The First Billion Years of the Universe - with Emma Chapman

[Music] thank you ever so much for the invitation to come tonight i'm really thrilled to be able to talk for the royal institution if not at the royal institution as much as i'd have liked to have been there i'm in my slippers right now and i've just had a cup of tea so i'm hoping that you're doing the same um as we go through about a billion years of history um and we're going to be talking about lots of mysteries i'm going to be talking to you tonight about lots and lots of big discoveries in astrophysics and one of the biggest discoveries that framed my childhood when i when i learned about it which was the discovery of tutankhamun's tomb so here on the left you can see howard carter and lord carnavan and they've just chipped away the first part of the tomb door from it's not been open for thousands of years and as howard carter held up a candle to the whole lord canaan said what can you see what can you see and howard carter just simply replied wonderful things wonderful things and everywhere the glint of gold which is a wonderful story and finding out about our history understanding these great discoveries was enough for me when i was a teenager and i'm still interested in it today but my my head was turned when i learned how much we didn't know about physics and then later how much we didn't know about the history of our universe so today tonight i'm going to be talking to you still about history still about uh where we come from so something we're fascinated out by as humans we want to always look back always ask who we are where we came from um and this starts even when we're children just as my fascination with egyptology did you are fascinated by lots of different things when you are a child you're fascinated with archaeology and history like i've just said uncovering the tombs you've you're fascinated with dinosaurs dinosaurs are the best and of course there's the one that caught my eye which is space all three of these like the holy triad of children's passions right um and so tonight we're going to be looking at this we're going to be blending space and history and sadly not dinosaurs the way i'm actually wearing dinosaur earrings i've just realized so that's nice um so i want to start tonight um properly off by talking about what is light we're going to be talking about light an awful lot tonight we're going to be talking about first light so when the lights first came on in the universe but we're also going to be talking about light as a diagnostic tool so how can we use all the different types of light to diagnose our universe as it were there's lots of different types of light the one we're familiar with is the optical wavelength so those the wavelengths of light currently entering your eye onto your retina so that you can see me waving at you there's lots of other different types of light that we're used to so for example radio light the radio wavelengths of the spectra because light is a spectrum and so it goes from very long wavelengths to very short wavelengths so with radio wavelengths we bounce them off the atmosphere of the universe for the universe atmosphere of the earth for example and they'll bounce back down allowing us to cover really long distances with our radio there's the infrared radio infrared radiation which we can use for example to track criminals as they run away on some american cop series or something we can use uv light to decorate ourselves nicely for when clubs used to exist or for example if you're watching csi they can also be used to find gruesome discoveries of where you can find the bodies and then the last one we might be familiar with for example is x-rays so when you break your arm for example the doctor might first say oh yes that's definitely broken you're using optical light to notice that it's at a completely wrong angle but you'd be a bit worried if they didn't also use x-rays to diagnose exactly how it's broken exactly how to fix it and so with light acting as a spectrum as it is as i've just gone from small wavelength to long wavelengths we use the same kind of spectrum to diagnose our universe so here we've got centaurus a a galaxy so you can kind of see fairly big compared to the stars but when we actually look at it in radio waves this galaxy is revealed to its true self so we see these incredible radio waves rodeo lobes ejecting material out of the central black hole and if we just had an optical telescope we'd say oh well that's about it there's certainly no sign of a black hole the way we're looking at it now but if we switch this radio telescope on at the same time then suddenly what we can see is a great big sign saying black hole here so using all of these different wavelengths to find out different things about our universe is is what we do on a daily basis these are very different types of light as you've probably noticed from the different kinds of well different types it's all the same thing it's all the same light but they're all very different wavelengths but the one thing they really have in common is that they're incredibly incredibly fast so the speed of light is around 300 million meters per second that's really really fast which means that when i wave at you you don't really see any lag at all so if i wave at you then hopefully you're sat on your sofa or your bean bag or whatever and you're waving back because you can you can see it almost instantaneously but now let's imagine that we were actually on the moon so on the moon what would happen would be um you would have a signal going so you would wave at your friend on the moon and they would wave back and because it's only 1.3 seconds in light time away you're quite happy with that your friend's waving back and um there we go little friend waving back and so your friendship stays intact but if we then go on to the next slide yep um yeah sorry and i've got to go on to the next side so it's going to take me a minute now let's imagine that our friend was on the moon on the mars sorry and if you've got the same kind of signal going towards mars then you can wave at your friend but it takes four minutes for the light to actually get to them and another four minutes for it to get back and so by that time you're pretty sad because you think that your friend is just completely forgotten about you just left my duplo person somewhere there okay now oh dear sorry i've just gone on too far then there we go okay and now uh you might have heard the very quietable fact that the light that we see from the sun is actually eight minutes