Kind: captions
Language: en
[Music]
It's a mysterious force that shapes our
universe.
It feels familiar, but it's far stranger
than anyone ever imagined.
And yet, one man's brilliant mind tamed
it.
gravity.
Using simple thought experiments, Albert
Einstein made an astonishing discovery.
Time and space are shaped by matter.
>> We get rid of this force of gravity and
instead we have curvature of spaceime.
>> Right now the space around me is being
squeezed and stretched.
>> He called it the general theory of
relativity.
How did one person working almost
entirely alone change everything we
thought we knew about the universe?
>> Einstein is toiling as the world seems
to fall apart.
>> He was able with pure thought to solve
the riddle of the universe. inside
Einstein's mind. right now on Nova.
[Music]
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[Music]
Gravity,
the most familiar yet most mysterious of
nature's forces.
100 years ago, Albert Einstein made a
mindblowing discovery.
what we feel as gravity is in fact the
push and pull of space and time itself.
He called his idea general relativity.
It is perhaps the most remarkable feat
of thinking about nature to come from a
single mind.
>> General relativity is undoubtedly one of
the greatest scientific theories ever
conceived. It's a theory of space, time,
and gravity.
one mathematical sentence and from it
you can derive the understanding of the
entire universe on the largest scales
and that is beautiful.
>> Only now a century after it was first
proposed do we have the technology to
explore the extremes of Einstein's great
theory.
Super massive black holes at the center
of galaxies.
Waves of gravity that distort space and
time, the evolution of our entire
universe.
How did a concept that explained so much
come from the mind of one man?
Einstein had a magical talent. He could
take a hard physical problem and boil it
down to a powerful visual image, a
thought experiment.
Suddenly he realizes this is how the
world works. All of this abstract
nonsense is the correct theory of
reality.
>> To gain an insight into Einstein's mind
and the true wonder of general
relativity, we need to trace the crucial
thought experiments that led to his
great breakthrough.
The seeds for his ideas were planted
when he was just a child.
[Music]
Einstein grew up in a small house in
Munich in southern Germany. His unique
personality was evident early on.
>> Like many great innovators, Einstein was
a rebel, a loner, but deeply curious.
He was slow in learning to speak as a
child. so slow that his parents
consulted a doctor, but he later said
that that's maybe why he thought in
visual thought experiments.
His sister remembers him building little
card towers using playing cards.
He was a daydreamer, but he was deeply
persistent.
Einstein's father, Herman, manufactured
electrical equipment.
He nurtured his son's interest in
science. On one occasion, he brought him
a compass.
>> Now, you and I maybe remember getting a
compass when we were kids, and we're
like, "Oh, look, the needle twitches and
points north." But then we're on to
something else. Like, oh, look, there's
a dead squirrel. But for Einstein, after
getting that compass, he developed a
lifelong devotion to understanding how
things can be forced to move even though
nothing's touching them.
[Music]
The young Einstein became gripped by a
desire to understand the underlying laws
of nature.
He developed a unique way of thinking
about the physical world. Inspired by
his favorite book,
>> the book Einstein loved told little
stories like what it be like to travel
through space or go through an
electrical wire.
and it made Einstein think visually.
>> These imagined situations that we often
call thought experiments became a
defining feature of Einstein's thinking.
One of the critical thought experiments
that Einstein began to play with very
young at around the age of 16 was trying
to imagine what would happen if he could
catch up with a light wave. It's one
thing to imagine light waves zooming
past him at some imp seemingly
impossible speed,
but what if he could somehow just propel
himself really quickly? What would it
look like if he could catch up with that
light wave? What would he see?
[Music]
He said it caused him to walk around in
such anxiety his palms would sweat. Now,
you and I may remember was causing our
palms to sweat at age 16. and it was not
a light being. But that's why he's
Einstein.
[Music]
This dreamlike thought about the nature
of light was Einstein's first step on
the path to his great theory.
It stayed with him throughout his time
at school and college.
He was extremely gifted in science and
math as a young person and very bad at
other classes mostly because he kept
cutting class and being very rude to his
teachers. Many teachers from when his
high school days on were convinced he'd
never amount to anything. He was a
discipline problem. I mean he was bad
news.
>> He applies to the second best university
in Zurich, the Zurich Polytech, and gets
rejected. I'd love to meet the
admissions director who rejected Albert
Ein. But eventually he gets in and he
does moderately well but not good enough
to get a teaching fellowship and so he
ends up at the burn Swiss patent office
as a third class examiner.
