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It's a mysterious force
that shapes our universe.
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It feels familiar,
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but it's far stranger
than anyone ever imagined.
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And yet, one man's
brilliant mind tamed it.
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Gravity.
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Using simple
thought experiments,
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Albert Einstein made
an astonishing discovery:
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time and space
are shaped by matter.
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You get rid of this force
of gravity,
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and instead, we have
curvature of spacetime.
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Right now, the space around me
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is being squeezed and stretched.
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He called it the "General Theory
of Relativity."
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How did one person,
working almost entirely alone,
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change everything we thought
we knew about the universe?
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Einstein is toiling
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as the world seems
to fall apart.
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He was able with pure thought
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to solve the riddle
of the universe.
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"Inside Einstein's Mind,"
right now on NOVA.
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Gravity.
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The most familiar yet most
mysterious of nature's forces.
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100 years ago, Albert Einstein
made a mind-blowing discovery:
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what we feel as gravity
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is in fact the push and pull
of space and time itself.
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He called his idea
"general relativity."
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It is perhaps
the most remarkable feat
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of thinking about nature
to come from a single mind.
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General relativity
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is undoubtedly one of the
greatest scientific theories
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ever conceived.
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It's a theory of space, time,
and gravity.
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One mathematical sentence,
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and from it, you can derive
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the understanding
of the entire universe
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on the largest scales,
and that is beautiful.
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Only now, a century
after it was first proposed,
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do we have the technology
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to explore the extremes
of Einstein's great theory.
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Supermassive black holes
at the center of galaxies.
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Waves of gravity that
distort space and time.
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The evolution
of our entire universe.
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How did a concept
that explains so much
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come from the mind of one man?
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Einstein had a magical talent.
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He could take a hard,
physical problem
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and boil it down
to a powerful visual image,
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a thought experiment.
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Suddenly he realizes,
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"This is how the world works.
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All this abstract nonsense is
the correct theory of reality."
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To gain an insight
into Einstein's mind
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and the true wonder
of general relativity,
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we need to trace
the crucial thought experiments
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that led to his great
breakthrough.
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The seeds for his ideas
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were planted
when he was just a child.
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Einstein grew up
in a small house in Munich,
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in southern Germany.
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His unique personality
was evident early on.
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Like many great innovators,
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Einstein was a rebel, a loner,
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but deeply curious.
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He was slow in learning to speak
as a child,
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so slow that his parents
consulted a doctor,
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but he later said that
that's maybe why he thought
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in visual thought experiments.
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His sister remembers him
building little card towers
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using playing cards.
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He was a daydreamer,
but he was deeply persistent.
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Einstein's father, Hermann,
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manufactured electrical
equipment.
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He nurtured his son's interest
in science.
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On one occasion,
he brought him a compass.
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Now, you and I maybe remember
getting a compass
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when we were kids,
and we were like,
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"Oh look, the needle twitches
and points north,"
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but then we're on
to something else,
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like, "Oh look,
there's a dead squirrel."
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But for Einstein,
after getting that compass,
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he developed a lifelong devotion
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to understanding how things
can be forced to move
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even though nothing's
touching them.
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The young Einstein
became gripped by a desire
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to understand the underlying
laws of nature.
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He developed a unique way
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of thinking
about the physical world
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inspired by his favorite book.
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The book Einstein loved
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told little stories,
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like what it'd be like
to travel through space
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or go through
an electrical wire.
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And it made Einstein think
visually.
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These imagined situations
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that we often call
"thought experiments"
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became a defining feature
of Einstein's thinking.
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One of the critical
thought experiments
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that Einstein began to play with
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very young,
around the age of 16,
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was trying to imagine
what would happen
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if he could catch up
with a light wave.
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It's one thing to imagine
a light wave zooming past him
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at some seemingly
impossible speed,
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but what if he could somehow
just propel himself
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really quickly?
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What would it look like
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if he could catch up
with that light wave?
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What would he see?
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He said it caused him
to walk around in such anxiety,
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his palms would sweat.
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Now, you and I may remember
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what was causing our palms
to sweat at age 16,
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and it was not a light beam.
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But that's why he's Einstein.
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This dream-like thought
about the nature of light
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was Einstein's first step
on the path to his great theory.
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It stayed with him throughout
his time at school and college.
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He was extremely gifted
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in science and math
as a young person
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and very bad at other classes,
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mostly because
he kept cutting class
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and being very rude
to his teachers.
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Many teachers
from his high school days on
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were convinced he'd never amount
to anything.
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He was a discipline problem,
and he was bad news.
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He applies to the second best
university in Zurich,
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the Zurich Polytech,
and gets rejected.
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I'd love to meet
the admissions director
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who rejected Albert Einstein.
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But eventually he gets in,
and he does moderately well,
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but not good enough
to get a teaching fellowship.
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And so he ends up
at the Bern Swiss patent office
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as a third class examiner.
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Undaunted by his
university results,
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Einstein started work
at the patent office in 1902,
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age 23.
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Here, his job was to assess
the originality of new devices.
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He was immersed
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in the kinds
of technical details
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that he'd been fascinated by
as a very young kid.
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And here he was,
sitting in the kind of wave
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of the modern age.
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This was the era
of electrification.
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So all the latest clever ideas
for switching technology,
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for coordinating clocks
in particular,
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those were all
passing through his office.
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Time zones had recently been
introduced in central Europe,
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and accurately
synchronizing clocks
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was a major challenge
of the day.
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Switzerland was a world leader
in time technology.
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Dozens of patents to link clocks
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passed through
Einstein's office.
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He could whip through
these patent applications,
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and then out of his drawer,
he'd pull his physics notes,
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and his boss was very indulgent
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and would sort of turn
a blind eye
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as Einstein was doing
his theories in his spare time.
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It's really important
to remember that
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theoretical physics was new
when Einstein was a young man.
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You could do quite a lot
of this work by reading
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a relatively small number
of science journals
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and making the calculations
yourself.
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Einstein's world in 1905
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was dominated
by two kinds of physics.
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One was about 200 years old,
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founded by Isaac Newton,
a British natural philosopher.
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For Newton, all there is
in the world is matter moving.
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Newton showed that the motion
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of falling apples
and orbiting planets
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are governed by the same force:
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gravity.
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His equations are so effective,
we still use them today
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to send probes to the farthest
reaches of the solar system.
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The other important theory
of Einstein's day
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covered electricity
and magnetism.
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That branch of physics
had been revolutionized in 1865
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by the Scottish physicist
James Clerk Maxwell.
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Maxwell's theory describes light
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as an electromagnetic wave
that travels at a fixed speed.
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In Newton's world,
the speed of light is not fixed.
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Einstein could see that
there's a contradiction
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between Newton and Maxwell.
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They just don't fit together.
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And one of the things
Einstein hated... hated...
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Was contradiction.
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If there's one kind of physics
that says this
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and another kind of physics
that says that
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and they're different,
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that's a sign that something's
gone wrong and it needs fixing.
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For months, Einstein wrestles
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with the problem.
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Eventually,
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to resolve this contradiction,
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he focuses on a key element
of speed: time.
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He realized that
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any statement about time
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is simply a question
about what is simultaneous.
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For example, if you say
the train arrives at 7:00,
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that simply means that
it gets to the platform
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simultaneous with the clock
going to 7:00.
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In a brilliant
thought experiment,
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he questions what "simultaneous"
actually means
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and sees that the flow of time
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is different for an observer
that is moving
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versus one that is
standing still.
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He imagines a man
standing on a railway platform.
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Two bolts of lightning strike
on either side of him.
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The man is standing
exactly halfway between them
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and the light from each strike
reaches his eyes
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at exactly same moment.
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For him, the two strikes
are simultaneous.
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Then Einstein imagines a woman
on a fast-moving train,
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Traveling at close to the speed
of light,
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what would she see?
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As the light travels out
from the strikes,
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the train is moving towards one
and away from the other.
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Light from the front strike
reaches her eyes first.
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For the woman on the train,
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time elapses
between the two strikes.
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For the man on the platform,
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there is no time
between the strikes.
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This simple thought
has mind-blowing significance.
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Simultaneity,
and the flow of time itself,
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depends on how you're moving.