old so i've got a pretty giant sun here but i can't actually fit it in the thing but anyway so light takes about eight minutes to get to um the sun and it takes about eight minutes to get back by which time you've just lost all hope that your friends even seen you and the friendship's probably broken now what this means is that because the light takes eight minutes to get to us we are seeing the sun eight minutes ago so anything that happens on the sun whether it's your friend waving whether it's a solar flare whether it's a supernovae we will only learn about it eight minutes later now we can extend that even to a um even to a larger scale so let's say that we were going to wave to our alien friend in a completely different galaxy a nearby galaxy now the light because this galaxy is so far away the light would take an incredible 2.5 million years to get to that galaxy and another 2.5 million years for our friend to wave back by which time we're not just really sad we're actually also really really really dead which is a problem now this again is really great because what it means is that we can look back in time we can look back 2.5 million

years ago and see andromeda or whatever nearby galaxy is we can see our nearby galaxy as it was two and a half million years ago and also er equivalently our alien is actually not waving if they're if they are observing us right now they're not observing us um watching a royal institution lecture they're actually observing the earth 2.5 million years ago so what they're seeing is one of the first ancestral branches of humanity which is pretty pretty crazy right but this is exactly what we're doing on a daily basis in astrophysics we the the further the longer the light has taken to get you the longer you are looking the farther you are looking back in time so we can really use this to fill fill out the timeline of our universe uh so here we've got a timeline um of about 14 billion years because we think that give or take that's roughly how long the universe has been knocking around for we know lots about earth because we can just look out the window for a start we can do lots of tests on it so we can put that on on our notice board and be pretty happy that we know lots about it as we go a little bit further back in time as i've said a few seconds away is the moon about four minutes away is mars in terms of light travel time but we can still find out a lot about them in fact you know there's plans to put boots on the moon boots on mars so it will be that we are even going to have humanity back on these structures at some point soon uh and then we've got the closest galaxy to us that's about 2.5 million years away andromeda and even further we can look back even further with incredible telescopes and see galaxies from millions to even billions of years old and indeed the hubble deep field is a photograph which was taken by the hubble space telescope and what it did was it stared at a tiny patch of the sky about a tenth of the area of the moon um a patch of sky that big and it stared at it for for a while and what it found was um deep as in very deep in light travel time it found galaxies all over that patch of sky so just thousands of galaxies and i'll do a bit of a larger image of that later but the point is we can really push back to about a billion years after the big bang maybe 800 million but it's a bit contested so a billion years after the big bang and we can even jump much further back now so to go right to the start of this universal timeline we know quite a bit about the big bang now we've got a lot of theories for 100 years now all about how the universe started as an infinitely dense point and expanded out a huge amount to the universe that we see today and we've even managed to measure the radiation from that this big bang which i'm going to go into a lot more in a minute so my point here is is that even though this is not remotely to scale the point i want you to take away is that we've managed to fill out huge chunks of our timeline and we can be really really smug about that but there's a whole era missing of about a billion years in length and we call this the era of the first stars so if we look on a bit of a prettier image here it's kind of just saying the same thing which is what happened here what happens where the question marks are we know that there was a big bang we know that when we look around us now there is incredible diversity incredible complexity in terms of structure how on earth do we go from one to the other and so let's have a look here there we go um as i've just mentioned we believe that there is a big bag now the big bang as i've just mentioned to you is this this infinitely dense point expanding out which is entirely preposterous i say it very easily in one sentence but actually to believe that there is a big bang to understand why we believe there is a big bang is a whole different thing entirely and so i'm going to start going into a little bit about the evidence for the big bang because it is important because if there isn't a big bang if there isn't a start to the universe as some people did believe 100 years ago they thought that the universe was infinite in time infinite in space and so forth there wasn't the first of anything so if i'm going to talk to you about first light the first baby steps of the universe um the first stars then there's not much point me doing it at all if there wasn't a big bang if there wasn't a first of everything so the first thing i want to convince you of tonight is that there was a big bang and the first piece of evidence that we can give for this is how the surrounding galaxies are moving if you think back to the last action movie that you watched so probably starring bruce willis and arnold schwarzenegger and sylvester stallone i'm not sure but imagine that there is a gigantic explosion now what you see is you see the people you see the debris you see the buildings you see it all flying apart you see them all moving away from each other as they're as they're blown apart blown away hopefully not blown apart blown away by these incredible explosions um and what we actually see in the surrounding galaxies is a very similar thing so as you can i'm still not sure if you can see my pointer but it doesn't matter um hopefully you'll see the red arrows here and the point is that when we measure how all of the galaxies around us are moving they're all moving away and we could be pretty sure about this because how these first galaxies are moving we can find out by looking at the light they emit so here what