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00:00the mastery of time this is one of humankind's biggest obsessions since
00:23humans learned how to count we've tried to understand and measure the observable
00:27phenomena of time whether past present or future time is undoubtedly one of the most complex notions
00:36in our universe if we send satellites into space today it's thanks to this rudimentary
00:43instrument a stick that projects a shadow over the centuries making time has been the
00:53object of a perpetual scientific quest from the moment we control time we control people
01:01today a group of experts made up of astrophysicists engineers and historians
01:09is following in the footsteps of these genius inventors who revolutionized our perception of
01:14time and of the world in fact with relativity Einstein showed that absolute rigid time does
01:21not exist the question Huygens posed was how to ensure that between each tick and talk we
01:33always have one second this epic gave birth to extraordinary machines thanks to them men
01:46have tamed the earth cycles they escaped the oceans traps traced maps secured transport and built the
01:58foundations of our modern economy before launching clocks into space precious ally or formidable enemy time
02:11dictates the rhythm of our lives
02:13the fourth signal it will be 21 hour and 46 minutes
02:23the fourth signal it will be 21 hour and 46 minutes
02:31the fourth signal it will be 21 hour and 46 minutes
02:35perched on the heights of france's capital the paris observatory looks like a sleeping ship
02:55yet within the secular institution is the heart of a machine that never stops beating
03:01it is here that for 350 years men and women have made our common time
03:11this evening the astrophysicist pacom delva is accompanied by denis avoir science historian and
03:17specialist in time measurement
03:19like the astronomers of antiquity the two scientists observe the movement of the stars a sign of the passing of time
03:37not yet ah there's saturn
03:40You can really see the stars moving here, and when you look in the eyepiece, it's very
03:52obvious.
03:53If we don't use the motor to follow the movement of the sky, in fact, the planets move out
03:58of the eyepiece very quickly, so we really see time passing.
04:03This is linked to the Earth's rotation on itself, and as our position on Earth is fixed,
04:08we see the whole sky moving.
04:34To find the origin of the measurement of time, we must go back to the prehistoric
04:38era.
04:39The measurement of time begins with the first humans.
04:48We have no writings, but we suppose it was by observing the Sun and the alternation of
04:53day and night.
04:55Then the discovery of the Moon, that illuminates the nights.
04:59And the Moon resumes the same configuration after about 30 days.
05:04These two stars quickly become the masters of the division of time in the long term.
05:15At its inception, the measurement of time was based on careful observation of natural phenomena.
05:22The survival of our distant ancestors depended closely on the position and rotation of the
05:30Earth in relation to the Sun.
05:31Thus, the day is devoted to hunting or gathering.
05:35At night, Paleolithic peoples protect themselves from the cold and predators, while awaiting the
05:42return of the solar star.
05:48Before taming time, these nomads live according to the rhythm of nature and the seasons, synchronized
05:55to the cycle of plants or the movement of herds of herbivores.
06:01The measurement of time is born with mathematic measurement and certain testimonies claim it
06:19starts with the Babylonians and the Egyptians.
06:24Here in Iraq, three millennia ago, the Babylonians living on the banks of the Euphrates left us
06:33a scientific legacy in the field of mathematics.
06:44Engraved within tight lines, in cuneiform script, clay tablets reveal how Babylonian scholars divide
06:49the year into 12 months of 30 days.
06:58These first calendars, based on the cycles of the Moon, make it possible to anticipate
07:02the return of the seasons, the periods of rain and strong heat which return according to
07:07the lunar cycles.
07:16Babylonian astronomy was extremely elaborate.
07:19They were able to predict in the long term the position of the Sun, the Moon, and the
07:23planets in the sky.
07:25They had what are called ephemeris.
07:28This means they have a perfect mastery of time.
07:31And this observation of time was done with the most rudimentary instrument of astronomy,
07:36the Nomen, which makes it possible to determine the fundamental constants of astronomy.
07:42Denis Savoie is a specialist of mnemonics, the art of designing and tracing sundials.
07:57With this measuring instrument, the Nomen, Babylonian scientists measured time.
08:03Thanks to mathematics, this data enabled them to better control time.
08:08This instrument dates back to ancient times, 2,000 years before Jesus Christ.
08:29If we send satellites into space today, it's thanks to this rudimentary instrument that projects
08:34a shadow.
08:36This Nomen is very simple.
