Lord Rees: Life in the cosmos

so good evening and welcome to the inaugural maddingly lecture um the maddingly lectures are the Institute of continuing education's new public lecture series here at maddingley Hall um I'm the director of continuing education and the first thing I would like to do this evening is to take the opportunity to introduce the vice Chancellor Professor sesek borich um so that I can then allow him to introduce our speaker tonight Lord Ree and um then to chair questions at the end of the lecture so the vice Chancellor the University's 345th Vice Chancellor was installed very recently on the 1st of October uh 2010 so I'm particularly um grateful that you're able to join us this evening so early in your term um cek was previously chief chief executive of the UK's medical research Council um and prior to that from 2001 to 2007 was at Imperial College London as principal of the faculty of medicine and later as Deputy recor where he led the development of of interdisciplinary research between engineering physical sciences and biom Medicine in a sense however this is a return to home as s leek started in 1988 as a lecturer in medicine here at Cambridge um from where he went on to be professor of medicine at the University of Wales in Cardiff um where he led research which um carried out pioneering work on vaccines for which she was kned in 2001 and in particular LED um clinical trials in therapeutic vaccine development for HPV um human papala virus uh which is one cause of cervical cancer cek was the founding uh fellow of the Academy of Medical Sciences in 1996 and member of its Council from 1997 to 2002 and he became a fellow of the Royal Society in 2008 so I would like to welcome s leek and Lady borich um and just before I hand over to the vice Chancellor just to remind you that if you have your mobile phones please could you switch them off at this point so thank you well Rebecca thank you very much indeed um firstly congratulations on the initiation of this lecture series and actually of The Institute of continuing education it's my first visit here but it's wonderful to see the programs and the activities that you plan uh for the future with a team so the very best of luck and I do hope I will have the opportunity to attend many of the events that you have here there's an oldfashioned cliche which is the speaker needs no introduction unfortunately for me today that is Absol absolutely true and I could sit down at this point uh Lord Martin Ree is or was in until December president of the Royal Society and probably I would say one of the if not the most eminent scientist in the United Kingdom he was uh astronomer Royal as well as uh holding a series of titles including uh the master of Trinity College here in Cambridge his interest in astronomy and in cosmology are well known to all of us but perhaps for most of us he has become in many ways the voice of British Science through the last two to three years it has been my privilege to work very closely with Martin and he has been a consumate voice of good advice warning against where it's appropriate warning against the issues about reductions in support for Science and the impact that this would actually have on this country always doing so on the basis of where evidence will be able to support that particular call and those of you who may doubt it please get onto your I player and listen to the wreath lectures because you actually need to hear no more than how convincing uh Lord Martin Rees can be and I'm sure today he'll be just as convincing in his chosen topic of life in the cosmos Martin over to you [Applause] thank you very much Vice chancelor ladies and gentlemen okay yes right if you were to take 10,000 people at random 99,999 would have something in common their business lies on or near the surface of the Earth and the Oddball will be an astronomer and I'm one of that small minority in fact uh if you were to do the survey not in a random place on Earth but in King's parade you'd find a slightly higher proportion of astronomers uh maybe one in a thousand or one in 500 because uh Cambridge is I'm glad to say one of the places where astronomers are heavily concentrated we one of the world centers for astronomy and I'm privileged to be uh part of this community so uh with that let me emphasize that astronomy is not just for astronomers I think it's important that uh the night sky is something which has fascinated uh people from the dawn of humanity we've all had different environments to grow up in but we all looked up the same night sky and wondered about it interpreted in different ways so the night sky is part of our environment um and uh it's something that we have all wondered about and also it's part of our culture to understand astronomy and uh its nature and we now know that our Origins lie in the stars and that our remote descendants May Roam among them and I'll ask in this lecture what were the features of our universe that allowed stars and planets to form and which led on this planet to the emergence of our biosphere where in the famous words of Darwin the closing words the species whilst this planet has been cycling on according to the fixed law of gravity from so simple a beginning forms most wonderful have been and are being evolved well astronomers tried to go back before Darwin simple beginning to set the earth and the atoms that it was made of in a broader context and we also want to ask the question could there be life elsewhere but before that I want to say a few words about uh whether human life is going to go into space are we going to go beyond the Earth ourselves and people for centuries have speculated about that and among them was uh the great Isaac Newton probably the most eminent alumnus of this University um and uh uh he um speculated about life in space he was incidentally a most unattractive personality quite unlike Darwin he was solitary and obsessive when young Vain and vindictive in his old age so he wouldn't have been attractive although on an IQ test he'd have beaten almost anyone else hands down and he was the first really to think about how In Darwin's phrase planets go cycling on in orbit this is a nice picture taken from the English translation of his great book The prinkipia you can see what's happening uh um a cannon is firing uh a projectile from a Mountaintop and if it's fired fast enough then the uh trajectory curves downwards no faster than the earth curves away underneath it it goes into orbit this I think is still the neatest way to explain uh to uh uh beginners the nature of orbital flight it's quite easy to understand stand here now Newton could have calculated that to go into orbit the cannon has to fire the projectile at 18,000 mil hour far far beyond of course the capacity of the Canon of his time and as most of you know it was until 1957 that the Sputnik went up into orbit and after that things move very fast it was only 12 years later that we got views like this from people orbiting uh the the moon and uh the moon landing was 12 years after Sputnik only 66 years after the r Brother's first flight and most of us probably then expected that by now there would have been a Luna base maybe an expedition to Mars but that hasn't happened 2001 didn't resemble Arthur C