Our Universe and How It Works - with Jo Dunkley

[Music] so I am completely delighted to be able to tell you about our magnificent universe my favorite thing so and I want to tell you about our quest to try and understand this bigger thing that we are a part of and the reason that I find it so compelling is that it's our home we are here on earth but we're part of something much bigger and the stuff that out it's out there is part of our home too and it's also our story if we think about how we owners came to be here we came to be here through this long process this bigger process that's embedded in the story of our universe so those two things are bring it into our home here and so I'm a professional astronomer I try and ask questions about the universe those are the questions that I find most compelling it's what's drawn me to study the universe and the kind of questions I have and the questions that I talk about also in my new book are these I want to know what is space and what is our place in it our place here on earth I'd like to know if there's life elsewhere which is in a such an exciting question that we're making huge progress on I'd like to know if the universe had a beginning and what that even means and I'd like to know what if anything lies beyond our laws of physics the things we understand already and so as an astronomer we have to kind of pick the thing that we're going to spend our time particularly researching and my area that I particularly research is cosmology and cosmology is the such as the area of astronomy in which we answer questions about the whole universe on average we don't worry so much about the details and we ask questions like how old is it and what's it made of on on the whole and is it growing and what's going to happen to it in the future and this is this is my telescope my team's telescope the Atacama cosmology telescope it's one of the highest in the world it's in the northern deserts of Chile in the Atacama Desert and it's 5000 meters up in the air and we use it to stare as far out into space and back in time as we possibly can and I use it to try and understand the origins of the universe but we're going to start a little closer than the most distant parts of the universe and a bit closer to home because I want to start by taking you out through out through our home our universe from the place that we're most familiar with out to the far reaches out to the far edges so our home in the universe the thing that we are most familiar with the thing that we know we're a part of is the solar system that's the thing that that we learn about first and and we know we've got our eight planets used to be nine eight planets and a whole bunch of rocks orbiting around our wonderful Sun the source of our heat and light and one thing I find astonishing about our solar system is actually how big and very empty it is if you were to imagine fitting the solar system into this Hall into this room and you imagine Neptune for example the stuff beyond Neptune but that's imagine Neptune circling around this room round the edge then the Sun in the middle of this room would just be the size of a peppercorn just a couple of millimeters across and the earth which is a hundred times smaller would just be a speck of dust and and the rest of that whole space the thing we think of as kind of jam-packed full of planets is actually completely empty these things are tiny and the solar system itself is pretty big although we're going to go bigger out to Neptune is about three billion miles but these numbers start to become a little bit intangible and what we like as astronomers to make things manageable space is really big and it can kind of overwhelm you if you don't come up with ways of trying to handle them and so what one thing we use a lot of is using a measurement of distance that is how far light can travel in a given time so light is the fastest thing we know of it travels it it travels at this incredible pace and 200,000 miles a second and we think of how long light takes to reach places and so it takes about five hours from light to get from Neptune into us and that's compared for example the moon our closest neighbor takes light takes about a second to reach us from there so Neptune really is pretty far away so it's kind of phenomenal that we can send out probes through the solar system to go and visit these places and we've known actually how big the solar system is since the 1760s when there were these marvelous expeditions I would say the first big international astronomy collaboration took place when teams of astronomers from around the world went on these phenomenal expeditions to different locations around Earth to go and observe the transit of Venus across the Sun and by observing it from different locations on the earth they were able to judge how far away venus is by watching the different paths of the planet across the Sun's face and they got the measurement really remarkably well about a hundred million miles from us to the Sun and that set the scale of the solar system now is that we can go and send probes out into the solar system but that's as far really as we can go there are wonderful ideas about going out to the Stars but really they're really far away it's realistically we're gonna have to only sit here on earth and look if we want to go out further so the nearest stars to us our very nearest neighbors Proxima Centauri and it's light takes 4 years to reach us four whole years since the light set off and reaching our eyes most of the stars the beautiful stars that you see above us are tens of years hundreds of years thousands of years that light takes to reach us and if you think about the Orion constellation the beautiful Orion's their stars in Orion's belt those like the light from those who set off a thousand years and have been travelling for a thousand years and just now you see them in the sky and so we have this sort of cocoon of stars around us but they are they are this incredible distance away and now we've known about how far those are away since the 1800s and the way we kind of figure out where they are uses this neat method of parallax which we're gonna actually all try right now so let's say I wanted to measure the length of my arm but I couldn't be bothered to measure it actually with a ruler okay so there's a different way you can do it you can use a thing called parallax which is you hold out your arm in front of you and let's all do that now yeah good and I want to measure the distance to my finger now close one eye and see where your finger is is compared to the wall behind other people behind you okay and now close the other eye you should see it move yeah good now bring your ha I'm closer to your face as if you had a really short arm and now do it again moves further good okay that's parallax so here I it moves that the further it moves the closer it is to you and if I know the distance between my two eyes a few centimeters and I know the angle that my finger moves then I can use simple right angle triangle trigonometry that many people have learnt in school to figure out the length of my arm maybe 60 centimeters and that's all very