i'm showing you in the color is an example spectrum we call it so all of the different colors of light that a galaxy might give out all of its stars give out at the same time and normally you would expect this spectrum to be quite full which means lots lots and lots of color so you know gaps and when you get gaps in your spectrum as you can see here with the with the dark lines we call those absorption lines what that tells you is that there is a certain chemical element so let's for argument say call it calcium for this for this um demonstration um if there's calcium present in that galaxy in large amounts then that calcium likes to absorb wavelengths of a very very specific wavelength specific to that element and so what you'll find is you'll find absorption lights and it's kind of like a barcode which tells you exactly what the ingredients are so we can look at this spectra on earth and we can tell that there is um calcium present in that in that galaxy now if the galaxy moves away from us what happens is that we perceive the light from um that galaxy to be what we call redshifted we perceive those absorption lines to be moved up the spectrum to the red waves so uh redshifted and as well if the galaxy is moving towards us then what we do is we see those absorption lines shifted to the blue end and we know that's not where that no what we know that's not where they are meant to be because we can put calcium in a laboratory we can chuck a whole load of light at it and we can figure out which photons which wavelengths it prefers so this is a really cool way of figuring out what speed and what direction etc all of these different galaxies are um traveling out and like i said apart from andromeda part of my andromeda which is moving towards us on a collision course um it's the vast majority of these galaxies we see moving away from us at very very very high speeds which is an indication that a big explosion has happened and you can't really get a bigger explosion than the entire universe starting um with with an incredible inflation period the second piece of evidence for the big bang is the radiation that it leaves behind it's got a very grand name the cosmic meaning all around us kind of thing big scales microwave meaning microwave wavelengths background meaning it's not in your face and radiation okay so as the universe is expanding then the radiation of the big bang it moves to longer and longer wavelengths this radiation is everywhere this radiation is pervading the whole universe and as it goes larger it loses energy it loses energy it loses energy until eventually those though that light gets shifted straight out of the visible wavelengths and into something much longer the microwaves for example the radio a little bit and interestingly if you are old enough to have had an analog television when you were young um or even older then you will um know that when you used to tune the stations between the different tv channels you got a hissy kind of static like and interestingly a significant portion small but their portion of that static noise was actually from the cosmic microwave background um good i've just realized my video wasn't on sorry so you couldn't you couldn't see me gesticulating wildly but nevertheless um and what we can see with the telescope is not just this static on the television but you can actually see the cosmic microwave background in full glory and full color and so we have these space telescopes that have been for the last couple of decades really filling in this information so the point i want you to take home is that we have seen this is that the big bang there's there's more than that in terms of evidence but the two big pieces for most astrophysicists is the movement of the galaxies and the fact we can actually measure the leftover radiation to exactly what is predicted by big bang theory and so even though the idea of a big bang is completely preposterous it's also completely acceptable and completely believed pretty much within mainstream astronomy so that means for us is that there were first stars that there there were these these first um entities that we want to find out about but one question is is a really good question to have that you might be too afraid to ask is well hang on if there was a big bang that's already completely ridiculous so is it possible that the first stars the first galaxies um just popped out of that big bang completely fully formed is it that we don't really need to find out how those entities got created and how they formed but actually that the first stars just went pop out of the big bang well we know from understanding the physical mechanisms behind the big bang what was going on we know that just after the big bang it was incredibly incredibly hot incredibly incredibly violent and so you have all of these photons going all around and basically messing up building anything taller than anything um anything greater in size than a helium or hydrogen atom so hydrogen atom is made of just for example one proton so if we use it like that and helium is made from two protons and two neutrons and some electrons and what i always imagine is is that if you are in a room of sugar crazed toddlers sugar crazed toddler then you can try and build a bigger tower a bigger atom but it won't be too long until you get your little friend coming along cracking it down into its constituent parts so while you might try to build a toilet tower and you might succeed sometimes it's really not so long until eventually you're just left with your basic building blocks and that's exactly the same in the early universe try as you might you might build up lithium but you'll end up with just hydrogen and just helium and that's certainly not what constitutes a first star so we definitely need to figure out how we got from a universe that was just hydrogen just helium all the way up to where you've got galaxies you've got planets you've got carbon-based life forms that breathe in oxygen how did we get to all of that so hopefully i've convinced you that there were first stars and now i won't need to convince you about why we need to care about the first stars so we're missing around a billion years of our timeline which is a huge amount and missing a billion years of a 14 billion year timeline is um really equivalent to missing for example your the the day of your child's birth right up to their first day at school so if you consider how much stuff happens in that time it's a really formative time and if we were to imagine uh our alien from andromeda coming down to see us and we