Category
📺
TVTranscript
00:00Transcription by CastingWords
00:30CastingWords
01:00CastingWords
01:30The age and size of the cosmos are written in light.
01:40The nature of beauty and the substance of the stars, the laws of space and time.
01:48They were there all along, but we never saw them until we devised a more powerful way of seeing.
01:57The story of this awakening has many beginnings and no ending.
02:03Its heroes come from many times and places.
02:06An ancient Chinese philosopher.
02:09A wizard who amazed the caliphs of 11th century Iraq.
02:13A poor German orphan enslaved to a harsh master.
02:16Each one brought us a little closer to unlocking the secrets hidden in light.
02:24Most of their names are forever lost to us.
02:31But somewhere long ago, someone glanced up to see light perform one of its magic tricks.
02:38Who knows?
03:02Maybe that quirk of light inspired the very first artists.
03:06Where did all this come from?
03:20How did we evolve from small, wandering bands of hunters and gatherers living beneath the stars
03:27to become the builders of a global civilization?
03:31How did we get from there to here?
03:33There's no one answer.
03:36Climate change, the domestication of fire, invention of tools, language, agriculture, all played a role.
03:46Maybe there was something else too.
03:49In China, more than 2,000 years ago, a philosopher named Mo Tzu is said to have observed that light
03:56could be made to paint a picture inside a locked treasure room.
04:00This was the description of the first camera.
04:06The camera obscura.
04:08The prototype of all image-forming cameras, including the one that's bringing you this picture.
04:13Taking advantage of this funny thing that light does resulted in what could be called the first movie.
04:22Mo Tzu, master of light, worked against all forms of darkness.
04:26A military genius who only used his talents to prevent violence.
04:32He was legendary for traveling among the kingdoms of the warring states,
04:36employing ingenious strategies to talk kings out of going to war.
04:41He was one of the first to dream of universal love and an end to poverty and other forms of inequality,
04:47of government, and for the people.
04:49And to argue against blind obedience to ritual and authority.
04:55In his writings, you can find early stirrings of the scientific approach.
04:59By Mo Tzu's time, the Chinese had already been recording their thoughts in books for at least 1,000 years.
05:06Still, our knowledge of him is only fragmentary.
05:09It consists largely of a collection of essays attributed to him and his disciples.
05:13In one of them, entitled Against Faith, a three-pronged test for every doctrine is proposed.
05:20Question its basis.
05:22Ask if it can be verified by the sights and senses of common people.
05:27Ask how it is to be applied and if it will benefit the greatest number.
05:30Most of us know Emperor Qin for the army of 7,000 terracotta warriors.
06:00That guard his tomb.
06:06In Emperor Qin's drive to consolidate his far-flung empire,
06:10he took drastic measures to standardize everything within it.
06:15This included mandating a single coinage,
06:18making uniform all weights and measures,
06:20the widths of carts and roads,
06:22as well as the precise way the Chinese language was to be written,
06:26including what you are allowed to write and think.
06:31Emperor Qin's philosophy, the only one permitted, was called legalism,
06:36which was just what it sounded like.
06:38Do as the law says, or else.
06:42It's a philosophy that's not highly conducive to questioning authority.
06:47That all the books of the hundred schools of thought shall be burned,
06:56that anyone who uses history to criticize the present
06:59shall have his family executed.
07:02The works of Motsur and Confucius and other philosophers
07:07were destroyed in the world's first book burning.
07:11Hundreds of scholars bravely resisted by trying to preserve the forbidden books.
07:16They were buried alive at the capital.
07:20Science needs the light of free expression to flourish.
07:23It depends on the fearless questioning of authority,
07:28the open exchange of ideas.
07:30Sparks of curiosity in the writings of Motsur and his disciples
07:34were effectively stomped out.
07:38It would be another thousand years before the next movie.
07:41Luckily, our ship of the imagination
07:46can take us anywhere in space and time.
07:50The ancient Chinese and Greeks observed
08:00that light could be made to do wonderful things.
08:03But no one asked that question favored by small children and geniuses alike.
08:08Why?
08:10Until a thousand years ago.
08:12In the city of Basra, Iraq, there lived another master of light.
08:24Ibn al-Hazin had a passionate desire to understand nature.
08:29He questioned everything,
08:31especially those things that everyone else took for granted.
08:36How do we see? he asked.
08:39Some of the great authorities who came before him
08:42had taught that rays come out of our eyes
08:45and travel to the objects we see
08:47before returning to our eyes.
