Cosmos (1980): Season 1, Episode 9 - The Lives of the Stars - full transcript
Carl Sagan examines the life cycle of stars from their creation to their deaths.
Subtitles downloaded from www. OpenSubtitles. org
If you wish to make
an apple pie from scratch...
...you must first invent the universe.
Thank you very much.
Suppose I cut a piece...
...out of this apple pie.
Crumbly, but good.
And now suppose we cut
this piece in half, or more or less.
And then cut this piece in half...
...and keep going.
How many cuts before we get
down to an individual atom?
The answer is about
90 successive cuts.
Of course, this knife isn't
sharp enough...
...the pie is too crumbly...
...and an atom is too small
to see in any case.
But there is a way to do it.
It was here at
Cambridge University in England...
...that the nature of the atom was
first understood...
...in part by shooting pieces
of atoms at atoms...
...and seeing how they bounce off.
A typical atom is surrounded...
...by a kind of cloud of electrons.
The electrons are electrically
charged, as the name suggests...
...and they determine the chemical
properties of the atom.
For example, the glitter of gold...
...or the transparency of the solid...
...that's made from the atoms
silicon and oxygen.
But deep inside the atom...
...hidden far beneath
the outer electron cloud...
...is the nucleus, composed chiefly
of protons and neutrons.
Atoms are very small.
100 million of them, end to end,
would be about so big.
And the nucleus is 100,000 times
smaller still.
Nevertheless, most of the mass
in an atom is in the nucleus.
The electrons are by comparison...
...just bits of moving fluff.
Atoms are mainly empty space.
Matter is composed chiefly
of nothing.
When we consider cutting this
apple pie, but...
...down beyond a single atom...
...we confront an infinity
of the very small.
And when we look up
at the night sky...
...we confront an infinity
of the very large.
These infinities are among the most
awesome of human ideas.
They represent an unending regress
which goes on...
...not just very far, but forever.
Have you ever stood between two
parallel mirrors...
...in a barbershop, say...
...and seen a very large
number of you?
Or you could use...
...two flat mirrors...
...and a candle flame...
...you would see a large number
of images...
...each the reflection
of another image.
You can't really see an infinity
of images...
...because the mirrors aren't
perfectly flat and aligned.
And there's a candle or
a candle flame in the way...
...and light doesn't travel
infinitely fast.
When we talk of real infinities...
...we're talking about a quantity
larger than any number.
No matter what number you have in
mind, infinity is larger.
There's a nice way
to write large numbers.
You can...
...write the number 1000...
...as 10 to the power three...
...meaning, a one
followed by three zeros.
Or a million is written as
10 to the power six...
...meaning, a one
followed by six zeros.
There's no largest number. If anybody
gives you a candidate...
...you can always add the
number one to it.
But there certainly are
very big numbers.
The American mathematician Edward
Kasner once asked his nephew...
...to invent a name for
an extremely large number:
10 to the power 100...
...which I can't write out all the
zeros because there isn't room.
The boy called it a googol.
If you think a googol is large,
consider a googolplex.
It's 10 to the power of a googol.
That is, a one followed, not by
100 zeros...
...but by a googol zeros.
Now, by comparison...
...with these enormous numbers...
...the total number of atoms
in that apple pie...
...is only about 10 to the 26th.
Tiny compared to a googol and...
...of course, much, much less
than a googolplex.
The number
of elementary particles...
...protons, neutrons and electrons...
...in the accessible universe...
...is of the order of 10 to the 80th.
A one followed by 80 zeros.
Still much, much less than a googol...
...and vastly less than a googolplex.
And yet, these numbers, the googol
and the googolplex...
...do not approach, they come
nowhere near infinity.
In fact, a googolplex is precisely
as far from infinity...
...as is the number one.
We started to write out
a googolplex...
...but it wasn't easy.
It's a very big number.
Writing out a googolplex is a
spectacularly futile exercise.
A piece of paper large enough to
contain the zeros in a googolplex...
...couldn't be stuffed into
the known universe.
Fortunately...
...there's a...
...much simpler
and more concise way...
...to write a googolplex.
Like this.
And infinity...
...can be represented like this.
This is the Cavendish Laboratory
at Cambridge University...
...where the constituents of the atom
were first discovered.
The realm of the very small.
From the time of Democritus,
in the fifth century B.C...
...people have speculated
about the existence of atoms.
For the last few hundred years,
there have been persuasive...
...but indirect arguments that all
matter is made of atoms.
But only in our time, have we actually
been able to see them.
Here the red blobs are the random
throbbing motions...
...of uranium atoms...
...magnified 100 million times.
How Democritus of Abdera
would've enjoyed this movie.
We pretty much take atoms for granted.
And yet, there are so
many different kinds...
...lovely and useful at
the same time.
Look.
There are some 92 chemically
distinct kinds of atoms...
...naturally found on Earth.
They're called the chemical elements.
Virtually everything
we see and know...
...all the beauty
of the natural world...
...is made of these
few kinds of atoms...
...arranged in harmonious
chemical patterns.
Here we've represented
all 92 of them.
At room temperature, many of
them are solids.
A few are gases.
And two of them...
...bromine and mercury,
are liquids.
They're arranged in order
of complexity.
Hydrogen, the simplest element,
is element number 1.
And uranium, the most complex...
...is element 92.
Some elements are very familiar.
For example...
...silicon, oxygen, magnesium,
aluminum, iron...
...those that make up the Earth.
Or hydrogen, carbon, nitrogen,
oxygen, phosphorus, sulfur...
...the elements that are
essential for life.
Other elements are
spectacularly unfamiliar.
For example, hafnium.
Erbium.
Dysprosium.
Praseodymium.
Elements we don't bump
into in everyday life.
By and large, the more familiar an
element is, the more abundant it is.
There's a great deal of iron
on the Earth.
Not all that much yttrium.
The fact...
...that atoms are composed of only
three kinds of elementary particles...
...protons, neutrons and electrons...
...is a comparatively recent finding.
The neutron was not discovered
until 1932.
And it, like the electron and
the proton, were discovered here...
...at Cambridge University.
Modern physics and chemistry
have reduced the complexity...
...of the sensible world
to an astonishing simplicity.
Three units, put together
in different patterns...
...make, essentially, everything.
A neutron is electrically neutral...
...as its name suggests.
A proton has a positive
electrical charge...
...and an electron an equal,
negative electrical charge.
Since every atom is
electrically neutral...
...the number of protons
in the nucleus...
...must equal the number of electrons
far away in the electron cloud.
The protons and neutrons, together,
make up the nucleus of the atom.
Now, the chemistry of an atom,
the nature of a chemical element...
...depends only on the number
of electrons...
...which equals the number of protons,
which is called the atomic number.
Chemistry is just numbers.
An idea which would have
appealed to Pythagoras.
If you're an atom...
...and you have just one proton...
...you're hydrogen.
Two protons, helium.
Three, lithium.
Four, beryllium.
Five protons, boron.
Six, carbon, and seven, nitrogen.
Eight, oxygen, and so on.
All the way to 92 protons...
...in which case your name is uranium.
Protons have positive
electrical charges...
...but like charges repel each other.
So why does the nucleus hold together?
Why don't the electrical
repulsion of the protons...
...make the nucleus fly to pieces?
Because there's another
force in nature.
Not electricity, not gravity...
...the nuclear force.
We can think of it as short-range...
...hooks which start working...
...when protons or neutrons
are brought very close together.
The nuclear force can overcome...
...the electrical repulsion of the
protons.
Since the neutrons exert
nuclear forces...
...but not electrical forces...
...they are a kind of glue which holds
the atomic nucleus together.
A lump of two protons
and two neutrons...
...is the nucleus of a helium atom...
...and is very stable.
Three helium nuclei, stuck together by
nuclear forces...
...makes carbon.