want to he wants to learn all about the human lifetime so what happens in the average human lifetime so average one you you start with a baby you become a child you possibly procreate and then you enter the autumn and winter of your life but if our uh alien flies down to earth and only has limited time limited research funds is really tired then they might only take samples they might only photograph for example certain humans in certain types and they might end up with incomplete data which is exactly what we're looking at with the first stars and it doesn't take too much imagination to think well okay i heard that person talking about where babies come from so maybe that's actually what's happening here um this model it fits our data perfectly excellent job done time for a beer and so our alien would just float off happily back to andromeda completely unaware that they've made completely incorrect conclusions because of their missing data because of their incomplete data and as i've said we're missing about um that first billion years of of life which is equivalent to your first five six years of childhood and it's no wonder that as astrophysicists we're kind of quaking in our boots about what what what's being missed the next reason to care is because the first stars themselves are extraordinary so i study them because i love them because i find them absolutely fascinating and because to heart back to my my egyptological days they are lost so they are something that we can't look up in our backyard i can't walk in walk next door and talk to an ancient egyptian it's just not possible anymore and they're different so this is our sun this is an incredible image of our sun um you can see some solar flares you can see sunspots we love our sun very much for for many many reasons um and for the first star here i've had to kind of put an artist's impression which was basically me just going powerpoint artists effects and making it look a bit fuzzy um because we haven't got a single picture of a first star they're not around anymore or are they we'll talk about that later but mostly they're not around anymore so we can't take pictures of them um but we know a lot about them because like i said we can do the kind of maths of what the chemical cooling reactions were how big a star could get how small a star could get we can do all these calculations so to the best of our knowledge these first stars were about 100 times the mass of our sun some simulations even think that they were up to a thousand times the massive sum which is a really really huge amount that's a really really big difference and it's very difficult to kind of imagine but for the sake of the fun um it's kind of the difference between a red squibble and a great panda that's a huge difference in terms of mass and it's what we are looking at with these first stars and this analogy stretched analogy works even better because like the great panda which is on the verge of extinction it's it's the same thing with our first stars we think they are either extinct or on the verge of extinction so definitely worth looking up the reason we think that um we can't see them around us anymore that they are extinct is if we look at the mass lifetime relationships of stars so if we have our first star they are really really massive and really really massive stars guzzle through their hydrogen that they are fusing so all of the fuel that gives out the heat and the light they guzzle through that fuel at an incredible pace because they're just just more gravity more contraction more pressure and so they will have a short lifetime of say a million to probably near 100 million years which is really really short in terms of stars because stars like our sun they like the friend that you take to a restaurant and they just pick over a side salad they are very leisurely in terms of their consumption of hydrogen and so they will last more like 10 billion years before they run out of fuel and that's just about the lifetime of our sun so our sun's near 9 billion years of which it's halfway through which is good um don't like to think about the end of that half to be honest but uh it's also the time that andromeda is due to collide so i'll be sure rubbish time all around but who knows maybe we'll have managed to get some kind of extra galactic uh movement by them so we think that these first stars are extraordinary in themselves but also because they're extinct and more than that they're not just contained in themselves are very interesting to look at and then we move on to the next thing in the museum they actually change the universe in a way that no other star has managed to do in quite such a dramatic fashion um and they're very very different in that they contain fewer metals um and we categorize our stars as astrophysicists in many many ways because we like collecting things and what we call these first stars are metal-free and that is because they formed out of gas that is just hydrogen and just helium um and so i'm just trying to yep so you can see the hydrogen and the helium on this uh image here and every other um element on this periodic table you might be having ptsd harking back to your chemistry lessons right now from when you had to go why do you mean we've been brilliant um as astrophysicists we're really used to rounding up absolutely everything alone universe because huge distances huge time scales we round everything up and so we've rounded up the periodic table too because pretty much everything's hydrogen helium and then everything else we just call is metals so sorry to any chemists that are present but um that's the way it is and so if we go back to this lovely picture here then what we're saying is that here we've got an arrow talking about how the stars evolved over the timeline of a universe so we start off with just hydrogen and helium and so we call these stars metal free these stars fuse the hydrogen helium into slightly heavier elements like lithium beryllium and carbon nitrogen oxygen and as they explode they send all of these materials flying um and then they can come together when the when the gas is cooled down they can come together and all that gas can come together form a new star but this time it's got a bit more metals in so it's metal poor and then we go on to the stage where our sun is at now to the stage of our universe where we're producing lots of kind of sunlight um stars and they are what we call little rich so they've got lots of metals and it's actually still just a small percentage compared to the hydrogen in the star but it's there