Cosmos: A Personal Voyage - Episode 8 (Carl Sagan)
-
0:53 - 0:59SAGAN: We are drifting in
a great ocean of space and time. -
0:59 - 1:02In that ocean, the events
that shape the future... -
1:02 - 1:07...are working themselves out.
-
1:07 - 1:10Each creature and every world,
to the remotest star... -
1:10 - 1:13...owe their existence to...
-
1:13 - 1:15...the great, coursing,
implacable forces of nature... -
1:15 - 1:21...but also, to minor happenstance.
-
1:21 - 1:25We are carried with our planet
around the sun. -
1:25 - 1:28The Earth has made more than
4 billion circuits of our star... -
1:28 - 1:32...since its origin.
-
1:32 - 1:36The sun itself travels about
the core of the Milky Way galaxy. -
1:36 - 1:39Our galaxy is moving
among the other galaxies. -
1:39 - 1:44We have always been space travelers.
-
1:44 - 1:50These fine sand grains are all,
more or less, uniform in size. -
1:50 - 1:54They're produced from bigger rocks
through ages of... -
1:54 - 1:58...jostling and rubbing,
abrasion and erosion. -
1:58 - 2:02Driven in part by
the distant moon and sun. -
2:02 - 2:06So the roots of the present
lie buried in the past. -
2:06 - 2:14We are also travelers in time.
-
2:14 - 2:15But trapped on Earth...
-
2:15 - 2:19...we've had little to say about
where we go in time and space... -
2:19 - 2:20...or how fast.
-
2:20 - 2:24But now we're thinking
about true journeys in time... -
2:24 - 2:30...and real voyages
to the distant stars. -
2:30 - 2:35A handful of sand contains
about 10,000 grains... -
2:35 - 2:37...more than all the stars
we can see... -
2:37 - 2:40...with the naked eye
on a clear night. -
2:40 - 2:42But the number of stars we can see...
-
2:42 - 2:46...is only the tiniest fraction
of the number of stars that are. -
2:46 - 2:50What we see at night
is the merest smattering... -
2:50 - 2:52...of the nearest stars...
-
2:52 - 2:56...with a few more distant bright
stars thrown in for good measure. -
2:56 - 3:00Meanwhile, the cosmos
is rich beyond measure. -
3:00 - 3:03The number of stars
in the universe... -
3:03 - 3:06...is larger than all the grains
of sand on all the beaches... -
3:06 - 3:12...of the planet Earth.
-
3:12 - 3:17Long ago, before we had figured out
that the stars are distant suns... -
3:17 - 3:20...they seemed to us
to make pictures in the sky. -
3:20 - 3:24Just follow the dots.
-
3:24 - 3:28The Big Dipper constellation
today in North America... -
3:28 - 3:30...has had many other incarnations.
-
3:30 - 3:32Every culture, ancient and modern...
-
3:32 - 3:36...has placed its totems
and concerns among the stars. -
3:36 - 3:44From a Chinese bureaucrat
to a German wagon. -
3:44 - 3:48But very ancient cultures would have
seen different constellations... -
3:48 - 3:52...because the stars move
with respect to one another. -
3:52 - 3:57We can give a computer the present
positions and motions of stars... -
3:57 - 4:03...and then run the patterns
back into time. -
4:03 - 4:07Every constellation is a single frame
in a cosmic movie... -
4:07 - 4:09...but because our lives
are so short... -
4:09 - 4:11...because star patterns
change slowly... -
4:11 - 4:14...we tend not to notice
it's a movie. -
4:14 - 4:19A million years ago,
there was no Big Dipper. -
4:19 - 4:22Our ancestors, looking up
and wondering about the stars... -
4:22 - 4:27...saw some other pattern
in the northern skies. -
4:27 - 4:31We can also run a constellation,
Leo the Lion, say, forward in time... -
4:31 - 4:37...and see what the patterns
in the stars will be in the future. -
4:37 - 4:39A million years from now,
Leo might be renamed... -
4:39 - 4:43...the constellation
of the Radio Telescope. -
4:43 - 4:46Although I suspect radio telescopes
then will be as obsolete... -
4:46 - 4:48...as stone spears are now.
-
4:48 - 5:01Or, here's the constellation
of Cetus the Whale. -
5:01 - 5:06A million years ago, it may have
been called something else. -
5:06 - 5:12Perhaps the Spear.
-
5:12 - 5:22Now, let's run fast-forward
through a billion nights. -
5:22 - 5:24Millions of years from now...
-
5:24 - 5:36...some other very different image
will be featured in this cosmic movie. -
5:36 - 5:40In Orion the Hunter,
things are changing... -
5:40 - 5:42...not only because
the stars are moving... -
5:42 - 5:45...but also because
the stars are evolving. -
5:45 - 5:49Many of Orion's stars are
hot, young and short-lived. -
5:49 - 5:52They're born, live and die within
a span of only a few million years. -
5:52 - 5:56If we run Orion forward in time...
-
5:56 - 5:59...we see the births
and explosive deaths... -
5:59 - 6:01...of dozens of stars...
-
6:01 - 6:07...flashing on and winking off
like fireflies in the night. -
6:07 - 6:11If we wait long enough,
we see the constellations change. -
6:11 - 6:15But if we go far enough,
we also see the star patterns alter. -
6:15 - 6:17Two-dimensional constellations...
-
6:17 - 6:21...are only the appearance of stars
strewn through three dimensions. -
6:21 - 6:27Some are dim and near,
others are bright but farther away. -
6:27 - 6:29Could a space traveler
actually see... -
6:29 - 6:32...the patterns of
the constellations change? -
6:32 - 6:38For that, you must travel roughly as
far as the constellation is from us. -
6:38 - 6:41Here, we're traveling
hundreds of light-years... -
6:41 - 6:49...circling all the way around
the stars of the Big Dipper. -
6:49 - 6:51Inhabitants of planets
around other stars... -
6:51 - 6:54...will see different constellations
than us... -
6:54 - 7:05...because their vantage points
are different. -
7:05 - 7:09Here we are
in the constellation Andromeda... -
7:09 - 7:14...or at least a model of it
next to the constellation Perseus. -
7:14 - 7:16Andromeda, in the Greek myth...
-
7:16 - 7:20...was the maiden
who was saved by Perseus... -
7:20 - 7:22...from a sea monster.
-
7:22 - 7:27This star just above me
is Beta Andromedae... -
7:27 - 7:30...the second brightest star
in the constellation... -
7:30 - 7:33...75 light-years from the Earth.
-
7:33 - 7:37The light by which we see this star...
-
7:37 - 7:41...has spent 75 years
traversing interstellar space... -
7:41 - 7:43...on its journey to the Earth.
-
7:43 - 7:47In the unlikely event
that Beta Andromedae... -
7:47 - 7:50...blew itself up
a week ago Tuesday... -
7:50 - 7:53...we will not know of it
for another 75 years... -
7:53 - 7:57...as this interesting information,
traveling at the speed of light... -
7:57 - 8:01...crosses the enormous
interstellar distances. -
8:01 - 8:04When the light we see
from this star set out... -
8:04 - 8:06...on its long
interstellar voyage... -
8:06 - 8:09...the young Albert Einstein...
-
8:09 - 8:12...working as a Swiss patent clerk...
-
8:12 - 8:16...had just published his epochal
special theory of relativity... -
8:16 - 8:19...here on Earth.
-
8:19 - 8:20We see...
-
8:20 - 8:24...that space and time
are intertwined. -
8:24 - 8:27We cannot look out into space...