Four helium nuclei makes oxygen.
There's no difference between
four helium nuclei...
...stuck together by nuclear forces
and the oxygen nucleus.
They're the same thing.
Five helium nuclei makes neon.
Six makes magnesium.
Seven makes silicon.
Eight makes sulfur, and so on.
Increasing the atomic
numbers by two...
...and always making
some familiar element.
Every time...
...we add or subtract one proton...
...and enough neutrons
to keep the nucleus together...
...we make a new chemical element.
Consider mercury:
If we subtract one proton
from mercury...
...and three neutrons,
we convert it into gold.
The dream of the ancient alchemists.
Beyond element 92, beyond uranium...
...there are other elements.
They don't occur naturally
on the Earth.
They're synthesized by
human beings and...
...fall to pieces pretty rapidly.
One of them, element 94,
is called plutonium...
...and is one of the most
toxic substances known.
Where do the naturally occurring
chemical elements come from?
Perhaps a separate creation
for each element?
But all the elements are made of the
same elementary particles.
The universe, all of it,
everywhere...
...is 99.9% hydrogen and helium.
The two simplest elements.
In fact, helium...
...was detected on the sun before it
was ever found on the Earth.
Might the other chemical elements
have somehow...
...evolved from hydrogen
and helium?
To avoid the electrical repulsion...
...protons and neutrons must be brought
very close together so the hooks...
...which represent nuclear forces...
...are engaged.
This happens only at very high
temperatures, where particles...
...move so fast that there's no
time for electrical repulsion to act.
Temperatures of tens of
millions of degrees.
Such high temperatures are
common in nature.
Where?
In the insides of the stars.
Atoms are made in the
insides of stars.
In most of the stars we see, hydrogen
nuclei are being jammed together...
...to form helium nuclei.
Every time a nucleus of helium is made,
a photon of light is generated.
This is why the stars shine.
Stars are born in great
clouds of gas and dust.
Like the Orion Nebula,
1500 light-years away...
...parts of which
are collapsing under gravity.
Collisions among the atoms heat
the cloud until, in its interior...
...hydrogen begins to fuse
into helium...
...and the stars turn on.
Stars are born in batches.
Later, they wander out
of their nursery...
...to pursue their destiny
in the Milky Way.
Adolescent stars, like the Pleiades...
...are still surrounded
by gas and dust.
Eventually, they journey
far from home.
Somewhere there are stars formed from
the same cloud complex as the sun...
...5 billion years ago.
But we do not know which
stars they are.
The siblings of the sun...
...may, for all we know, be on the
other side of the galaxy.
Perhaps they also warm nearby
planets as the sun does.
Perhaps they too have presided...
...over the evolution
of life and intelligence.
The sun is the nearest star,
a glowing sphere of gas...
...shining because of its heat,
like a red-hot poker.
The surface we see in ordinary visible
light is at 6000 degrees centigrade.
But in its hidden interior...
...in the nuclear furnace where
sunlight is ultimately generated...
...its temperature is
20 million degrees.
In x-rays...
...we see a part of the sun
that is ordinarily invisible...
...its million-degree halo of gas...
...the solar corona.
In ordinary visible light, these
cooler, darker regions...
...are the sunspots.
They are associated with
great surges of flaming gas...
...tongues of fire which would engulf
the Earth if it were this close.
These prominences are guided
into paths determined...
...by the sun's magnetic field.
The dark regions of the x-ray sun...
...are holes in the solar corona...
...through which stream the protons
and electrons of the solar wind...
...on their way past the planets
to interstellar space.
All this churning power is driven
by the sun's interior...
...which is converting 400 million
tons of hydrogen into helium...
...every second.
The sun is a great fusion reactor...
...into which a million Earths
would fit.
Luckily for us, it's safely placed...
...150 million kilometers away.
It is the destiny of stars
to collapse.
Of the thousands of stars you see
when you look up at the night sky...
...every one of them is living in
an interval between two collapses.
An initial collapse of...
...a dark interstellar gas cloud
to form the star...
...and a final collapse
of the luminous star...
...on the way to its ultimate fate.
Gravity makes stars contract unless
some other force intervenes.
The sun is an immense ball
of radiating hydrogen.
The hot gas in its interior tries
to make the sun expand.
The gravity tries to make
the sun contract.
The present state of the sun is
the balance of these two forces...
...an equilibrium between
gravity and nuclear fire.
In this long middle age
between collapses...
...the stars steadily shine.
But when the nuclear fuel is exhausted,
the interior cools...
...the pressure no longer supports
its outer layers...
...and the initial collapse resumes.
There are three ways that stars die.
Their fates are predestined.
Everything depends on their
initial mass.
A typical star with a mass
like the sun...
...will one day
continue its collapse...
...until its density becomes very high.
And then the contraction is stopped...
...by the mutual repulsion of...
...the overcrowded electrons
in its interior.
A collapsing star twice as
massive as the sun...
...isn't stopped by the
electron pressure.
It goes on falling in on itself...
...until nuclear forces
come into play...
...and they hold up the
weight of the star.
But a collapsing star three times as
massive as the sun isn't...
...stopped even by nuclear forces.
There's no force known that can
withstand this enormous compression.
And such a star has
an astonishing destiny.
It continues to collapse...
...until it vanishes utterly.
Each star is described by the force
that holds it up against gravity.
A star that's supported by
the gas pressure...
...is a normal, run-of-the-mill star
like the sun.
A collapsed star that's held up
by electron forces...
...is called a white dwarf.
It's a sun shrunk to
the size of the Earth.
A collapsed star supported
by nuclear forces...
...is called a neutron star.
It's a sun shrunk to
the size of a city.
And a star so massive that
in its final collapse...
...it disappears altogether...
...is called a black hole.
It's a sun with no size at all.
But on their ways to their
separate fates...
...all stars experience
a premonition of death.
Before the final
gravitational collapse...
...the star shudders and
briefly swells into some...
...grotesque parody of itself.
With its last gasp,
it becomes a red giant.
Some 5 billion years from now...
...there will be a last,
perfect day on Earth.
Then, the sun will slowly change...
...and the Earth will die.
There is only so much
hydrogen fuel in the sun.
When it's almost all
converted to helium...
...the solar interior will continue
its original collapse.
Higher temperatures in its core will
make the outside of the sun expand...
...and the Earth will
become slowly warmer.
Eventually, life will be
extinguished...
...the oceans will evaporate
and boil...
...and our atmosphere will
gush away to space.
The sun will become a bloated
red giant star...
...filling the sky...
...enveloping and devouring
the planets Mercury and Venus.
And probably the Earth as well.
The inner solar system will
reside inside the sun.
But perhaps by then, our
descendants...
...will have ventured somewhere else.
In its final agonies, the sun
will slowly pulsate.
By then, its core will have
become so hot...
...that it temporarily converts
helium into carbon.
The ash from today's nuclear fusion
will become the fuel...
...to power the sun near the end of
its life in its red giant stage.
Then the sun will lose
great shells...
...of its outer atmosphere to space...
...filling the solar system
with eerily glowing gas.
The ghost of a star, outward bound.
Perhaps half the mass of the sun
will be lost in this way.
Viewed from elsewhere, our system
will then resemble...
...the Ring Nebula in Lyra...
...the atmosphere of the sun
expanding outward like a soap bubble.
And at the very center will be
a white dwarf.
The hot exposed core of the sun...
...its nuclear fuel now
exhausted, slowly cooling...
...to become a cold, dead star.
Such is the life of an ordinary star.
Born in a gas cloud,
maturing as a yellow sun...
...decaying as a red giant...
...and dying as a white dwarf
enveloped in its shroud of gas.
Suppose, as we traveled through
interstellar space...
...in our ship of the imagination...
...we could sample the cold,
thin gas between the stars.
We would find a great
preponderance of hydrogen...