08:38It's a stick that we plant vertically on a flat surface and will watch the end of the shadow.
08:45And throughout the day, at regular intervals, we use pebbles to mark the end of the shadow.
08:51We obtain a curve on the ground called a hyperboule, and we see there is a time of day when the shadow is the shortest.
08:59At this time, the Sun is in the geographic south, at its highest.
09:05And this is where Babylonian astronomers measure the length of the shadow.
09:09And from the measurement of this length, they deduce parameters such as latitude, obliquity, length of the seasons, the solstice, etc.
09:22The shadow of the Nomen shows that the Earth rotates both on itself and around the Sun, with an inclined axis of rotation.
09:30It is this inclination which causes the variation of the height of the Sun during the year, and which therefore causes the phenomenon of the seasons.
09:39Babylonian astronomers observe that at the winter solstice, the Sun is lowest in the sky, and that it produces a very long shadow.
09:49At the summer solstice, the Sun is at its highest. It therefore produces a very short shadow.
09:59Scientists also note two periods during the year, when the length of the days is equal to the length of the nights.
10:05These are the equinoxes. Thus, the solstices and the equinoxes divide the year into four periods – spring, summer, autumn and winter.
10:19We're starting to master these cycles. And time quickly becomes a major issue, because it allows the forecasting of phenomena, the organization of society, of social life, of economic life.
10:31And from the moment we control time, we control people.
10:36Ancient civilizations, like the Babylonians or the Egyptians, are therefore limited to the description of observable phenomena.
10:51It was not until the 5th century BC that scholars and Greek philosophers engaged in a new stage in the manufacture of time.
10:59They will manage to materialize the passing of time by inventing prodigious machines.
11:11In the alleys of central Athens, a tiny museum is dedicated to the technologies of ancient Greece.
11:17It is here that a former engineer reconstructed one of the most significant inventions of that era.
11:32The klepsidra, meaning water thief in Greek, is the very first autonomous water clock.
11:38It is the work of a mechanical genius, Tijibius of Alexandria.
11:42I started my research in 1981. At the time I was studying at Polytechnic in Athens.
11:50I'm a mechanical engineer. With the help of one of my teachers, I immersed myself in the technologies of ancient Greece.
11:57I looked for the sources of these extraordinary inventions. And little by little, I started to find solutions.
12:02The Tijibius clock is an extraordinary invention. It's the first hydraulic clock.
12:20Our main source of research was inspired by the drawings of Vitruvius, a Roman architect, who described the inventions of Tijibius.
12:27This water clock is truly admirable because it works with a gear system based on a ratio of 1 to 365.
12:43It has rods, cogs, and internal worm gears that Vitruvius describes in detail.
12:48Tijibius' klepsidra consists of a system with three receptacles supplied by a water source and fitted with a piston operated with compressed air, a first of its kind.
13:04An ingenious cogwheel mechanism makes it possible to indicate the exact time, whatever the length of the day of year.
13:11The remains of this brilliant invention can be found in a little-known part of the Agora of Athens.
13:18This octagonal tower indicated the direction of the winds and housed Tijibius' monumental clock.
13:25The remains of this brilliant invention can be found in a little-known part of the Agora of Athens.
13:32This octagonal tower indicated the direction of the winds and housed Tijibius' monumental clock.
13:39The tower of the winds is revolutionary because it shows the time to the citizens.
13:58In each of the building's eight sides, there were solar clocks, so the people of Athens could see both from the outside and the inside.
14:13From the outside when it was sunny, and in general Athens is sunny, but also from the inside at night and when there were clouds.
14:23Inside the tower of the winds, there was a system which was fed by water from outside the building.
14:42So it is a clock fed by a small source called the clepsydra.
14:48It is a symbol of power.
14:55It shows the power of Athens, which has mastered time, and displays time to the Athenians and to the city's visitors.
15:07To make public life uniform, the Greeks focused on time and developed instruments available to all to situate themselves in time.
15:15Throughout antiquity, people lived with unequal hours, which did not last 60 minutes as today.
15:22A day was split into 12 intervals.
15:25At the summer solstice, when the day is longest, the hour counts 80 minutes.
15:30On the other hand, in winter, as days are shorter, the hour is about 40 minutes.
15:35In the third century BC, the Romans didn't take long to appropriate the inventions of Greek culture.
15:52Heirs to the gnomans, sundials are the basis of ancient Roman time keeping.
16:01Sundials appear everywhere in the city and become common instruments.
