
T vs minus T. So if you follow up backwards in time
entropy disorder starts to go in that direction
inflation happens backwards in that direction
So you have this two-headed arrow of time picture and the beauty of that is the full system is is completely time reversal invariant
zoom same thing back
So you have a nice picture of the multiverse which automatically contains an arrow of time which was not put in by hand
But arises naturally just from the evolution of laws of physics that we think we already understand
David you're the natural person to
Critique this because you you this is the man who coined the term the past hypothesis
Which a very simple coinage but is really caught on the past hypothesis explain with the past
although I don't think it's in such dramatic conflict with this the
Usually before we were considering
Theories of the kind that we're just described we used to we used to think that we needed to make a special posit
to the effect that
that there was a
Initial state of the universe where the entropy was very low
What's going on in in Sean's proposal is is that the idea is being floated that maybe
The cosmos doesn't have anything like an equilibrium condition. That is the cosmos
there isn't any upper bound to the entropy that that the cosmos can have so
So wherever you start out
Entropy is going to go up from both sides of that. It doesn't matter what kind of state that is. That's still going to be
That's still going to be a situation in which on either side of this minimum
You have the equivalent of a past hypothesis. You're just not
You're not claiming that that things can't be and you know that things can't be traced back even
Behind that so this seems to me not something
Not something that contradicts the past hypothesis
It's an it's an attempt to put something like a past hypothesis in a larger framework
Well, you know at the moment there's this huge controversy over
the
over
inflationary theories in the multiverse, you know, we have the - - of the creators of
The theory of cosmic inflation here on stage when the third
Arguably the third father of the theory inflation is Paul Steinhardt. Who's the Albert Einstein professor of physics at Princeton and he's now become
an adversary of the of the theory of inflation
And there in the Scientific American I believe there was an article
published by Steinhardt and some collaborator
Hydrators arguing that the theory of inflation was a bit of a failed research paradigm
Tell us why there's so much suspicion about the theory of inflation among
You know pertinent perfectly reputable physicists Barry you you good Barry's a good friend of Steinhart so he can give the I know
Steinhardt now the others about but I'm not a party to that because I'm not a cosmologists
But it does remind me of a famous remark that Lev Landau famous physicist
Russian physicists made about
Cosmologists, I think the rim barkos something like this
cosmologists often an error never in doubt
That's good, oh I think all cosmologists you must be taught this in the very beginning
That wasn't even your to explain to us why
Why they're unhappy I mean it's there are two reasons as far as I understand it
There are our intrinsic problems with the theory of inflation. It's in a way. It's too elastic
there are too many versions of their hundreds of proposals for a theory of inflation and they all
hypothesize a
field that does just what you want the field to do and there's no empirical evidence that this field exists and the other problem is
That it implies the existence a multiverse in which anything that can happen will happen. So how do you test them thing?
So that's a very cool three
Reasons, I don't think that I think there's reasons to think that the kinds of fields responsible for inflation could exist
and so I don't think that that's their objection so much, but I do think that their objections that are interesting to
Philosophers that you mentioned one. Is that as I think you mentioned earlier
inflation was introduced in order to explain certain things about the
initial
Initial conditions in the early universe like that. The universe has a very flat geometry that the universe
is very homogeneous and
These need to be put in by hand in the Big Bang account without inflation inflation
looked as though it was giving an explanation of
This would look like fine-tuning, but their worry is and also Roger Penrose is worried
Is that more fine-tuning is really needed to get inflation going in the first place. That's one worry
Another is that inflation is really a whole
model a big framework of theories with a lot of free parameters in them and by changing the values that parameters the
the the
Potential energy of the field and the curve of the field and so on
You can get it to adjust various
empirical consequences
And that that objections seems that somewhat at odds with their other main and very interesting to a philosopher objection
and that is if inflation is generically leads to internal inflation the production of all of these
pocket universes and if in these pocket universes can be very different maybe even fill up the whole landscape of string theory as I
think some people think
Then it looks like the theory itself is predicting that
Anything that can happen will happen as Allen has been quoted is as saying and it looks as though a theory like that
Just can't have empirical evidence for it. And that's a really interesting issue to hash through
Maybe a little bit too in a house for here
I don't know but it's so I want to give you an idea of the the
different proposals of poor periods of inflation
Yours verse you used the term inflation first to refer to this cosmological theory then you came up with
chaotic inflation which became internally eternal inflation
Steinhardt was extended inflation and then we have we have also
Extended I should double inflation triple inflation hybrid inflation mutated hybrid inflation
tilted hybrid inflation hyper extended placeand and invariably super natural inflation
And that's just that there are hundreds of others not all of which have names. I'm sorry. I'm not
First because there are much more okay
But what is important about them that all of them are just
versions of one general principle and this principle is that in the very beginning of the universe for whatever reasons and we can
Speculate whether it was tunneling from nothing as Alex Vilenkin
suggested or some features of wave function of the universe or whatever the
region of space tiny tiny region of space filled with some special kind of matter
Which is not very specific and then the space if you follow equations of motion
Which anybody can solve it's really really simple start expanding
Exponentially and then after that it produces big chunk of space which is much bigger than people
Expected before and after that decaying field produce all matter in the universe
And it looks like science fiction you solve equation. You see that's how it is. So that's a basic principle
after that, you start
Fine-tuning what if I need to adjust some parameters?