Clark's Vision any more than for 1984 resembled Orwells that's because the political impetus for man space flight was lost after the Apollo Venture and only the middle-aged can remember seeing live on TV Neil Armstrong's first small steps young people today indeed uh know that the Americans landed on the moon just as they know the Egyptians built the pyramids but both Enterprises may seem driven by by equally Arcane National goals but it was a heroic episode and I'm rather proud to have this uh um picture signed by seven of the Apollo Astronauts and since that time hundreds of astronauts have uh not been to the moon but they've circled the Earth many in this Space Station activities that compared to Apollo seem perhaps neither very inspiring nor very practical but despite this sort of languishing of manspace flight unman probes to other to other planets have revealed varied and distinctive worlds and let me show you first a few pictures of Mars uh this is a a picture of the surface of Mars and here are some taken from uh the European space agencies Mars Express this is a big crater um and uh the next picture is going to show a closeup of the side of the crater there slightly terrestrial looking landscape but you can see that Mars has very uh interesting uh terrain indeed and uh this is the Phoenix uh spacecraft which landed on Mars a couple of years ago uh this is going to dig down to a depth of about a meter uh to analyze the sample uh not to bring it back to Earth of course of course but to analyze it in situ and of course space probes have been further uh here's Jupiter it's moons first discovered by Galileo of course uh this is Europa which is a closeup of Europa it's got almost certainly oceans under this deep ice here's Saturn um a spacecraft called Cassini uh went to Saturn a few years ago and is still orbiting around taking close-ups of all the moons and one of the most remarkable outcomes of this was the exploit of a European robotic probe called hyans which was released from Cassini and what we supposed to do was to land on Titan which is the giant Moon of Saturn the biggest moon in the solar system uh it was supposed to open a parachute and land on a Surface about which we knew very little and it did just that here the left and in the middle are pictures taken on the way down there on the right is where it landed now this looks uh rather like terrestrial um uh topography Rivers even a little Lake but there's a difference um these rivers are liquid methane the temperature is- 170° uh centigrade and those those little rocks are solid methane probably so no sort of beachfront property there it's not a very comfortable place but uh this is remarkable achievement because this robot it was been control from Earth because a radio signal takes hours to get uh to Saturn and back so for the last two weeks when it was released from Cassini this uh craft was on its own this is a great Triumph of technology that it did this well I hope that during the next few decades the entire solar system system would be explored and mapped by flotillas of tiny robotic craft doing things like this on all the objects in the solar system but are people going to follow them this shows Harish SMI the last man on the moon the Practical case for sending people into space is getting weaker all the time with each advance in robotics and miniz indeed as a scientist or practical man I see no case for sending people into space at all but as a human being I am quite an Enthusiast for man space missions is I hope some people now living will walk on Mars it should be a long range adventure for at least a few humans but this goal is actually receding NASA's firm plans don't even include a return to the Moon I think that's really because NASA projects are always very expensive because they have to be uh um achieve very high safety standards uh to commit civilians to something like that but I think therefore that uh future expeditions to the Moon Beyond will only be politically and financially feasible if they are cut price Ventures perhaps privately funded accepting higher risks and perhaps bearhead by individuals who will accept these risks and even oneway tickets there be people who will do that and perhaps private sponsorship and I could talk a bit more about this afterwards it's not crazy I think to do it that way but it will be dangerous and remember that nowhere in our solar system offers an environment even as Clement as the Antarctic or the top of Everest so it's uh kidding yourself to think that uh going into space is an escape from the Earth's problems we've got to solve the Earth's problems here on Earth not in space but there could nonetheless if we think a few centuries ahead be self-sufficient groups of pioneers living away from the earth they would surely then use all the resources of genetic genetic technology to modify themselves and their descendants to adapt to an alien environment of much lower Gravity the posthuman era would then have begun and Machines of human intelligence could then spread still further and whether the future lies in the long run with Organic post humans or with robots is a matter for debate well our Earth is very tiny but it could therefore be the seed from which life could spread through the Galaxy in a very long run but let's now widen our gaze beyond our solar system far beyond the reach of any probe we can now conceive to take 10 of thousands of years for any probe to actually get to even the nearest star so could there be life out there already Among the Stars what about the Stars themselves we've learned enough about stars to understand them their life cycle we see places where stars are forming here in the Eagle Nebula about 7,000 light years away there is enough Dusty gas to form hundreds of new stars like our sun and solar systems and we see stars dying this is what our son will look like in six billion years he's another star dying in a rather messy way as it were here and some Stars particular big stars die rather explosively this is a famous optic called The Crab Nebula uh which is the exploding debris from a supernova explosion witnessed by by Chinese astronomers in the year 1054 ad the star flared up then we now see this exploding debris you might think that uh these dying Stars far away are irrelevant to us but were it not for these exploding Stars we wouldn't be here the reason for that is that stars derive their energy by nuclear fusion they start with hydrogen and helium and they gain by turning hydrogen into helium then helium into carbon into oxygen into iron and so on and then when they die they throw it all back into Interstellar space and new stars form from it and in fact I'm not going to explain all this diagram but there's a sort of uh uh ecology going on in interstellar space uh where uh new stars form and then when they die they throw back material into space and that space is uh uh enriched with the uh um uh heavy elements of the periodic table which are uh made during the lifetime of the star and then they make new stars and we can understand enough about this to understand why oxygen and carbon are common gold and uranium are rare and how they came to be in our solar system we know that every atom in our bodies was made in a star which died before