16:05In the gardens of the Villa Borghese in Rome, one can still admire the inventions of that time, when the hour intervenes in many aspects of daily life, both private and public.
16:20These sundials have a double function, a social function to indicate the time to the citizens, but they are also prestigious objects.
16:33This sculpted one in Villa Borghese is quite extraordinary.
16:37The owner wants to exhibit all his scientific knowledge and the sculpture that goes around it.
16:43They're not just scientific objects, they're also art.
16:46And we have to show off our wealth and knowledge.
16:49In general, there's a motto.
16:50Seneca had a beautiful one.
16:52We have very little time.
16:54We already lost a lot.
16:56And others are amusing, like, it's later than you think.
16:59These mottos evoke the passage of time from a philosophical and religious point of view.
17:07In Rome during the time of Augustus and Caesar, there are plenty of sundials.
17:21And people are complaining.
17:22They're used to eating when they're hungry, but now with sundials they have to eat at noon on the dial.
17:27They're already prisoners of time.
17:37They're being worn when they're 처z of pity.
17:38They are very
17:46In front of the Italian parliament stands an imposing monument.
17:49A vestige of Rome's greatness and of Roman scientific knowledge.
17:56We're in front of the obelisk that Augustus brought back from the city of Heliopolis,
18:06in Egypt, to celebrate his victory over Egypt.
18:09And he places this obelisk on the field of Mars in Rome, which will constitute a meridian.
18:15It's a gigantic gnomon, which indicates both solar noon and the date at the same time.
18:24This 22-meter high obelisk measures the lengthening or shortening of the days during the year.
18:39Archaeologists recently discovered that this monument, inaugurated ten years before our
18:43era, was unique in its size and antiquity.
18:47Emperor Augustus placed the gigantic obelisk on a vast square paved with marble, about 500
18:53feet by 230 feet.
18:58Astronomical graduations were traced on the ground, on the north-south axis, with bronze
19:03inscriptions, a few of which have been found.
19:05It also serves as a calendar, because for the Romans, time is not just the hour, but also
19:20long-term time management of days and months.
19:25And we must remember that before Augustus, during Julius Caesar's rule, they already had
19:29a calendar, the Republican calendar, dating back to the 8th century BC.
19:35This calendar had the particularity that it was left to the favor of the Pontiffs.
19:40And at the end of the year, they added a month or two to stay in line with the seasons.
19:45But what happens is this calendar becomes a means of political corruption.
19:50Depending on whether the Pontiffs have friends or enemies in power, they lengthen or shorten
19:55the length of the year.
19:57And it arrives at such a cacophony that when Julius Caesar comes to power, they celebrate
20:02the harvest in the springtime.
20:05Caesar wants to bring some order into the Roman agenda.
20:13The choices the Emperor makes are not without consequences for our current calendar.
20:18He first decides that the year begins on January 1st.
20:22He then designates new months according to the names of the gods and goddesses.
20:26Januarius for Janus, god of beginnings and gates, becomes the month of January.
20:31Or Junius for Juno, the goddess of family, becomes the month of June.
20:36The new calendar also makes references to Julius Caesar's family and his adopted son, with
20:41Julius and Augustus for the months of July and August.
20:46The first thing Julius Caesar does is hire Sosigen, an astronomer, to reform this calendar,
20:52and then to bring the calendar back in line with the seasons.
20:55Caesar will have a year with 455 days.
20:58This is called the year of confusion.
21:00And he then established what is called the Julian calendar, which has a leap year every
21:04four years.
21:05This dates from 45 to 46 BC.
21:11This is how Caesar created the longest year, a year of 15 months.
21:19After a flourishing ancient period in the field of instruments for measuring time, the race
21:24for accuracy continues considerably in the Muslim countries, with immense progress in the fields
21:29of mathematics, geometry, or physics.
21:36But in Europe, in the Christian world, this is not what will happen.
21:44In the late Middle Ages and the 13th century, a mechanical invention will influence all humankind
21:50for ages to come.
22:01Preserved like a treasure, the astronomical clock of Borges Cathedral is the work of Jean Foussouris,
22:08a French astronomer and mathematician.
22:14Today, visitors to the cathedral can admire an intricate mechanism which not only tells the
22:20time, rings the bells, but also indicates the cycles of the moon and the sun.
22:27We are inside Jean Foussouris' clock and we can clearly see the folio here.