of the theory to describe whatever they the experimenters are going to bring us and what if I
Try to implement it in string theory supergravity grant. In fact theory
That's why many people's is just that many different versions. They based on the same principle now, let's compare
with the history of standard
model of elementary particle physics
Describing weak strong and electromagnetic interactions just in describing weak and electromagnetic
interactions required 20
Parameters to adjust the theory to describe experimental data
marzo, the Higgs boson very large
Nobody could predicted mass of the top quark very large, but people knew that top quark is necessary
So what is necessary to achieve is some framework and then feed the data at the moment?
there are some inflationary models which
Require just a single parameter
to describe all
Inflation related data which Planck satellite and other experiments given one parameter is enough. Is it complicated?
I don't think so. Look
Here's something that people may be puzzled about one. Here's two claims about inflation as it's practiced now one
That there is spectacular
enormous, ly impressive agreement between its predictions and what we see
Second that it's a theory that predicts that everything that can happen
will okay and will for certain and there's prima facie an
obvious puzzle about how to put these two
remarks together with one another
if you know go back to your
analogy of the earth
Expanding. There are all these different countries. They have different laws there an infinite number of them
In fact, they have very very different laws. Things are very different going from one country to another
Somebody's about to open his eyes and would like information from science about what he should expect to see
Okay
it seems like if you have if you have a situation that the picture of the world is there's this enormous earth on which
there an infinite number of places and
everything
Describable is happening in one or another of those places. This is going to give the person
exactly zero information
About what he should expect to see and in this case, it seems puzzling
Good, so this is but presumably you understand puzzlement. Yeah and good
Okay
You want answer this but
Since I'm the one who keeps getting quoted saying that in the multiverse anything that can happen will happen an infinite number of times even
Let me just clarify that sentence
If something has a probability of ten to the minus six it means if you do something five times
It's very unlikely to happen if you do it ten to the six times
It's likely to happen. Once if you do it an infinite number of times, it's likely to happen has to happen
In fact an infinite number of times, but the probability is still ten to the minus one-sixth
If you do only make a finite number of observations the probability of you seeing that is very small as I like to say
Even if there is a multiverse
Unfortunately, the probability of my winning the lottery tomorrow is not high
It remains not but let me just jump in there. Okay, go ahead
What you're saying implies that the picture comes along?