...an element as old as the universe.
We would find carbon,
oxygen, silicon.
The most abundant atoms in the
cosmos, apart from hydrogen...
...are those most easily made
in the stars.
But we would also find
a small proportion of rare elements.
Praseodymium, say, or gold.
They're not made in red giants.
Such elements are manufactured in
one of the most dramatic gestures...
...of which a star is capable.
A star more than about one and
a half times the mass of the sun...
...cannot become a white dwarf.
It will end its life by
blowing itself up...
...in a titanic stellar explosion
called a supernova.
There has been no supernova explosion
in our province of the galaxy...
...since the telescope's invention...
...and our sun will not
become a supernova.
But in our imagination...
...we can fulfill the dream of many
earthbound astronomers...
...and safely witness, close-up,
a supernova explosion.
Most of stellar evolution takes
millions or billions of years.
But the interior collapse that
triggers a supernova explosion...
...takes only seconds.
The star becomes brighter than
all the other stars in the galaxy...
...put together.
If a nearby star became
a supernova...
...it would be calamity enough for
the inhabitants of this alien system.
But if their own sun went supernova...
...it would be
an unprecedented catastrophe.
Worlds would be charred and vaporized.
Life, even on the outer planets,
would be extinguished.
In our ship of the imagination, we
are now backing away from the star.
But the explosion fragments...
...traveling almost at the speed
of light, are overtaking us.
Individual atomic nuclei, accelerated
to high speeds in the explosion...
...become cosmic rays.
This is another way that stars return
the atoms they've synthesized...
...back into space.
The shock wave
of expanding gases...
...heats and compresses
the interstellar gas...
...triggering a later generation
of stars to form.
In this sense also...
...stars are phoenixes
rising from their own ashes.
The cosmos was originally
all hydrogen and helium.
Heavier elements were made
in red giants and in supernovas...
...and then blown off to space...
...where they were available
for subsequent generations...
...of stars and planets.
Our sun is probably a
third-generation star.
Except for hydrogen and helium...
...every atom in the sun and the Earth
was synthesized in other stars.
The silicon in the rocks, the oxygen
in the air, the carbon in our DNA...
...the gold in our banks, the
uranium in our arsenals...
...were all made thousands
of light-years away...
...and billions of years ago.
Our planet, our society
and we ourselves...
...are built of star stuff.
We're in a lava tube.
A cave carved through the Earth...
...by a river of molten rock.
To do a little experiment...
...we've brought a Geiger counter...
...and a piece of uranium ore.
The Geiger counter is sensitive to
high-energy charged particles...
...protons, helium nuclei, gamma rays.
If we bring it close
to the uranium ore...
...the count rate, the number of
clicks, increases dramatically.
We also have a lead canister here.
And if I drop the uranium ore...
...into the canister, which absorbs
the radiation, and cover it up...
...I then find the count-rate
goes down substantially...
...but it doesn't go down to zero.
What's the source of the
remaining counts?
Some of them come from radioactivity
in the walls of the cave.
But there's more to it than that.
Some of the counts are due to
high-energy charged particles...
...which are penetrating the
roof of the cave.
We are listening to cosmic rays.
Every second they are penetrating
my body...
...and yours.
They don't do much damage. Cosmic
rays have bombarded the Earth...
...for the entire history of
life on our planet.
But they do cause some mutations...
...and they do affect life
on the Earth.
The cosmic rays, mainly protons...
...are penetrating through the meters
of rock in the cave above me.
To do this, they have to
be very energetic and in fact...
...they are traveling almost
at the speed of light.
Think of it.
A star blows up...
...thousands of light-years
away in space...
...and produces cosmic rays which...
...spiral through the Milky Way
galaxy for...
...millions of years until,
quite by accident...
...some of them strike the Earth...
...penetrate this cave,
reach this Geiger counter...
...and us.
The evolution of life on Earth is
driven in part through mutations...
...by the deaths of distant stars.
We are, in a very deep sense...
...tied to the cosmos.
Our ancestors knew this well.
The movements of the sun, the moon,
and the stars...
...could be used by those skilled in
such arts to foretell the seasons.
So the ancient astronomers
all over the world...
...studied the night sky with care...
...memorizing and recording the
position of every visible star.
To them, the appearance of any new
star would have been significant.
What would they have made of the
apparition of a supernova...
...brighter than every other
star in the sky?
On July 4th, in the year 1054...
...Chinese astronomers recorded what
they called a guest star...
...in the constellation of
Taurus the Bull.
A star never before seen
burst into radiance...
...became almost as bright
as the full moon.
Halfway around the world, here in
the American Southwest...
...there was then a high culture,
rich in astronomical tradition.
They too must have seen this
brilliant new star.
From carbon-14 dating...
...of the remains of a charcoal fire,
we know that in this very spot...
...there were people living
in the 11th century.
The people were the Anasazi, the
antecedents of the Hopi of today.
And one of them
seems to have drawn...
...on this overhang, protected
from the weather...
...a picture of the new star.
Its position near the crescent moon
would have been just what we see here.
And the handprint is, perhaps...
...the artist's signature.
This remarkable star is now
called the Crab Supernova.
"Nova" from the Latin word for new
and "Crab" because...
...that's what an astronomer centuries
later was reminded of...
...when looking at this explosion or
remnant through the telescope.
The Crab is a star that
blew itself up.
The explosion was seen
for three months.
It was easily visible
in broad daylight.
And you could read by it at night.
Imagine the night when that...
...colossal stellar explosion...
...first burst forth.
A thousand years ago...
...people gazed up in amazement
at the brilliant new star...
...and wondered what it was.
We are the first generation
privileged to know the answer.
Through the telescope we have seen
what lies today...
...at the spot in the sky noted
by the ancient astronomers.
A great luminous cloud,
the remains of a star...
...violently unraveling itself back
into interstellar space.
Only the massive red giants
become supernovas.
But every supernova was
once a red giant.
In the history of the galaxy...
...hundreds of millions of red
giants have become supernovas.
The bit of the star that isn't blown
away collapses under gravity...
...spinning ever faster like a
pirouetting ice skater...
...bringing in her arms.
The star becomes a single, massive
atomic nucleus...
...a neutron star.
The one in the Crab Nebula
is spinning 30 times a second.
It emits a beamed pattern of light...
...and seems to us to be blinking on
and off with astonishing regularity.
Such neutron stars are
called pulsars.
Neutron star matter...
...weighs about a mountain
per teaspoonful.
So much that if I had a piece of it
here and let it go...
...I could hardly
prevent it from falling.
It would effortlessly pass through the
Earth like a...
...a knife through warm butter.
It would carve a hole for itself
completely through the Earth...
...emerging out the other side
perhaps in China.
The people there might be
walking along when a...
...tiny lump of neutron star matter
comes booming out of the ground...
...and then falls back again.
The incident might...
...make an agreeable break in the
routine of the day.
The neutron star matter, pulled
back by the Earth's gravity...
...would plunge again
through the Earth...
...eventually punching hundreds of
thousands of holes...
...before friction with the interior
of our planet stopped the motion.
By the time it's at rest at
the center of the Earth...
...the inside of our world would look
a little bit like Swiss cheese.
There are places in the galaxy
where a neutron star and a red giant...
...are locked in a mutual
gravitational embrace.
Tendrils of red giant star stuff...
...spiral into a disc
of accreting matter...
...centered on the hot neutron star.
Every star exists in
a state of tension...
...between the force that
holds it up...
...and gravity, the force that
would pull it down.
If gravity were to prevail, a
stellar madness would ensue...
...more bizarre than
anything in wonderland.
Alice and her colleagues feel,
more or less...
...at home in the gravitational
pull of the Earth...
...called one g,
"g" for Earth gravity.
What would happen if we made the
gravity less, or more?
At lower gravity, things get lighter.
