{"version":"1.0.0","segments":[{"startTime":6.825,"endTime":11.645,"body":"Oh, that"},{"startTime":13.755,"endTime":14.845,"body":"It's been quite a long day."},{"startTime":15.345,"endTime":16.725,"body":"Uh, thank you all for coming."},{"startTime":16.895,"endTime":19.685,"body":"Thank you for, uh, making it on this lovely evening."},{"startTime":20.505,"endTime":26.733,"body":"Um, I suppose one of the things I want to say this evening is that"},{"startTime":26.733,"endTime":30.885,"body":"physics is hard, or maybe we could be more specific."},{"startTime":31.085,"endTime":37.251,"body":"I suppose cosmology, the study of the universe as a whole is hard, but it,"},{"startTime":37.251,"endTime":38.485,"body":"it's not hard."},{"startTime":38.605,"endTime":41.125,"body":"I think for the reasons that lots of you think it might be."},{"startTime":41.235,"endTime":47.576,"body":"It's not hard because studying the universe as a whole is inherently complex and the"},{"startTime":47.576,"endTime":48.845,"body":"universe is simple."},{"startTime":49.165,"endTime":53.248,"body":"I mean, one, especially once you decide you don't care about details, like all the"},{"startTime":53.248,"endTime":57.331,"body":"stuff that happens down here, how you form planet stars, galaxies, life, biology, chemistry, all"},{"startTime":57.331,"endTime":58.965,"body":"that, let's ignore all of that."},{"startTime":59.385,"endTime":64.358,"body":"If we just write down the equations that explain the past, present, and future of"},{"startTime":64.358,"endTime":65.685,"body":"the universe, they're simple."},{"startTime":65.745,"endTime":69.366,"body":"You can fit them on a couple of pages of a four paper, and it's"},{"startTime":69.366,"endTime":72.987,"body":"much easier predict the fate of the universe than it is to tell you which"},{"startTime":72.987,"endTime":75.885,"body":"way a cricket ball will spin as it leaves a bowler's hand."},{"startTime":75.955,"endTime":76.725,"body":"This is true."},{"startTime":77.755,"endTime":84.485,"body":"It's also not hard because we're short of ideas about how the universe might behave."},{"startTime":84.485,"endTime":90.413,"body":"We're not short of theories, of speculations, of crazy ideas about what might be the"},{"startTime":90.413,"endTime":94.365,"body":"fundamental reasons for the universe behaving the way it does."},{"startTime":94.465,"endTime":98.405,"body":"We get, lots of us get emails all the time from people who've had a"},{"startTime":98.405,"endTime":100.245,"body":"bright idea about how the universe works."},{"startTime":100.345,"endTime":102.205,"body":"And these emails are, I, I like getting them."},{"startTime":102.205,"endTime":105.886,"body":"It's nice to know people are thinking about these things, but there's a sort of"},{"startTime":105.886,"endTime":109.567,"body":"impression that the person writing often has done the hard work of how the idea"},{"startTime":109.567,"endTime":111.285,"body":"and could we fill in the details."},{"startTime":111.915,"endTime":115.57,"body":"Like we've all been sitting around in what one of my colleagues calls the Hollywood"},{"startTime":115.57,"endTime":119.226,"body":"version of science, where we all sit around until somebody has an idea and goes,"},{"startTime":119.226,"endTime":120.445,"body":"my God, I've got it."},{"startTime":120.445,"endTime":122.965,"body":"And then we all run off and prove them right?"},{"startTime":123.025,"endTime":123.965,"body":"It doesn't work like that."},{"startTime":123.965,"endTime":124.845,"body":"We've got lots of ideas."},{"startTime":124.905,"endTime":131.58,"body":"The hard bit is getting an idea that matches the vast amount of information that"},{"startTime":131.58,"endTime":133.805,"body":"we have about the universe."},{"startTime":133.875,"endTime":138.832,"body":"That your bright idea about why the universe is expanding or how much matter there"},{"startTime":138.832,"endTime":140.485,"body":"is or how atoms behave."},{"startTime":141.305,"endTime":145.411,"body":"Can you get your bright idea to not break what we already know about the"},{"startTime":145.411,"endTime":145.685,"body":"universe?"},{"startTime":145.705,"endTime":151.202,"body":"That's the hard bit, because we've got more than a century of cosmological observations, which"},{"startTime":151.202,"endTime":156.7,"body":"we believe in, and most of them, the single observation that constrains our ideas most"},{"startTime":156.7,"endTime":162.198,"body":"comes from what I've been calling the oldest light in the universe, the cosmic microwave"},{"startTime":162.198,"endTime":162.565,"body":"background."},{"startTime":162.785,"endTime":166.543,"body":"And that's what I'm gonna talk about this evening, if I can get up onto"},{"startTime":166.543,"endTime":167.045,"body":"the stage."},{"startTime":168.185,"endTime":174.715,"body":"Now, when I talk about observations in the universe, there's a fundamental fact that I've"},{"startTime":174.715,"endTime":181.245,"body":"mentioned several times in these lectures, which is that light travels at a finite speed."},{"startTime":181.985,"endTime":187.062,"body":"So what we see of the universe is not the universe as it is now,"},{"startTime":187.062,"endTime":191.125,"body":"but we see objects as they were when the light left them."},{"startTime":191.265,"endTime":197.283,"body":"So the unsettling version of this is that light travels at about a foot per"},{"startTime":197.283,"endTime":197.685,"body":"nanosecond."},{"startTime":198.545,"endTime":202.604,"body":"So if you look down and see your feet, if you are sitting, you're seeing"},{"startTime":202.604,"endTime":206.663,"body":"your feet as they were three say, billions of a second ago, not as they"},{"startTime":206.663,"endTime":207.205,"body":"are now."},{"startTime":208.165,"endTime":210.165,"body":"I don't really know what to do with that feeling."},{"startTime":210.525,"endTime":212.245,"body":"\u003claugh\u003e, it's kind of unsettling."},{"startTime":212.445,"endTime":213.685,"body":"I suggest trying to forget it."},{"startTime":214.145,"endTime":216.565,"body":"Uh, we will go to larger scales."},{"startTime":216.825,"endTime":220.685,"body":"We see the sun as it was eight minutes ago."},{"startTime":221.425,"endTime":226.581,"body":"And so if I get rid of the sun by clicking my fingers, that doesn't"},{"startTime":226.581,"endTime":226.925,"body":"work."},{"startTime":227.165,"endTime":227.445,"body":"I hope."},{"startTime":227.785,"endTime":231.014,"body":"Um, but you can't prove that I haven't done it for another eight minutes because"},{"startTime":231.014,"endTime":231.445,"body":"it's light."},{"startTime":231.655,"endTime":233.205,"body":"We'll still be streaming towards us."},{"startTime":233.505,"endTime":236.817,"body":"And actually we know for reasons I can talk about it in the question is"},{"startTime":236.817,"endTime":238.805,"body":"gravity travels at the speed of light as well."},{"startTime":239.225,"endTime":243.8,"body":"And so the sun's gravitational influence we experience as it was based on where the"},{"startTime":243.8,"endTime":245.325,"body":"sun was eight minutes ago."},{"startTime":245.985,"endTime":247.645,"body":"We look further into the night sky."},{"startTime":247.665,"endTime":249.325,"body":"You can take your pick of the naked eye stars."},{"startTime":249.415,"endTime":254.183,"body":"Let's do Dene in the constellation of Nus, the Northern Cross or swan, which is"},{"startTime":254.183,"endTime":257.045,"body":"particularly prominent in the northern hemisphere at the minute."},{"startTime":257.425,"endTime":260.644,"body":"Um, denim's actually one of the more luminous of the naked eye stars."},{"startTime":261.105,"endTime":264.925,"body":"So we see it as it was about two and a half thousand years ago."},{"startTime":265.465,"endTime":267.285,"body":"So we're looking back into the past again."},{"startTime":267.285,"endTime":270.39,"body":"If Deni had disappeared in the last two and a half thousand years, we wouldn't"},{"startTime":270.39,"endTime":270.805,"body":"see it."},{"startTime":270.945,"endTime":276.645,"body":"And of course, anyone on a planet around de Dene will see us as we"},{"startTime":276.645,"endTime":279.685,"body":"were, uh, a couple of thousand years ago."},{"startTime":280.625,"endTime":281.325,"body":"We can go further."},{"startTime":281.785,"endTime":286.868,"body":"We can look at the, uh, furthest object that's easily visible with the naked eye,"},{"startTime":286.868,"endTime":287.885,"body":"the Andromeda Galaxy."},{"startTime":287.885,"endTime":289.325,"body":"Here it is M 31."},{"startTime":289.745,"endTime":294.17,"body":"Um, in the autumn, if you're lucky and you're in a dark sky, you know"},{"startTime":294.17,"endTime":298.005,"body":"where you're looking and you've got clear skies and your vision's pretty good."},{"startTime":298.265,"endTime":302.885,"body":"You can just about see a smudge of light that is the Andromeda galaxy."},{"startTime":303.465,"endTime":309.24,"body":"And those photons, those particles of light, which are reaching you from Andromeda, have been"},{"startTime":309.24,"endTime":311.165,"body":"traveling for 2.2 million years."},{"startTime":312.315,"endTime":316.271,"body":"Some of you in the audience, perhaps the younger members of the audience, you could"},{"startTime":316.271,"endTime":318.645,"body":"just about see triangular the next big galaxy out."},{"startTime":318.645,"endTime":322.245,"body":"And that's 2.7 million, uh, light years away."},{"startTime":322.665,"endTime":327.609,"body":"Um, so we're going into the past, the cluster, for example, this is an image"},{"startTime":327.609,"endTime":331.565,"body":"that was released just this week by the European Euclid, uh, telescope."},{"startTime":331.565,"endTime":336.775,"body":"Something that's designed to make observations that help with this problem of understanding the universe"},{"startTime":336.775,"endTime":338.165,"body":"on the largest scale."},{"startTime":338.165,"endTime":344.237,"body":"Mostly it's a beautiful picture, um, but it's also showing us a cluster called able"},{"startTime":344.237,"endTime":348.285,"body":"2 3 90, which is 2.7 billion light years away."},{"startTime":348.905,"endTime":352.708,"body":"And so we are now at the point when you get this far into the"},{"startTime":352.708,"endTime":356.005,"body":"universe, the idea of a present of today's universe has sort of vanished."},{"startTime":356.065,"endTime":359.445,"body":"We are seeing in these images a deep past."},{"startTime":360.685,"endTime":365.295,"body":"Galaxies are different, different processes are happening, the universe is a different place, but we"},{"startTime":365.295,"endTime":366.525,"body":"get to observe it."},{"startTime":367.505,"endTime":369.485,"body":"And of course, we can go even deeper."},{"startTime":369.995,"endTime":375.485,"body":"This is a recent image from the JWST, our newest space telescope."},{"startTime":376.065,"endTime":378.645,"body":"And many of these dots are interesting."},{"startTime":378.645,"endTime":383.59,"body":"Many of these dots are galaxies, not nearby stars, but one of them down here"},{"startTime":383.59,"endTime":388.535,"body":"in the bottom corner, which delights in the name GNZ one one, sorry, it's American"},{"startTime":388.535,"endTime":389.525,"body":"GNZ one one."},{"startTime":390.145,"endTime":391.925,"body":"Um, I've been told I've got to translate that."},{"startTime":392.345,"endTime":395.925,"body":"Um, this is a galaxy, this little dot."},{"startTime":396.045,"endTime":402.105,"body":"I know it doesn't look like much, but this is a galaxy seen 430 million"},{"startTime":402.105,"endTime":404.125,"body":"years after the big bank."},{"startTime":404.225,"endTime":406.725,"body":"So more than 13 billion years ago."},{"startTime":407.505,"endTime":411.72,"body":"And it, we are looking at one of the earliest active galaxies that have ever"},{"startTime":411.72,"endTime":413.125,"body":"been seen in this image."},{"startTime":413.145,"endTime":417.926,"body":"So we really get to write down the long pass, the long history of the"},{"startTime":417.926,"endTime":418.245,"body":"universe."},{"startTime":418.985,"endTime":423.066,"body":"Now, I said this image was from JWST, and I don't have an image of"},{"startTime":423.066,"endTime":427.147,"body":"it in action because it sits more than a million miles away from us on"},{"startTime":427.147,"endTime":430.685,"body":"earth, but here it is, just before launch, it's gold mirrors folded away."},{"startTime":430.685,"endTime":435.31,"body":"And it, when it's sitting on there, that structure, which is about the size of"},{"startTime":435.31,"endTime":438.085,"body":"a lawn tennis court, is, um, a sun shield."},{"startTime":438.945,"endTime":444.032,"body":"So it's designed when in flight to always protect the mirrors and the instruments of"},{"startTime":444.032,"endTime":447.085,"body":"the telescope, uh, from the light of the sun."},{"startTime":447.785,"endTime":452.162,"body":"Um, it's quite a fun fact, which is that you can measure its effectiveness in"},{"startTime":452.162,"endTime":454.205,"body":"the same units that you do sunscreen."},{"startTime":454.785,"endTime":460.565,"body":"And so that sunshield, which costs many, many, many, many, many mil millions of dollars,"},{"startTime":460.565,"endTime":464.805,"body":"has an SPF factor of 1 million, um, just as designed."},{"startTime":464.995,"endTime":467.085,"body":"It's quite nice that it, you can use these familiar units."