Profound Mysteries & Discoveries of the Cosmos | SPACE DOCUMENTARY BOX-SET | 2HR 15 MIN Run Time

there is one very important caveat to this picture recent research suggests that eternal inflationary models may be eternal in the future but not in the past they never stop but they may have to start i can't give you a definitive answer to this ultimate question because nobody yet knows i can quote from andre linder's recent review of inflationary cosmology inflationary cosmology after plunk 2013. in other words there was a beginning for each part of the universe and there will be an end for inflation at any particular point but there will be no end for the evolution of the universe as a whole in the eternal inflation scenario and at present we do not know whether there was a single beginning of the evolution of the universe as a whole at some moment t equals zero which was traditionally associated with the big bang and so we reached the end defining the big bang as the initial hot dense phase of our observable universe that gave rise to the cmb 380 000 years later we understand what happened before there was a period of inflationary expansion which could have been driven by a scalar field in accord with the known laws of physics that inflationary expansion is probably still going on somewhere spawning an incalculable number of universes as we speak and it will continue doing this forever we live in an eternal universe in which everything that can happen does happen and we are one of the things that can happen did the whole universe have a beginning an essential external cause in the spirit of leibniz is god we still don't know possibly there was a mother of all big bangs and if so we will certainly need a quantum theory of gravity to say anything more what does this mean the wonderful thing for me is that nobody knows because the philosophical and indeed theological consequences of eternal inflation have not been widely debated and discussed my hope is that in trying to summarize the issues regrettably briefly and necessarily superficially in the television series these ideas will be accessible to a wider audience and stimulate discussion this is desirable and necessary because ideas are the lifeblood of civilization and societies assimilate ideas and become comfortable with their implications through understanding and debate if eternal inflation is the correct description of our universe it will be the artists philosophers theologians novelists and musicians alongside the physicists who explore its meaning what does it mean if the existence of our universe is inevitable what does it mean if we are not special in any way what does it mean if our observable universe with all its myriad galaxies and possibilities is a vanishingly small leaf on an ever-expanding fractal tree of universes what does it mean if you are because you have to be i can't tell you i can only ask what does it mean to you for small creatures such as we the vastness is bearable only through love carl sagan but how on earth does a cell learn how to engulf another one and survive how did endosymbiosis arise a clue and perhaps an even more significant bottleneck may be found in another prerequisite for the cambrian explosion the eukaryotic cell all multicellular organisms are made up of cells known as eukaryotes cells with a nucleus and a host of specialized structures each charged with performing specific tasks the eukaryotic cells in every living thing look so similar that an alien biologist knowing nothing about planet earth would immediately recognize that human eukaryotes are closely related to those from a blade of grass the earliest known eukaryotic cells date from around 2 billion years ago beyond this simpler cells known as prokaryotes were the only living things on the planet bacteria and archaea the two single-celled kingdoms of life that still flourish today are prokaryotes they are simple in the sense that they lack the vast specialized machinery of the eukaryotes although as we've seen they do possess some vital and extremely complex abilities photosynthesis being a very good example the most striking difference between eukaryotes and prokaryotes is the eukaryote cell nucleus which contains most of its dna in the story of evolution of life on earth however it's the small amount of dna stored outside the nucleus that's most revealing almost all eukaryotic cells contain structures called mitochondria the word almost is used a lot in biology unlike physics there always seem to be one or two exceptions that ruin sentences in books like this most biologists believe that even the eukaryotes that don't possess mitochondria did so at some point in the past however so we can take it that these structures are ubiquitous mitochondria are the power stations of the cell and their job is to produce atp around 80 percent of your energy comes from the atp produced in mitochondria and without them you certainly wouldn't exist a clue as to their evolutionary origin is contained in their dna which is stored in loops and kept separate from the genetic material in the cell nucleus bacteria also store their dna in loops and this is not a coincidence the mitochondria were once free living bacteria the obvious question is how did the bacterial mitochondria get inside the cells of every complex organism on the planet the answer is through endosymbiosis just as for the chloroplasts but there is not universal agreement on the detail and the detail matters a great deal what's not in question is that the mitochondria are bacterial in origin the debate surrounds the nature of the original host cell one camper biologists believes that the host cell was already a eukaryote which over many millions of years had evolved an ability called phagocytosis the ability to ingest other cells this is a traditional darwinian explanation one in which complex traits evolve gradually over time via mutations and natural selection if this is true then it's possible to view the eukaryotic cell as just another evolutionary innovation albeit a very important one that might crop up anywhere given enough time the other possibility which is favored by many biologists has different implications the idea is that the swallowing of the proto-mitochondrial cell was the origin of the eukaryotic cell itself there was no such thing as phagocytosis or the eukaryotic cell before this singular event and this fateful encounter changed everything recent dna evidence suggests that the host cell was probably an archaean one of the two great prokaryotic domains somewhere in some primordial ocean this simple prokaryote managed to swallow a bacterium a trick that neither cell possessed before and against terrific odds the pair survived and multiplied the archaean gained a huge advantage a previously unimaginable energy supply from the bacterium sophisticated atp factory the bacterium also gained an advantage it was protected and over eons could specialize and concentrate entirely on producing energy for its host if this theory is correct the origin of complex life on earth was a complete accident without access to the energy supply from the mitochondria all the complexities of the eukaryotic cell which are absolutely necessary for complex multicellular life would never have evolved earth would be a living planet today but a planet of prokaryotes and certainly not home to a civilization i cannot tell you which of these two theories is true if it were obvious then all academic biologists would agree but my impression is that the fateful encounter is currently the more widely accepted theory and if it is correct then this has very important consequences for estimating the probability of the evolution of intelligent life eukaryotes are absolutely essential for intelligence there is no biologist who would suggest that the prokaryotes for all their ingenuity in developing photosynthesis and mitochondrial machinery would have managed to construct radio telescopes given enough time in the following wind without eukaryotes there would be only slime i think these are very important points to consider in the drake equation if it is correct that at least two of the necessary foundations for the emergence of complex multicellular life on earth arose from barely credible accidents then they might be seen as potential bottlenecks in the evolution of intelligence elsewhere in the milky way so where are we in our attempt to estimate the chances that given the origin of life on a planet intelligence will arise this is where we move from science to speculation and opinion and with these caveats let me give you my personal view given the eukaryotic cell and an oxygen atmosphere life on earth became diverse and complex relatively quickly it's almost certainly no coincidence that the cambrian explosion followed soon after a rapid rise in the oxygen content of the atmosphere whether it's possible to claim that intelligence on the scale necessary to build a civilization is likely given the right biological building blocks in enough time half a billion years let's say is another question we simply don't know and the very specific conditions in the african rift valley that led to the emergence of early modern humans only two hundred and fifty thousand years ago might suggest that civilization level intelligence is a rare development even given animals are sophisticated as primates never mind a eukaryote and an oxygen atmosphere an optimist would assert that there are billions of potential homes for life in the milky way and that since life emerged on earth pretty much as soon as it could at the end of the violence of the haideon then the milky way must be teeming with life and therefore civilizations i would agree that the milky way must be teeming with life i think there's a sense of chemical inevitability about it even accepting this line of argument however a pessimist would surely point to the evolution of the eukaryotic cell and oxygenic photosynthesis as being potential bottlenecks on earth it took life over three billion years to get to the eve of the cambrian that's three billion years of planetary stability a quarter of the age of the universe if just one of the necessary steps the fateful encounter let's say was at the fortunate end of a probability distribution then one can easily imagine that the 20 billion earth-like worlds in the milky way could all be covered in prokaryotic slime a living galaxy yes but a galaxy filled with intelligence given what we know about the ascent from to civilization on earth i'm not so sure let's take one final journey back to green bank in 1961. drake and his colleagues with far less evidence than we have today concluded that our galaxy seems remarkably conducive to life full of earth-like worlds warmed by the glow of benign stars they too believed that a good fraction of these billions of worlds must be home to life and given that darwin's law of evolution by natural selection must apply across the universe they concluded that intelligence must have emerged on at least some of these planets as i've argued above i'm not so sure about intelligence but we must at least consider the possibility that potential evolutionary bottlenecks like the eukaryotic cell and oxygenic photosynthesis aren't as bad as they might appear in this case the final term in the drake equation becomes all-important perhaps it is l the lifetime of civilizations that is the fundamental reason for the great silence this is a sobering thought the reason we've made no contact with anyone is not because of a lack of stars or planets or living things it's because of the inbuilt and unavoidable stupidity of intelligent beings this might seem a bit strong but it's a view shared at green bank by manhattan project veteran philip morrison morrison was intimately involved in the design and development of the first atomic bomb and he helped load little boy onto a nola gay destined for hiroshima the fact that human beings had deployed a potentially civilization-destroying weapon twice against civilian targets and that morrison had personally loaded one of the bombs must have never left him and on the eve of the cuban missile crisis it must have seemed likely that we would do it again on a much grander scale drake realized this as well which is certainly one of the reasons why he introduced the time that a technological civilization can endure into his equation we can after all only communicate with nearby civilizations if they exist at the same time as us this is a possible resolution to the fermi paradox civilizations inevitably blow themselves up soon after acquiring radio technology and therefore the milky way will remain forever silent apart from the briefest non-overlapping flickers of intelligence this might seem like a solipsistic cystic conceit how can we possibly assume that human stupidity is universal we can't of course but just as for the biological arguments we made against the inevitable emergence of complex life on an otherwise living world we only have the earth as a guide and extrapolating from our own experience is the best we can do on earth rutherford discovered the atomic nucleus in 1911 and we destroyed two cities and killed over two hundred thousand of our fellow human beings with nuclear technology thirty four years later about seventeen years after that having seen the devastation nuclear weapons can cause khrushchev and kennedy came close to ending it all and to this day we don't know how close we came to eliminating the fruits of almost four billion years of evolution here on earth it appears that sanity perspective and an appreciation of the rarity and value of civilization emerges after and not before the capability to build big bombs we have the bombs but i don't think enough of us have the rest why should other young civilizations be any different if this is the reason for the great silence then i suppose we might take comfort in the fact that we are not the only idiots to have existed in the milky way but that's the coldest comfort i can imagine the above might be seen as a naive rant of course one could argue that mutually assured destruction the guiding principle of the cold war did act to stabilize our civilization and is still doing so today perhaps no intelligent beings will knowingly destroy their civilization which is what global nuclear war on earth would surely do after all kennedy and khrushchev ultimately took this view similarly one assumes that the submersion of miami and norwich by rising sea levels would silence the so-called climate change skeptics i'd call them something different and trigger a change of policy that will avert catastrophic civilization threatening climate change in good time it seems to me however that a small planet such as earth cannot continue to support an expanding and flourishing civilization without a major change in the way we view ourselves the division into hundreds of countries whose borders and interests are defined by imagined local differences and arbitrary religious dogma both of which are utterly irrelevant and meaningless on a galactic scale must surely