Near zero g, the slightest motion
sends our friends...
...floating and tumbling in the air.
Little blobs of liquid
tea are everywhere.
Curious.
If we now return the gravity
to one g...
...it's raining tea, and our friends
fall back to Earth.
I've been to a couple of
parties like that myself.
At higher gravities, two or
three g's, say, things get...
...really laid back.
Everyone feels heavy and leaden.
Except by special dispensation...
...the Cheshire cat.
As a kindness, we remove them.
At thousands of g's,
trees become squashed.
At 100,000 g's, rocks
become crushed by their own weight.
At all these gravities, a beam of
light remains unaffected...
...continuing up in a straight line.
But at billions of g's...
...a beam of light feels the gravity
and begins to bend back on itself.
Curiouser and curiouser.
Such a place, where the gravity is so
large that even light can't get out...
...is called a black hole.
It's a star in which light
itself is imprisoned.
Black holes were
theoretical constructs...
...speculated about since 1783.
But in our time, we've
verified the invisible.
This bright star has a
massive, unseen companion.
Satellite observatories find the
companion to be an x-ray source...
...called Cygnus X-1.
These x-rays are like
the footprints...
...of an invisible man
walking in the snow.
The x-rays are thought to be
generated by friction...
...in the accretion disc
surrounding the black hole.
The matter in the disc
slowly disappears...
...down the black hole.
Massive black holes, produced by the
collapse of a billion suns...
...may be sitting at the centers
of other galaxies...
...curiously producing great
jets of radiation...
...pouring out into space.
At high enough density,
the star winks out...
...and vanishes from our universe
leaving only its gravity behind.
It slips through a self-generated
crack in the space-time continuum.
A black hole is a place
where a star once was.
Here we have a flat two-
dimensional surface...
...with grid lines on it, something
like a piece of graph paper.
Suppose we take a small mass...
...drop it on the surface and
watch how the surface distorts...
...or puckers into
the third physical dimension.
Gravity can be understood as
a curvature of space.
If our moving ball approaches a
stationary distortion...
...it rolls around it like a
planet orbiting the sun.
In this interpretation, due to
Einstein, gravity is only a pucker...
...in the fabric of space which
moving objects encounter.
Space is warped by mass into an
additional physical dimension.
The larger the local mass, the
greater is the local gravity...
...and the more intense is
the distortion...
...or pucker, or warp of space.
So, by this analogy...
...a black hole is a kind of
bottomless pit.
What would happen if you fell in?
Assuming you could survive the
gravitational tides...
...and the intense radiation flux,
it is just barely possible...
...that by plunging into
a black hole...
...you might emerge in another
part of space-time.
Somewhere else in space...
...some-when else in time.
In this view, space is...
...filled with a network
of wormholes...
...something like the wormholes
in an apple.
Although by no means is this
point demonstrated...
...it is merely an exciting suggestion.
If it is true...
...then perhaps there exist
gravity tunnels...
...a kind of interstellar or
intergalactic subway...
...which would permit you
to get from...
...here to there in much less than
the usual time.
A kind of cosmic rapid transit system.
We cannot generate black holes...
...our technology is far
too feeble to...
...move such massive amounts
of matter around.
But perhaps someday, it will be
possible to voyage hundreds or...
...thousands of light-years to
a black hole like Cygnus X-1.
We would plunge down to emerge...
...in some unimaginably
exotic time and place.
Our common-sense notions of reality
severely challenged.
Perhaps the cosmos is infested
with wormholes...
...every one of them a
tunnel to somewhere.
Perhaps other civilizations, with
vastly more advanced technologies...
...are today riding the
gravity express.
It's even possible that a
black hole is a gate...
...to another, and
quite different, universe.
The lives and deaths of the stars...
...seem impossibly remote
from human experience...
...and yet we're related in the most
intimate way to their life cycles.
The very matter that makes us up...
...was generated long ago and far away
in red giant stars.
A blade of grass,
as Walt Whitman said...
"... is the journey work of the stars. "
The formation of the solar system...
...may have been triggered by a
nearby supernova explosion.
After the sun turned on...
...its ultraviolet light poured
into our atmosphere.
Its warmth generated lightning.
And these energy sources sparked
the origin of life.
Plants harvest sunlight...
...converting solar into
chemical energy.
We and the other animals are
parasites on the plants.
So we are, all of us, solar-powered.
The evolution of life is
driven by mutations.
They are caused partly by natural
radioactivity and cosmic rays.
But they are both generated in the
spectacular deaths of massive stars...
...thousands of light-years distant.
Think of the sun's heat on your
upturned face...
...on a cloudless summer's day.
From 150 million kilometers away...
...we recognize its power.
What would we feel on its seething,
self-luminous surface...
...or immersed in its heart
of nuclear fire?
And yet, the sun is an ordinary,
even a mediocre star.
Our ancestors worshiped the sun
and they were far from foolish.
It makes good sense to revere
the sun and the stars.
Because we are their children.
We have witnessed the life
cycles of the stars.
They are born, they mature
and then they die.
As time goes on, there are
more white dwarfs...
...more neutron stars,
more black holes.
The remains of the stars accumulate...
...as the eons pass.
But interstellar space also becomes
enriched in heavy elements...
...out of which form new generations
of stars and planets...
...life and intelligence.
The events in one star can influence
a world halfway across the galaxy...
...and a billion years in the future.
The vast interstellar clouds
of gas and dust...
...are stellar nurseries.
Here first begins the inexorable
gravitational collapse...
...which dominates the
lives of the stars.
Massive suns may evolve through the
red giant stage in only millions of years.
Dying young, never leaving the
cloud in which they were born.
Other suns, longer-lived, wander
out of the nursery.
Our sun is such a star...
...as are most
of the stars in the sky.
Most stars are members of double
or multiple star systems...
...and live to process their nuclear
fuel over billions of years.
The galaxy is 10 billion years old.
Old enough to have spawned...
...only a few generations
of ordinary stars.
The objects we encounter
in a voyage through the Milky Way...
...are stages in the life cycle
of the stars.
Some are bright and new...
...and others are as ancient as
the galaxy itself.
Surrounding the Milky Way
is a halo of matter...
...which includes
the globular clusters...
...each containing up to
a million elderly stars.
At the centers of globular clusters
and at the core of the galaxy...
...there may be massive black holes
ticking and purring...
...the subject of future exploration.
We on Earth marvel,
and rightly so...
...at the daily return
of our single sun.
But from a planet orbiting a star
in a distant globular cluster...
...a still more glorious dawn awaits.
Not a sunrise, but a galaxy-rise.
A morning filled with
400 billion suns...
...the rising of the Milky Way.
An enormous spiral form
with collapsing gas clouds...
...condensing planetary systems,
luminous supergiants...
...stable middle-aged stars...
...red giants, white dwarfs, planetary
nebulas, supernovas...
...neutron stars, pulsars,
black holes and...
...there is every reason to think,
other exotic objects...
...that we have not yet discovered.
From such a world, high above
the disc of the Milky Way...
...it would be clear as it is
beginning to be clear on our world...
...that we are made
by the atoms in the stars...
...that our matter
and our form are determined...
...by the cosmos
of which we are a part.
I only have a moment, but I wanted you
to see a picture of Betelgeuse...
...in the constellation Orion.
The first image of the surface
of another star.
But the most exciting recent
stellar discovery...
...has been of a nearby supernova...
...in a companion galaxy
to the Milky Way.
We are here seeing chemical elements
in the process of synthesis...
...and have had our first glimpse
of the supernova...
...through a brand-new field:
neutrino astronomy.
And we're now seeing, around
neighboring stars...
...discs of gas and dust just
like those needed to explain...
...the origin of the planets
in our solar system.
Worlds may be forming here.
It's like a snapshot of our
solar system's past.