-
8:27 - 8:31...without looking back into time.
-
8:31 - 8:34The speed of light is very fast...
-
8:34 - 8:38...but space is very empty...
-
8:38 - 8:41...and the stars are very far apart.
-
8:41 - 8:45The distances that we've been
talking about up to now... -
8:45 - 8:49...are very small
by the usual astronomical standards. -
8:49 - 8:51In fact, the distance
from the Earth... -
8:51 - 8:54...to the center
of the Milky Way galaxy... -
8:54 - 8:57...is 30,000 light-years.
-
8:57 - 9:03From our galaxy to the nearest
spiral galaxy like our own... -
9:03 - 9:05...called M31 ...
-
9:05 - 9:08...and which is also within,
that means behind... -
9:08 - 9:11...the constellation Andromeda...
-
9:11 - 9:16...is 2 million light-years.
-
9:16 - 9:19When the light we see today
from M31 ... -
9:19 - 9:22...left on its journey for Earth...
-
9:22 - 9:24...there were no human beings...
-
9:24 - 9:27...although our ancestors
were nicely evolving... -
9:27 - 9:31...and very rapidly,
to our present form. -
9:31 - 9:34There are much greater distances
in astronomy. -
9:34 - 9:38The distance from the Earth
to the most distant quasars... -
9:38 - 9:41...is 8 or 10 billion light-years.
-
9:41 - 9:46We see them as they were before
the Earth itself accumulated... -
9:46 - 9:50...before the Milky Way galaxy
was formed. -
9:50 - 9:54The fastest space vehicles ever
launched by the human species... -
9:54 - 9:55...are the Voyager spacecraft.
-
9:55 - 9:58They are traveling so fast...
-
9:58 - 10:02...that it's only
10,000 times slower... -
10:02 - 10:03...than the speed of light.
-
10:03 - 10:06The Voyager spacecraft
will take 40,000 years... -
10:06 - 10:08...to go the distance
to the nearest stars... -
10:08 - 10:12...and they're not even headed
towards the nearest stars. -
10:12 - 10:15But is there a method
by which we could travel... -
10:15 - 10:18...in a conveniently short time
to the stars? -
10:18 - 10:21Can we travel close
to the speed of light? -
10:21 - 10:24And what's magic
about the speed of light? -
10:24 - 10:29Can't we travel faster than that?
-
10:29 - 10:33It turns out that
there is something very strange... -
10:33 - 10:35...about the speed of light.
-
10:35 - 10:37Something that provides the key...
-
10:37 - 10:42...to our understanding
of time and space. -
10:42 - 10:44The story of its discovery...
-
10:44 - 10:49...takes us to Tuscany
in northern Italy. -
10:49 - 10:52There's something timeless
about this place. -
10:52 - 11:08A century ago, it probably
looked very much the same. -
11:08 - 11:13If you had traveled these roads
in the summer of 1895... -
11:13 - 11:17...you might have come upon a
16-year-old German high-school dropout. -
11:17 - 11:20His teacher told him that
he'd never amount to anything... -
11:20 - 11:24...that his attitude destroyed
classroom discipline... -
11:24 - 11:26...that he should drop out.
-
11:26 - 11:28So he left and came here...
-
11:28 - 11:31...where he enjoyed
wandering these roads... -
11:31 - 11:35...and giving his mind
free rein to explore. -
11:35 - 11:38One day, he began
to think about light... -
11:38 - 11:40...about how fast it travels.
-
11:40 - 11:43We always measure
the speed of a moving object... -
11:43 - 11:46...relative to something else.
-
11:46 - 11:50I'm moving at about 10 kilometers
an hour relative to the ground. -
11:50 - 11:52But the ground isn't at rest.
-
11:52 - 11:56The Earth is turning at more
than 1600 kilometers an hour. -
11:56 - 11:58The Earth itself is
in orbit around the sun. -
11:58 - 12:02The sun is moving among
the drifting stars, and so on. -
12:02 - 12:06It was hard for the young man
to imagine some absolute standard... -
12:06 - 12:19...to measure all these
relative motions against. -
12:19 - 12:23He knew that sound waves are
a vibration of the air... -
12:23 - 12:26...and their speed is measured
relative to the air itself. -
12:26 - 12:30But sunlight travels across
the vacuum of empty space. -
12:30 - 12:32"Do light waves move
relative to something else? -
12:32 - 12:39And if so," he wondered,
"relative to what?" -
12:39 - 12:44That teenage dropout's name...
-
12:44 - 12:45...was Albert Einstein.
-
12:45 - 12:54And his ruminations changed the world.
-
12:54 - 12:59He had been fascinated
by Bernstein's 1869... -
12:59 - 13:03...People's Book of Natural Science.
-
13:03 - 13:07Here, on its very first page...
-
13:07 - 13:12...it describes the astonishing speed
of electricity through wires... -
13:12 - 13:14...and light through space.
-
13:14 - 13:19Einstein wondered, perhaps for
the first time, in northern Italy... -
13:19 - 13:23...what the world would look like if
you could travel on a wave of light. -
13:23 - 13:26To travel at the speed of light.
-
13:26 - 13:31What an engaging and magical thought
for a teenage boy on the road... -
13:31 - 13:46...where the countryside is dappled
and rippling in sunlight. -
13:46 - 13:50You couldn't tell you were on a light
wave if you were traveling with it. -
13:50 - 13:53If you started on a wave crest...
-
13:53 - 13:58...you would stay on the crest and
lose all notion of it being a wave. -
13:58 - 14:33Something funny happens
at the speed of light. -
14:33 - 14:37The more Einstein thought about it,
the more troubling it became. -
14:37 - 14:40Paradoxes seemed to pop up all over...
-
14:40 - 14:42...if you could travel
at the speed of light. -
14:42 - 14:46Certain ideas had been
accepted as true... -
14:46 - 14:51...without sufficiently
careful thought. -
14:51 - 14:56One of those ideas had to do
with the light from a moving object. -
14:56 - 15:00The images by which we see the world
are made of light... -
15:00 - 15:02...and are carried
at the speed of light... -
15:02 - 15:06...300,000 kilometers a second.
-
15:06 - 15:10You might think that the image of me
should be moving out ahead of me... -
15:10 - 15:13...at the speed of light
plus the speed of the bicycle. -
15:13 - 15:16If I'm moving towards you
faster than a horse-and-cart... -
15:16 - 15:20...then my image should be
approaching you that much faster. -
15:20 - 15:25My image ought to arrive earlier.
-
15:25 - 15:28But in reality
you don't see any time delay. -
15:28 - 15:32In a near collision, for example,
you see everything happen at once. -
15:32 - 15:36Horse, cart, swerve, bicycle.
All simultaneous. -
15:36 - 15:40But how would it look if
it were proper to add the velocities? -
15:40 - 15:44Since I'm heading toward you, you'd
add my speed to the speed of light. -
15:44 - 15:50So my image ought to arrive before
the image of the horse-and-cart. -
15:50 - 15:52I'd be cycling towards you
quite normally. -
15:52 - 15:56To me, a collision
would seem imminent. -
15:56 - 15:59But you'd see me swerve
for no apparent reason... -
15:59 - 16:03...and have a collision with nothing.
-
16:03 - 16:06Now, the horse-and-cart
aren't headed towards you. -
16:06 - 16:10Their image would arrive only
at the speed of light. -
16:10 - 16:13Could it seem to me that
I just missed colliding... -
16:13 - 16:16...while to you it wasn't even close?
-
16:16 - 16:18In precise laboratory experiments...
