
English: 
So thank you, it's a it's a great pleasure to join you at this gathering and
I'm going to
focus my attention on
an area of physics
That I think fits in well with the themes that you have been hearing about in other arenas other areas
because I'm going to be talking about the science of black holes, and this is a particular area that
demonstrates how those ideas that may seem
Ridiculous are crazy to one age
Can ultimately not only
Be experimentally an observation supported but in the next age can migrate
to
Canonical form to everything that everybody always thought was true. Everything everybody thought was right
So in a way if I was going to give one

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Takeaway message if I can use that
Unfortunate language for what I'll be talking about here today. It's that skepticism
is
an art not an algorithm and
that's absolutely vital because when you approach certain ideas as if there is a fixed set of
criteria by which you're going to judge the things that you consider to be true and the things that you do not consider to be
True you can inadvertently
Cut out a whole collection of ideas
That you simply at that moment in time
don't have the
intellectual
architecture to judge and that certainly is the case with the science of
Black holes now. I
Recognize that people come to this gathering of the whole variety of different backgrounds
There are some of you who no doubt could stand up here and give the talk

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Dovan and grappled with them fully so in order to give everybody a little bit of something
I'm going to art fairly basic and then as I get toward the end of the talk, I will
be taking on things that are right now at the cutting edge and as Barry just mentioned to me since this is
the last talk
There's no place that anybody has to get to
so I
think probably sometime within four or five hours we should
We should cover everything that I'd like to cover
No, so so toward the end as I as I migrate into more of the cutting edge thinking about things
I will try to draw a fairly sharp line between
those things that we now

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Have great confidence in because of
Observation and experiment and those things which are still in that
Fuzzy but fertile place where people are developing the ideas and we don't yet know if they are
Right or wrong? All right, so to get into the subject
Black holes. It's a
area of investigation
That relies upon our understanding of the force of gravity
So to get us all on the same page
of course the first person to really think deeply in a quantitative way about the force of gravity is
Isaac Newton and
If you cast your minds way back to the late 1600s
Again, a very different era than the one that we experienced a time. In fact when
The Black Death was waging a winning war against humanity and to escape the scourge

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Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Newton retreats to his family's home in the countryside of England and
There in pretty much isolation
But using the power of thought the power of calculation the power of curiosity the power of wonder the power of observation
Newton won a very different kind of
Battle for all of us because by the time it was safe for him to go back to the University of Cambridge
he would throw into dazzling relief a fundamental fact a
fundamental law about how
the universe works and that of course is the law of
Gravity the universal law of gravity. It's a law that we still teach to kids
Around the world you all know it F equals G m1 m2 over R squared. That wasn't meant to be funny
But I'm glad someone thought it was humorous
There it is the law of gravity on a t-shirt now if you're not into equations
the way of thinking about it in pictorial form is this

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English: 
you've got say a star think of it like the Sun a planet like the earth and using that little bit of
mathematics we can make predictions
For where the planet should be at any given moment and the wonderful thing is you look up into the night sky and the planets
are just
Where the mathematics says that they should be. So this was one of those
astonishing moments in the history of intellectual thought where a whole collection of
Phenomenon taking place out there in the heavens and in fact down here on earth was encapsulated in a little piece of mathematics
articulated by a handful of symbols
That indeed as we saw can fit on a t-shirt now when something like that happens
It captures people's attention
Right. That's not the end of a story, right?
that's the beginning of a story because now you can take an idea which was previously only
understood in a qualitative sense, and now you can put

English: 
quantitative power
mathematical rigour behind those
Phenomenon and in that way try to go further and that's what a number of people did
After Newton gave the world his universal law of gravity and in particular
Some began to think about a very simple
pedestrian concept which is the concept of
Escape velocity. So once you understand gravity
You can ask yourself the question
If you say have a planet, let's focus on planet Earth and you have a cannon you can ask yourself
What happens if you fire the cannon in a vertical direction?
now, of course if you just give the cannonball a little bit of a kick
We all know what happens goes up comes down. In fact, you can using Newton's laws
You can predict exactly how high it will go. It's a
simple and traditional high school problem to do

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Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
So now if you give that cannonball a little bit of a stronger kick it goes up higher
Still of course comes back down
but according to Newton's law of gravity you give that ball enough of a kick and
It won't come down it will
escape the gravitational pull of
The earth and in fact using that equation on the t-shirt
You can calculate the speed that you need to give the cannonball in order that it will not come down and the answer is?
That's right, the answer is? escape velocity what's the number?
Yeah, I don't know mile but I should know it but that sounds right it's about 11 kilometers per second so whoever said 7
Was that you?
Very good. I think y'all applause for the gentleman that I can draw that good. All right, so that's absolutely true
But now an interesting theoretical question comes to mind, which is this that number depends upon the size of the earth