Undaunted by his university results,
Einstein started work at the patent
office in 1902, age 23.
Here his job was to assess the
originality of new devices.
>> He was immersed in the kinds of of sort
of technical details that he had been
fascinated by as as a very young kid.
And here he was sitting in, you know,
the kind of wave of of of the modern
age. This was the era of
electrification.
So all the latest clever ideas for
switching technology, for coordinating
clocks in particular, those were all
passing through his office.
Time zones had recently been introduced
in central Europe, and accurately
synchronizing clocks was a major
challenge of the day.
Switzerland was a world leader in time
technology.
Dozens of patents to link clocks passed
through Einstein's office. He could whip
through these patent applications and
then out of his drawer he'd pull his
physics notes and his boss was very
indulgent and would sort of turn a blind
eye as Einstein was doing his theories
in his spare time.
It's really important to remember that
theoretical physics was new when
Einstein was a young man.
You could do quite a lot of this work by
reading a relatively small number of
science journals and making the
calculations yourself.
Einstein's world in 1905 was dominated
by two kinds of physics. One was about
200 years old, founded by Isaac Newton,
British natural philosopher. For Newton,
all there is in the world is matter
moving.
>> Newton showed that the motion of falling
apples and orbiting planets are governed
by the same force,
gravity.
His equations are so effective we still
use them today to send probes to the
farthest reaches of the solar system.
The other important theory of Einstein's
day covered electricity and magnetism.
That branch of physics had been
revolutionized in 1865
by the Scottish physicist James Clark
Maxwell.
Maxwell's theory describes light as an
electromagnetic wave that travels at a
fixed speed.
In Newton's world, the speed of light is
not fixed.
Einstein could see that there's a
contradiction between Newton and
Maxwell. They just don't fit together.
And one of the things Einstein hated
hated was contradiction.
If there's one kind of physics that says
this and another kind of physics that
says that and they're different, that's
a sign that something's gone wrong and
it needs fixing.
[Music]
For months, Einstein wrestles with the
problem.
Eventually to resolve this contradiction
he focuses on a key element of speed
time.
He realized that any statement about
time is simply a question about what is
simultaneous. For example, if you say
the train arrives at 7, that simply
means that it gets to the platform
simultaneous with the clock going to
seven. In a brilliant thought
experiment, he questions what
simultaneous actually means and sees
that the flow of time is different for
an observer that is moving versus one
that is standing still.
He imagines a man standing on a railway
platform.
Two bolts of lightning strike on either
side of him.
The man is standing exactly halfway
between them and the light from each
strike reaches his eyes at exactly the
same moment. For him, the two strikes
are simultaneous.
[Music]
Then Einstein imagines a woman on a
fastm moving train
traveling at close to the speed of
light.
What would she see?
[Music]
As the light travels out from the
strikes,
the train is moving towards one and away
from the other. Light from the front
strike reaches her eyes first.
For the woman on the train, time elapses
between the two strikes.
For the man on the platform, there is no
time between the strikes.
This simple thought has mindblowing
significance.
simultaneity
and the flow of time itself depends on
how you're moving.
If there's no such thing as
simultaneity, then there's no such thing
as absolute time everywhere throughout
the universe and Isaac Newton was wrong.
>> This concept that time and space as well
are relative became known as special
relativity.
It led to remarkable results such as the
famous equation relating energy to mass.
>> Einstein published this article in 1905
to exactly no acclaim. Most people
ignored it. This was not uh setting the
world on fire. Uh, two years go by
before a very eminent physicist uh,
Johannes Stark invites Einstein to write
a review article on Einstein's own work
precisely because no one was paying
attention and he begins thinking about
ways to generalize them to push his own
results from 1905. What if he considers
not only a train moving at a fixed speed
past the platform, what if that train
begins to speed up or slow down? What if
there's acceleration?
>> Adding acceleration to the equations was
his first task.
Then there was that mysterious Newtonian
force of gravity to contend with. In
Newton's theory, gravity is a force that
acts instantaneously.
But special relativity says that's
impossible. Nothing can travel faster
than light.
>> What Newton's theory tells you is that
suppose the sun were to disappear, the
orbit of the earth should change at that
very moment. But the notion of at that
very moment in two different places is
exactly one of these notions that
special relativity has told you isn't a
good physics notion.