},{"startTime":467.625,"endTime":473.887,"body":"And the reason you go to all that trouble, the reason that you have to"},{"startTime":473.887,"endTime":477.645,"body":"keep JWST cold is that it's an infrared telescope."},{"startTime":478.105,"endTime":482.605,"body":"It doesn't work in the light that we can see, but it works at light"},{"startTime":482.605,"endTime":484.405,"body":"at longer wavelengths in the infrared."},{"startTime":484.625,"endTime":490.467,"body":"And it has to be an infrared telescope in order to see galaxies like this"},{"startTime":490.467,"endTime":492.805,"body":"one, because they shine most brightly."},{"startTime":492.805,"endTime":496.725,"body":"When you get to the distant universe, the galaxies shine most brightly."},{"startTime":496.865,"endTime":500.445,"body":"Not in visible light then, but in the infrared."},{"startTime":501.625,"endTime":506.357,"body":"And this should seem like a puzzle, I think to you, because when we say"},{"startTime":506.357,"endTime":511.089,"body":"that galaxies are shining, mostly what we mean is that the stars in them are"},{"startTime":511.089,"endTime":511.405,"body":"shining."},{"startTime":511.435,"endTime":516.783,"body":"When we see this galaxy as it was, uh, more than 13 billion years ago,"},{"startTime":516.783,"endTime":522.131,"body":"what we're seeing is starlight from more than 13 billion years ago, and stars locally"},{"startTime":522.131,"endTime":527.479,"body":"in the galaxies that surround us and in our own Milky Way stars like Dene"},{"startTime":527.479,"endTime":531.045,"body":"shine most brightly in the visible region of the spectrum."},{"startTime":531.065,"endTime":534.725,"body":"Indeed, that's probably why it's the visible region, right?"},{"startTime":534.865,"endTime":537.805,"body":"We evolved to make use of the light from the sun."},{"startTime":537.825,"endTime":543.09,"body":"It makes sense that we see in regions of the spectrum where the sun is"},{"startTime":543.09,"endTime":548.005,"body":"bright, but these galaxies, which still have stars, shine most brightly in the infrared."},{"startTime":548.225,"endTime":553.682,"body":"And it turns out that's not because the stars are different, but because the light"},{"startTime":553.682,"endTime":557.685,"body":"from them has been affected by its passage through the universe."},{"startTime":558.385,"endTime":561.525,"body":"We say it's been redshift, it's been moved to the red."},{"startTime":561.525,"endTime":567.125,"body":"And we can measure this redshift very precisely by looking at the spectra of stars."},{"startTime":567.825,"endTime":569.325,"body":"So here's an image I've shown before."},{"startTime":569.365,"endTime":574.001,"body":"I think this is the spectrum of the sun, um, with the light split out"},{"startTime":574.001,"endTime":576.165,"body":"so that it forms the whole rainbow."},{"startTime":576.305,"endTime":577.885,"body":"And we've wrapped it round on this picture."},{"startTime":578.265,"endTime":583.497,"body":"But you can see that in the spectrum there are these dark lines, these fingerprints"},{"startTime":583.497,"endTime":588.729,"body":"that tell us about the presence of different atoms in this, uh, in the stars,"},{"startTime":588.729,"endTime":590.125,"body":"in the sun's atmosphere."},{"startTime":590.145,"endTime":594.957,"body":"So the two broad black bands that you see in the yellow there tell us"},{"startTime":594.957,"endTime":598.165,"body":"that the sun has sodium in its atmosphere, for example."},{"startTime":598.785,"endTime":603.24,"body":"And when we look at distant galaxies, we see the same pattern of fingerprints, but"},{"startTime":603.24,"endTime":604.725,"body":"all shifted to the red."},{"startTime":604.985,"endTime":606.325,"body":"And we call that the red shift."},{"startTime":606.705,"endTime":610.442,"body":"And so it tells us that something has happened to the light from these distant"},{"startTime":610.442,"endTime":612.685,"body":"galaxies while it's been on its way to us."},{"startTime":613.065,"endTime":617.135,"body":"We think the stars are normal, but this redshift has happened and we've been stunning"},{"startTime":617.135,"endTime":621.205,"body":"this sort of thing for a long while, for more than a hundred years now."},{"startTime":621.205,"endTime":625.525,"body":"And a, a, a slightly unsung hero, uh, of this story is this guy."},{"startTime":625.525,"endTime":631.461,"body":"This is Vesto schleifer, uh, pictures as a, a relatively young astronomer, I think it"},{"startTime":631.461,"endTime":633.045,"body":"has to be said."},{"startTime":633.685,"endTime":637.485,"body":"I was determined at one point this lecture was going to be about vesto lifer."},{"startTime":637.645,"endTime":640.365,"body":"'cause I think his work is incredible, uh, as you'll see."},{"startTime":640.825,"endTime":643.965,"body":"Um, but he turns out to be incredibly boring \u003claugh\u003e."},{"startTime":644.205,"endTime":645.125,"body":"I mean, I'm sure he was lovely."},{"startTime":645.265,"endTime":646.645,"body":"I'm sure he had hobbies and stuff."},{"startTime":646.645,"endTime":651.061,"body":"But the historical record records that he grew up in a fat scientific family went"},{"startTime":651.061,"endTime":654.005,"body":"to college, liked astronomy because he had a good professor."},{"startTime":654.385,"endTime":657.742,"body":"His brother, who was an astronomer, got him a job at an observatory, and then"},{"startTime":657.742,"endTime":659.085,"body":"he stayed there for 53 years."},{"startTime":659.825,"endTime":664.537,"body":"Um, so, you know, I can't really make much of a lecture of that, but"},{"startTime":664.537,"endTime":667.365,"body":"what I can tell you about is his results."},{"startTime":667.425,"endTime":673.329,"body":"So he was working at, um, Lowell Observatory, the place where, um, first of all,"},{"startTime":673.329,"endTime":679.234,"body":"Lowell said his astronomers to look for canals on Mars a few years earlier, where"},{"startTime":679.234,"endTime":683.565,"body":"Pluto actually under the supervision of Slyer, was discovered in 1930."},{"startTime":684.105,"endTime":687.462,"body":"Uh, though of course that's turned out not to be a planet, and we can"},{"startTime":687.462,"endTime":689.925,"body":"fight about that again in the questions, uh, if you like."},{"startTime":690.305,"endTime":695.386,"body":"Um, but he was interested not in solar system astronomy, but in studying the broader"},{"startTime":695.386,"endTime":695.725,"body":"universe."},{"startTime":696.265,"endTime":700.623,"body":"And he got engaged in the problem of what was called then the problem of"},{"startTime":700.623,"endTime":701.205,"body":"the nebula."},{"startTime":701.205,"endTime":705.405,"body":"The fuzzy things that you see in the sky, the things that aren't stars."},{"startTime":706.065,"endTime":710.224,"body":"And it was known in the early 20th century, as I've covered in previous lectures,"},{"startTime":710.224,"endTime":712.165,"body":"that some of them were spiral nebula."},{"startTime":712.315,"endTime":713.405,"body":"They had a spiral structure."},{"startTime":713.405,"endTime":717.155,"body":"And those appeared to be different from things like the Orion Nebula, which we now"},{"startTime":717.155,"endTime":718.405,"body":"know to be star forming."},{"startTime":718.765,"endTime":719.005,"body":"Regents."},{"startTime":720.355,"endTime":725.205,"body":"Schleifer used the powerful telescopes level to take spectra of these spiral nebula."},{"startTime":725.905,"endTime":731.591,"body":"And he noticed that within them, the lines, those fingerprints that I showed on the"},{"startTime":731.591,"endTime":734.245,"body":"previous slide was shifted back and forth."},{"startTime":734.315,"endTime":739.94,"body":"Some of them were shifted to the blue, sorry, some galaxies, some spiral nebula showed"},{"startTime":739.94,"endTime":745.565,"body":"lines shifted to the blue and some showed them shifted to the red over time."},{"startTime":745.865,"endTime":750.281,"body":"And by 1917, when he read this paper, it was clear that there were more"},{"startTime":750.281,"endTime":751.165,"body":"red than blue."},{"startTime":751.545,"endTime":756.202,"body":"He, at the time in this paper, he reports a ratio of 21 redshifted galaxies"},{"startTime":756.202,"endTime":757.445,"body":"to four blue shifted."},{"startTime":758.065,"endTime":764.13,"body":"So he sees this imbalance in the universe, and he interprets this shift as motion"},{"startTime":764.13,"endTime":767.365,"body":"that these galaxies are moving relative to us."},{"startTime":768.665,"endTime":773.506,"body":"He does that because you can make an analogy between this kind of shift and"},{"startTime":773.506,"endTime":778.348,"body":"a Doppler shift, uh, the kind of thing that causes an ambulance siren to change"},{"startTime":778.348,"endTime":780.285,"body":"pitch as it flashes past you."},{"startTime":781.355,"endTime":782.725,"body":"It's not quite the right analogy."},{"startTime":782.835,"endTime":784.245,"body":"It's not quite the right physics as it turns out."},{"startTime":784.245,"endTime":787.068,"body":"But it's a good thing to bear in mind that you can convert these things"},{"startTime":787.068,"endTime":787.445,"body":"to velocity."},{"startTime":788.065,"endTime":792.765,"body":"Um, now he's excited by this because to him, this tells us, tells us that"},{"startTime":792.765,"endTime":797.465,"body":"we live in a galaxy, the fact that all these galaxies are moving relative to"},{"startTime":797.465,"endTime":802.165,"body":"us, but our nearby stars are not, tells him that we live in a galaxy."},{"startTime":802.945,"endTime":808.273,"body":"So he is most engaged in the fact that he's shown that the Milky Way"},{"startTime":808.273,"endTime":810.405,"body":"is something like those distant objects."},{"startTime":810.945,"endTime":813.725,"body":"And he says that we can work out how the Milky Way is moving."},{"startTime":813.905,"endTime":818.273,"body":"He says it's moving at 700 kilometers per second, a number that I'll come back"},{"startTime":818.273,"endTime":818.565,"body":"to."},{"startTime":819.625,"endTime":822.965,"body":"But his results are used by a much more famous astronomer."},{"startTime":822.965,"endTime":829.765,"body":"They're picked up by man with a pipe around town, Edwin Hubble, um, down the"},{"startTime":829.765,"endTime":835.205,"body":"road in California, um, who was studying the same sets of galaxies."},{"startTime":835.665,"endTime":837.245,"body":"Now, Hubble was more interesting."},{"startTime":837.285,"endTime":841.518,"body":"I I, I've always been a big Hubble fan, partly because he's one of the,"},{"startTime":841.518,"endTime":845.751,"body":"unlike sch fu who seemed to have been born to this Hubble, definitely fought for"},{"startTime":845.751,"endTime":847.445,"body":"and chose to be an astronomer."},{"startTime":847.905,"endTime":852.964,"body":"Um, he originally under parental pressure, became a lawyer and was given the best training,"},{"startTime":852.964,"endTime":855.325,"body":"I think, at the University of Chicago."},{"startTime":855.705,"endTime":859.286,"body":"And then he was a Rhodes Scholar in Oxford, where I've looked and looked and"},{"startTime":859.286,"endTime":859.525,"body":"looked."},{"startTime":859.525,"endTime":862.965,"body":"And we have no record of him taking any interest in astronomy whatsoever."},{"startTime":863.565,"endTime":867.577,"body":"I thought I'd find the, you know, the lectures that converted Hubble from law to"},{"startTime":867.577,"endTime":867.845,"body":"astronomy."},{"startTime":868.185,"endTime":871.968,"body":"Um, but he was doing all of this as law, which he then went on"},{"startTime":871.968,"endTime":872.725,"body":"to practice halfheartedly."},{"startTime":873.145,"endTime":875.445,"body":"He said before chucking it for astronomy."},{"startTime":875.445,"endTime":879.563,"body":"And there's this great quote, he says, even if I knew I was second or"},{"startTime":879.563,"endTime":881.485,"body":"third rate, it was astronomy that mattered."},{"startTime":882.105,"endTime":886.285,"body":"Um, and I could, I suppose, work most of a lecturer around that."},{"startTime":886.445,"endTime":888.885,"body":"I found some nice color, I've actually known for a while."},{"startTime":888.905,"endTime":892.976,"body":"So the great fact about Hubble is, is that he was on a championship basketball"},{"startTime":892.976,"endTime":894.605,"body":"team when he was at college."},{"startTime":895.545,"endTime":897.205,"body":"And you're thinking, why am I telling you that?"},{"startTime":897.305,"endTime":897.885,"body":"I'm telling you that?"},{"startTime":898.125,"endTime":900.565,"body":"'cause the basketball has been to space \u003claugh\u003e."},{"startTime":901.105,"endTime":905.663,"body":"So this is the basketball on the space shuttle Atlantis, while it was visiting the"},{"startTime":905.663,"endTime":910.221,"body":"Hubble Space Telescope, which you can see just popping out the top of the picture"},{"startTime":910.221,"endTime":910.525,"body":"there."},{"startTime":910.945,"endTime":912.965,"body":"Um, so that's pretty good bragging rights."},{"startTime":913.045,"endTime":917.978,"body":"I think I've actually, I've held the basketball that went to space that Edwin Hubble"},{"startTime":917.978,"endTime":918.965,"body":"once played with."},{"startTime":919.105,"endTime":922.645,"body":"So, you know, I'm practically as famous as him, I think."},{"startTime":923.225,"endTime":926.005,"body":"Um, I'm also terrible at basketball."