-
16:18 - 16:22...scientists have never observed
any such thing. -
16:22 - 16:25If the world is to be understood...
-
16:25 - 16:30...if we are to avoid logical paradoxes
when traveling at high speeds... -
16:30 - 16:33...then there are rules
which must be obeyed. -
16:33 - 16:38Einstein called these rules
the special theory of relativity. -
16:38 - 16:40Light from a moving object
travels at the same speed... -
16:40 - 16:44...no matter whether the object
is at rest or in motion. -
16:44 - 16:49"Thou shalt not add my speed
to the speed of light." -
16:49 - 16:54Also, no material object can travel
at or beyond the speed of light. -
16:54 - 16:58Nothing in physics prevents you from
traveling close to the speed of light. -
16:58 - 17:0299.9 percent the speed of light
is just fine. -
17:02 - 17:05But no matter how hard you try...
-
17:05 - 17:08...you can never gain
that last decimal point. -
17:08 - 17:10For the world
to be logically consistent... -
17:10 - 17:14...there must be a cosmic speed limit.
-
17:14 - 17:17The crack of a whip is,
due to its tip... -
17:17 - 17:22...moving faster
than the speed of sound. -
17:22 - 17:23It makes a shock wave...
-
17:23 - 17:27...a small sonic boom
in the Italian countryside. -
17:27 - 17:29A thunderclap has a similar origin.
-
17:29 - 17:35So does the sound of
a supersonic airplane. -
17:35 - 17:40So why is the speed of light a barrier
any more than the speed of sound? -
17:40 - 17:42The answer is not just that...
-
17:42 - 17:45...light travels a million times
faster than sound. -
17:45 - 17:49It's not merely an engineering problem
like the supersonic airplane. -
17:49 - 17:53Instead, the light barrier is
a fundamental law of nature... -
17:53 - 17:55...as basic as gravity.
-
17:55 - 17:59Einstein found his absolute framework
for the world: -
17:59 - 18:04This sturdy pillar among all
the relative motions of the cosmos. -
18:04 - 18:08Light travels just as fast,
no matter how its source is moving. -
18:08 - 18:12The speed of light is constant,
relative to everything else. -
18:12 - 18:18Nothing can ever catch up with light.
-
18:18 - 18:22Einstein's prohibition against
traveling faster than light... -
18:22 - 18:25...seems to clash with
our common sense notions. -
18:25 - 18:28But why should we expect
our common sense notions... -
18:28 - 18:31...to have any reliability
in a matter of this sort? -
18:31 - 18:35Why should our experience
at 10 kilometers an hour... -
18:35 - 18:38...constrain the laws of nature...
-
18:38 - 18:43...at 300,000 kilometers a second?
-
18:43 - 18:46Relativity sets limits...
-
18:46 - 18:50...on what humans ultimately can do.
-
18:50 - 18:52The universe is not required...
-
18:52 - 19:00...to be in perfect harmony
with human ambition. -
19:00 - 19:03Imagine a place
where the speed of light... -
19:03 - 19:07...isn't its true value
of 300,000 kilometers a second... -
19:07 - 19:10...but something a lot less.
-
19:10 - 19:13Let's say, 40 kilometers an hour...
-
19:13 - 19:16...and strictly enforced.
-
19:16 - 19:20Just as in the real world we can
never reach the speed of light... -
19:20 - 19:22...the commandment here is still...
-
19:22 - 19:26..."Thou shalt not travel
faster than light." -
19:26 - 19:31We can do thought experiments on
what happens near the speed of light... -
19:31 - 19:38...here 40 kilometers per hour,
the speed of a motor scooter. -
19:38 - 19:43You can't break the laws of nature.
There are no penalties for doing so. -
19:43 - 19:45The real world and this one...
-
19:45 - 19:49...are merely so arranged
that transgressions can't happen. -
19:49 - 19:56The job of physics is to find out
what those laws are. -
19:56 - 19:59Before Einstein,
physicists thought that... -
19:59 - 20:01...there were privileged frames
of reference... -
20:01 - 20:04...some special places and times...
-
20:04 - 20:07...against which everything else
had to be measured. -
20:07 - 20:10Einstein encountered
a similar notion in human affairs. -
20:10 - 20:13The idea that the customs
of a particular nation... -
20:13 - 20:17...his native Germany
or Italy or anywhere... -
20:17 - 20:22...are the standard which all
other societies must be measured. -
20:22 - 20:25But Einstein rejected the strident
nationalism of his time. -
20:25 - 20:29He believed every culture
had its own validity. -
20:29 - 20:31Also in physics,
he understood that... -
20:31 - 20:33...there are no privileged
frames of reference. -
20:33 - 20:37Every observer,
in any place, time or motion... -
20:37 - 20:40...must deduce
the same laws of nature. -
20:40 - 20:43(SPEAKING IN ITALIAN)
-
20:43 - 20:47A speed is simply how much space
you cover in a given time... -
20:47 - 20:53...as any kid on
a motor scooter knows. -
20:53 - 20:55Since near the velocity of light...
-
20:55 - 20:58...we cannot simply add speeds...
-
20:58 - 21:02...the familiar notions of
absolute space and absolute time... -
21:02 - 21:05...independent of your
relative motion, must give way. -
21:05 - 21:08That's why, as Einstein showed...
-
21:08 - 21:12...funny things have to happen
close to the speed of light. -
21:12 - 21:16There, our conventional perspectives
of space and time... -
21:16 - 21:21...strangely change.
-
21:21 - 21:25Your nose is just a little closer
to me than your ears. -
21:25 - 21:28Light reflected off your nose
reaches me... -
21:28 - 21:29...an instant in time
before your ears. -
21:29 - 21:33But suppose I had a magic camera...
-
21:33 - 21:36...so that I could see
your nose and your ears... -
21:36 - 21:39...at precisely the same instant?
-
21:39 - 21:40(SCOOTER STARTS UP)
-
21:40 - 21:42(SCOOTER HONKS)
-
21:42 - 21:48With such a camera you could take
some pretty interesting pictures. -
21:48 - 21:52Paolo says goodbye to
his little brother, Vincenzo... -
21:52 - 21:55-Ciao, Vincenzo.
-Ciao, Paolo. -
21:55 - 21:56...and rides off.
-
21:56 - 21:59He's now going more than
half the speed of light. -
21:59 - 22:02He is almost catching up
with his own light waves. -
22:02 - 22:05This compresses the light waves
in front of him... -
22:05 - 22:06...and his image becomes blue.
-
22:06 - 22:11The shorter wavelength is
what makes blue light waves blue. -
22:11 - 22:15Also Paolo becomes skinny
in the direction of motion. -
22:15 - 22:17This isn't just some optical illusion.
-
22:17 - 22:21It really happens when you travel
near the speed of light. -
22:21 - 22:26As he roars away, he leaves his own
light waves stretched out behind him. -
22:26 - 22:27Long light waves are red.
-
22:27 - 22:32We say that his receding image
is red-shifted. -
22:32 - 22:38Now Paolo leaves for
a short tour of the countryside. -
22:38 - 22:43He experiences something
even stranger. -
22:43 - 22:46Everything he can see is squeezed...
-
22:46 - 22:49...into a moving window
just ahead of him... -
22:49 - 22:52...blue-shifted at the center,
red-shifted at the edges. -
22:52 - 22:56To a passerby, Paolo appears
blue-shifted when approaching... -
22:56 - 22:58...red-shifted when receding.
-
22:58 - 23:01But to him, the entire world
is both coming and going... -
23:01 - 23:03...at nearly the speed of light.
