Fascinating Truths About Our Universe | Cosmic Vistas Season 5 Compilation | Spark

[Music] [Music] thank you high above a rust-colored planet an alien spacecraft prepares for landing it has traveled for nearly nine months hurtling through more than half a billion kilometers of interplanetary space now as it plunges toward Mars the robot visitor sheds its protective cocoon just 20 meters from the surface it hovers then carefully lowers itself on a specially designed points for 16 seconds the robot's fate hangs by a nylon thread its Mission has begun a mission in the name of curiosity [Music] I was looking for a nickname for its 2012 Mars Rover it could hardly have chosen a better one than curiosity eight years before its two predecessors spirit and opportunity had proved that roving Vehicles could revolutionize our understanding of the red planet Curiosity Rover technology had Advanced and scientists were in the driver's seat [Music] scientists were by enemy an ambitious goal missions had shown that in the distant past Mars had standing water on its surface [Music] now curiosity would go one step further and try to determine if Mars could once have supported life [Music] that's a more challenging question to answer and researchers needed a bigger Rover to answer it at 900 kilos curiosity is the size of a small car allowing it to carry 15 times more scientific Hardware than previous Rovers it's the most sophisticated Suite of instruments ever to land on another planet and for the Mars program it's a big shift in approach earlier Rovers were designed to be like wandering geologists traveling over the landscape of Mars with a tool kit similar to one that a human astronaut might carry by comparison curiosity is an entire laboratory on wheels equipment includes a laser capable of zapping rocks up to six meters away in order to read their chemical composition and its two meter long robot arm carries a camera and a spectrometer for examining the surface up close as well as a drill for extracting Rock samples that can be tested by various experiments inside the Rover [Music] this is a planetary Explorer like no other [Music] and so is the place it's set out to explore [Music] in planning curiosity's Mission scientists spent years combing through satellite images looking for a landing site that might offer signs of a habitable past on Mars the search Led them here to Gale crater its 150 kilometers across with a five and a half kilometer high mountain rising from its Center like most craters on Mars it Formed billions of years ago destroyed collided with the planet's surface the force of the impact blasted a giant hole in the Martian bedrock a crater on Mars is easy to understand but a mountain inside a crater is much harder to explain how could such a towering feature have grown out of a deep basin scientists now suspect the answer is that the mountain didn't grow at all rather it was left behind as other material was removed here is that sometime after Gale crater formed it was blanketed with Dusty sediment eventually layer upon layer of sediment filled the crater to the brim and Beyond later wind chiseled that sediment away it scoured out the crater walls but left a large mound in the middle the mound's official name is aeolus mons but NASA's scientists have dubbed it Mount sharp after Robert sharp a pioneer of planetary geology Mount sharp is what brings curiosity to Gale crater scientists hope that by climbing its Rocky flanks the Rover will be able to read millions of years worth of geologic history laid down one layer at a time of those layers are plainly visible from orbiting satellites the lowest layers are the oldest they're of special interest because the data suggests they're made of clay which means they were likely deposited by water long ago moving further up the mountain other layers May reveal how those watery conditions changed over time the upper reaches of the mountain appear to be made up of material that was deposited by wind once the planet became dry and Dusty from top to bottom the mountain seems to present the complete story of Mars foreign as soon as curiosity landed scientists were thrilled not only had the Rover touched down safely Mount sharp was in plain sight it towered on the horizon in one of curiosity's first pictures from the surface but the mountain was eight kilometers away and scientists knew it would take the Rover more than a year to get there for the long Trek began they decided to explore curiosity's immediate surroundings it was to be the first test of their new laboratory on Mars but little did they know just how much that test would reveal when curiosity set down on the floor of Gale crater it became the seventh spacecraft to land successfully on Mars but more than any of its predecessors curiosity was built to Journey far beyond its Landing site the Rover's main objective was to reach Mount sharp and study its layered geology those layers could already be seen in the distance on the Mountain's lower slopes in that direction curiosity had a chance to visit other points of interest closer to hand [Music] just a few steps from where curiosity stood scientists could see where the Rover's descent stage had blasted away loose dust and gravel the exposed patches showed that the soil was only a few centimeters deep in this part of the crater below it lay what looked to scientists like a type of conglomerate rock a rock made up of smaller pieces cemented together this was intriguing but curiosity did not Venture any closer in part to avoid contamination from any lingering traces of Rocket exhaust instead scientists now had a different idea not far from where curiosity landed satellite images showed where a river had once spilled into the crater the riverbed ended in a fan-shaped deposit left behind by water spreading sediments out over the crater floor it was always the plan to try to land near this feature and now curiosity was right on the edge of it by using the satellite imagery as a guide scientists could see that just a few hundred meters from The Landing site lay a point where the river deposit intersected with an older Terrain this looked like a promising spot to learn more about the ancient history of the crater floor even though going there would mean driving away from Mount sharp for a Time in the end The Detour would take far longer than scientists expected but it would eventually lead to a big discovery as curiosity began moving over the landscape it came across clues that pointed to an intriguing past that Gail created there were more examples of the conglomerate rock that had been exposed at the Landing site this time jutting out of the ground like pieces of broken sidewalk and when the Rover zoomed in for a closer look it found Pebbles that looked rounded as though by water [Music] this is typical of what is found in ancient stream bands on Earth [Music] already the geologic story emerging from Gale crater looked like an exciting one but filling in the details would take time carefully gathered data scientists were striving to understand if Mars could have supported life long ago but given the Rover's capabilities there was also a more immediate question could there be something alive on Mars right now and there was a chance that Curiosity might provide the answer by plucking it out of thin air for 10 years scientists had been tantalized by reports of Trace Amounts of methane in the Martian atmosphere the reports were mainly based on observations made from Earth but the presence of methane was also indirectly confirmed by Mars Express an orbiting spacecraft run by the European Space Agency the earth-based observations show that the methane seemed to be concentrated around particular features on the Martian surface like these giant gashes called nearly Fosse where spacecraft have also found signs of carbon-bearing minerals [Music] if correct this was a major find on Earth methane gas is produced by living things it's a Tell-Tale sign of biological activity [Music] methane gas can also be produced chemically but that requires the right kind of minerals along with water and plenty of heat either way methane would mean that Mars was not a dead world but a geologically and possibly biologically active one somewhere below the surface now curiosity was in a position to weigh in on Martian methane unlike earlier Rovers it had the technology to directly measure the chemical composition of the atmosphere [Music] over an eight-month period that's exactly what the Rover did the result was a surprise the Rover found no significant amounts of methane on Mars either the methane reported earlier had completely vanished through some unknown process or because of a misreading of data those earlier reports were wrong this is not the first time Mars has given scientists contradictory evidence related to alien life but with the methane question out of the way at least for now curiosity still had plenty to do and its exploration of the red planet was about to take an exciting turn at a spot called Yellowknife Bay more than two months into its Mission at Gale crater NASA's curiosity of Rover stopped to capture a breathtaking panorama the result is this mind-blowing 1.3 billion pixel image it's the most detailed picture ever taken from the surface of Mars [Music] by this point the Rover had driven about 400 meters not a great distance but a journey with many stops that allowed scientists to gather data about the geologic history of this unusual site to the right lay the rising slopes of Mount sharp the Rover's ultimate destination but straight ahead scientists could now see a dramatic change in scenery here the Gravelly terrain that the Rover had been traveling on since it landed ended abruptly up ahead lay a more complex looking surface with different layers of rock exposed in the form of assorted steps and slabs scientists were Keen to explore this location which they called Yellowknife Bay the name is a tribute to the capital of the Northwest Territories frequent jumping off point for geologic Expeditions in Canada's North by now they'd had a chance to zap a rock with the Rover's onboard laser and scoop up some soil for analysis but neither The Rock nor the soil could tell them much about Gale crater that's because the rock had been blasted there by a meteorite impact while the soil had been