22:44This horizontal bar with the two masses which balance it.
22:47Here the drive axis with two small pallets.
22:51And the escape wheel we see turning here.
22:54And the weight at the bottom that drives it all.
22:57It's extraordinary because it is practically the only one which is still in use in France.
23:06This new generation mechanical clock has three essential parts.
23:12A weight, an escape wheel, and a verge escapement.
23:17The weight causes the needle to rotate.
23:21The escape wheel transmits the driving force of the weight to the cog.
23:28And the verge escapement coupled to the escape wheel serves as a horizontal balance.
23:34These beats are the units which give the fractions of time.
23:38This formidable technical innovation triggered a great vogue for mechanical clocks in the
23:4314th century all over Europe.
23:49This system is really the beginning of clock making.
23:52It is an absolute splendor and it will last until the 17th century with the invention of the
23:57pendulum clock by Christian Hugens.
24:07Christian Hugens is a Dutch scientist who will put his genius at the service of the Sun King.
24:12A member of the Academy of Sciences, the young man attended the construction of the Paris Observatory
24:18in 1667.
24:20This institution was to become a major center of scientific conquest.
24:25We are in the Paris Observatory.
24:27It is one of the benchmarks of world time measurement.
24:32There are many in this race which will add more precision and time keeping.
24:37And the instruments are built here.
24:40Experiments are made.
24:41Clocks are tested.
24:42Reports are made.
24:43in the very center of time measurement.
24:49With Hugens, we have clocks that we call high precision.
24:54Because Hugens was not only able to use the pendulum as a clock regulator, he was also able to maintain
25:00this regularity over time.
25:05The principle of this technical revolution is linked to two major innovations.
25:11The first is a pendulum, which under the effect of gravity makes a return trip once per second.
25:17This is its frequency.
25:19The second novelty is the lever escapement system, which allows the oscillations of the pendulum
25:25to be counted precisely.
25:29The biggest problem is constant isochronism.
25:32What does isochronism mean?
25:34Isos means equal.
25:36And chronos means time.
25:38So the question Hugens asked himself was how to make sure that between the tick and tock,
25:43we always have one second.
25:45And that all ticks and tocks are equal.
25:55Christian Hugens seems to have befriended Louis XIV.
26:02In 1673, he dedicated his last work to him on watchmaking mechanics.
26:10Invited to Versailles a few years earlier, Hugens presented the Sun King with his latest invention,
26:16a clock driven by a pendulum whose beat seems eternal.
26:25He explained to the amazed court that, thanks to this pendulum,
26:32the timepiece only advances or lags by 15 seconds a day.
26:42It is a veritable leap forward in the race for precision.
26:45Galileo believed that a precision clock or an instrument for measuring time was an instrument
27:10for accompanying astronomical observations and that the solution was in astronomical observations.
27:17But Hugens was convinced that if he found a way to take time keeping with him on a boat,
27:22he would solve the problem of determining longitude.
27:29To find your exact bearings on the Earth's surface, you need to know two coordinates.
27:34Latitude and longitude, which determine the angle between our position and a reference meridian,
27:43like that of Paris or Greenwich.
27:53For latitude, it is possible to locate yourself in relation to the pole star,
27:58always fixed in the sky of the Northern Hemisphere.
28:01But longitude requires comparing the time on the meridian of origin
28:09to that of the place where we presently are.
28:14A difference of four minutes corresponds to one degree of longitude,
28:18or about a hundred kilometers on the equator.
28:21At the time, on-board clocks did not withstand sea travel.
28:38Roll, pitch and dust disrupted them.
28:43Thus, navigators did not have a reliable means on board to determine their longitudinal position.
28:51But the English have not yet said their last word.
28:53Despite several promising experiments with Christian Hugens' clocks on board French Navy ships,
28:59the 17th century ended without finding a solution to the question of measurement of longitude.
29:09For most scientists, it even appears to be unanswerable.
29:13The flying
29:14tentadores did not have a terrible plan,
29:16but Jamaicans did not have yet said their last word.
29:18This has helped drive the sun to guerre ont西,
29:20but they also took the time of Cooper Karenchan's
29:43The scientific battle for longitudes is being fought from Greenwich Observatory in London.
29:52It is on this hill that the famous Meridian was drawn and that, in 1675, Greenwich Mean Time,
29:59the average time of Greenwich was established. It was also here that we maintain the memory
30:04of a drama that turned the history of time upside down.