-
23:03 - 23:06Roadside houses and trees
that has already gone past... -
23:06 - 23:10...still appear to him at the edge
of his forward field of view... -
23:10 - 23:14...but distorted and red-shifted.
-
23:14 - 23:20When he slows down,
everything again looks normal. -
23:20 - 23:22Only very close
to the speed of light... -
23:22 - 23:27...does the visible world
get squeezed into a kind of tunnel. -
23:27 - 23:30You'd see these distortions if you
traveled near the speed of light. -
23:30 - 23:33Someday, perhaps,
interstellar navigators... -
23:33 - 23:36...will take their bearings
on stars behind them... -
23:36 - 23:43...whose images have all crowded
together on the forward view screen. -
23:43 - 23:46The most bizarre aspect of traveling
near the speed of light... -
23:46 - 23:50...is that time slows down.
-
23:50 - 23:52All clocks,
mechanical and biological... -
23:52 - 23:55...tick more slowly
near the speed of light. -
23:55 - 23:59But stationary clocks tick
at their usual rate. -
23:59 - 24:01If we travel close to light speed...
-
24:01 - 24:09...we age more slowly
than those we left behind. -
24:09 - 24:13Paolo's watch and his internal
sense of time show... -
24:13 - 24:16...that he has been gone from
his friends for only a few minutes. -
24:16 - 24:21But from their point of view,
he has been away for many decades. -
24:21 - 24:26His friends have grown up,
moved on and died. -
24:26 - 24:28And his younger brother has been...
-
24:28 - 24:33...patiently waiting
for him all this time. -
24:33 - 24:38The two brothers experience
the paradox of time dilation. -
24:38 - 24:43They've encountered
Einstein's special relativity. -
24:43 - 24:58Vincenzo.
-
24:58 - 25:00This was just a thought experiment.
-
25:00 - 25:03But atomic particles traveling
near the speed of light... -
25:03 - 25:07...do decay more slowly
than stationary particles. -
25:07 - 25:11As strange and counterintuitive
as it seems... -
25:11 - 25:16...time dilation is a law of nature.
-
25:16 - 25:19Traveling close
to the speed of light... -
25:19 - 25:23...is a kind of elixir of life.
-
25:23 - 25:26Because time slows down
close to the speed of light... -
25:26 - 25:29...special relativity provides us...
-
25:29 - 25:33...with a means of going to the stars.
-
25:33 - 25:36This region of northern Italy
is not only the caldron... -
25:36 - 25:40...of some of the thinking
of the young Albert Einstein... -
25:40 - 25:44...it is also the home
of another great genius... -
25:44 - 25:46...who lived 400 years earlier.
-
25:46 - 25:50Leonardo da Vinci.
-
25:50 - 25:54Leonardo delighted
in climbing these hills... -
25:54 - 25:58...and viewing the ground
from a great height... -
25:58 - 26:00...as if he were soaring like a bird.
-
26:00 - 26:03He drew the first aerial views...
-
26:03 - 26:07...of landscapes, villages,
fortifications. -
26:07 - 26:11I've been talking about Einstein
in and around this town of Vinci... -
26:11 - 26:14...in which Leonardo grew up.
-
26:14 - 26:17Einstein greatly respected Leonardo...
-
26:17 - 26:20...and their spirits, in some sense...
-
26:20 - 26:48...inhabit this countryside still.
-
26:48 - 26:51Among Leonardo's
many accomplishments... -
26:51 - 26:55...in painting, sculpture,
architecture, natural history... -
26:55 - 27:00...anatomy, geology,
civil and military engineering... -
27:00 - 27:02...he had a great passion.
-
27:02 - 27:06He wished to construct a machine...
-
27:06 - 27:08...which would fly.
-
27:08 - 27:12He made sketches of such machines,
built miniature models... -
27:12 - 27:18...constructed great,
full-scale prototypes. -
27:18 - 27:23And not a one of them ever worked.
-
27:23 - 27:27There were no machines of adequate
capacity available in his time. -
27:27 - 27:32The technology was just not ready.
-
27:32 - 27:35The designs, however, were brilliant.
-
27:35 - 27:38For example, this bird-like machine...
-
27:38 - 27:44...here in the Leonardo Museum
in the town of Vinci. -
27:44 - 27:49Leonardo's great designs encouraged
engineers in later epochs... -
27:49 - 27:53...although Leonardo himself
was very depressed at these failures. -
27:53 - 27:55But it's not his fault...
-
27:55 - 27:59...he was trapped in the 15th century.
-
27:59 - 28:03A somewhat similar case
occurred in 1939... -
28:03 - 28:08...when a group of engineers called
the British Interplanetary Society... -
28:08 - 28:10...decided to design a ship...
-
28:10 - 28:13...which would carry people
to the moon. -
28:13 - 28:16Now, it was by no means
the same design... -
28:16 - 28:21...as the Apollo ship which actually
took people to the moon years later. -
28:21 - 28:23But that design suggested that...
-
28:23 - 28:25...a mission to the moon
might one day... -
28:25 - 28:28...be a practical
engineering possibility. -
28:28 - 28:30Today...
-
28:30 - 28:35...we have preliminary
designs of ships... -
28:35 - 28:38...which will take people
to the stars. -
28:38 - 28:43They are constructed in Earth orbit
and from there... -
28:43 - 28:48...they venture on their great
interstellar journeys. -
28:48 - 28:50One of them...
-
28:50 - 28:54...is called Project Orion.
-
28:54 - 28:56It utilizes nuclear weapons...
-
28:56 - 29:00...hydrogen bombs
against an inertial plate. -
29:00 - 29:05Each explosion providing
a kind of "putt-putt"... -
29:05 - 29:09...a vast nuclear motorboat in space.
-
29:09 - 29:13Orion seems entirely practical...
-
29:13 - 29:15...and was under development
in the U.S... -
29:15 - 29:19...until the signing
of the international treaty... -
29:19 - 29:23...forbidding nuclear weapons
explosions in space. -
29:23 - 29:28I think, the Orion starship
is the best use of nuclear weapons... -
29:28 - 29:41...provided the ships don't depart
from very near the Earth. -
29:41 - 29:44Project Daedalus is
a recent design... -
29:44 - 29:47...of the British
Interplanetary Society. -
29:47 - 29:51It assumes the existence
of a nuclear fusion reactor... -
29:51 - 29:53...something much safer
and more efficient... -
29:53 - 30:01...than the existing nuclear
fission power plants. -
30:01 - 30:03We do not yet have fusion reactors.
-
30:03 - 30:12One day, quite soon, we may.
-
30:12 - 30:16Orion and Daedalus might go...
-
30:16 - 30:19...10 percent the speed of light.
-
30:19 - 30:23So a trip to Alpha Centauri,
4 1/2 light-years away... -
30:23 - 30:27...would take 45 years,
less than a human lifetime. -
30:27 - 30:31Such ships could not travel
close enough to the speed of light... -
30:31 - 30:34...for the time-slowing effects
of special relativity... -
30:34 - 30:36...to become important.
-
30:36 - 30:39It does not seem likely
that such ships... -
30:39 - 30:42...would be built before
the middle of the 21 st century... -
30:42 - 30:46...although we could build
an Orion starship now. -
30:46 - 30:51For voyages beyond the nearest stars,
something must be added. -
30:51 - 30:54Perhaps they could be used
as multigeneration ships... -
30:54 - 30:57...so those arriving would be
the remote descendants... -
30:57 - 31:02...of those who had originally
set out centuries before. -
31:02 - 31:06Or perhaps some safe means
of human hibernation might be found... -
31:06 - 31:10...so that space travelers might be
frozen and then thawed out... -
31:10 - 31:14...when they arrive at
the destination centuries later. -
31:14 - 31:19But fast interstellar space flight
approaching the speed of light... -
31:19 - 31:21...is much more difficult.