carried in on the Wind so to understand the hidden history of the crater curiosity needed some local Bedrock to drill into it began by sidling up to this intriguing outcrop made up of thin layers of sedimentary rock some of the layers were at different angles suggesting The Rock was made from sediments deposited by flowing water along an undulating stream bed after a close inspection of this outcrop curiosity worked its way down slope to find an underlying layer of sandstone and beneath that the Rover found still another layer this one was mudstone a type of rock made of fine silt or clay that was deposited long ago perhaps at the bottom of an ancient Lake The Rock was veins of that were deposited by water flowing through cracks and in some places curiosity could see sphericals little round balls of minerals that precipitated out of water here were signs not only of rock that formed in water but that had been exposed to water at different times in its history and here at last was a place where curiosity could drill down to find out more fully scouting the terrain scientists chose a rock they named John Klein after a deputy project manager with the rover mission who died in 2011. using its robotic arm curiosity reached down and swiveled its drill into position the drill punched a small hole into the Rock producing a tablespoon's worth of fine powder which the arm delivered to the Rover's onboard experiments for analysis unlike most of the Martian surface the powder was gray rather than red in color that meant the minerals inside the rock had been sealed off from the atmosphere for billions of years here was a rock that offered a direct Connection to the Past in March 2013 seven months after curiosity arrived on Mars scientists were ready to share their results a detailed analysis showed that the minerals in the Rock had formed in water that was much like fresh water on Earth non-acidic and not very salty furthermore there were chemicals in the rock that the right kind of microbes can use to drive metabolism curiosity had found the key ingredients that could have allowed life to flourish when there was water in Gale crater [Music] mission accomplished while it's still not known if Mars ever harbored life scientists can now say life was at least possible there billions of years ago thank you with the discovery came the news that the Rover's Mission had changed having answered its original question curiosity would now try to find out where and how to search for signs of past life on Mars by the summer of 2013 the mission reached a major turning point after making several more follow-up measurements scientists said goodbye to Yellowknife Bay forever and put the Rover on course for Mount Sharp the first phase of the mission was over and there were new discoveries ahead but before it left curiosity provided its own glimpse of Life on Mars by using its robot arm to take this striking self-portrait at John Klein Rock [Music] it may be a long time yet before we know if there ever really was life on Mars but we know that curiosity is there and that's a terrific start [Music] [Music] [Music] yes [Music] for our prehistoric ancestors recognizing patterns was a key to survival as they made their way in the world they saw patterns in the landscape patterns in the weather patterns in the behavior of birds and animals and when they looked up at the night sky they saw patterns too [Music] what they found is that the Stars aren't spread evenly across the sky many of the brightest stars seem to be grouped in a way that naturally draws the eye and as Earth turns these Stars seem to move together reinforcing the impression that they are related [Music] by playing connect the dots with these groups of stars ancient people transform them into pictures often of mythical creatures and characters from great Legends [Music] we know them as the constellations [Music] the constellations are still with us today and they're a reminder of our ancestors enduring fascination with the Stars but there can be even more to these ancient star pictures than meets the eye sometimes Stars we see together in the sky really are related a case in point is one of the most familiar star patterns of them all the Big Dipper the name reflects the way these Seven Stars are arranged in the sky together they resemble the outline of a pot with a handle there are other ways of seeing it though in some folk Traditions it's not the Dipper but the wagon or the plow and for the ancient Greeks and Romans it was The Great Bear Ursa Major in Latin the official name astronomers still use for this constellation to Modern Eyes turning these Stars into the image of a bear seems a bit of a stretch [Music] the bear is usually portrayed with the handle of the Big Dipper as its long tail even though real bears don't have long tails but the bear connection makes more sense when we consider that the ancient Greeks called this constellation arctos a name that gives us the word Arctic foreign major may be our link to a much older tradition of bear Legends one that stretches back to the end of the last ice age when the inhabitants of Europe and Asia were Nomads wandering in a great northern wilderness perhaps they were the ones who first connected the most powerful animal in their world to the most prominent star pattern in their sky so it seems fitting that in more recent times astronomers have learned that the stars of The Big Dipper are themselves a Wandering band of Stellar nomads became clear in 1869 when British astronomer Richard Proctor noticed that five out of the seven main stars in the Dipper are all moving through space at the same speed in the same direction like airplanes flying in formation Proctor had discovered what we now call the Ursa Major Association foreign half a billion years ago these stars formed together in a cloud of gas and dust today we can find the same kind of raw material adrift in other regions of our galaxy one of the nearest is called the Taurus molecular cloud in this gorgeous view from the European Southern Observatory we can see sections of the cloud wafting across the starry background [Music] over time gravity can concentrate dark clouds like this turning them into clusters of brilliant young Stars but even though they are siblings such stars are unlikely to stay together forever and star clusters tend to spread apart as they drift through the Galaxy and that means the Ursa Major group may be a lot bigger than it seems extending well beyond the five Big Dipper stars that Proctor once connected even serious the brightest star in the night sky was once thought to be a member of this group more recent data now suggest it's too young to have formed along with the Ursa Major Association in 2003 a detailed survey Based on data from the hipparchos satellite found that 59 stars are likely members these stars are scattered across 30 light years of space with the center of the group located about 80 light years from our solar system in Galactic terms this is remarkably close it's purely by chance that our existence happens to coincide with the moment when Earth is on the outskirts of this passing system millions of years from now those Stars will have moved on and the Big Dipper will be no more but astronomers have discovered that Ursa Major is not the only constellation with a hidden connection among its Stars [Music] throughout history when adventurers and Traders headed east or west to distant lands they knew they were bringing their constellations with them as Earth turns places on the globe that are at similar latitudes like Europe Asia and North America will see the same Stars those who travel South experience something very different Earth doesn't turn north to south so there are stars and constellations that can never be seen from northern latitudes it's here in the South that we find Centaurus it's a sprawling constellation that the ancient Greeks pictured as a spear-wielding centaur the imaginary creature that is half man half horse like Ursa Major The Great Bear the outline of the Centaur may not seem obvious to Modern Eyes but there's no mistaking the two brightest stars in this constellation known as Alpha and beta Centauri together they point to another group of four stars which the Ancients also imagined as part of the centaur today we identify this group as a separate constellation and it's one of the most famous the Southern Cross whether it's one constellation or two the combination of the Southern Cross with Alpha and beta Centauri forms the dominant star pattern of the southern hemisphere but how did the ancient Greek astronomers know about these Stars which can't even be seen from Greece the answer is precession [Music] change in the direction of Earth's axis as our planet slowly swivels around like a big gyroscope in space because of procession the stars of Centaurus and the Southern Cross have shifted over the centuries once long ago they were visible from Europe now they've become for the South what the Big Dipper is in the North stars in Centaurus and the Southern Cross are moving through space with a similar speed and direction but this Association is far younger than the Ursa Major group and it contains stars that are much brighter many are blue giant Stars thousands of times more luminous than our sun blue stars burn out quickly the hottest ones only last a few million years a tiny fraction of our Sun's age as they use up their fuel blue stars eventually expand and change into red supergiants this has already happened to the brightest member of the group The brilliant red star Antares Antares is part of Scorpius a different constellation but its motion connects it to the stars of the Centaur and the cross collectively they are the Scorpius Centaurus Association the ultimate fate of these bright stars is to die in spectacular fashion [Music] as each one runs short of fuel its core will collapse triggering a supernova a violent Stellar explosion that rips the star apart the explosion produces a blast of energized gas that spreads out into the surrounding space for hundreds of light years this too has already happened in the Scorpius Centaurus Association [Music] the entire group including most of the stars of the Southern Cross sit inside a bubble about 400 light years across astronomers suspect the bubble was formed by one or more of the