solar system formed we know indeed that we have inside each of us atoms that came from thousands of different Stars spread through the entire Milky Way so we are literally the ashes of long dead stars or if you're less romantic we are nuclear waste from the fuel that made stars shine and I'd like to put in a plug for Fred Hil who is in fact my predecessor iscl me professor of astronomy here and he was the person who more than anyone else uh explained and Quantified this wonderful story which shows that we are linked to the stars in an even more intimate way than the astrologers think we are actually made of Stardust and all the atoms that we are made of do have this history which we can trace back to far earlier times than when the earth was formed we've now in just the last 10 years or Al learned something which makes the night sky much more interesting than it was to our forebears we've learned that most of the Stars we see in the sky aren't just twinkling Points of Light they're orbited by planets just as our sun is orbited by the planets we are familiar with including the Earth most of these planets aren't detected directly they're detected in the fashion indicated here if a star is orbited by a planet then what actually happens is that both the star and the planet orbit around the center of mass of the system it's called The Barry Center the planet moves in its orbit the star being heavier moves in a much smaller orbit and even if it's not possible to observe the planet it has proved possible to observe the small motions of a star induced by an orbiting planet and by this method in the last 10 years several hundred stars have been observed to have planets around them and it's possible to infer the mass of the planet and to infer its orbital period don't worry about the details but I just uh put up here on this slide this is a list of stars which are inferred to have at least two planets discovered this way by sort of for analysis of the Motions of the the star and there's one star which is known to have at least five planets uh found in this way now most of the planets found in this way are Big Planets they're rather like uh Jupiter and Saturn the Giants of our solar system it's not possible by this indirect technique to uh um find a Planet like the Earth because that would induce a motion of only a few ctim m/ second in the star it's orbiting and that centim per second motion is too small to detect by the methods used but there is another way which is going to uh within the next year or two uh tell us how many Earth life planets there are orbiting other stars and this is uh being done mainly by a spacecraft called Kepler which was launched in March last year what Kepler is doing is it's uh looking at the same part of the sky continuously it's looking at a a region 7° across and it's look measuring the brightness of 100,000 stars in that part of the sky with a Precision of better than one part 10,000 doing that every half hour and what it's looking for is a Transit by a planet because supposing that there's a a star and there's a planet and the plane of your orbits um along our line of sight and if the planet moves across in front it blocks out a bit of a staright and the uh brightness of the star will dip a bit as shown as shown there and if you have an earthlike Planet orbiting a sunlike star then just the ratio of areas it's about one in 10,000 so the dip is just one part in 10,000 but the Kepler Mission um ought to be able to detect that and uh um in order to be sure you've seen a planet then you've got to see three of these dips occurring regularly and uh if it's like the earth going around the Sun that's going to take three years and so we'd have to wait a EUR two before we we get uh some data from Kepler on earth live planets but it'll come and uh that'll give us an indication for how many planets there are that are close to the size of the Earth to the size of Jupiter now this is still a bit unsatis Ying because we're seeing the shadow of the planets not uh the planets themselves but to detect an earthlike Planet orbiting another star is a much more challenging task it's very challenging because let's imagine you were looking at our solar system from 50 light years away dist of a nearby star supposing some alien astronomers right there looking at us then from a distance of 50 light years our sun would look a very ordinary star and the Earth would look in Carl seager's nice phrase like a pale blue dot about 10 billion times fainter than the Sun and separated from it by a tiny angle fra Arc second so the task is really like looking for a farfly next to a search light it's a real challenge you need sensitivity and resolution and we have to wait some time until we have a raise like this in space or the next generation of telescopes like this on the ground look at the scale of the lorri there but one of these is being talked about to be built in the next 15 years and they will be able to detect um pale blue dots orbiting other stars that might be like the earth now once one of these can be detected then you can learn a surprisingly amount about it because again suppose the alien astronomers were looking at our sun and our Earth then they would find that uh the shade of blue would be slightly different depending on whether the Pacific Ocean or the land mass of Eur Asia was facing so alien astronomers from 50 lies years away could infer that the Earth had continents and oceans the length of the day something of the climate and seasons and perhaps by studying the reflected light that there was oxygen or ozone in the atmosphere and that's the kind of we' be doing uh in about 20 years um when we can detect Earth lifelines around other stars and once we can find one we can find zillions of them so this would be a very exciting uh development well the next question of course is do we expect life on any of these and this is a much more difficult question because uh we know too little about how life began here on Earth to be able to say whether life is likely or unlik likely of course people are looking for evidence for life in our solar system uh in all these sorts of places no one's very optimistic uh the best you might find on Mars is sort of freeze-dried bacteria that lived a few billion years ago and now dead and we don't hold out much hope elsewhere but uh on these other plants around other stars then of course there may very well be life there may very well be a biosphere and and it's obviously sensible to focus on earthlike planets orbiting stars like the sun some people of course um have argued that our Earth is very special indeed um won't go into this but they've they said that we're Earth's special it's got a moon that's special and that Jupiter has to be there Etc um but I think we mustn't be uh too impressed by this sort of argument I mean we've evolved in symbiosis with our environment and we wouldn't be the way we are unless the Earth had its properties but that doesn't mean that uh there couldn't have been life in a rather different environments uh we have clearly evolved um to fit our environment but uh it's rather like saying is it amazing that your legs are just long enough to reach the ground it's not really amazing at all um and and it may not be amazing that we fit