with some set of probabilities of this being the world that's realized or that being the word that's realized and my
Understanding of the current status of the theory in which people are looking for a so-called measure over these worlds
Which would provide us with the with the probability you're talking about is is an element of the theory which is so far
Not in place. Okay, which we're hoping is going to be in place and is going to give us the right
Probabilities is going to identify what we see as a high probability kind of an event
Would somebody be wrong to say oh I see so
The hard part hasn't even begun yet. Okay, all of the physics of this is going to rest in the choice of a measure
That part that's a notion of
uncertainty onto which we haven't even dipped or
Into which we haven't even dipped our toes yet. Would that be a fair thing to say? I think I'll be a slight exaggeration
I mean I
Said no a lot of what Dave Dave just said is true
There is a measure problem and I was just gonna get there honestly
Whenever
physicists talk about the measure problem
they're talking about a fiendishly difficult problem having to do with defining probabilities when you have you know, in an infinite number of
you know possible events and it's all physicists say
You know tend to skirt it they tend to because it does seem to be all insoluble in every context in which it arises
But so the measure of problem means a problem with defining probabilities. That's that's all yeah
vacation so
People work on inflationary cosmology are aware of this major problem
When we say it's an unsolved problem, I don't know
It's either an unsolved problem or a problem for which we have multiple solutions. Those are kind of equivalent statements more or less
We don't yet know what the right solution is
We certainly do have proposals which define probabilities and ways which seem to be perfectly consistent with everything that we know of so
We think of this decision of how to define a measure as an empirical decision
We do have ways which work empirically I should also emphasize that there's no doubt that it's possible to define
Probabilities on infinite spaces mathematicians will be doing that for ages for a century anyway
So the only quit is their many choices usually and that's the issue here
So we do have to find the right choice, but there doesn't seem to be any problem in finding choices that are very sensible
What we still need and hope to find is a way of definitively determining what the right measure, okay
Look, let's get away from the measure problem. It's just too hard and let's get on something simple like anti-de sitter space conformal field theory
Duality and the holographic principle, which you have to talk about because we haven't heard enough from you
You have two interesting takes on the fundamental nature reality
So in in string theory we have seen these remarkable statements which we refer to as dualities
Which is the interesting situation that the same physics is?
described by different
theories different mathematical languages if you will and so there isn't a
sensible
Way to ask the question. Which one is correct?
They are they're both correct in this particular example of duality, which is referred to as a DSC Ft
duality or gauge gravity duality
the two sides that describe the same physics are
A theory of gravity in particular string theory. Okay living in higher dimensions
Which is precisely
equivalent to a theory without gravity a so called gauge the
conformal field theory
living in lower dimensions
in fact, you can think of it as living on the boundary of the space-time that the gravity lives in and
Well, it is believed more generally more generally so studying black holes that any theory of gravity has this
Holographic nature to it that you can encode all the information that's happening in such a theory
with a lower dimensional
To it if you could only see the shadows on the wall
You couldn't reconstruct everything that was going on at the cocktail party in the room right with shadows indeed
You couldn't tell enough neither
Can we tell with movies which seemed a little bit better than shadows and yet they are supposed to be you know
Two-dimensional representations of our three-dimensional world because you don't see what's behind that, you know foreground things or stuff like that
So here in this holographic duality, we would have, you know, clever shadows
Er things that actually know the entire sea, okay, so indeed that's very counterintuitive
You fit all this information on a lower dimensional theory
But maybe the point to make is that a theory of gravity
Already does not have as much room in it as you might have thought
And that is the reason for that is is gravity in once you have gravity
You can collapse black holes, for example
Which is a very generic
type of behavior and
If you try to say pack in as much information as you can in a given
region
Say in this room
Okay, now we can think you bring your book and we can read it in that some amount of information. I bring another book
and the great brings one more book and so forth and we can pack this room with books and that's still
There's no problem with that
But once we sort of tried to packing so many books that we would sort of
Push at the limit of how much information can be packed in
Gravity takes over and the whole thing will collapse into a black hole and now we'll see that in fact the amount of information
Scales only with sort of the surface area of this room rather than with a volume
Okay, so gravity has somehow built in the structure of having being describable by a lower dimensional sea
Okay, so that's called the holographic principle. Now this duality is a concrete realization of that
This so-called EDS CFT duality. The ATS side is
Stands for anti-de sitter. It's a particular space-time that has a negative cosmological constant
So very different from the expanding universe that we're living in
But nevertheless because it's a theory of gravity it contains black holes
And in fact, we believe that black holes are behave just like the black holes that you know, we see out
in our in our universe and
Now the miracle is that yes, there is this other description this lower dimensional description
That now does not have gravity. It does not have black holes
but everything that sort of is happening around us all these black holes and stuff like that are
described in this completely different language
It's very square
But it's a same same physics is happening in this in the bulk theory in the higher dimensional theory
You've got a black hole in the boundary theory, which is a complete description as well
The what looks like a black hole is actually a bath of gluons and quarks
so
David being a philosopher is concerned with reality as it is in itself. He wants to know which is real
They're black holes, or maybe that's a naive question
I'm being forced to say something that I don't
That I'm not sure I believe I mean I guess there is maybe here's a way to put the question look
Physics has tons of mathematical equivalences
So we can talk about
Say the the condition of a classical system of particles
Portrayed in three-dimensional space or we can talk about it in configuration space or we can talk about it in phase space
All of these are in a very straightforward sense mathematically equivalent
mapable into each other isomorphic to each other
There is a temptation to say in the classical case
Yes, but notwithstanding these
isomorphisms
the three-dimensional space is the real one the
Three-dimensional space is the physical one
Is there an analogous question?