association's stars going Supernova during the past 15 million years [Music] the bubble can't be seen with an ordinary telescope but in this map of the Milky Way in radio waves part of it shows up as a giant Loop in the foreground astronomers call it Loop one our own solar system lies just outside Loop one in another smaller bubble this local bubble may also have been caused by one or more supernovas perhaps when the Scorpius Centaurus Association was closer to Earth than it is now this idea was strengthened in 2004 when researchers discovered a rare isotope called iron 60 in sediment deposited at the bottom of the Pacific Ocean iron 60 is produced in Supernova explosions this suggests that sometime in the last 3 million years Earth was in close proximity to a supernova such an event may have had serious consequences for life one group of researchers has even speculated that a major Extinction of corals and other marine life about two and a half million years ago was caused by a supernova blasting Earth's atmosphere with radiation temporarily destroying the ozone layer so far this idea remains speculative and there are reasons to be skeptical astronomers have calculated that a supernova would have to be within 26 light years of Earth to cause such severe damage to our planet while that's not impossible a supernova going off so close to us so recently would be quite a coincidence what we do know is that our planet did change at that time some creatures dying out and some new groups appearing including the first members of our own genus homo [Music] whether our pre-human ancestors Were Somehow affected by a nearby Supernova remains an open question but when we look to Centaurus and the Southern Cross we're reminded that hidden connections between the Stars May sometimes include us winter in the northern hemisphere is the time when many of the brightest stars can be seen High overhead among them are Castor and Pollux these Stars almost identical in brightness are the Gemini twins they're part of a constellation that depicts two brothers in the heavens but these stars are not related at just 34 light years from Earth Pollux is both closer and older than caster which is 50 light years away they are siblings in name only it's the same story with another well-known winter constellation Cassiopeia named after a mythical Queen the five brightest stars in Cassiopeia form a w pattern that's easy to spot in the northern sky but in this case the grouping is pure coincidence the stars in The W are spread out along a line of sight that ranges from about 50 to over 500 light years away they too are not related nevertheless most stars must have relatives somewhere because Stars tend to form in clusters within vast clouds of dust and gas [Music] if we look towards the stars of the Southern Cross we can see a recent example near The Cross but six thousand light years further away lies one of the greatest treasures of the Southern sky in the 19th century astronomer John Herschel called this the jewel box star cluster with its concentration of hot blue stars and bright red giants the cluster reminded Herschel of a casket full of precious stones today astronomers estimate the cluster contains about 100 stars that formed around 12 million years ago as the cluster ages the brightest stars will quickly exhaust their fuel and burn out in some cases going Supernova like the stars of the Scorpius Centaurus Association [Music] those stars that remain will continue to travel together like the Ursa Major group but over billions of years they're destined to drift apart and lose each other Among the Stars of the Milky Way our own son is one such star now four and a half billion years old it too must have relatives somewhere out there in the galaxy some of those sibling Stars could have planets and even life since life here is based on the chemical ingredients that went into forming the sun it would be fascinating to see what happened to the same ingredients elsewhere but could we find the sun's long-lost relatives are they hidden somewhere Among The Familiar constellations one approach to answering these questions is to look at the nearest stars and see if any have strong similarities to our sun here's star of all is Alpha Centauri although it appears to the eye as a single point of light Alpha Centauri is actually a multiple system made up of three stars in orbit around each other the smallest is a red dwarf star known as Proxima Centauri because it's also the closest of the three the entire system is only 4.3 light years from us that's still thousands of times further than the most distant planet in our solar system but for a star it's very very close in fact it's so close that Alpha Centauri can't be a member of the Scorpius Centaurus Association it just happens to be in the foreground when we look toward those Stars similarly someone living on a planet in the Alpha Centauri system would see our sun as part of the constellation Cassiopeia giving the W an extra zigzag but even if such a planet exists we already know that any creatures living there cannot be our Galactic cousins [Music] the Alpha Centauri system is older than the Sun and it's moving on its own separate course after its closest approach about 27 000 years from now the system will gradually start to pull away from us and it will eventually Fade Into The Starry background meanwhile the search for our son's true siblings continues in 2013 astronomers conducted a careful study of 30 Stars known to have ages compositions and motions similar to the Sun after a close examination only one of the 30 qualified as a possible true sibling to the son it lies just over 100 light years away in the constellation Hercules it doesn't have a name just a catalog number hd162826 but this one candidate sibling could soon be joined by others in December 2013 Europe launched the Gaia mission it's a space telescope that will help construct a 3D catalog of nearly a billion stars roughly one percent of the Milky Way's total Stellar population as never before Gaia will reveal precisely where all the stars are around us and show us how they're moving in doing so it will reveal which stars are truly associated with one another including those that might have a connection to our son [Music] long ago our ancestors looked for patterns in the stars and they invented the constellations groups of stars that have a story to tell now Gaia is giving us a more sophisticated way of observing the stars but we're still looking for patterns [Music] what we find will reveal revealing unseen relationships Among the Stars around us and give us a new set of stories it may even give us a story that includes us [Music] story of a great family of stars that formed together in a cloud spread out into the Galaxy and along the way brought the Galaxy to life [Music] [Music] foreign [Music] not so long ago astronomers thought they were getting close to understanding what the universe is made of foreign first there's matter which makes up the stars and galaxies that light up our night sky then there's dark matter it's thought to be an unidentified type of particle that gives off no light but we know it exists because of its gravitational pull only recently have astronomers discovered that there's a third presence in our universe and it's not any type of matter at all it's a mysterious phenomenon that could literally be caused by empty space all dark energy and its growing influence in the universe is so important it will dictate the ultimate fate of everything else the only trouble is cosmologists aren't sure what dark energy is finding out has become one of the greatest scientific quests of our time [Music] foreign the seeds of the quest were planted nearly a century ago that's when astronomers first became aware that the tiny blobs and swirls of light they could see in their telescopes were galaxies galaxies are vast systems of stars like our own Milky Way But far off in the cosmic distance here the Hubble Space Telescope peers across the edge of the Milky Way toward the constellation Centaurus to reveal the spiral galaxy M83 compared to other galaxies M83 is a close neighbor to the Milky Way just 15 million light years away but this entire system is rapidly moving away from us at the rate of over 500 kilometers every second much farther off in space there are countless more galaxies that are doing the same thing here the Hummel telescope explores a giant elliptical galaxy surrounded by a swarm of smaller Neighbors this cluster of galaxies is more than 30 times farther away from us than M83 and it's receding at more than 10 000 kilometers per second no matter where we look in the universe astronomers have found that the farther a galaxy is from us the faster it's moving away in the 1920s it was astronomer Edwin Hubble who first grasped the meaning of this relationship Hubble realized that all the galaxies must be spreading apart from each other which makes more distant galaxies appear to recede more quickly the discovery led to a mind-blowing conclusion our universe is not static but expanding outward in all directions and as space expands it's taking the galaxies with it [Music] an expanding universe is a strange idea to come to grips with but it makes sense if the universe were static gravity would have pulled all the galaxies together by now the expansion explains why this hasn't happened but it also leads to another powerful conclusion because space is growing it must have been smaller in the past at some point the entire universe we can see today was confined in a volume of space smaller than an atom so much matter and energy contained in such a tiny region is unimaginable but it's this situation that led to the Big Bang the fiery birth of the universe having discovered the Big Bang astronomers realized they could determine when it happened simply by measuring the rate at which the galaxies are flying apart and then working backwards to measure the expansion astronomers need to look at several galaxies and compare two things distance and speed it is the easy part when objects are moving the light they give off shifts in frequency in direct proportion to speed this is called the Doppler effect here on Earth it's used to measure the velocity of approaching storms and it's the principle behind police radar measuring the distance to a