be addressed if we are to confront global problems such as mutually assured destruction asteroid threats climate change pandemic disease and who knows what else and flourish beyond the 21st century the very fact that the preceding sentence sounds hopelessly utopian might provide a plausible answer to the great silence so are we alone what then is the range of estimates for the number of civilizations in the milky way given the limited evidence we have at our disposal during the filming of human universe frank drake told me that the green bank meeting came up with a number of around ten thousand and he sees no reason to change that estimate this would be wonderful and makes the search for signals from these civilizations one of the great scientific quests of the 21st century i strongly support seti because contact with just one alien civilization would be the greatest discovery of all time and it's worth the investment on that basis alone there is however one piece of evidence that might suggest a more lonely position for us on our little home world in 1966 the mathematician and polymath john von neumann published a series of lectures entitled theory of self-reproducing automata in which he analyzed in great detail the possibility of constructing machines capable of building copies of themselves such machines exist in nature of course all living things do this routinely in principle therefore one might imagine a sufficiently advanced civilization building a self-replicating von neumann space probe and launching it out to explore the galaxy on reaching a solar system the probe would mine the planets moons and asteroids extracting the materials necessary to build one or more copies of itself the newly minted probes would launch themselves out to neighboring solar systems and repeat the process spreading across the milky way even given the vast distances between the stars computer models assuming currently envisioned rocketry technology suggests that such a strategy could result in the exploration of the entire milky way galaxy within a million years science fiction it certainly sounds like it but if there's no objection in principle to the construction of a von neumann probe then one has to develop an argument as to why we don't see any the reason that this is difficult to do is due to time scales the milky way has been capable of supporting life for over ten thousand million years it is possible to envisage many millions of civilizations rising and falling over such vast expanses of time and if only one had developed a successful von neumann probe then the galaxy should be filled with its progeny there should be at least one von neumann probe operating in our solar system today carl sagan and the astronomer william newman noticed a flaw in this line of argument if the probes multiply exponentially and unchecked then one can show that they consume the resources of the entire galaxy relatively quickly and we'd certainly have noticed that or more accurately we wouldn't be here to notice that sagan reasoned that this obvious risk would be sufficient to prevent any civilization intelligent enough to build von neumann probes from actually doing so they would be doomsday machines other astronomers have counted that it wouldn't be beyond the width of such an advanced intellect to build in some fail-safe mechanism that guaranteed for example only one probe per solar system or a finite lifetime for each probe others have argued that there may indeed be a von neumann probe operating in our solar system today with appropriate fail-safe mechanisms installed to stop it eating everything if such a probe were relatively small perhaps sitting amongst the asteroids or even the kuiper belt of icy comets beyond the orbit of neptune then we'd almost certainly be unaware of its presence von neumann probes wouldn't be the only signatures of ultra advanced civilizations imagine a civilization many millions of years ahead of us carrying out engineering projects on a galactic scale imagine interstellar starships or great space colonies constructed in otherwise uninhabitable solar systems why not what signature will we leave on the sky if we survive and prosper that long none of these questions is trivial because the sheer immensity of the time scales available for life to evolve in the milky way galaxy forces us to consider them why should we be the most advanced civilization in the galaxy when we've only been building spacecraft for half a century in a 13 billion year old universe i don't have an answer to this it bothers me perhaps the distances between the stars are indeed too great or perhaps there are insurmountable difficulties in building self-replicating machines or starships but i can't think what they might be i am tempted therefore to make the following argument for the purposes of debate i think that advanced space-faring civilizations are extremely rare not because of astronomy but because of biology i think the fact that it took almost four billion years for a civilization to appear on earth is important this is a third of the age of the universe which is a very long time coupled with the remarkable contingency of the evolution of the eukaryotic cell and oxygenic photosynthesis not to mention the half a billion years from the cambrian explosion to the very recent emergence of homo sapiens and civilization i think this implies that technological civilizations are stupendously rare colossally fortuitous accidents that happen on average in much fewer than one in every 200 billion solar systems this is my resolution to the fermi paradox we are the first civilization to emerge in the milky way and we are alone that is my opinion and given our cavalier disregard for our own safety it terrifies me what do you think but why some say the moon why choose this is our goal and they may well ask why climb the highest mountain why 35 years ago fly the atlantic we choose to go to the moon president john f kennedy field if his epitaph read john young the ultimate explorer young smiled and in a test pilot's drawl replied i'd feel sorry for the guy who wrote it young was and still is a hero of mine my first vivid memory of live space exploration was watching space shuttle columbia climb on a tower of bright vapor into a blue cape sky on the 12th of april 1981. it was midday in manchester the easter holidays and i was 13 years old because of a two-day launch delay colombia's test flight took place precisely 20 years to the day after yuri gagarin made his black and white voyage into orbit on the 12th of april 1961 but young and his co-pilot bob crippen in their orange spacesuits were astronauts from the color age the future as distant from the russian hero as gleaming white-winged columbia was from vostok one equidistant from both was apollo which young flew to the moon twice it was the age of optimism the age of wonder the golden age when the ape went into space when unflappable aviator young whose pulse rate did not increase during the launch of nasa's only manned spacecraft ever to have flown without an unmanned test flight piloted colombia back for a flawless manual landing at edwards air force base two days later he turned to krippen and said we're not too far away the human race isn't from going to the stars in 2014 the stars feel further away than they did in 1981. the international space station is a wonderful piece of engineering that has allowed us to learn how to live and work in near-earth orbit but it is no closer to the stars than colombia its construction is no mean achievement one of the most important things to realize about engineering at the edge is that the only way to learn is to actually do it you can't think your way into space you have to fly there but i can't help but feel in the words of billy bragg that the space race is over and we've all grown up too soon it was different in gagarin's day nobody's born to be a spaceman where apes honed by natural selection to operate in the great rift valley gagarin's father was a carpenter and his mother was a milk maid both worked on a collective farm gagarin's first job at the age of 16 was in a steel mill but after showing an aptitude for flight as an air cadet he joined the military when 21 and was posted to the first czecholovsk air force pilot school in orenburg rising through the ranks he made a name for himself as a skilled and intelligent aviator and in early 1960 he was chosen along with 19 other elite pilots for the newly established space program standing just five foot two inches tall gagarin had the right stuff and was perfect for the tiny vostok spacecraft whose single seat crew compartment was only 2.3 meters in external diameter after a year of training nikolai kamenin head of the cosmonaut program chose gagarin ahead of his rival german titov just four days before the flight the history books are filled with the names of great men and women whose presence in the collective memory of humanity was assured by the slimmest of margins gagarin alongside armstrong will be remembered for as long as there are humans in the cosmos the name of the equally brilliant titov russian's second cosmonaut has faded away gagarin's flight was a true journey into the unknown strapped on top of the vostok k rocket which flew 13 times and made it into space on 11 occasions the 27 year old performed like a true test pilot despite a two-hour delay during which every component of the spacecraft hatch was taken apart and rebuilt while gagarin remains strapped into his seat his heart rate was recorded at 64 beats per minute just before launch this is not to say that gagarin wasn't fully aware of what he was about to do before boarding gagarin made one of the great speeches of the age dear friends both known and unknown to me fellow russians and people of all countries and continents in a few minutes a mighty spaceship will carry me into the far away expanses of space what can i say to you in these last minutes before the start at this instant the whole of my life seems to be condensed into one wonderful moment everything i have experienced and done till now has been in preparation for this moment you must realize that it is hard to express my feeling now that the test for which we have been training long and passionately is at hand i don't have to tell you what i felt when it was suggested that i should make this flight the first in history was it joy no it was something more than that pride no it was not just pride i felt great happiness to be the first to enter the cosmos to engage single-handed in an unprecedented duel with nature could anyone dream of anything greater than that but immediately after that i thought of the tremendous responsibility i bought to be the first to do what generations of people had dreamed of to be the first to pave the way into space for mankind this responsibility is not toward one person not toward a few dozen not toward a group it is a responsibility toward all mankind toward its present and its future am i happy as i set off on this space flight of course i'm happy after all in all times an epochs the greatest happiness for man has been to take part in new discoveries it is a matter of minutes now before the start i say to you until we meet again dear friends just as people say to each other when setting out on a long journey i would like very much to embrace you all people known and unknown to me close friends and strangers alike see you soon it's too easy to attach trite labels to human actions magnificent horrific and everything in between based on a simplified view of their causes one can argue that the rockets carried aloft the egos of the superpowers alongside the astronauts and this is surely right but gagarin spoke these words and i challenge anyone to read them and not detect sincerity all our actions mask a morass of motivations worthy and less so and the greatest human adventures are no less noble for that at 907 am local time gagarin blasted off from baikonur cosmodrome in kazakhstan as every russian cosmonaut has done since within 10 minutes he was orbiting earth at an altitude of 380 kilometers his route took him across the siberian wastes and the pacific ocean above the hawaiian islands past the tip of south america and into the south atlantic where he was greeted by a second sunrise before a 42 second de-orbit burn over the angolan coast slowed vostok 1 into a parabolic orbit and an 8g deceleration inside earth's thickening atmosphere the journey once around his home world took one hour and 48 minutes gagarin ejected from the capsule seven kilometers above ground and as planned cosmonaut and spacecraft completed the final descent apart gliding back to earth by parachute gagarin landed 280 kilometers away from the intended landing site near the russian city of engels dressed in orange space suit and white helmet a farmer and his daughter bore sole witness to his historic return when they saw me in my spacesuit and the parachute dragging alongside as i walked they started to back away in fear recollected gagarin later i told them don't be afraid i am a soviet citizen like you who has descended from space and i must find a telephone to call moscow primates appeared relatively recently in the history of life on earth studies of mitochondrial dna suggest the strepsirini suborder containing the ancestors of madagascar's lemurs diverged from our own haploreini suborder approximately 64 million years ago which implies that a common ancestor was present before this time but not a great deal earlier the first complete primate fossil found to date is that of a tree dwelling creature known as archicebus achilles dated at 55 million years old discovered in the fossil beds of central china in 2013 this tiny creature would have been no bigger than a human hand making it not only the oldest but also one of the smallest known primates our family known as the hominidae or more commonly the great apes share a common ancestor with old world monkeys around twenty five million years ago the road out of addis towards the three thousand meter guasa plateau is excellent to a point and then not excellent the scenery on the other hand improves with altitude golden grass is illuminated by shifting lambert light through dark clouds cling to near vertical mountainsides framing pristine villages along the high valley floors it is fresh cold and insect-less on the peaks above the rift a place to drink tea and eat shiro a spiced ethiopian stew of chickpeas and lentils after a night in the cold but magnificently desolate gwasa community lodge we set off at dawn to intercept the gelada baboons on their way back to their caves and ledges from early morning foraging expeditions on the higher slopes the gelada baboons are a species of old world monkey found only in the ethiopian highlands they are the only surviving species of the genus therapicus that once thrived across africa and into southern europe and india the males in particular are powerful long-haired animals weighing over 20 kilograms with a bright red flash of skin on their white chests i was told not to look them