-
31:21 - 31:24That's an objective
not for a hundred years... -
31:24 - 31:27...but for a thousand
or for 10 thousand... -
31:27 - 31:32...but it also is possible.
-
31:32 - 31:35A kind of interstellar ramjet
has been proposed... -
31:35 - 31:38...which scoops up
the hydrogen atoms... -
31:38 - 31:40...which float between the stars...
-
31:40 - 31:45...accelerates them into an engine
and spits them out the back. -
31:45 - 31:48But in deep space,
there is one atom... -
31:48 - 31:52...for every 10 cubic centimeters
of space. -
31:52 - 31:54For the ramjet to work...
-
31:54 - 31:57...it has to have a frontal scoop...
-
31:57 - 32:00...hundreds of kilometers across.
-
32:00 - 32:04Reaching relativistic velocities,
the hydrogen atoms will be moving... -
32:04 - 32:07...with respect
to the interstellar spaceship... -
32:07 - 32:09...at close to the speed of light.
-
32:09 - 32:11If precautions aren't taken...
-
32:11 - 32:16...the passengers will be fried
by these induced cosmic rays. -
32:16 - 32:18There's a proposed solution:
-
32:18 - 32:21A laser is used to strip
electrons off the atoms... -
32:21 - 32:25...and electrically charge them
while they're some distance away. -
32:25 - 32:28And an extremely strong
magnetic field... -
32:28 - 32:32...is used to deflect
the charged atoms into the scoop... -
32:32 - 32:33...and away from the spacecraft.
-
32:33 - 32:35This is engineering...
-
32:35 - 32:39...on a scale so far
unprecedented on the Earth. -
32:39 - 32:53We are talking of engines
the size of small worlds. -
32:53 - 32:58Suppose that the spacecraft is
designed to accelerate at 1 g... -
32:58 - 33:01...so we'd be comfortable aboard it.
-
33:01 - 33:03We'd go closer and closer
to the speed of light... -
33:03 - 33:06...until the midpoint of the journey.
-
33:06 - 33:08Then the spacecraft is
turned around... -
33:08 - 33:13...and we decelerate at 1 g
to the destination. -
33:13 - 33:17For most of the trip, the velocity
would be close to the speed of light... -
33:17 - 33:20...and time would
slow down enormously. -
33:20 - 33:23By how much?
-
33:23 - 33:27Barnard's Star could be reached
by such a ship... -
33:27 - 33:30...in eight years, ship time.
-
33:30 - 33:34The center of the Milky Way galaxy
in 21 years. -
33:34 - 33:38The Andromeda galaxy in 28 years.
-
33:38 - 33:41Of course, the people
left behind on the Earth... -
33:41 - 33:43...would see things
somewhat differently. -
33:43 - 33:45Instead of 21 years to the galaxy...
-
33:45 - 33:49...they would measure it
as 30,000 years. -
33:49 - 33:50When we got back...
-
33:50 - 33:55...very few of our friends
would be around to greet us. -
33:55 - 33:57In principle, such a journey...
-
33:57 - 34:01...mounting the decimal points closer
and closer to the speed of light... -
34:01 - 34:05...would even permit us to
circumnavigate the known universe... -
34:05 - 34:09...in 56 years, ship time.
-
34:09 - 34:14We would return tens
of billions of years... -
34:14 - 34:16...in the far future...
-
34:16 - 34:19...with the Earth a charred cinder...
-
34:19 - 34:22...and the sun dead.
-
34:22 - 34:26Relativistic space flight makes
the universe accessible... -
34:26 - 34:29...to advanced civilizations...
-
34:29 - 34:31...but only to those
who go on the journey... -
34:31 - 34:34...not to those who stay home.
-
34:34 - 34:39These designs are probably further...
-
34:39 - 34:44...from the actual interstellar
spacecraft of the future... -
34:44 - 34:47...than Leonardo's models are...
-
34:47 - 34:51...from the supersonic transports
of the present. -
34:51 - 34:53But if we do not destroy ourselves...
-
34:53 - 34:58...I believe that we will,
one day, venture to the stars. -
34:58 - 35:01When our solar system
is all explored... -
35:01 - 35:37...the planets of other stars
will beckon. -
35:37 - 35:43Space travel and time travel
are connected. -
35:43 - 35:45To travel fast into space...
-
35:45 - 35:51...is to travel fast into the future.
-
35:51 - 35:56We travel into the future,
although slowly, all the time. -
35:56 - 36:00But what about the past?
Could we journey into yesterday? -
36:00 - 36:04Many physicists think this is
fundamentally impossible... -
36:04 - 36:06...that we could
not build a device... -
36:06 - 36:09...which would carry us
backwards into time. -
36:09 - 36:13Some say that even if we were
to build such a device... -
36:13 - 36:14...it wouldn't do much good.
-
36:14 - 36:17We couldn't significantly
affect the past. -
36:17 - 36:20For example, suppose you
traveled into the past... -
36:20 - 36:23...and somehow or other prevented...
-
36:23 - 36:26...your own parents from meeting.
-
36:26 - 36:30Why, then you would probably
never have been born... -
36:30 - 36:32...which is something
of a contradiction, isn't it... -
36:32 - 36:35...since you are clearly there.
-
36:35 - 36:36Other people think that...
-
36:36 - 36:40...the two alternative histories
have equal validity... -
36:40 - 36:43...that they're parallel threads,
skeins of time... -
36:43 - 36:50...that they could exist side by side.
-
36:50 - 36:52The history in which
you were never born... -
36:52 - 36:56...and the history that
you know all about. -
36:56 - 36:59Perhaps time itself has
many potential dimensions... -
36:59 - 37:03...despite the fact that
we are condemned to experience... -
37:03 - 37:05...only one of those dimensions.
-
37:05 - 37:09Now, suppose you could go back
into the past... -
37:09 - 37:13...and really change it by,
let's say something like... -
37:13 - 37:17...persuading Queen Isabella not
to bankroll Christopher Columbus. -
37:17 - 37:20Then you would have set into motion...
-
37:20 - 37:23...a different sequence
of historical events... -
37:23 - 37:26...which those people
you left behind you in our time... -
37:26 - 37:29...would never get to know about.
-
37:29 - 37:31If that kind of time travel
were possible... -
37:31 - 37:34...then every imaginable sequence...
-
37:34 - 37:37...of alternative history...
-
37:37 - 37:40...might in some sense really exist.
-
37:40 - 37:43Would it be possible
for a time traveler... -
37:43 - 37:46...to change the course of history
in a major way? -
37:46 - 37:52Well, let's think about that.
-
37:52 - 37:54History consists for the most part...
-
37:54 - 37:59...of a complex multitude
of deeply interwoven threads... -
37:59 - 38:01...biological, economic
and social forces... -
38:01 - 38:05...that are not so easily unraveled.
-
38:05 - 38:10The ancient Greeks imagined the course
of human events to be a tapestry... -
38:10 - 38:16...created by three goddesses:
the Fates. -
38:16 - 38:20Random minor events generally
have no long-range consequences. -
38:20 - 38:23But some which occur
at critical junctures... -
38:23 - 38:26...may alter the weave of history.
-
38:26 - 38:29There may be cases where
profound changes can be made... -
38:29 - 38:32...by relatively trivial adjustments.