And there are so many such
discs being found these days...
...that planets may be very common
among the stars of the Milky Way.
Best watched using Open Subtitles MKV Player
If you wish to make
an apple pie from scratch...
...you must first invent the universe.
Thank you very much.
Suppose I cut a piece...
...out of this apple pie.
Crumbly, but good.
And now suppose we cut
this piece in half, or more or less.
And then cut this piece in half...
...and keep going.
How many cuts before we get
down to an individual atom?
The answer is about
90 successive cuts.
Of course, this knife isn't
sharp enough...
...the pie is too crumbly...
...and an atom is too small
to see in any case.
But there is a way to do it.
It was here at
Cambridge University in England...
...that the nature of the atom was
first understood...
...in part by shooting pieces
of atoms at atoms...
...and seeing how they bounce off.
A typical atom is surrounded...
...by a kind of cloud of electrons.
The electrons are electrically
charged, as the name suggests...
...and they determine the chemical
properties of the atom.
For example, the glitter of gold...
...or the transparency of the solid...
...that's made from the atoms
silicon and oxygen.
But deep inside the atom...
...hidden far beneath
the outer electron cloud...
...is the nucleus, composed chiefly
of protons and neutrons.
Atoms are very small.
100 million of them, end to end,
would be about so big.
And the nucleus is 100,000 times
smaller still.
Nevertheless, most of the mass
in an atom is in the nucleus.
The electrons are by comparison...
...just bits of moving fluff.
Atoms are mainly empty space.
Matter is composed chiefly
of nothing.
When we consider cutting this
apple pie, but...
...down beyond a single atom...
...we confront an infinity
of the very small.
And when we look up
at the night sky...
...we confront an infinity
of the very large.
These infinities are among the most
awesome of human ideas.
They represent an unending regress
which goes on...
...not just very far, but forever.
Have you ever stood between two
parallel mirrors...
...in a barbershop, say...
...and seen a very large
number of you?
Or you could use...
...two flat mirrors...
...and a candle flame...
...you would see a large number
of images...
...each the reflection
of another image.
You can't really see an infinity
of images...
...because the mirrors aren't
perfectly flat and aligned.
And there's a candle or
a candle flame in the way...
...and light doesn't travel
infinitely fast.
When we talk of real infinities...
...we're talking about a quantity
larger than any number.
No matter what number you have in
mind, infinity is larger.
There's a nice way
to write large numbers.
You can...
...write the number 1000...
...as 10 to the power three...
...meaning, a one
followed by three zeros.
Or a million is written as
10 to the power six...
...meaning, a one
followed by six zeros.
There's no largest number. If anybody
gives you a candidate...
...you can always add the
number one to it.
But there certainly are
very big numbers.
The American mathematician Edward
Kasner once asked his nephew...
...to invent a name for
an extremely large number:
10 to the power 100...
...which I can't write out all the
zeros because there isn't room.
The boy called it a googol.
If you think a googol is large,
consider a googolplex.
It's 10 to the power of a googol.
That is, a one followed, not by
100 zeros...
...but by a googol zeros.
Now, by comparison...
...with these enormous numbers...
...the total number of atoms
in that apple pie...
...is only about 10 to the 26th.
Tiny compared to a googol and...
...of course, much, much less
than a googolplex.
The number
of elementary particles...
...protons, neutrons and electrons...
...in the accessible universe...
...is of the order of 10 to the 80th.
A one followed by 80 zeros.
Still much, much less than a googol...
...and vastly less than a googolplex.
And yet, these numbers, the googol
and the googolplex...
...do not approach, they come
nowhere near infinity.
In fact, a googolplex is precisely
as far from infinity...
...as is the number one.
We started to write out
a googolplex...
...but it wasn't easy.
It's a very big number.
Writing out a googolplex is a
spectacularly futile exercise.
A piece of paper large enough to
contain the zeros in a googolplex...
...couldn't be stuffed into
the known universe.
Fortunately...
...there's a...
...much simpler
and more concise way...
...to write a googolplex.
Like this.
And infinity...
...can be represented like this.
This is the Cavendish Laboratory
at Cambridge University...
...where the constituents of the atom
were first discovered.
The realm of the very small.
From the time of Democritus,
in the fifth century B.C...
...people have speculated
about the existence of atoms.
For the last few hundred years,
there have been persuasive...
...but indirect arguments that all
matter is made of atoms.
But only in our time, have we actually
been able to see them.
Here the red blobs are the random
throbbing motions...
...of uranium atoms...
...magnified 100 million times.
How Democritus of Abdera
would've enjoyed this movie.
We pretty much take atoms for granted.
And yet, there are so
many different kinds...
...lovely and useful at
the same time.
Look.
There are some 92 chemically
distinct kinds of atoms...
...naturally found on Earth.
They're called the chemical elements.
Virtually everything
we see and know...
...all the beauty
of the natural world...
...is made of these
few kinds of atoms...
...arranged in harmonious
chemical patterns.
Here we've represented
all 92 of them.
At room temperature, many of
them are solids.
A few are gases.
And two of them...
...bromine and mercury,
are liquids.
They're arranged in order
of complexity.
Hydrogen, the simplest element,
is element number 1.
And uranium, the most complex...
...is element 92.
Some elements are very familiar.
For example...
...silicon, oxygen, magnesium,
aluminum, iron...
...those that make up the Earth.
Or hydrogen, carbon, nitrogen,
oxygen, phosphorus, sulfur...
...the elements that are
essential for life.
Other elements are
spectacularly unfamiliar.
For example, hafnium.
Erbium.
Dysprosium.
Praseodymium.
Elements we don't bump
into in everyday life.
By and large, the more familiar an
element is, the more abundant it is.
There's a great deal of iron
on the Earth.
Not all that much yttrium.
The fact...
...that atoms are composed of only
three kinds of elementary particles...
...protons, neutrons and electrons...
...is a comparatively recent finding.
The neutron was not discovered
until 1932.
And it, like the electron and
the proton, were discovered here...
...at Cambridge University.
Modern physics and chemistry
have reduced the complexity...
...of the sensible world
to an astonishing simplicity.
Three units, put together
in different patterns...
...make, essentially, everything.
A neutron is electrically neutral...
...as its name suggests.
A proton has a positive
electrical charge...
...and an electron an equal,
negative electrical charge.
Since every atom is
electrically neutral...
...the number of protons
in the nucleus...
...must equal the number of electrons
far away in the electron cloud.
The protons and neutrons, together,
make up the nucleus of the atom.
Now, the chemistry of an atom,
the nature of a chemical element...
...depends only on the number
of electrons...
...which equals the number of protons,
which is called the atomic number.
Chemistry is just numbers.
An idea which would have
appealed to Pythagoras.
If you're an atom...
...and you have just one proton...
...you're hydrogen.
Two protons, helium.
Three, lithium.
Four, beryllium.
Five protons, boron.
Six, carbon, and seven, nitrogen.
Eight, oxygen, and so on.
All the way to 92 protons...
...in which case your name is uranium.
Protons have positive
electrical charges...
...but like charges repel each other.
So why does the nucleus hold together?
Why don't the electrical
repulsion of the protons...
...make the nucleus fly to pieces?
Because there's another
force in nature.
Not electricity, not gravity...
...the nuclear force.
We can think of it as short-range...
...hooks which start working...
...when protons or neutrons
are brought very close together.
The nuclear force can overcome...
...the electrical repulsion of the
protons.
Since the neutrons exert
nuclear forces...
...but not electrical forces...
...they are a kind of glue which holds
the atomic nucleus together.
A lump of two protons
and two neutrons...
...is the nucleus of a helium atom...
...and is very stable.
Three helium nuclei, stuck together by
nuclear forces...
...makes carbon.
Four helium nuclei makes oxygen.
There's no difference between
four helium nuclei...