our environment and therefore I think one should be open-minded and might to look for evidence of Life on all other kinds of planets and of course science fiction uh writers have given given us all kinds of other ideas floating creatures in the atmospheres of planets like Jupiter or even creatures not on planets at all and incidentally I tell my students that uh uh it's a a good stimulus to your imagination to read science fiction and uh um first grade science fiction is probably better than second grade science in that it's more entertaining and perhaps no more likely to be wide of the Mark um well um of course even if simple life is common then it's a separate question whether um it develops into what we call Advanced life still less intelligent life we don't know because there's a lot of debate as you probably know about whether if evolution will rerun on the Earth where you end up with human beings or not you might end up a planet covered with insects or something like that we just don't know what's contingent and what is inevitable about Evolution here on the earth um and so I think have to be entirely open-minded and realize that uh um we don't understand uh the origin of life on Earth of course there are people who think they do know about this and uh there been UFOs here and they've been visited and abducted and I get letters from people like this um in my rose astronomer Royal I mean I uh do two things I encourage them to write to each other that's often a good move um um uh and also I would say to them more seriously do they really think think that if the aliens had made the effort to come to the Earth and had the technology to do this would they just have uh desroyed a few corn fields and made corn circles met one or two well-known cranks and gone away again it doesn't seem very likely so I'm pretty convinced that we haven't yet uh been visited by aliens U but nonetheless it's not crazy to believe that they may exist out there and I think it's a good idea to use all possible methods to search for them well of course um there are as you probably know um some efforts being made to uh uh look for sort of some sort of signals of the kind that might uh emanate from a planet where there is intelligent life um and uh uh I don't hold my breath success I'm glad people are doing this because of course to detect any manifestly artificial signal even it was as boring as um the digit of pie or um set of prime numbers or something would carry the momentous message that uh maths and logic if not Consciousness was not limited to the hardware in human skulls but it evolved somewhere else so that would be crucially important would we have any common culture with these aliens uh well actually we would because um even if they live on planet Zog and have seven tentacles uh they would be made of the same atoms as us they'd gaze out if they had eyes on the same Cosmos and uh this physics would be the same so we would have something in common um and might maybe could understand their messages but of course um we would uh um have plenty of time to think about sending a message back because remember that the nearest such life would be many light years away and so it would take decades to send the signal so there's no scope for a Snappy repar as it were um but of course there may not be anything out there perhaps all these searches will fail it could be that Earth's inter biosphere is unique even if simple life is common elsewhere and that may be disappointing to some people but it would have its upside because our tiny planet would then small though it is be perhaps the most important place in the Galaxy perhaps even a seed from which life could spread through the entire galaxy but it's no saying that uh absence of evidence isn't evidence of absence and they're C even if we don't detect anything be intelligences that are leading conservative lives out there or so different from us that we couldn't recognize them at all well that's a difficult subject because biology is very hard I'm to go back to the simplicities of the physical world uh but extend our gaze still further from our own Milky Way galaxy to other galaxies if we were to get two million light years away from the Sun and look back at our galaxy we see something like this this is in fact I'm sure most of you know the Andromeda galaxy our nearest Neighbor In Space 2 million light years away and it's a spinning disc viewed obliquely almost Ed on where all the stars are orbiting around some Central Hub and these galaxies are the basic building blocks of the large scale Universe here's another one a disc viewed almost face off you might ask um how can we astronomers um understand uh the nature of these what they're made of what their Dynamics is ETC we can't do experiments on them of course in the way that particle physics can crft particles together in accelerator but we can do experiments in the virtual world of our computer we can ask what would happen if you crash two galaxies together and here's a simple picture of what happens two galaxies are falling together the gravitational pull of every Star in one is acting on every other and you end up with a sort of mess like this so that's a calculation we then look in this sky and apart and as well as the galaxies I showed you we see galaxies like that and it's a pretty fair assumption that what happened here is rather like what happened in that movie two Galaxies have got dangerously close the gravity of each one has pulled out a tidal stream on the others and perhaps these if we came back in a 100 million years would have emerged completely because remember that last move was speeded up by about 10 to 15 from real time uh so it's by doing these calculations with different assumptions about the mass and uh uh Etc that we can come to understand in quite a lot of detail galaxies and of course we have huge numbers of galaxies to study uh this is a um map as it were of all the galaxies within a few hundred million light years of us they're grouped together in clusters now the one thing we know about galaxies um is that uh they're moving away from us this is a famous expansion of universe discovered by Edwin Hubble in the 1930s and there's a Edwin Hubble heavy smoker there as you can see and he uh was the person who uh first realized that the galaxies were moving apart from each other what he found was what's symbolized here that um the further away a galaxy is the fastest moving from us by uh symbolized by the longer arrows further away now at First Sight when people are told this they think this must mean that we are in some Central position but it doesn't mean that as I can illustrate by this picture imagine this infinite ltis and imagine that all the rods lengthened a certain C rate then if you sit on one of the vertices then the other vertices will recede from you at a speed proportional to the number of intervening links so the whole network will seem to expand and that's quite a good way to visualize the expanding Universe if you imagine the galaxies linked together by rods and all the rods lengthen at the same time uh then uh um that that's uh going to give you the uh law that Hubble discovered there's just one thing which is not uh um fully represented in this picture and better by this second