In the kinds of equivalence is that you're talking well there may be several things one could say about this
Maybe you think even in the classical case the question doesn't make sense
Well, although most people would think it does. I think there's a, you know hidden assumption in this which is
Who is asking okay, so you are asking and you are sort of local?
object and to use
Talking in sort of the position space. It's most natural
So then that somehow singles out a preferred description because in some sense
you're sort of providing the
Basis on which to ask this question, but what is it? I don't understand how I'm I'm part of this description -
There's an old question attributed to Vidkun Stein people said to him
people said to him, you know, he said I can't understand why I the the
Copernican theory was counterintuitive
And people said well because it looks like the earth goes it looks like the Sun goes around the earth and Vic and Stein
No, but Vic and Stein reportedly said what would it look like if it looked like the earth goes around the Sun?
And
So I take it the same question applies here. So is the claim?
Sure if I prefer to describe things in 3-dimensional space, of course
I'll be describing them in 3-dimensional space if there's some psychological
Feature of me which prefers three-dimensional space, of course, I'll describe them in three dimensions
most people would say and it sounds like you think the
You think the right thing to say about this is just that it's a mistake. Most people would say in classical mechanics
No, there's some metaphysically significant sense in which the physical space is
Three-dimensional and in which the others and in which the others are just sort of abstract mathematical
representations you think in the classical
Is that if your brain is flashed on the wall right thing good exactly, right
But your brain is a blast on the wall according to
But that is the same brain is the one that's in the three dimensional space I
Think those are two things
Aren't they the same thing good if they're the same thing then?
It's a linguistic question. Right? We have different descriptions of the same thing and that thing is
You know, there is one thing but we're describing them in different
Languages and now you're sort of trying to force me to say well isn't one preferred
To the other because we somehow have this gut feeling that yes. We are living again
I'm not trying to force you to say anything that the
But it's just a question in the simple classical case. Most people would say indeed
This is how people are taught physics. Oh, I see what's going on
The real deal is three-dimensional space and there are particles moving around in three-dimensional space
There are various other abstract mathematical representations which are useful in certain contexts
Configuration space phase space so on and so forth
These are useful. There are all kinds of problems where I'm going to turn to those
But there's some sense in which I'm going to think
What's really going on is the three-dimensional space with the particles moving around in it?
And and it's not that I'm claiming. That's obviously right? It's
Interesting that that's what most people even people with a physics education
Would tend to say it's convenient and it's convenient psychologically, but why is it crucial?
Because somebody wants to know what's the dimensionality of space and
And it sounds to them David. What's your answer to that by the way? Yeah, very counterintuitive
Answer. Yeah, that's another story. Okay, just tell me how many dimensions space
n times the number of well
The number of elementary degrees of freedom. Yeah. So what's the order of magnitude is it about it's it's really big. Yeah
So we have 12 minutes left and the two topics I thought were interesting were you're getting onto the soft ones
beauty is a guide to truth in physics that maybe - but but but George is interested in the
limits of physics and the limits of science and if we knew the universal wavefunction
Could we predict that the we were gonna get together and have this particular conversation and say these particular things?
Does it leave any room for free will this and you have a notion of top-down causation?
Which I'm very skeptical of but I want to hear about it. I want to be
Free will is a difficult one, but let me make the following statement
According to the standard big bank till it's heaven period of inflation. I'm happy with that
We've got the last scattering surface. We matter and radiation decouple we've got particles on the last scattering
so it was a question of the following if we knew everything about the last scattering service to the
Finest detail could we predict what is happening in this room at this moment?