Galaxy is a much tougher problem and for most of the 20th century doing it with accuracy was beyond the ability of even the biggest telescopes that would change when the Hubble Space Telescope was launched [Music] off giving astronomers a new and better view of the galaxies but what they didn't know then is that it would also provide the first clue to the existence of dark energy [Music] by the 1990s astronomers knew the Hubble Space Telescope was their key to measuring the age of the universe freed from the distorting effects of Earth's atmosphere the Hubble had the power to peer into nearby galaxies and for the first time see individual Stars within those galaxies [Music] but astronomers weren't just looking for stars in general they were hoping to spot cepheid variables cephian variables are extremely useful because they pulse with a regular cycle and the brighter they Shine the slower they pulse so just by timing a cepheid's pulsations astronomers can tell how much light it's giving off and therefore how far away it must be starting in 1993 a team of astronomers used the Hubble to hunt for cepheid variables hidden in nearby galaxies and they found plenty the cepheids gave them a way to measure the distance to each Galaxy Meanwhile by using the Doppler shift astronomers could directly measure how fast those same galaxies are receding from us as the universe expands the final step is just arithmetic for each Galaxy the speed divided by the distance is the expansion rate of the universe foreign the more galaxies are measured the more confident the result and by knowing how fast the universe is expanding astronomers could then work out when it all began [Music] it was one of the Hubble's most important results but when the answer began to emerge in 1994 astronomers were puzzled their calculations showed that the Universe was less than 12 billion years old that was younger than earlier estimates and it didn't match well with some other evidence evidence that included white dwarf stars tiny Stellar relics no bigger than Earth that are left over when stars like our sun burn themselves out [Music] the oldest white dwarf stars can be found inside globular clusters these are vast spherical swarms of stars that date back to the formation of our galaxy because white dwarf stars cool as time passes astronomers can look for the coolest dimmest white dwarfs in a cluster and use them to measure the cluster's age [Music] but here's the problem the oldest white dwarfs seem to be more than 12 billion years old that would make them older than the universe which doesn't make sense somehow somewhere astronomers were missing a key piece of information [Music] in 1998 the missing piece finally turned up and it changed everything it involved another way of measuring the distances to the galaxies this method is based on a particular type of exploding star which can be seen from a much greater distance than a cepheid variable the explosion involves two stars in orbit around each other one is a tiny white dwarf the other a massive red giant scenario Hot Gas escaping from the Giant star is pulled by gravity onto the white dwarf companion eventually so much matter Falls onto the white dwarf that it becomes unstable this triggers a thermonuclear explosion and the white dwarf goes supernova crucial for astronomers is that the trigger point for the explosion is always the same and so supernovas of this type always shine at about the same Peak brightness and just as with cepheid variables knowing the true brightness of something means knowing its distance but supernovas can be spotted in galaxies that are even farther away and their light is reaching us from a more remote time in the past so by measuring the distance to these far-off supernovas and their host galaxies astronomers could check to see if the expansion of the universe has changed over time they were expecting to find the expansion gradually slowing down that's because the gravity of all the matter and dark matter in the universe acts like a brake pedal on Cosmic expansion the more matter the more gravity and the more gravity the harder it is for things to fly apart but remarkably they found the opposite the expansion of the universe appears to be speeding up this surprise Discovery explains the contradiction over the age of the universe if space is expanding at a faster rate now than in the past then it must have taken longer for the universe to reach its current size that would make the age of the universe greater than 12 billion years the latest estimate puts it at 13.8 billion years old which is older than any known star but if the universe is accelerating what's causing it [Music] just like dark matter there was no way to observe this new phenomenon directly so cosmologists called it dark energy [Music] of observations suit and firmed and strengthened the case for dark energy and by 2011 three astronomers involved in the initial find saw Pearl mutter Brian Schmidt and Adam Reese were awarded the Nobel Prize with the discovery of dark energy the universe had become a more interesting and more mysterious place now it was up to cosmologists to understand what an accelerating universe meant for their theories for us [Music] in 2001 cosmologists were given a new way to see dark Energy's role in the universe it was wmet an orbiting spacecraft designed to map The Cosmic microwave background the background is a form of Relic light that was emitted a few hundred thousand years after the big bang when the universe was still white hot [Music] because of the Doppler shift this signal is no longer visible to the eye but it can be detected in the microwave part of the spectrum one of the Signal's key features is that it contains tiny fluctuations that wmap saw as Speckles across the microwave sky this turned out to be incredibly handy for cosmologists because the average size of those Speckles is related to the total amount of matter and energy in the universe the data reveal that total is far greater than all the galaxies combined [Music] all the matter we can see only adds up to a five percent slice of the cosmic pie but the galaxies are embedded within vast concentrations of dark matter that add up to much more foreign Dark Matter contributes another 27 percent to the Pine that still leaves more than two-thirds of the contents of the universe unaccounted for it's this missing share that cosmologists now say is taken up by dark energy the mysterious entity that is causing the expansion of the universe to speed up but to understand what this really means for the universe we need to know what dark energy is foreign has already been around for about a century it's called the cosmological constant it's a mathematical term that Albert Einstein added to his theory of general relativity in order to counterbalance gravity Einstein used it to explain why all the matter in the universe hadn't converged in one place but once astronomers discovered the universe was expanding Einstein realized he didn't need the cosmological constant after all he even called it his biggest blunder cosmology was back the idea is that space has its own built-in energy and that this energy has a repulsive effect as the universe expands more space leads to more repulsion so the expansion speeds up like a runaway train so far the observations agree with this idea but there are other theories too for example it could be that dark energy is the result of a previously undiscovered force of nature if so its influence might gradually weaken over time or there could be a more chilling possibility rather than a constant the acceleration of the universe could itself be accelerating in that case it will eventually overtake all other forces pulling apart individual galaxies stars and finally atoms cosmologists call this scenario the Big Rip English between these possibilities a u.s-led team of scientists has launched the dark energy survey this project uses a special camera installed on a telescope in Chile that can look for evidence of dark energy in a number of ways one of the ways involves probing the large-scale structure of the universe [Music] this structure looks like a cosmic spider web with all the galaxies concentrated in enormous strands that separate empty voids millions of light years across if measured carefully the regular spacing of these strands can be used like a giant ruler to measure how the expansion of space has changed over time the dark energy survey began in late 2013. to help pin down Dark Energy scientists hope to measure as many as 300 million galaxies over a five-year period meanwhile in Canada astronomers have realized that they can do with radio waves with the dark energy camera does with light their project involves a series of trough-like radio antennas each one a hundred meters long the troughs are used to map the distribution of distant clouds of Intergalactic hydrogen which pass overhead as the Earth turns the advantage of this method is that the hydrogen clouds are easier to detect than individual galaxies so astronomers can use them to peer back to earlier times in Cosmic history when it might be easier to distinguish between rival theories of dark energy looking further ahead the European space agency has proposed a Space Telescope named Euclid that is specially designed for the task of measuring Dark Energy it could launch as early as 2020. says pursuing a dark energy telescope of its own called W first currently set to launch in 2024. years ago no one knew Dark Energy existed now understanding it has become our Cosmic priority and there's something very appropriate about that foreign billions of years ago any civilizations that were around may not have discovered Dark Energy because the acceleration of the universe was still too small to notice at that time and trillions of years from now future civilizations won't see it either by then space will be growing so fast that light from the cosmic background along with most of the galaxies won't be able to cross it as those galaxies disappear over the cosmic Horizon they'll take the evidence for Dark Energy along with them [Music] perhaps the greatest revelation of all not only is there much more to understand about the universe than astronomers once thought it appears that that understanding is a limited time offer [Music] [Music] foreign [Music] on