and it's enough for us to categorize it i'll just flick through my lovely slides here yeah okay so as i've said you can have you have diffusion lots and lots of fusion to have your elements and boom you manage to take all of those heavier elements and seed the local universe such that the gas is no longer primordial it's no longer pristine it's no longer just hydrogen helium it's actually got carbon nitrogen oxygen and so early in the universe what we're looking at is as i've said just hydrogen just helium nothing nothing very interesting to look at at all as i've mentioned before with the cosmic microwave background where it's very early on it was you know very bright you would have probably seen it as well as um yeah you would have seen it um as the universe cooled down to say 500 000 years after the big bang then everything was very dark everything was incredibly boring and so if you had your tardis and you went back in time and you saw it you'd be really really bored because this is what you would see it's not my presentation broken um but somehow we get to the point of seeing galaxies all around us just like this and as i promised this is a slightly larger version of the hubble ultra deep field and this this is on my this is on my um in my kitchen it's on the big canvas on my kitchen wall because i just love it i can stare at this for hours because if you if you just look at some of these spirals like on the right hand of the image you've got this yellow gorgeous spiral you've got really flat spirals looked out from the edge on you've got orange ellipticals every piece of light on here is a galaxy which apart from the odd interloper style but the vast majority are galaxies which is just fascinating to me because this came from a postage stamp size so less than a tenth what is it i think it's if you hold out your thumb and you close your eye that's about the the patch of the sky that's that's covered um even smaller than that about a tenth of that that's covered by this this kind of structure and the only reason that this can happen at all is because you have the metals to form them and it's only because of the first stars that we created those metals and we were able to then go on to forming galaxies and planets and of course us okay so hopefully i've now convinced you that there were first stars and hopefully i've also convinced you that they were extraordinary and worth learning about and what the aim of this game is of course is to go from a rubbish artist impression that i mocked up to an actual image an actual learning about that first star so how can we do this well we can start by looking back in time take a drink for a moment while you read that terribly inspirational quote um i spent a long time at the start of this talk convincing you that as astronomers we can look back in time which is a skill set you have to have on your cv um and what that means is that of course if you were on andromeda or a nearby galaxy then you might see the one of the ancestral branches of humanity now to turn that around all we need to do then is is we need to tune into light that has traveled so far to get to us it's lost so much energy against the expansion of the universe just like the cosmic megawatt background that it's shifted from the shorter wavelengths into the longer wavelengths if we tune into that wavelength just like we tune into a radio station then we might be able to see the light from this era of the first stars and that's what we're doing um and this is just as crazy and just as real as for example if i was interested in ancient egypt and the speed of light was much much much much much much slower then we could just use clever optics to look back at egypt from where i am now and i would be able to see them building the pyramids first hand so not a simulation not what we think from from the the tombs and the writings but actually see ancient egyptians building these pyramids and that's what we're doing we are using the fact that light has a finite speed how much energy is how we can tune it in we're using all of that to actually see light from the area of the first stars to actually see these this era begin and how it how it progressed and ultimately how it ended and the second stars came along now to do that we can't unfortunately just use a handheld garden space garden telescope as you've seen here we use something called a radio antenna and that's because the light has been um redshifted so much you can see here so i was talking about red shifters which will go to the longer wavelengths so you're getting into longer wavelengths as it travels near the earth and so that's no longer in the optical part of the spectrum that's in the radio part of the spectrum and so what we do is we use radio telescopes and here's one i made earlier so this is a an artist's impression on the of an amalgamation really of real real uh antennas and the background of the the milky way and what these this is is called the square kilometer array so this is the second big telescope in my life i'll get onto the first in a minute um but it's very simple technology in some ways because as you can see this is basically what we call a christmas tree antenna um not just making that up for the festive season but it is because they look roughly like christmas trees and because we decorate them accordingly every december and the idea of this is that we can put loads and loads of these antennas out and we can tune in to the right wavelengths that we know that this this light from the first stars is is at the minute because it's traveled so far to get to us and we can pick up that radiation and we can learn things about the first stars but how do we actually do that well what we're doing when we're tuning in is we are taking the temperature of those first stars we're taking the temperature of the surrounding gas at that time actually this is one way we can do it one way you can find the first stars so on the top here i've got the age of the universe going from the left which is very young and going all the way to the right which is present day now on the left what i want you to see is that before the first stars came to life then we just got a universe of hydrogen of helium photons and if we take the temperature of that gas then it's very very cold there's nothing much heating up you can't see anything so it's very very cold but what we can tune into specifically is that as i've got a picture here between the uh the blue thermometer and the red thermometer is that we can tune into something called 21 centimeter radiation and this is the