...stuck together by nuclear forces
and the oxygen nucleus.
They're the same thing.
Five helium nuclei makes neon.
Six makes magnesium.
Seven makes silicon.
Eight makes sulfur, and so on.
Increasing the atomic
numbers by two...
...and always making
some familiar element.
Every time...
...we add or subtract one proton...
...and enough neutrons
to keep the nucleus together...
...we make a new chemical element.
Consider mercury:
If we subtract one proton
from mercury...
...and three neutrons,
we convert it into gold.
The dream of the ancient alchemists.
Beyond element 92, beyond uranium...
...there are other elements.
They don't occur naturally
on the Earth.
They're synthesized by
human beings and...
...fall to pieces pretty rapidly.
One of them, element 94,
is called plutonium...
...and is one of the most
toxic substances known.
Where do the naturally occurring
chemical elements come from?
Perhaps a separate creation
for each element?
But all the elements are made of the
same elementary particles.
The universe, all of it,
everywhere...
...is 99.9% hydrogen and helium.
The two simplest elements.
In fact, helium...
...was detected on the sun before it
was ever found on the Earth.
Might the other chemical elements
have somehow...
...evolved from hydrogen
and helium?
To avoid the electrical repulsion...
...protons and neutrons must be brought
very close together so the hooks...
...which represent nuclear forces...
...are engaged.
This happens only at very high
temperatures, where particles...
...move so fast that there's no
time for electrical repulsion to act.
Temperatures of tens of
millions of degrees.
Such high temperatures are
common in nature.
Where?
In the insides of the stars.
Atoms are made in the
insides of stars.
In most of the stars we see, hydrogen
nuclei are being jammed together...
...to form helium nuclei.
Every time a nucleus of helium is made,
a photon of light is generated.
This is why the stars shine.
Stars are born in great
clouds of gas and dust.
Like the Orion Nebula,
1500 light-years away...
...parts of which
are collapsing under gravity.
Collisions among the atoms heat
the cloud until, in its interior...
...hydrogen begins to fuse
into helium...
...and the stars turn on.
Stars are born in batches.
Later, they wander out
of their nursery...
...to pursue their destiny
in the Milky Way.
Adolescent stars, like the Pleiades...
...are still surrounded
by gas and dust.
Eventually, they journey
far from home.
Somewhere there are stars formed from
the same cloud complex as the sun...
...5 billion years ago.
But we do not know which
stars they are.
The siblings of the sun...
...may, for all we know, be on the
other side of the galaxy.
Perhaps they also warm nearby
planets as the sun does.
Perhaps they too have presided...
...over the evolution
of life and intelligence.
The sun is the nearest star,
a glowing sphere of gas...
...shining because of its heat,
like a red-hot poker.
The surface we see in ordinary visible
light is at 6000 degrees centigrade.
But in its hidden interior...
...in the nuclear furnace where
sunlight is ultimately generated...
...its temperature is
20 million degrees.
In x-rays...
...we see a part of the sun
that is ordinarily invisible...
...its million-degree halo of gas...
...the solar corona.
In ordinary visible light, these
cooler, darker regions...
...are the sunspots.
They are associated with
great surges of flaming gas...
...tongues of fire which would engulf
the Earth if it were this close.
These prominences are guided
into paths determined...
...by the sun's magnetic field.
The dark regions of the x-ray sun...
...are holes in the solar corona...
...through which stream the protons
and electrons of the solar wind...
...on their way past the planets
to interstellar space.
All this churning power is driven
by the sun's interior...
...which is converting 400 million
tons of hydrogen into helium...
...every second.
The sun is a great fusion reactor...
...into which a million Earths
would fit.
Luckily for us, it's safely placed...
...150 million kilometers away.
It is the destiny of stars
to collapse.
Of the thousands of stars you see
when you look up at the night sky...
...every one of them is living in
an interval between two collapses.
An initial collapse of...
...a dark interstellar gas cloud
to form the star...
...and a final collapse
of the luminous star...
...on the way to its ultimate fate.
Gravity makes stars contract unless
some other force intervenes.
The sun is an immense ball
of radiating hydrogen.
The hot gas in its interior tries
to make the sun expand.
The gravity tries to make
the sun contract.
The present state of the sun is
the balance of these two forces...
...an equilibrium between
gravity and nuclear fire.
In this long middle age
between collapses...
...the stars steadily shine.
But when the nuclear fuel is exhausted,
the interior cools...
...the pressure no longer supports
its outer layers...
...and the initial collapse resumes.
There are three ways that stars die.
Their fates are predestined.
Everything depends on their
initial mass.
A typical star with a mass
like the sun...
...will one day
continue its collapse...
...until its density becomes very high.
And then the contraction is stopped...
...by the mutual repulsion of...
...the overcrowded electrons
in its interior.
A collapsing star twice as
massive as the sun...
...isn't stopped by the
electron pressure.
It goes on falling in on itself...
...until nuclear forces
come into play...
...and they hold up the
weight of the star.
But a collapsing star three times as
massive as the sun isn't...
...stopped even by nuclear forces.
There's no force known that can
withstand this enormous compression.
And such a star has
an astonishing destiny.
It continues to collapse...
...until it vanishes utterly.
Each star is described by the force
that holds it up against gravity.
A star that's supported by
the gas pressure...
...is a normal, run-of-the-mill star
like the sun.
A collapsed star that's held up
by electron forces...
...is called a white dwarf.
It's a sun shrunk to
the size of the Earth.
A collapsed star supported
by nuclear forces...
...is called a neutron star.
It's a sun shrunk to
the size of a city.
And a star so massive that
in its final collapse...
...it disappears altogether...
...is called a black hole.
It's a sun with no size at all.
But on their ways to their
separate fates...
...all stars experience
a premonition of death.
Before the final
gravitational collapse...
...the star shudders and
briefly swells into some...
...grotesque parody of itself.
With its last gasp,
it becomes a red giant.
Some 5 billion years from now...
...there will be a last,
perfect day on Earth.
Then, the sun will slowly change...
...and the Earth will die.
There is only so much
hydrogen fuel in the sun.
When it's almost all
converted to helium...
...the solar interior will continue
its original collapse.
Higher temperatures in its core will
make the outside of the sun expand...
...and the Earth will
become slowly warmer.
Eventually, life will be
extinguished...
...the oceans will evaporate
and boil...
...and our atmosphere will
gush away to space.
The sun will become a bloated
red giant star...
...filling the sky...
...enveloping and devouring
the planets Mercury and Venus.
And probably the Earth as well.
The inner solar system will
reside inside the sun.
But perhaps by then, our
descendants...
...will have ventured somewhere else.
In its final agonies, the sun
will slowly pulsate.
By then, its core will have
become so hot...
...that it temporarily converts
helium into carbon.
The ash from today's nuclear fusion
will become the fuel...
...to power the sun near the end of
its life in its red giant stage.
Then the sun will lose
great shells...
...of its outer atmosphere to space...
...filling the solar system
with eerily glowing gas.
The ghost of a star, outward bound.
Perhaps half the mass of the sun
will be lost in this way.
Viewed from elsewhere, our system
will then resemble...
...the Ring Nebula in Lyra...
...the atmosphere of the sun
expanding outward like a soap bubble.
And at the very center will be
a white dwarf.
The hot exposed core of the sun...
...its nuclear fuel now
exhausted, slowly cooling...
...to become a cold, dead star.
Such is the life of an ordinary star.
Born in a gas cloud,
maturing as a yellow sun...
...decaying as a red giant...
...and dying as a white dwarf
enveloped in its shroud of gas.
Suppose, as we traveled through
interstellar space...
...in our ship of the imagination...
...we could sample the cold,
thin gas between the stars.
We would find a great
preponderance of hydrogen...
...an element as old as the universe.
We would find carbon,
oxygen, silicon.