-
38:32 - 38:37The further in the past such an event
is, the more powerful its influence. -
38:37 - 38:41What if our time traveler had
persuaded Queen Isabella that... -
38:41 - 38:43...Columbus' geography was wrong?
-
38:43 - 38:47Almost certainly, some other European
would have sailed to the New World. -
38:47 - 38:49There were many inducements:
-
38:49 - 38:53The lure of the spice trade,
improvements in navigation... -
38:53 - 38:55...competition among
rival European powers. -
38:55 - 38:59The discovery of America
around 1500 was inevitable. -
38:59 - 39:03Of course, there wouldn't be any
postage stamps showing Columbus... -
39:03 - 39:06...and the Republic of Colombia
would have another name. -
39:06 - 39:14But the big picture would have
turned out more or less the same. -
39:14 - 39:18In order to affect
the future profoundly... -
39:18 - 39:21...a time traveler
has to pick and choose. -
39:21 - 39:25He'd probably have to intervene
in a number of events... -
39:25 - 39:27...which are
very carefully selected... -
39:27 - 39:33...so he could change
the weave of history. -
39:33 - 39:35It's a lovely fantasy...
-
39:35 - 39:42...to explore those other worlds
that never were. -
39:42 - 39:46If you had H.G. Wells' time machine...
-
39:46 - 39:49...maybe you could understand
how history really works. -
39:49 - 39:52If an apparently pivotal person
had never lived... -
39:52 - 39:56...Paul the Apostle or Peter the Great
or Pythagoras... -
39:56 - 40:00...how different would
the world really be? -
40:00 - 40:02What if the scientific tradition...
-
40:02 - 40:05...of the ancient Ionian Greeks...
-
40:05 - 40:08...had prospered and flourished?
-
40:08 - 40:11It would have required
many social factors at the time... -
40:11 - 40:13...to have been different...
-
40:13 - 40:16...including the common feeling...
-
40:16 - 40:18...that slavery was right and natural.
-
40:18 - 40:22But what if that light
that had dawned... -
40:22 - 40:26...on the eastern Mediterranean
some 2500 years ago... -
40:26 - 40:28...had not flickered out?
-
40:28 - 40:32What if scientific method
and experiment... -
40:32 - 40:34...had been vigorously pursued...
-
40:34 - 40:36...2000 years before
the industrial revolution... -
40:36 - 40:38...our industrial revolution?
-
40:38 - 40:43What if the power of this new mode
of thought, the scientific method... -
40:43 - 40:45...had been generally appreciated?
-
40:45 - 40:49I think we might have saved
10 or 20 centuries. -
40:49 - 40:52Perhaps the contributions
that Leonardo made... -
40:52 - 40:55...would have been made
1000 years earlier... -
40:55 - 40:59...and the contributions
of Einstein 500 years ago. -
40:59 - 41:01Not that it would have
been those people... -
41:01 - 41:04...who would've made
those contributions... -
41:04 - 41:08...because they lived only
in our timeline. -
41:08 - 41:11If the Ionians had won...
-
41:11 - 41:15...we might by now, I think,
be going to the stars. -
41:15 - 41:20We might at this moment have
the first survey ships... -
41:20 - 41:25...returning with astonishing results
from Alpha Centauri... -
41:25 - 41:30...and Barnard's Star,
Sirius and Tau Ceti. -
41:30 - 41:33There would now be great fleets...
-
41:33 - 41:35...of interstellar transports...
-
41:35 - 41:38...being constructed in Earth orbit...
-
41:38 - 41:41...small, unmanned survey ships...
-
41:41 - 41:44...liners for immigrants, perhaps...
-
41:44 - 41:47...great trading ships...
-
41:47 - 41:50...to ply the spaces
between the stars. -
41:50 - 41:54On all these ships
there would be symbols... -
41:54 - 41:57...and inscriptions on the sides.
-
41:57 - 41:59The inscriptions,
if we looked closely... -
41:59 - 42:02...would be written in Greek.
-
42:02 - 42:04The symbol...
-
42:04 - 42:08...perhaps, would be the dodecahedron.
-
42:08 - 42:12And the inscription on the sides
of the ships to the stars... -
42:12 - 42:14...something like:
-
42:14 - 42:22"Starship Theodorus
of the Planet Earth." -
42:22 - 42:28If you were a really
ambitious time traveler... -
42:28 - 42:31...you might not dally
with human history... -
42:31 - 42:34...or even pause to examine
the evolution on Earth. -
42:34 - 42:36Instead, you would journey back...
-
42:36 - 42:38...to witness the origin
of our solar system... -
42:38 - 42:44...from the gas and dust
between the stars. -
42:44 - 42:45Five billion years ago...
-
42:45 - 42:49...an interstellar cloud was
collapsing to form our solar system. -
42:49 - 42:53Most clumps of matter
gravitated towards the center... -
42:53 - 42:55...and were destined
to form the sun. -
42:55 - 43:00Smaller peripheral clumps
would become the planets. -
43:00 - 43:04Long ago, there was a kind of
natural selection among the worlds. -
43:04 - 43:09Those on highly elliptical orbits
tended to collide and be destroyed... -
43:09 - 43:13...but planets in circular orbits
tended to survive. -
43:13 - 43:15But if events had been
a little different... -
43:15 - 43:17...the Earth would never have formed...
-
43:17 - 43:21...and another planet at another
distance from the sun would be around. -
43:21 - 43:24We owe the existence of our world...
-
43:24 - 43:30...to random collisions
in a long-vanished cloud. -
43:30 - 43:34Soon, the central mass
became very hot. -
43:34 - 43:38Thermonuclear reactions were initiated
and the sun turned on... -
43:38 - 43:43...flooding the solar system
with light. -
43:43 - 43:44But the growing smaller lumps...
-
43:44 - 43:47...would never achieve
such high temperatures... -
43:47 - 43:50...and would never generate
thermonuclear reactions. -
43:50 - 43:54They would become
the Earth and the other planets... -
43:54 - 44:03...heated not from within,
but mainly by the distant sun. -
44:03 - 44:05The accretion continued until...
-
44:05 - 44:08...almost all the gas and dust
and small worldlets... -
44:08 - 44:15...were swept up
by the surviving planets. -
44:15 - 44:17Our time traveler would witness...
-
44:17 - 44:26...the collisions
that made the worlds. -
44:26 - 44:28Except for the comets and asteroids...
-
44:28 - 44:31...the chaos of the early
solar system was reduced... -
44:31 - 44:34...to a remarkable simplicity:
-
44:34 - 44:38Nine or so principal planets
in almost circular orbits... -
44:38 - 44:44...and a few dozen moons.
-
44:44 - 44:49Now, let's take a different look.
-
44:49 - 44:51If we view the solar system edge on...
-
44:51 - 44:54...and move the sun
off-screen to the left... -
44:54 - 44:57...we see that
the small terrestrial planets... -
44:57 - 45:01...the ones about as massive as Earth,
tend to be close to the sun. -
45:01 - 45:05The big Jupiter-like planets tend
to be much further from the sun. -
45:05 - 45:09But is that the way it has to be?
-
45:09 - 45:11Computer studies suggest...
-
45:11 - 45:14...that there may be many
similar systems about stars... -
45:14 - 45:22...with the terrestrials in close
and the Jovian planets further away. -
45:22 - 45:26But some systems might have Jovians
and terrestrials mixed together. -
45:26 - 45:31There may be great worlds
like Jupiter looming in other skies. -
45:31 - 45:36Rarely, the Jovian planets
may form close to the star... -
45:36 - 45:42...the terrestrials trailing away
towards interstellar space. -
45:42 - 45:44Our familiar arrangement of planets...