30:08One of Britain's greatest naval disasters occurred in 1707 on the 22nd of October.
30:13Sir Cloudsley Shovel, who had been stationed in the Mediterranean, sailed back to England
30:18and lost four of his ships on the islands of Scilly, including himself.
30:23Approximately 1,400 to 2,000 lives were lost.
30:31The charts were incorrect, their navigational calculations were incorrect,
30:35their latitude had not been correctly observed, and the islands were positioned 50 miles northwards
30:40on the charts of where they actually were.
30:42This did bring to Britain, to the public, the enormous problems that sailors faced at sea.
30:52Following this maritime disaster, in 1714, the British Admiralty launched a competition
30:58for scientists and watchmakers so that they could develop the first marine clock
31:03capable of giving the correct longitude without error.
31:10The reward was in a tier system, so the more accurate your longitude determinations were by your methods,
31:16the more money you would get for your efforts.
31:19So the biggest reward that the board offered was £20,000,
31:22if you could determine the longitude within half a degree or within 30 geographical miles.
31:28In 1730, a genius clockmaker will take up the challenge.
31:45After inventing high-performance wooden mechanisms for the period,
31:49John Harrison dedicated himself to the design of a perfectly precise marine chronometer.
31:55The famous navigator James Cook would later be the first to experience Harrison's timepieces
32:02on his travels around the world.
32:07The greatest challenges for a clock to work at sea, or a marine timekeeper,
32:10was it had to be able to deal with the motion of the vessel,
32:14it had to deal with quite extreme temperature variations,
32:17and it had to deal with the problem of oil,
32:21because any clock that's going to run for a long period of time,
32:25the oil would prevent it from keeping its accuracy.
32:28So Harrison's designs are based on the theory of a pendulum clock.
32:45The driving, the power is a mainspring.
32:48He devised a self-maintaining power system,
32:51so that the clocks wouldn't run down when they were wound up.
32:54That's one of Harrison's great inventions.
32:57The other thing that Harrison did was he made two barbell constructions
33:01that worked simultaneously,
33:03so any movement would be counteracted by the movement on the opposite ends.
33:07They were connected with springs,
33:09which Harrison called artificial gravity.
33:12In 1736, John Harrison embarks on an English Navy ship with his sea clock,
33:22for a crossing to Lisbon.
33:25This trip is a test for the commission of longitudes.
33:31But his chronometer reacted very badly in the difficult conditions at sea.
33:39It was impossible for him to obtain reliable calculations,
33:42which would have allowed the ship to determine its position on the nautical charts.
33:47Once in Portugal, however, the clockmaker doesn't give up.
33:51He knows his invention needs some fine tuning.
33:54On the return trip to Portsmouth, Harrison finally calculates the exact position of the ship.
34:11The success of his trip earned him a scholarship of 500 pounds.
34:15Having a longitude method wasn't going to give them the edge over other countries.
34:20They already had that.
34:22It was just quicker, cheaper, more efficient.
34:25So it was an economic thing, really.
34:27It would give them an economic benefit in trade.
34:30Over the next 30 years, Harrison will not stop perfecting his clock.
34:36John Harrison won the Royal Admiralty Award.
35:05But he was followed in Paris by a French clockmaker, Ferdinand Berthoud,
35:10who managed to design his own chronometer.
35:14Thus determining a geographical position on land or at sea is inseparable from the measurement of time.
35:23The more precise this measurement, the more accurate our positioning will be.
35:28But to achieve this level of accuracy, it is still necessary to benefit from a common timescale.
35:34A universal temporal language.
35:36In other words, the same time for all, standard and unified.
35:40In the early 19th century, while the world still lives according to solar time,
35:45the industrial revolution radically changes our perception of time.
35:49With the invention of the railway, engineers will have to overcome a major obstacle.
35:53How to carry travelers on different timescales across countries.
36:01There are church sundials, station clocks, hours of astronomical observatories.
36:06But which schedule will be the standard?
36:11Travelers never stop adjusting their watches.
36:13As for locomotive engineers, despite their hourly indicators,
36:17they are never immune to a delay due to a breakdown or an unforeseen event,
36:21which always leads to more confusion.
36:28In the United States, a passenger crossing the country must reset his watch 75 times.
36:34One day in August 1883, a train left Providence City on the east coast, travelling north.
36:43At the same time, at the other end of the railway line,
36:45a train leaves a station heading south.