08:50But al-Hazin reasoned that the stars were too far distant
08:54for something in our eyes to travel all the way to them
08:56and back in the blink of an eye.
08:59Excellent reasoning.
09:01But al-Hazin didn't stop there.
09:03He searched for ways to compel nature to divulge her secrets.
09:07His culture was open to new ideas and questioning.
09:10It was the golden age of science in the Islamic world.
09:15One that stretched from Cordoba in Spain
09:18all the way to Samarkand in Central Asia.
09:22Christian and Jewish scholars were honored guests
09:25at the research institutes of Baghdad, Cairo,
09:28and other Islamic capitals.
09:31Instead of burning books,
09:32the caliphs sent emissaries around the world
09:35in search of books.
09:36The caliphs lavishly funded projects
09:54to translate, study, and preserve them
09:56for future generations.
09:58Much of the light of ancient Greek science
10:00would have been permanently extinguished
10:01without their efforts.
10:02The reawakening to science
10:05that took place in Europe
10:06hundreds of years later
10:07was kindled by a flame
10:09that had been long tended
10:10by Islamic scholars and scientists.
10:13The Arabs also imported ideas
10:15from India to the West,
10:17including the so-called Arabic numerals
10:19that we all use today,
10:21and the concept of zero.
10:24which comes in handy
10:28when you want to write
10:29billions and billions.
10:33Arabic astronomy was so influential
10:35that we still call most of the bright stars
10:37by their Arabic names,
10:39and the ales in algebra,
10:41algorithm, alchemy, and alcohol
10:44are just some of the traces left
10:46from the time when Arabic
10:48was the language of science.
10:50In the 11th century,
10:53Ibn al-Hazan set about
10:55trying to test his ideas
10:56about light and how we see.
10:59So he devised an experiment
11:00to determine how light moves.
11:03He erected a tent in full daylight
11:04and sealed it tightly
11:06so that only a single ray of light
11:08could pierce its inner darkness.
11:11With little more than his brains
11:12and a straight piece of wood,
11:14a ruler,
11:15al-Hazan had accomplished
11:16a great leap forward
11:17in the history of science.
11:18He discovered
11:20that light moves in straight lines.
11:27But he was just getting started.
11:30Al-Hazan figured out
11:31that the key to forming any image,
11:33whether you're talking about an eye
11:34or camera obscura,
11:36is a small opening
11:37to restrict the light
11:38that can enter
11:39an otherwise darkened chamber.
11:41That aperture
11:42excludes the chaos
11:44of extraneous light rays
11:45that surround us.
11:47The smaller the aperture,
11:48the fewer directions
11:49that light can come from.
11:51And that makes the image sharper.
11:53So instead of being blinded
11:55by the light,
11:56we can see everything
11:57it has to show us.
11:59Al-Hazan made his own
12:00camera obscura
12:02and dazzled the caliphs.
12:04A camera obscura
12:06works best in bright light.
12:08The stars of the night sky
12:09are way too dim for this.
12:10We somehow need a bigger opening
12:13to collect light.
12:14But we also need
12:15to maintain focus.
12:18A telescope
12:19collects light
12:20from any spot
12:21in its field of view
12:22across the entire lens
12:24or mirror.
12:25An opening
12:25much larger
12:26than the camera obscura hole.
12:29This is one
12:30of the first telescopes.
12:31The one that Galileo
12:34looked through
12:34in 1609.
12:37With it,
12:38he pulled aside
12:39the heavy curtain
12:40of night
12:41and began
12:42to discover
12:43the cosmos.
12:44The lens
12:58made it possible
12:59for a telescope
12:59to have a much larger
13:01light-collecting area
13:02than our eyes have.
13:04Big buckets
13:05catch more rain
13:06than small ones.
13:08Modern telescopes
13:09have larger collecting areas,
13:11highly sensitive detectors,
13:12and they track
13:13the same object
13:14for hours at a time
13:15to accumulate
13:16as much of its light
13:17as possible.
13:19Space-based telescopes
13:20such as Hubble
13:21have captured light
13:22from the most distant
13:23and ancient galaxies,
13:25giving us vastly clearer
13:27pictures of the cosmos.
13:30Alhazen discovered
13:31how images
13:32are formed by light,
13:34but that was far
13:34from his greatest achievement.
13:36Ibn Alhazen
13:37was the first person
13:38ever to set down
13:39the rules of science.
13:41He created
13:42an error-correcting mechanism
13:43a systematic
13:45and relentless way
13:46to sift out
13:47misconceptions
13:47in our thinking.