English: 
So the question people asked was well
Like what if you make the earth bigger right a bigger planet and you want again to cause a cannonball to escape?
Well, you need a more powerful cannon if the planet is larger and again using Newton's laws
You can calculate kick it with a sufficient speed and it will escape the pull of that planet
But then an interesting question comes to mind from that which is what if you're firing not
metallic spheres what if you're
firing balls of light
photons
Well photons they have a speed right they have an intrinsic speed right? I can pull the audience again
But it will depend upon the units that you like to use some wise person will say well it's one in the appropriate units
But you know, which is true
186,000 miles per second 671 million miles per hour 300 million meters per hour, whatever unit you'd like
There is a speed of light right and that is a number and you can ask yourself

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
well, you know since that's such a large number in a situation like this you
anticipate that it won't be too hard to cause that light to escape but this fella right here a
clergyman
a clergyman named John Mitchell
He wondered way back when what would happen if you had say a star?
which if you think about it a star is nothing but a sequence of light cannons all
around the surface of the body that are firing balls of light outward and the question is if you have a
star and
You imagine it getting ever more massive then the escape velocity
Will go up and up and at some point you can imagine making the Stars so big
That the escape velocity is bigger than the speed of light
What then would happen. Well, the light would go up
Come down would not be able to escape
So this is the earliest

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Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Incarnation of an idea of a black hole wasn't called a black hole back then but it's the same basic idea
A body whose gravitational pull is so powerful. That light cannot escape now. Here's the thing
this analysis that was done by Mitchell way back seventeen hundred's using Newton's laws of gravity, but
Newton himself knew
That his understanding of gravity was incomplete
However powerful it was he recognized indeed that there was a missing piece and he wasn't happy about this. In fact, he was kind of
Embarrassed
by this recognition
Because although he had written down a formula that gives you the strength of the gravitational pull of a massive body
He was unable to answer the question of how gravity actually exerts its influence, right?
I mean if you have the Sun here and have the earth here
you basically got empty space between them and

English: 
Newton wondered and he pondered and he couldn't figure out how it could be that one body over here could affect another body over here
Without any mutual contact, right? That's the kind of idea you look at it and it is crazy
How could a body exert influence across the vacuum of empty space?
this is the question that
Newton asked himself and indeed in his Principia
He writes that the answer to that important question how gravity exerts its influence. He said I leave that
To the consideration of the reader
All right, he knew it was an open problem he couldn't figure out and said you figure it out right and
Nobody could figure it out. Right? Most people didn't even think about it until
One particular unusual thinker who could look at things in a different way

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Came along and
Albert Einstein had that uncanny ability to look at the most basic of questions and just
See them differently. So starting in about 1907 Einstein
Focuses his attention on trying to figure out how the force of
gravity works and
others at the time
some of the most
Respected
Insightful
Physicists in the world said to Einstein do not work on gravity
It's too hard of a problem. Even if you make headway, no one's going to believe you
you're going to ruin your career if you focus on a problem of that nature and

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Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
These were the kinds of people whose advice you should trust right? These were the individuals that
Had transformed our understanding of the world in an earlier
era an earlier generation and yet the whole
Power of science is that you can have new thinkers come along and basically say to everything that happened before ok
Got it
but I'm going to in my own direction and
that is the kind of thinker that Albert Einstein was so he stays with this problem goes against the advice and by
1915 about eight ten years later he comes up with what he believes to be the answer for how gravity works
I think many of you are familiar with the idea for those that aren't let me just say it in
Metaphor first and I'll show you a little visual on it
Einstein basically says look if the puzzle is you got the Sun here
You got the earth here and there's only empty space between them right? So, how could they be influencing each other?