36:51The two locomotives are going at full speed on a single track.
36:54The engineers have the same schedules, but do not have the same time on their watch.
37:04In a blind curve, the two trains collide, creating a twisted tragedy of metal.
37:13The toll is terrible, 14 dead and 17 injured.
37:19After numerous accidents of this kind all over the world,
37:23synchronizing railway clocks becomes a priority.
37:26In 1884, after heated exchanges, particularly between France and the United States,
37:41the Washington Conference chose the Greenwich Meridian as a reference
37:45for the creation of a system of time zones.
37:48It is the one we know today.
37:56Paradoxically, it is at this moment that our conception of time,
38:03which passes in an identical way for everyone,
38:05will be radically called into question.
38:11Astrophysicist Pacom Delva is an heir to this revolution in Switzerland
38:16more than 100 years ago by modern physics
38:19when Albert Einstein published his theory of relativity.
38:21It's funny because during that period we were trying to harmonize the same time for everyone,
38:31for France's railway stations and around the world.
38:34Einstein with relativity showed us that absolute rigid time does not exist.
38:40And that's what relativity actually shows us.
38:44That everyone has their own time.
38:46And so it's paradoxical.
38:49Because today we have this illusion that we all have the same time.
38:54But in fact, it's virtual.
38:56It's fabricated.
39:07This cyclist has the impression that the city is passing by her.
39:11But we can just as well say that the motionless spectators in this scene
39:14have the impression that it is the bike that's scrolling by.
39:19These two equivalent perceptions describe the principle of relativity.
39:25Likewise, Albert Einstein declares that this impression of passing time
39:33is explained by our displacement in space-time.
39:36In order to explain the genesis of this innovative theory,
39:43Pacum Delva goes to the places that served as young Einstein's laboratory, in a manner of speaking.
39:49So you have to imagine it's 1905.
39:56Albert Einstein lives just a little below here.
39:59To go to work at the patent office, which is a little further north,
40:02he always passed by here and saw the clock tower.
40:06And so he's confronted with certain questions of time, the nature of time, etc.
40:17In 1905, the public clocks in Bern were electronically coordinated for 15 years already.
40:23Albert Einstein had been studying the patents relating to time synchronization for three years.
40:28And then one day, the young man has a revelation.
40:34Absolute simultaneity does not exist.
40:38Two simultaneous events for one observer are not necessarily the same for another observer.
40:47Those who preceded us and those who preceded Albert Einstein have all contributed elements.
40:53And for me, it's really a common work where sometimes a genius like Einstein will come to add a touch,
41:01and he'll succeed with the synthesis of various theories of his era.
41:06And he makes a leap in understanding.
41:11While other people cling to older ideas, staying in tradition, they can't make that conceptual leap.
41:17But Einstein manages to do it, like Kepler did before him, like Galileo and other greats.
41:27They managed to create something new.
41:31Like Galileo, who describes that all bodies fall at the same speed in a vacuum, whatever their mass.
41:35Physics sometimes progresses against common sense.
41:48Einstein's theory of relativity is no exception to this rule.
41:53Albert Einstein made many thought experiments.
42:00We can also do a thought experiment, like Einstein.
42:04Suppose I ask a friend to come with me to Bern.
42:08We take the train in Paris, but we don't take the same train.
42:11I'll take a high-speed train, which will arrive and burn fairly quickly, as quickly as possible.
42:20My friend takes a much slower train, it will arrive later.
42:24In Paris, we take two very precise watches, like those we make today with atomic clocks, and we synchronize them.
42:33We put the same time on each watch in Paris before leaving.
42:38I arrive much faster than him in Bern, and once in Bern, I wait for him.
42:44I wait for his train, which goes much slower.
42:48And once it arrives, we compare our watches.
42:52Well, the time that elapsed between these two events,
42:56the departure from Paris when I synchronized my watch with my friend,
42:59and the arrival of my friend in Bern, when we re-compared our watches,
43:05between these two events, we don't have the same durations,
43:09because our two trains did not go at the same speed.
43:12The difference on the watches will be a fraction of a nanosecond.
43:20With Einstein, it's the end of the great universal beat, translated by the ticking of clocks.
43:25Physicists will gradually take the reins to impose a conventional and purely manufactured time with full knowledge.
43:44In a world launched headlong into the quest for even greater precision,
43:49physicists in Einstein's wake will soon rethink our machines to manufacture time.