Could we predict physically what you have just said, my claim is absolutely not there isn't the faintest chance
That would be true. The reason is because for many many reasons
I'll just take two when this quantum uncertainty between here and there and I could amplify on it the second one
Is that what what coin of what because knowledge do is they?
Characterize something called the transfer function which goes from here to here. We have difficulty even explaining a black hole
Dark halos, and so on we have difficulty
characterizing the distribution of galaxies in practical terms is not the faintest chance, but
Supposing there was a chance of doing that then you would be telling me that somehow the words
You've just said we're written into the last scattering surface by some Demiurge and I don't happen to believe that that could possibly have happen
So the real statement is the last scattering surface set up the conditions, whereby
Higher level beings like you and me could come into being where we have
psychological powers in which we can argue at a psychological level and that
Psychological level has real causal powers, which are allowed by the physics, but they are not
Predicated by the physics the physics cannot tell you what you are going to say in
Psychological terms because you're doing a logical argument and the physics has no
Concept what that logical argument is and which you said is a highly heterodox point of view. And does anyone here agree with that
Does anyone here because it seems to violate
the unitarity of quantum mechanics and I
Believe quantum mechanics is unitary because I happen to believe that mission take place every time my measurement takes place is not unity. Sorry
I don't know. I don't understand what any quantum physicist says quantum mechanics is unitary
So do you think this is important because it does leave
A note London opening to a robust notion of free will yep. Okay and
Surely this must have raised some hackles here
These are excessively polite people, but they're raging inside
I would like to get one
clarification from suckage about what what a measurement is in your view so weather measurements before there were people and
Quantum measurement problem we're getting into which is really
Measurement is coming because people first discovered this in laboratories
But a measurement takes place where in a superposition goes to an eigenfunction
That's a non unitary process because you lose the information
About the superposition and you end up with one specific that happens all the time everywhere
it happened in the early universe where nuclear synthesis took place long before there was a when does it what are the well
It's the law that determines when that happens. We do not know that's one of the big things
We don't know how it happens and we have no specific
Characterization or when it happens is one of the biggest Kuna the foundations of quantum mechanics
Yeah, those pictures of the screen with the particles coming on to the screen and you cannot predict where the next particle come on
Those wonderful pictures the particles. Come on one by one. Nobody can predict where the next one come but eventually you put up
Those it builds up to those interaction patterns in which you can predict with great fidelity
What the final?
Statistical thing will be but you cannot predict what the next one will be and that is the evidence for what I've just been says
That consistent with the average interpretation or many other interpretations of our mechanics that do not invoke this mysterious
Giveaway function give me some way of
Experimentally showing the Everitt interpretation is true just weak
So look
As Jim said we're getting here into
altogether different territory of
the measurement problem in quantum mechanics, but
We now have lots of ways of thinking about the measurement
It's too early to know just as with choosing between inflationary theories
It's too early to know which if any of the ones we have now is going to turn out to be correct
But but we have lots of ways of thinking about them which contradict
crucial assumptions that you were making on our us supporting the Everest interpretation, which is putting no
I'm not I'm not actually I'm a I'm a very
I'm a very trenchant critic of the Everett
Interpretations, no one uses the term ever ideas in any world
They're three of three or four interpretations. They're all good. So there is this puzzle
If we come back to my question
I think Ellen and says there's ilion's of other worlds out there in which we each said different things
Rather than what we actually sit here
I think it is simpler makes more sense to say the Grail emergence takes place in which we do have real psychological powers
And in which we can make logical arguments came to logical conclusions lead to what we say
And I think that is what has happens
Not that there's a zillions of other possible things happening out there which we cannot prove how happening
okay, I would say nobody on stage agrees with that but
Actually the whole discussion
brings us a little bit back to
Discussed and that is about the measure problem because right now we're returning to the measurement problem
Which is a different problem
Which is however very much related
because in both cases were talking about whether there was something in the early universe, which was definitely
Defined before anybody have seen it
because the measure problem is
What is the problem over the first event? Which now?
Nobody have seen it. Then the wave function was not reduced and stuff like that
So what is interesting about that is the measurement problem is?
discussed by everyone for almost a hundred years and
you can really
Find people who are complete in all details agree about the solution of this measurement problem and nevertheless
Quantum mechanics works pretty well everywhere agree about that
So I think that this is very similar to what happens with inflationary cosmology
which we do there are not so many people who absolutely agree about which
probability measure in in world many world while many universe interpretation of
Inflationary theory is better. But what more or less everybody agrees among?