},{"startTime":926.065,"endTime":929.285,"body":"It turns out, um, what Hubble was doing was slightly different."},{"startTime":929.305,"endTime":935.516,"body":"So Lyer had looked at the spectra, but Hubble was taking deep pictures of the"},{"startTime":935.516,"endTime":940.485,"body":"galaxies around us using the large telescopes at Mount Wilson in California."},{"startTime":941.105,"endTime":946.437,"body":"Um, so that on the left is a modern picture of the Andromeda Galaxy, but"},{"startTime":946.437,"endTime":951.769,"body":"on the right here is Hubble's picture from 1923 using the great a hundred inch"},{"startTime":951.769,"endTime":952.125,"body":"telescope."},{"startTime":952.125,"endTime":952.605,"body":"So what's that?"},{"startTime":952.605,"endTime":955.765,"body":"That's about two and a half meters the mirror across."},{"startTime":956.345,"endTime":959.405,"body":"And you can see he's marked a couple of N points on here."},{"startTime":959.405,"endTime":961.005,"body":"There's one in the middle, there's one a bit further up."},{"startTime":961.375,"endTime":964.685,"body":"Those he thinks are Novi, they're exploding stars."},{"startTime":964.875,"endTime":967.605,"body":"They've appeared since his previous observation."},{"startTime":968.025,"endTime":971.828,"body":"And there's one in the top right where he's labeled it n and then he"},{"startTime":971.828,"endTime":975.125,"body":"is crossed it out and written var, which is not a sporting reference."},{"startTime":975.705,"endTime":982.146,"body":"Um, this is the discovery of a variable star, a star that's changing in brightness"},{"startTime":982.146,"endTime":983.005,"body":"over time."},{"startTime":983.065,"endTime":987.245,"body":"It appears and disappears as he takes images of this galaxy from night to night."},{"startTime":987.905,"endTime":991.925,"body":"And in fact, it's a type of variable called a PhET."},{"startTime":992.825,"endTime":995.925,"body":"Now a Cepheid variable, and this is the pattern of that star."},{"startTime":995.925,"endTime":999.045,"body":"These are modern observations of hubble's variable star."},{"startTime":999.305,"endTime":1002.845,"body":"You can see it goes up and down in brightness with this regular pattern."},{"startTime":1003.385,"endTime":1007.957,"body":"And the crucial thing is that the speed with which it does that tells you"},{"startTime":1007.957,"endTime":1012.53,"body":"how bright it is, or rather how luminous it is, how much power it's putting"},{"startTime":1012.53,"endTime":1013.445,"body":"out in it."},{"startTime":1013.555,"endTime":1014.085,"body":"It's light."},{"startTime":1014.545,"endTime":1018.754,"body":"And so if you know how luminous something is and you know how distant and"},{"startTime":1018.754,"endTime":1022.963,"body":"you know how bright it appears in the sky, you can work out a distance"},{"startTime":1022.963,"endTime":1023.525,"body":"to it."},{"startTime":1024.065,"endTime":1029.237,"body":"So Hubble has this method which builds on great work by, uh, Henrietta Levitt and"},{"startTime":1029.237,"endTime":1034.409,"body":"others, uh, particularly the women of Harvard Observatory in the first couple of decades of"},{"startTime":1034.409,"endTime":1035.444,"body":"the 20th century."},{"startTime":1035.865,"endTime":1039.659,"body":"Um, but Hubble's able to make these observations because he is got access to these"},{"startTime":1039.659,"endTime":1040.165,"body":"big telescopes."},{"startTime":1040.305,"endTime":1044.954,"body":"And so he is able to measure the distance to the galaxies that slider is"},{"startTime":1044.954,"endTime":1045.885,"body":"taking spectra of."},{"startTime":1046.704,"endTime":1048.725,"body":"And the results are quite striking."},{"startTime":1048.735,"endTime":1050.045,"body":"These are hubble's results."},{"startTime":1050.155,"endTime":1056.08,"body":"I've re plotted them, but I put nearby galaxies on the left and distant galaxies"},{"startTime":1056.08,"endTime":1058.845,"body":"on the right and on the Y-axis."},{"startTime":1058.845,"endTime":1061.165,"body":"So at the top here though, that's the amount of redshift."},{"startTime":1061.185,"endTime":1063.445,"body":"So the higher up you are, the more redshift there is."},{"startTime":1063.545,"endTime":1066.085,"body":"You can interpret that as a velocity if you want."},{"startTime":1066.425,"endTime":1070.696,"body":"And so what you can see is that there's a rule here that we now"},{"startTime":1070.696,"endTime":1072.405,"body":"call the Hubble la Matra law."},{"startTime":1072.905,"endTime":1077.721,"body":"And the rule is that the further away a galaxy is, the faster it's moving"},{"startTime":1077.721,"endTime":1078.685,"body":"away from us."},{"startTime":1078.825,"endTime":1083.125,"body":"The greater the redshift, the further away a galaxy is, the faster it's moving."},{"startTime":1083.625,"endTime":1086.485,"body":"Here's the modern version done with the Hubble Space Telescope."},{"startTime":1086.505,"endTime":1089.565,"body":"And you can see that the results are, are really quite convincing."},{"startTime":1089.565,"endTime":1096.237,"body":"And that observation is, I think, the most important ever made in the subject of"},{"startTime":1096.237,"endTime":1100.685,"body":"astronomy, because from that, we get all of modern cosmology."},{"startTime":1101.345,"endTime":1104.09,"body":"And to show you why that is, I I think we need a, a slightly"},{"startTime":1104.09,"endTime":1105.005,"body":"different universe to think about."},{"startTime":1105.005,"endTime":1105.925,"body":"And I like using this."},{"startTime":1105.925,"endTime":1110.725,"body":"This is an Escher, um, print they called Cubic Space Division."},{"startTime":1111.425,"endTime":1114.76,"body":"Um, and I want you to imagine that we live on this cube that's at"},{"startTime":1114.76,"endTime":1115.205,"body":"the bottom."},{"startTime":1115.425,"endTime":1119.045,"body":"So we are just here, um, all clustered on this cube."},{"startTime":1120.105,"endTime":1125.484,"body":"And I want you to imagine that in this universe that Asher's visualized and that"},{"startTime":1125.484,"endTime":1130.863,"body":"I'm talking about, the rods that join the cubes together are all expanding and they're"},{"startTime":1130.863,"endTime":1133.015,"body":"all expanding at the same rate."},{"startTime":1133.075,"endTime":1134.735,"body":"And it doesn't matter what that rate is."},{"startTime":1135.345,"endTime":1138.855,"body":"Let's say it's uh, I dunno, 10 miles an hour, we'll do something like that."},{"startTime":1139.675,"endTime":1142.866,"body":"So the first thing you realize is that if we're on our cube at the"},{"startTime":1142.866,"endTime":1146.058,"body":"bottom and all the rods are expanding, it's going to look like all the other"},{"startTime":1146.058,"endTime":1147.335,"body":"cubes are rushing away from us."},{"startTime":1148.185,"endTime":1152.623,"body":"We're gonna feel like we're in the center of some great expansion, but that would"},{"startTime":1152.623,"endTime":1154.695,"body":"be true, whichever cube we lived on."},{"startTime":1155.235,"endTime":1160.998,"body":"So there's nothing special about the fact that we look like we're at the center"},{"startTime":1160.998,"endTime":1162.535,"body":"here, second this cube."},{"startTime":1162.635,"endTime":1165.84,"body":"So if we are here, this cube here is gonna rush away from us at"},{"startTime":1165.84,"endTime":1166.695,"body":"10 miles an hour."},{"startTime":1167.435,"endTime":1170.69,"body":"But this one in the top right is gonna go away at 20 miles an"},{"startTime":1170.69,"endTime":1173.946,"body":"hour because there are two rods between us and it, and each one's expanding at"},{"startTime":1173.946,"endTime":1174.815,"body":"10 miles an hour."},{"startTime":1175.635,"endTime":1180.96,"body":"So there's a rule in this universe that the further away a cube is, the"},{"startTime":1180.96,"endTime":1182.735,"body":"faster it's receding from us."},{"startTime":1183.235,"endTime":1186.015,"body":"The further away the cube is, the faster it's receding from us."},{"startTime":1186.015,"endTime":1189.615,"body":"That's the same rule that we found with hubble's observations."},{"startTime":1190.715,"endTime":1197.331,"body":"And so replace the cubes with galaxies, ignore the expanding rods and say it's space"},{"startTime":1197.331,"endTime":1198.655,"body":"itself that's expanding."},{"startTime":1199.835,"endTime":1203.785,"body":"And you get Hubble's law back at the cost of emitting that we live in"},{"startTime":1203.785,"endTime":1204.575,"body":"an expanding universe."},{"startTime":1204.835,"endTime":1209.975,"body":"That's the fundamental insight that leads us to what we'd call the Big Bang theory."},{"startTime":1209.975,"endTime":1216.38,"body":"Because if you live in this universe where things are expanding, we can run this"},{"startTime":1216.38,"endTime":1222.785,"body":"backwards and you get to a point where all the cubes are next to each"},{"startTime":1222.785,"endTime":1229.19,"body":"other, a dense universe that hap that then exists just after the start of a"},{"startTime":1229.19,"endTime":1230.045,"body":"universal expansion."},{"startTime":1230.045,"endTime":1233.325,"body":"So that's the moment, just after whatever the Big Bang was."},{"startTime":1233.905,"endTime":1235.525,"body":"And so that's the observational evidence."},{"startTime":1235.525,"endTime":1237.245,"body":"There are other lines that support it."},{"startTime":1237.425,"endTime":1243.565,"body":"That's the observational evidence that supports this crazy idea of a big bang."},{"startTime":1244.105,"endTime":1247.685,"body":"And I should say in passing that it is a crazy idea, right?"},{"startTime":1247.745,"endTime":1252.5,"body":"The idea that the universe had this moment where things came into being perhaps, and"},{"startTime":1252.5,"endTime":1254.085,"body":"then there was this expansion."},{"startTime":1254.085,"endTime":1256.965,"body":"That's not simple physics at all."},{"startTime":1256.965,"endTime":1258.565,"body":"That's not obvious that it should be."},{"startTime":1258.565,"endTime":1263.831,"body":"So, and in fact, the name Big Bang came from somebody who believed that the"},{"startTime":1263.831,"endTime":1264.885,"body":"idea was ludicrous."},{"startTime":1265.185,"endTime":1270.545,"body":"It was given by the great Cambridge, um, cosmologist, Fred Hoyle, um, the man who"},{"startTime":1270.545,"endTime":1273.405,"body":"with others explained how stars produce heavy elements."},{"startTime":1273.705,"endTime":1275.125,"body":"He thought this idea was ridiculous."},{"startTime":1275.145,"endTime":1278.729,"body":"And, and Big Bang was used by him for the first time in a radio"},{"startTime":1278.729,"endTime":1279.685,"body":"address as an insult."},{"startTime":1279.685,"endTime":1283.885,"body":"You know, this, this, this Big Bang theory can't make any sense."},{"startTime":1283.945,"endTime":1285.205,"body":"That's what it was supposed to be."},{"startTime":1286.065,"endTime":1291.962,"body":"Um, there have, by the way, been attempts to remove the name because it's, it's"},{"startTime":1291.962,"endTime":1294.715,"body":"slightly, I dunno, it's slightly confusing, right?"},{"startTime":1294.745,"endTime":1296.595,"body":"That we're not saying there was an explosion."},{"startTime":1296.595,"endTime":1299.427,"body":"We're just saying there was a time when all the cubes were on top of"},{"startTime":1299.427,"endTime":1301.315,"body":"each other and the universe was in this dense state."},{"startTime":1302.255,"endTime":1308.635,"body":"Um, sky and Telescope Magazine in the nineties ran a competition to replace Big Bang."},{"startTime":1308.635,"endTime":1313.075,"body":"They asked for suggestions and there was a strong second place showing for horrendous space,"},{"startTime":1313.075,"endTime":1317.515,"body":"KA bluey, uh, which some of you may recognize from Calvin and Hobbes, but it's"},{"startTime":1317.515,"endTime":1318.995,"body":"a bit of a mouthful."},{"startTime":1319.135,"endTime":1321.635,"body":"And Big Bang won the contest."},{"startTime":1323.615,"endTime":1324.755,"body":"So we're stuck with it."},{"startTime":1325.255,"endTime":1326.355,"body":"But it raises questions."},{"startTime":1326.355,"endTime":1331.475,"body":"It raises questions like what caused the Big Bang?"},{"startTime":1331.645,"endTime":1334.515,"body":"We've got this moment, which seems to be a moment of origin."},{"startTime":1335.455,"endTime":1336.395,"body":"So what caused it?"},{"startTime":1336.395,"endTime":1340.908,"body":"And this was a, a question that was immediately obvious to those who were working"},{"startTime":1340.908,"endTime":1343.315,"body":"on theory alongside Hubble and and so on."},{"startTime":1343.575,"endTime":1347.795,"body":"And there was a nice idea that maybe you had a cyclical universe."},{"startTime":1347.895,"endTime":1352.312,"body":"So the universe would expand, perhaps it would slow down, it would reverse, it would"},{"startTime":1352.312,"endTime":1356.73,"body":"contract and it would come back to whatever the opposite of a big bang is"},{"startTime":1356.73,"endTime":1359.675,"body":"and tends these days to be called the Big Crunch."},{"startTime":1360.255,"endTime":1363.423,"body":"But there was a brief period where it was called, it was a big bang"},{"startTime":1363.423,"endTime":1363.635,"body":"backwards."},{"startTime":1363.635,"endTime":1366.835,"body":"So it's the gab, which I think is about right."},{"startTime":1367.775,"endTime":1370.925,"body":"If you're watching at home, you can play that backwards and see if I got"},{"startTime":1370.925,"endTime":1371.555,"body":"that vaguely right."