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English: 
He says the only way they can influence each other must be to make use of empty space itself
Empty space itself must be able to do something
It must not simply be an inert backdrop, right? It must actually be part of the dynamical unfolding and
That's a startling idea and yet it's the one that he pursues and ultimately
Turns it into a rigorous mathematical formulation
So the metaphorical version goes like this forget about grab it in the universe for a moment a little
Complicated and stem think about a rubber sheet that stretched nice and taut between us right here. Imagine
I take a marble and I set it rolling on the surface in your mind's eye
You can picture exactly what will happen. The marble goes in a nice straight line trajectory
nothing
Complicated if I now change the situation a little bit. I take a bowling ball put it right in the middle of the rubber sheet
Now the sheets curved it's warped

English: 
And your minds I take that marble again set it rolling and you can picture it doesn't go in the same straight line
Trajectory any longer now instead the marble goes in a curved trajectory
Because rolling on the curved surface of the rubber sheet, that's the basic idea
But now we take it over to the universe instead of a rubber sheet space
Instead of a bowling ball think of any astronomical object and the idea is merely by a virtue of that objects presence within space it
Curves, it warps the environment around it and that
Curvature affects the motion of other bodies that are moving through that realm. So in visual form, it looks like this
So this is 3d space a little hard to picture and work with so I'd like to go to a two-dimensional version
That will capture all the ideas
So as you see space is flat when there's nothing there
But if we bring in a massive body like the Sun the fabric
Curves and the earth - it also curves the environment around it and now focus your attention on the moon
Because this is the point

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Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
The moon is kept in orbit because it's rolling along a valley in the curved environment that the earth
creates this according to Einstein is how
Gravity works and if you pull back you see that the earth is kept in orbit for exactly the same reason
Rolling along a valley and the curved environment that the Sun creates
that's the beautiful picture that Einstein comes up with and again, it's not just
pictures animation
There's mathematics behind this, right?
slightly more complicated
Mathematics and Newton's form of that we teach the high school kids, but there you see it again
Fits nicely with the right font size on a t-shirt
And that mathematics allows you to make predictions
so Einstein does make a prediction and the prediction has to do with the

English: 
Motion of distant starlight as it travels across space to the earth in two
Circumstances the first one here when the earth is on that side of the Sun compared to six months later
When the earth is on the other side of the Sun and that light has to go through the curved
Region near the Sun and his mathematics predicts the angle between the straight trajectory
six months earlier and the curved trajectory six months later and that prediction is ultimately borne out through
observations that took place on May 29 1919
so just over a hundred years ago and
indeed his prediction is
confirmed as you see
men of science more or less agog of a result of the Eclipse
Observations Einstein theory triumphs stars not where they seem to recalculate to be, but nobody need worry

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
On September 22nd 1999 Einstein gets a telegram alerting him
To the success of the observations. He's with a student at the time
Ilish nighter and she says to him
Professor Einstein what would you have said had the observations not confirmed your prediction Einstein?
Famously said I would be sorry for the dear Lord for the theory is
Correct
So with that great success
again, people notice people pay attention and
one particular
Mathematician scientist named Karl, Schwarzschild
Who at the time was actually stationed at the Russian front during World War one?
he
starts to think
About Einsteins ideas and comes to sort of an amazing

English: 
Conclusion. So there there he is, you know, he's supposed to be calculating artillery trajectories, but he finds that kind of boring
So no, he's just sitting there in the trench
Doing other calculations and sort of amazingly luckily for him fortuitously for us
Einstein's manuscript just happens to float out of space drops into his hand a hand
I should say for you skeptics that looks just like my hand for whatever reason but he starts to to calculate with Einsteins
Manuscript and he realizes that if you have a spherical body and you crush it down to a sufficiently small size
the warp in the fabric of space will be so severe that nothing that gets too close will be able to escape and that
nothing
even includes light itself
so here we have another version of
John Mitchell's idea that he derived using Newton's view of gravity. We see it
reappearing in

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Schwarzschild's analysis using
more refined version of gravity
so once again
we have the possibility here of an object that will not allow light to escape and
Therefore is black a black hole
So in the Einsteinian description, it'd be something like this. The warping space is so deep
that if you turn to flashlight on the vicinity of this curvature
Instead the light going out into space where you say could see it if you're far away
The light gets pulled in to the gravity. Well and therefore that region
Looks dark. Now this of course is an animation of
the mathematical description
What would an object like this actually look like out there in space?
well
Since it's black it would be hard to see but objects are always in an environment and that environment often has

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
gas and dust particles
So this is what it would look like something like this you have dust and gas swirling around this region
Which itself is dark we can see the light from outside the region and that's what allows us in
principle to recognize that one of these
Objects is there now?
when Einstein learned
about
These black hole solutions to his equations to his theory of gravity
He actually did not believe it and it took me a while to find what I considered to be. You know a nice
skeptical
Expression if you will on Einsteins face, right and it's not hard to understand why
Einstein was indeed skeptical that. These black holes would actually be real there are a number of reasons
Some are technical but others are