So you've now got this challenge of
trying to work out how to take the
success of Newton's theory of gravity
but fit it into this new special
relativistic picture.
It was only when Einstein began to
understand the link between gravity and
acceleration
that things began to fall into place.
We all know that if when we are
accelerated and of course now we have uh
cars and airplanes to uh give us the
physical feeling.
If you're in an airplane and it's taking
off, you are pushed back in your chair.
You feel actually kind of a force
pushing you back which feels very
similar to the force of gravity. But you
need kind of the brilliance of Einstein
to explain why they are related.
Suddenly he hits upon what he describes
as the happiest thought of his life.
If gravity and acceleration feel the
same, perhaps they are the same.
[Music]
Again, he examines the idea in a
beautiful thought experiment. He
imagines a man in a box floating
weightlessly in a distant region of
space in zero gravity.
Suddenly, the man stops floating and
accelerates downward until he's standing
in the box.
What has happened?
Either the box is now close to a planet
and the force of gravity has pulled the
man to the floor
or someone has attached a rope and the
box is now being pulled continuously and
accelerated upwards.
So, which is it?
Gravity
or acceleration?
[Music]
Without being able to see outside, the
man can't tell what's causing his fall
to the floor.
Einstein realized that there is no way
to tell the difference between sitting
in a gravitational field and being
accelerated. That these are equivalent
situations.
The fact that these two effects are the
same, give the same result, means that
gravity is acceleration, it's not just
like acceleration,
it's the same thing.
It's a big breakthrough.
Einstein's theory of special relativity
worked for motion at a constant speed.
By extending his ideas to acceleration,
he could begin to formulate a new theory
of gravity.
[Music]
In 1912, Einstein is living in Zurich
with his wife Maleava and two young
sons, Hans and Edward.
The academic world had realized the
importance of special relativity, and
his career had taken off. He's now a
professor at the esteemed Swiss Federal
Institute of Technology, but spends as
much time as possible working on his
theory.
He needs mathematics that describes how
objects move in space and time and soon
realizes that the best tool for the job
is a strange but powerful concept called
spacetime.
>> If I think of space, I know that I can
find anything if I know where it is.
North, south, east, west, and up, down,
three points. But that doesn't mean I
can find it because I also have to know
where it is in time. And so if we start
to think to know everything about an
event in the universe, I have to know
not just its spatial coordinates but
also its time coordinate, I can begin to
think about where it is in spaceime.
[Music]
>> Imagine a camera filming an action,
capturing each moment in time as a
single frame.
[Music]
Einstein basically tells us, think of
the movie real.
So you have all these little pictures.
Now cut them apart one by one and stack
them on top of each other.
You get this pile. And if you go up in
the pile, you go up in time. And now
kind of glue them all together into one
big block.
And that block has both space and time.
And that's the space-time continuum.
[Music]
It's almost looking at a movie not frame
by frame, but seeing the whole movie at
once.
They would now be kind of two strands
going up in space and time and they
would be kind of spaghetti strands.
In fact, uh we all are spaghetti strands
moving in this space time.
Einstein feels that spacetime is the
natural arena in which his theory of
relativity should play out.
But now he needs sophisticated
mathematics.
By your standard or mine, Einstein was
good at math. He was Einstein, but he
was not really a mathematician, per se.
He didn't prove theorems. He didn't pour
over math books. He was a physicist. He
did thought experiments. He thought of
very tangible, concrete situations and
what would happen. So, when it came time
for him to really bear down to the
absolute cutting edge mathematics of his
day, he required help.
[Music]
At university, Einstein had skipped the
geometry classes, letting his friend
Marcel Gman take notes for him. Gman had
excelled in geometry and was now
chairman of the math department.
He suggests Einstein uses advanced
mathematics in which the shape of space
and time could be curved.
Because spacetime has a geometry, he
thinks to himself, well, maybe it's the
actual shape of spaceime itself that is
giving rise to gravity.
>> After months of work, Einstein has an
extraordinary idea.
What if space time is shaped by matter
and that's what we feel as gravity?
In struggling to figure out what causes
gravity, then Einstein has this great
insight, it is simply that a mass
distorts the shape of spaceime around
it. So we get rid of this force of
gravity and instead we have curvature of
spaceime in Einstein's universe. Then if
space were empty, it would be flat.
There'd be nothing going on. But as soon
as you put objects down, they warp the
space and time around them.
And that causes a deviation of the
geometry. So that now things start
moving.