},{"startTime":1372.175,"endTime":1376.393,"body":"Um, and that's really nice 'cause then you just have a universe that bounces along"},{"startTime":1376.393,"endTime":1376.675,"body":"forever."},{"startTime":1377.575,"endTime":1382.909,"body":"You never need to explain what happens, except that it was obvious even by the"},{"startTime":1382.909,"endTime":1385.755,"body":"fifties, that there's a problem with this idea."},{"startTime":1386.255,"endTime":1389.795,"body":"And the problem is that the universe changes its contents."},{"startTime":1390.455,"endTime":1394.363,"body":"So let's go back to that distant JWST image and this blob of a galaxy"},{"startTime":1394.363,"endTime":1398.271,"body":"that I am gonna keep showing you until you are excited by it, even though"},{"startTime":1398.271,"endTime":1399.835,"body":"it's a a small red dot."},{"startTime":1400.935,"endTime":1405.795,"body":"One of the things that's exciting about this is that we've detected gas around it."},{"startTime":1406.775,"endTime":1411.593,"body":"And the gas is almost entirely hydrogen, we think, but definitely helium and not much"},{"startTime":1411.593,"endTime":1411.915,"body":"else."},{"startTime":1413.015,"endTime":1416.435,"body":"And so in our modern cosmology, this makes sense."},{"startTime":1417.095,"endTime":1422.566,"body":"The early Big bang, the conditions that existed right in that moment where things were"},{"startTime":1422.566,"endTime":1425.485,"body":"very dense, we think produced hydrogen and helium."},{"startTime":1425.785,"endTime":1430.285,"body":"And so the fact that there's galaxy, which is only a few hundred million years"},{"startTime":1430.285,"endTime":1434.785,"body":"after the Big Bang, has this pristine gas around it that suggests that it's young,"},{"startTime":1434.785,"endTime":1435.685,"body":"that makes sense."},{"startTime":1435.685,"endTime":1438.845,"body":"That's what we'd expect for a galaxy that's in the first flush of youth."},{"startTime":1440.025,"endTime":1445.05,"body":"But what bothered people in the fifties is that over time, as this universe evolves"},{"startTime":1445.05,"endTime":1450.075,"body":"from here to us today and onwards, stars turn hydrogen helium into heavier elements into"},{"startTime":1450.075,"endTime":1455.1,"body":"the carbon, oxygen, nitrogen, and everything else that we are made of, uh, into iron"},{"startTime":1455.1,"endTime":1457.445,"body":"and explosions, produce gold and so on."},{"startTime":1457.505,"endTime":1460.165,"body":"The universe becomes polluted with these heavy metals."},{"startTime":1460.785,"endTime":1465.271,"body":"And so if you have the cyclical universe from Big Bang to nab nib, definitely"},{"startTime":1465.271,"endTime":1467.365,"body":"the first one was better nab nib."},{"startTime":1467.625,"endTime":1472.405,"body":"Um, then shouldn't you inherit some of the leftovers of the previous universe?"},{"startTime":1473.185,"endTime":1478.0,"body":"You need a magical process that destroys everything and gets it back to pristine hydrogen"},{"startTime":1478.0,"endTime":1479.605,"body":"to explain what we're seeing."},{"startTime":1480.785,"endTime":1485.285,"body":"And so they started to look for evidence of such a process."},{"startTime":1486.745,"endTime":1488.245,"body":"And that's the next bit of the story."},{"startTime":1488.265,"endTime":1490.125,"body":"But it starts in a, a, a very different place."},{"startTime":1490.225,"endTime":1493.005,"body":"It starts with an extremely large balloon."},{"startTime":1493.955,"endTime":1495.645,"body":"This is a balloon called Echo one."},{"startTime":1495.955,"endTime":1498.045,"body":"This is its first inflated test."},{"startTime":1498.625,"endTime":1504.285,"body":"Um, and this is I think the simplest working satellite ever launched into space."},{"startTime":1504.625,"endTime":1506.045,"body":"It was just a big balloon."},{"startTime":1506.705,"endTime":1510.045,"body":"Uh, it got to space, it got to the very upper atmosphere of the Earth."},{"startTime":1510.075,"endTime":1511.045,"body":"It's a massive project."},{"startTime":1511.825,"endTime":1516.479,"body":"And the idea of echo one, and there was an Echo two and a couple"},{"startTime":1516.479,"endTime":1521.134,"body":"of others as well, is that these launched in the early sixties were passive communication"},{"startTime":1521.134,"endTime":1521.445,"body":"satellites."},{"startTime":1522.305,"endTime":1526.497,"body":"So in other words, you put these big shiny balloons up in the upper atmosphere"},{"startTime":1526.497,"endTime":1530.689,"body":"and then if you want to communicate with somebody who's over the horizon via radio,"},{"startTime":1530.689,"endTime":1533.205,"body":"you can bounce your radio signals off the balloon."},{"startTime":1534.035,"endTime":1536.045,"body":"It's really simple, but it works right?"},{"startTime":1536.625,"endTime":1537.485,"body":"And it's important."},{"startTime":1538.945,"endTime":1545.483,"body":"So this was an attempt to improve radio communications, but which triggered a huge interest"},{"startTime":1545.483,"endTime":1552.021,"body":"in trying to understand the kind of background interference that you got when you did"},{"startTime":1552.021,"endTime":1553.765,"body":"this sort of communication."},{"startTime":1553.865,"endTime":1557.99,"body":"No doubt, even if you had a powerful radio transmitter, bouncing in off a shiny"},{"startTime":1557.99,"endTime":1562.115,"body":"balloon in the upper atmosphere means that the signal coming back down to your target"},{"startTime":1562.115,"endTime":1563.765,"body":"station is gonna be really weak."},{"startTime":1564.185,"endTime":1566.925,"body":"And this is even more true when things got a bit more advanced."},{"startTime":1567.395,"endTime":1572.474,"body":"When we had the first communications satellites, this is a model of Telstar, which was"},{"startTime":1572.474,"endTime":1574.845,"body":"the first privately built and supported satellite."},{"startTime":1575.305,"endTime":1576.845,"body":"Um, Telstar was a relay."},{"startTime":1577.065,"endTime":1579.984,"body":"So you could beam television signals up to it and then it would beam them"},{"startTime":1579.984,"endTime":1582.125,"body":"back down to earth, but it was going to be faint."},{"startTime":1582.145,"endTime":1587.329,"body":"And people built big instruments like this at and t ground station in Maine that"},{"startTime":1587.329,"endTime":1592.513,"body":"were built just to communicate with this one satellite so that we could communicate across"},{"startTime":1592.513,"endTime":1593.205,"body":"the globe."},{"startTime":1594.705,"endTime":1600.664,"body":"But understanding the background as so often in radio astronomy in particular, but in astronomy"},{"startTime":1600.664,"endTime":1603.445,"body":"as a whole had become really important."},{"startTime":1604.265,"endTime":1605.645,"body":"And that brings us to this instrument."},{"startTime":1605.715,"endTime":1609.845,"body":"This is the Big ear which exists in home Dell in New Jersey."},{"startTime":1610.585,"endTime":1612.005,"body":"Um, it's still there."},{"startTime":1612.465,"endTime":1615.005,"body":"It looks rather like it does did in this picture."},{"startTime":1615.075,"endTime":1618.408,"body":"It's just been announced that it's gonna be preserved as a historical monument, which is"},{"startTime":1618.408,"endTime":1621.742,"body":"great 'cause when I went to see it, I had to break through a fence"},{"startTime":1621.742,"endTime":1623.965,"body":"in a Nokia car park to go and see it."},{"startTime":1624.385,"endTime":1628.525,"body":"Um, but standing on here are two gentlemen called Penzias and Wilson."},{"startTime":1629.075,"endTime":1634.212,"body":"They were engineers at Bell Labs who were given the task of characterizing the background"},{"startTime":1634.212,"endTime":1635.925,"body":"that was interfering with transmissions."},{"startTime":1635.925,"endTime":1636.765,"body":"Tooth thicks."},{"startTime":1636.765,"endTime":1637.565,"body":"Like Telstar."},{"startTime":1638.345,"endTime":1640.205,"body":"You could see that they have their giant antenna."},{"startTime":1640.875,"endTime":1643.805,"body":"There's the shed on the end is where the electronics live."},{"startTime":1643.825,"endTime":1646.245,"body":"So that's where the re uh, receiver is."},{"startTime":1646.305,"endTime":1651.318,"body":"So this collects radio waves, focuses them down into the shed, the, and crucially the"},{"startTime":1651.318,"endTime":1656.331,"body":"whole thing rotates so that they can swing it around the sky and try and"},{"startTime":1656.331,"endTime":1659.005,"body":"work out what the source of the background."},{"startTime":1659.195,"endTime":1659.485,"body":"It's."},{"startTime":1659.485,"endTime":1662.165,"body":"Now, I, uh, this thing is a museum piece."},{"startTime":1662.705,"endTime":1666.925,"body":"Um, we couldn't build one of these just for demonstration purposes."},{"startTime":1666.965,"endTime":1669.765,"body":"I did ask, but apparently Conway Hall isn't quite big enough."},{"startTime":1670.185,"endTime":1673.885,"body":"Um, so I've bought my own device that's operating at the same wavelengths."},{"startTime":1673.885,"endTime":1676.965,"body":"Now, some of you may recognize the rough form of this thing."},{"startTime":1677.585,"endTime":1682.365,"body":"Um, some of you may not, but this is what they used to look like."},{"startTime":1682.985,"endTime":1687.885,"body":"Um, and this, so this has an antenna and it's tuned to a particular frequency."},{"startTime":1688.385,"endTime":1694.078,"body":"And as you could see, it's receiving static because analog television transmissions were turned off"},{"startTime":1694.078,"endTime":1696.735,"body":"in this country about 10 years ago."},{"startTime":1696.875,"endTime":1698.295,"body":"So this is all we can get."},{"startTime":1699.395,"endTime":1703.335,"body":"But this is operating at the same wavelengths as the big air."},{"startTime":1703.335,"endTime":1708.035,"body":"And so this is picking up the same static that Penia and Wilson we're trying"},{"startTime":1708.035,"endTime":1708.975,"body":"to, um, attract."},{"startTime":1709.195,"endTime":1710.775,"body":"So you can actually see it this evening."},{"startTime":1710.775,"endTime":1712.135,"body":"This is a live demonstration."},{"startTime":1712.135,"endTime":1712.935,"body":"This isn't recorded."},{"startTime":1713.555,"endTime":1715.735,"body":"Uh, I hope, I hope, I hope you're enjoying it."},{"startTime":1716.195,"endTime":1718.495,"body":"Um, I know, I know."},{"startTime":1718.495,"endTime":1719.855,"body":"Perhaps it's more interesting than lecture."},{"startTime":1719.855,"endTime":1725.645,"body":"Nevermind, um, they found that most of their signal, 95% of it was due mostly"},{"startTime":1725.645,"endTime":1731.436,"body":"to atmospheric effects, to distant lightning storms, to things happening in the upper atmosphere to"},{"startTime":1731.436,"endTime":1736.455,"body":"the radio background that the earth creates it's magnetic field and the atmosphere."},{"startTime":1737.435,"endTime":1740.903,"body":"But they found there was a remnant about 5% of the signal would not go"},{"startTime":1740.903,"endTime":1741.135,"body":"away."},{"startTime":1741.475,"endTime":1747.043,"body":"And they spent a long time mapping the sky to see where that 5% was"},{"startTime":1747.043,"endTime":1747.415,"body":"brightest."},{"startTime":1747.415,"endTime":1750.853,"body":"And I've got, I actually re plotted it for you, but this is a, this"},{"startTime":1750.853,"endTime":1753.375,"body":"is their data plotted on a modern map of the sky."},{"startTime":1753.395,"endTime":1757.388,"body":"So I've got the whole sky and this shows you all the variation that they"},{"startTime":1757.388,"endTime":1757.655,"body":"detected."},{"startTime":1758.235,"endTime":1759.615,"body":"It was completely uniform."},{"startTime":1760.435,"endTime":1764.718,"body":"So this is coming from wherever they pointed their antenna, they received a signal with"},{"startTime":1764.718,"endTime":1765.575,"body":"the same strength."},{"startTime":1765.835,"endTime":1768.918,"body":"And if this thing was more stable, I could rotate it and show you that"},{"startTime":1768.918,"endTime":1769.535,"body":"this doesn't change."},{"startTime":1769.635,"endTime":1771.935,"body":"And discovered earlier that doesn't work very well."},{"startTime":1771.995,"endTime":1772.815,"body":"So we won't do that."},{"startTime":1773.315,"endTime":1778.965,"body":"Now, if you have a uniform signal, it's usually a sign that something's wrong with"},{"startTime":1778.965,"endTime":1780.095,"body":"the instrument, right?"},{"startTime":1780.095,"endTime":1784.005,"body":"That there's a cable loose, or the antenna's got its own source of noise."},{"startTime":1784.245,"endTime":1785.925,"body":"'cause as you swing it around the sky, nothing changes."},{"startTime":1786.625,"endTime":1788.365,"body":"It, it seems clear or it'll be noise."},{"startTime":1788.425,"endTime":1793.756,"body":"My favorite analogy for this is the 19th century astronomer who reported the discovery of"},{"startTime":1793.756,"endTime":1796.245,"body":"giant an like forms on the moon."},{"startTime":1796.725,"endTime":1800.405,"body":"'cause he could see them through his eyepiece whenever he looked at the moon."},{"startTime":1800.705,"endTime":1803.245,"body":"And it was only when he realized that he could also see them."