a day that begins like any other Dawn breaks and the sun climbs up into the Eastern sky but as its Rays illuminate the world no one senses that a strange transformation is about to begin gradually a slight indentation appears in the great Round Disc of the Sun minute by minute it grows until after an hour more than half the sun has disappeared now the day has become noticeably less bright and shadows are getting Sharper as the sun Narrows to a slender Crescent birds become agitated can by what seems like night arriving far too soon then Darkness descends and up above there's a strange almost magical spectacle in place of the sun it looks like a perfectly round black hole has been punched in the sky all around it there's a ghostly white aura the world is captivated by the Ethereal beauty of a total eclipse of the Sun [Music] we can only imagine how our prehistoric ancestors might have reacted to this incredible natural phenomenon especially if It Came Upon them without warning to them a total eclipse might have seemed like the end of the world or perhaps aside from the gods as impressive as an eclipse can be even more impressive is the fact that ancient people came to understand what causes them and even how to predict them foreign the key is realizing that eclipses involve both the Sun and the Moon a solar eclipse occurs when the moon passes in front of the sun casting its shadow on Earth's surface and when the moon moves to the opposite side of its orbit so that it travels through Earth's Shadow the result is a lunar eclipse [Music] but knowing exactly when an eclipse will take place is a bit more challenging foreign although the moon circles around earth once a month eclipses are far less common [Music] because a slight tilt in the moon's orbit means that most of the time the Shadows cast by the Moon and the Earth don't line up in quite the right way in any given year only four or five eclipses are possible usually in pairs one lunar and one solar some of these eclipses are partial which means that only part of the sun is blocked or only part of the moon is shadowed if not expected such eclipses can easily pass unnoticed other eclipses happen when the weather is overcast or they may appear in remote corners of the world such as the high Arctic or Antarctica where few people are watching when all of these variables are factored in it means very few people see more than a handful of eclipses over the course of a lifetime foreign of these most will be lunar eclipses simply because when a lunar eclipse is underway it can be seen anywhere that the Moon is visible roughly half the world at any given time so that our prehistoric ancestors almost certainly knew that eclipses can happen but it wasn't until ancient skywatchers started keeping careful records over many generations that a longer term pattern in eclipses began to emerge [Music] that pattern is called the Saros cycle and it was first discovered sometime after 750 BC by astronomers who lived in Mesopotamia modern-day Iraq they were among the first to notice that lunar eclipses with very similar characteristics seem to repeat every 6585 days that's just over 18 years a period known as one seraphs solar eclipses follow this pattern too but it was harder for ancient people to detect this because solar eclipses in the same 18-year series happen in different parts of the world [Music] here for example is a spectacular image of a total eclipse of the sun observed in Mexico in July 1991. the next eclipse in this series happened right on schedule 18 years later in July 2009 but it was seen in China it takes three Saros about 54 years for a similar solar eclipse to appear in roughly the same part of the world nevertheless it's recorded that by around 585 BC the Greek astronomer thales successfully predicted a solar eclipse today such ancient records can serve a scientific purpose that's because astronomers can compare where eclipses were seen long ago to where the calculations say they should have been seen the differences reveal slight changes in Earth's rotation over thousands of years today scientists can predict exactly where and when eclipses will be seen but that doesn't make them any less interesting Instead The Mystery of eclipses has been replaced by anticipation and for many a deep desire to witness one of the most breathtaking sights in nature although the timing of an eclipse can be predicted to the second Eclipse Watchers know that the end result can still be a surprise for total eclipses of the Moon most of the surprise comes from Earth's atmosphere as the lunar eclipse proceeds the moon first slides into Earth's outer Shadow known as the penumbra where only a portion of the Sun's light is prevented from reaching the Moon this penumbral phase of the eclipse is barely noticeable later the moon May hit the inner Shadow the Umbra at this point a partial lunar eclipse begins with some of the Moon clearly in darkness but even if the lunar eclipse is total and the moon enters the Umbra completely it doesn't disappear instead a portion of the Sun's light is refracted or bent as it passes through Earth's atmosphere and then redirected toward the Moon the light has a reddish tinge because it's red sunlight that can pass through the atmosphere most easily just as it does during sunset but how bright and how red the eclipsed moon appears depends strongly on how much sunlight gets through when Earth's upper atmosphere is clear the moon takes on a coppery color when it's not so clear the result is a dark Crimson or even brownish lunar eclipse [Music] this was proved to dramatic effect after the 1991 eruption of Mount Pinatubo in the Philippines it was the largest volcanic eruption in over a century and it lofted an estimated 20 tons of sulfur dioxide into the atmosphere it's produced a global Haze layer that lasted for months and when a total lunar eclipse occurred in December 1992 the moon was so dark it nearly disappeared foreign solar eclipses also vary in their appearance but the reasons have more to do with Observer location and being in the right place at the right time usually takes some planning during a solar eclipse the moon's Shadow sweeps across Earth's surface any place where the shadow hits will at least see a partial eclipse of the Sun but to see a total solar eclipse you need to be standing near the center of the moon's shadow in a Zone that's often only a hundred kilometers or so wide depending on latitude this central part of the Shadow traces a long narrow track called the path of totality on either side of the path the solar eclipse is only partial inside it viewers are treated to the full spectacle of a total solar eclipse getting on to the path of totality is well worth it because it's only here that the most dramatic effects of a solar eclipse can be experienced and the difference between a partial and a total eclipse of the sun is literally night and day even when it's only partly visible the sun's blazing surface known as the Photosphere easily outshines anything else in the sky [Music] but once the Photosphere is fully covered by the moon the sun's wispy outer atmosphere appears this is the corona [Music] it's made up of ionized particles that have been blasted from the Photosphere and heated to over a million degrees the Corona's feather-like structure is shaped by a powerful magnetic field which is generated inside the Sun and extends far out into space the field changes with an 11-year cycle that relates to the appearance of sunspots darker cooler regions on the sun's surface when the sunspot cycle is at its maximum the corona tends to be round and symmetrical foreign spots it becomes long and spindly it's this elongated version of the corona that may have led to the ancient Egyptian symbol of the winged Sun a total eclipse also offers a rare chance to study the long loops and filaments of plasma that are caught up in the sun's magnetic field prominences all right in the middle of a total eclipse when the sun is completely covered prominences can often be seen glowing ruby red around the moon's dark perimeter time and it's also fleeting [Music] because of the speed at which the moon's Shadow passes across Earth's surface a total eclipse generally only lasts a few minutes at most in the final second as sunlight creeps around the moon's receding Edge a sudden flare shines forth creating the illusion of a diamond ring in the sky for those watching the diamond ring is like a parting gift from the solar eclipse and a confirmation that something truly incredible has taken place [Music] on the dry frigid Plains of Mars The Sun Shines pale and weak but while the Sun is far away solar eclipses are not Mars is orbited by two small moons both of which can cross in front of the Sun as seen from the Martian surface no human has ever experienced this but NASA's Curiosity Rover has and it's recorded them [Music] this is curiosity's view of a solar eclipse on Mars since the moons are small and irregular in shape the sun is never blocked completely although interesting the effects of a Martian solar eclipse are not especially dramatic on Earth it's a very different story does this have a history of making deep Impressions wherever they appear [Music] in some cases they have changed the course of history in March 1504 Christopher Columbus was beached in Jamaica when a book of astronomical tables alerted him to an approaching lunar eclipse he used the eclipse to his Advantage impressing the local tribes people with his apparent control of the event and persuading them to keep his crew supplied with food two centuries later in response to a challenge from U.S authorities Ashani spiritual leader named tenskwatawa motivated his followers by forecasting the total solar eclipse of June 1806. under the leadership of his brother Tecumseh those followers would go on to play a key role in the war of 1812. meanwhile the Spanish astronomer Jose Joaquin de Ferrer traveled to the U.S to observe the same 1806 eclipse it's thought that he coined the term Corona to describe what he saw around the eclipsed Sun Eclipse science got another boost 30 years later when Francis Bailey a retired stockbroker with no formal training in astronomy traveled to Scotland to observe a solar eclipse [Music] the eclipse was not total because at that moment the moon was at a more distant point in