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
fairly straightforward to grasp
When you put numbers in to figure out the amount of crushing
that you need to
Exert on a spherical body to create a black hole
Then burrs seem absurd, right so to turn the Sun into
A black hole you'd have to squeeze the entire Sun to a couple kilometers across
To turn the earth into a black hole. You need to crush it down to about half an inch
across and
I didn't actually come here
with say a model of the earth as a black hole, but as I was
Contemplating my remarks just 15 minutes ago
Ray, is that correct? Yes in the front row here
completely independently showed up with an
engineered

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Sphere whose size is exactly what it would need to be
To turn the earth into a black hole not quite as heavy
But nevertheless it gets the size right so thank you for the for the prop but as you can imagine
If you talk about crushing the earth into this
That seems ludicrous
Right that seems absurd and that's why Einstein
Did not warm to this idea
But thankfully when Einstein frowned on this idea people didn't give up
Right, it's not as though you look at the master of an earlier age who had seen much further than anybody else and somehow you
Accord them some kind of extra
Right to truth right? That's at that stage an
Informed opinion, but it is not truth

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
so others stayed at it and indeed they came up with the mechanism a
physical mechanism that might actually crush an object like a star or a planet to a
Fantastically small size and that mechanism goes like this. So
Imagine you have a large star say a red giant
This star supports its own enormous weight
By nuclear processes that happen deep in the core that generate an outward pressure
Now sooner or later every star will use up its nuclear fuel and when that happens
You don't have an outward push any longer. So the star begins to?
Implode in on itself just by its own weight the force of gravity that makes the center hotter denser. Ultimately it
Explodes setting off a shock wave that ripples through the various layers of the star and when it gets to the star surface it
blows off the

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Surface and of course what we call the supernova explosion
And what remains can no longer support its weight at all and therefore just collapses
Right down to an arbitrarily small size
Collapses into at least what the mathematics says would be a black hole
So now not only do you have the mathematical?
Possibility that black holes will be out there you now have a mechanism by which you can imagine
them actually forming
That's good, but it's still not actual
observational evidence and the first evidence came from
studying our own Milky Way galaxy the
center of our Milky Way galaxy we believe there is a black hole and you can begin to see why as you look at the
trajectories of stars

English: 
They get whipped around the center of our galaxy
this is based on real data and you can see that stars are being whipped around at speeds of upwards of 10 million miles an
Hour, and when you look at what object in the small region at the center could exert the gravitational pull to do that
the mathematics shows that the only
Object that would have sufficiently powerful gravitational pull would be a black hole an enormous block called millions of times
The mass of the Sun so the case began to be made that these objects are actually real
However much Einstein thought they would not be
But the clincher for the case for black holes actually happens in our era right and I'll give you the two
vital pieces of discovery that have happened in fairly recent times and
They actually come from Einsteins work himself

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
So in 1916 and in 1918
Einstein writes two papers, they weren't on black holes per se they were on the possibility of
gravitational waves
Right the basic idea that's being expressed in these mathematical equations. Is that if
Space is like a rubber sheet right before I put a bowling ball on it
But now let me leave the sheet nice and flat here instead
Imagine I go up to the sheet and I start tapping its surface you all know what will happen
I'll send out a sequence of
Ripples on the surface waves if you will on the surface of the rubber sheet now Einstein's mathematics
Basically said look if we think about space and time
As an eye dynamical entity then as objects move through the environment
They should in essence tap the rubber sheet. Send out ripples in the fabric of space
Send out

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
gravitational waves
Now Einstein himself had a fairly
Curious relationship with this insight
because
over the years
he became
quite
uncertain of whether
These ripples in the fabric of space a could be detectable, but even more deeply whether they were actually real
Because the mathematics of Einstein's theory is so subtle
That sometimes even Einstein couldn't quite figure it all out a
Sort of a weird thought right, you know Einstein the equations in the general theory of relativity
they are called the Einstein field equations and
Yet in analyzing those equations
There were issues that I son himself had trouble fully coming to terms with and it wasn't really until the 1960s
when the next generation of thinkers took Einsteins