},{"startTime":1803.245,"endTime":1808.518,"body":"When he looked at Mars and Venus and several stars that he realized that the"},{"startTime":1808.518,"endTime":1809.925,"body":"ants were local, right?"},{"startTime":1809.995,"endTime":1811.485,"body":"They lived in the eyepiece."},{"startTime":1811.905,"endTime":1813.845,"body":"The paper was it's true story."},{"startTime":1813.915,"endTime":1815.165,"body":"It's a genuinely true story."},{"startTime":1815.165,"endTime":1816.485,"body":"And the paper was retracted."},{"startTime":1816.905,"endTime":1821.123,"body":"Um, and I have checked, I have never seen giant ants on any of those"},{"startTime":1821.123,"endTime":1821.405,"body":"bodies."},{"startTime":1821.465,"endTime":1822.805,"body":"So we know that was noise, right?"},{"startTime":1822.805,"endTime":1823.965,"body":"That was, that was a mistake."},{"startTime":1824.265,"endTime":1824.725,"body":"And pen."},{"startTime":1824.865,"endTime":1827.965,"body":"And Wilson originally thought that they had a similar problem."},{"startTime":1829.415,"endTime":1835.894,"body":"Their paper tells us that their antenna was coated with what they called a white"},{"startTime":1835.894,"endTime":1842.373,"body":"dielectric substance, which was deposited there by pigeons that had taken up roost in the"},{"startTime":1842.373,"endTime":1842.805,"body":"antenna."},{"startTime":1844.545,"endTime":1846.685,"body":"And they found a solution."},{"startTime":1847.225,"endTime":1851.165,"body":"And this is this, this might be my favorite slide of all year."},{"startTime":1851.275,"endTime":1856.965,"body":"This is the actual pigeon trap they built to, to catch the pigeons."},{"startTime":1856.965,"endTime":1860.445,"body":"This is currently in the collections of the Smithsonian Museum."},{"startTime":1861.225,"endTime":1865.21,"body":"So if you're ever in Washington DC you can go and ask to see this"},{"startTime":1865.21,"endTime":1866.805,"body":"pigeon trap, which I highly recommend."},{"startTime":1866.805,"endTime":1871.11,"body":"Weirdly, the bits, the electronics from the antenna are in Berlin, but DC got the"},{"startTime":1871.11,"endTime":1871.685,"body":"pigeon trap."},{"startTime":1872.265,"endTime":1875.605,"body":"Um, somewhere there's a museum story about that."},{"startTime":1876.025,"endTime":1877.685,"body":"Um, they caught the pigeons."},{"startTime":1878.575,"endTime":1881.725,"body":"Let's assume that they took them a long way away and released them safely."},{"startTime":1881.965,"endTime":1883.325,"body":"I haven't been able to find any records."},{"startTime":1883.915,"endTime":1889.245,"body":"They came back and then they scrubbed the antenna with toothbrushes."},{"startTime":1890.345,"endTime":1894.782,"body":"So I want you to imagine being a highly trained engineer who solved 95% of"},{"startTime":1894.782,"endTime":1898.925,"body":"the problem that you were set getting rid of this noise in the background."},{"startTime":1899.545,"endTime":1901.205,"body":"And there's 5% left."},{"startTime":1902.345,"endTime":1906.677,"body":"And I want you to imagine that that's led you to catch some pigeons and"},{"startTime":1906.677,"endTime":1909.565,"body":"then scrub your antenna clean of what they've left behind."},{"startTime":1910.585,"endTime":1913.645,"body":"He says, suddenly realizing, I dunno if I can swear aggression, but nevermind."},{"startTime":1913.985,"endTime":1918.325,"body":"You, you, you understand the role of the pigeons, um, scrubbed with toothbrushes."},{"startTime":1918.545,"endTime":1923.345,"body":"And then I want you to imagine to go, you go back into your cabin,"},{"startTime":1923.345,"endTime":1928.145,"body":"you turn on the, your electronics again, and you find that that hum that background"},{"startTime":1928.145,"endTime":1929.425,"body":"noise is still there."},{"startTime":1930.405,"endTime":1934.785,"body":"And I want you somehow to imagine that you are excited by that."},{"startTime":1936.205,"endTime":1938.745,"body":"And that you don't just write in the report."},{"startTime":1938.795,"endTime":1942.305,"body":"There is a background harm which, uh, remains anomalous done."},{"startTime":1942.935,"endTime":1945.105,"body":"Instead, they started seeking explanations."},{"startTime":1945.405,"endTime":1951.405,"body":"And in seeking explanations, they were put in touch with a group of cosmologists just"},{"startTime":1951.405,"endTime":1957.405,"body":"down the road at Princeton, who'd been thinking about building an experiment to detect a"},{"startTime":1957.405,"endTime":1963.405,"body":"background hum at exactly these frequencies because they realized that that was their solution to"},{"startTime":1963.405,"endTime":1965.005,"body":"the bouncing universe properly."},{"startTime":1965.025,"endTime":1971.407,"body":"You see, if that dense state that happens just after the Big Bang is also"},{"startTime":1971.407,"endTime":1977.79,"body":"a time in the universe's history where it was very hot, then atoms can be"},{"startTime":1977.79,"endTime":1982.045,"body":"ripped apart by the aftermath of this hot big bang."},{"startTime":1982.785,"endTime":1988.702,"body":"And so even if you start your universe with a complex set of pre-made atoms"},{"startTime":1988.702,"endTime":1994.62,"body":"and maybe even molecules, if you go through a hot big bang, then you reduce"},{"startTime":1994.62,"endTime":1998.565,"body":"everything to a sea of particles right at the beginning."},{"startTime":2000.065,"endTime":2005.782,"body":"In fact, if it's hot enough, you can't even have atoms, can't even have neutral"},{"startTime":2005.782,"endTime":2011.499,"body":"atoms because the electrons which normally orbit the protons or the the atomic nuclei will"},{"startTime":2011.499,"endTime":2013.405,"body":"run free in the universe."},{"startTime":2014.225,"endTime":2018.765,"body":"And so we predict that that early universe should be a sea of electrons."},{"startTime":2019.425,"endTime":2020.965,"body":"And that has interesting effects."},{"startTime":2021.825,"endTime":2026.75,"body":"The effect is that light traveling in that early universe won't go more than a"},{"startTime":2026.75,"endTime":2031.676,"body":"fraction of a centimeter before it hits an electron and is scattered in a random"},{"startTime":2031.676,"endTime":2032.005,"body":"direction."},{"startTime":2032.745,"endTime":2036.924,"body":"So if I kick my fingers and send you all back to a time 200,000"},{"startTime":2036.924,"endTime":2041.103,"body":"years after the big, which I, I can't do, but you know, you can imagine,"},{"startTime":2041.103,"endTime":2045.283,"body":"uh, if you're there in the first few hundred thousand years after the Big Bang,"},{"startTime":2045.283,"endTime":2049.462,"body":"you'll find yourself inside a luminous fog because light won't be able to travel for"},{"startTime":2049.462,"endTime":2053.085,"body":"more than a few a centimeter or so in front of your face."},{"startTime":2053.465,"endTime":2056.764,"body":"And so it'll bounce around, bounce around and bounce around."},{"startTime":2057.105,"endTime":2064.026,"body":"But we know the universe is expanding and as it expands, it calls and there"},{"startTime":2064.026,"endTime":2070.947,"body":"comes a point about 380,000 years after the Big Bang where all the electrons can"},{"startTime":2070.947,"endTime":2073.255,"body":"be captured by the nuclei."},{"startTime":2073.255,"endTime":2077.334,"body":"An event that happens really quickly, it takes about a year for the whole universe"},{"startTime":2077.334,"endTime":2080.054,"body":"to go from a sea of electrons to empty space."},{"startTime":2081.034,"endTime":2087.503,"body":"And at that point, light which is bouncing around can suddenly travel across the whole"},{"startTime":2087.503,"endTime":2087.935,"body":"universe."},{"startTime":2088.955,"endTime":2090.895,"body":"So this is a, a nice example of that."},{"startTime":2091.565,"endTime":2094.455,"body":"This is an artwork called Blind Light by Anthony Gormley."},{"startTime":2095.085,"endTime":2098.375,"body":"It's a box of fog with some lights in it, if you'll forgive the description."},{"startTime":2098.915,"endTime":2102.335,"body":"But the point is, from outside there's a light bulb in there somewhere."},{"startTime":2102.915,"endTime":2105.695,"body":"The light bounces around, but it keeps hitting water molecules."},{"startTime":2106.075,"endTime":2110.009,"body":"And it bounces from water molecule, from to water molecule to water molecule to water"},{"startTime":2110.009,"endTime":2112.895,"body":"molecule until it happens to hit the edge of the glass."},{"startTime":2113.715,"endTime":2117.575,"body":"And if it scatters in the right direction, it travels out across the room."},{"startTime":2118.155,"endTime":2121.961,"body":"And we perceive it as having come from a glowing edge of this box of"},{"startTime":2121.961,"endTime":2122.215,"body":"fog."},{"startTime":2123.235,"endTime":2128.648,"body":"So when we look back at the early universe, we encounter light that has bounced"},{"startTime":2128.648,"endTime":2131.535,"body":"around from electron electron to electron to electron."},{"startTime":2131.675,"endTime":2136.025,"body":"And then suddenly when the electrons have disappeared, it flies across the universe and it's"},{"startTime":2136.025,"endTime":2138.925,"body":"detected by this device, by this television next to me."},{"startTime":2138.945,"endTime":2145.92,"body":"So 5% of that static on this screen now genuinely comes from a time 380,000"},{"startTime":2145.92,"endTime":2148.245,"body":"years after the Big Bang."},{"startTime":2149.465,"endTime":2153.031,"body":"That's what's been getting in the way of trying to watch, I dunno, late night"},{"startTime":2153.031,"endTime":2155.885,"body":"comedy on channel four 30 years ago, I suppose in my case."},{"startTime":2156.385,"endTime":2161.994,"body":"Anyway, we can actually study this first light, this early light, we call it the"},{"startTime":2161.994,"endTime":2167.603,"body":"cosmic microwave background and later satellites because it's best to do this from space and"},{"startTime":2167.603,"endTime":2168.725,"body":"not with televisions."},{"startTime":2169.025,"endTime":2172.165,"body":"Um, started to find structure in the background."},{"startTime":2172.945,"endTime":2176.579,"body":"The first thing you see if you, if you have a sensitive instrument, not just"},{"startTime":2176.579,"endTime":2179.245,"body":"the, the big ear, is that you see there's a dipole."},{"startTime":2179.985,"endTime":2185.765,"body":"So this is a map of the sky again and it's slightly hotter and colder."},{"startTime":2186.185,"endTime":2189.005,"body":"Um, think of it as brighter and fainter at particular wavelengths."},{"startTime":2189.225,"endTime":2191.605,"body":"And this is because we're moving through space."},{"startTime":2192.625,"endTime":2196.75,"body":"So this tells us about the Earth's motion and it turns out we're heading towards"},{"startTime":2196.75,"endTime":2198.125,"body":"something called the Greater Tractor."},{"startTime":2199.145,"endTime":2202.829,"body":"Um, something, a collection of about a hundred thousand galaxies, a few hundred million light"},{"startTime":2202.829,"endTime":2205.285,"body":"years away, but we can get rid of this pattern."},{"startTime":2205.865,"endTime":2211.053,"body":"And then you see this and this stripe along the middle is actually our galaxy"},{"startTime":2211.053,"endTime":2215.205,"body":"getting in the way dust in our galaxy emits at these wavelengths."},{"startTime":2215.205,"endTime":2217.525,"body":"So you take that away and then you end up here."},{"startTime":2219.525,"endTime":2225.983,"body":"And these blobs, which were first seen by a satellite called Kobe in results released"},{"startTime":2225.983,"endTime":2232.441,"body":"in 1992 are I think the thing that convinced most working cosmologists, that our model"},{"startTime":2232.441,"endTime":2235.025,"body":"of the Big Bang was real."},{"startTime":2236.165,"endTime":2240.957,"body":"And it's because if you have a completely uniform universe that doesn't look like the"},{"startTime":2240.957,"endTime":2245.75,"body":"universe that we see today, the universe that we see today, and these are, is"},{"startTime":2245.75,"endTime":2249.585,"body":"the map of our local universe that I showed in lecture one."},{"startTime":2250.135,"endTime":2252.265,"body":"This is data from the Sloan Digital Sky Survey."},{"startTime":2252.265,"endTime":2254.305,"body":"You'll see our universe today is lumping."},{"startTime":2254.555,"endTime":2258.246,"body":"There are places where there are lots of galaxies and there are places where there"},{"startTime":2258.246,"endTime":2258.985,"body":"are very few."},{"startTime":2260.005,"endTime":2265.121,"body":"But if we have a microwave background, an early universe that's completely uniform, then it"},{"startTime":2265.121,"endTime":2266.145,"body":"will remain uniform."},{"startTime":2266.145,"endTime":2269.105,"body":"You won't be able to form the lumpy universe that we see today."},{"startTime":2269.605,"endTime":2274.994,"body":"But once we discovered that there were tiny fluctuations and they're small, they're about one"},{"startTime":2274.994,"endTime":2279.665,"body":"part in 10,000 difference in density or temperature between each of these blobs."},{"startTime":2280.095,"endTime":2286.225,"body":"Once we discovered there were these differences, we could work out how galaxies form."},{"startTime":2287.205,"endTime":2292.536,"body":"And we do that using supercomputers like this one, which is artfully framed in a"},{"startTime":2292.536,"endTime":2295.025,"body":"a an old deconsecrated church in Barcelona."