Everything wants to move as simple as
possible through space and time.
But Einstein tells us that mass sculpts
space and time. And it's the curved
motion through this sculpture as the
force of gravity.
We have this feeling that the reason I
can feel pressure on the soles of my
feet that the reason things are going to
drop when I throw them are because
there's a force attracting us down to
the center of the earth. What general
relativity tells you is that's not the
right way to think about what's going on
there. What's really going on is that
your natural path in spaceime would take
you to the center of the earth. And
what's actually happening is the floor
is getting in the way. It's pushing you
upwards.
We look at it, we go, "Ah, the force of
gravity." But Einstein says, "No, no,
no. The curvature of spaceime,
it's a stunning insight. Just as an ant
might feel forces pulling it left and
right as it walks over crumpled paper
when it's simply the shape of a surface
dictating its path. Einstein saw that
what we feel as the force of gravity is
in fact the shape of the spaceime we're
moving through.
Einstein now has everything he needs to
formulate his final theory of gravity.
But he makes a critical mistake. He
misinterprets one of his equations and
unaware of his error continues working
on incorrect ideas.
>> The point at which Einstein is going to
give the most essential equations of the
theory. Einstein considers something
like them and then says, "Ah, but these
don't work." And then writes down the
wrong equations.
What follows are alternations of
confidence and despair as he convinces
himself that everything is fine with
this theory and then he realizes that
things aren't so good with the theory.
It is a long dark period for Einstein as
he struggles to reconcile himself with a
theory that is just not working.
Two years later, Einstein is in Berlin.
At just 36 years old, he has one of the
most prestigious positions in physics,
but he is still struggling with his
theory.
By 1950, he'd reach the pinnacle of the
profession. He's in the Prussian Academy
and a professor at the University of
Berlin, but his marriage has fallen
apart. His wife and his two kids have
moved back to Switzerland.
So, he's pacing around almost all alone
in this apartment in Berlin.
And now he has a competitor.
Einstein had enthusiastically shared his
ideas with the brilliant mathematician
David Hilbert.
Hilbert was so impressed he decided to
work on the theory himself.
Einstein is now in a race to the finish
with one of the world's best
mathematicians.
This is unfolding in a remarkably
dramatic period in history. World War I
has begun to ravage central Europe.
Einstein is not just toiling sort of in
the abstract. He's toiling as as the
world seems to fall apart.
By November 1915,
Einstein is scheduled to present his
work in a series of four weekly lectures
at the esteemed Prussian Academy. But
he's struggling to formulate his ideas.
[Music]
In the midst of these challenges,
letters arrive from his wife in Zurich,
pressing the issue of his financial
obligations to his family and discussing
contact with his sons.
As his lectures begin, his theory is
still far from complete.
The pressure on Einstein is huge.
He would give a lecture, revise it, give
it again, spot mistakes, correct them,
get up on the podium, explain what was
wrong in the previous week's lecture,
correct it, and then move on. and then
do that again and again for four weeks
running.
His work to convince them of the truth
of this absolutely radical new theory of
relativity that he was proposing is one
of the most intense periods of work in
the history of science.
Somehow he's able to focus on his theory
with an incredible intensity
and he makes his breakthrough.
He tests his equations on a problem that
Newton's theory of gravity couldn't
solve.
The orbit of Mercury.
Mercury's path around the sun has an
anomaly that Newton's theory can't
explain. It deviates slightly each time
it goes round.
Einstein calculates the orbit with his
new equations.
The answer is correct.
Exactly what astronomers had observed.
He'd found the final equations for his
general theory of relativity.
[Music]
You have to think about the hubris of
being Albert Einstein. He had already
thrown out Newtonian mechanics with
special relativity and then he had gone
off on his little personal quest to
incorporate gravity. And at the end of
the day, he boils it down to a
prediction for a number that had been
observed, the procession of the orbit of
Mercury. And miraculously, when the
pages of algebra work out to their end,
you get the right answer. And suddenly,
it's not just playing with equations
anymore. He realizes this is how the
world works. All of this abstract
nonsense is the correct theory of
reality.
Einstein is at last able to present a
successful theory. That's a triumphant
moment, one of the great moments in the
history of physics. And for Einstein, a
victory very much against the odds. And
he'd won.
On the 25th of November 1915,
Einstein lays out his findings in his
climactic fourth lecture at the Prussian
Academy.
He presents general relativity.
The theory can be written as a single
equation. It condenses sprawling
complexities into a beautifully compact
set of symbols.