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If there's no such thing
as simultaneity,
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then there's no such thing
as absolute time everywhere
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throughout the universe,
and Isaac Newton was wrong.
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This concept that time,
and space as well, are relative
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became known as
special relativity.
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It led to remarkable results,
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such as the famous equation
relating energy to mass.
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Einstein published
this article in 1905
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to exactly no acclaim.
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Most people ignored it.
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This was not setting the world
on fire.
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Two years go by
before a very eminent physicist,
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00:14:03,453 --> 00:14:05,920
Johannes Stark, invites Einstein
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00:14:05,922 --> 00:14:08,122
to write a review article
on Einstein's own work,
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precisely because no one
was paying attention.
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And he begins thinking
about ways to generalize
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00:14:13,663 --> 00:14:15,463
and to push his own results
from 1905.
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What if he considers
not only a train
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moving at a fixed speed
past the platform?
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00:14:20,303 --> 00:14:22,370
What if that train begins
to speed up or slow down?
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What if there's acceleration?
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00:14:24,140 --> 00:14:28,609
Adding acceleration to the
equations was his first task.
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Then there was that mysterious
Newtonian force of gravity
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to contend with.
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00:14:36,285 --> 00:14:38,052
In Newton's theory,
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00:14:38,054 --> 00:14:41,655
gravity is a force
that acts instantaneously.
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But special relativity says
that's impossible...
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Nothing can travel
faster than light.
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00:14:49,065 --> 00:14:50,931
What Newton's theory
tells you is that
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00:14:50,933 --> 00:14:53,601
suppose the sun
were to disappear,
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the orbit of the earth should
change at that very moment.
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00:14:56,672 --> 00:14:58,906
But the notion of
"at that very moment"
257
00:14:58,908 --> 00:15:02,009
in two different places
is exactly one of these notions
258
00:15:02,011 --> 00:15:03,544
that special relativity
has told you
259
00:15:03,546 --> 00:15:04,945
isn't a good physics notion.
260
00:15:04,947 --> 00:15:10,251
So you've now got this challenge
of trying to work out
261
00:15:10,253 --> 00:15:12,319
how to take the success
of Newton's theory of gravity
262
00:15:12,321 --> 00:15:15,423
but fit it into this new
special relativistic picture.
263
00:15:15,425 --> 00:15:19,794
It was only when Einstein
began to understand the link
264
00:15:19,796 --> 00:15:22,129
between gravity and acceleration
265
00:15:22,131 --> 00:15:26,400
that things began
to fall into place.
266
00:15:28,304 --> 00:15:30,805
We all know that
when we are accelerated,
267
00:15:30,807 --> 00:15:33,741
and of course now we have cars
and airplanes
268
00:15:33,743 --> 00:15:37,745
to give us the physical feeling,
269
00:15:37,747 --> 00:15:40,081
if you're in an airplane
and it's taking off,
270
00:15:40,083 --> 00:15:41,882
you are pushed back
in your chair,
271
00:15:41,884 --> 00:15:44,085
you feel actually kind of
a force pushing you back,
272
00:15:44,087 --> 00:15:47,054
which feels very similar
to the force of gravity.
273
00:15:47,056 --> 00:15:49,723
But you need the brilliance
of Einstein
274
00:15:49,725 --> 00:15:52,726
to explain why they are related.
275
00:15:54,097 --> 00:15:56,630
Suddenly, he hits
upon what he describes as
276
00:15:56,632 --> 00:16:00,701
the happiest thought
of his life.
277
00:16:00,703 --> 00:16:04,371
If gravity and acceleration
feel the same,
278
00:16:04,373 --> 00:16:09,076
perhaps they are the same.
279
00:16:09,078 --> 00:16:12,613
Again, he examines the idea
280
00:16:12,615 --> 00:16:15,716
in a beautiful
thought experiment.
281
00:16:15,718 --> 00:16:18,185
He imagines a man in a box
282
00:16:18,187 --> 00:16:21,689
floating weightlessly
in a distant region of space
283
00:16:21,691 --> 00:16:23,023
in zero gravity.
284
00:16:26,262 --> 00:16:28,028
Suddenly, the man stops floating
285
00:16:28,030 --> 00:16:33,467
and accelerates downward
until he's standing in the box.
286
00:16:33,469 --> 00:16:36,570
What has happened?
287
00:16:38,674 --> 00:16:41,509
Either the box
is now close to a planet
288
00:16:41,511 --> 00:16:47,948
and the force of gravity
has pulled the man to the floor,
289
00:16:47,950 --> 00:16:51,152
or someone has attached a rope
290
00:16:51,154 --> 00:16:54,455
and the box is now
being pulled continuously
291
00:16:54,457 --> 00:16:56,824
and accelerated upwards.
292
00:17:00,596 --> 00:17:03,731
So which is it?
293
00:17:03,733 --> 00:17:06,467
Gravity?
294
00:17:06,469 --> 00:17:09,737
Or acceleration?
295
00:17:09,739 --> 00:17:13,440
Without being able
to see outside,
296
00:17:13,442 --> 00:17:17,478
the man can't tell what's
causing his fall to the floor.
297
00:17:17,480 --> 00:17:19,446
Einstein realized
298
00:17:19,448 --> 00:17:22,183
there is no way
to tell the difference
299
00:17:22,185 --> 00:17:24,185
between sitting
in a gravitational field
300
00:17:24,187 --> 00:17:25,686
and being accelerated.
301
00:17:25,688 --> 00:17:28,055
These are equivalent situations
302
00:17:28,057 --> 00:17:30,391
The fact that these two effects
are the same,
303
00:17:30,393 --> 00:17:31,926
give the same result,
304
00:17:31,928 --> 00:17:34,562
means that gravity
is acceleration.
305
00:17:34,564 --> 00:17:36,197
It's not just like acceleration;
306
00:17:36,199 --> 00:17:38,465
it's the same thing.
307
00:17:38,467 --> 00:17:42,703
It's a big breakthrough.
308
00:17:42,705 --> 00:17:47,808
Einstein's theory
of special relativity worked
309
00:17:47,810 --> 00:17:51,679
for motion at a constant speed.
310
00:17:51,681 --> 00:17:54,281
By extending his ideas
to acceleration,
311
00:17:54,283 --> 00:17:58,219
he could begin to formulate
a new theory of gravity.
312
00:18:14,170 --> 00:18:19,173
In 1912, Einstein is living
in Zurich with his wife Mileva
313
00:18:19,175 --> 00:18:21,609
and two young sons,
Hans and Eduard.
314
00:18:21,611 --> 00:18:26,046
The academic world had realized
the importance
315
00:18:26,048 --> 00:18:30,017
of special relativity,
and his career had taken off.
316
00:18:30,019 --> 00:18:31,685
He's now a professor
317
00:18:31,687 --> 00:18:34,255
at the esteemed Swiss Federal
Institute of Technology,
318
00:18:34,257 --> 00:18:40,427
but spends as much time as
possible working on his theory.
319
00:18:40,429 --> 00:18:42,529
He needs mathematics
320
00:18:42,531 --> 00:18:46,467
that describes how objects move
in space and time
321
00:18:46,469 --> 00:18:50,170
and soon realizes that
the best tool for the job
322
00:18:50,172 --> 00:18:56,443
is a strange but powerful
concept called "spacetime."
323
00:18:56,445 --> 00:18:58,445
If I think of space,
324
00:18:58,447 --> 00:19:01,749
I know that I can find anything
if I know where it is
325
00:19:01,751 --> 00:19:05,419
north-south, east-west,
and up-down, three points.
326
00:19:05,421 --> 00:19:07,154
But that doesn't mean
I can find it,
327
00:19:07,156 --> 00:19:09,323
because I also have to know
where it is in time.
328
00:19:09,325 --> 00:19:11,125
And so if we start to think,
329
00:19:11,127 --> 00:19:14,228
to know everything
about an event in the universe,
330
00:19:14,230 --> 00:19:17,197
I have to know not just
its spatial coordinates,
331
00:19:17,199 --> 00:19:19,199
but also its time coordinate.
332
00:19:19,201 --> 00:19:22,169
I can begin to think
about where it is in spacetime.