The most abundant atoms in the
cosmos, apart from hydrogen...
...are those most easily made
in the stars.
But we would also find
a small proportion of rare elements.
Praseodymium, say, or gold.
They're not made in red giants.
Such elements are manufactured in
one of the most dramatic gestures...
...of which a star is capable.
A star more than about one and
a half times the mass of the sun...
...cannot become a white dwarf.
It will end its life by
blowing itself up...
...in a titanic stellar explosion
called a supernova.
There has been no supernova explosion
in our province of the galaxy...
...since the telescope's invention...
...and our sun will not
become a supernova.
But in our imagination...
...we can fulfill the dream of many
earthbound astronomers...
...and safely witness, close-up,
a supernova explosion.
Most of stellar evolution takes
millions or billions of years.
But the interior collapse that
triggers a supernova explosion...
...takes only seconds.
The star becomes brighter than
all the other stars in the galaxy...
...put together.
If a nearby star became
a supernova...
...it would be calamity enough for
the inhabitants of this alien system.
But if their own sun went supernova...
...it would be
an unprecedented catastrophe.
Worlds would be charred and vaporized.
Life, even on the outer planets,
would be extinguished.
In our ship of the imagination, we
are now backing away from the star.
But the explosion fragments...
...traveling almost at the speed
of light, are overtaking us.
Individual atomic nuclei, accelerated
to high speeds in the explosion...
...become cosmic rays.
This is another way that stars return
the atoms they've synthesized...
...back into space.
The shock wave
of expanding gases...
...heats and compresses
the interstellar gas...
...triggering a later generation
of stars to form.
In this sense also...
...stars are phoenixes
rising from their own ashes.
The cosmos was originally
all hydrogen and helium.
Heavier elements were made
in red giants and in supernovas...
...and then blown off to space...
...where they were available
for subsequent generations...
...of stars and planets.
Our sun is probably a
third-generation star.
Except for hydrogen and helium...
...every atom in the sun and the Earth
was synthesized in other stars.
The silicon in the rocks, the oxygen
in the air, the carbon in our DNA...
...the gold in our banks, the
uranium in our arsenals...
...were all made thousands
of light-years away...
...and billions of years ago.
Our planet, our society
and we ourselves...
...are built of star stuff.
We're in a lava tube.
A cave carved through the Earth...
...by a river of molten rock.
To do a little experiment...
...we've brought a Geiger counter...
...and a piece of uranium ore.
The Geiger counter is sensitive to
high-energy charged particles...
...protons, helium nuclei, gamma rays.
If we bring it close
to the uranium ore...
...the count rate, the number of
clicks, increases dramatically.
We also have a lead canister here.
And if I drop the uranium ore...
...into the canister, which absorbs
the radiation, and cover it up...
...I then find the count-rate
goes down substantially...
...but it doesn't go down to zero.
What's the source of the
remaining counts?
Some of them come from radioactivity
in the walls of the cave.
But there's more to it than that.
Some of the counts are due to
high-energy charged particles...
...which are penetrating the
roof of the cave.
We are listening to cosmic rays.
Every second they are penetrating
my body...
...and yours.
They don't do much damage. Cosmic
rays have bombarded the Earth...
...for the entire history of
life on our planet.
But they do cause some mutations...
...and they do affect life
on the Earth.
The cosmic rays, mainly protons...
...are penetrating through the meters
of rock in the cave above me.
To do this, they have to
be very energetic and in fact...
...they are traveling almost
at the speed of light.
Think of it.
A star blows up...
...thousands of light-years
away in space...
...and produces cosmic rays which...
...spiral through the Milky Way
galaxy for...
...millions of years until,
quite by accident...
...some of them strike the Earth...
...penetrate this cave,
reach this Geiger counter...
...and us.
The evolution of life on Earth is
driven in part through mutations...
...by the deaths of distant stars.
We are, in a very deep sense...
...tied to the cosmos.
Our ancestors knew this well.
The movements of the sun, the moon,
and the stars...
...could be used by those skilled in
such arts to foretell the seasons.
So the ancient astronomers
all over the world...
...studied the night sky with care...
...memorizing and recording the
position of every visible star.
To them, the appearance of any new
star would have been significant.
What would they have made of the
apparition of a supernova...
...brighter than every other
star in the sky?
On July 4th, in the year 1054...
...Chinese astronomers recorded what
they called a guest star...
...in the constellation of
Taurus the Bull.
A star never before seen
burst into radiance...
...became almost as bright
as the full moon.
Halfway around the world, here in
the American Southwest...
...there was then a high culture,
rich in astronomical tradition.
They too must have seen this
brilliant new star.
From carbon-14 dating...
...of the remains of a charcoal fire,
we know that in this very spot...
...there were people living
in the 11th century.
The people were the Anasazi, the
antecedents of the Hopi of today.
And one of them
seems to have drawn...
...on this overhang, protected
from the weather...
...a picture of the new star.
Its position near the crescent moon
would have been just what we see here.
And the handprint is, perhaps...
...the artist's signature.
This remarkable star is now
called the Crab Supernova.
"Nova" from the Latin word for new
and "Crab" because...
...that's what an astronomer centuries
later was reminded of...
...when looking at this explosion or
remnant through the telescope.
The Crab is a star that
blew itself up.
The explosion was seen
for three months.
It was easily visible
in broad daylight.
And you could read by it at night.
Imagine the night when that...
...colossal stellar explosion...
...first burst forth.
A thousand years ago...
...people gazed up in amazement
at the brilliant new star...
...and wondered what it was.
We are the first generation
privileged to know the answer.
Through the telescope we have seen
what lies today...
...at the spot in the sky noted
by the ancient astronomers.
A great luminous cloud,
the remains of a star...
...violently unraveling itself back
into interstellar space.
Only the massive red giants
become supernovas.
But every supernova was
once a red giant.
In the history of the galaxy...
...hundreds of millions of red
giants have become supernovas.
The bit of the star that isn't blown
away collapses under gravity...
...spinning ever faster like a
pirouetting ice skater...
...bringing in her arms.
The star becomes a single, massive
atomic nucleus...
...a neutron star.
The one in the Crab Nebula
is spinning 30 times a second.
It emits a beamed pattern of light...
...and seems to us to be blinking on
and off with astonishing regularity.
Such neutron stars are
called pulsars.
Neutron star matter...
...weighs about a mountain
per teaspoonful.
So much that if I had a piece of it
here and let it go...
...I could hardly
prevent it from falling.
It would effortlessly pass through the
Earth like a...
...a knife through warm butter.
It would carve a hole for itself
completely through the Earth...
...emerging out the other side
perhaps in China.
The people there might be
walking along when a...
...tiny lump of neutron star matter
comes booming out of the ground...
...and then falls back again.
The incident might...
...make an agreeable break in the
routine of the day.
The neutron star matter, pulled
back by the Earth's gravity...
...would plunge again
through the Earth...
...eventually punching hundreds of
thousands of holes...
...before friction with the interior
of our planet stopped the motion.
By the time it's at rest at
the center of the Earth...
...the inside of our world would look
a little bit like Swiss cheese.
There are places in the galaxy
where a neutron star and a red giant...
...are locked in a mutual
gravitational embrace.
Tendrils of red giant star stuff...
...spiral into a disc
of accreting matter...
...centered on the hot neutron star.
Every star exists in
a state of tension...
...between the force that
holds it up...
...and gravity, the force that
would pull it down.
If gravity were to prevail, a
stellar madness would ensue...
...more bizarre than
anything in wonderland.
Alice and her colleagues feel,
more or less...
...at home in the gravitational
pull of the Earth...
...called one g,
"g" for Earth gravity.
What would happen if we made the
gravity less, or more?
At lower gravity, things get lighter.
Near zero g, the slightest motion
sends our friends...
...floating and tumbling in the air.