eer diagram this as's angels and devils and uh this extra effect stems from the fact that uh light takes a long time to get to us from these distant galaxies many billions of years in some cases and so if we look a long way away we're looking back in time to when the rods were shorter when the lattice was more compressed and so we actually see when we look out into space and back in time is better represented by this picture here when as we look far away we see things as they were younger and when everything is more closely packed together and we can in fact look very far back indeed uh this picture is taken with a very large telescope and it shows a small patch of Sky it would take a 100 patches like this one to cover the full moon in the sky just very small one and it would look completely blank looked at with a small telescope but here with a really big telescope you see these several hundred smudges each of those smudges is a Galaxy many of them fully the equal of our galaxy or Andromeda looking so small and faint because of the huge distance and we're looking back at these galaxies to a time when they only recently formed and in fact if we study light from them we can see they're not like our galaxy in two respects first they've got more gas in them which hasn't yet made it into stars and secondly if you take the Spectrum you can see how much carbon oxygen Etc there is in them and there less than there is in a present day Galaxy because there hasn't been time for the uh stars to make all those heavy elements uh in in this galaxy and so uh if we look at Andromeda then maybe there are astronomers on Andromeda looking back at us but there are certainly no astronomers on these very distant galaxies because there's been no time uh for the uh elements to U be produced to make planets which require lots of silicon oxygen and iron Etc and so therefore for the scant chance of life but what about still earlier times before the first galaxies for formed uh we are confident it have been since the 1960s that everything start started off in what we locally called The Big Bang everything was hot and dense the best evidence for this uh is uh symbolized in this picture here um even in Galactic space it's not completely cold it's warmed to about 3° above absolute zero by very weak microwaves and these microwaves If You observe different frequency they have what physicist know as a black body Spectrum which is what you would expect if this radiation was produced in conditions like the center of a star where everything is very hot and dense and as the universe expanded and cooled this radiation shifted into the uh infrared and then into the microwave band uh but it's still around it fills the universe got nowhere else to go and this is a relic of the time when Universe was only a few seconds old well when people are told that the Universe started off as this sort of amorphous farall uh one question they ask is well how did it get from that state to the present Universe uh where we have um tremendous structures we have stars and galaxies Etc it may seem contrary to U the um famous second or thir dyamics which says that order gets washed out but the reason that doesn't happen is its effect of gravity what gravity does is that if there's a tiny density contrast then as Universe expands that a slightly over dened region lags behind more and more and eventually condenses out and I'm going to show you another movie which shows a uh U simulation of a region of the universe big enough to make several hundred galaxies and uh the expansion is being subtracted out so everything is looking at the same scale um and uh um if you look the time is is on the B there and you see that structures are forming the universe expands density contrast grow and in percep initial fluctuations eventually uh condense out into um what turn into galaxies today so this is uh the way in which we think an almost a morphous early Universe uh developed into into galaxies and we'd like of course to understand this in a lot of detail um and um I'm just went have time to go through this but uh we can ask what did the universe have to be like to allow this transition from something that was initially featureless and dense to something which developed structures and then develops planets and then eventually life and uh these are some of the prerequisites I go through this fairly quickly well there's got to be gravity to pull structures together but it turns out the the weaker gravity is the better because uh that allows very large structures to form If gravity was much stronger then objects as big as us would get crushed by gravity which would not be good so we want a very weak force of gravity uh obviously things must be in thermodynamic equilibrium uh we've got to end up with some places which are hot and some which are cold um we need to have um matter antimatter asymmetry because if we had equal amounts of matter and antimatter then as the fireball cooled down that in our we'd have just radiation no atoms so we need that and we also need what I call non-trivial Chemistry uh we need um uh fundamental laws such that the nuclear force and electromagnetic force um are in Balance because in a complex atom like an atom nucleus of oxygen then's a balance between the nuclear force holding it together the electric forces tearing it all apart so we need some sort of find tuning there and of course we need stars to form maybe second generation stars because the first generation stars make the uh uh the first most chemical elements and we also need the expansion to happen um at a well-tuned rate because if the universe was expanding too slowly it would recollapse very quickly before there was time for anything to happen if it was expanding so fast then uh structures wouldn't be able to pull themselves together because of gravity so we have to understand this sort of well-tuned expansion rate and we also uh need to uh postulate some nonzero fluctuations in the very early Universe because if the universe started off completely smooth then it would now after 13 billion years be just cold neutral hydrogen no stars no galaxies and no people so the challenge of uh cosmologist is to try and understand uh why the universe was set up this way now the one thing we do uh suspect is that uh to answer that question we have to go back not to the first second of the universe but to the first tiny tiny fra of a second and the problem there is that if you extrapolate back to the first tiny fraction of a second everything gets hotter and hotter and denser and denser and conditions are reached where we lose our foothold in experiment the densities and energies are such that we can't produce them in the lab the energies are far higher even than you can produce in the LHC at Geneva and so we are in speculative territory but the answers to the questions of why the universe is way it is would only be found found when we can go back very early on some people would say very far back indeed to the first trillionth of a trillion a trillion of a second and that's when the actual Universe was that big and you what we call our present Universe was just just that that size and that's the era when we believe that many of the important uh process were imprinted and it's a challenge