333
00:19:24,874 --> 00:19:28,108
Imagine a camera
filming an action,
334
00:19:28,110 --> 00:19:35,082
capturing each moment in time
as a single frame.
335
00:19:42,291 --> 00:19:45,426
Einstein basically tells us,
"Think of the movie reel."
336
00:19:45,428 --> 00:19:50,597
So you have
all these little pictures.
337
00:19:50,599 --> 00:19:53,033
Now, cut them apart one by one
338
00:19:53,035 --> 00:19:54,535
and stack them on top
of each other,
339
00:19:54,537 --> 00:19:57,471
you get this pile.
340
00:19:57,473 --> 00:20:00,874
And if you go up in the pile,
you go up in time.
341
00:20:00,876 --> 00:20:05,713
And now kind of glue them
all together into one big block,
342
00:20:05,715 --> 00:20:11,218
and that block
has both space and time,
343
00:20:11,220 --> 00:20:15,589
and that's the spacetime
continuum.
344
00:20:15,591 --> 00:20:19,326
It's almost looking at a movie
not frame by frame,
345
00:20:19,328 --> 00:20:21,729
but seeing the whole movie
at once.
346
00:20:21,731 --> 00:20:25,332
They would now be
kind of two strands
347
00:20:25,334 --> 00:20:28,068
going up in space and time,
348
00:20:28,070 --> 00:20:31,372
and they would be
kind of spaghetti strands.
349
00:20:31,374 --> 00:20:34,308
In fact, we all are
spaghetti strands
350
00:20:34,310 --> 00:20:36,410
moving in this spacetime.
351
00:20:40,216 --> 00:20:45,052
Einstein feels that spacetime
is the natural arena
352
00:20:45,054 --> 00:20:48,088
in which his theory
of relativity should play out.
353
00:20:48,090 --> 00:20:53,794
But now he needs
sophisticated mathematics.
354
00:20:53,796 --> 00:20:56,263
By your standard or mine,
Einstein was good at math.
355
00:20:56,265 --> 00:20:57,531
He was Einstein.
356
00:20:57,533 --> 00:21:00,000
But he was not really
a mathematician per se.
357
00:21:00,002 --> 00:21:02,336
He didn't prove theorems,
he didn't pore over math books.
358
00:21:02,338 --> 00:21:03,470
He was a physicist.
359
00:21:03,472 --> 00:21:04,938
He did thought experiments.
360
00:21:04,940 --> 00:21:07,608
He thought of very tangible,
concrete situations
361
00:21:07,610 --> 00:21:09,042
and what would happen.
362
00:21:09,044 --> 00:21:11,578
So when it came time for him
to really bear down
363
00:21:11,580 --> 00:21:13,847
to the absolute cutting edge
mathematics of his day,
364
00:21:13,849 --> 00:21:15,649
he required help.
365
00:21:15,651 --> 00:21:22,055
At university, Einstein had
skipped the geometry classes,
366
00:21:22,057 --> 00:21:26,593
letting his friend Marcel
Grossman take notes for him.
367
00:21:26,595 --> 00:21:29,296
Grossman had excelled
in geometry
368
00:21:29,298 --> 00:21:32,766
and was now chairman
of the math department.
369
00:21:32,768 --> 00:21:37,438
He suggests Einstein
uses advanced mathematics
370
00:21:37,440 --> 00:21:42,743
in which the shape of space
and time could be curved.
371
00:21:42,745 --> 00:21:45,045
Because spacetime
has a geometry,
372
00:21:45,047 --> 00:21:47,314
he thinks to himself,
373
00:21:47,316 --> 00:21:49,716
"Well, maybe it's the actual
shape of spacetime itself
374
00:21:49,718 --> 00:21:51,485
that is giving rise to gravity."
375
00:21:51,487 --> 00:21:59,487
After months of work, Einstein
has an extraordinary idea.
376
00:22:00,663 --> 00:22:07,134
"What if spacetime
is shaped by matter,
377
00:22:07,136 --> 00:22:10,103
and that's what we feel
as gravity?"
378
00:22:10,105 --> 00:22:14,441
In struggling to figure out
what causes gravity then,
379
00:22:14,443 --> 00:22:16,810
Einstein has this great insight.
380
00:22:16,812 --> 00:22:18,645
It is simply that a mass
381
00:22:18,647 --> 00:22:21,949
distorts the shape of spacetime
around it.
382
00:22:21,951 --> 00:22:25,285
So you get rid of this force
of gravity,
383
00:22:25,287 --> 00:22:29,656
and instead we have
curvature of spacetime.
384
00:22:29,658 --> 00:22:31,258
In Einstein's universe then,
385
00:22:31,260 --> 00:22:33,994
if space were empty,
it would be flat.
386
00:22:33,996 --> 00:22:35,329
There'd be nothing going on.
387
00:22:35,331 --> 00:22:37,464
But as soon as you
put objects down,
388
00:22:37,466 --> 00:22:40,734
they warp the space and time
around them,
389
00:22:40,736 --> 00:22:44,404
and that causes a deviation
of the geometry
390
00:22:44,406 --> 00:22:47,207
so that now things start moving.
391
00:22:50,613 --> 00:22:53,947
Everything wants to move
as simple as possible
392
00:22:53,949 --> 00:22:56,650
through space and time.
393
00:22:56,652 --> 00:23:02,222
But Einstein tells us that mass
sculpts space and time,
394
00:23:02,224 --> 00:23:05,325
and it's the curved motion
through this sculpture
395
00:23:05,327 --> 00:23:06,960
that's the force of gravity.
396
00:23:09,632 --> 00:23:11,198
We have this feeling that
397
00:23:11,200 --> 00:23:13,600
the reason I can feel pressure
on the soles of my feet,
398
00:23:13,602 --> 00:23:15,836
that the reason things are going
to drop when I throw them,
399
00:23:15,838 --> 00:23:17,170
are because there's a force
400
00:23:17,172 --> 00:23:19,406
attracting us down
to the center of the earth.
401
00:23:19,408 --> 00:23:22,509
What general relativity tells
you is that's not the right way
402
00:23:22,511 --> 00:23:24,144
to think about
what's going on there.
403
00:23:24,146 --> 00:23:30,183
What's really going on is that
your natural path in spacetime
404
00:23:30,185 --> 00:23:32,052
would take you to the center
of the earth,
405
00:23:32,054 --> 00:23:34,121
and what's actually happening is
the floor is getting in the way,
406
00:23:34,123 --> 00:23:35,856
it's pushing you upwards.
407
00:23:35,858 --> 00:23:40,627
When we look at it, we go,
"Ah, the force of gravity"
408
00:23:40,629 --> 00:23:43,196
But Einstein says, "No, no, no,
the curvature of spacetime."
409
00:23:48,103 --> 00:23:52,472
It's a stunning insight.
410
00:23:52,474 --> 00:23:57,010
Just as an ant might feel forces
pulling it left and right
411
00:23:57,012 --> 00:23:59,112
as it walks over crumpled paper
412
00:23:59,114 --> 00:24:03,383
when it's simply the shape
of a surface dictating its path,
413
00:24:03,385 --> 00:24:07,754
Einstein saw that what we feel
as the force of gravity
414
00:24:07,756 --> 00:24:12,826
is in fact the shape of the
spacetime we're moving through.
415
00:24:16,899 --> 00:24:20,200
Einstein now has
everything he needs
416
00:24:20,202 --> 00:24:23,437
to formulate his final theory
of gravity.
417
00:24:23,439 --> 00:24:27,174
But he makes a critical mistake.
418
00:24:27,176 --> 00:24:30,143
He misinterprets
one of his equations,
419
00:24:30,145 --> 00:24:32,212
and unaware of his error,
420
00:24:32,214 --> 00:24:36,650
continues working
on incorrect ideas.
421
00:24:36,652 --> 00:24:39,653
The point at which Einstein
is going to give
422
00:24:39,655 --> 00:24:41,588
the most essential equations
of the theory,
423
00:24:41,590 --> 00:24:43,890
Einstein considers
something like them
424
00:24:43,892 --> 00:24:46,460
and then says,
"Ah, but these don't work,"
425
00:24:46,462 --> 00:24:48,195
and then writes down
the wrong equations.