English: 
Ideas and pushed them further
that
Systematic mathematical methods were developed to fully understand
what qualities of the equations were mathematical artifacts and what qualities of the
Mathematical equations should describe something actually out there in the world and by that point by the 1960s
It became perfectly clear that if you did have for instance two neutron stars
Or even black holes that were orbiting each other in space. They would disturb the fabric of space and sent out
These ripples now. How would you detect that?
well
The mathematics made it quite clear to if you're downstream from these ripples safer on planet earth far away
Then as the waves go by they will stretch and compress stretch and compress
planet Earth
now I
Should emphasize that this video is not to scale

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
And
When you do the calculation you find that for a typical?
Astrophysical event
The amount by which earth would be stretched and compressed would be less than an atomic diameter
so now you see the other part of
Einstein's
discomfort with the notion of gravitational waves, it would seem that they are just
Undetectable, I mean, how could you ever possibly?
detect
the stretching or compressing of the earth or an object on the earth if the amount by which its length
changes is a fraction of an atomic diameter and
again
the beauty of the progression of scientific ideas
Is that sure you can be deeply skeptical that you'd ever be able to measure anything like that?

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
but the next generation comes along and
Says well, maybe we can and that's what happened here. So in the
1950s 1960s
Ideas were developed for trying to actually measure these
ripples if they're out there and
Two machines were built in the United States one in Washington state one in Louisiana. And as you can see here each of these machines
Involves two arms basically two tunnels at right angles to each other
so if I match the
Orientation on screen something like this and the idea is that light beams are sent down these two tunnels
They bounce off of mirrors and they come back and when the light recombines
The pattern that arises when the light crosses itself is highly sensitive to the exact distance that the light
has traveled so just to sort of see a picture of what that would be like if we
dive in to one of these tunnels

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Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
They're four kilometer long tunnels you then send a laser beam that goes down the tunnel
Races along hits a mirror at the far end and comes back and this is happening in both of those tunnels
simultaneously and the way the light comes back and crosses itself at the center is
highly sensitive to the lengths of the two arms the two tunnels and that means that if a
Gravitational wave were to roll by and effect the lengths of these two tunnels
Even by a tiny amount at least according to the calculations
It should affect the way the light crosses itself the way the light as we say
Interferes with itself as the two wave trains along the two tunnels cross
so this idea was put forward in the in the
1960s as a means of possibly detecting these ripples in the fabric of space and
thankfully the National Science

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Foundation decided to fund the actual building of the devices that I showed you there and
at first for many decades
nothing turned up and
I should tell you that the general feeling in the community of physicists was
That the people working on gravitational wave detection
We're off the wall
they were doing something that was just
impossible right and
yet they stayed at it and
Amazingly on September 14th of 2015
just two days after an
Upgrade to these machines was put into place
This is what happened
the two
detectors twitched
For about 200 milliseconds and they twitched in exactly the same way at two distant locations

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English: 
across the United States and that coincidence
allowed scientists to
argue that they had detected the first
Gravitational wave now I should say
this signal
September of 15 the announcement of a discovery was in February of 16
Because during those months
these researchers were
Desperately trying to prove that this wasn't a real signal right they were desperately trying to prove that
Maybe this was an artifact or maybe
Two trees happened to collapse in exactly the same time in Louisiana or Washington State or the more likely
possibility was
the team of researchers had put in place a mechanism by which

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
Test signals were put into the device
To see if everybody was awake and would capture the signal if it was actually
There, you know you put in a test signal and you come in the next day you say to the graduate student itself
Anything interesting happened last night? No, no, nothing. Nothing at all
And that's the graduate student that you know, you send to work on another project in another group, right?
so, you know the researchers they turn you know to
The first person who was charged with randomly putting in these tests and say, uh, did you do it?
Wasn't me you go to the second one did you do it? No, and they go down the line
everybody says I didn't do it start to think maybe maybe it's real and
they beat on it and they beat on it and they eliminate all other potential explanations and
Come to the conclusion that it is real

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
And in fact, they don't just come to the conclusion that the signal is real. They can reverse-engineer it
Based on the precise way in which the two devices shook
For a fraction of a second they can figure out what?
Astrophysical event must have happened
To give rise to a ripple in the fabric of space
that would look just like that by the time it washes by our shores and
the
explanation for that signal ultimately is this and this is where it ties into our theme here the
Explanation is that
1.3 billion
years ago two black holes
We're orbiting each other 1.3 billion light years away. Now, this is a time when there are you know?
Single-celled organisms floating around a primordial earth, right?
These two black holes are orbiting each other near the speed of light and ultimately they smash into each other and in that collision