-
45:44 - 45:47...is only one,
perhaps typical, case... -
45:47 - 45:51...in the vast expanse of systems.
-
45:51 - 45:56Often, one fledgling planet
accumulates so much gas and dust... -
45:56 - 45:58...that thermonuclear reactions
do occur. -
45:58 - 46:01It becomes a second sun.
-
46:01 - 46:08A binary star system has formed.
-
46:08 - 46:12From most of these worlds,
the vistas will be dazzling. -
46:12 - 46:15Not one of them will be
identical to the Earth. -
46:15 - 46:20A few will be hospitable.
Many will appear hostile. -
46:20 - 46:23Where there are two suns in the sky...
-
46:23 - 46:30...every object will cast two shadows.
-
46:30 - 46:33What wonders are waiting for us...
-
46:33 - 46:36...on the planets of the nearby stars?
-
46:36 - 46:38Are there radically
different kinds of worlds... -
46:38 - 46:45...unimaginably exotic forms of life?
-
46:45 - 46:48Perhaps in another century or two...
-
46:48 - 46:51...when our solar system
is all explored... -
46:51 - 46:54...we will also have put
our own planet in order. -
46:54 - 46:58Then we will set sail for the stars...
-
46:58 - 47:04...and the beckoning worlds
around them. -
47:04 - 47:07In that day, our machines
and our descendants... -
47:07 - 47:11...approaching the speed of light,
will skim the light-years... -
47:11 - 47:16...leaping ahead through time,
seeking new worlds. -
47:16 - 47:21Einstein has shown us
that it's possible. -
47:21 - 47:23We will journey simultaneously...
-
47:23 - 47:27...to distant planets
and to the far future. -
47:27 - 47:29Some worlds, like this one...
-
47:29 - 47:32...will look out onto
a vast gaseous nebula... -
47:32 - 47:34...the remains of a star...
-
47:34 - 47:40...that once was and is no longer.
-
47:40 - 47:43In all those skies,
rich and distant... -
47:43 - 47:46...and exotic constellations...
-
47:46 - 47:50...there may be a faint yellow star...
-
47:50 - 47:53...perhaps barely visible
to the naked eye... -
47:53 - 47:56...perhaps seen only
through the telescope. -
47:56 - 48:00The home star of a fleet
of interstellar transports... -
48:00 - 48:02...exploring this tiny region...
-
48:02 - 48:06...of the great Milky Way galaxy.
-
48:06 - 48:10The themes of space and time
are intertwined. -
48:10 - 48:14Worlds and stars, like people...
-
48:14 - 48:18...are born, live and die.
-
48:18 - 48:20The lifetime of a human being
is measured in decades. -
48:20 - 48:23But the lifetime of the sun...
-
48:23 - 48:28...is a hundred million times longer.
-
48:28 - 48:31Matter is much older than life.
-
48:31 - 48:34Billions of years before
the sun and Earth even formed... -
48:34 - 48:38...atoms were being synthesized
in the insides of hot stars... -
48:38 - 48:42...and then returned to space
when the stars blew themselves up. -
48:42 - 48:46Newly formed planets were
made of this stellar debris. -
48:46 - 48:55The Earth and every living thing
are made of star stuff. -
48:55 - 48:58But how slowly, in our human
perspective, life evolved... -
48:58 - 49:07...from the molecules of the early
oceans to the first bacteria. -
49:07 - 49:10Evolution is not immediately
obvious to everybody... -
49:10 - 49:14...because it moves
so slowly and takes so long. -
49:14 - 49:17How can creatures who
live for only 70 years... -
49:17 - 49:21...detect events that
take 70 million years to unfold? -
49:21 - 49:28Or 4 billion?
-
49:28 - 49:30By the time
one-celled animals had evolved... -
49:30 - 49:38...the history of life
on Earth was half over. -
49:38 - 49:41Not very far along to us,
you might think... -
49:41 - 49:44...but by now almost all
the basic chemistry of life... -
49:44 - 49:47...had been established.
-
49:47 - 49:49Forget our human time perspective.
-
49:49 - 49:52From the point of view of a star...
-
49:52 - 49:55...evolution was weaving
intricate new patterns... -
49:55 - 50:01...from the star stuff on
the planet Earth, and very rapidly. -
50:01 - 50:05Most evolutionary lines
became extinct. -
50:05 - 50:07Many lines became stagnant.
-
50:07 - 50:09If things had gone
a bit differently... -
50:09 - 50:11...a small change of climate,
say, or... -
50:11 - 50:13...a new mutation...
-
50:13 - 50:16...or the accidental death
of a different humble organism... -
50:16 - 50:23...the entire future history of life
might have been very different. -
50:23 - 50:26Maybe the line to an intelligent
technological species... -
50:26 - 50:32...would have passed through worms.
-
50:32 - 50:34Maybe the present masters
of the planet... -
50:34 - 50:40...would have had ancestors
who were tunicates. -
50:40 - 50:42We might not have evolved.
-
50:42 - 50:45Someone else,
someone very different... -
50:45 - 50:52...would be here now in our stead,
maybe pondering their origins. -
50:52 - 50:55But that's not what happened.
-
50:55 - 50:58There's a particular sequence
of environmental accidents... -
50:58 - 51:01...and random mutations
in the hereditary material. -
51:01 - 51:05One particular timeline
for life on Earth... -
51:05 - 51:11...in this universe.
-
51:11 - 51:14As a result, the dominant organisms
on the planet today... -
51:14 - 51:18...come from fish.
-
51:18 - 51:23Along the way, many more species
became extinct than now exist. -
51:23 - 51:26If history had
a slightly different weave... -
51:26 - 51:31...some of those extinct organisms
might have survived and prospered. -
51:31 - 51:35But occasionally, a creature
thought to have become extinct... -
51:35 - 51:37...hundreds of millions
of years ago... -
51:37 - 51:40...turns out to be alive and well.
-
51:40 - 51:45The coelacanth, for example.
-
51:45 - 51:50For 3 1/2 billion years, life had
lived exclusively in the water. -
51:50 - 51:52But now, in a great
breathtaking adventure... -
51:52 - 51:54...it took to the land.
-
51:54 - 51:56But if things had gone
a little differently... -
51:56 - 51:59...the dominant species might
still be in the ocean... -
51:59 - 52:09...or developed spaceships to
carry them off the planet altogether. -
52:09 - 52:11From our ancestors, the reptiles...
-
52:11 - 52:14...there developed
many successful lines... -
52:14 - 52:17...including the dinosaurs.
-
52:17 - 52:20Some were fast, dexterous
and intelligent. -
52:20 - 52:22A visitor from
another world or time... -
52:22 - 52:25...might have thought them
the wave of the future. -
52:25 - 52:30But after nearly 200 million years,
they were suddenly all wiped out. -
52:30 - 52:33Perhaps it was a great meteorite
colliding with the Earth... -
52:33 - 52:35...spewing debris into the air,
blotting out the sun... -
52:35 - 52:38...and killing the plants
that the dinosaurs ate. -
52:38 - 52:45I wonder when they first sensed
that something was wrong. -
52:45 - 52:49The successors of the dinosaurs
came from the same reptilian stock... -
52:49 - 52:56...but they survived the catastrophe
that destroyed their cousins. -
52:56 - 52:59Again, there were many branches
which became extinct. -
52:59 - 53:01And had events been
a little different... -
53:01 - 53:08...those branches might have led
to the dominant form today. -
53:08 - 53:11For 40 million years, a visitor
would not have been impressed... -
53:11 - 53:13...by these timid little creatures...