13:49Finding truth
13:51is difficult,
13:53and the road to it
13:55is rough.
13:57As seekers
13:58after truth,
13:59you will be wise
14:00to withhold judgment
14:01and not simply
14:02put your trust
14:03in the writings
14:04of the ancients.
14:05You must question
14:07and critically examine
14:08those writings
14:09from every side.
14:11You must submit
14:13only to argument
14:14and experiment
14:15and not to the sayings
14:16of any person.
14:18For every human being
14:20is vulnerable
14:21to all kinds
14:22of imperfection.
14:24As seekers
14:25after truth,
14:26we must also suspect
14:27and question
14:28our own ideas
14:29as we perform
14:31our investigations
14:32to avoid falling
14:33into prejudice
14:34or careless thinking.
14:37Take this course
14:38and truth
14:40will be revealed
14:41to you.
14:42This is the method
15:01of science.
15:02So powerful
15:03that it has carried
15:04our robotic emissaries
15:05to the edge
15:06of the solar system
15:07and beyond.
15:10It has doubled
15:11our lifespan.
15:13Made the lost world
15:14to the past
15:15come alive.
15:18Science has enabled us
15:19to predict events
15:20in the distant future
15:21and to communicate
15:24with each other
15:25at the speed of light
15:26as I am with you
15:27right at this moment.
15:29This way of thinking
15:30has given us powers
15:31that Al Hazen himself
15:32would have regarded
15:33as wizardry.
15:38But it was he
15:39who put us
15:39on this rough
15:41endless road.
15:44And now it has taken us
15:46to a place
15:46where even light
15:48itself
15:49is enshrouded
15:51in darkness.
16:00Light has properties
16:01unlike anything else
16:02in the realm
16:03of human existence.
16:04Take the speed of light.
16:06The basic particle
16:07of light,
16:07a photon,
16:08is born traveling
16:09at the speed of light
16:11as it emerges
16:11from an atom
16:12or a molecule.
16:14A photon never knows
16:15any other speed.
16:16And we have not found
16:17another phenomenon
16:18that accelerates
16:19from zero to top speed
16:20instantaneously.
16:22Nothing else
16:23can move as fast.
16:24When we try
16:25to accelerate
16:25other particles
16:26closer and closer
16:27to the speed of light,
16:28they resist more and more
16:29as though they're getting
16:30heavier and heavier.
16:31no experiment
16:32yet devised
16:33has ever made a particle
16:34move as fast as light.
16:44What was that?
16:46You hear something?
16:49Was I?
16:50Oh, yeah.
16:50I don't know
16:51anything else in life
16:52that behaves like light.
16:54I cannot reconcile
16:56its strange properties
16:58with everything else
16:59my senses tell me.
17:01Our urge
17:01to trust our senses
17:02overpowers
17:04what our measuring devices
17:05tell us about
17:05the actual nature
17:06of reality.
17:08Our senses work fine
17:09for life-size objects
17:10moving at mammal speeds,
17:12but they're ill-adapted
17:13for their wonderland laws
17:15and light speed.
17:20We don't even know
17:21why there's a cosmic speed limit.
17:23Time stands still
17:25when you're traveling
17:26at the speed of light.
17:28But it is light anyway.
17:34Isaac Newton's
17:35enduring fascination
17:36with light
17:36began when he was a child.
17:42In this very house.
17:49By the time
17:50he was in his 20s,
17:51Newton became
17:52the first person
17:53to decipher
17:54the mystery
17:55of the rainbow.
18:00Newton discovered
18:01that sunlight
18:02or white light
18:03is a mixture
18:04of all the colors
18:05of the rainbow.
18:08Major discovery.
18:11He named
18:11the displays of colors
18:13a spectrum
18:13from the Latin
18:15for phantom
18:16or apparition.
18:17begging your pardon,
18:31Master Newton.
18:32The cook Fred said
18:33that your dinner
18:33will spoil, sir.
18:37No, Isaac,
18:39don't put the magnifying glass down.
18:41Something even more amazing
18:42is hidden in the light.
18:44A code,
18:44a key to the cosmos.
18:53Isaac Newton
18:54didn't miss much,
18:55but that one
18:56was a beaut.
18:57He just walked
18:58right past the door
18:59to a hidden universe.
19:00A door that would not
19:01swing open again
19:02for another 150 years.
19:04It would fall on
19:05another scientist
19:06working in the year 1800
19:08to stumble
19:09on a piece of evidence
19:10for the unseen worlds
19:12that surround us.