>> So the formula is really simple. G menu
equals
>> G for the shape of space time and T for
the distribution of mass and energy.
>> So this very simple formula captures all
of Einstein's general relativity. It's a
beautiful simple equation but it's a lot
of work to unpack the symbols the
mathematical symbols and see how in this
very simple formula the whole geometry
of the universe is hidden. It's kind of
an acquired taste to see the beauty.
It's also a signature formula for
Einstein. The true mark of his genius is
that he combines two elements that
actually live in different universes.
The left hand side lives in the world of
geometry, of mathematics. The right hand
side lives in a world of physics, of
matter and movement. And so perhaps the
most powerful ingredient of the equation
is this very simple
equal sign here. These two lines that
actually are connecting the two worlds.
And it's quite appropriate. They're two
lines because it's two-way traffic.
Matter tells space and time to curve.
Space and time tells matter to move.
[Music]
When Einstein presented his great
theory, few people understood it.
He needed a way to prove to the world
that the counterintuitive features of
his theory were real.
The general theory of relativity made
predictions of things which look really
strange.
For example, the idea that light bends
when it passes near a very heavy body.
No one had ever looked for that. No one
had ever observed it. Einstein was
desperate desperate to get astronomers
to make that test.
Einstein's theory predicts that when
light from a distant star travels close
to the sun, the warped space around the
sun bends the light's path.
In May 1919, the English astronomer
Arthur Edington traveled to the African
island of Principe to record images that
would show this phenomenon.
What Edington had been able to do was
take photographs of stars during a total
eclipse of the sun. So the moon blocked
most the brightness of the sun and
little pin pricks of light could be seen
around the sun otherwise we'd be lost in
the glare. And Edington and his
colleagues were able to measure that the
appearance of those stars had been
shifted compared to where they would
have been had that big mass of the sun
not been deflecting that light from far
away. So Edington's able to show that
Einstein's general relativity theory is
right and a revolution in science has
been accomplished.
[Music]
When the eclipse experiments prove
Einstein's theory right, he rockets to
fame. Not just because he's explained a
new way of looking at the universe, but
at the end of World War I, you had the
predictions of a German scientist be
proven right by some British astronomers
and it becomes headlines across the
world. New York Times says, "Lights all
a skew at the heavens. Men of science
more or less a go." This is back when
newspapers knew how to write great
headlines. But Einstein kind of loves
this fact that he is now an icon of
science.
>> Einstein becomes a worldwide celebrity.
The icon of genius we still recognize
today.
The only person who was more widely
known was Charlie Chaplan and they got
on like a house on fire. Chaplain said,
"The reason they all love me is because
they understand everything I do, and the
reason they love you is that they don't
understand anything you do. Can you
explain that?" And Einste said,
[Music]
>> "But in 1930s Berlin, the Nazi party is
gaining power.
As a Jewish scientist, Einstein becomes
increasingly caught up in the political
turmoil.
Einstein's theories became a target.
They were deemed sort of aesthetically
repugnant to a kind of Aryan
sensibility. So people attacked not just
Einstein, the Jewish scientist, but they
would actually have people denouncing
general relativity.
>> In January, Nobel Prize mathematician
Albert Einstein visited California.
>> He begins to make trips to America where
he is welcomed with open arms. Germany's
loss, America's game.
>> And in 1933, he settles in Princeton
with his second wife, Elsa, taking up a
position at the Institute for Advanced
Study.
[Music]
Today, the institute is headed by
Professor Robert Digraph.
he basically was still very much by
himself uh just actually as he was in
Berlin uh just concentrating on this on
his deep ideas and struggling with the
uh understanding the universe uh of
course his office was here
>> at the institute Einstein worked to
unify his theory of gravity with the
other laws of physics
with Einstein you see this phenomena you
with many great scientists
that they climb this very high mountain
and instead of celebrating their success
uh they privileged to see a much wider
landscape and they see all these
mountains behind it and I think he was
very much aware how much still there was
to be done
till the very last days of his life. He
was trying to push these equations and
and find a description of nature, all of
nature in terms of the geometry of space
and time.
But general relativity was fading from
mainstream science.
Physics was now focused on the quantum
theory of atoms and tiny particles,
a theory incompatible with Einstein's
ideas.
but one that could be tested in the lab.
Most of general relativity was then
beyond the reach of experiment.