-
53:13 - 53:20...but they led to all
the familiar mammals of today. -
53:20 - 53:23And that includes the primates.
-
53:23 - 53:27About 20 million years ago,
a space time traveler... -
53:27 - 53:30...might have recognized
these guys as promising... -
53:30 - 53:34...bright, quick, agile,
sociable, curious. -
53:34 - 53:37Their ancestors were once
atoms made in stars... -
53:37 - 53:40...then simple molecules,
single cells... -
53:40 - 53:42...polyps stuck to the ocean floor...
-
53:42 - 53:46...fish, amphibians, reptiles, shrews.
-
53:46 - 53:51But then they came down
from the trees and stood upright. -
53:51 - 53:53They grew an enormous brain...
-
53:53 - 53:57...they developed culture,
invented tools... -
53:57 - 54:02...domesticated fire.
-
54:02 - 54:05They discovered language and writing.
-
54:05 - 54:07They developed agriculture.
-
54:07 - 54:13They built cities and forged metal.
-
54:13 - 54:17And ultimately,
they set out for the stars... -
54:17 - 54:24...from which they had come
5 billion years earlier. -
54:24 - 54:25We are star stuff...
-
54:25 - 54:32...which has taken its destiny
into its own hands. -
54:32 - 54:34The loom of time and space...
-
54:34 - 54:39...works the most astonishing
transformations of matter. -
54:39 - 54:41Our own planet is only a tiny part...
-
54:41 - 54:44...of the vast cosmic tapestry...
-
54:44 - 54:56...a starry fabric
of worlds yet untold. -
54:56 - 55:00Those worlds in space
are as countless... -
55:00 - 55:04...as all the grains of sand
on all the beaches of the Earth. -
55:04 - 55:08Each of those worlds
is as real as ours. -
55:08 - 55:10In every one of them,
there's a succession of... -
55:10 - 55:15...incidents, events, occurrences
which influence its future. -
55:15 - 55:19Countless worlds,
numberless moments... -
55:19 - 55:23...an immensity of space and time.
-
55:23 - 55:25And our small planet,
at this moment... -
55:25 - 55:30...here, we face
a critical branchpoint in history. -
55:30 - 55:33What we do with our world right now...
-
55:33 - 55:36...will propagate down
through the centuries... -
55:36 - 55:39...and powerfully affect
the destiny of our descendants. -
55:39 - 55:43It is well within our power
to destroy our civilization... -
55:43 - 55:46...and perhaps our species as well.
-
55:46 - 55:49If we capitulate to superstition...
-
55:49 - 55:52...or greed or stupidity...
-
55:52 - 55:56...we can plunge our world into
a darkness deeper than the time... -
55:56 - 56:00...between the collapse of classical
civilization and Italian Renaissance. -
56:00 - 56:03But we are also capable...
-
56:03 - 56:05...of using our compassion
and our intelligence... -
56:05 - 56:08...our technology and our wealth...
-
56:08 - 56:11...to make an abundant
and meaningful life... -
56:11 - 56:13...for every inhabitant
of this planet... -
56:13 - 56:18...to enhance enormously
our understanding of the universe... -
56:18 - 56:37...and to carry us to the stars.
-
56:37 - 56:39In our motorbike sequence...
-
56:39 - 56:42...we showed how
the landscape might look... -
56:42 - 56:45...if we barreled through it
at close to light speed. -
56:45 - 56:48Since then,
inspired by this sequence... -
56:48 - 56:52...Ping-Kang Hsiung
at Carnegie Mellon University... -
56:52 - 56:54...produced an exact
computer animation. -
56:54 - 56:58This is what you'd see if you
traveled at ordinary speeds... -
56:58 - 57:00...through this red and white lattice.
-
57:00 - 57:02But this is how it would appear...
-
57:02 - 57:07...if you were traveling
at close to the speed of light. -
57:07 - 57:11We're probably many centuries away
from traveling close to light speed... -
57:11 - 57:14...and experiencing time dilation.
-
57:14 - 57:17But even then,
it might not be fast enough... -
57:17 - 57:21...if we wanted to travel
to some distant place in the galaxy... -
57:21 - 57:24...and then come back to Earth
in our own epoch. -
57:24 - 57:27Some years after completing Cosmos...
-
57:27 - 57:32...I took time out from
my scientific work to write a novel. -
57:32 - 57:34A novel about travel...
-
57:34 - 57:38...to the center
of the Milky Way galaxy. -
57:38 - 57:41I was willing to imagine
beings and civilizations... -
57:41 - 57:43...far more advanced than we...
-
57:43 - 57:47...but I wasn't willing
to ignore the laws of physics. -
57:47 - 57:52Was there, even in principle,
a way to get very quickly... -
57:52 - 57:55...to 30,000 light-years from Earth?
-
57:55 - 57:57So I asked my friend...
-
57:57 - 58:00...Kip Thorne of the California
Institute of Technology. -
58:00 - 58:04He's a leading expert
on the nature of space and time. -
58:04 - 58:06Kip thought about it for a while...
-
58:06 - 58:10...and then answered with
about 50 lines of equations... -
58:10 - 58:12...which showed that
a really advanced civilization... -
58:12 - 58:18...might establish
and hold open wormholes... -
58:18 - 58:23...which we might think of as tubes
through the fourth dimension... -
58:23 - 58:25...which connect the Earth
with another place... -
58:25 - 58:29...without having to traverse
the intervening distance. -
58:29 - 58:34Something like crawling
through a wormhole in an apple. -
58:34 - 58:36I was happy with this result...
-
58:36 - 58:40...and used it as
a key plot device in Contact. -
58:40 - 58:42But such wormholes through space...
-
58:42 - 58:45...would also be time machines,
it seemed to me. -
58:45 - 58:48And I used that notion
in my novel Contact as well. -
58:48 - 58:52Kip Thorne and his colleagues
later proved, or so it seemed... -
58:52 - 58:55...that time travel
of this sort was possible. -
58:55 - 58:59Here, look at this.
-
58:59 - 59:02The key question being explored now...
-
59:02 - 59:05...is whether such time travel
can be done consistently... -
59:05 - 59:10...with causes preceding effects, say,
rather than following them. -
59:10 - 59:12Does nature contrive it...
-
59:12 - 59:15...so that even with a time machine,
you can't intervene... -
59:15 - 59:18...to prevent your own conception,
for example? -
59:18 - 59:22Even if time travel of this sort
is really possible... -
59:22 - 59:25...it's far in
our technological future. -
59:25 - 59:29But maybe other beings
much more advanced than we... -
59:29 - 59:32...are voyaging to the far future
and the remote past... -
59:32 - 59:35...not a measly 40 years ago
on Earth... -
59:35 - 59:38...but to witness
the death of the sun, say... -
59:38 -...or the origin of the cosmos.
- Title:
- Cosmos: A Personal Voyage - Episode 8 (Carl Sagan)
- Description:
-
Episode 8: "Travels in Space and Time"
English, Spanish, and Hebrew subtitles included.
If you like this series, buy it!
- http://www.amazon.com/Cosmos-Carl-Sagan-DVD-Set/dp/B000055ZOB
- http://www.dvdtalk.com/reviews/4774/cosmos-carl-sagan/Playlist: http://www.youtube.com/playlist?p=PL474A7F1BA0FCEF8C
Content property of Koch Entertainment (Entertainment One) - http://bit.ly/gWINrr
- Duration:
- 01:01:36
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