in the eye so i didn't fifty thousand years ago as our planet emerged from the last ice age the gelada retreated into the highlands above the rift where they still live uniquely among extant primates as graminivores on a diet made up almost entirely of the tough high altitude grasses and occasional herbs they approach with nonchalant agility in small groups which reflect the most complex social structure of any non-human primate most of the groups i saw contained one or two males and perhaps eight or ten females and they're young these are referred to as reproductive units and clearly defined hierarchies exist within them females usually remain in the same unit for life but males move between them every four or five years there are also male only units of 10 or 15 individuals these social units are arranged into higher groupings known as bands herds and communities the community we encountered numbered several hundred individuals who wandered past in their little tribes females and young pausing to eat groom and play whilst the larger males eyed us closely despite the 25 million years separation in evolutionary time the gelada are very easy to anthropomorphize especially from a vantage point amongst them probably because their behavior seems reminiscent of our own and their babies are cute like us they spend most of their time on the ground and operate in social groups some researchers familiar with the geladas claim they exhibit the most sophisticated communication behavior of any non-human primate employing gestures and a range of different vocalizations strung together into sequences communicating reassurance appeasement solicitation aggression and defense for all their sophistication however the gelada are a long way from possessing anything more complex than the simplest of human characteristics and abilities this is of course an utterly obvious observation they are monkeys but what isn't obvious is why the gelada separated from our common ancestor at the same time but that self-evident statement leads to a deeper question what is it that happened to our ancestors during those 25 million years that led us to the stars and left them on the hillsides of the guasa plateau eating grass i am an aviation geek i love aircraft as i set off to film the african scenes for eight man spaceman i noticed that the ethiopian airlines boeing 787 i boarded at london heathrow bound for addis ababa registration etaos was named lucy on the morning of the 24th of november 1974 donald johansson and a team of archaeologists were searching for bone fragments at a site near the ahwash river in ethiopia the area was known to be a site rich in rare hominid fossils but on that particular morning johansson and his graduate student tom gray found little to inspire them as is often the way in science however a dash of serendipity coupled with an experienced scientist who understands how to increase the chances of receiving its benefits made a seminal contribution to the understanding of human evolution johansson shouldn't even have been there he had planned to spend time back at the camp updating his field notes but as they prepared to leave johansson decided to wander over to a previously excavated gully and have one last look even though they'd surveyed the area before this time johansson's eye was drawn to something lying partially hidden on the slope closer inspection revealed it to be an arm bone and a host of other skeletal fragments a piece of skull a thigh bone vertebra ribs and jaw all emerged from the ground and crucially they were all part of a single female skeleton the find triggered a three-week excavation during which every last scrap of fossil al-288 hyphen 1 was recovered they named it lucy after track three side one of sergeant pepper's lonely hearts club band because this was 1974 and they played it a lot on their tape recorder home taping kills music they used to say back then but it also names airliners lucy lived 3.2 million years ago in the open savannah of ethiopia's afar depression standing just over one meter tall and weighing less than 30 kilograms she would have looked more ape-like than a human her brain was small about one-third of the size of a modern humans and not much larger than the chimpanzees the anatomy of her knee the curve of her spine and the length of her leg bones suggest that lucy regularly walked upright on two legs although there are a handful of scientists who would disagree what is generally agreed upon however is that lucy was a member of the extinct hominin species australopithecus afarensis and she was either one of our direct ancestors or very closely related to them her bipedalism was probably an evolutionary adaptation caused by climate change in the rift as the number of trees reduced and the landscape became more savannah-like the arboreal existence of our more distant ancestors became less favored and the increasing distances between trees selected for australopithecus's upright gate made travel across the ground more efficient in who speaks for earth the 13th chapter of carl sagan's cosmos there are two pictures set side by side one is a footprint covered by volcanic ash 3.7 million years ago near lytoli in tanzania probably made by an australopithecus afarensis like lucy some four hundred thousand kilometers away and three point seven million years later another hominin footprint was left in the dust of the sea of tranquility together they speak eloquently of our unlikely magnificent ascent from the rift valley to the stars the time scale is ridiculously small less than a tenth of one percent of the period of time during which life has existed on earth lucy was little more than an upright chimpanzee an animal a genetic survival machine we bring art science literature and meaning to the earth we are a world away and yet separated by the blink of an eye our obligation to survive is owed not just to ourselves but also to that cosmos ancient and vast from which we spring wrote sagan i'd like to add that we owe it to lucy as well before astrology was consigned to the status of trifling funfair entertainment by science it was believed that the position of the planets against the distant stars had a profound effect on people's daily lives if you don't know what the stars or planets actually are this is at least within the bounds of reason but as our understanding of physics improved so it became clear that there's no way that the position of a distant planet relative to the fixed stars can have any effect on the behavior of a human being on the surface of the earth the planets can and do affect the earth's motion through the solar system over time scales far greater than those of human lifetimes though and recent research suggests that long-term changes in earth's orientation and orbit may have played a crucial role in hominid evolution polaris is a true giant almost 50 times the diameter of our sun it is also a seafied variable one of the valuable standard candles upon which the astronomical distance scale rests at a distance of only 434 light years it's both the closest seafied and one of the brightest stars in the sky dominating the constellation ursa minor polaris also happens to be aligned directly with the earth's spin axis and this special position on the celestial north pole makes it invaluable to navigators as the earth spins on its axis polaris sits serenely as all other stars rotate around it at any point in the northern hemisphere your latitude is the angle between polaris and the horizon zero degrees north at the equator where polaris is on the horizon and 90 degrees north of the pole where polaris is directly overhead as viewed from oldham lancashire uk polaris sits at an angle of 53.54 degrees above the horizon christopher columbus and ferdinand magellan relied on polaris as they crossed the oceans and explored new worlds perhaps more surprisingly on board apollo 8 jim lovell carried a sextant as a backup navigational device designed by the mit instrument laboratory in cambridge massachusetts it may not have looked traditional but it operated in exactly the same manner as the one constructed by instrument maker john bird in 1757 polaris was one of apollo's key navigational stars it was paired with gamma cassiopeia on lovell's charts which was known in apollo jargon as navi the name was coined by gus grissom on apollo 1 as a prank it was his middle name ivan backwards two other navigational stars gamma valorum and iota usa major were named rhaegor after roger chaffee and dino case aft ed white ii [Music] using the stars for navigation might seem hopelessly old-fashioned but if you think about it for a moment you'll realize that there's no other way that a spacecraft in deep space can orient itself other than relative to the fixed stars on the celestial sphere a spacecraft will often shift its position relative to the stars but on earth things feel different because our orbit around the sun is relatively stable from year to year there are wobbles on relatively short time scales associated with changes in the speed of earth's rotation and these lead to the insertion of leap seconds to keep our atomic clock synchronized with the heavens between 1972 and 1979 nine leap seconds had to be inserted whilst none was needed between the beginning of 1999 and the end of 2005. earth's rotation rate is noticeably chaotic when compared to the accuracy of atomic clocks the largest short-term contribution to changes in earth's rotation comes from the gravitational influence of the moon which acts to slow down the rate of spin by around 2.3 milliseconds per century due to friction between the tidal bulges in the oceans and the rotating solid earth beneath but there are also longer term changes the most pronounced of these is known as axial precession or more commonly the procession of the equinoxes the earth spins on its axis like a gyroscope and because it spins it bulges out at the equator because the earth isn't a perfect sphere the gravitational influence of the sun and moon exerts a torque on the earth that causes its spin axis to sweep round in a circle once every twenty six thousand years this is not subtle because the spin axis itself is tilted at twenty three degrees relative to the plane of earth's orbit and precession therefore has a large effect on the night sky that was first documented by the greek astronomer hipparchus around 150 bce procession manifests itself as a shift in the position of the celestial pole relative to the fixed stars there will come a time in the not too distant future when polaris will no longer sit above the celestial north pole as our spin axis traces out a circle in the sky in about 3000 years time navigators of the future will rely on gamma cpi as a backup for their gps systems as they sail across the seas of our planet and in eight thousand years it will be the bright star deneb the identity of the north star has altered many times throughout human history as the egyptians finished building the great pyramid of giza in 2560 bce alpha draconis lay closest to the celestial pole two and a half thousand years later as the romans did things for us kokob the second brightest star in ursa minor and its neighbor fercard were known as the guardians of the pole precession therefore affects navigation but more importantly it also affects our climate the 23 degree tilt of earth's spin axis is responsible for the seasons summer in the northern hemisphere occurs when the north pole is tilted towards the sun leading to constant daylight within the arctic circle half a year later and the geometry is reversed with the south pole receiving 24-hour daylight and the southern hemisphere experiencing summer precession alone would have no effect on the climate if the earth's orbit were a perfect circle but it isn't it's elliptical with the sun at one focus at the turn of the 21st century it happens to be the case that the earth is at its closest approach to the sun known as perihelion in january just after the winter solstice when the north pole is pointing away from the sun this makes northern winters slightly milder than they would otherwise be because the earth receives a little bit more solar radiation during the northern winter in around ten thousand years time however precession will have carried the earth's spin axis around by a half turn and it will be the north pole that points towards the sun at perihelion making northern hemisphere summers slightly warmer and winters cooler the more elliptical the earth's orbit the more pronounced this effect this is where things get a little more complicated but it's the complication that matters for our story the planets are significantly further away than the moon but also significantly more massive and their constantly shifting positions induce periodic changes to our orbit over long time scales jupiter has the most pronounced effect due to its large mass and relative proximity the largest of these changes occurs on a time scale of 400 000 years picture the earth's orbit becoming periodically more elliptical and more circular stretching back and forth with a period of 400 000 years this oscillation modulates the effect of precession on the climate at the times when the earth's orbit is at its most elliptical the changes due to procession will be at their most pronounced this effect is known as astronomical or orbital forcing of the climate there are many such resonances in earth's orbit another important change in the eccentricity of the ellipse occurs every 100 000 years furthermore the tilt of the axis itself swings back and forth between around 22 and 25 degrees on a 41 000 year cycle the whole solar system is like a giant bell ringing with many hundreds of harmonics driven by the gravitational interactions between the sun planets and moons over many thousands of years these shifts in the earth's orbit and orientation relative to the sun have led to dramatic changes in climate and are certainly one of the key mechanisms that drive the earth into and out of ice ages it is perhaps obvious that these long-term shifts in climate should have had an effect on the evolution of life ice ages present a significant challenge to animals and plants and this will provoke an evolutionary response via natural selection more surprisingly recent research has suggested a direct link between precession the four hundred thousand year eccentricity cycle and the evolution of early modern humans the great rift valley evocative words that immediately suggest origins there are many reasons i love visiting ethiopia i love the people i love the food i love the high altitude freshness of addis i love the mountains and valleys and high plains i even loved visiting er to ale the legendary shield volcano at the alpha triple junction known as the gateway to hell although i probably won't do it again but i also love an idea it's impossible to visit this ancient country and not catch a glimpse in your peripheral vision of a chain of ghosts stretching back ten thousand generations because it is firmly embedded in popular culture that we came from here every