426
00:24:52,935 --> 00:24:57,971
What follows are alternations
of confidence and despair
427
00:24:57,973 --> 00:25:00,641
as he convinces himself
that everything was fine
428
00:25:00,643 --> 00:25:02,643
with this theory,
and then he realizes
429
00:25:02,645 --> 00:25:04,578
that things aren't so good
with the theory.
430
00:25:08,417 --> 00:25:12,319
It is a long, dark period
for Einstein
431
00:25:12,321 --> 00:25:14,521
as he struggles
to reconcile himself
432
00:25:14,523 --> 00:25:17,724
with a theory
that is just not working.
433
00:25:22,364 --> 00:25:26,333
Two years later,
Einstein is in Berlin.
434
00:25:26,335 --> 00:25:29,703
At just 36 years old,
he has one of the most
435
00:25:29,705 --> 00:25:32,739
prestigious positions
in physics.
436
00:25:32,741 --> 00:25:35,776
But he is still struggling
with his theory.
437
00:25:42,951 --> 00:25:46,386
By 1915, he'd reached
the pinnacle of the profession.
438
00:25:46,388 --> 00:25:48,388
He's in the Prussian Academy
439
00:25:48,390 --> 00:25:50,457
and a professor
at the University of Berlin.
440
00:25:50,459 --> 00:25:52,426
But his marriage
is falling apart,
441
00:25:52,428 --> 00:25:55,696
his wife and his two kids
have moved back to Switzerland,
442
00:25:55,698 --> 00:25:58,865
so he's pacing around
almost all alone
443
00:25:58,867 --> 00:26:00,434
in this apartment in Berlin.
444
00:26:02,771 --> 00:26:04,938
And now he has a competitor.
445
00:26:08,644 --> 00:26:11,411
Einstein had enthusiastically
shared his ideas
446
00:26:11,413 --> 00:26:14,181
with the brilliant mathematician
David Hilbert.
447
00:26:14,183 --> 00:26:17,517
Hilbert was so impressed,
448
00:26:17,519 --> 00:26:20,654
he decided to work
on the theory himself.
449
00:26:22,224 --> 00:26:24,458
Einstein is now
in a race to the finish
450
00:26:24,460 --> 00:26:29,596
with one of the world's
best mathematicians.
451
00:26:31,834 --> 00:26:33,333
This is unfolding
452
00:26:33,335 --> 00:26:36,670
in a remarkably dramatic period
in history.
453
00:26:36,672 --> 00:26:40,674
World War I has begun
to ravage central Europe.
454
00:26:40,676 --> 00:26:44,611
Einstein is not just toiling
in the abstract;
455
00:26:44,613 --> 00:26:47,280
he's toiling as the world
seems to fall apart.
456
00:26:52,020 --> 00:26:57,224
By November 1915, Einstein
is scheduled to present his work
457
00:26:57,226 --> 00:26:59,893
in a series
of four weekly lectures
458
00:26:59,895 --> 00:27:01,862
at the esteemed
Prussian Academy.
459
00:27:01,864 --> 00:27:07,000
But he's struggling
to formulate his ideas.
460
00:27:07,002 --> 00:27:09,302
In the midst
of these challenges,
461
00:27:09,304 --> 00:27:11,471
letters arrive
from his wife in Zurich
462
00:27:11,473 --> 00:27:13,306
pressing the issue
463
00:27:13,308 --> 00:27:15,909
of his financial obligations
to his family
464
00:27:15,911 --> 00:27:18,712
and discussing contact
with his sons.
465
00:27:21,316 --> 00:27:23,917
As his lectures begin,
466
00:27:23,919 --> 00:27:28,255
his theory is still
far from complete.
467
00:27:28,257 --> 00:27:31,158
The pressure on Einstein
is huge.
468
00:27:34,363 --> 00:27:38,965
He would give a lecture,
revise it, give it again.
469
00:27:38,967 --> 00:27:42,803
Spot mistakes, correct them,
get up on the podium,
470
00:27:42,805 --> 00:27:45,372
explain what was wrong
in the previous week's lecture,
471
00:27:45,374 --> 00:27:47,774
correct it and then move on,
472
00:27:47,776 --> 00:27:51,411
and then do that again and again
for four weeks running.
473
00:27:53,949 --> 00:27:58,885
His work to convince them
of the truth
474
00:27:58,887 --> 00:28:03,657
of this absolutely radical
new theory of relativity
475
00:28:03,659 --> 00:28:05,458
that he was proposing
476
00:28:05,460 --> 00:28:07,928
is one of the most intense
periods of work
477
00:28:07,930 --> 00:28:09,296
in the history of science.
478
00:28:18,974 --> 00:28:21,875
Somehow, he's able
to focus on his theory
479
00:28:21,877 --> 00:28:27,347
with an incredible intensity,
and he makes his breakthrough.
480
00:28:27,349 --> 00:28:30,684
He tests his equations
on a problem
481
00:28:30,686 --> 00:28:34,821
that Newton's theory of gravity
couldn't solve:
482
00:28:34,823 --> 00:28:38,191
the orbit of Mercury.
483
00:28:38,193 --> 00:28:42,596
Mercury's path around the sun
has an anomaly
484
00:28:42,598 --> 00:28:45,232
that Newton's theory
can't explain:
485
00:28:45,234 --> 00:28:48,134
it deviates slightly
each time it goes round.
486
00:28:51,240 --> 00:28:55,809
Einstein calculates the orbit
with his new equations.
487
00:28:55,811 --> 00:28:58,445
The answer is correct,
488
00:28:58,447 --> 00:29:02,716
exactly what astronomers
had observed.
489
00:29:02,718 --> 00:29:05,619
He'd found the final equations
490
00:29:05,621 --> 00:29:08,388
for his general theory
of relativity.
491
00:29:19,368 --> 00:29:21,234
You have to think about the
hubris of being Albert Einstein.
492
00:29:21,236 --> 00:29:23,703
He had already thrown out
Newtonian mechanics
493
00:29:23,705 --> 00:29:25,739
with special relativity,
and then he had gone off
494
00:29:25,741 --> 00:29:28,108
on his little personal quest
to incorporate gravity.
495
00:29:28,110 --> 00:29:31,845
And at the end of the day,
he boils it down to a prediction
496
00:29:31,847 --> 00:29:33,947
for a number
that had been observed:
497
00:29:33,949 --> 00:29:35,849
the procession
of the orbit of Mercury.
498
00:29:35,851 --> 00:29:38,451
And, miraculously,
when the pages of algebra
499
00:29:38,453 --> 00:29:41,288
work out to their end,
you get the right answer.
500
00:29:41,290 --> 00:29:43,857
And suddenly, it's not just
playing with equations anymore;
501
00:29:43,859 --> 00:29:46,426
he realizes
this is how the world works.
502
00:29:46,428 --> 00:29:50,764
All this abstract nonsense is
the correct theory of reality.
503
00:29:52,701 --> 00:29:57,437
Einstein is at last able
to present a successful theory.
504
00:29:57,439 --> 00:29:59,372
That's a triumphant moment,
505
00:29:59,374 --> 00:30:01,775
one of the great moments
in the history of physics,
506
00:30:01,777 --> 00:30:08,315
and, for Einstein, a victory
very much against the odds,
507
00:30:08,317 --> 00:30:10,216
and he'd won.
508
00:30:14,656 --> 00:30:20,660
On the 25th of November 1915,
Einstein lays out his findings
509
00:30:20,662 --> 00:30:26,399
in his climactic fourth lecture
at the Prussian Academy.
510
00:30:26,401 --> 00:30:31,571
He presents general relativity.
511
00:30:31,573 --> 00:30:35,075
The theory can be written
as a single equation.
512
00:30:35,077 --> 00:30:38,378
It condenses
sprawling complexities
513
00:30:38,380 --> 00:30:42,248
into a beautifully compact set
of symbols.
514
00:30:44,753 --> 00:30:48,221
So the formula is really simple:
G-mu-nu equals...
515
00:30:48,223 --> 00:30:51,224
G for the shape of spacetime
516
00:30:51,226 --> 00:30:55,929
and T for the distribution
of mass and energy.