Little blobs of liquid
tea are everywhere.
Curious.
If we now return the gravity
to one g...
...it's raining tea, and our friends
fall back to Earth.
I've been to a couple of
parties like that myself.
At higher gravities, two or
three g's, say, things get...
...really laid back.
Everyone feels heavy and leaden.
Except by special dispensation...
...the Cheshire cat.
As a kindness, we remove them.
At thousands of g's,
trees become squashed.
At 100,000 g's, rocks
become crushed by their own weight.
At all these gravities, a beam of
light remains unaffected...
...continuing up in a straight line.
But at billions of g's...
...a beam of light feels the gravity
and begins to bend back on itself.
Curiouser and curiouser.
Such a place, where the gravity is so
large that even light can't get out...
...is called a black hole.
It's a star in which light
itself is imprisoned.
Black holes were
theoretical constructs...
...speculated about since 1783.
But in our time, we've
verified the invisible.
This bright star has a
massive, unseen companion.
Satellite observatories find the
companion to be an x-ray source...
...called Cygnus X-1.
These x-rays are like
the footprints...
...of an invisible man
walking in the snow.
The x-rays are thought to be
generated by friction...
...in the accretion disc
surrounding the black hole.
The matter in the disc
slowly disappears...
...down the black hole.
Massive black holes, produced by the
collapse of a billion suns...
...may be sitting at the centers
of other galaxies...
...curiously producing great
jets of radiation...
...pouring out into space.
At high enough density,
the star winks out...
...and vanishes from our universe
leaving only its gravity behind.
It slips through a self-generated
crack in the space-time continuum.
A black hole is a place
where a star once was.
Here we have a flat two-
dimensional surface...
...with grid lines on it, something
like a piece of graph paper.
Suppose we take a small mass...
...drop it on the surface and
watch how the surface distorts...
...or puckers into
the third physical dimension.
Gravity can be understood as
a curvature of space.
If our moving ball approaches a
stationary distortion...
...it rolls around it like a
planet orbiting the sun.
In this interpretation, due to
Einstein, gravity is only a pucker...
...in the fabric of space which
moving objects encounter.
Space is warped by mass into an
additional physical dimension.
The larger the local mass, the
greater is the local gravity...
...and the more intense is
the distortion...
...or pucker, or warp of space.
So, by this analogy...
...a black hole is a kind of
bottomless pit.
What would happen if you fell in?
Assuming you could survive the
gravitational tides...
...and the intense radiation flux,
it is just barely possible...
...that by plunging into
a black hole...
...you might emerge in another
part of space-time.
Somewhere else in space...
...some-when else in time.
In this view, space is...
...filled with a network
of wormholes...
...something like the wormholes
in an apple.
Although by no means is this
point demonstrated...
...it is merely an exciting suggestion.
If it is true...
...then perhaps there exist
gravity tunnels...
...a kind of interstellar or
intergalactic subway...
...which would permit you
to get from...
...here to there in much less than
the usual time.
A kind of cosmic rapid transit system.
We cannot generate black holes...
...our technology is far
too feeble to...
...move such massive amounts
of matter around.
But perhaps someday, it will be
possible to voyage hundreds or...
...thousands of light-years to
a black hole like Cygnus X-1.
We would plunge down to emerge...
...in some unimaginably
exotic time and place.
Our common-sense notions of reality
severely challenged.
Perhaps the cosmos is infested
with wormholes...
...every one of them a
tunnel to somewhere.
Perhaps other civilizations, with
vastly more advanced technologies...
...are today riding the
gravity express.
It's even possible that a
black hole is a gate...
...to another, and
quite different, universe.
The lives and deaths of the stars...
...seem impossibly remote
from human experience...
...and yet we're related in the most
intimate way to their life cycles.
The very matter that makes us up...
...was generated long ago and far away
in red giant stars.
A blade of grass,
as Walt Whitman said...
"... is the journey work of the stars. "
The formation of the solar system...
...may have been triggered by a
nearby supernova explosion.
After the sun turned on...
...its ultraviolet light poured
into our atmosphere.
Its warmth generated lightning.
And these energy sources sparked
the origin of life.
Plants harvest sunlight...
...converting solar into
chemical energy.
We and the other animals are
parasites on the plants.
So we are, all of us, solar-powered.
The evolution of life is
driven by mutations.
They are caused partly by natural
radioactivity and cosmic rays.
But they are both generated in the
spectacular deaths of massive stars...
...thousands of light-years distant.
Think of the sun's heat on your
upturned face...
...on a cloudless summer's day.
From 150 million kilometers away...
...we recognize its power.
What would we feel on its seething,
self-luminous surface...
...or immersed in its heart
of nuclear fire?
And yet, the sun is an ordinary,
even a mediocre star.
Our ancestors worshiped the sun
and they were far from foolish.
It makes good sense to revere
the sun and the stars.
Because we are their children.
We have witnessed the life
cycles of the stars.
They are born, they mature
and then they die.
As time goes on, there are
more white dwarfs...
...more neutron stars,
more black holes.
The remains of the stars accumulate...
...as the eons pass.
But interstellar space also becomes
enriched in heavy elements...
...out of which form new generations
of stars and planets...
...life and intelligence.
The events in one star can influence
a world halfway across the galaxy...
...and a billion years in the future.
The vast interstellar clouds
of gas and dust...
...are stellar nurseries.
Here first begins the inexorable
gravitational collapse...
...which dominates the
lives of the stars.
Massive suns may evolve through the
red giant stage in only millions of years.
Dying young, never leaving the
cloud in which they were born.
Other suns, longer-lived, wander
out of the nursery.
Our sun is such a star...
...as are most
of the stars in the sky.
Most stars are members of double
or multiple star systems...
...and live to process their nuclear
fuel over billions of years.
The galaxy is 10 billion years old.
Old enough to have spawned...
...only a few generations
of ordinary stars.
The objects we encounter
in a voyage through the Milky Way...
...are stages in the life cycle
of the stars.
Some are bright and new...
...and others are as ancient as
the galaxy itself.
Surrounding the Milky Way
is a halo of matter...
...which includes
the globular clusters...
...each containing up to
a million elderly stars.
At the centers of globular clusters
and at the core of the galaxy...
...there may be massive black holes
ticking and purring...
...the subject of future exploration.
We on Earth marvel,
and rightly so...
...at the daily return
of our single sun.
But from a planet orbiting a star
in a distant globular cluster...
...a still more glorious dawn awaits.
Not a sunrise, but a galaxy-rise.
A morning filled with
400 billion suns...
...the rising of the Milky Way.
An enormous spiral form
with collapsing gas clouds...
...condensing planetary systems,
luminous supergiants...
...stable middle-aged stars...
...red giants, white dwarfs, planetary
nebulas, supernovas...
...neutron stars, pulsars,
black holes and...
...there is every reason to think,
other exotic objects...
...that we have not yet discovered.
From such a world, high above
the disc of the Milky Way...
...it would be clear as it is
beginning to be clear on our world...
...that we are made
by the atoms in the stars...
...that our matter
and our form are determined...
...by the cosmos
of which we are a part.
I only have a moment, but I wanted you
to see a picture of Betelgeuse...
...in the constellation Orion.
The first image of the surface
of another star.
But the most exciting recent
stellar discovery...
...has been of a nearby supernova...
...in a companion galaxy
to the Milky Way.
We are here seeing chemical elements
in the process of synthesis...
...and have had our first glimpse
of the supernova...
...through a brand-new field:
neutrino astronomy.
And we're now seeing, around
neighboring stars...
...discs of gas and dust just
like those needed to explain...
...the origin of the planets
in our solar system.
Worlds may be forming here.
It's like a snapshot of our
solar system's past.
And there are so many such
discs being found these days...
...that planets may be very common
among the stars of the Milky Way.
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