to think of some indirect way in which we can get uh an observation or empirical handle on this extreme physics well um just uh I put up this Hazard warning sign because I want to uh just spend the next few minutes on some slightly more speculative issues um one important question is how extensive is the physical reality within the remit of science now I've already said that we can see huge numbers of galaxies we can see Galaxy is out to uh about 10 billion light years but there's a limit to what we can see because light hasn't had time to reach us um from Beyond a certain distance because the univ is a finite age and just as if you're in the middle of the ocean there's a horizon around you but you don't think the ocean stops at your horizon same may be true of the universe and most of us suspect that there is a lot more to our universe than the huge volume we can see in fact I think most of us bet it goes on thousands of times further the reason for that is that if we look as far as we can in that direction and in that direction the differences are only one part in 100,000 so if there's any sort of gradient towards an edge then it's a very very gentle gradient but Universe could go on Far Far further still not to to 10 to the^ 100 light years or even far far more than that could even go on so far that all combinatory options are fulfilled and that there's another Earth where um there's another set of people in lecture room like this you know that happens in principle uh if the Universe goes goes on far enough but this of course let me EMP is far far far beyond what uh uh we can ever directly observe and even that's not all because what I've talked about now is the aftermath of our big bang as it were but some people think that our big bang was not the only one and could be other completely disjoint space times one idea is what goes under the name of brain Worlds the analogy here is suppose you imagine a whole lot of um uh ants crawling around on a sheet of paper that's their two-dimensional Universe they might be unaware of another set of ants on a parallel sheet of paper now one dimension up we may be in uh uh a similar uh situation in that there could be another Universe just that far away from ours but if that distance is measured in some fourth spatial Dimension and we're imprisoned in R3 then we wouldn't know about it and that's a possibility another idea uh is that uh um these um uh it's almost like a vast version of Fred horo steady state universe where um um Big Bangs are happening um in a very complicated way symbolized in this sort of cartoon so what what we think of as our our universe with our Horizon lot Beyond is just one sort of bubble and there are a whole lot of others and this is an idea which uh um is taken quite seriously and it raises the other question about um if there are many Big Bangs um then would they all be governed by the same laws because we know that the uh physical laws um that Prevail on uh Earth and in the lab are the same as in a distant Galaxy uh we know that uh if you take the spectrum of light of a galaxy the hren atoms oxygen atoms are just the same but of course on a still vaster scale that may not be the case and it could be that uh um our laws are sort of fine-tuned in a way that doesn't happen in some of the other universes so uh this is again a speculation if I wanted a logo for my uh research area I'd pick this one and or aborus it depicts the interconnectedness of the uh microw World on the left and the Cosmos on the right and there are lots of links between the very small and the very large our everyday world of life and mountains is determined by atomic physics and chemistry Stars halfway up on the right derive their energy from a nuclear within those atoms halfway up on the left and though I haven't had time to describe it galaxies are held together by the gravity not just of what we see but of dark matter which is set of particles subnuclear particles made in the big bag so there is a a link there as well the left hand side the microw world is the domain of the quantum the right hand side is the domain of gravity and Einstein's theory and to just think about 20th century physics the two great highlights were Einstein's theory of gravity and the quantum theory and these haven't yet been meshed together that doesn't actually matter very much because uh if you're a chemist you don't worry about the gravitational force between two atoms in your molecule because that's about 40 PS of 10 weaker than electric forces on the other hand if you're an astronomer trying to work out the orbits of planets or stars then you don't worry about the fuzziness induced by quantum mechanics because uh everything so big that that's unimportant but conceptually one does want to mesh these together and the context where we need that unification is the one symbolized as it were gastronomically at the top of the picture uh when uh the entire universe is squeezed to the tiny size I mentioned because then Quantum fluctuation could as it were shake the entire universe and we won't be able to fully understand those processes until we have a theory uh which uh unifies um the quantum world with the space and time ideas of Einstein and that is a challenge unfinished business for physicists but before leaving this diagram I want to emphasize something else which is that um not only do we want to link the very large and the very small at the top but as the third Frontier the very complicated and that's emphasized by what's at the bottom namely us we are the most complicated things in the universe and uh we are neither as small as atoms nor as large as stars and we are complicated to an extent that we are the main challenge to science in fact uh um I show here um this is uh a drawing by Isaac Newton's least favorite F FRS uh Robert hook this is his first picture of a flea taken through a microscope and I want to say it show this because even a flea is far more complicated than atom or a star because there's layer upon layer of incate structure in in something like this and uh that is why uh most scientists work neither on the very small on the left nor on the very large on the right but on the very complex that is the greatest of all challenges to science and incidentally we are a human beings midway between the atoms and the stars um if you it would take about as many human bodies to make up the Sun as there are atoms in each of us the geometric mean of the mass of a proton and the mass of a the sun is 50 kilog within factor of two I guess of the mass of most people in this audience so we are uh Midway and to understand ourselves we have to understand the atoms we're made of but we also have to understand the stars that made those atoms well finally I want to draw back from the cosmos from what may even be a vast array of cosmoses governed by different laws and focus closer to the here and now I'm often asked is there a special perspective that astronomers can offer to science and philosophy well first of all obviously we view our home planet in a vast Cosmic context and in the coming decades we'll learn where there's life out there so we can think about vast spatial extents and incidentally um that doesn't make us any more Serene people say does the fact that I think