},{"startTime":2295.565,"endTime":2297.385,"body":"Uh, just looks fantastic."},{"startTime":2298.085,"endTime":2302.206,"body":"Um, and what we do is we can take the blobs that we see in"},{"startTime":2302.206,"endTime":2303.305,"body":"the cosmic microwave background."},{"startTime":2304.405,"endTime":2309.305,"body":"We scatter material matter in this distribution in the computer."},{"startTime":2310.125,"endTime":2310.905,"body":"So you get this."},{"startTime":2311.045,"endTime":2314.863,"body":"And in a picture like this, which is of the computer simulation, the bright bits"},{"startTime":2314.863,"endTime":2316.645,"body":"are the places where there's more matter."},{"startTime":2317.225,"endTime":2319.445,"body":"And the dark bits are places where there's very little."},{"startTime":2319.945,"endTime":2325.845,"body":"And this, this is, uh, what, 15 uh, million years after the beginning."},{"startTime":2325.945,"endTime":2331.954,"body":"The differences are pretty subtle, but gravity works to exaggerate those changes over time because"},{"startTime":2331.954,"endTime":2337.963,"body":"the bits of the, the universe that already have more matter than the average will"},{"startTime":2337.963,"endTime":2339.165,"body":"accumulate more matter."},{"startTime":2339.755,"endTime":2341.565,"body":"They have a stronger gravitational pull."},{"startTime":2342.105,"endTime":2346.295,"body":"And so as time goes on through a billion years, nearly 5 billion years up"},{"startTime":2346.295,"endTime":2350.486,"body":"to today, we go from a very smooth universe to the lumpy one that we"},{"startTime":2350.486,"endTime":2351.045,"body":"see today."},{"startTime":2352.195,"endTime":2355.405,"body":"I've taken out the expansion in these images so you can see what's going on."},{"startTime":2355.405,"endTime":2359.785,"body":"And here, here's a movie showing roughly the same thing where you can see the"},{"startTime":2359.785,"endTime":2361.245,"body":"structure becomes defined over time."},{"startTime":2362.265,"endTime":2366.336,"body":"And the game we can now play is that we can compare this to the"},{"startTime":2366.336,"endTime":2367.965,"body":"universe that we see around us."},{"startTime":2369.545,"endTime":2374.315,"body":"And then because we know the starting conditions from the CMB, we can work out"},{"startTime":2374.315,"endTime":2379.085,"body":"what other ingredients we need in the universe to produce the one that we see."},{"startTime":2379.625,"endTime":2384.755,"body":"And so this is the fundamental observation that's taught us so much about the universe"},{"startTime":2384.755,"endTime":2389.885,"body":"comparing these simulations to things like the Sloan set of data gives us the recipe."},{"startTime":2390.145,"endTime":2395.309,"body":"So it tells us, for example, that we know that there's six or seven times"},{"startTime":2395.309,"endTime":2400.474,"body":"as much matter in the universe than we can account for in normal matter in"},{"startTime":2400.474,"endTime":2405.295,"body":"hydrogen, helium and all the rest in protons and neutrons and all the rest."},{"startTime":2405.315,"endTime":2409.055,"body":"We know that that's dark matter, dunno what it is."},{"startTime":2409.075,"endTime":2410.055,"body":"But we know that it's there."},{"startTime":2410.435,"endTime":2414.815,"body":"We also know through comparisons like this, that the fate of the universe is settled."},{"startTime":2415.485,"endTime":2420.219,"body":"That the expansion of the universe is actually speeding up for reasons that we don't"},{"startTime":2420.219,"endTime":2420.535,"body":"understand."},{"startTime":2421.115,"endTime":2424.015,"body":"Um, we tend to label that dark energy, but we don't know what it is."},{"startTime":2424.475,"endTime":2429.61,"body":"And so we don't get our a nib, we get an ever expanding universe at"},{"startTime":2429.61,"endTime":2430.295,"body":"the end."},{"startTime":2431.475,"endTime":2433.575,"body":"And so this is the game that cosmologists play."},{"startTime":2433.575,"endTime":2437.865,"body":"This is why it's hard because I have to, when I write down my new"},{"startTime":2437.865,"endTime":2442.156,"body":"idea for a cosmological theory, I have to still produce a universe that looks like"},{"startTime":2442.156,"endTime":2443.015,"body":"what we see."},{"startTime":2443.975,"endTime":2447.387,"body":"I have to get the cosmic microwave background right and I have to tie them"},{"startTime":2447.387,"endTime":2447.615,"body":"together."},{"startTime":2448.435,"endTime":2449.775,"body":"And that's really hard."},{"startTime":2450.805,"endTime":2456.107,"body":"What we'd like to happen actually is for the observations to disagree with each other"},{"startTime":2456.107,"endTime":2456.815,"body":"a bit."},{"startTime":2457.295,"endTime":2460.055,"body":"'cause then we'd have a clue as to which ideas might be good ones."},{"startTime":2460.635,"endTime":2466.26,"body":"And we're beginning to get the idea that that might be possible from two sets"},{"startTime":2466.26,"endTime":2471.135,"body":"of observations, trying to measure something fundamental, something that Hubble himself would've recognized."},{"startTime":2472.995,"endTime":2476.855,"body":"All we want to do is measure the current expansion speed of the universe."},{"startTime":2477.755,"endTime":2479.775,"body":"How fast is the universe expanding?"},{"startTime":2480.715,"endTime":2485.533,"body":"So it's sometimes called the Hubble constant, though it's not constant, it's just the current"},{"startTime":2485.533,"endTime":2485.855,"body":"value."},{"startTime":2486.635,"endTime":2488.815,"body":"Now, there are two broadly, two ways of doing this."},{"startTime":2489.435,"endTime":2492.095,"body":"One is that we can look at the cosmic microwave background."},{"startTime":2493.105,"endTime":2495.725,"body":"We can do that extrapolation to what we see today."},{"startTime":2495.745,"endTime":2500.645,"body":"We can compare the two and we can work out how much expansion there's been."},{"startTime":2500.675,"endTime":2502.525,"body":"It's a bit like having a cosmic ruler."},{"startTime":2502.525,"endTime":2505.445,"body":"We can take features in the cosmic microwave background."},{"startTime":2505.905,"endTime":2509.448,"body":"We can look at our distribution of galaxies and say, okay, we've found the same"},{"startTime":2509.448,"endTime":2509.685,"body":"feature."},{"startTime":2510.145,"endTime":2513.245,"body":"So we've literally measured how much bigger the ruler has got."},{"startTime":2514.155,"endTime":2514.885,"body":"It's really simple."},{"startTime":2514.995,"endTime":2516.725,"body":"It's a physicist's way to do it."},{"startTime":2517.145,"endTime":2518.005,"body":"Um, it's elegant."},{"startTime":2518.705,"endTime":2520.525,"body":"Um, it's difficult."},{"startTime":2520.595,"endTime":2521.165,"body":"It's tricky."},{"startTime":2521.265,"endTime":2524.853,"body":"You've gotta get the statistics right, but it it, but, but it, but it's nice"},{"startTime":2524.853,"endTime":2527.725,"body":"and simple or you do a better version of what Hubble did."},{"startTime":2528.745,"endTime":2530.725,"body":"And he measured distances with stars."},{"startTime":2530.905,"endTime":2532.485,"body":"Now we use exploding stars."},{"startTime":2532.555,"endTime":2536.822,"body":"This is a type one, a supernova, uh, the death of a giant star in"},{"startTime":2536.822,"endTime":2538.245,"body":"a nearby galaxy M 82."},{"startTime":2538.705,"endTime":2541.765,"body":"And these always go bang with roughly the same brightness."},{"startTime":2542.425,"endTime":2546.781,"body":"So if they go bang with the same brightness, then we can work out their"},{"startTime":2546.781,"endTime":2549.685,"body":"distance compare by comparing to how bright they actually are."},{"startTime":2550.585,"endTime":2554.485,"body":"And we can measure the expansion rate that way between us and the galaxy."},{"startTime":2555.025,"endTime":2560.038,"body":"And the thing is that when you do this, the two methods now seem to"},{"startTime":2560.038,"endTime":2561.375,"body":"disagree with each other."},{"startTime":2562.255,"endTime":2565.969,"body":"Although I I I'm gonna have annoyed people possibly one or two of them in"},{"startTime":2565.969,"endTime":2567.455,"body":"the room by saying they disagree."},{"startTime":2567.555,"endTime":2569.655,"body":"So, uh, I'll show you the actual results."},{"startTime":2569.755,"endTime":2574.186,"body":"So this is over time and in black, uh, so this is the speed with"},{"startTime":2574.186,"endTime":2576.255,"body":"which we think the universe is expanding."},{"startTime":2576.275,"endTime":2580.815,"body":"So you can see it's roughly 70 kilometers per second per mega parsec."},{"startTime":2581.395,"endTime":2583.935,"body":"So a mega parsec is about 3 million light years."},{"startTime":2584.675,"endTime":2589.375,"body":"And so for every 3 million light years, every second that gets 70 kilometers bigger."},{"startTime":2590.235,"endTime":2592.455,"body":"So you'll see that that's not very much right?"},{"startTime":2592.675,"endTime":2596.706,"body":"So that's why we don't really notice the expansion of space in our daily lives,"},{"startTime":2596.706,"endTime":2596.975,"body":"right?"},{"startTime":2597.045,"endTime":2600.874,"body":"It's a small account unless you're looking on very large scales in black are the"},{"startTime":2600.874,"endTime":2604.704,"body":"results from the people who study the microwave background in blue are the people who"},{"startTime":2604.704,"endTime":2605.215,"body":"study supernova."},{"startTime":2605.215,"endTime":2608.695,"body":"And there's this gap in between that's opened up in the last few years."},{"startTime":2609.355,"endTime":2614.095,"body":"Now scientists in particular when they say two datasets don't agree with each other."},{"startTime":2614.635,"endTime":2616.575,"body":"So to my joy, I really like this."},{"startTime":2616.575,"endTime":2618.935,"body":"We've decided this isn't a disagreement and it's not an argument."},{"startTime":2619.205,"endTime":2620.615,"body":"This is a tension."},{"startTime":2621.995,"endTime":2627.666,"body":"So this is known as the Hubble tension and it's the biggest problem in cosmology"},{"startTime":2627.666,"endTime":2629.935,"body":"that these two methods, Derek agree."},{"startTime":2629.935,"endTime":2635.201,"body":"Either we don't understand something about super novy or we don't understand something about the"},{"startTime":2635.201,"endTime":2636.255,"body":"cosmic microwave background."},{"startTime":2636.255,"endTime":2641.678,"body":"And remember, the early universe is simple or there's something really wrong with almost everything"},{"startTime":2641.678,"endTime":2645.655,"body":"I've told you \u003claugh\u003e, and we don't know which it is."},{"startTime":2645.655,"endTime":2649.255,"body":"What we need a more supernova and help is coming."},{"startTime":2649.825,"endTime":2654.454,"body":"We're building the Vera Rubin Observatory in Chile, um, which I've mentioned before, but I'm"},{"startTime":2654.454,"endTime":2658.775,"body":"really excited now 'cause the camera here, it is this beast of a thing."},{"startTime":2659.005,"endTime":2666.135,"body":"This 3,200 megapixel camera arrived at the observatory, uh, just the other day."},{"startTime":2666.235,"endTime":2668.415,"body":"So about this photo is about a week old."},{"startTime":2668.875,"endTime":2672.125,"body":"Um, this camera is the biggest camera ever built for astronomy."},{"startTime":2672.545,"endTime":2677.304,"body":"Uh, and Reuben will do many things, but we're going to discover more supernova every"},{"startTime":2677.304,"endTime":2679.525,"body":"month than we found in human history."},{"startTime":2680.785,"endTime":2682.165,"body":"So we've got more supernova coming."},{"startTime":2682.165,"endTime":2686.307,"body":"We'll be able to do these measurements more accurately and maybe the tension will go"},{"startTime":2686.307,"endTime":2687.965,"body":"away or maybe it will stay."},{"startTime":2689.385,"endTime":2692.779,"body":"We can also look at the microwave background in new ways, which we do for"},{"startTime":2692.779,"endTime":2693.685,"body":"all sorts of reasons."},{"startTime":2693.795,"endTime":2695.325,"body":"This time we're doing it from the ground."},{"startTime":2695.875,"endTime":2700.682,"body":"This is the high Andes in Chile, the site of a, an observatory that's been"},{"startTime":2700.682,"endTime":2702.605,"body":"built now called the Simons Observatory."},{"startTime":2702.905,"endTime":2709.245,"body":"An international collaboration involving American, Canadian, Chilean, British, and many more, uh, cosmologists."},{"startTime":2709.945,"endTime":2716.472,"body":"And they're going to look at the microbe background primarily to try and uncover evidence"},{"startTime":2716.472,"endTime":2722.565,"body":"of what happened in the first few, not even milliseconds of the universe's history."},{"startTime":2722.665,"endTime":2728.485,"body":"The very beginnings may have left their imprints on this oldest light of all."},{"startTime":2729.625,"endTime":2734.996,"body":"But what's fun about this is that the biggest problem isn't working out the physics"},{"startTime":2734.996,"endTime":2740.368,"body":"of this or, or looking for the signals that they hope to find because that"},{"startTime":2740.368,"endTime":2741.085,"body":"stuff's simple."