When Einstein died in 1955, age 76,
his theory was seen as one with little
hope of future discovery.
The best theories in physics always take
us to places where the people who
invented them didn't imagine. And a
truly wonderful theory like general
relativity predicts all sorts of things
that Einstein didn't conceive of. The
theory has a life of its own. We
understand general relativity much
better right now than Albert Einstein
ever did.
And liftoff of the space shuttle
discovery with the Hubble Space
Telescope. Our window on the universe.
>> Today 100 years after general relativity
was first presented.
>> Telescopes released. Okay. Thank you.
New technology is allowing us to explore
the most remarkable predictions of the
theory. An expanding universe, black
holes, ripples in spaceime,
[Music]
and perhaps the most bizarre, the idea
that not just space, but time itself is
distorted by heavy objects.
Okay. So, uh,
>> to prove it, a team of physicists is
carrying out a remarkable experiment.
>> They're using two atomic clocks that are
in near perfect sync, accurate to a
billionth of a second.
The master clock remains at sea level,
while they take the second clock to the
top of New Hampshire's Mount Coney.
General relativity tells us that as you
move away from the mass of the planet,
time should speed up.
[Music]
After 4 days at the top of the mountain,
the test clock is taken back to the lab
for comparison.
There they compare it to the sea level
master clock. We'll put that one into
channel A.
>> 4 days ago, they were ticking in unison.
>> Master clock and channel B.
>> But what about now?
>> You guys ready? This is it right here.
The time interval counter is going to
show us the time difference between
these two clock ticks.
>> 20 nconds.
You can see the time difference between
them represented here graphically of the
clock that was up at the mountain for 4
days and our master clock.
gravity, the distortion of space and
time becomes weaker as you move away
from the surface of the planet. So while
the test clock was up the mountain, time
sped up.
>> It's now 20 nanconds, 20 billionth of a
second ahead of the sea level clock.
>> This is really awesome.
This distortion of time has surprising
consequences.
The global positioning system, something
we all take for granted, wouldn't work
without taking this into account.
The engineers who built the GPS system
we use every day to pinpoint locations
had to ensure it adjusted for the time
difference between clocks on satellites
and receivers on the ground. If they
didn't, GPS would be off by six miles
every day.
>> Your GPS units use the results of
general relativity. When you navigate in
your car, you perhaps should give a word
of thanks to Uncle Albert.
Of all general relativity's predictions
that new technology has allowed us to
explore,
there's one that's straight out of
science fiction.
A black hole.
Everything that we're familiar with in
ordinary life is made from matter,
but not black holes. Black holes are
made from warped space and time.
and nothing else.
A black hole is an object that is
spherical like a star or like the earth
with a sharp boundary called the horizon
through which nothing can come out. So
it casts a shadow on whatever is behind
it. It's just a black black shadow.
Unbelievably black.
This simulation shows the distortion of
starlight around a black hole.
Even though Einstein knew his theory
predicted black holes, he found it hard
to believe they would really exist in
nature.
In the 1960s, Professor Kip Thorne
worked on the mathematical concept of
black holes.
The idea made sense on paper, and he
began to feel that these science
fiction-like objects might actually be
real. Must be here somewhere. It's in in
one of these piles.
>> Kip Thorne made a bet with fellow
physicist Stephven Hawking about whether
or not a strong source of X-rays known
as Signis X1 was in fact a black hole.
>> I think it's in here.
Yeah, here we go. Relative stars and
black holes. Yeah, there it is.
So, that is a copy of the famous bet.
Um, Stephen Hawking Bet's one-year
subscription to Penthouse magazine is
against Hipthornne's wager of a
four-year subscription to a political
magazine called Private Eye. That signis
X1 does not contain a black hole of mass
above the Chandra Cigar limit. It's
witnessed this 10th day of December
1974.
Stephven Hawking had a terribly uh deep
investment in it actually being a black
hole. Uh and so he made the bet against
himself as a insurance policy that at
least he would get something out of it
if Signis X1 turned out not to be a
black hole. The mount evidence mounded
thereafter over the period of the 70s
and 80s. And in uh June 1990, Stephen
snuck into my office and signed off on
the bet that finally the evidence was
absolutely overwhelming that Signis X1
really is a black hole.
And uh Penthouse magazine arrived. He
sent me the British version of
Penthouse, which was ever so much more
runchy than the American Penthouse.
Actually enough to make my face turn red
when when I received it at first.