radiation that is coming from the area of the first stars what it is is that when you have a complete hydrogen atom through a proton and an electron uh then that very specific makeup can produce a photon which um travels off with a wavelength of exactly exactly 21 centimeters which by the time it's reached us by the time it's been stretched it's lost all those energy it's at wavelengths of nearer two meters which is why we use radio telescopes because that's the right wavelength for radio so now let's look at what happens when the first stars come to life so you have all this hydrogen pervading the universe what happens is that this hydrogen starts to come together it comes together closer and closer closer through gravity it gets pushed together by constant gravitational uh pressure and then suddenly right at the center you get this fusion you get these first stars turning on and it happens over here it happens over here it happens over here one by one lighting up the universe so like fireflies in the night just just coming on like that just switching on the fairy lights if you will but as these first stars come on they heat the rest of the hydrogen that hasn't become a star so there's still lots of hydrogen floating around lots of clouds of hydrogen um and a bit of helium and what these first stars do is they heat this hydrogen um and what we measure when we measure this 21 centimeter radiation is we measure a jump in temperature and so when we measure that jump we know that the universe is the the light from that time is coming from a time where the first stars have come alive and then as we go longer so longer from the age of the universe to let's say a billion years after the big bang what happens is not only do these first stars heat the hydrogen but by now you've actually got the second generation of stars and you've got the first galaxies and at this point what what happens is something called ionization which i've got here between the red and the empty thermometers what happens is the photons that are being emitted by these first stars and galaxies and everything like that it breaks apart this hydrogen it breaks it apart completely so the proton and the electron are completely split and so no 21 centimeter radii radiation at all can be produced and what this means is that suddenly you're not you can't measure any temperature of the of the hydrogen gas because it's just not emitting those photons anymore for you to pick up so you have an empty thermometer as it were but that still tells us something so even measuring when we get no reading of temperature tells us when these first galaxies have managed to ionize all of that gas how how big were they how how many there were to be able to do it in that time frame okay so a bit more of a just to hammer home what it is we're actually observing um i've got the same timeline here but in red i'm kind of representing all of the radiation that comes from this time um and what we would actually observe so with these radio telescopes what we can do is we can build up a picture of all of that hydrogen across an area of the sky so we tune it in we tune into exactly the wavelength so about two meters that we're expecting this first light signal to come to and what we observe at first is we observe the light from what's called the dark ages so it's dark for an obvious reason as i've said because it is actually dark um the first stars haven't come on so what we see is in our picture is we see a complete completely full picture of hydrogen because there's tons of hydrogen it's all held together it's proton electrons together so there's lots of this 21 centimeter asia lovely as we move on these first stars start to um ionize and heat their local hydrogen and it's what call what we call a swiss cheese model so i've got here's again here's one i made earlier and i was just telling the producers this stinks i just realized i'm not gonna use this as a prop again but um yeah you get you get bubbles and we call this the swiss cheese model put that over there um and as as the first galaxies come on uh and the second generation of stars start emitting lots of ionising radiation so lots of this lots of these photons not only do you not you get nice kind of nice clean swiss cheese like bubbles when the first galaxies come on the first black holes actually you get a huge amount of radiation which makes very very large very very wispy bubbles which coalesce very quickly which overlap and eventually you really kind of get your empty thermometer so in the black here is an absence of 21 centimeter radiation so you start to measure nothing at all and what we can do with our um our radio telescopes now is we can reverse engineer this so what we are going to measure and what we are measuring is this bottom row so we are measuring all of these images throughout about a billion year lifetime the first billion years of our universe we're building an actual home movie so not simulation but an actual movie of how this hydrogen is changing and while that might not seem particularly impressive compared to say the hubble ultra deep field uh images where you've got all these beautiful galaxies i'm showing you some red with some black holes in which i get it it's underwhelming but it's all about what we can infer from this time and remember we are talking 13 billion years ago so give us a little bit of slack um so if we measure a completely complete picture of hydrogen then we can know that that points back to the dark ages that's when the dark ages are happening as we go through our movie it's still full it's still full it's still full oh there's the first there's the first holes it's the first kind of swiss cheese we see and we start measuring that upturn in temperature just before that and that we call the cosmic dawn and so from looking at these bubbles how big they were how many they were we can really start to infer what the first sources were how many first stars how long did they live when did the second population of stars come around when did the first black holes come around we can tell all of this actually by just looking at these bubbles so it might be low tech might be low production value but it's incredible in my mind anyway and it's something we've managed to do actually so the first detection of the cosmic dawn of the end of the dark ages the start of the cosmic dawn was tentatively made in february 2018 i say tentatively because it is yet to be validated by another experiment this is a really really hard experiment and so to really believe the result we need we need validation