its orbit than usual that meant it was too small to cover the sun completely so Bailey saw what is now called an annular Eclipse during which the exposed portion of the sun forms a ring or annulus around the Moon bayley noticed that in some places the ring was so thin that the Silhouettes of mountains on the moon broke through it turning the ring into a string of beads this effect has been called Bailey's beads ever since count of the phenomenon was so intriguing that by 1842 the next eclipse in Europe Drew many more astronomers Eclipse science was shifting into high gear over the following decades several key discoveries were made during eclipses of the Sun but what may be the most scientifically significant eclipse of all time came in 1919. all right only a few years earlier Albert Einstein had published his theory of general relativity which United space and time and predicted that gravity bends light the theory offered a completely new way of thinking about the universe the challenge was finding a way to test it soon realized that during a total solar eclipse it might be possible to see if the Sun's gravity had an effect on the incoming light of background stars stars that would normally be too hard to observe while the sun is shining nearby in the spring of 1919 an expedition led by a British astronomer Arthur Eddington set out to put Einstein to the test [Music] watching from an island off the west coast of Africa Eddington woke up on the day of the eclipse May 29th to overcast skies and heavy rain miraculously just 18 minutes before totality the clouds began to break up by observing through clear patches Eddington was able to make the crucial measurement when Eddington presented his results back in England he showed that the background Stars had shifted just as predicted by Einstein's theory [Music] but first not all of his colleagues were convinced but the news caused a global sensation and overnight Einstein became a household name [Music] today the effect of gravity on light has become a powerful tool in cosmology it can be used to turn vast clusters of galaxies into enormous natural lenses that can magnify our view of the more distant universe but it all started with a solar eclipse [Music] 100 years after Eddington Eclipse chasing is no longer just for scientists it's practically a sport each time there's a total solar eclipse in an interesting part of the world thousands travel just to be there and the experience and be truly amazing and someday that experience will no longer exist solar eclipses happen because the sun and the moon appear to be almost exactly the same size in our sky the result is pure Magic but it's also a pure coincidence foreign s show us the Earth's rotation is gradually slowing down over time in response the Moon is gradually moving further away eventually the moon will no longer appear large enough to cover the sun entirely astronomers estimate that the last total solar eclipse in Earth's history will happen about 600 million years from now foreign [Music] that still leaves us with many more chances to see one of the most incredible sights in the universe [Music] but why wait [Music] horses are a natural wonder that seemed tailor-made for humans to enjoy and they're a reminder that even here on Earth we live in a larger Cosmic reality a reality that seems Unlimited in its capacity to enchant us [Music] foreign [Music] [Music] as a species we have always been fascinated by the Stars when Twilight deepens and thousands of pinpoints of light appear in the night sky we are naturally moved by The Wonder of it all and by our desire to understand it but for all those who Ponder the nature of the Stars the universe poses a special challenge because how can we hope to understand what we cannot touch foreign [Music] the remoteness of the Stars means that we can't just reach out and grab them to see what they're made of but remoteness is not an insurmountable barrier to understanding over the centuries astronomers have learned that the stars do reveal their secrets when we learn to look at them in the right way at first ancient thinkers compared the Stars to what they knew from everyday life foreign [Music] fifty BC the Greek philosopher Annex agoris reasoned that the stars must be like stones glowing with extreme heat but too far away for us to feel their warmth in fact there was an element of truth to this but when Aristotle looked to the Stars a century later he disagreed Aristotle said the Stars couldn't be made of fire stone or anything that we experience on Earth because Stars behave differently instead of moving in straight lines like falling objects the Stars spin in circles around us as they rise and set each night [Music] and the Stars never seem to change Aristotle thought they were Eternal made out of a Heavenly substance called The Ether Aristotle's ideas would hold sway for the next 18 centuries until astronomers started to see things differently first they realized that the Stars aren't spinning in circles after all it's we who are spinning by living on a rotating planet that is also following a curving path around the Sun then in 1572 a brilliant new star suddenly appeared in the constellation Cassiopeia for a time it outshone every other star in the sky after many months it gradually faded from sight today we know this Celestial interloper was a supernova explosive death of a massive star the remains of that explosion can still be seen as a vast bubble in Space over 8 000 light years away but what really mattered to astronomers back then was that the Supernova proved that even Stars can sometimes change then came the telescope [Music] the device that revolutionized astronomy by making distant objects appear closer through the telescope the planets were transformed from dots in the sky into full-fledged worlds [Music] the telescope also confirmed that the stars were much further away than ancient astronomers had ever imagined far enough to be distant versions of our own Sun increasingly it no longer made sense to think of Heaven and Earth as separate both are governed by the same principles in 1687 Isaac Newton demonstrated this once and for all by showing that his famous law of gravity applies to the moon and planets just as it does to Apples falling from a tree but it was another discovery of newtons that would ultimately allow astronomers to learn what stars are made of Optics published in 1704 Newton showed how white light is a combination of all the colors of the help of a prism of glass those colors can be separated into a spectrum like a rainbow Newton explained how rainbows work but it wasn't until 1802 that an English chemist named William walliston took the Spectrum one step further walliston improved the separation of the colors of light by first passing sunlight through a narrow slit and then a prison that's when he noticed that the sun's Spectrum contained a few thin dark lines walleston thought the lines were borders separating the colors but he had only seen the tip of the iceberg in 1814 a German instrument maker named Joseph fraunhofer invented a device for measuring the refraction of light through different types of glass [Music] when used with sunlight the device allowed fraunhofer to see the same dark lines in the spectrum that walliston had seen but he also saw hundreds more [Music] fraunhofer didn't know it yet but his device called the spectroscope would eventually be used to crack the mystery of what the sun and the stars are made of [Music] figure out how to read the hidden message in those lines and turn a Celestial barcode into a new form of astronomical knowledge [Music] in the scientific Journey there have always been moments when progress has seemed impossible that was the case in 1835 when the French philosopher August kumpt wrote that the chemical composition of the Stars would forever be beyond the limits of human knowledge compt assumed that scientists would have to travel to the Stars to learn what they're made of [Music] foreign but thanks to the invention of the spectroscope he was soon to be proven wrong the spectroscope works by dispersing light into a spectrum of colors from red to Violet it also shows that the sun's spectrum is riddled with fine dark lines because light is a wave the lines Mark particular wavelengths where some of the energy in the Sun's light has gone missing but where did it go [Music] in the 1850s two German physicists Robert Bunsen and Gustav kirkhov teamed up to find out their experiments showed that when light passes through a gas the atoms in the gas absorb some of the light but only at certain specific wavelengths which depend on the properties of that particular type of atom that explains the lines in the sun's Spectrum which are called absorption lines [Music] kirchhoff and Bunsen realized the lines act as a chemical fingerprint because they reveal which gases are present in the sun's atmosphere but that's only half the story when atoms are energized in the right way they can emit light too this creates a spectrum of bright lines known as emission lines which are the counterparts to the dark absorption lines for astronomers all of these spectral lines both bright and dark revealed a link between the Earth and Sky in the laboratory they could measure the Spectra of gases and Flames using known materials then they could compare these results to the Spectra of the sun and stars for the first time the chemistry of the universe was on display [Music] starting in 1862 the English astronomer William Huggins was among the first to attach a spectroscope to his telescope and explore the heavens in a new way he was later joined by his wife and scientific collaborator Margaret from their home-built observatory near London Huggins recorded the Spectra of many stars and other celestial objects [Music] among his targets was the great nebula in Orion a misty patch of light located near the stars of Orion's belt Huggins found that the nebulous Spectrum consisted entirely of bright emission lines especially lines corresponding to hydrogen here was evidence that the nebula was really a vast cloud of glowing gas perhaps a cloud that might someday condense to form new stars in 1864 Huggins saw something a bit different when he turned his spectroscope on the cat sign nebula an expanding shell of gas blown off of a Dying star [Music] the cat's eye produced a bright green emission line that didn't seem to correspond to any known element Huggins dubbed the mystery substance nebulum [Music] it would take over 60 years before astronomers realized that the green line is produced by atoms of oxygen with two electrons Stripped Away this energized State reveals the high temperature and low pressure environment within the nebula which is expanding at nearly 60 000 kilometers per hour in 1868 the spectroscope really did lead to the discovery of something entirely new in August of that year French astronomer Jules Jansen used a spectroscope during a total eclipse of the Sun Jansen was hoping to isolate the light from a solar prominence a glowing ribbon of ionized gas suspended in the sun's powerful magnetic field foreign normally prominences are impossible to see because the surface of the Sun is so bright [Music] but during a total eclipse any large prominence is on the edge of the sun are immediately visible to the eye and when Jansen turned his spectroscope on one of them he saw some emission lines he didn't recognize in fact they didn't correspond to any known gas foreign Jansen soon found he could spot the same emission lines in the sun's Spectrum without needing an eclipse to do it the same time in England an astronomer named Norman Locker had seen the emission lines too like Jansen lock here recognized that the lines were produced by a previously unknown element He named it helium after Helios the Greek god of the sun it would take 27 more years before the existence of helium was finally confirmed in the laboratory but its discovery on the sun made Jensen unlock your famous [Music] Locker went on to become the founding editor of the scientific journal Nature [Music] by the end of the 19th century the spectroscope had proved its worth in decoding the chemistry of the sun and the Stars but its greatest Triumph was still to come [Music] by 1925 it seemed that the quest to understand what stars are made of had come full circle 24 centuries earlier and naxagoras had written that stars are fiery stones now the spectroscope was suggesting something similar by pointing it at the sun and a distant Stars astronomers could see spectral lines that corresponded to sodium calcium magnesium iron and many other elements that are commonly found in minerals on Earth this persuaded the American astronomer Henry Norris Russell to suggest that if Earth's crust were heated up to the Sun's temperature it would share the sun's Spectrum Russell was a leading Authority on stars and his view defined the scientific mainstream but Russell's Universe was about to change [Music] for that change had been laid years earlier by a remarkable group of women in Cambridge Massachusetts who were hired to work at the Harvard College Observatory [Music] in an age before computers the observatory's director ee Pickering was dealing with a vast flood of new data from the heavens the development of Photography and spectroscopy together meant that the Spectra of thousands upon thousands of stars could now be captured and recorded on photographic plates it was a data overload and Pickering needed help he didn't have the budget to hire an army of astronomers so in 1881 Pickering hired his housekeeper Willamina Fleming Fleming had been a school teacher in Scotland and she soon mastered the art of cataloging stars according to their spectral lines she came up with her own classification scheme and ultimately examined some 10 000 individual stars on photographic plates Pickering hired more women to help and put Fleming in charge over the next 30 years they would lay the foundations for modern astrophysics [Music] one of the most important members of the team was Annie Jump Cannon who arrived at the observatory in 1896 [Music] as she gained experience Canon became truly prolific at cataloging Stars based on their Spectra at her best she could catalog three stars per minute it's estimated that over her lifetime she classified about 500 000 Stars by eye more than anyone else in history foreign as she worked Canon Hit Upon a more advanced system for classifying the Stars her approach showed that there was a progression in the spectral lines as one moved from Star type to Star type some lines becoming stronger and others fading away this was an important clue but it would take another astronomer to understand what it meant foreign Cecilia Payne grew up in England where she became fascinated with the science of the Stars but she soon learned that opportunities for women in astronomy were virtually non-existent in 1923 Payne arrived at Harvard College Observatory to join a newly launched graduate program there working with Canon's data pain began to see the underlying physics behind the classification scheme she realized that a spectrum is really a way to measure a star's temperature stars at different temperatures energize the atoms of various elements in different ways leading to a unique set of spectral lines its analysis also showed something else the dominant element in all of the stars appeared to be hydrogen in 1925 Payne summarized her findings in her PhD thesis but when Henry Norris Russell read an advanced copy he thought her conclusion about hydrogen had to be wrong pain then added a line to the thesis that undermined her boldest discovery within four years Russell realized it was he who was wrong and he admitted it Cecilia Payne's astonishing Insight was correct today astronomers know that hydrogen is the most abundant element in the stars and that points the way to an amazing scientific story [Music] it's now clear that stars are born out of clouds of hydrogen gas like the Orion Nebula that William Huggins once studied once they form the stars shine because of nuclear reactions that turn the hydrogen into helium and other heavier elements [Music] eventually Stars die and the elements they've created are released back into space just as they are in the Cat's Eye Nebula says the stars are seeding the Universe with the raw material needed to produce planets and life [Music] this is the great secret that the spectroscope has revealed secret unraveled over a century and a half by a succession of remarkable men and women [Music] stars are made of but in a very real sense we've also learned that we Are Made of Stars foreign [Music] gazing into the night sky it's easy to be awed by the Grandeur of our universe [Music] it's not just that space is Big it's that our place in it is so little and as our knowledge of the universe has grown so too has the realization that most of it is completely unsuitable for life foreign [Music] between the Searing heat of the stars and the frigid depths of space it's clear that Life as we know it can only Survive by clinging to those few rocky planets that are lucky enough to exist in the narrow zone between two hot and too cold while the rest of the universe can be breathtakingly beautiful it seems utterly indifferent to our existence if it's just the opposite what if all this is here because we're here [Music] it's called the anthropic principle it's the idea that our Cosmic reality is a product of the fact that we're living in it that may seem like a backwards argument but some cosmologists say it may be the only way to explain why the universe is the way it is foreign ancient times the universe didn't need that kind of explaining with so much order and complexity in the world it was logical to imagine that a Divine being of some kind just made it that way yet in ancient Greece philosophers took a different path they tried to explain the universe in terms of natural laws in many cases they guessed wrong about the causes of various phenomena and also about our place in the universe [Music] for example Aristotle argued that Earth had to be at the center of the cosmos with the stars and planets circling around it but while this conclusion was mistaken the approach taken by Aristotle and other philosophers would eventually develop into modern science with its emphasis on observation and reasoning yes it was a progression that took many centuries but by the early 1500s our current understanding of the universe was starting to emerge [Music] the key step was taken by Nicholas Copernicus a Polish Church official and administrator who was also a brilliant astronomer Copernicus realized that the Motions of the planets made a lot more sense if the sun rather than Earth was at the center of the solar system [Music] when copernicus's ideas were published after his death in 1543 the Scientific Revolution began [Music] at first the copernican system was controversial for religious reasons but also because it seemed to defy common sense after all to any Observer Standing On Solid Ground and looking up at the night sky it really does seem as though Earth is at the center but copernic is this great achievement was finding a deeper logic to the Natural Order of Things [Music] that logic tells us that it makes little sense for Earth to be at the center of everything because that would mean humans just happen to be living at the most special place in the universe for centuries ever since astronomers have embraced what's now known as the copernican principle foreign states that our place in the universe is very unlikely to be uniquely special rather the way we perceive the universe is likely pretty close to what other observers would experience from their locations in the 20th century this premise became the Bedrock of modern cosmology [Music] around CE astronomers realized that nearly all the galaxies are moving away from us the copernican principle pointed the way to a dramatic discovery it's not that we're at a special place that the galaxies just happen to be receding from rather all of the galaxies must be moving away from each other as the entire universe expands our location may have its own particular details but the universe looks about the same no matter where you are as telescopes improve the copernican principle continued to fit the accumulation of evidence the universe has turned out to be full of galaxies similar to our own stretching off in all directions for billions of light years we're not at the center and neither is anyone else because as far as we can see the universe has no Center and no preferred direction to look [Music] but cosmologists were beginning to notice