one of us is related to someone who lived in ethiopia hundreds of thousands of years ago it is the garden of eden the place where humanity began what popular culture has yet to assimilate however is the fortuitous and precarious nature of the ascent of man when i was growing up i remember talk of the missing link that elusive fossil that would tie us definitively to our ape-like ancestors when i started school dna sequencing was not yet invented and lucy hadn't been unearthed today we have a significantly more complete view of how australopithecines like lucy are related to modern humans and whilst the details are still debated and new evidence is continually updating the standard model of hominin evolution it's now possible to tell the broad sweep of the story in some detail the members of our human evolutionary family are referred to as hominins the split between hominins and the ancestor of the chimpanzee occurred at some point before five million years ago in africa and by four million years ago australopithecus afarensis lucy was present their brain size was approximately 500 cc around the same as a chimpanzee and less than one-third that of a modern human around 1.8 million years ago there was a step change in both brain size and the number of hominin species in the east african rift several species of arginus homo appeared including homo habilis and homo erectus they lived for a time alongside other species including several australopithecines and a genus known as paranthropus there are anthropologists who prefer to classify parathropus as a different species of australopithecus i make this point not to be confusing but to highlight an important fact the study of hominin evolution is a difficult area and it's not surprising that there are ongoing debates about the classification of two million year old fossils and dna sequences what's important for our story however and what nobody disputes is that there seems to have been a jump in both brain size and the number of species of hominins in the rift valley region around 1.8 million years ago by around 1.4 million years ago only one of these species had survived homo erectus with a brain size of 1000 cc the next milestone is the appearance of homo heidelbergensis around 800 000 years ago homo heidelbergensis is generally accepted to be the ancestor of homo sapiens and the neanderthals who lived alongside us in europe until around 45 000 years ago and possibly later homo heidelbergensis represented another jump in brain size up to around 1400 cc which is close to that of modern humans in the late 1960s and early 1970s two hominin skulls were found near the omo river in ethiopia known as omo-1 and omo-2 argon dating of the volcanic sediments around the level they were found dates them at 195 000 plus or minus 5 000 years old these are the earliest fossilized remains to have been identified as homo sapiens the interesting question is what caused these rapid increases in brain size driving hominin intelligence from the chimpanzee-like capabilities of australopithecus to modern humans in only a few million years again this is a very active area of research and there are differences of opinion amongst experts this is the nature of science at the frontier of knowledge and this is what makes science exciting and successful the model we are focusing on is the most widely accepted theory of human evolution it is known as the recent single origin hypothesis or more colloquially the out of africa model and the dates and locations we've described so far might be referred to as textbook there is broad consensus therefore about the when and the where but not why and it is to why that we now turn there's a trend towards larger brain size over the four million years since the emergence of australopithecus but the trend is not gradual there's a large jump around 1.8 million years ago with the emergence of homo erectus and another jump just under 1 million years ago with homo heidelbergensis the final jump occurs when homo sapiens emerges 200 000 years ago the time period around 1.8 million years ago also corresponds to a leap in the number of hominin species present in the rift valley there were at least five or six species living side by side suggesting that something interesting occurred around this time which may have been responsible for or was a contributing factor to the observed increase in brain size particularly in homo erectus the large number of deep water lakes appearing temporarily in the rift valley around 1.8 million years ago indicates that at this time the climate and in particular the level of rainfall was varying quickly and violently similar climate variation occurs around 1 million years ago and 200 000 years ago and this appears to be correlated with increasing hominin brain size the theory is that rapidly changing climactic conditions in the rift valley at these specific times played an important role in driving the increases in brain size the selection pressures that may have led to these increases are unclear selection for adaptability was probably an important factor but social factors such as the ability to live in large groups and intraspecies competition as a result of the larger number of species living side by side particularly around 1.8 million years ago must also have played a role having said that it does appear that climate variation in the rift valley 1.8 million 1 million and 200 000 years ago could have been a contributing factor to the development of our intelligence this is known as the pulse climate variability hypothesis we can now bring all these threads together to reveal a surprising and for me dizzying hypothesis which if correct sheds new light on the immensely contingent nature of the existence of our modern civilization or in simpler language why we are bloody lucky to be here the three dates 1.8 million one million and two hundred thousand years ago correspond to the times when the earth's orbit was at its most elliptical as described earlier the mechanism by which climate changes due to procession at these times is well understood the pulse climate variability hypothesis asserts that the unique geology and position of the great rift valley amplified these changes and that early hominins responded by increasing their brain size if this is correct our brains evolved as a response to changes in the earth's orbit driven by the precise arrangement of the orbits of the other planets around the sun and precession driven primarily by the gravitational interaction between the moon and earth's axial tilt both of which date back to a collision early in the history of the solar system and all this is plainly blind luck without an inconceivably unlikely set of coincidences and the way these conspired together to change the climate in one system of valleys in wonderful ethiopia we wouldn't exist if this is correct then what a response i held a brain for the cameras at saint paul's teaching hospital in addis it is the most complex single object in the known universe a most intricate example of emergent complexity assembled over four billion years by natural selection operating within the constraints placed upon it by the laws of physics and the particular biochemistry of life on earth the brain contains around 85 billion individual neurons which is of the same order as the number of stars in an average galaxy but that doesn't begin to describe its complexity each neuron is thought to make between ten thousand and one hundred thousand connections to other neurons making the brain a computer way beyond anything our current technology can simulate when we do manage to simulate one i have no doubt that sentience will emerge consciousness is not magic it is an emergent property consistent with the known laws of nature but that doesn't lessen the wonder one iota out of this evolutionary marvel we emerge thoughts feelings hopes and dreams exist on earth because of electrical activity inside a 1.5 kilogram blob of stuff which hasn't changed much since the earliest modern humans began the long journey out of africa if you could travel back in time and bring a newborn baby from 200 000 years ago into the 21st century allowing it to grow up in our modern society with a modern education it could achieve anything a modern child could it could even become an astronaut which sets up one more question if the hardware was present two hundred thousand years ago then what changed to lift us from the great rift valley into space the best thing we can do now is just to listen and hope said cliff mitchell moore broadcasting from the bbc studios 24 minutes from the expected splashdown of apollo 13. on the 17th of april 1970 i was too young to watch the live broadcast but i've seen the recording many times since grainy pictures from the deck of the uss iwo jima its flight deck crammed with nervous sailors off the coast of samoa patrick moore and jeffrey pardo grim-faced in the studios and james burke famously with fingers crossed behind his back apollo control houston we've just had loss of signal from honeysuckle honeysuckle creek tracking station in canberra australia was the last ground station to contact apollo 13 before it entered the earth's atmosphere on its way home signal lost during re-entry is routine high drama on all space missions the ionization of the atmosphere caused by the frictional heating of the spacecraft blocks radio signals typically resulting in radio silence for four minutes on apollo 13 six minutes passed in silence the brilliance of the bbc's quartet of commentators was in the silence they allowed on the airwaves the only sound was the static of the nasa feed a moment of genuine tension no need for vacuous media babble nobody could bring themselves to speak we'll only know whether that heat shield was damaged by that explosion three days ago when they come out of radio blackout in just over two minutes said burke silence as four minutes passed houston reports ten seconds to end of radio blackout silence houston we've had a report that orion 4 aircraft has acquisition of signal they're through says burke let's not anticipate because the parachutes may have been damaged shoots should be out murmurs burke not broadcasting just saying there they are there they are they've made it remarks more and then applause i make it no more than five seconds late shouts burke no more than five seconds late the safe return of apollo 13 was arguably nasa's finest hour 55 hours 54 minutes and 53 seconds into the mission three hundred and twenty thousand kilometers from earth lunar module pilot jack swigert switched on a system of steering fans in the hydrogen and oxygen tanks in the service module a routine procedure a piece of teflon insulation inside the tank had been damaged it was later discovered by a series of unlikely events that happened on the ground during the preparation of the spacecraft for flight the wire shorted the tank exploded and the side of the service module was blown off critically damaging the spacecraft's power supply systems and venting the crew's oxygen supply out into space the command module the only part of the spacecraft capable of surviving a re-entry through the earth's atmosphere was now running on batteries and with a rapidly diminishing oxygen supply that would not keep the astronauts alive long enough to return to earth the only option was to shut down the command module and retreat to the lunar module effectively using it as a life raft lovell later spoke of how he didn't regret the mission at all he was robbed of his moon landing which must have been doubly frustrating given he'd already flown to the moon on the historic apollo 8 mission but his reaction revealed in interviews in later life offers great insight into the character of a test pilot we were given the situation lovell explained to really exercise our skills and our talents to take a situation which was almost certainly catastrophic and come home safely that's why i thought that 13 of all the flights including apollo 11 that 13 exemplified a real test pilot's flight both lovell and hayes have said that the idea of not returning safely to earth never really came up there was nothing there that said irrefutably we don't have a chance hayes was correct of course because they did return safely but they only had enough food and water to sustain two people for a day and a half and had to improvise a carbon dioxide filter to provide them with enough breathable air for the return journey locked in the lunar module with limited supplies of food and water and temperatures dropping towards freezing life was far from comfortable with the command module powered down to preserve the sparse battery supplies left after the loss of the fuel cells the crew had to survive in a hostile environment with limited resources like so many outposts of human civilization throughout history shortage of water was a primary concern water was critical on the lunar module for two reasons as well as being needed to keep the crew hydrated and to rehydrate the food it also cooled the electrical systems on the spacecraft conserving water therefore became a critical part of the plan to return to earth reducing their intake to just one-fifth of a normal human water ration each of the crew suffered severe dehydration and together they lost 31.5 pounds in weight nearly 50 more than any other apollo crew despite the discomfort setting a new mission trajectory and navigating their way along it remained the primary challenge the standard way to make in-flight course corrections on apollo was to use the command module's main engine but the system was located close to the damaged site and mission controllers decided that lighting it was too great a risk instead the decision was made to use the lm's descent engine to send them around the far side of the moon and back to earth in four and a half days this is known as a free return trajectory a slingshot around the moon at the correct angle to return directly to earth no one knew if an engine designed for a completely different purpose would perform this function successfully but they knew that if it failed they would not return five hours after the initial explosion the lm engine was fired for a 35 second burn successfully putting the crew onto a free return trajectory this solved one problem but raised another calculations of the trajectory estimated return to earth 153 hours after launch which would push the key reserves on the craft too low for comfort so it was decided to speed up the spacecraft with another burn cutting the total time of the voyage by 10 crucial hours such were the slim margins on apollo 13. the main navigation system in the command module was out of action so lovell had to calculate the correct navigational inputs while back at base mission control worked through the same calculations as a cross check lovell also got to use his sextant which he played with on apollo 8 to navigate by the stars for real the calculations are preserved as handwritten notes in the lunar module systems activation checklist this was the checklist loveland