but everything looks pretty good actually and what they measured was was this this change in temperature which showed the first stars had started um and that was at about 180 million years after the big bang um so we've got a marker we've got a timeline for when the pyramids were built if you were um that was the square kilometer array that i was talking to you about uh that's being built in the next couple of years i'll go on to that a little bit more in a minute but the low frequency array in the netherlands is the telescope which uh is is closest to my heart at the minute because it's the first telescope that i used and it's the one that i continue to use today and again the technology is a bit underwhelming if i'm honest but um you've got the antennas here on the top right and then about 48 of those are under all of these black tarpaulin squares in the background um and i can't remember what my t-shirt says but i feel like it might be fitting for tonight something like oh well never mind a translation it appears everything in my life is spectacularly going wrong or something like that very british problems but anyway um so with the lofa we've been observing for about 10 years now and it's mostly based in the netherlands but it also stretches out to a lot of europe and so we've got stations in france in italy in england and wales all of these different islands sorry in all of these different places and and so by combining the signals from all of these different times we were able to tune into this this 13 billion years ago i said that we've been observing for 10 years so you might ask well surely you should have done it by now surely you should have come up with something more than just the starting point at 180 million years the reason is is that it's really really difficult because when you you might you might have had this question already but when you have this this light from the first stars weaving its way to you it gets to you to wavelength about two meters so we tune in to a wavelength of about two meters great problem is is that a lot of stuff including mobile phones um solar solar panels wind farms all of these things produce interference that is at a wavelength of two meters tons of stuff in our galaxy produces stuff at this wavelength as well so it's like having driving along your road and tuning into lovely calm classical radio first stars when suddenly a pirate radio station comes out of nowhere and it um starts giving out a very very different kind of noise so let's say heavy death metal or something like that um and that's the problem and it means that our first star signal is buried just a like archaeological um under about a signal of around ten thousand ten thousand ish times um the size of the first star signal so that's a huge huge problem to have to deal with um but it's not one without hope this is my person this is what i do on a day job and it's the the the first star signal is kind of is is a different shape just as if you were listening to these two stations you could still tell which part of which signal belong belonged at each uh um to each station because they're playing very different kinds of music and it's exactly the same with what i do um in this okay so we've talked about lofa i'll just be very brief on square club to array but um it's going to be awesome uh whereas lofar's got about 3 500-ish antennas um just a couple of thousand anyway um with square kilometer array we're going to be building 512 stations so 130 000 antennas um in total in the western australian desert because it's really quiet there which is what you need for big radio experiments that are trying to listen into the early very quiet signal from the very first stars um and it is an incredible undertaking it's such an incredible undertaking that the uk government was fighting to get to be one of the first to actually donate money to it which just shows you you know getting money out of our government is no easy thing but they were jumping on the ska to to give their amount of money in and it's because it's driving innovation so this is one of my reasons to care about astronomy if you don't care about astronomy and it's that for example the fiber optic cable that we we need to connect all of these uh antennas together could could wrap around the earth twice for example that's a huge amount and we're driving innovation there because these fiber optic cables cannot move data quick enough for us we have to delete data sadly on the fly as as it's happening because we can't store it all uh we're filling about 35 000 dvds uh a day like a million laptops per year anyway um and it's a huge amount of data that's overloading computing chips it's heating them up so we're driving innovation in how to call these computer ships so there's a huge amount of investment in this next generation in this next generation telescope the square kilometer array like i said it's turning on in a few years we'll probably get the first real science results uh probably more like five years six years um maybe even a bit longer than that but that's that's not too long to wait but while we wait there are uh another couple of place another couple of ways that we can look at these first stars um and i will spend a bit of time on them now so stellar archaeology is one of my favorites so i'm just using this to track which slide i want there we go um stella archaeology is is one of my favorite areas for obvious reasons just because of the name and what stellar archaeology is is not looking back to the birth of these first stars but actually kind of looking at um the the artifacts that that got left behind now you might say well hang on how did anything get left behind because what you've said is that they lived very very short lifetimes of a million to 100 million years um and that's absolutely true we think that most of the first stars were very massive and so far so lived very very short lifetimes but we also think because of lots of simulations now that these first stars were born with sibling stars and we think these sibling stars were probably a few of them and they're probably much lower mass such low mass about 80 percent the size of our sun that they would have had a lifetime or will have a lifetime of about 13 billion years which gives them just enough time to still be around today in our local milky way the problem is that these first stars um [Music] were pristine in nature so as i've said you've got this it's like hanging your beautiful white jazz white and washing out into your london backyard uh it starts off really lovely it