English: 
They generate a tidal wave in the fabric of space whose energy output is 50 times the energy output of every single star
in
every single galaxies in the observable universe you put all that together and it doesn't even match the power of
That tidal wave in the fabric of space. Now that tidal wave in the fabric space is very far away
It starts to spread out in all directions at the speed of light. So part of it is racing toward planet Earth again
Nothing happening on planet Earth
But there's a long journey that that wave has to travel and as it travels it spreads out and as it spreads it dilutes
When that wave is about a hundred thousand light years from us
It goes through the Dark Matter halo of the Milky Way galaxy and it continues to race
Onward right and as that waver
Just planet earth when it is a hundred light years away about a hundred years ago an individual named Albert Einstein

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
starts to think about the possibility there might be these ripples in the fabric of space completely unaware that a big one is
Already racing toward planet Earth and does these calculations that I've described?
Nobody really thinks that you can detect them but some very prescient
researchers when that wave is about 50 light-years away begin to build the first detector in hopes that might actually
Detect one of these ripples in the fabric of space and when that wave is two light days away
They turn on the newly revamped version of that experiment and two days later that wave washes by planet Earth
And gives rise
to that signal
Now if that
progression
Doesn't fill you with awe and reverence
For what the human brain is capable of doing if that doesn't sort of get the heart pounding a little bit
Check your pulse
and

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English: 
that's the kind of progression that
fills us with utter astonishment
You start with an idea
that's
crazy
mathematics
some guy in a trench in World War one is fiddling with the equations and
Gives rise ultimatelly to a confirmation that two black holes collided with each other
Sometime ago but it's still not the most direct evidence
even more direct evidence would come from taking a snapshot of
A black hole and that's what another team set out to do the event horizon
Telescope a consortium of radio telescopes around the globe
that by combining the data that they receive aim to
In essence take a radio photograph of a black hole and I think as many of you saw
this image

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
was released
so months ago last spring the first
direct image of a black hole
now a lot of
media
interest focused on this photograph
Rightfully, so I have to say though some folks who they said it kind of
Confidentially, they sort of said to me friends of mine
You know, it's not that
Great a photo of a of a black. It's very hard to please, you know, some people
You know, it's only eight radio telescopes. So it's in some sense, you know limited in its pixels, you know
people will do better, but the amazing thing to me is
Literally one week after this
Photograph was released a far sharper image of a black hole was in
fact released and that of course is

Italian: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

English: 
As you all know page 30 of the redacted Muller report
So
That somebody grown out there
So this is
The culmination of a long journey but again, it's not the end of a journey
We now know that these things are real, but now we need to deeply understand them. And so what I'll do in the
remaining three hours is
Don't worry Alvie I'll be gentle or reaching the end in the remaining time
I'm just going to describe some of the
the theoretical puzzles that we're still grappling with when it comes to black holes and
Some of the places we'll get one place in particular
Seems as crazy today as the possibility of black holes must have seemed a hundred years ago

English: 
That doesn't mean that what I'm about to tell you is true. Of course
But it does suggest that it's worthy of
Detailed scrutiny because the sequence of ideas that we have been following has yielded
Ultimately evidence and data confirming ideas that many of the smartest people on the planet
Didn't think was actually correct. All right, so
the puzzle in particular to have in mind
Has to do with what happens to an object when it falls over the edge of a black
Hole, right, so imagine that there's a black hole out there in space and I take out my wallet and I throw my wallet
Into the black hole it reaches the edge the event horizon as you call it and it goes over
Now according to Einstein's equations when an object falls over the edge of a black hole it is gone

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Right. Nothing can get out of a black hole. The gravity is too strong and therefore once it goes over the edge
finished now
That sets up a great deal of tension
with our
understanding of the universe given to us by quantum mechanics and
I don't have time to go into quantum mechanics in a detail
But I'll just give you the qualitative feel for why this is deeply puzzling
any object
carries information
Right my wallet in particular. It's got obvious information credit card numbers photographs things of that sort
But there's also information in how the molecules and atoms of my wallet are
arranged to create that physical structure and
If an object falls over the edge of a black hole and is permanently gone. That means the information content
It has is also permanently gone and if you lose
information if there are sinks of
information

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Then quantum mechanics loses what it requires to make predictions of how the world will unfold
So if information can actually truly be destroyed
then our
understanding of how the world progresses will radically change
Now Stephen Hawking believed for a very long time
That information would be lost. Just as Mulvaney said get over it, right?
That was the that was the approach that Stephen Hawking took
many other physicists did not believe that that was a right way of looking at things and in particular a
Resolution to the puzzle was put forward again. Theoretically based on ideas that come from string theory which goes like this
Imagine you throw your wallet in and instead of all of the information going in to the black hole solely
imagine that a copy of the information gets smeared out on