Experimentalists with whom we're discussing it who are providing us with data?
so more or less everybody agrees that if you have a given
Inflationary theory it gives them predictions which they check and the checking so far was pretty successful
Let me take a simpler example. We've come into existence through Darwinian evolution now
My claim is the following Darwinian evolution is consistent with physics, but it is not implied by physics
There is no physics textbook in which you will read the chapter on Darwinian even because it isn't a physics result. It's a biology result
Couple of things. I mean one thing that's striking is that people could come away from here
Learning that there are two big issues in the philosophical foundations of physics that are on the table
The measurement problem is Andrews saying the measurement problem
old one in the foundations of quantum mechanics and the measure problem a
Newer one was important difference in the two cases in the case of the measurement problem
there's quantum mechanics everyone learns or takes physics learns how to use it to make predictions in the
experiments that they do
what they
Disagree with is what's really going on when measurements are being made what the reality Iying reality is
George has one view David may have another view and I have another view in the case of the measure problem
It's a problem that arises for a particular theory in cosmology the theory of inflation
And it's really a question of whether or not the theory itself makes any predictions at all
Until the measure problem is actually solved. So these are two rather different both very important and interesting
issues
We have three minutes left on the notion of beauty beauty very fuzzy notion, but people great physicists like Stephen Weinberg
the father of the standard model says that you know
We're now in an era where we don't have a lot of
experimental data and observational data that we've reached the limits of the you know, there won't be a
Bigger particle accelerator than the Large Hadron Collider built in the foreseeable future. We're sort of up against an empirical wall and when that happens
Physicists rely on their sense of beauty and beauty has been a very reliable guide to truth
Weinberg said when he was a graduate student at Harvard Paul Dirac
Came and said to the graduate students don't pay attention to what your equations mean. Just pay attention to how beautiful they are and
And this is a kind of a weirdly mystical Lotus eating notion, but beauty has proved to be a reliable guide to truth
in the past and
now we were in a situation where theories like
String theory which were thought to be beautiful initially are now looking rather ugly and people would make the same claim about inflation
but I I will name them because I
Did Sheldon Glashow he said it's like metal he said it's like medieval
Sheldon Glashow in 71 suggested he is alternative to the standard model of electromagnetic
Interactions standard model was based on the theory. Sorry for math
Su 2 cross you want two different groups two different coupling constants many particles
Anomalies doesn't work and he suggested his own beautiful mostly symmetric model vector model. No anomalies
Everything is great and everybody sir. Oh, yeah
electroweak theory one Uppsala model
No
It's that
Because it is not beautiful and Shelley glacial model is so beautiful
And then they discovered neutral currents and they're very shaded glacial model. Okay
He got his Nobel Prize, but the one vessel our model survived
So that's how it was Eddie got a character named after about the Big Bang theory the TV show right? Do you have one?
No, there's no Andre. There's a shelter
Anyone else have anything to say on any epigrammatic observations to make on beauty is a guide to truth and
It's just two facts
Yeah
Well, first of all, I would dispute that string theory is not beautiful, but that's that's me
But but I think okay, the the word beauty has all these other meanings. I would I would think
simplicity and internal consistency are much more descriptive and certain types of logical rigidity and the
Example of that was general relativity you alter it a little bit it crashes whereas string theory is very elastic
No, no. Well, you might be I mean it has that the internal consistency is
very
powerful
tool in fact, it's very restrictive and of I mean
it's clear to all of us that whatever we propose as a theory can't be neutrally, you know self inconsistent and
But you might think that that's a useless thing because you know just about anything you propose you can fiddle around with
To make it self consistent, but that doesn't happen
And so this takes us much further along than than one might have thought and it turns out I mean the physics
packages itself in some nice way and yeah, it's
This here predicts multiverse, so it was really beautiful but yeah
Okay, so we've heard we've come to the end
We've heard the we've heard a scientific account of the universe and we've heard the philosophers commenting on it
So I think we should just give the last word to religion
So the religious story is in the beginning there was nothing and God said
Let there be light and there was still nothing, but now you could see it
And then I have to say, thank you again everyone
You