517
00:30:55,931 --> 00:30:59,132
So this very simple formula
518
00:30:59,134 --> 00:31:02,268
captures all of Einstein
general relativity.
519
00:31:02,270 --> 00:31:04,137
It's a beautiful,
simple equation
520
00:31:04,139 --> 00:31:07,107
but it's a lot of work
to unpack the symbols,
521
00:31:07,109 --> 00:31:08,975
the mathematical symbols,
522
00:31:08,977 --> 00:31:11,611
and see how
in this very simple formula,
523
00:31:11,613 --> 00:31:14,247
the whole geometry
of the universe is hidden.
524
00:31:14,249 --> 00:31:19,419
It's kind of an acquired taste
to see the beauty.
525
00:31:19,421 --> 00:31:22,522
It's also a signature formula
for Einstein.
526
00:31:22,524 --> 00:31:26,793
The true mark of his genius
is that he combines two elements
527
00:31:26,795 --> 00:31:29,362
that actually live
in different universes.
528
00:31:29,364 --> 00:31:32,198
The left hand side lives
in the world of geometry,
529
00:31:32,200 --> 00:31:33,600
of mathematics.
530
00:31:33,602 --> 00:31:35,935
The right hand side lives
in the world of physics,
531
00:31:35,937 --> 00:31:37,670
of matter and movement.
532
00:31:37,672 --> 00:31:42,909
And so perhaps the most powerful
ingredient of the equation
533
00:31:42,911 --> 00:31:46,179
is this very simple
equal sign here,
534
00:31:46,181 --> 00:31:49,682
these two lines that actually
are connecting the two worlds,
535
00:31:49,684 --> 00:31:51,618
and it's quite appropriate
they're two lines
536
00:31:51,620 --> 00:31:53,319
because it's two-way traffic.
537
00:31:53,321 --> 00:31:58,091
Matter tells space and time
to curve,
538
00:31:58,093 --> 00:32:01,728
space and time tells matter
to move.
539
00:32:13,175 --> 00:32:15,608
When Einstein presented
his great theory,
540
00:32:15,610 --> 00:32:17,877
few people understood it.
541
00:32:17,879 --> 00:32:21,014
He needed a way
to prove to the world
542
00:32:21,016 --> 00:32:24,651
that the counterintuitive
features of his theory
543
00:32:24,653 --> 00:32:26,619
were real.
544
00:32:30,025 --> 00:32:32,926
The general theory of relativity
545
00:32:32,928 --> 00:32:36,863
made predictions of things
which looked really strange.
546
00:32:39,134 --> 00:32:42,335
For example,
the idea that light bends
547
00:32:42,337 --> 00:32:45,238
when it passes near
a very heavy body.
548
00:32:45,240 --> 00:32:46,706
No one had ever looked for that.
549
00:32:46,708 --> 00:32:49,275
No one had ever observed it.
550
00:32:49,277 --> 00:32:51,077
Einstein was desperate,
551
00:32:51,079 --> 00:32:55,548
desperate to get astronomers
to make that test.
552
00:32:55,550 --> 00:32:58,017
Einstein's theory predicts that
553
00:32:58,019 --> 00:33:01,821
when light from a distant star
travels close to the sun,
554
00:33:01,823 --> 00:33:08,094
the warped space around the sun
bends the light's path.
555
00:33:08,096 --> 00:33:13,766
In May 1919, the English
astronomer Arthur Eddington
556
00:33:13,768 --> 00:33:17,570
traveled to the African island
of Principe to record images
557
00:33:17,572 --> 00:33:22,509
that would show this phenomenon.
558
00:33:22,511 --> 00:33:24,177
What Eddington
had been able to do
559
00:33:24,179 --> 00:33:26,179
was take photographs of stars
560
00:33:26,181 --> 00:33:28,014
during a total eclipse
of the sun
561
00:33:28,016 --> 00:33:31,151
so the moon blocked most
of the brightness of the sun
562
00:33:31,153 --> 00:33:34,020
and little pinpricks of light
could be seen around the sun...
563
00:33:34,022 --> 00:33:36,189
Otherwise, it would be lost
in the glare...
564
00:33:36,191 --> 00:33:38,458
And Eddington and his colleagues
were able to measure
565
00:33:38,460 --> 00:33:41,895
that the appearance
of those stars had been shifted
566
00:33:41,897 --> 00:33:43,429
compared to where
they would have been
567
00:33:43,431 --> 00:33:45,965
had that big mass of the sun
not been deflecting that light
568
00:33:45,967 --> 00:33:48,401
from far away.
569
00:33:48,403 --> 00:33:51,638
So Eddington's able to show
570
00:33:51,640 --> 00:33:55,508
that Einstein's general
relativity theory is right
571
00:33:55,510 --> 00:34:00,213
and a revolution in science
has been accomplished.
572
00:34:08,623 --> 00:34:12,258
When the eclipse experiments
prove Einstein's theory right,
573
00:34:12,260 --> 00:34:15,662
he rockets to fame.
Not just because he's explained
574
00:34:15,664 --> 00:34:17,897
a new way of looking
at the universe,
575
00:34:17,899 --> 00:34:19,999
but at the end of World War I,
576
00:34:20,001 --> 00:34:24,470
you had the predictions
of a German scientist
577
00:34:24,472 --> 00:34:27,273
be proven right
by some British astronomers,
578
00:34:27,275 --> 00:34:29,309
and it becomes headlines
across the world.
579
00:34:29,311 --> 00:34:30,577
The New York Times says,
580
00:34:30,579 --> 00:34:33,313
"Lights all askew
at the heavens,
581
00:34:33,315 --> 00:34:36,115
men of science
more or less agog."
582
00:34:36,117 --> 00:34:37,517
This is back when newspapers
583
00:34:37,519 --> 00:34:39,152
knew how to write
great headlines.
584
00:34:39,154 --> 00:34:41,788
But Einstein kind of loves
this fact
585
00:34:41,790 --> 00:34:44,023
that he is now an icon
of science.
586
00:34:47,996 --> 00:34:51,631
Einstein becomes
a worldwide celebrity,
587
00:34:51,633 --> 00:34:56,135
the icon of genius
we still recognize today.
588
00:34:56,137 --> 00:35:01,040
The only person
who was more widely known
589
00:35:01,042 --> 00:35:02,842
was Charlie Chaplin,
590
00:35:02,844 --> 00:35:05,745
and they got on
like a house on fire.
591
00:35:05,747 --> 00:35:09,616
Chaplin said, "The reason
they all love me
592
00:35:09,618 --> 00:35:12,218
"is because they understand
everything I do,
593
00:35:12,220 --> 00:35:13,720
"and the reason they love you
594
00:35:13,722 --> 00:35:15,521
"is that they don't understand
anything you do.
595
00:35:15,523 --> 00:35:16,689
Can you explain that?"
596
00:35:16,691 --> 00:35:18,391
And Einstein said...
597
00:35:22,664 --> 00:35:28,668
But in 1930s Berlin,
the Nazi party is gaining power.
598
00:35:28,670 --> 00:35:32,939
As a Jewish scientist, Einstein
becomes increasingly caught up
599
00:35:32,941 --> 00:35:36,442
in the political turmoil.
600
00:35:36,444 --> 00:35:38,544
Einstein's theories
became a target.
601
00:35:38,546 --> 00:35:40,313
They were deemed
aesthetically repugnant
602
00:35:40,315 --> 00:35:42,982
to a kind of Aryan sensibility.
603
00:35:42,984 --> 00:35:45,952
So people attacked not just
Einstein the Jewish scientist,
604
00:35:45,954 --> 00:35:47,553
but they would actually
have people
605
00:35:47,555 --> 00:35:49,055
denouncing general relativity.
606
00:35:52,927 --> 00:35:55,561
In January, Nobel Prize
mathematician Albert Einstein
607
00:35:55,563 --> 00:35:56,929
visited California...
608
00:35:56,931 --> 00:35:59,132
He begins to make trips
to America,
609
00:35:59,134 --> 00:36:02,635
where he is welcomed
with open arms.
610
00:36:02,637 --> 00:36:06,272
Germany's loss, America's gain.