19:17By night,
19:18William Herschel
19:18scanned the heavens
19:19with the largest telescope
19:21of his time.
19:22By day,
19:23Herschel performed experiments.
19:25From Newton's earlier work,
19:26it was known that sunlight
19:28is a blend
19:28of different colors.
19:29And everyone knew,
19:31just from being outside,
19:33that sunlight
19:33carries heat.
19:34William Herschel
19:38asked whether
19:38some colors of light
19:40carry more heat
19:41than others.
19:42The nature
19:43of scientific genius
19:44is to question
19:45what the rest of us
19:46take for granted
19:47and then do the experiment.
19:52The thermometer
19:53that Herschel placed
19:54outside the spectrum
19:56was his control.
19:59The control
20:00in any experiment
20:01always lacks
20:02the factor being tested.
20:04That way you know
20:05if what you're testing
20:06is really the thing
20:07responsible
20:08for the observation.
20:10In Herschel's experiment,
20:11the relationship
20:11between color
20:12and temperature
20:13was being tested.
20:14And so his control
20:15was a thermometer
20:17over the part
20:18of the white sheet
20:19that was not illuminated
20:20by sunlight at all.
20:25There's that sound again.
20:27What is that?
20:28What is that?
20:28What is that?
20:30Okay, red light
20:36is warmer
20:36than blue light.
20:38Interesting discovery,
20:39but not exactly
20:40revolutionary.
20:41No, there's nothing wrong
21:06with your thermometer.
21:06You've just discovered
21:09a new kind of light.
21:20Herschel was the first
21:21to detect this unseen presence
21:23lurking just below
21:24the red end
21:24of the spectrum.
21:26That's why it came
21:27to be called infrared.
21:29Infra is Latin
21:30for the word below.
21:31It's invisible.
21:33Our eyes are not sensitive
21:34to this kind of light,
21:35but our skin is.
21:36We feel it as heat.
21:38Now, that's a really
21:39big discovery,
21:40but far greater secrets
21:41were still hiding
21:42deep inside the light.
21:50At about the same time
21:51that William Herschel
21:52was discovering
21:53an infrared light
21:54in his parlor in England,
21:55a young boy
21:56named Joseph Fraunhofer
21:58was trapped
21:58in hopeless drudgery.
22:00He stood over a cauldron
22:02of toxic chemicals
22:03and endlessly stirred.
22:08Joseph had been orphaned
22:09at the age of 11
22:10and given to a harsh master
22:13named Weichelberger,
22:14the royal mirror maker.
22:17He prevented Joseph
22:19from going to school.
22:20Instead, Joseph labored
22:22in the glassmaking workshop
22:23by day
22:24and tended to the master's
22:26household chores
22:27by night.
22:27until Joseph got his big brain.
22:46Weichelberger's house
22:47collapsed.
22:48Maximilian, the future king of Bavaria, hurried to the scene of the calamity to see if he
23:11could help. Maximilian was known for taking an interest in his subjects, which was highly
23:17unusual for its time. In attracting the concern of the future king of Bavaria, young Joseph
23:36Fraunhofer found an aperture into a different universe, and not just for himself. Prince
23:45Maximilian gave Joseph money and asked his privy counselor to provide further help to the boys
23:50should it be needed. Weichelberger continued to exploit him and prevent him from attending
24:01school. But the prince's counselor intervened, offering Joseph a position at the optical
24:07institute. This small gesture of kindness really paid off.
24:12By the time he was 27, Joseph Fraunhofer was the world's leading designer of high-quality
24:32lenses, telescopes, and other optical instruments. His firm was housed here in the old Benedict
24:37Abbey. In the early 19th century, this was top-secret, ultra-high technology. The Benedictine monks
24:49of earlier times had taken a vow of secrecy. This local tradition and the ability to restrict
24:55access to Fraunhofer's laboratory allowed him to maintain control of trade and state secrets.
25:07Fraunhofer was experimenting with prisms to find the best types of glass for precision lenses.
25:12How, he wondered, could he get a better look at the spectrum that a prism produced?
25:21Friedrich, bring me the theodolite, please.
25:25Okay, while Fraunhofer sets up his theodolite, as a kind of telescope, I want to show you something
25:31in another part of the Abbey.
25:32Sound waves are so beautiful to hear.
25:44Imagine how beautiful they'd be to see.
25:49You ever wondered why organ pipes have different lengths?
25:53I press a key.
25:55It sends compressed air into a particular pipe, producing sound waves.