something curious while our view of the universe may not be special the universe as a whole does appear to be very special indeed what makes it special are the laws of physics that govern our reality and as cosmologists started to consider these laws more closely they found themselves heading in a New Direction one that for the first time in nearly 500 years was leading them away from Copernicus [Music] reverse is a place of extraordinary diversity and from the planets of our solar system to the distant galaxies the more we explore the more variety we see but underlying this variety is a deeper simpler picture [Music] so far just about everything we've observed can be explained with a basic set of natural laws these are the rules that dictate better and energy behave they include the properties of fundamental particles and the forces that operate between them but while these rules explain a lot nothing seems to explain why the rules are so perfectly set up to produce a universe that can support life [Music] take gravity for example relative to all the other forces in nature it's extremely weak that's why a toy magnet can easily overcome the gravity of the entire Earth and lift up a paper clip but if gravity were any stronger the result would be a disaster [Music] Universe the matter inside Stars would be squeezed together more tightly this would speed up nuclear reactions and cause stars to burn out sooner with just a modest increase in the force of gravity no star would last long enough for life to appear and evolve foreign yet if gravity were much weaker then Stars wouldn't shine at all in the same way particle physics is full of what seemed to be chance numbers and relationships that we depend on for our existence the neutron and the proton are almost equal in Mass but the neutron is slightly heavier by about 0.14 percent if it were the other way around atoms wouldn't exist [Music] a more subtle example suggests that our universe is perfect for the emergence of life based on carbon the only kind of life we know [Music] carbon atoms have the property that they can reform long chains which are essential for a large organic molecules the kind of molecules needed to make working cells foreign but carbon forms only in the cores of stars and when physicists began to work out exactly how that happens they discovered a curious puzzle it takes 12 particles to make the nucleus of a carbon atom six protons and six neutrons Stars build up carbon by starting with helium each helium nucleus has two protons and two neutrons first two heliums come together to form beryllium eight beryllium eight is highly unstable and likely to fall apart in less than a trillionth of a second unless one more helium comes along [Music] stars that happens often enough but here's the problem when you add beryllium and helium together the result has too much energy instead of making carbon they should just fly apart in 1953 the British astronomer Fred Hoyle realized there was a way around this problem he predicted there was an excited form of carbon that closely matched the higher energy level of beryllium plus helium Hoyle was right the excited carbon state was discovered soon after his prediction its existence makes it far more likely that beryllium and helium will morph into carbon once they've come together energized state of carbon just right to allow this to happen to understand why this is a problem imagine pressing the emergency button to stop a fast-moving elevator then the door opens and you discover that the place where the elevator has stopped perfectly matches the floor where people can step off in other words it's sheer coincidence yet it's a coincidence that we owe Our Lives to over the years physicists have come across other examples like this cases where if the numbers were changed just slightly we wouldn't be here no one would be here it's this realization that's brought us to the anthropic principle the term was coined in 1973 by the Australian cosmologist Brandon Carter who divided the anthropic principle into two versions the weak version is simply the argument that our place and time in the universe is special because it's compatible with the existence of life if it wasn't we wouldn't be around to experience it but there's a stronger version too which suggests that the Universe isn't possible unless at some point it allows life to evolve otherwise the laws of physics are just too much of a coincidence once Carter formulated these definitions it became clear that the anthropic principle presents a challenge to the traditional way of doing science ever since Copernicus astronomers have been working on the premise that the universe is independent of our presence in it with this premise in mind many cosmologists resisted the anthropic principle hoping that scientific progress would eventually lead us to a better understanding of the laws of nature but then a surprising development put the anthropic principle back in the spotlight along with a stunning theory about the true nature of our Cosmic reality [Music] in 1998 astronomers made a discovery that would forever change our understanding of the universe they found evidence for Dark Energy a mysterious phenomenon that permeates all of space and is causing the expansion of the universe to speed up this is big news because it helps explain everything from the age of the universe to its long-term future presence of dark energy also carries huge implications for the anthropic principle of all the COS coincidences that seem to make our universe suitable for Life Dark Energy may be the biggest Coincidence of all this is because the density of dark energy is so extraordinarily small just a tiny fraction of a fraction of a fraction more than zero so far there's nothing in the laws of physics that predicts why dark energy density should have such a minuscule value it seems to be completely arbitrary it's just a little more Dark Energy the early Universe would have expanded too quickly for matter to come together to form galaxies [Music] without galaxies there would be no stars no planets and no possibility of life foreign scientists this is a philosophical problem because how can you explain a universe that seems to be tailor-made for us [Music] in fact the discovery of dark energy has now been used in some religious circles as an argument for why there must be a Divine creator but scientists have found another way of looking at the problem consider the case of Earth in our solar system among the planets Earth seems uniquely well positioned for life if it were a little bit closer to the Sun it would be too hot if it were a little bit farther it would be too cold there's no reason for Earth to be at just the right distance from the Sun for life to flourish so is this another example where scientists have to take the anthropic principle into account the answer is no for a very obvious reason Earth is not the only planet in our solar system there are several other planets and many more have been discovered around other stars [Music] estimated that there are billions of planets in our Milky Way alone each with its own characteristics and temperature means Earth is no coincidence it's just one of billions of possibilities and since we can only exist on a planet like Earth it makes sense that this is the kind of planet we happen to be living on now cosmologists have applied the same reasoning as a way of dealing with the anthropic principle because what if our universe is not the only one instead of one Universe with one set of physical laws that just coincidentally happen to be perfect for life what if there are countless other universes in which the laws of physics can come in any possible form larger picture of reality has become so compelling that cosmologists have given it a name it's called The Multiverse if it's true then as vast as our universe may seem to us it's merely a bubble in a multi-dimensional cosmos where other universes are popping up all the time each with its own value for dark energy [Music] since only a very very few of those universes would be livable then it's no coincidence that we find ourselves living in one it's a startling conclusion and even though it hasn't been proven it's supported by two different fields of research one is string theory it's a mathematical method of explaining the laws of nature that turns out to have a vast number of possible solutions some theorists now say all those different solutions correspond to different universes in the Multiverse secondly scientists who are probing the early Universe have found that what they're seeing is consistent with a theory called Cosmic inflation the idea is that our universe emerged from a small patch of space that released energy by inflating at an exponential rate if that's correct then other universes should be doing the same thing in an eternally inflating Multiverse [Music] there are plenty of reasons to be cautious about this picture for one thing it means we have to conjure up a vast number of other universes just to explain this one and if it's true it means there will never be one set of physical laws that predicts our reality because in the Multiverse so many other realities are equally possible thank you as strange as it seems this picture may be our only way of explaining what astronomers have found because of the Multiverse the anthropic principle is now at the center of one of the most fascinating debates in the history of science it's a debate that involves everything we know about the universe and possibly everything we can know where that debate will lead us is still unknown but it will surely be shaped by what we learn as astronomers continue to probe the universe to its limits in the meantime we already know that despite the copernican principle there is one way in which our perspective on the universe is special [Music] because it's only in our lifetime that Humanity finally has the tools to reveal how rich and potentially vast are cosmic Vista truly is [Music] thank you

Channel: Spark

Views: 3,382,747

Keywords: Spark, Science, Technology, Engineering, Learning, How To, education, documentary, factual, mind blown, construction, building, full documentary, space documentary, bbc documentary, Science documentary

Id: uHLmh6yphUc

Length: 132min 48sec (7968 seconds)

Published: Sun Dec 11 2022