Today we have evidence suggesting that
there are millions of black holes in our
galaxy alone.
But perhaps the most profound prediction
of general relativity is that our
universe had a hot dense beginning that
we call the big bang.
The discovery that distant galaxies are
moving away from us and that there's a
background radiation permeating space
provided evidence for the big bang and a
universe that's growing.
>> With this picture of of the expanding
universe, there is natural questions. Is
the universe slowing down as it expands?
Is it so dense that someday it'll come
to a halt and collapse? Will the
universe come to an end? These seem like
good questions.
>> To find answers, in the 1990s, Saul
Pearl Mutter and his team observed
exploding stars called supernovi to
track the growth of the universe.
>> When we made the measurement, we
discovered that the universe isn't
slowing down enough to come to a halt.
In fact, it's not slowing at all. It's
speeding up. The universe is expanding
faster and faster. But what's pushing
it?
>> In order to explain the acceleration of
the universe within Einstein's theory of
general relativity, we're considering a
energy spread throughout all of space
that we've never seen before. We don't
know what it is. We call it dark energy.
And if so, it would require something
like 70% of all the stuff of the
universe to be in this form of
previously unknown dark energy. So this
is a lot to swallow. And you might
imagine that at that point you should go
back and revisit your theory. The
problem is that Einstein's theory is so
elegant and it predicts many many many
digits of precision that it's very very
difficult to come up with any other
theory.
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There is one final prediction of general
relativity that remains untested.
gravitational waves.
>> There are huge things in the universe
happening like black holes colliding or
stars exploding and they create these
gravitational waves, waves in the shape
of space and time that travel through
the universe at the speed of light. And
so right now the space around me is
being squeezed and stretched by
gravitational waves just getting here
from let's say two black holes colliding
a billion lighty years away.
But the squeezing and stretching is so
minute, I absolutely could not
personally detect it. And so what we're
trying to do is build an instrument that
can.
>> In Louisiana and Washington state, a
vast experiment called LIGO is in the
final phases of calibration.
It's hoped that laser beams traveling 2
and 1/2 miles between precisely aligned
mirrors will measure the squeezing of
space caused by gravitational waves.
This could open up an entirely new
window on the universe.
[Music]
For 100 years, general relativity has
been proven to be correct. time and time
again. But Einstein himself knew that
his great theory had limits. It remains
incompatible with the quantum world of
tiny atomic particles.
Here at the Institute for Advanced
Study, where Einstein worked, the
world's leading theoretical physicists
are trying to solve the problem Einstein
never could.
finding a single set of rules that
applies to both the cosmic and atomic
scales, a unified theory, the holy grail
of physics.
>> We are now in what at this time is the
school of physics. So here uh people are
still struggling with many of the same
issues that Einstein was struggled and
are still trying to capture the uh the
laws of the universe uh from this very
small to the very large uh in a single
equation and it's still blackboards that
are the uh the weapon of choice.
the brightest minds of the world are
coming here uh to work 24 hours, seven
days a week uh struggling to to grasp
the great mysteries of the universe. And
I think we're still driven by the same
dream that at some point we can capture
everything in elegant mathematics.
>> 100 years after Einstein transformed our
understanding of nature, the stage is
set for the next revolution.
When we finally move beyond Einstein, it
might be another singular genius that
comes along. Someone struggling in a
poor school in Kenya right now that we
don't know about. Or it might be 20
different people with 20 different
points of view gradually building brick
by brick to finally figure out a more
comprehensive view that includes general
relativity in it.
I think the most important thing that
you learn from Einstein you just the
power of an idea if it's correct you
know it's just you it's unstoppable
it's extremely encouraging that know he
was able with pure thought to solve the
riddle of the universe
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>> once we had general relativity the world
changed completely our point of view on
the world changed completely. I mean,
the origin of the universe is a
prediction straight out of general
relativity. We didn't have that before.
>> I often wonder what Einstein would make
of today's theoretical physics. And I
think he would really be saying, you
know, get on with it, get the right
story, get the details right.
You know, you have the huge universe and
it obeys certain laws of nature. But
where in the universe are these laws
actually discovered? Where are they
studied?
And then you go to this tiny planet and
there just this one individual Einstein
who captures it.
And now there's a small group of people
walking in his footsteps and trying to
push it further.
And I often feel well you know this is a
small part of the universe that actually
is reflecting upon itself that try to
understand itself.
[Music]
This program is available with PBS
Passport and on Amazon Prime Video
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