hayes would have used to fly down to the moon's surface now useless lovely used the waste paper to write down instructions to put the ship on course for earth two hours after they rounded the far side of the moon the lm engine fired following lovell's handwritten checklist increasing the speed of the spacecraft by eight hundred and sixty feet per second and buying them 10 precious hours the most dramatic rescue in the history of human space flight stands as a testament to the brilliance of the three test pilots lovell hayes and swigert and also to the brilliance of the engineers on the ground who simply knew their stuff nasa's apollo engineers were young by today's standards the average age of the team in mission control for the splashdown of apollo 11 was 28 years old this is one of the reasons why the united states reaped such a colossal economic reward from its investment in apollo the generation of scientists and engineers who worked on and were inspired by apollo went out into the wider economy and delivered a huge investment return a series of studies including one by chase econometrics showed that for every dollar invested in apollo at least six or seven dollars was returned as increased gdp growth this should of course be bloody obvious new knowledge grows gdp but every generation of politicians seems to require re-educating to understand the difference between spending and investment and while i'm politicizing let me say that the usual political argument that public support is needed for such large investments is drivel firstly the investment in nasa wasn't that large never exceeding 4.5 of the federal budget throughout the lifetime of apollo and secondly it is a politician's job to lead from the front make the case that investment in knowledge in pushing the boundaries of human capabilities and exploring all frontiers both physical and intellectual is the key to the future wealth prosperity and security of civilization aspire to be kennedy not a hand-wringing apologist for intellectual and technological decline the nine apollo flights to the moon remain the furthest modern humans have explored beyond the rift valley in our two hundred thousand year history homo sapiens first left africa in large numbers 60 000 years ago so on geological time scales we didn't hang around our ancestors followed waves of earlier hominins homo erectus were in southeast asia 1.6 million years ago and half a million years later neanderthals had colonized europe and homo floresiensis were in southern asia the details of the migration sixty thousand years ago are particularly well understood as a result of the combination of genetic archaeological and linguistic studies the precision comes in part from the tracking sequences of mitochondrial dna which is passed down from the mother and not shuffled by sex this makes it relatively stable and easy to track changes are caused by mutations alone the most widely accepted interpretation of the data suggests that a small population of between one thousand and two thousand five hundred individuals left east africa sixty thousand years ago and moved north across the red sea and through arabia the group then split moving into southern europe forty three thousand years ago and traveling through india and into australia on roughly the same time scale the crossing into north america via east and russia was probably later around 15 000 years ago these early groups of humans were hunter-gatherers it's been estimated that the basic social units would have reached a maximum of around 150 individuals this is known as dunbar's number after the british anthropologist robin dunbar who suggests that the largest social group amongst any given population of primates is related to the size of their brains specifically the neocortex dunbar's number can be observed today in the size of the average person's social network both in the real world and online our hardware the brain has not changed appreciably since the first humans appeared in africa 200 000 years ago these social groups would have lived in loosely bound tribes perhaps reaching a size of between one and two thousand individuals operating within an area of around 100 kilometers populations would stabilize perhaps in response to social factors but also as a result of increased mortality rates caused by parasitic diseases and diminishing per capita resource availability before fragmenting and spreading in this fashion the rate of progression of our ancestors across the globe has been estimated to have been around 0.5 kilometers per year or 15 kilometers per generation population density did not rise significantly beyond these levels until these proto-societies shifted from a hunter-gatherer lifestyle to agriculture around twelve thousand years ago this shift was the trigger for the development of civilization the most important single step following the migration out of africa in the journey from apeman to spaceman there are many competing theories as to the reason for the domestication of crops but many note the correlation between the first evidence of agriculture and the beginning of the current interglacial period known as the holocene twelve thousand years ago in the fertile crescent around modern-day jordan and syria people known as the natufians were beginning to settle into larger communities perhaps because of the relatively benign climate the area would have been forested and rich in wild cereals fruits and nuts rather than the austere desert of today one theory is that a brief one thousand year cold period known as the younger dryas beginning around 10800 bce triggered drier conditions in the region forcing the natufians to begin cultivating the previously abundant wild crops on which they had come to rely whatever the reason it generally agreed that the foundational crops of modern agriculture including wheat barley peas and lentils were all to be found in the fertile crescent by 9000 bce and by 8000 bce the banks of the nile were being cultivated at approximately the same time evidence of farming can be found in asia's indus valley in china and in mesoamerica this suggests that there was no single environmental or developmental cause for agriculture because it appeared independently at many sites across the world rather our large brains and relatively large social groups were ready to take up the challenge when the need arose once agriculture was established larger numbers of people could live together taking advantage of the more stable food supply the freedom from continual hunting and gathering would have introduced a new aspect to human life free time and it was used to great effect some of the earliest farmers settled in a place known as beda in modern day jordan around 7000 bce living in round stone-built houses they grew barley and wheat and kept domesticated goats engaged in ritual and ceremony and buried their dead importantly each of these activities was carried out in specific areas of the settlements the beginning of town planning by the second century bce a semitic people known as the nabataeans lived around bader they employed new technologies to increase the reliability of farming and constructed walled agricultural terraces on the hillsides around the village to collect and store water animal husbandry was also expanding with the domestication of cows pigs donkeys and horses even previously dangerous animals were coerced into living with humans there is evidence that the nabataeans kept dogs as the great empires of egypt greece and rome prospered the nabataeans remained partially nomadic driving their camel trains across the desert along the long established trade routes between north africa and india and the great cities of the mediterranean but then around 150 bce they decided to try something different a few kilometers south of bader in a narrow gorge naturally formed in the soft sandstone rock they built the city of petra today tourists stream through a magnificent passageway lined with buildings carved out of the desert rocks and known as the sikh but two thousand years ago the great and good of mesopotamia rome and egypt would have walked this route into this jewel of late antiquity the grandeur of the buildings is still overwhelming they stand not as great architecture for their time but as simply great with no caveat the most famous is called al-khasne which means treasure box because of the carved urn above the entrance which bedouin legend has it contains the treasure of a pharaoh monumental architecture is a common feature in the rise of human civilization it is a statement of power and grandeur to impress and cow outsiders but it also serves an internal purpose cementing the position of the rulers in the hierarchy and therefore providing the stability and security on which civilization rests over time a virtuous circle emerges the buildings help the civilization prosper and the more prosperous the civilization the more impressive the buildings become petra's wealth was derived from its location built within a natural gorge the area is prone to flash floods which provided precious water in a landscape that was arid by the time the nabataeans began to build the city also sits at the fulcrum of the ancient nomadic trade routes along which wood spices incense and dyes were transported from africa and india and into the great mediterranean civilization beyond the appetite of the greeks and romans for exotic goods was insatiable black pepper alone fetched 40 times its own weight in gold in a roman market petra because of its strategic location controlled all that trade and taxed it today 1500 years after the city was abandoned it is still a magnificent site an overused but entirely accurate statement talk to an archaeologist however and you quickly realize how much more impressive it would have been in its heyday the hillsides running down the valley from the carved tombs are scattered with rocks but closer inspection reveals them to be bricks the remains of houses temples and palaces everything from alhasner to the houses would have been covered in white plaster and painted in bright colors which would have appeared resplendent against the monochrome desert sands to build on this scale required a huge labor force petra was home to at least 30 000 people living in a few square kilometres of desert such a population density required technological innovation on a metropolitan scale and the nabataeans perhaps more than any other civilization in antiquity were masters of fluid engineering virtually every drop of rainwater that fell on the surrounding hillsides was captured in grooves and stored in giant reservoirs and cisterns they were better at plumbing than the romans who employed the petron engineers in rome petra had the world's first pressurized water system which could deliver 12 million gallons of water a day into the city outside the city the irrigation system continued out into the surrounding fields lining the hillsides in still visible terraces the nabataeans didn't simply build a city they terraformed a landscape i stood and imagined the ancient valley views with some awe the mountain slopes would have been green with maize barley pulses and vineyards a desert turned green and feeding this grandest of desert civilizations for six centuries whenever i see the ruins of petra rome athens or cairo i wonder what earth would be like today if the great civilizations of antiquity had not fallen i blame the philosophers for not discovering the scientific method earlier and inventing the electric motor how hard can it be agriculture then was fundamentally important to the rise of civilization because it enabled large numbers of people to live in one place and gave them access to resources and time which would have been unavailable to hunter-gatherers with resources and time comes the division of labor freeing up a small but important subset of individuals to engage in pursuits other than those necessary for immediate survival farmers stonemasons priests soldiers administrators and artisans emerge together with a ruling class who begin to direct the construction of monumental architecture partly for their own selfish ends and cities like petra become possible petra was a relative latecomer in the emergence of the cities and civilizations of antiquity the first great ancient civilization the old kingdom of egypt arose around 2600 bce along the fertile and farmed banks of the nile and precisely the same pattern of agriculture followed by social stratification ritual and monumental architecture can be seen present also in the old kingdom and possibly developed there was the one final vitally important innovation we will soon discuss the written word it all seems so simple when written down on a piece of paper the bbc prepares something known as a call sheet which tells a film crew everything they need to know about a trip call sheets are very neat all the timings work beautifully carefully documenting flights ground transfers to locations and filming and rest periods all of course in accordance with health and safety regulations and all that things never quite work out the way they're envisaged back in the office of course but filming the return of the expedition 38 crew from the international space station to the kazakh steppe in march 2014 was the wildest adventure i've experienced the call sheets said that we would fly into astana on the 8th of march arriving at 1am on the 9th into our hotel after a leisurely breakfast at 9 00 am we drive to a city called karaganda which has a spectacular statue of yuri gagarin in the town square there we'd meet up with our drivers who embedded with ross cosmos the russian space agency would drive us out to the landing site the following morning arriving in time for a hot meal and a good rest on the step ready to film the landing on the morning of the 11th after of course a hot breakfast we'd then drive back to the airport hop on a flight and be home in time for lunch on the 12th a doddle bollocks the step of central kazakhstan in march is a featureless frozen wilderness covering around eight hundred thousand square kilometers of the country's interior there are no towns and few roads just tufts of stunted brown grass and snow fading into an ice gray leavened sky in march 2014 temperatures were unseasonably cold falling below minus 20 degrees c at night and it was snowing our team had standard 4x4 vehicles which got stuck in the snow by mid-afternoon the day before the landing even though we'd set off three hours earlier than the 6am officially sanctioned health and safety call time because of the weather this was problematic because our eight man spaceman film was constructed carefully around this moment the return of three human beings from space over vodka cold meat and bread we discussed our options we'd been helped along the snowy roads by a russian team from the siberian city of tobolsk in two spectacular six-wheel drive vehicles hand built by a company called petrovic tobolsk is best known for being the place dissidents were sent during the soviet era tsar nicholas ii and