},{"startTime":2741.485,"endTime":2743.725,"body":"Remember, physics isn't hard for the reasons you think."},{"startTime":2745.055,"endTime":2749.849,"body":"Their big problem is that our galaxy gets in the way that the dust in"},{"startTime":2749.849,"endTime":2754.005,"body":"our galaxy shines brightly at these wavelengths and will interfere with these measurements."},{"startTime":2754.705,"endTime":2757.125,"body":"But what's great is that we're building an observatory."},{"startTime":2757.125,"endTime":2758.365,"body":"They can do cosmology."},{"startTime":2758.895,"endTime":2765.687,"body":"Other astronomers will use this data designed to discover the very early history of our"},{"startTime":2765.687,"endTime":2768.405,"body":"universe to study our galaxy today."},{"startTime":2769.065,"endTime":2773.397,"body":"And so a new understanding of the dust in our galaxy, the raw materials that"},{"startTime":2773.397,"endTime":2777.73,"body":"form planets and which will go on to form the next generation of stars and"},{"startTime":2777.73,"endTime":2781.485,"body":"soul systems, will come from a project that's thinking about things that happen."},{"startTime":2781.925,"endTime":2784.245,"body":"13.8 billion years ago."},{"startTime":2785.845,"endTime":2791.731,"body":"I started by saying that physics isn't hard, but what I hope I've said in"},{"startTime":2791.731,"endTime":2797.617,"body":"the six lectures this year is that our, our ingenuity in inventing new ways to"},{"startTime":2797.617,"endTime":2800.365,"body":"discover and observe the universe is unbounded."},{"startTime":2801.385,"endTime":2806.763,"body":"And that as we found more ways to make careful measurements, often simple measurements very"},{"startTime":2806.763,"endTime":2812.141,"body":"carefully, we've unveiled a rich and varied history that goes from the microwave background just"},{"startTime":2812.141,"endTime":2817.519,"body":"after whatever it was that the Big Bang was all the way through to the"},{"startTime":2817.519,"endTime":2822.898,"body":"point where we have a planet with people not just capable, but willing to come"},{"startTime":2822.898,"endTime":2826.125,"body":"and hear about this stuff on a Wednesday evening."},{"startTime":2827.365,"endTime":2832.661,"body":"I want to end this year's series of lectures, um, with a few lines from"},{"startTime":2832.661,"endTime":2837.605,"body":"a poem by Rebecca Elson, a poet who was also somebody who researched cosmologies."},{"startTime":2837.875,"endTime":2840.925,"body":"He's, she studied the universe on the largest scales."},{"startTime":2841.345,"endTime":2848.103,"body":"And I think it captures how I want everyone to feel about our observations of"},{"startTime":2848.103,"endTime":2849.005,"body":"the universe."},{"startTime":2849.825,"endTime":2858.814,"body":"She says we astronomers are nomads, merchants and circus folk all the world, our tempt,"},{"startTime":2858.814,"endTime":2866.605,"body":"we are industrious, we breed enthusiasms and we honor our responsibility to awe."},{"startTime":2866.935,"endTime":2867.725,"body":"Thank you very much."},{"startTime":2879.115,"endTime":2879.585,"body":"Thank you"},{"startTime":2884.315,"endTime":2884.665,"body":"Chris."},{"startTime":2884.665,"endTime":2885.425,"body":"Thank you so much."},{"startTime":2885.495,"endTime":2886.785,"body":"That is absolutely terrific."},{"startTime":2887.085,"endTime":2889.225,"body":"Uh, we do have some, uh, time for questions."},{"startTime":2889.285,"endTime":2892.401,"body":"If, uh, we'll take a mixture from the hall and I've got quite a lot"},{"startTime":2892.401,"endTime":2893.025,"body":"online as well."},{"startTime":2893.205,"endTime":2896.649,"body":"So if we don't get through all the questions, um, do keep an eye out"},{"startTime":2896.649,"endTime":2898.945,"body":"on our YouTube channel, on your podcast channel of choice."},{"startTime":2899.345,"endTime":2901.665,"body":"'cause we will have, uh, I'm sure a follow up on those."},{"startTime":2901.885,"endTime":2904.985,"body":"Um, if you're in the hall, please wait for the microphone to arrive with you."},{"startTime":2904.985,"endTime":2906.545,"body":"So we've got one right at the back over there."},{"startTime":2907.235,"endTime":2907.585,"body":"Hello."},{"startTime":2907.645,"endTime":2908.625,"body":"Uh, thank you Chris."},{"startTime":2908.645,"endTime":2910.305,"body":"It was a fascinating lecture."},{"startTime":2910.965,"endTime":2916.57,"body":"Um, I'm quite naive, but you said some of the simplest ideas, uh, create a"},{"startTime":2916.57,"endTime":2918.065,"body":"huge amount of research."},{"startTime":2919.445,"endTime":2924.373,"body":"One thing I'm aware of is that the further into space we look, we look"},{"startTime":2924.373,"endTime":2929.302,"body":"further back in time so that we get towards 13 billion years ago, we get"},{"startTime":2929.302,"endTime":2930.945,"body":"to near the Big Bang."},{"startTime":2931.565,"endTime":2937.578,"body":"And your evidence is that because of the red shift, things are moving away, accelerating"},{"startTime":2937.578,"endTime":2940.785,"body":"more rapidly and things locally are not accelerating."},{"startTime":2941.495,"endTime":2946.463,"body":"Does that suggest that maybe we're looking at the acceleration just because of the Big"},{"startTime":2946.463,"endTime":2951.431,"body":"Bang near the Big bang rather than locally and we're we're getting the wrong end"},{"startTime":2951.431,"endTime":2952.425,"body":"of the stick?"},{"startTime":2952.655,"endTime":2953.945,"body":"Yeah, this is a really good question."},{"startTime":2954.005,"endTime":2957.281,"body":"So just to paraphrase briefly and I, there was more to this, but let me"},{"startTime":2957.281,"endTime":2960.557,"body":"answer one aspect of it, which was, you know, we know that the expansions that"},{"startTime":2960.557,"endTime":2962.305,"body":"we seem to think the expansion is accelerating."},{"startTime":2962.405,"endTime":2964.785,"body":"So is it just that it was different in the past?"},{"startTime":2964.925,"endTime":2967.185,"body":"And as we look back, we're seeing these, these effects."},{"startTime":2967.245,"endTime":2969.105,"body":"So people have have thought about that."},{"startTime":2969.605,"endTime":2974.336,"body":"One thing you might predict, if that's right, is that we wouldn't necessarily be in"},{"startTime":2974.336,"endTime":2976.545,"body":"the center of whatever change that was."},{"startTime":2976.765,"endTime":2980.792,"body":"So what people do is they look at maybe if I just use this half"},{"startTime":2980.792,"endTime":2984.819,"body":"of the sky, do I still see evidence for acceleration exactly the same as I"},{"startTime":2984.819,"endTime":2985.625,"body":"see this way?"},{"startTime":2985.925,"endTime":2987.865,"body":"And as far as we can tell, there's no difference."},{"startTime":2987.865,"endTime":2992.436,"body":"And so it's quite hard to explain unless there's some magical reason why we're right"},{"startTime":2992.436,"endTime":2994.265,"body":"in the middle of this expansion."},{"startTime":2994.265,"endTime":2998.255,"body":"And remember that I said just from the fact it's expanding, there's no reason that"},{"startTime":2998.255,"endTime":2999.585,"body":"we're in a special place."},{"startTime":3000.245,"endTime":3004.284,"body":"So you either, you either have to, to say that we are really lucky and"},{"startTime":3004.284,"endTime":3007.785,"body":"we're in the middle and this is happening, or you need another explanation."},{"startTime":3007.785,"endTime":3009.705,"body":"But it's, it's not a naive question at all."},{"startTime":3009.735,"endTime":3013.55,"body":"It's really important to consider these effects 'cause we are looking at a universe that's"},{"startTime":3013.55,"endTime":3015.585,"body":"changing as the light was traveling towards us."},{"startTime":3015.965,"endTime":3017.465,"body":"So thank thanks for getting us started."},{"startTime":3017.475,"endTime":3018.105,"body":"Great question."},{"startTime":3018.605,"endTime":3021.705,"body":"Um, I I'll take one, uh, online and then we'll go back into the all."},{"startTime":3021.705,"endTime":3026.437,"body":"So, uh, um, uh, one which I was tempted to ask myself actually, which, uh,"},{"startTime":3026.437,"endTime":3031.169,"body":"um, if the universe is expanding, are there any theories about what it is expanding"},{"startTime":3031.169,"endTime":3031.485,"body":"into?"},{"startTime":3031.705,"endTime":3033.445,"body":"Oh, I hate this question \u003claugh\u003e."},{"startTime":3034.075,"endTime":3038.728,"body":"It's not that it's a, it's not that it's a bad question, I promise it's"},{"startTime":3038.728,"endTime":3043.381,"body":"not, it's a perfectly sensible question, but I know I'm not gonna say anything that's"},{"startTime":3043.381,"endTime":3048.034,"body":"satisfying \u003claugh\u003e, but let me talk for 60 seconds in the hope that I might"},{"startTime":3048.034,"endTime":3048.965,"body":"hit on something."},{"startTime":3049.025,"endTime":3053.965,"body":"So the reason it's not a good question is that it's perfectly reasonable, right?"},{"startTime":3054.025,"endTime":3058.045,"body":"You are imagining when I say the universe is expanding, you've all got in your"},{"startTime":3058.045,"endTime":3062.065,"body":"head a thing that's probably round and has got some stars on it called the"},{"startTime":3062.065,"endTime":3063.405,"body":"universe that's getting bigger, right?"},{"startTime":3063.955,"endTime":3067.874,"body":"That all makes sense, you know, that's why if you call it the big bang,"},{"startTime":3067.874,"endTime":3069.965,"body":"fine, it exploded and then it expanded outwards."},{"startTime":3069.965,"endTime":3071.325,"body":"We can all do that in our heads as well."},{"startTime":3071.425,"endTime":3075.268,"body":"But the question I have to ask you is where you think you're watching that"},{"startTime":3075.268,"endTime":3075.525,"body":"from?"},{"startTime":3076.235,"endTime":3080.032,"body":"Because if you've got this ball of stars that's getting bigger, you are viewing that"},{"startTime":3080.032,"endTime":3081.045,"body":"from outside the universe."},{"startTime":3081.945,"endTime":3085.908,"body":"And so that's not all I can say is that that's not a sensible place"},{"startTime":3085.908,"endTime":3086.965,"body":"to put yourself, right?"},{"startTime":3086.995,"endTime":3088.605,"body":"That doesn't exist in our physics."},{"startTime":3088.945,"endTime":3091.445,"body":"You've given yourself a godlike view of the thing."},{"startTime":3091.985,"endTime":3096.845,"body":"And so what it is, is it, it, it's not an expansion, it's a stretch."},{"startTime":3097.345,"endTime":3102.729,"body":"So it would be like, imagine if we turned this stage into a travelator that"},{"startTime":3102.729,"endTime":3104.165,"body":"split down the middle."},{"startTime":3104.225,"endTime":3106.405,"body":"So you started going that way and I started going this way."},{"startTime":3107.435,"endTime":3110.685,"body":"We'd be getting further apart 'cause the stage itself would be expanding."},{"startTime":3110.985,"endTime":3114.713,"body":"And I think I've now taught for long enough that you've forgotten that I haven't"},{"startTime":3114.713,"endTime":3118.442,"body":"answered the question, but there is no good answer to that because it rubs up"},{"startTime":3118.442,"endTime":3119.685,"body":"against how we visualize things."},{"startTime":3119.865,"endTime":3120.725,"body":"So yeah, sorry."},{"startTime":3120.725,"endTime":3124.57,"body":"If you, if you're online and you know an answer, please put it in the"},{"startTime":3124.57,"endTime":3126.365,"body":"comments and I'll credit you forevermore \u003claugh\u003e."},{"startTime":3126.865,"endTime":3128.245,"body":"Um, yeah, thanks very much Chris."},{"startTime":3128.385,"endTime":3133.34,"body":"Um, you mentioned earlier that, um, some, um, astronomers, uh, had difficulty accepting the Big"},{"startTime":3133.34,"endTime":3137.965,"body":"Bang theory because it didn't seem like, um, essentially good physics or understandable physics."},{"startTime":3138.505,"endTime":3142.972,"body":"And of course, um, Fred Hoyle and others championed as an alternative, the steady state"},{"startTime":3142.972,"endTime":3147.44,"body":"theory of the universe, which was, um, the idea of an ever evolving, ever expanding"},{"startTime":3147.44,"endTime":3149.525,"body":"universe with no beginning and no end."},{"startTime":3149.745,"endTime":3154.175,"body":"To what extent, with the luxury of hindsight, bearing in mind that the steady state"},{"startTime":3154.175,"endTime":3158.605,"body":"theory is now rejected by almost all astronomers, to what extent did the steady state"},{"startTime":3158.605,"endTime":3162.445,"body":"theory seem like better physics, if you like, than the Big Bang theory?"},{"startTime":3162.635,"endTime":3162.925,"body":"Yeah,"},{"startTime":3162.925,"endTime":3164.205,"body":"It's a good, it's a good question."},{"startTime":3164.545,"endTime":3167.205,"body":"Um, so the, yeah, as you, you described it very succinctly."},{"startTime":3167.205,"endTime":3170.973,"body":"So the steady state was, it didn't try to deny the fact there was an"},{"startTime":3170.973,"endTime":3173.485,"body":"expansion, but the idea was that you'd have no beginning."},{"startTime":3173.555,"endTime":3178.299,"body":"That, that the expansion would be, there'd be constant creation of space and presumably raw"},{"startTime":3178.299,"endTime":3179.565,"body":"materials and so on."