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The edge of the black hole that can be sort of stored as bits zeros and ones. I've schematically drawn here so much
So the idea would go that if you recover that
information because it's on the outside of the black hole after all you could use it to reconstruct any
object that went inside
now it's not that the wallet didn't fall into the black hole it did but the idea is that there's
information on the edge the event horizon the surface of the black hole that
is able to capture every quality of
the object to fill in the wallet so much so that you could actually read
The object if you wanted to now that notion
That you can have a three-dimensional object within an environment. That's fully
described by data on a thin two-dimensional surface that surrounds it should ring a bell and
that Bell is

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English: 
Holograms right. So what is a hologram a hologram is a thin piece of plastic?
Which when you illuminate it correctly
yields a
realistic three-dimensional image
So the idea here is that you can have a three-dimensional object
inside of a black hole
fully
Articulated by data on this thin two-dimensional surface that surrounds us. So this gives rise to what's known as the holographic
principle
the idea
That there's a dual description of the world
You've got the ordinary description that we're familiar with three-dimensional solid
objects
But there's an alternative description
Using data on a two-dimensional surface that surrounds those objects now this particular case
made use if you will of
Black holes in a detailed way but then people said look
Space inside a black hole where the wallet is and space outside of black hole
They're basically the same thing space is space

English: 
So if the wallet inside the black hole can be described by data on a surface that surrounds it. Maybe that's true
Absolutely everywhere, maybe every three-dimensional object regardless of where it is has a dual alternative
Description as a hologram data stored on a two-dimensional surface that surrounds it
So an image that you might have would be this. I don't know if you can see it. Hopefully you can back there
I can't see it up here. But say this is planet Earth. Can you see the holographic surface that surrounds it which holds information?
that describes the comings and goings of
Everything that happens in that real 3-dimensional world, but stored on a two-dimensional surface
so this
Notion that emerges from these ideas
Suggests that you and I and everything else we are just the holographic
projection of

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English: 
Data that lives on a distant thin two-dimensional surface, perhaps at the boundary of the observable universe
Not illuminated by a laser with a real hologram, but rather
illuminated by the laws of physics you
And I are just Holograms
Now it's right to chuckle at that idea
It's a strange idea but nevertheless it's where this sequence of ideas has taken us
now
Whether it's right or wrong will have to be ultimately determined by
future experiments future
observations
But to me, it's utterly remarkable how simply by sort of following the dots?
Starting with Einstein and the development of his equations. We come to a picture of the world that does sound absurd and
Yet that absurd picture may actually be right
Now I could stop here
but there was one other thing I was

English: 
Going to tell you about but you'll have to tell me if you've got patience for one other crazy
Idea, all right
all right, so so I'll go through it relatively quickly as time is short and
The ideas are a little bit tricky. So
To fully explain them would take a long time
So I'm now going to cater a little bit more to those who have some familiarity with some of these concepts
But the final thing I'll tell you about is this
We're now approaching the 85th anniversary of two other papers of Albert Einstein on
May 15th of
1935
Einstein wrote a paper with two colleagues
Podolsky and Rosen on something called quantum entanglement
How many people are familiar with that idea a lot of you so that's the idea that you can have two distant objects that somehow

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behave as though they're connected by invisible quantum threads a very strange idea again one that Einstein
Resisted his paper was basically trying to say look how crazy it is. That quantum mechanics is suggesting this possibility
But yet, we now believe that it's not just crazy. It's right
second paper that Einstein wrote in 1935 was in June of
1935 a paper
again with Nathan Rosen Podolski was not part of this paper and
The second paper was on the idea of wormholes, right? Everybody's
Encountered that idea if you watch Deep Space nine or any number of science fiction films have the notion of wormholes
Which are tunnels that connect to distant regions of space?
Einstein did not think that these two papers had anything to do with each other
Completely different ideas and yet in the last few years. We've come to think that those two

English: 
1935 papers may be deeply connected and the connection may actually explain how the fabric of space itself
Is actually threaded and that's what I'm gonna spend my last six minutes quickly describing to you
so the first idea
this idea of
Wormholes just to give you a picture to have in mind
Imagine you've got two distant regions that create a kind of tunnel between them a kind of shortcut
Between one region of space and another so that's the paper
I think I said you and I actually think as July of 1935 that Einstein comes up with this idea
Solves the equations of general relativity and shows that you could in principle have structures like this
And here's the other idea quantum entanglement
The main paper in which you can have two distant particles that are somehow
Connected by these invisible quantum threads and for me to describe what I want to tell you about
I've got to be a little bit more precise