his family enjoyed the tobolskian hospitality for a year before being transported to a caterinburg to be shot mendeleev the inventor of the periodic table was born there but so is rasputin it's a tough place and they know how to build tough vehicles our guide from ross cosmos managed to radio the petrovic team and they agreed that if we could catch them up in the frozen wilderness they could take two of us out to the landing site the cameraman and i jumped aboard a pair of snowmobiles and headed out into the rapidly dimming late afternoon twilight in search of the men from siberia it was a difficult decision to jump on the snowmobiles we didn't have a satellite phone because they are illegal in kazakhstan and nobody spoke english so we couldn't quite assess the level of difficulty associated with finding these two siberian needles in a kazakh step and we didn't know who the siberians actually were it seemed that they were freelancers hired to take photographs and broadcast live television pictures back from the landing site for the russian space agency we also had to decide whether we could make the film with only two people much as i spend a lot of time dreaming about jettisoning directors producers and executives there is a reason why we usually take a crew of six sound is particularly important you don't really miss the sound man until he's not there our sound man on the series is called andy but we always call him sound man there are too many other things to remember as it turned out the petrovic crew were a hospitable and professional bunch although their willingness to spend many days out in the wilderness waiting for the soyuz they'd driven down from siberia and were in no hurry to get home played on our minds approaching midnight on the night before the landing we received a message from ross cosmos that the landing might be postponed due to the poor weather and the decision was made to camp out on the step and wait in the distance we could make out a small group of farm buildings through the snow and we headed towards them in broken english one of the crew told us that it is a kazakh tradition to welcome travellers into your home at any time of the day or night and offer them food and so we found ourselves inside a farmhouse that appeared to have heated walls and resembled the inside of an oven eating a feast of jam bread assorted sweets and horse all washed down with vodka which the petrovic crew carried in large crates alongside their satellite broadcasting hardware it was unforgettable at 4 am soaked in vodka the call came through commander alia kotov sergey ryazanskiy and mike hopkins had climbed aboard the soyuz and were preparing to depart the international space station i was elated because i genuinely thought the landing would be called off and i had no idea what that would have meant other than waiting for the storms to clear on the step at 602 kazakh time the soyuz tma-10m the 199th soyuz to fly since 1967 undocked from the iss this is the point of no return except in an emergency just two hours and twenty eight minutes later it fired its engine for a pre-programmed burn of four minutes and forty four seconds this reduced the spacecraft's velocity by 128 meters per second relative to the station which in its orbit that day was traveling at 7 358 meters per second that number is not arbitrary it is given by a simple equation which can be derived easily from newton's law of gravitation and his second law of motion f equals m a we leave it as an exercise for the listener to show that these two laws of nature can be rearranged to show that the velocity v of any object in a circular orbit a distance r from the center of the earth mass m e is given by v equals the square root of g m e over r to derive this result you need to know that the force required to maintain an object of mass m in a circular orbit is mv squared over r the space station orbits at an altitude of between 330 and 445 kilometers let's choose the middle ground of 387 kilometers this is a back of the envelope calculation estimate is the name of the game as my old physics teacher used to say at school the radius of the earth is 6 378 kilometers and the mass of the earth is 5.97219 times 10 to the 24 kilograms newton's gravitational constant is 6.67384 times 10 to the minus 11 meters cubed per kilogram per second squared do the calculation yourself math is good for you with these numbers v is approximately 7 675 meters per second which is close enough the difference is due to the precise altitude of the iss that day i love doing little calculations like this they reveal the immense power of mathematical physics this really is the orbital velocity of the international space station and it is forced to be so by laws of nature first published by isaac newton in 1687. if you've never done a calculation like this before you should feel elated the biologist edward o wilson called this feeling the ionian enchantment a poetic term he introduced to describe the realization credited to thales of miletus in 600 bce that the natural world is orderly and simple and can be described with great economy by a small set of laws it is nothing short of wonderful that we can calculate the orbital velocity of the international space station together and this points us neatly towards the story of the last great innovation in the ascent from eight man to space man i began my degree at the university of manchester in 1992 which is when i started doing physics full time i gained my phd in 1998 and spent the next 11 years working as a particle physicist at the diesel laboratory in hamburg fermilab in chicago and cern in geneva in 2009 i began filming wonders of the solar system which slowed down my research a bit but i've been at it now for 22 years which is almost half my life in that time i've learned a lot about how to be a scientist how to think about scientific problems how to make measurements of nature particularly the behavior of subatomic particles and how to interpret those measurements to generate new knowledge and make new discoveries but given all that there's no way i would be able to calculate the orbital velocity of the international space station from scratch given newton's laws it's trivial without them it would be virtually impossible newton's laws are far from obvious they took newton a scientific lifetime to produce and he was a genius one of the greatest scientific minds of all time and even he didn't start from scratch he relied heavily on the previous works of galileo euclid and a hundred other philosophers geometers and mathematicians whose names have been forgotten but whose works remain as cornerstones of our scientific culture the reason we could run through that simple calculation together is that the thoughts and discoveries of these generations of philosophers scientists and mathematicians were not lost they were preserved forever in the written word [Music] writing appears to have arisen independently in several different cultures just as with the development of agriculture and just as agriculture triggered the birth of civilization 12 000 years ago so the emergence of writing supported a rapid increase in the complexity of civilization the earliest known system of writing is generally accepted to be cuneiform the sumerian system that emerged around 5000 years ago in the cities of mesopotamia although it's possible that egyptian hieroglyphs may predate it literally meaning wedge-shaped cuneiform comprises a thousand or more symbols created using a stylus made from reed that was pressed into a soft clay tablet following cuneiform and hieroglyphs other forms of script emerged in greece china india and later central america writing seems not to have arisen out of a deep human need to share and record intimate thoughts and lay down knowledge for future generations that would be far too romantic rather it appears to have served a more practical purpose revealed in a set of around 150 nabataean scrolls discovered by archaeologists in 1993 the scrolls date from around 550 ce in the final period before petra was abandoned one of the most intact documents relates to a court case between two priests it is alleged that one of the priests decided to run away from their shared house taking a key to one of the upstairs rooms two wooden beams that presumably held the roof up six birds and a table this is probably how writing began the invention upon which modern human history rests arose disappointingly for admin purposes this is seen not only in the relatively late nabataean scrolls but in many of the early texts cuneiform developed because of a need to keep track of trade and accounts in the increasingly complex economy of mesopotamia egyptian hieroglyphs may be an exception as there is a strong ritual component but there's also evidence of their early use in commerce administration trade and law the foundations of a modern society information about the natural world was also recorded in hieroglyphs we see the cycle of the seasons chronicled as well as important environmental events there are also some beautiful early examples of the use of writing to express deeper human desires and feelings that resonate strongly today and show yet again that our ancestors had inner lives not too distant from our own but the oldest surviving papyrus documents from the old kingdom are marvelously prosaic from dynasty five in the reign of pharaoh jedkari is ac between 2437 and 2393 bce can be found an early version of the parrot sketch as rey hathor and all the gods desire that king is ac should live forever and ever i am lodging a complaint through the commissioners concerning a case of collecting a transport fare and so the letters continue whilst the tombs are covered in the names of pharaohs and stories of the gods the people of egypt were using writing as we do today and i find it wonderful reassuring and moving in a funny sort of way to hear ancient voices complaining down the years perhaps we humans really will never change from dynasty 20 a millennium later during the reign of ramesses the third and fourth between 1182 and 1145 bce the complaints continue the scribe amen act your husband took a coffin from me saying i shall give the calf in exchange for it but he hasn't given it until this day i mentioned this to parquet who replied give me a bed in addition to it and i will bring you the calf when it is mature and i gave him the bed neither the coffin nor the bed is yet here to this day if you were going to give the ox send it on but if there is no ox return the bed and the coffin alongside the letters the ritual the complaints the admin and the legal documents there was also a sophisticated literary and storytelling tradition in ancient egypt and a powerful appreciation of the value of the written word three thousand years ago on the banks of the nile during the reign of queen twosret somebody wrote a eulogy for the writers these sage scribes their names endure for eternity although they are gone although they have completed their lifetimes and all their people are forgotten they did not make themselves pyramids of bronze with steli of iron they made heirs for themselves as the writings and teachings that they begat departing life has made their names forgotten writings alone make them remembered taken from the tale of sinoway and other egyptian poems 1940 to 1640 bc writing was the final pivotal moment in our ascent from early agrarian civilizations to the international space station because it frees the acquisition of knowledge from the limits of human memory the hardware restrictions set down in the rift valley two hundred thousand years ago no longer matter writing allows a practically unlimited amount of information to be passed from generation to generation and to be shared across the world knowledge is no longer lost but is always added to it becomes widespread accessible and permanent a little boy from oldham lancashire can inhabit the mind of newton assimilate his lifetime's work and derive new knowledge from it writing created a cultural ratchet an exponentiation of the known that allowed humanity to innovate and invent way beyond the constraints of a single human brain we now work together as a single mind spread across the planet and with a memory as long as history it is this collective effort enabled by the written word that carried us the human race paragon of animals from the great rift valley to the stars i deliberately borrow from shakespeare the most precious objects on earth are not gems or jewels but ink marks on paper no single human brain could conceive of hamlet principia mathematica or codex lester they were created by and belong to the entire human race and the library of wonders continues to grow johannes kepler is rightly best known for his laws of planetary motion that paved the way for newton to write principia hidden within his illustrious cv however is a publication that had a rather more whimsical earthbound ambition two years after publishing the first part of astronomia nova in 1609 kepler published a short 24 page paper entitled de nive sex angular on the six cornered snowflake it is a beautiful example of a curious scientific mind at work in the dark december of 1610 kepler was walking across the charles bridge in prague when a snowflake fell on the lapel of his coat in the freezing night he stopped and wondered why this ephemeral sliver of ice possessed a six-sided structure in common with all other snowflakes notwithstanding their seemingly infinite variation others had noticed this symmetry before but kepler realized that the symmetry of a snowflake must be a reflection of the deeper natural processes that underlie its formation since it always happens when it begins to snow that the first particles of snow adopt the shape of small six cornered stars there must be a particular cause wrote kepler for if it happened by chance why would they always fall with six corners and not with five or seven kepler hypothesized that this symmetry must be due to the nature of the fundamental building blocks of snowflakes this stacking of frozen globules as he referred to it must be the most efficient way of building a snowflake from the smallest natural unit of a liquid-like water to my mind this is a leap of genius and a tremendously modern way of thinking about physics the study of symmetry in nature lies at the very heart of the standard model and abstract symmetries known as gauge symmetries are now known to be the origin of the forces of nature this is why the force carrying particles in the standard model are known as gauge bosons kepler was searching for the atomic structure of snow before we knew atoms existed motivated by the observation of a symmetry in nature the six-sided shape of all snowflakes the inspiration for this idea which is way ahead of its time came from a peculiar source in the years leading up to the publication of de nieve sex angular kepler had been in communication with thomas harriet an english mathematician and explorer amongst multiple claims to fame harriet was the navigator on one of sir walter