611
00:36:06,274 --> 00:36:09,609
And in 1933,
he settles in Princeton
612
00:36:09,611 --> 00:36:12,145
with his second wife Elsa,
613
00:36:12,147 --> 00:36:14,714
taking up a position at the
Institute for Advanced Study.
614
00:36:17,919 --> 00:36:23,456
Today, the Institute is headed
by Professor Robbert Dijkgraaf.
615
00:36:23,458 --> 00:36:27,460
He basically was still
very much by himself,
616
00:36:27,462 --> 00:36:29,696
just actually
as he was in Berlin,
617
00:36:29,698 --> 00:36:33,132
just concentrating
on his deep ideas
618
00:36:33,134 --> 00:36:36,903
and struggling
with understanding the universe.
619
00:36:36,905 --> 00:36:39,272
Of course, his office was here.
620
00:36:39,274 --> 00:36:42,108
At the Institute,
621
00:36:42,110 --> 00:36:44,944
Einstein worked to unify
his theory of gravity
622
00:36:44,946 --> 00:36:48,381
with the other laws of physics.
623
00:36:51,019 --> 00:36:52,785
With Einstein,
you see this phenomena
624
00:36:52,787 --> 00:36:54,354
you see with many great
scientists...
625
00:36:54,356 --> 00:36:57,890
That they climb
this very high mountain
626
00:36:57,892 --> 00:37:02,929
and instead of celebrating
their success,
627
00:37:02,931 --> 00:37:06,265
they're privileged to see
a much wider landscape,
628
00:37:06,267 --> 00:37:08,901
and they see all these mountains
behind it.
629
00:37:08,903 --> 00:37:11,237
And I think he was
very much aware
630
00:37:11,239 --> 00:37:15,141
how much still there was
to be done.
631
00:37:15,143 --> 00:37:18,010
Till the very last days
of his life,
632
00:37:18,012 --> 00:37:20,413
he was trying to push
these equations
633
00:37:20,415 --> 00:37:25,218
and find a description
of nature, all of nature,
634
00:37:25,220 --> 00:37:30,790
in terms of the geometry
of space and time.
635
00:37:30,792 --> 00:37:36,262
But general relativity was
fading from mainstream science.
636
00:37:36,264 --> 00:37:38,865
Physics was now focused
637
00:37:38,867 --> 00:37:43,369
on the quantum theory
of atoms and tiny particles,
638
00:37:43,371 --> 00:37:47,507
a theory incompatible
with Einstein's ideas,
639
00:37:47,509 --> 00:37:51,110
but one that could be tested
in the lab.
640
00:37:51,112 --> 00:37:53,646
Most of general relativity
641
00:37:53,648 --> 00:37:57,517
was then beyond the reach
of experiment.
642
00:37:57,519 --> 00:38:02,588
When Einstein died in 1955,
age 76,
643
00:38:02,590 --> 00:38:05,958
his theory was seen as one
644
00:38:05,960 --> 00:38:09,495
with little hope
of future discovery.
645
00:38:09,497 --> 00:38:12,932
The best theories in physics
always take us to places
646
00:38:12,934 --> 00:38:14,834
where the people who invented
them didn't imagine.
647
00:38:14,836 --> 00:38:17,737
And a truly wonderful theory
like general relativity
648
00:38:17,739 --> 00:38:19,439
predicts all sorts of things
649
00:38:19,441 --> 00:38:21,941
that Einstein
didn't conceive of.
650
00:38:21,943 --> 00:38:23,576
The theory has a life
of its own.
651
00:38:23,578 --> 00:38:26,813
We understand general relativity
much better right now
652
00:38:26,815 --> 00:38:28,948
than Albert Einstein ever did.
653
00:38:30,919 --> 00:38:34,287
Liftoff of space shuttle
Discovery
654
00:38:34,289 --> 00:38:37,957
with the Hubble space telescope,
our window on the universe.
655
00:38:37,959 --> 00:38:40,059
Today, 100 years
after general relativity
656
00:38:40,061 --> 00:38:41,527
was first presented...
657
00:38:41,529 --> 00:38:44,130
Telescopes released,
okay, thank you.
658
00:38:44,132 --> 00:38:47,500
...new technology
is allowing us to explore
659
00:38:47,502 --> 00:38:50,970
the most remarkable predictions
of the theory:
660
00:38:50,972 --> 00:38:52,672
an expanding universe,
661
00:38:52,674 --> 00:38:58,744
black holes,
ripples in spacetime,
662
00:38:58,746 --> 00:39:03,749
and perhaps the most bizarre,
663
00:39:03,751 --> 00:39:07,420
the idea that not just space,
but time itself
664
00:39:07,422 --> 00:39:11,290
is distorted by heavy objects.
665
00:39:11,292 --> 00:39:14,961
To prove it,
a team of physicists
666
00:39:14,963 --> 00:39:16,562
is carrying out
a remarkable experiment.
667
00:39:19,400 --> 00:39:24,237
They're using two atomic clocks
that are in near perfect sync,
668
00:39:24,239 --> 00:39:27,273
accurate to a billionth
of a second.
669
00:39:27,275 --> 00:39:30,376
The master clock
remains at sea level
670
00:39:30,378 --> 00:39:33,746
while they take the second clock
671
00:39:33,748 --> 00:39:36,449
to the top of New Hampshire's
Mount Sunapee.
672
00:39:36,451 --> 00:39:40,152
General relativity tells us that
as you move away
673
00:39:40,154 --> 00:39:46,893
from the mass of the planet,
time should speed up.
674
00:39:49,430 --> 00:39:52,865
After four days
at the top of the mountain,
675
00:39:52,867 --> 00:39:55,735
the test clock is taken back
to the lab for comparison.
676
00:39:58,940 --> 00:40:03,409
There, they compare it
to the sea level master clock.
677
00:40:03,411 --> 00:40:05,177
We'll put that one
into Channel A.
678
00:40:05,179 --> 00:40:08,147
Four days ago,
they were ticking in unison.
679
00:40:08,149 --> 00:40:09,582
Master clock in Channel B.
680
00:40:09,584 --> 00:40:10,750
But what about now?
681
00:40:10,752 --> 00:40:11,884
You guys ready?
682
00:40:11,886 --> 00:40:13,052
This is it right here.
683
00:40:13,054 --> 00:40:14,554
The time interval counter
is gonna show us
684
00:40:14,556 --> 00:40:17,623
the time difference
between these two clock ticks.
685
00:40:19,260 --> 00:40:21,027
20 nanoseconds.
686
00:40:21,029 --> 00:40:23,563
You can see the time
difference between them
687
00:40:23,565 --> 00:40:25,431
represented here graphically
688
00:40:25,433 --> 00:40:27,733
of the clock that was up
at the mountain for four days
689
00:40:27,735 --> 00:40:29,969
and our master clock.
690
00:40:29,971 --> 00:40:34,240
Gravity, the distortion
of space and time,
691
00:40:34,242 --> 00:40:37,777
becomes weaker as you move away
from the surface of the planet.
692
00:40:37,779 --> 00:40:41,847
So while the test clock
was up the mountain,
693
00:40:41,849 --> 00:40:44,417
time sped up.
694
00:40:44,419 --> 00:40:49,255
It's now 20 nanoseconds,
695
00:40:49,257 --> 00:40:53,492
20 billionths of a second,
ahead of the sea level clock,
696
00:40:53,494 --> 00:40:54,727
This is really awesome.
697
00:40:58,032 --> 00:41:02,735
This distortion of time
has surprising consequences.
698
00:41:02,737 --> 00:41:05,271
The Global Positioning System,
699
00:41:05,273 --> 00:41:08,307
something we all take
for granted,
700
00:41:08,309 --> 00:41:12,378
wouldn't work without
taking this into account.
701
00:41:12,380 --> 00:41:14,714
The engineers who built
the GPS system
702
00:41:14,716 --> 00:41:16,849
we use every day
to pinpoint locations
703
00:41:16,851 --> 00:41:21,087
had to ensure it adjusted
for the time difference
704
00:41:21,089 --> 00:41:25,625
between clocks on satellites
and receivers on the ground.
705
00:41:25,627 --> 00:41:31,130
If they didn't, GPS would be off
by six miles every day.