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Certainly on the entanglement and idea and to do that
I'm going to use the canonical example that everybody talks about with entanglement which has to do with spin
Particles in the world elementary particles all spin around like little tops amazingly they can only spin in one of two directions
clockwise or counterclockwise
And with counterclockwise, we call it spin up if it's clockwise
We call it spin down now the weird thing of quantum mechanics is it describes the world in probabilistic terms?
So you can have a particle that's 50% spinning up and 50% chance of spinning down
Actually hovering in a mixture of two of those possibilities
Simultaneously and only when you measure the particle
Does it kind of snap out of the haze and spin up or snap out of the haze and spin down?
That's the weirdness of quantum physics
Now I want you to take this idea with me one step further because what Einstein was imagining is two
Particles each of which is spinning up and down simultaneously

English: 
You separate them very far apart and according to his calculations if you measure one particle and it snaps out of the haze
The distant particle also must snap out of the haze even though you didn't do anything to it
that Einstein said is
spooky
do something here affecting something over there and that was his argument the world can't be spooky and
therefore quantum mechanics cannot be a full theory of the world, but the reality of it is
This kind of effect is now observed all the time. So you have two distant particles
Say one in Las Vegas the other in New York I go over to the one in Las Vegas
I measure it and the one in New York is forced out of the quantum haze at the same moment a very
very strange idea but this quantum entanglement we think

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Together with einstein's idea of wormholes may actually give us our deepest understanding of the fabric of space and it goes like this
so imagine I focus in
on a
black hole and
That black hole say could be floating in space
and as I mentioned before this holographic idea tells us that this black hole has an
Alternative description in terms of a thin sphere that surrounds it basically at the event horizon
So in order to show that I'm going to go down to sort of a two-dimensional version that's easier for us to see
and that red
Surface there is the holographic surface surrounding the black hole again one dimension lower just for visualization purposes
the new idea is this
Imagine we have two copies. That is two black holes
each is described in this holographic language as a surface that surrounds it and

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Imagine further that we take einstein's idea of quantum entanglement and we entangle those two outer surfaces
what would that entail for the geometry of the interior region and here is
the beautiful insight
Calculations reveal that entangling the stuff on the outside is tantamount to connecting the inner stuff with a wormhole
So here are two of Einstein's ideas from 1935
Entanglement on the outside and wormholes on the inside and we recognize that they are the same thing just described in two
different languages
Einstein I think will be shocked in many ways by the picture I'm showing you right here
but it's a picture that comes right out of our
analysis with string theory and in fact
Some researchers have taken this picture and pushed it even a little further
Because they have realized that that entanglement that I'm showing you

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connecting these two copies of a black hole to black holes if you will you can actually apply this
Entanglement to one copy you can entangle that outer surface with itself
and when you do that
there's something amazing that pops out of the equations if you start to cut the lines of entangle and look at the
Entanglement line the old line at the top. I'm about to cut it right now
So there we go as I'm gonna cut that guy away. What does that imply?
For the geometry in the inner description it
entails that the geometry gets cut in half the
actual space itself gets cut in half if
You sever some of the lines of quantum entanglement and now I'm going to keep on doing that
I'm going to cut more and more lines. I'm going to cut some on the left
What does that correspond to it?
Corresponds to also cutting the space further in half in another way and now I'm just going to sort of let this go

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Cut lines of entanglement see what it does to the geometry and the geometry basically pixel eights. It falls apart
Which means if I turn this story around backwards in order to have a fabric of space?
You have to stitch together the individual
Placket the individual pixels. How do you stitch them together?
You stitch it together with the threads of quantum entanglement
So the fabric of space itself
may emerge
From an idea that Einstein didn't like but yet
Introduced with his paper on entanglement the fabric of space may be stitched with the threads of quantum entanglement
Again, a wild strange crazy sounding idea
But naturally comes out of the mathematics and we have sort of grown to have a degree of confidence
not necessarily that all math tells us the true workings of the world, but certainly is worth our

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Focus to try to determine whether these ideas are right or wrong because the payoff and the depth of understanding
Would be utterly astounding
So I will conclude here. Thank you very much
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