rally's voyages to the new world and had been asked to solve a seemingly simple mathematical problem rally wanted to know how best to stack cannonballs to make the most efficient use of the limited space on the ship's deck harriet was driven to explore the mathematical principles of sphere packing which in turn led him to develop an embryonic model of atomic theory and inspire kepler's consideration of the structure of snowflakes kepler imagined replacing cannonballs with globules of ice and supposed that the most efficient arrangement creating the greatest density of globules was the six-sided hexagonal form he observed in the snowflake on his shoulder kepler also observed hexagonal structures across the natural world from beehives to pomegranates and snowflakes and presumed that there must be some deeper reason for its ubiquity hexagonal packing as kepler referred to it must be the tightest possible so that in no other arrangement could more pellets be stuffed into the same container this became known as the kepler conjecture it took almost 400 years to prove kepler's conjecture and this required the help of a 1990s supercomputer despite the time lag kepler's work had a more immediate impact inspiring the beginnings of modern crystallography that led eventually to the discovery of the structure of dna what a lovely example of serendipity coupled with curiosity and sprinkling of genius from cannonballs to snowflakes to the code of life as for kepler's original thought on that frozen bridge he never found the connection between the underlying structure of his ice globules and hexagonal symmetry of snowflakes even though he realized that the regular patterns must reveal something about the shape of the building blocks of snowflakes and the details of the packing he couldn't explain the ornate complexity or the flatness of the structure instead he acknowledged his failure with the good grace of a true scientist i have knocked on the doors of chemistry he writes at the end of his paper and seeing how much remains to be said on this subject before we know the cause i would rather hear what you think my most ingenious man than wear myself out with further discussion three and a half centuries later japanese physicist yukichiro nakayara made the first artificial snowflakes in the laboratory writing in 1954 he describes the process that begins not with the snowflake itself but with smaller substructures called snow crystals which are in turn built up from collections of ice crystals the globules kepler was searching for the hexagonal packing that kepler suspected to be the origin of the snowflake symmetry begins with the formation of these ice crystals when water molecules link together in a hexagonal structure via hydrogen bonds hydrogen bonding occurs because of the structure of the water molecules themselves with a greedy oxygen atom hungry for electrons grabbing them off two hydrogen atoms forming covalent bonds that lock the h2o molecules together leaving a residual positive electrical charge in the vicinity of the two protons and a negative charge in the vicinity of the oxygen this slight separation of charge in the water molecules allows them to bind together into larger structures through the mutual attraction and repulsion of the electrical charges just as an electron is bound into its position around an atomic nucleus the entire configuration including the structure of the oxygen nucleus and the single protons that comprise the hydrogen nuclei can be predicted in principle by the standard model of particle physics yet the details of any particular snowflake are beyond computation because the seemingly infinite variety reflects the precise history of the snowflake itself once ice crystals form as agglomerations of water molecules held together by hydrogen bonds they cluster around dust particles in the air building on their underlying hexagonal symmetry to form larger snow crystals as the crystals begin the long journey down to earth they join in ever larger more complex combinations shaped by endless variations of air temperature wind patterns and humidity into myriad unique forms the symmetry is all that remains of the simplicity and it takes a careful and patient eye to see the endless variation for what it is a reflection of the complex history of the snowflake convoluted with the underlying simplicity of the laws of nature the most vivid example of emergent complexity and the closest to our hearts is life the origin of life on earth has a sense of inevitability about it because its basic processes are chemical reactions that will proceed given the right conditions those conditions were present in the oceans of earth 3.8 billion years ago possibly earlier and they led to the emergence of single-celled organisms the fateful encounter which produced the eukaryotic cell around 2 billion years ago looks rather more like blind chance but it happened here and laid the foundations for the cambrian explosion 530 million years ago there is a bit of hand waving going on here though and to make a more persuasive case that all the complexity of darwin's endless forms most beautiful can at least in principle emerge from simple underlying laws one more example is in order perhaps the most beautiful manifestation of the artful complexity of nature can be found in the spots stripes and patterns on the coats and skin of living things emergent pattern writ large across venomous striped surgeonfish emperor angelfish zebra swallowtail butterflies and the big cats of africa and asia everyone agrees that these patterns evolved as a result of natural selection of one form or another and the raw material for the variation was provided by random mutations in the genetic code but a very challenging scientific question of fundamental importance in modern biology is precisely how patterns such as these appear how the leopard got its spots zebra moved away to some little thorn bushes where the sunlight fell all stripey and the giraffe moved off to some tallish trees where the shadows fell all blotchy now watch said the zebra and the giraffe this is the way it's done one two three and where's your breakfast all they could see were stripy shadows and blotched shadows in the forest but never a sign of zebra and giraffe that's a trick worth learning take a lesson from it leopard then the ethiopian put his five fingers close together and pressed them all over the leopard and wherever the five fingers touched they left five black marks all close together roger kipling's just so story how the leopard got his spots tells the story of an ethiopian man and a leopard they went hunting together but one day the man noticed that the leopard wasn't very successful the reason he deduced was that the leopard had a plain sandy coat whereas all the other animals had camouflage that's a trick worth learning leopard he said taking his fingers and thumb and pressing them into the leopard's coat to give it the distinctive five-pointed pattern if you don't believe in evolution by natural selection this is the most plausible theory open to you if you do then what remains is to identify the mechanism by which the pattern is formed the answer might appear to be solely a matter of genetics but genes are not the whole story it would take a terrific amount of information to instruct every single cell to cover itself according to its position on the leopard skin and this is indeed not what is done nature is frugal and deploys a much more efficient mechanism for producing camouflage patterns i get to say yet again that this is an active area of research and therefore exciting the reason for the attention is that camouflage patterns on the skin self-organize during the development of the embryo and embryonic development is of course fundamental to an understanding of biology in the case of the leopard it is thought though not proven that the camouflage is an example of a touring pattern named after the great bletchley park code breaker and mathematician alan turing in 1952 turing became interested in morphogenesis the process by which an animal develops its shape and patterning he was particularly interested in the mathematics behind regularly repeating patterns in nature such as the fibonacci numbers and golden ratio in the leaf arrangements of plants and the scales of pineapples and the appearance of camouflage patterns such as the tiger's stripes and the leopard spots turing's influential and groundbreaking paper the chemical basis of morphogenesis published in march 1952 begins with a simple statement it is suggested that a system of chemical substances called morphogens reacting together and diffusing through a tissue is adequate to account for the main phenomena of morphogenesis these systems are known as reaction diffusion systems and they can produce patterns from a featureless initial mixture if the two reactants diffuse at different speeds imagine a dry field full of grasshoppers they are strange grasshoppers because when they get warm they sweat generating a large amount of moisture now imagine that the field is set alight in several different places the flames will spread at some fixed speed and if there were no grasshoppers the whole fields would be charred as the flames approach the grasshoppers however they will start to sweat dampening the grass behind them and inhibiting the flames as they hop away ahead of the approaching flames depending on the different parameters including the different speeds of the flames and the grasshoppers and the amount of sweat necessary to quell the advancing flames a touring pattern can be formed with areas of charred grass and green areas where the inhibiting grasshoppers prevented the fire from taking hold it is thought that the leopard gets its spots in this way during embryonic development an activator chemical fire spreads through the skin and stimulates the production of the dark pigmented spots charred grass but is inhibited by another chemical sweating grasshoppers spreading with a higher diffusion rate the precise pattern produced depends on the constants of nature of the system such as the speeds at which the chemicals diffuse and on what a mathematician would call the boundary conditions the size and geometry of the grassy field in our analogy in embryonic development it is the size and shape of the embryo when the reaction diffusion begins that determines the type of pattern produced a long and thin domain produces stripes a domain that is too small or too large produces uniform color in between can be found the distinctive coat patterns of cows giraffe cheetah and of course the leopard computer simulations of turing patterns have been remarkably successful not only in describing the generic features particularly of mammalian coats but also of some of the interesting details seen in nature for example the mathematical models predict that it is possible for spotted animals to have striped tails as cheetahs do but not for striped animals to have spotted tails and indeed no such examples exist kepler's snowflakes and the leopard spots are two picturesque examples of emergent complexity the appearance of intricate ordered patterns from the action of simple underlying laws nature contains systems far more complex than these of course you being a case in point but to return to the question at the beginning of our solipsistic meander the reason that you exist given the laws of nature is that you are allowed to just as all snowflakes and all leopards coats are unique in detail because of their individual formation histories so you are unique because no two human beings share a common history but we wouldn't read any deep meaning into the existence of one particular snowflake in a snowstorm and the same is true for you our focus should therefore shift from trying to explain the appearance of humans or our planet or even our galaxy to a rather deeper question the origin of the whole framework of space-time and the laws that govern it and the allowed structures within it what properties of the laws themselves are essential for galaxies planets and human beings to exist after all as we've noted the laws might be mathematically elegant and economical but they do contain a whole host of seemingly randomly chosen numbers discovered by experimental observation and with no known rhyme or reason to them the constants of nature such as the strength of the forces the masses of the particles and the amount of dark energy in the universe how dependent is our existence on these fundamental numbers [Music] our universe appears to be made for us we live on a perfect planet orbiting around a perfect star this is of course content-free whimsy the argument is backwards we have to be a perfect fit for the planet because we evolved on it but there are interesting questions when we look deeper into the laws of nature and ask what properties they must have to support a life in the universe take the existence of stars for example stars like the sun burn hydrogen into helium in their cores this process involves all four forces of nature working together gravity kicks it all off by causing clouds of dust and gas to collapse as the clouds collapse they get denser and hotter until the conditions are just right for nuclear fusion to occur fusion starts by turning protons into neutrons through the action of the weak nuclear force the strong nuclear force binds the protons and neutrons together into a helium nucleus which in itself exists on account of the delicate balance between the strong nuclear force holding it together and the electromagnetic force trying to blow it apart because of electrically charged protons when stars run out of hydrogen fuel they perform another series of equally precarious nuclear reactions to build carbon oxygen and the other heavy elements essential for the existence of life there are many examples of apparent fine tuning in nature if protons were not 0.2 percent more massive then they would be unstable and decay into neutrons that would certainly put an end to life in the universe because there would be no atoms the proton mass is ultimately set by the details of the strong and electromagnetic forces and by the masses of the constituent quarks which are set by the yukowa couplings to the higgs field in the standard model there really isn't much freedom at all the mother of all fine tunes however is the value of our old friend dark energy the thing that is causing our universe to gently accelerate in its expansion although dark energy contributes 68 of the energy density of the universe the amount of dark energy in a given volume of space is actually small very small 10 to the minus 27 kilograms per cubic meter to be precise the point is that every cubic meter of our universe has this amount of dark energy in it and that adds up explaining why dark energy has this small but non-zero value is one of the great problems in cosmology not least because if a particle physicist sits down with a quantum field theory and decides to calculate how big it should be it turns out that it would be more naturally of the order of 10 