},{"startTime":3179.825,"endTime":3183.583,"body":"So I think whether it's better physics at the time or not is a matter"},{"startTime":3183.583,"endTime":3184.085,"body":"of taste."},{"startTime":3184.405,"endTime":3188.083,"body":"I think it's about do, do you wrap up all the stuff we don't understand"},{"startTime":3188.083,"endTime":3190.045,"body":"and say, all right, that's the big bang."},{"startTime":3190.385,"endTime":3194.716,"body":"Or do you have a mysterious force that continually creates space that we also don't"},{"startTime":3194.716,"endTime":3195.005,"body":"understand?"},{"startTime":3195.105,"endTime":3197.285,"body":"So, so I think that really is a matter of taste."},{"startTime":3197.985,"endTime":3202.728,"body":"Um, what happened pretty quickly after that into the late sixties, just from things like"},{"startTime":3202.728,"endTime":3207.472,"body":"counting the number of things that radio telescopes could see on the sky was it"},{"startTime":3207.472,"endTime":3212.216,"body":"became clear that as we looked into the distant universe, it was different from the"},{"startTime":3212.216,"endTime":3213.165,"body":"present day universe."},{"startTime":3213.305,"endTime":3216.565,"body":"So things were closer together, stars were younger."},{"startTime":3217.145,"endTime":3222.226,"body":"And so once you get to that point, I think it's very difficult to explain"},{"startTime":3222.226,"endTime":3222.565,"body":"that."},{"startTime":3222.765,"endTime":3227.295,"body":"'cause you end up with a steady state that needs to create the illusion that"},{"startTime":3227.295,"endTime":3228.805,"body":"the distant universe is earlier."},{"startTime":3229.145,"endTime":3230.765,"body":"And at that point I think it falls apart."},{"startTime":3230.765,"endTime":3232.085,"body":"Now Hoyle wouldn't agree with that."},{"startTime":3232.085,"endTime":3235.376,"body":"He stuck to his guts all the way through into the 1980s when he was"},{"startTime":3235.376,"endTime":3238.668,"body":"doing things like picking fights with the Natural History Museum in his spare time, and"},{"startTime":3238.668,"endTime":3240.205,"body":"which of us hasn't uh, done that."},{"startTime":3240.785,"endTime":3243.605,"body":"Um, so, so, but I think at the time it makes sense."},{"startTime":3243.705,"endTime":3247.797,"body":"But there was a core group, mostly in the UK actually study state was the"},{"startTime":3247.797,"endTime":3251.89,"body":"British theory, uh, where there was a small group that clung on, I think passed"},{"startTime":3251.89,"endTime":3255.165,"body":"the point that the observational evidence had made it just more complicated."},{"startTime":3255.275,"endTime":3259.049,"body":"It's not that it's wrong, but you needed so many fudge factors that you were"},{"startTime":3259.049,"endTime":3261.565,"body":"essentially putting little big bangs in all over the place."},{"startTime":3261.585,"endTime":3264.085,"body":"And at that point you might as well have one big one \u003claugh\u003e."},{"startTime":3264.705,"endTime":3267.436,"body":"Um, I can take a couple more in line, one of which I think probably"},{"startTime":3267.436,"endTime":3268.165,"body":"can answer quite quickly."},{"startTime":3268.225,"endTime":3269.605,"body":"The other one might be a bit more involved."},{"startTime":3269.905,"endTime":3273.944,"body":"Um, one, this is a sympathy question really to the, someone was saying, I've asked"},{"startTime":3273.944,"endTime":3277.445,"body":"this every lecturer in this series, and sadly yet to see it asked."},{"startTime":3277.985,"endTime":3278.925,"body":"So on the last lecture,"},{"startTime":3278.935,"endTime":3280.085,"body":"Pluto is not a planet"},{"startTime":3280.685,"endTime":3284.965,"body":"\u003claugh\u003e, sorry, on the last lecture of the series, could it be the Mr."},{"startTime":3285.265,"endTime":3285.485,"body":"Ons?"},{"startTime":3286.225,"endTime":3289.525,"body":"It could always be the Mr Ons, but, um, no one will give me funding"},{"startTime":3289.525,"endTime":3290.405,"body":"to research that \u003claugh\u003e."},{"startTime":3290.405,"endTime":3292.685,"body":"So see also CLS and"},{"startTime":3292.875,"endTime":3293.165,"body":"Yeah."},{"startTime":3293.265,"endTime":3298.306,"body":"Um, um, uh, another one which we have potentially one for our professor of divinity,"},{"startTime":3298.306,"endTime":3303.348,"body":"but, um, uh, does it blow your mind as much as mine when you question"},{"startTime":3303.348,"endTime":3303.685,"body":"why?"},{"startTime":3303.685,"endTime":3307.885,"body":"Is there anything at all I get the expanding universe, but why anything at all"},{"startTime":3307.885,"endTime":3308.725,"body":"to begin with?"},{"startTime":3309.025,"endTime":3310.125,"body":"Yes, it, it really does."},{"startTime":3310.425,"endTime":3315.437,"body":"Um, and I, I try, I think one could distinguish when we say Big Bang,"},{"startTime":3315.437,"endTime":3318.445,"body":"I think we make things more complicated by meaning."},{"startTime":3318.575,"endTime":3321.445,"body":"There are two different things we, we mean when we say Big Bang."},{"startTime":3321.745,"endTime":3327.268,"body":"One is the fact that the universe was in a hot, dense state 13.8 billion"},{"startTime":3327.268,"endTime":3328.005,"body":"years ago."},{"startTime":3328.385,"endTime":3331.525,"body":"And I think as I've shown, there's lots of good observational evidence for that."},{"startTime":3332.075,"endTime":3336.685,"body":"There's also, when we say Big bang, we mean the moment at time equals zero."},{"startTime":3336.755,"endTime":3337.885,"body":"That started everything."},{"startTime":3338.265,"endTime":3342.537,"body":"And we don't have, we have no observational constraints on what that is other than"},{"startTime":3342.537,"endTime":3346.525,"body":"that the universe existed and it was in a form that it could evolve."},{"startTime":3347.025,"endTime":3348.205,"body":"But beyond that, it's very difficult."},{"startTime":3348.205,"endTime":3349.565,"body":"There's some mad theories, sorry."},{"startTime":3349.565,"endTime":3351.245,"body":"There are some speculative theories."},{"startTime":3351.485,"endTime":3356.485,"body":"\u003claugh\u003e,"},{"startTime":3352.025,"endTime":3357.538,"body":"You know, if you read enough science, um, popular science, you find theorists who are"},{"startTime":3357.538,"endTime":3362.685,"body":"peddling ideas like the universe causing itself because time is on a loop, obviously."},{"startTime":3363.145,"endTime":3367.304,"body":"Uh, and or, you know, there, there are nice ideas, there are fun ideas about"},{"startTime":3367.304,"endTime":3371.463,"body":"in the far future maybe our universe will, but off baby universes and that causes"},{"startTime":3371.463,"endTime":3373.405,"body":"the big bang and they're fun speculations."},{"startTime":3373.425,"endTime":3376.565,"body":"But we haven't yet worked out how to test any of those ideas."},{"startTime":3377.065,"endTime":3380.295,"body":"So we know that the universe was in a hot dead state 30 by 8"},{"startTime":3380.295,"endTime":3383.525,"body":"billion years ago after something called the Big Bang that we don't understand at all."},{"startTime":3383.935,"endTime":3388.818,"body":"Chris, there's, um, Alan go, I think his, his name is who, um, one of"},{"startTime":3388.818,"endTime":3392.725,"body":"his predictions was that there was a sudden expansion of the universe."},{"startTime":3392.985,"endTime":3394.525,"body":"Uh, I dunno if that was right at the beginning."},{"startTime":3395.025,"endTime":3400.529,"body":"Um, but what I wondered is if we could go back to that moment when"},{"startTime":3400.529,"endTime":3406.033,"body":"that sudden expansion was happening and we were making measurements, um, either quantum mechanical measurements"},{"startTime":3406.033,"endTime":3411.537,"body":"or astronomical measurements, would the laws of relativity and quantum mechanics hold at that moment"},{"startTime":3411.537,"endTime":3413.005,"body":"during that sudden expansion?"},{"startTime":3413.155,"endTime":3416.389,"body":"Yeah, so the expansion, I, I didn't quite recognize the name, but it may the"},{"startTime":3416.389,"endTime":3416.605,"body":"case."},{"startTime":3416.665,"endTime":3417.445,"body":"Oh, Alan Goth."},{"startTime":3417.445,"endTime":3417.885,"body":"Yes, of course."},{"startTime":3417.885,"endTime":3422.102,"body":"There's a group, people, including Goof, um, who in the eighties had this idea that"},{"startTime":3422.102,"endTime":3426.319,"body":"you can solve lots of problems in the universe, where if you have what they"},{"startTime":3426.319,"endTime":3427.725,"body":"call a period of inflation."},{"startTime":3428.305,"endTime":3432.301,"body":"So it's in the very early moments of the universe, this is what the people"},{"startTime":3432.301,"endTime":3436.298,"body":"building, the new cosmic microbe background telescope, hope to see the effects of in the"},{"startTime":3436.298,"endTime":3436.565,"body":"CMB."},{"startTime":3436.565,"endTime":3442.434,"body":"So, um, you need something like the vol when the volume, that is our everyday"},{"startTime":3442.434,"endTime":3445.565,"body":"universe, our observable universe today was a pinhead."},{"startTime":3446.145,"endTime":3451.209,"body":"You need to instantaneously turn it into a grapefruit, sorry, to something the size of"},{"startTime":3451.209,"endTime":3451.885,"body":"a grapefruit."},{"startTime":3452.475,"endTime":3454.285,"body":"Otherwise, that's a whole different cosmology."},{"startTime":3454.985,"endTime":3459.667,"body":"Uh, see there's a new idea, um, something so, so, but that needs to happen"},{"startTime":3459.667,"endTime":3463.725,"body":"in much less than a billion, billion, billion, billion billionth of a second."},{"startTime":3464.105,"endTime":3470.588,"body":"And that explains things like why the CMB is so uniform, because any structure would"},{"startTime":3470.588,"endTime":3471.885,"body":"be washed out."},{"startTime":3472.045,"endTime":3473.485,"body":"'cause we're now looking at a tiny fraction of it."},{"startTime":3473.825,"endTime":3475.245,"body":"So, so those are good ideas."},{"startTime":3476.065,"endTime":3477.365,"body":"Um, and we're trying to test them."},{"startTime":3477.525,"endTime":3480.605,"body":"I think most cosmologists believe in them, but we don't have any direct evidence."},{"startTime":3480.605,"endTime":3484.565,"body":"There was a false alarm back in 2015 where a bunch of people stunning."},{"startTime":3484.585,"endTime":3488.542,"body":"The microwave background thought they'd found evidence for it, and it turned out it was"},{"startTime":3488.542,"endTime":3490.125,"body":"our galaxy getting in the way."},{"startTime":3490.125,"endTime":3492.525,"body":"They'd mistaken the dust for the signal they were looking at."},{"startTime":3492.905,"endTime":3494.605,"body":"If you were there, what would you measure?"},{"startTime":3495.345,"endTime":3498.205,"body":"Or that's a question for somebody much more theoretical than me."},{"startTime":3498.745,"endTime":3503.728,"body":"Um, it's not a problem for relativity because space can expand as fast as it,"},{"startTime":3503.728,"endTime":3504.725,"body":"as it likes."},{"startTime":3504.725,"endTime":3509.525,"body":"There's no light, can't travel through space faster than the speed of light, but space"},{"startTime":3509.525,"endTime":3510.485,"body":"can speed up."},{"startTime":3510.485,"endTime":3513.685,"body":"So you can describe this stuff with the equations of general relativity."},{"startTime":3514.595,"endTime":3516.685,"body":"What on earth happening with quantum physics at the time?"},{"startTime":3516.875,"endTime":3522.35,"body":"It's difficult to say except that quantum physics tells us that empty space is full"},{"startTime":3522.35,"endTime":3523.445,"body":"of strange fluctuations."},{"startTime":3524.045,"endTime":3526.125,"body":"Particles appear and disappear all the time."},{"startTime":3527.385,"endTime":3532.935,"body":"If you suddenly inflate a universe where that's happening, you produce a set of ripples,"},{"startTime":3532.935,"endTime":3538.485,"body":"places that are slightly more dense and slightly less dense than you'd expect, you end"},{"startTime":3538.485,"endTime":3541.815,"body":"up with something that looks pretty much like this."},{"startTime":3542.675,"endTime":3548.427,"body":"And so the things, the seeds that go on to form the galaxies may have"},{"startTime":3548.427,"endTime":3551.495,"body":"been microscopic quantum fluctuations in the early universe."},{"startTime":3552.235,"endTime":3554.735,"body":"And if you understood all of that, you're better than I am \u003claugh\u003e."},{"startTime":3554.735,"endTime":3557.495,"body":"Uh, but those are the kinds of ideas that we're, we're playing with."},{"startTime":3557.795,"endTime":3559.255,"body":"So yeah, thank you for adding that in."},{"startTime":3559.255,"endTime":3559.975,"body":"That's a great question."},{"startTime":3560.315,"endTime":3565.633,"body":"Uh, ladies and gentlemen, um, we have had this evening a fascinating insight, uh, into"},{"startTime":3565.633,"endTime":3570.952,"body":"the beginning of the universe, but I'm afraid the end of time, uh, is already"},{"startTime":3570.952,"endTime":3572.725,"body":"sorry, is already upon us."},{"startTime":3573.145,"endTime":3579.895,"body":"Uh, please join me in thanking our speaker this evening, the 39th professor of astronomy"},{"startTime":3579.895,"endTime":3581.245,"body":"at Gresham College."},{"startTime":3581.515,"endTime":3582.925,"body":"Professor Chris into."}]}