26:01If we could slow the sound waves down a few hundred times, they would look like this.
26:10The length of the pipe determines the length of the sound wave that can fit inside it.
26:15A short pipe gives you a short sound wave.
26:19Short sound waves have high pitch or frequency.
26:25The distance between adjacent waves is called the wave length.
26:38A long pipe gives you a long sound wave with a low pitch or low frequency.
26:42holy than a sigh of Attack.
27:08along with a short sound wave.
27:10The Medieval Manuscript of this music, Carmina Burana, was discovered in this very abbey.
27:40Sound waves can't travel through a vacuum.
27:46They need matter to ride on, like molecules of air or water or rock.
27:51But light waves fly solo.
27:54They can move through empty space and fast, a million times faster than sound waves and air.
28:00And the wavelengths of the light we see are so much shorter than sound waves, about 50,000 light waves would fit right in here.
28:10Oh yeah, Fraunhofer.
28:21Just in time, we didn't miss it.
28:25Just as the wavelength of sound determines the pitch that we hear, the wavelength of light determines the color that we see.
28:32But how does a prism spread out the colors concealed in a beam of sunlight?
28:36When light travels through air or space, all its colors move at the same speed.
28:44But when it hits glass at an angle, the light slows down and changes direction.
28:53Inside the prism, each color moves at a different speed.
28:56In glass, violet light, which is carried by the shortest waves we see, slows down more than red light, which has the longest waves.
29:09These changes in speed pry the colors apart, sending their waves off in slightly different directions.
29:20And that's how a prism works.
29:26If I seem unduly emotional about this, it's because Joseph Fraunhofer is about to do what Isaac Newton could have done, but didn't.
29:35And it'll have a powerful effect on the course of my own life.
29:38You are witnessing the marriage of physics and astronomy, the birth of my own field of science.
30:08Astrophysics.
30:14Written in the light.
30:17Those vertical black lines.
30:21The secret code.
30:24Fraunhofer looked at them and wondered.
30:26Why?
30:31A code that comes to us from an alien universe.
30:38What is the message written in these dark vertical lines?
30:56It took a hundred years of thinking, questioning, searching to decipher it.
31:00Lovely, isn't it?
31:22Why?
31:24There are many layers to the fine structure of beauty.
31:29The chemistry of the earth and its atmosphere.
31:32The evolution of life.
31:35Many distinct threads.
31:36Let's just examine one at the surface.
31:41The colors of nature that dazzle us.
31:44What's really happening?
31:46How does the red, the blue, the astonishing palette of nature's colors?
31:51How do they happen?
32:01Lightwaves of different lengths from the sun strike the earth.
32:05The petals of these particular flowers absorb all the low-energy, long red wavelengths of light.
32:11But the petals reflect the shorter, high-energy, blue wavelengths.
32:16That interaction between starlight and petal, or water, or Van Gogh, is what makes blue.
32:24The longest waves, the ones we see as red, have the lowest energy.
32:32Color is the way our eyes perceive how energetic lightwaves are.
32:36A sunset, a flag, the eyes of your beloved, that shiny new car.
32:47The feelings they inspire happen when something inside you is triggered by a particular variation in the frequency and energy of lightwaves.
32:58And the secret message, those black vertical lines in Fraunhofer's spectrum, what makes them?
33:05They occur when the lightwaves of those particular colors are being absorbed.
33:11It happens on another level of reality, far smaller than the world we're used to operating in.
33:17To get there, we'll need to become 10 billion times smaller than we are.
33:24We could pick any one of these atoms.
33:27Let's go for the hydrogen atom.
33:30The hydrogen atom is the most plentiful kind of atom in the cosmos.
33:35And the simplest.
33:44It has only one electron.
33:48And only one proton.
33:50We've entered the quantum realm.
33:53It doesn't correspond to ordinary human experience.
33:57Common sense is no help here at all.
33:59Take the hydrogen atom's electron, for example.
34:05In an atom, an electron doesn't exist between orbitals.
34:09It disappears from one orbital and reappears in another.
34:12It's as if you took an elevator from the second floor to the fourth floor, but ceased to exist in between.
34:20And another thing.
34:21Quantum elevators only stop at certain floors.
34:23The sizes of the electron orbits are strictly limited and different for the atoms of every element.
34:30The force that holds an electron in orbit has nothing to do with gravity.
34:41It's a force of electrical attraction.
34:45The electron dances a wavy ring around the central nucleus of a hydrogen atom and makes quantum leaps from orbit to orbit, up or down.
34:53The larger the orbit, the greater the energy of an electron.