about these um enormous arrays make me more Serene about every day matters but I have to say I worry just as much about tomorrow next week as anyone else does but more seriously I think astronomers can offer a special perspective in a sense of an awareness of an immense future the stupendous time spans of the historic past the evolutionary past are part of common culture unless you're in candas or Alaska or some places like that where perhaps they aren't but apart from that we're all aware that we're the outcome of 4 billion years of evolution on Earth but I think even those of us who are um familiar with this tend to feel that somehow we humans are the end of the process we're the culmination of it but that hardly seems credible to any astronomer that's because as this crude time lapse which shows the formation of the the the the Sun and its eventual death the sun is less than halfway through its life it's been shining for four and a half billion years it will be another 6 billion before it runs out of fuel and and flares up and the expanding universe will continue perhaps forever to quote Woody Allen eternity is very long especially towards the end and any creature witnessing the sun's demise 6 billion years hence won't be human they'll be as different from us as as we are from a bug because there's been more time for evolution between now and then than there has up till now so post human evolution here on Earth and far beyond could be as prolonged as the darwinian evolution has led to us and even more wonderful and darn himself thought about this a bit one quote from from him and incidentally uh the future Evolution May well be even faster than natural selection where it takes a million years for a species to evolve this Evolution may take place on the technological time scale of genetics or of machines taking over and levels of intelligence or Insight may allow future beings to address questions we can't even pose just as quantum mechanics May flamu a chimpanzee uh there may be some of these important questions which will not be understood by human brains at all well back bit closer to the Earth we're all familiar with this picture of our planet from space I showed at the beginning where the Earth's delicate biosphere contrasts with the STA moonscape where the astronauts left their Footprints and we've had these images for about 40 years but suppose some aliens had been watching our planet for its entire history this four and a half billion years what would they have seen over nearly all that amend time us appearance would changed very gradually the continents drifted the ice cover waxed and waned successive species emerged evolved and became extinct but in just a tiny sliver of the Earth's history the last 1 millionth part that's just a few thousand years they would have seen the patterns of vegetation start to alter much faster than before this signaled of course the start of Agriculture and the appearance of human beings on the scene and the pace of change would be seen to accelerate as human populations grew and then these aliens watching us would have seen even more abrupt changes within 50 years little more than 100th of 1 millionth of the Earth's age the carbon dioxide in the Earth's atmosphere began to rise enormously fast the planet became an intense emitter of radio waves the total output from all TV stations and radars and something else unprecedented happened small projectiles launched from the Earth's surface escaped the biosphere completely they went into orbit they went to the moon or to the planets and Beyond well if they understood astrophysics the aliens could confidently have predicted that the biosphere would face Doom in a few billion years when the sun flares up and dies but could they have predicted this unprecedented runaway fever less than halfway through the Earth's life so this indicates that even in the sort of concertina timeline extending billions of years into the future as well as into the past this century is a rather special one it's the first in our planet's history where one species ours can really change Earth's entire future and could indeed jeopardize life's immense potential and I think what happens in future will obviously depend on whether we do evolve sustainably whether some of these projectiles launched from the earth do established independent communities away uh or whether uh there is a sort of spasm followed by silence as perceived by these aliens so it's clear that what happens is going to depend on us and that this blue dot in the cosmos is a special place maybe a unique place and also that we are its stewards at a especially crucial time especially crucial century and that I think is a message for all of us whether we're interested in astronomy or not so thank you very much [Applause] Martin thank you very much indeed uh questions um there has been one sort of evolutionary cycle um which was stopped by something or possibly stopped by something very large in the earth um could cosmologists have anything to say about How likely that is to happen again um well we do understand um asteroids and what that risk is um and uh uh it's fortunately low risk but it's easier to quantify that risk than many of the others that we can and so we know that an asteroid like the one which probably finish off the dinosaurs would uh impact once every um um 10 to the 8 years or thereabouts and smaller ones more more commonly and so we do know that we are risk from asteroids it's not the kind of risk to keep us awake at light I mean I'm more concerned about the uh the human induced risk which are much higher now than they were in the past the risk of a asteroid impact is no higher now than it ever ever was and it's a something which we can quantify but of course as I mentioned um it's uh a matter for debate uh what would have happened if uh those particular asteroids hadn't landed at the time they did would mammals are still taken over or or not and uh that of course is another uncertainty in working out the probability of the kind of evolution that happened here on Earth if you had starter conditions rather like the starter conditions on the Earth but we can quantify the uh the risk from asteroids and and just uh obviously the one that killed the the uh dinosaur was about 10 K kilometers across um the uh one that landed in Siberia about a century ago and devastated a forest about 100 square miles that was about 100 yards across um and uh that happens every few hundred years um one hopes the next one will miss highly populated areas um and uh uh intermediate as asteroid scale say half a kilometer um they're more serious if they land in the ocean because if they land in the middle of say the Atlantic Ocean they produce a tsunami hundreds of meters high and that would be the main catastrophic effect but uh again these don't keep me awake at night because they have very small risks but they're quantifiable risks and just one point um in the long run we may be able to do something about them because uh if one knows the orbits of asteroids well enough uh then obviously you can identify many years or even decades in advance those that might come close and uh it might be possible in future decades to sort of nudge them into a different or Orit you mentioned about in