starts off really metal free unpolluted but it's not too long until everything looks a bit rubbish um and it's the same with the first stars so whereas they start metal free they start pristine their outer layers very quickly can accrete metals they can get polluted by their local local surroundings and that happens for 13 billion years so stellar archaeology is about looking in our backyard looking at all these different stars and figuring out which ones are actually first stars under all that gunk and you might look at the wrong one a lot but you also might now and then get the right one and the problem is is that these stars are really really well camouflaged this only needs to be shown like twice so you can move on already but the point is is that you know they they look almost exactly the same as every other style and the the reason i talk a lot about egyptology at the same time is that there's so many parallels to be drawn because it's not often mentioned that when howard carter found the the tomb of tutankhamun he didn't just stumble across it what happened actually was that he bought the permit to dig there from um another fellow lord canaan paid for it and he spent five years gridding up the entire site and going square by square by square to the point where even lord carnarvon was saying that's it i'm cutting you off you've had enough of my money you've found absolutely nothing which point after five years howard carter says look just one more dig one more dig and i'm done guess what he finds which is crazy but true so at this point he finds you know the biggest archaeological discovery in in history and is rich beyond his wildest dreams at which point like lord carnavan presumably forgave him pretty quickly um and this is what we're going to do with our first stars so it's about looking at the entire milky way which is about 250 billion stars plus or minus 100 billion that's how many they are we can't count them um and it's about looking at each of the stars in our grid or the ones we think are most likely to be metal free how do you know that that's another another thing that we're struggling with really and you look at the light that's being emitted by those stars and as i said before if you have metals like carbon iron calcium present in your staff example you will get absorption lines in your spectra so you will get dark lines pertaining to those elements um and so what we want to do is we want to find a metal freestyle where we really can't really observe those absorption lines at all or we only observe the tiniest the the faintest gray of a line if you will that we can attribute only to pollution it's hard though because when you you have 250 billion stars to get through you can spend an awful lot of time looking up the wrong ones and this is a field that is incredibly interesting um it's incredibly challenging but i i think on the same time scale as you know building the square common terrain we're constantly pushing further down we've found even what we think to be a second generation star which is a star so old that we think it formed only from one supernovae what's a supernova you ask so supernovae is the third and final thing that i really want to talk to you about tonight because it's the third and final way that we can look at this era of the first stars now as i've mentioned unfortunately we can't see the light from the first stars themselves because it's just too faint the we can't pick up that signal optically but if these stars explode in what are the some of the brightest explosions in our universe which is a certain type of supernova so supernovae just means the whole star explodes basically we do have the option of the possibility rather of being able to absorb observe this light with um a big space telescope and so that's what the americans certainly are going to try and do it's not the only reason or by far the most important reason that they have built this telescope but what they're going to do is they're going to launch a rocket and they're going to do what's what i call an origami space telescope where over an agonizing month it folds out its five sun shields it just like your dining table if it's got leaves on it it unfolds each leaf to make a mirror which is quite frankly as as i write in the book just just terrifies me because the this has cost nine billion dollars nine billion dollars so far to build and the idea that it might not unfold correctly over that month um i mean i should say that you know they've tested it so much that their probability of going wrong is just miniscule now but still i'm a warrior and it would worry me um yeah if we can just thank you very much yeah nine billion dollars so you might be sat there going we're in the middle of a global pandemic nine billion dollars well obviously this nine billion dollars has been spent over a very long time because it takes a very long time to think up these experiments but as one astrophysicist is quoted as saying i'm not sure it's true but anyway the the the overlaying messages he said that that's only what americans spend on potato chips annually so actually nine billion dollars you have to set in the context and nine billion dollars it's fostered huge collaboration you need expertise from around the world you're creating new technologies like the the folding out the sun shields nobody's done that before nobody could do that before and it has applications in in defense in in military in all sorts um fiber optic cables all of these things that are coming from the square kilometer array but just for the science you know i won't apologize for saying that i want to do all of this not to create better fiber optic cable but because we can we can look back in time 13 billion years and observe these first stars forming we can observe them now we can observe them their artifacts and we can observe their deaths as well using the supernovae and the aim of the game is of course to go from we can detect the first stars to we have detected the first stars and i really do believe that's going to be in the next decade which is why i wrote a book really to pass on my excitement and i've touched on a lot of the subjects here but there's a lot more in there and at the end of it all it's incredible science which i just love and it's incredible discovery so wonderful things wonderful things all around and thank you so much for your attention and yeah there's my book it's really pretty so think about buying it for your loved ones or for yourself thank you you

2021-01-23 20:57

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