706
00:41:31,132 --> 00:41:33,165
Your GPS units
707
00:41:33,167 --> 00:41:36,102
use the results
of general relativity.
708
00:41:36,104 --> 00:41:38,571
When you navigate in your car,
709
00:41:38,573 --> 00:41:41,040
you perhaps should give a word
of thanks to Uncle Albert.
710
00:41:46,748 --> 00:41:49,582
Of all general relativity's
predictions
711
00:41:49,584 --> 00:41:52,618
that new technology
has allowed us to explore,
712
00:41:52,620 --> 00:41:57,957
there's one that's
straight out of science fiction:
713
00:41:57,959 --> 00:41:59,859
a black hole.
714
00:42:03,731 --> 00:42:07,466
Everything that we're
familiar with in ordinary life
715
00:42:07,468 --> 00:42:09,335
is made from matter.
716
00:42:09,337 --> 00:42:10,936
But not black holes.
717
00:42:10,938 --> 00:42:15,207
Black holes are made
from warped space and time
718
00:42:15,209 --> 00:42:19,445
and nothing else.
719
00:42:19,447 --> 00:42:23,649
A black hole is an object
that is spherical,
720
00:42:23,651 --> 00:42:26,352
like a star or like the Earth,
721
00:42:26,354 --> 00:42:29,221
with a sharp boundary
called the horizon
722
00:42:29,223 --> 00:42:33,426
through which nothing
can come out.
723
00:42:33,428 --> 00:42:37,797
So it casts a shadow
on whatever is behind it.
724
00:42:37,799 --> 00:42:43,235
It's just a black, black shadow,
unbelievably black.
725
00:42:43,237 --> 00:42:48,674
This simulation shows
the distortion of starlight
726
00:42:48,676 --> 00:42:51,477
around a black hole.
727
00:42:51,479 --> 00:42:55,181
Even though Einstein knew his
theory predicted black holes,
728
00:42:55,183 --> 00:43:00,286
he found it hard to believe they
would really exist in nature.
729
00:43:00,288 --> 00:43:03,823
In the 1960s,
Professor Kip Thorne
730
00:43:03,825 --> 00:43:07,860
worked on the mathematical
concept of black holes.
731
00:43:07,862 --> 00:43:10,663
The idea made sense on paper,
732
00:43:10,665 --> 00:43:15,034
and he began to feel that these
science fiction-like objects
733
00:43:15,036 --> 00:43:17,670
might actually be real.
734
00:43:17,672 --> 00:43:20,773
Must be here somewhere,
it's in one of these piles.
735
00:43:20,775 --> 00:43:24,543
Kip Thorne made a bet with
fellow physicist Stephen Hawking
736
00:43:24,545 --> 00:43:27,580
about whether or not
a strong source of x-rays
737
00:43:27,582 --> 00:43:31,383
known as Cygnus X-1
was in fact a black hole.
738
00:43:31,385 --> 00:43:32,985
I think it's in here.
739
00:43:32,987 --> 00:43:37,189
Yeah, here we go, relativity,
stars and black holes.
740
00:43:37,191 --> 00:43:39,191
Yeah, there it is.
741
00:43:39,193 --> 00:43:43,129
So that is a copy
of the famous bet.
742
00:43:43,131 --> 00:43:45,431
"Stephen Hawking
bets a one-year subscription
743
00:43:45,433 --> 00:43:47,199
"to Penthouse magazine
744
00:43:47,201 --> 00:43:49,368
"against Kip Thorne's wager
of a four-year subscription
745
00:43:49,370 --> 00:43:52,872
"to a political magazine called
Private Eye
746
00:43:52,874 --> 00:43:55,608
"that Cygnus X-1 does not
contain a black hole of mass
747
00:43:55,610 --> 00:43:57,676
"above the Chandrasekhar Limit.
748
00:43:57,678 --> 00:44:02,014
It's witnessed this 10th day
of December 1974."
749
00:44:02,016 --> 00:44:06,152
Stephen Hawking had
a terribly deep investment
750
00:44:06,154 --> 00:44:08,487
in it actually being
a black hole,
751
00:44:08,489 --> 00:44:14,660
and so he made the bet against
himself as an insurance policy
752
00:44:14,662 --> 00:44:16,662
that at least he would get
something out of it
753
00:44:16,664 --> 00:44:19,598
if Cygnus X-1 turned out
not to be a black hole.
754
00:44:19,600 --> 00:44:22,468
The evidence mounted thereafter
755
00:44:22,470 --> 00:44:24,603
over the period
of the '70s and '80s,
756
00:44:24,605 --> 00:44:27,940
and in June 1990,
757
00:44:27,942 --> 00:44:32,178
Stephen snuck into my office
and signed off on the bet,
758
00:44:32,180 --> 00:44:34,780
that finally, the evidence
was absolutely overwhelming
759
00:44:34,782 --> 00:44:37,783
that Cygnus X-1
really is a black hole.
760
00:44:37,785 --> 00:44:41,287
And Penthouse magazine arrived.
761
00:44:41,289 --> 00:44:43,088
He sent me the British version
of Penthouse,
762
00:44:43,090 --> 00:44:45,157
which was ever
so much more raunchy
763
00:44:45,159 --> 00:44:46,792
than the American Penthouse,
actually.
764
00:44:46,794 --> 00:44:50,796
Enough to make my face turn red
when I received it at first.
765
00:44:56,737 --> 00:44:59,638
Today, we have evidence
suggesting that
766
00:44:59,640 --> 00:45:04,310
there are millions of black
holes in our galaxy alone.
767
00:45:04,312 --> 00:45:08,714
But perhaps the most profound
prediction of general relativity
768
00:45:08,716 --> 00:45:13,152
is that our universe
had a hot, dense beginning
769
00:45:13,154 --> 00:45:16,188
that we call the big bang.
770
00:45:20,828 --> 00:45:24,630
The discovery that distant
galaxies are moving away from us
771
00:45:24,632 --> 00:45:29,668
and that there's a background
radiation permeating space
772
00:45:29,670 --> 00:45:32,271
provided evidence
for the big bang
773
00:45:32,273 --> 00:45:35,174
and a universe that's growing.
774
00:45:35,176 --> 00:45:37,910
With this picture
of an expanding universe,
775
00:45:37,912 --> 00:45:39,812
there were natural questions.
776
00:45:39,814 --> 00:45:42,681
Is the universe slowing down
as it expands?
777
00:45:42,683 --> 00:45:45,618
Is it so dense that someday,
778
00:45:45,620 --> 00:45:47,620
it will come to a halt
and collapse?
779
00:45:47,622 --> 00:45:49,321
Will the universe come
to an end?
780
00:45:49,323 --> 00:45:51,123
These seemed like
good questions.
781
00:45:51,125 --> 00:45:56,829
To find answers, in the 1990s,
Saul Perlmutter and his team
782
00:45:56,831 --> 00:46:00,966
observed exploding stars,
called supernovae,
783
00:46:00,968 --> 00:46:04,436
to track the growth
of the universe.
784
00:46:04,438 --> 00:46:07,673
When we made the measurement,
we discovered that the universe
785
00:46:07,675 --> 00:46:09,475
isn't slowing down enough
to come to a halt.
786
00:46:09,477 --> 00:46:11,510
In fact,
it's not slowing at all;
787
00:46:11,512 --> 00:46:13,078
it's speeding up!
788
00:46:13,080 --> 00:46:15,447
The universe is expanding
faster and faster.
789
00:46:15,449 --> 00:46:17,783
But what's pushing it?
790
00:46:17,785 --> 00:46:21,720
In order to explain
the acceleration of the universe
791
00:46:21,722 --> 00:46:24,023
within Einstein's theory
of general relativity,
792
00:46:24,025 --> 00:46:27,626
we're considering an energy
spread throughout all of space
793
00:46:27,628 --> 00:46:28,961
that we've never seen before.
794
00:46:28,963 --> 00:46:30,195
We don't know what it is.
795
00:46:30,197 --> 00:46:31,931
We call it dark energy.
796
00:46:31,933 --> 00:46:35,301
And, if so, it would require
797
00:46:35,303 --> 00:46:38,771
something like 70%
of all the stuff of the universe
798
00:46:38,773 --> 00:46:41,674
to be in this form of previously
unknown dark energy.