43:53At the Paris Observatory, you can still contemplate the mechanical instruments that revolutionized their time.
44:11Protected under their glass bells, here are the ancestors of our quartz clocks.
44:15From the 1930s, we will have extremely precise clocks.
44:19An astronomer who worked here, Nicholas Stoico, will notice that there is a drift between the moment of a star's passage to the meridian and the time given by the clock.
44:32These are very precise pendulum clocks, and compared to the time given by the quartz clock at the Berlin Observatory, we will find that the Earth seems to slow down in spring and accelerate in autumn.
44:44And he comes to understand that this slowing down and acceleration of the Earth's rotation is due to the trade winds.
44:54And so it dealt a fatal blow at the end of the 1950s to the standard of time.
44:59From now on, astronomers will lose time management to the benefit of physicists.
45:06By searching for what is most regular in nature, the movement of an electron in an atom, scientists invent the error of the measurement of atomic time.
45:21It is in one of these ancient astronomical domes that one of the most secret laboratories of the Paris Observatory is hidden.
45:41Astrophysicist Pacom Delva and his team monitor the proper functioning of one of the five atomic fountains in France.
45:51This type of clock, which produces our official universal time, is based on the vibration of the cesium atom.
46:10That's the cesium cell, with one gram of cesium.
46:14From this atom, we will define what is one second.
46:21When an atom is bombarded with energy, it vibrates.
46:24When an atom is bombarded with energy, it vibrates.
46:34It emits more than 9 billion magnetic pulses per second.
46:38Each time one arrives at the precise number of 9,192,631,770 beats, one second has elapsed.
46:52So, the seconds follow each other in an infinite manner.
46:55When we say that this clock is exact, it means that we can certify that the frequency we get today will be the same as next year, or in 10 years, or in 100 years.
47:10Today, the Paris Observatory is not only responsible for creating French legal time. Its mission is also to distribute it.
47:24This takes place in an ultra-protected room, where scientists watch over our time 24 hours a day.
47:34At the fourth signal, it will be 21 hours and 51 minutes.
47:40Here, we are in the National Time Reference Room, where French legal time is made from the signals of the clocks in the laboratory.
48:00We are going to synthesize French legal time with all these machines.
48:07Then we compare this legal time to other times in other countries.
48:12And from all these times, we will synthesize a global time, which is called UTC.
48:19And from this UTC, which will be referenced in Greenwich, we will add a certain number of hours, depending on the time zone where we are.
48:26When a second passes here on this clock, it's the same second at the same time which passes in the United States, Japan, China, Russia, etc.
48:37Even a very precise clock is not enough to establish a reference time.
48:55Even a very precise clock is not enough to establish a reference time.
49:03This is why this time broadcasting room is linked with other clocks located abroad or in space on board a satellite.
49:10These two antennas here send an electromagnetic signal into space, towards a geostationary satellite, meaning it remains fixed in the sky.
49:27And from these comparisons, we are going to create a common time that will be the same for everyone, on all continents, in all countries.
49:34Once it was on board ships. Nowadays, clocks navigate in space.
49:42The acceleration of time that we sometimes feel is thus the consequence of a fabrication of the same hour for all.
50:04A conventional, synchronized, and increasingly precise time.
50:11This time made by ultra-powerful computers has even become the key for all the applications in a digital world.
50:20Whether it's our satellite-guided trips, our telecommunications, which use even more data on synchronized networks,
50:32or our banking transactions, for which every millisecond is worth millions.
50:37Our interconnected world is now based on clocks that measure times even more precisely.
50:43With enormous industrial and economic challenges as a result.
50:50We have become dependent, even slaves, to these new temporal norms.
51:00Veritas filia temporis, the truth, daughter of time.
51:03To understand today's astronomy, today's challenges, you have to go back to the past.
51:07It's astonishing that at the time of the atomic clock and GPS, we can never forget that we are heirs to all these astronomers,
51:15and that our current division of time stems from human observations and from mathematical theories.
51:21Understanding ancient times helps shed light on today's science and modern astronomy.
51:26From now on, and with every passing second, we remember the geniuses who try to unravel one of the greatest mysteries of our existence.
51:40Einstein, Huygens, Galileo, Fusiris, or even Tejibius, they all in their own way shape the temporal language that brings us together today.
51:50To be continued...
51:51To be continued...
52:20To be continued...
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