to the 97 kilograms per cubic meter that's a lot bigger than 10 to the minus 27 kilograms per cubic meter over a million million million million million million million million million million million million million million million million million million million times bigger in fact that's embarrassing for the particle physicists of course but from the perspective of fine-tuning it's even worse if the value of dark energy were only 50 times larger than it is in our universe rather than somewhere else in this immensely large theoretical range then it would have become dominant in the universe around one billion years after the big bang during the time that the first galaxies were forming because dark energy acts to accelerate the universe's expansion and dilute matter and dark matter gravity would have lost the battle in such a universe and no galaxies or stars or planets or life would exist what could possibly account for this incredible piece of luck it can't really be luck the odds are too long by a jeffrey boycott innings one possibility is that there is some as yet unknown physical law or symmetry that guarantees that the amount of dark energy will be very close to but not quite zero this is certainly possible and there are physicists who believe that this may be the case the other possibility which was raised by one of the fathers of the standard model stephen weinberg is that the value of dark energy is anthropically selected anthropic arguments appear at one level to be a statement of the obvious the properties of the universe must be such that human beings can exist because human beings do exist this is of course true but it is fairly devoid of content from a physical perspective unless there is some way in which all possible values of dark energy and indeed all the other constants of nature are realized somewhere if for example there exists a vast possibly infinite swathe of different domains in the universe or indeed an infinity of other universes each with a different amount of dark energy selected by some mechanism from the span of allowed values then we would indeed have a valid anthropic explanation for our special human universe it must exist because they all do and of course we appear in the one that permits our existence but surely it makes no sense to take refuge in a vast infinity of universes to explain our existence absolutely correct if that's why the idea is introduced it's no better than a god of the gaps explanation if however there was some other reason based on observations and theoretical understanding that suggested an infinity of universes then such an anthropic explanation for our perfect human universe would be admissible remarkably and that remarkably overused word is appropriate for once this outlandish suggestion is a widely held view amongst many cosmologists if we look at our universe on the largest distance scales by which i mean at distance scales far larger than the size of single galaxies it has a number of properties that any theory of its origin has to explain the most precise picture of the young universe we have is the photograph of the cosmic microwave background radiation cmb taken by the planck satellite this is the afterglow of the big bang a photograph of the universe as it was 380 000 years after the initial hot dense phase when the expansion had cooled things down sufficiently for atoms to form the most obvious feature of the cmb is that it's extremely uniform glowing at a temperature of 2.72548 degrees above absolute zero with small fluctuations at the level of one part in 100 000 those very tiny temperature differences are represented by the colors in the photograph this uniformity is extremely difficult to explain in the standard big bang model for a simple reason our observable universe today is 90 billion light years across this means that if we look out to the cmb from opposite sides of the earth we are looking at two glowing parts of the ancient sky that are now separated by 90 billion light years the universe however is only 13.8 billion years old which means that light the fastest thing there is has only had time to travel 13.8 billion light years two opposite parts of the cmb could therefore never have been in contact with each other in the standard big bang model and there is absolutely no reason why they should be almost precisely the same temperature i've emphasized almost in the previous sentence because as we noted there are very slight variations in the cmb at the level of one part in 100 000 and these are very important the universe was never completely smooth and uniform everywhere and these variations in density are encoded into the cmb as differences in temperature the regions of slightly greater density ultimately seeded the formation of the galaxies and so without them we wouldn't exist what caused these small variations in the otherwise ultra smooth early universe another fundamental property of the universe that is difficult to explain is its curvature or lack of it which can also be measured from the cmb space appears to be absolutely flat a veritable ice rink in the standard big bang theory the universe doesn't have to be flat in fact it requires a great deal of fine tuning to keep it flat over 13.8 billion years of cosmic evolution instead the radius of curvature is measured to be much greater than the radius of the observable universe more than 60 orders of magnitude larger that's a big problem in the early 1980s the need to explain these and other properties of the observable universe led a group of russian and american physicists to propose a radical idea the modern version the best known proponents of which are alan guth andrei linder and alexey starabinsky is known as the theory of inflation we'll describe a particular version of inflation below driven by something called a scalar field which was first described by andre linde space-time existed before the big bang and for at least some of that time was described by einstein's theory of general relativity and a quantum field theory like the standard model the central idea in quantum theory is that anything that can happen does happen everything that is not explicitly ruled out by the laws of nature will happen given enough time one of the types of things permitted to exist in quantum field theory are scalar fields scalar fields have the property that they can cause space to expand exponentially fast given general relativity and quantum field theory therefore it must be the case that scalar fields will fluctuate into existence in such a way that an exponential expansion of space time is triggered in this exponential phase space time expands faster than the speed of light this might sound problematic if you know some relativity but it isn't the universal speed limit exists for particles moving through space-time but does not apply for the expansion of space-time itself in a tiny fraction of a second around 10 to the minus 35 seconds in fact an exponential expansion of this type can inflate a piece of space-time as tiny as the planck length to a quite mind-boggling size trillions of times larger than the observable universe any pre-existing curvature is completely washed out leading to a flat observable universe it's like looking at a square centimeter sized piece of the surface of a balloon of a light year in radius you won't see any curvature no matter how hard you try likewise any variations in density will be washed out leading to the smooth and uniform appearance of the cmb perhaps the greatest triumph of inflationary models such as these however is that they don't predict a completely uniform homogeneous and isotropic universe quantum theory doesn't allow for absolute uniformity empty space is never empty but a fizzing shifting soup of all possible quantum fields like the surface of a stormy ocean waves in the fields are constantly rising and falling and the exponential expansion can freeze these undulations into the universe remarkably when calculations using the known laws of quantum theory are carried out the sort of density fluctuations that result from such a mechanism are precisely of the form seen in the cmb these quantum fluctuations are the seeds of the galaxies and therefore the seeds of our existence frozen into the oldest light in the cosmos and photographed by a satellite built by the people of earth 13.8 billion years later inflation in this guys explains the observable properties of our universe and in particular all the details of the cmb which has been measured to high accuracy this is why it is currently widely accepted as an essential ingredient by many cosmologists as if this wasn't enough to get excited about however there is much more one obvious question that arises is this if inflation gets going how does it stop the answer is that inflation stops completely naturally but with a fascinating twist that drives right to the heart of our why are we here question the scalar field driving inflation fluctuates up and down in accord with the laws of quantum theory just like the waves on the surface of an ocean if the energy stored in the field is high enough inflation begins one might expect that such a rapid expansion would dilute the energy extremely rapidly causing inflation to stop but scalar fields have the interesting property that their energy density can stay relatively constant as space expands you can think of the expanding space as doing work on the field pumping energy into it and keeping its level high and in turn the high level of the field's energy continues to drive the expansion this might sound like the ultimate free lunch and in a sense it is almost although gradually the energy will become diluted and decay away the time this takes depends on the size of the initial fluctuation in the field and the details of the field itself but in general the higher the initial energy the longer the field takes to fall in value as the expansion continues an analogy often used to picture this scenario is to imagine a ball rolling down the side of a valley the height of the ball up the valley side represents the energy density of the scalar field when the ball is high up the energy in the field is high driving the inflationary expansion as the ball rolls slowly down the valley the energy reduces and inflation turns off at the valley floor the ball oscillates back and forth until it comes to rest the scalar field likewise oscillates and in doing so dumps its energy into the universe in the form of particles in so doing it creates a hot dense soup which we identify as the big bang in other words inflation ends naturally and the standard big bang follows the decay of the scalar field that drove inflation is the cause of the big bang let us step back a moment and recap with broad brushstrokes because we seem to be wandering onto leibniz's territory and that's an astonishing place for physics to have arrived at our claim is that there exists a quantum field that causes the universe to expand exponentially fast for some period of time and in doing so produces all the features of the universe we observe today including the existence of galaxies and the matter out of which they are made this is a triumph and is now part of cosmology textbooks before the big bang there was inflation fine our philosopher friends would say but what happened before inflation here we must leave the textbooks and become a little more speculative but not too speculative we're still going to be working within the domain of mainstream physics there is an extension of what we might term standard inflationary theory it's known as eternal inflation put simply there seems to be no reason why inflation should stop everywhere at the same time there should always be regions of the universe where the scalar field fluctuates to such high values that the exponential expansion continues and these regions will always come to dominate the universe however rare they may be because they are exponentially expanding where inflation stops big bangs herald the beginning of more sedately expanding regions like ours but elsewhere there is an ever growing expanding universe constantly spawning an infinity of big bangs this theory known as eternal inflation leads to an infinite immortal multiverse growing fractal-like without end this is truly mind-numbing but we must emphasize that it is an entirely natural extension of standard inflationary cosmology eternal inflation opens up even more exciting possibilities as we discussed above one of the great mysteries in physics today is the origin of the constants of nature such as the strength of gravity the masses of the particles and the value of dark energy these values appear to be fine-tuned for the existence of life and understanding where they come from is a prerequisite for understanding our existence in eternal inflationary models each mini universe can have different values of these constants and different effective laws of physics the word effective is important the idea is that there is some overarching framework out of which our laws and the constants of nature are selected if this is correct then each of the infinite number of mini universes that branch off the fractal inflationary multiverse can have different effective laws of physics and all possible combinations will be realized somewhere no matter how fine-tuned our laws appear for the existence of life it is inevitable that such many universes as ours will exist and there will be an infinite number of each possible set of combinations there is no fine-tuning problem given the multiverse we are inevitable yes in isolation the odds of you existing are almost vanishingly small but given a mechanism for producing human beings babies are born all the time and their existence is not surprising here we have a mechanism for producing universes and with an even greater statistical sledgehammer the mechanism doesn't simply produce a few billion of them it produces a potentially infinite number this is a quite stunning theoretical model and i understand that it sounds like wild speculation it isn't though inflation is probably correct in some form in the sense that before what we call the big bang there was an exponential expansion of space-time scalar fields which are known to exist have the correct properties to drive such an expansion although there are other theoretical models of inflation as well theoretical physicists studying inflationary models have discovered that almost all of them are eternal in the sense that they stop inflating in patches rather than all at once this means that the potential for creating universes in the guise of inflation is always expanding faster than it is decaying away and it will therefore never stop we live in an infinite eternal fractal multiverse comprised of an infinite number of universes like ours alongside an infinite number of universes with different physical laws we exist because it is inevitable almost

Channel: TV - Quantum Universe

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Id: IxXaGzUnBRI

Length: 138min 1sec (8281 seconds)

Published: Sun Jul 25 2021