799
00:46:41,676 --> 00:46:44,543
So this is a lot to swallow,
800
00:46:44,545 --> 00:46:46,478
and you might imagine that
at that point,
801
00:46:46,480 --> 00:46:47,980
you should go back
and revisit your theory.
802
00:46:47,982 --> 00:46:50,549
The problem is that Einstein's
theory is so elegant,
803
00:46:50,551 --> 00:46:54,653
and it predicts many, many,
many digits of precision,
804
00:46:54,655 --> 00:46:57,389
that it's very, very difficult
to come up
805
00:46:57,391 --> 00:46:59,591
with any other theory.
806
00:47:02,363 --> 00:47:06,832
There is one final prediction
of general relativity
807
00:47:06,834 --> 00:47:12,471
that remains untested:
gravitational waves.
808
00:47:12,473 --> 00:47:17,209
There are huge things
in the universe happening,
809
00:47:17,211 --> 00:47:20,145
like black holes colliding
or stars exploding,
810
00:47:20,147 --> 00:47:22,815
and they create these
gravitational waves...
811
00:47:22,817 --> 00:47:25,718
Waves in the shape
of space and time
812
00:47:25,720 --> 00:47:28,387
that travel through the universe
at the speed of light.
813
00:47:28,389 --> 00:47:31,090
And so right now,
the space around me
814
00:47:31,092 --> 00:47:34,093
is being squeezed and stretched
by gravitational waves
815
00:47:34,095 --> 00:47:37,563
just getting here
from, let's say, two black holes
816
00:47:37,565 --> 00:47:40,032
colliding a billion
light years away.
817
00:47:43,337 --> 00:47:45,938
But the squeezing and stretching
is so minute,
818
00:47:45,940 --> 00:47:48,874
I absolutely could not
personally detect it.
819
00:47:48,876 --> 00:47:52,544
And so what we're trying to do
is build an instrument that can.
820
00:47:52,546 --> 00:47:56,015
In Louisiana
and Washington state,
821
00:47:56,017 --> 00:47:58,984
a vast experiment called LIGO
822
00:47:58,986 --> 00:48:01,020
is in the final phases
of calibration.
823
00:48:01,022 --> 00:48:06,525
It's hoped that laser beams
traveling two-and-a-half miles
824
00:48:06,527 --> 00:48:08,861
between precisely aligned
mirrors
825
00:48:08,863 --> 00:48:10,996
will measure
the squeezing of space
826
00:48:10,998 --> 00:48:14,366
caused by gravitational waves.
827
00:48:14,368 --> 00:48:20,039
This could open up an entirely
new window on the universe.
828
00:48:26,480 --> 00:48:30,783
For 100 years,
general relativity
829
00:48:30,785 --> 00:48:34,086
has been proven to be correct
time and time again.
830
00:48:34,088 --> 00:48:38,957
But Einstein himself knew that
his great theory had limits.
831
00:48:38,959 --> 00:48:40,826
It remains incompatible
832
00:48:40,828 --> 00:48:45,964
with the quantum world
of tiny atomic particles.
833
00:48:45,966 --> 00:48:48,400
Here at the Institute
for Advanced study,
834
00:48:48,402 --> 00:48:50,102
where Einstein worked,
835
00:48:50,104 --> 00:48:53,038
the world's leading
theoretical physicists
836
00:48:53,040 --> 00:48:57,376
are trying to solve the problem
Einstein never could:
837
00:48:57,378 --> 00:48:59,912
finding a single set of rules
838
00:48:59,914 --> 00:49:03,849
that applies to both the cosmic
and atomic scales.
839
00:49:03,851 --> 00:49:07,786
A unified theory.
840
00:49:07,788 --> 00:49:10,722
The Holy Grail of physics.
841
00:49:10,724 --> 00:49:15,094
We are now in what at this time
is the school of physics.
842
00:49:15,096 --> 00:49:17,262
So here,
people are still struggling
843
00:49:17,264 --> 00:49:20,099
with many of the same issues
that Einstein would struggle
844
00:49:20,101 --> 00:49:25,537
and are still trying to capture
the laws of the universe
845
00:49:25,539 --> 00:49:30,542
from the very small to the very
large in a single equation.
846
00:49:30,544 --> 00:49:35,981
And it's still blackboards
that are the weapon of choice.
847
00:49:35,983 --> 00:49:40,953
The brightest minds of the world
are coming here
848
00:49:40,955 --> 00:49:43,956
to work 24 hours,
seven days a week,
849
00:49:43,958 --> 00:49:49,461
struggling to grasp the great
mysteries of the universe.
850
00:49:49,463 --> 00:49:52,231
And I think we are still driven
by the same dream:
851
00:49:52,233 --> 00:49:54,099
that at some point,
852
00:49:54,101 --> 00:49:57,069
we can capture everything
in elegant mathematics.
853
00:49:57,071 --> 00:49:59,771
100 years after Einstein
854
00:49:59,773 --> 00:50:03,242
transformed our understanding
of nature,
855
00:50:03,244 --> 00:50:07,546
the stage is set
for the next revolution.
856
00:50:07,548 --> 00:50:10,449
When we finally move
beyond Einstein,
857
00:50:10,451 --> 00:50:12,584
it might be another singular
genius that comes along...
858
00:50:12,586 --> 00:50:15,821
Someone struggling in a poor
school in Kenya right now
859
00:50:15,823 --> 00:50:17,156
that we don't know about.
860
00:50:17,158 --> 00:50:18,957
Or it might be
20 different people
861
00:50:18,959 --> 00:50:20,526
with 20 different points of view
862
00:50:20,528 --> 00:50:22,027
gradually building
brick-by-brick
863
00:50:22,029 --> 00:50:25,063
to finally figure out
a more comprehensive view
864
00:50:25,065 --> 00:50:27,566
that includes general
relativity in it.
865
00:50:34,575 --> 00:50:36,108
I think the most important thing
866
00:50:36,110 --> 00:50:39,144
that you learn from Einstein
is just the power of an idea.
867
00:50:39,146 --> 00:50:42,047
If it's correct, you know,
it's just unstoppable.
868
00:50:45,186 --> 00:50:48,754
It's extremely encouraging that
he was able with pure thought
869
00:50:48,756 --> 00:50:51,423
to solve the riddle
of the universe.
870
00:50:55,696 --> 00:50:58,197
Once we had general relativity,
871
00:50:58,199 --> 00:51:00,098
the world changed completely.
872
00:51:00,100 --> 00:51:02,067
Our point of view on the world
changed completely.
873
00:51:02,069 --> 00:51:04,336
I mean, the origin
of the universe
874
00:51:04,338 --> 00:51:06,705
is a prediction straight out
of general relativity.
875
00:51:06,707 --> 00:51:09,575
We didn't have that before.
876
00:51:09,577 --> 00:51:12,778
I often wonder
what Einstein would make
877
00:51:12,780 --> 00:51:15,380
of today's theoretical physics.
878
00:51:15,382 --> 00:51:17,683
I think he would really be
saying, you know,
879
00:51:17,685 --> 00:51:20,085
"Get on with it, get the right
story, get the details right."
880
00:51:23,290 --> 00:51:26,825
You know, you have
the huge universe,
881
00:51:26,827 --> 00:51:28,627
and it obeys
certain laws of nature,
882
00:51:28,629 --> 00:51:32,497
but where in the universe are
these laws actually discovered?
883
00:51:32,499 --> 00:51:35,200
Where are they studied?
884
00:51:35,202 --> 00:51:37,970
And then you go
to this tiny planet
885
00:51:37,972 --> 00:51:40,739
and there's this one individual,
Einstein, who captures this.
886
00:51:40,741 --> 00:51:43,208
And now there's
a small group of people
887
00:51:43,210 --> 00:51:46,478
walking in his footsteps
and trying to push it further.
888
00:51:46,480 --> 00:51:48,480
And I often feel,
889
00:51:48,482 --> 00:51:50,115
well, it's this small part
of the universe
890
00:51:50,117 --> 00:51:52,551
that actually is reflecting
upon itself,
891
00:51:52,552 --> 00:51:53,832
that tries to understand itself.