34:58An electron has to get energy to leap to a larger orbit, and it has to lose energy to jump back down.
35:04Every upward leap is caused by an atom absorbing a light wave.
35:10But we have no idea what causes the downward leaps.
35:15What we do know is that such leaps always produce a light wave whose color matches the energy difference between the orbitals.
35:28The sun's surface radiates light waves of all colors.
35:33If you look at sunlight through a prism, you'll see its spectrum.
35:36When you magnify the spectrum with a telescope, as Joseph Fraunhofer did, you raise the curtain on the electron dance within the atom.
35:48When the energy of the electron flags and it drops to a lower orbital, the light wave it emits scatters.
35:56Most of it doesn't reach us.
35:58That leaves a dark gap or a black vertical line in the spectrum.
36:01These dark lines are the shadows cast by hydrogen atoms in the atmosphere of the sun.
36:08Sodium atoms cast different shadows.
36:11Their electrons dance to a different tune.
36:14A grain of table salt is composed of sodium and chlorine atoms.
36:18Ten million billion of them doing their crazy dances in a single grain of salt.
36:24And a single iron atom with 26 electrons is like a great big production number in a Broadway musical.
36:36When you look at a star with a spectroscope, you see the dark lines from all the elements in its atmosphere.
36:43Show me the spectrum of anything, whether here on Earth or from a distant star, and I'll tell you what it's made of.
36:52Fraunhofer's lines are the atomic signatures of the elements writ large across the cosmos.
37:00As with every other major revelation in the history of science, it opened the way to newer and deeper mysteries.
37:06And to the revelation that there were many more secrets hiding in the light.
37:21When Joseph Fraunhofer combined a prism with a telescope and turned it towards the skies, he brought the stars much closer to us.
37:36When he was only 39, he contracted a fatal illness.
37:46Perhaps as a result of his early and long-term exposure to the toxic chemicals of glassmaking.
37:52You never know where the next genius will come from.
38:00How many of them do we leave in the rubble?
38:03The prince and his kingdom were immeasurably enriched by the act of kindness to a poor orphan.
38:11Fraunhofer's discoveries transformed Bavaria from a rural backwater to a technological powerhouse.
38:19As he lay dying, the government was desperate to preserve every shred of his precious knowledge about the high technology of optical glass.
38:27But it could only be divulged to a person with top security clearance, the director of the Mint.
38:35The government kept Fraunhofer's technology for making perfect optical glass a state secret for another hundred years.
39:00This would prove to be a major obstacle for someone we'll meet later in our journey.
39:06But Fraunhofer would allow no such secrecy where his pure scientific research was concerned.
39:11He knew that science requires openness to flourish.
39:14That our understanding of nature belongs to the world.
39:19As soon as Fraunhofer discovered the spectral lines, he published everything he knew about them.
39:23And the reverberations of his momentous discovery echoed still.
39:32His spectral lines revealed that the visible cosmos is all made of the same elements.
39:43The planets.
39:53The stars.
39:54The galaxies.
39:54We, ourselves, and all of life.
40:16The same star stuff.
40:23He made it possible for us to know what's in the atmospheres of other worlds.
40:31And in galaxies millions of light years away.
40:35Spectral lines revealed not only the composition of far off objects, but also their motion towards or away from us.
40:42Using them, we discovered that our universe is expanding.
40:45But perhaps the greatest revelation of spectroscopy is the discovery of the thing it cannot see.
40:57A hidden universe of dark matter.
41:00Six times more massive than the familiar cosmos.
41:03It's made of some mysterious substance that does not emit, reflect, or absorb any kind of light.
41:09We only know it's there because of its gravity, which pulls on all the galaxies and speeds up the visible stars within them.
41:21There are many more kinds of light than our eyes can see.
41:26Confining our perception of nature to visible light is like listening to music in only one octave.
41:32There are so many more.
41:37They differ only in wavelength, but over a huge range.
41:41For instance, infrared light.
41:49The kind that William Herschel discovered.
41:52Or X-ray light.
41:59Or radio light.
42:02Or in gamma-ray light.
42:13These are not just different ways of seeing the same thing.
42:17These other kinds of light reveal different objects and phenomena in the cosmos.
42:22In gamma-ray light, for example, we can see mysterious explosions in distant galaxies that we would otherwise miss.
42:32And in microwave light, we can see all the way back to the birth of our universe.
42:39We have only just opened our eyes.
42:43We have only just opened our eyes.
42:48We have never opened our eyes.
42:57You