of yes um well well of course um uh they're in detectable by that method uh if um we are looking in the orbital plane and so uh when we know how many kepers uh detected then of of course assuming that the orientations of the planes are random uh we can infer that the total number is going to be higher than the number that we see by some geometrical factor which you can calculate is probably about 50 because um the um alignment has to be within about half a degree in order for us to see the otation no no no so so the uh um the Kepler spacecraft is looking it's looking at 100,000 okay and I mean suppose supposing that it detects um say 100 planets like the Earth then uh from simple geometry you could say well that probably means that around those stars there are maybe five or 10 thousand altoe yes interested in your views about dark matter I understand as also Dark Energy do you think they'll turn out to be real that or are symbolic of oh no dark matter um I think is uh is certainly there this is a um um particles which uh um contribute about um 80 or 90% of the mass of all galaxies and without which galaxies would fly apart you couldn't understand their Dynamics and uh you couldn't understand understand their formation and uh in those that calculation I showed two galaxies crashing together then you get a quite different result if you don't put in the dark matter so all we can say is that the dark matter is some uh kind of particles that are electrically neutral and so don't emit or absorb light um and we can infer their total am we don't know what they are they may be the kind of things the LHC will find we may detect them directly um but I I think um there's nothing implausible about their existence there are lots of cans of the particles and there's no reason why everything in Universe should Shine Anymore than everything on the earth shines so I don't think that's what's called dark energy is slightly different um this is um uh uh some feature of empty space which actually uh causes the expanding Universe uh to accelerate rather than slow down because if there was just gravity of all the galaxies you would expect that the expansion would gradually be slowing down um but in fact that is not observed to be the case and for the last half of the universe's uh age it's been speeding up not slowing down and what this tells us is that there is um uh some some sort of energy like a sort of tension in empty space which pushes things apart and cancels out gravity and uh this is sometimes called Dark Energy and this is very mysterious indeed um and I think we won't understand that until we've achieved the unification at the top of the snake which I mentioned um because uh it's probably an effect of space um at the most fundamental level and uh most people expect that just as um this lecton if if we divide chop it up into smaller and smaller pieces we get out of atoms most people suspect the same is true of space and you can't divide space or indeed time indefinitely and when you get down to a certain scale space develops very complicated properties the problem is that the scale on which the structure of space is expected to manifest itself is a billion billion times smaller than Atomic nucleus 10 33 cm so that's very far from being observed but on that tiny scale then many people particular those who are developing so-call string theories believe that uh um what we think of as a point in space um if you magnify it enough is actually so tightly wrapped origami in several extra Dimensions which we don't detect because they're not wrapped up so uh that's a long way of saying that the nature of space at the tiny level is very complicated and until we understand that we won't understand why there is this Force which causes a um an acceleration of of the universe this force is overwhelmed by gravity locally and even in our galaxy but when everything else is so dilute and therefore gravity is not very effective then this Force dominates that's a rather long answer to the question uh yes earlier slides you you show you you had Stellar Wind yes what is Stellar Wind uh well that's a part of particles being blown off of course this the sun has a wind the solar wind which is a particles um coming coming out of the sun which of course interact with the magnetosphere produce the Aurora Etc and their strength depends the solar cycle um so that that is an example and most stars have winds but uh um the kind of winds that were mentioned there were um those that carry a much larger Mass flux than the solar wind and would be a way in which the um uh uh the star can lose quite a bit of its material before it eventually ends it life exploding the the solar wind is carrying away 10us 4 solar masses per year so that's only one part in 10 to the fourth of s's Mass over his entire lifetime where some stars have winds which are um harving their Mass over their lifetime and so uh the uh um replenishment of interstellar material from stars comes partly by Steady Mass loss our winds and partly by the explosive Mass loss but most stars have have some sort of wind coming out including the Sun Well Martin all says is fantastic thank you what a wonderful start of the series and I just want to hand over to Rebecca but firstly thank you very [Applause] much well thank you I'd like to thank the vice Chancellor for chairing this evening and of course a huge thank you um to Lord Reese for an incredibly stimulating lecture I think we could hardly have got off to a better start with our migy lecture Series so as a small token of our thanks and our appreciation I'd like to present you Martin with um a gift just a small second thank you very [Applause] much it goes without saying of course that events such as these don't happen by themselves um so I also have a a great deal of thanks to give to my colleagues without whom tonight wouldn't have happened so so thank you to my colleagues um and I'd also like to say that I hope that we'll see many of you back here at the Institute of continuing education at maddingley Hall um not only for future maddingley lectures which are listed in your program and also on our website um but also studying with us um whether it's for one of our astronomy courses um or some other of our courses that have caught your imagination and um I should say that we have a huge range of courses so there's a a lot of scope for catching your imagination we have um typically over 10,000 student enrollments per year um and offer short non- accredited courses through to accredited undergraduate and postgraduate level programs through to part-time master's degrees um in subjects for your personal interest and for professional um development and diversification as well as our International summer schools that attract well over a thousand students to Cambridge each year so all in all we're helping to share Cambridge with the world and to enrich and transform lives so all of you will be very welcome to return to us again so thank you [Applause]

Channel: Cambridge University

Views: 15,645

Keywords: Cambridge University, Lecture, Lord Rees, Astronomer Royal, Trinity College, astronomy, cosmology, big bang, ICE, Madingley Hall, Madingley Lectures

Id: CBo7xJPVgZM

Length: 71min 37sec (4297 seconds)

Published: Tue Feb 08 2011