well not so useful for the length of my arm but really useful for stars because I can't get to a star but what I can do is I can do parallax so for stars the length of my arm now becomes the distance to a distant star and my two eyes now become the earth six months apart so what you do is you sit on earth and you look at a star against the backdrop of more distant stars and then you wait six months for the earth to go around the Sun halfway around and you look at it again from the other eye and you see what angle it moves through and the bigger an angle it moves through the closer it is to you and so now the distance between your two eyes becomes twice the distance of the Earth to the Sun about two hundred million miles and so it's a really pretty ginormous triangle we love triangles in astronomy we we love enormous triangles so this this gave the first measurement to the Tudors to their stars but again back in the 1800s and this told us how far away they are now the stars around us are actually just part of something bigger we're going to keep going out until we get to the edges there are a little group of stars around us they're just part of a much vaster thing which is the a wonderful galaxy that we live in the Milky Way galaxy and that's a collection about a hundred billion stars that are all gathered together by the force of gravity of those stars pulling them together into this wonderful swirling disk and sometimes when we're lucky here on earth we actually get to see it and this is an image up here of how we would see the disk of the Milky Way galaxy in the night sky now from London you don't get to see that but and I've only seen it a few times and it's phenomenal so I urge you if you have ever chance just to go to a really dark sky please go because it is incredible and so what is this we're living in this big disk this this disk of a galaxy and why do we see that strip of light at across the sky this is where this mysterious saucepan they'd become comes in handy okay so imagine what we think we have is we have this there's this disc a swirling disc of stars and we are living in it and we think we're living in it about half way from the middle to the edge in our little group of local stars and because we're kind of embedded in the disk if I like if I'm in the disk like this and I look straight the sick disk of stars then I'll see a band of light exactly where that disk is but if I look out either side I see very little there aren't very many stars in those directions or conversely if I looked across that direction I'd see a band of light too so this band of light that you can see in the sky that we call the Milky Way and it's called the Milky Way because it looks like Milky Way is just us seeing being inside at the disk of stars and seeing a bright light where you see that edge but but how do we know is that this and it's it's big enough so we think now we have pretty good measurements but the size of this this this this disk of stars that we live in is about a hundred thousand light-years from side to side so if you set light off on a journey it would take a hundred thousand years to get from one side of our galaxy to the other and so let's just remember so so if our group of stars around us we're just the ones like tens of light-years away from us then we would be like again little peppercorn like bobbing around the galaxy as it spins around and the whole thing spins around every two hundred million years or so this giant gradually rotating disk and but then then we might ask a question well how do we know even the extent of our Milky Way because again all we get to do and as astronomers is we sit here on earth and we look and and that's all very well but inferring where things are when you all you can see is this kind of two-dimensional surface around you can get quite challenging and the key to this came from this fantastic astronomer Henrietta Swan Leavitt who I would say it's not nearly famous enough because she did this awesome thing she was an astronomer working in at the turn of the last century at in the States she was working at Harvard College Observatory and she started working there in the late 1890s and she was part of this amazing group of women astronomers known as the Harvard computers who were hired by another astronomer Edward Pickering to analyze photographic images of stars that were taken by their male colleagues because as a woman at that time you weren't allowed to use the telescope god forbid and and and he gathered this group of women to study plates after plates for the growth plates of images of stars to classify them to measure their brightness --is to measure their colors and it was really hard work and they weren't read out to do what they wanted they were just kind of set set to work they weren't paid very much but they turned out to be really quite good at it and she discovered this amazing property which is there were these two stars that that varied their brightness with time so most stars kind of a constants just twinkling the sky in their brightness is constant but some of them vary and there's this particular class of stars called Cepheid variables which actually pulsate over time they grow and shrink and as they grow and shrink they change their brightness and she discovered this pattern about these stars which was that the longer they took to pulsate the brighter they were intrinsically and so a star that took weeks or months to pulsate was much brighter than one that took just days and this actually proved to be the key to unlocking the whole scale of our galaxy and actually our universe as well because there's this key thing if you if there's this relationship between the time a star takes the pulse and how intrinsically bright it is then you can figure out how far away it is from you because the problem usually in astronomy is that if all stars were the same brightness as each other intrinsically if everything was like a hundred watt light bulb then you could figure out where things were in space just by saying how bright did they look you know standard hundred watt light bulb if it's closer to you it looks bright if it's further away it looks dimmer but if you don't know how bright it was to begin with you can't tell where it is but these things these Cepheid starts if you could only measure their timing of how quickly they pulsed which is a relatively easy measurement to do you then know intrinsically how bright they are and then you measure how bright they seem and you can figure out where they are and so this one never made this discovery in 1908 and then really quickly astronomers took this this this this law it's now called Levitz law and figured out how big they thought how big as a Milky Way galaxy is this is an artist's impression of what we think it looks like we'll never be able to take our own picture of it because we can never get outside it it's just much too big there's nowhere we could ever ever time out so we think it's this swirling these swirling arms of stars swirling in in the dark the darker bits of where we think we have sort of debris we call it dust cosmic dust grains that's intermixed with the stars and also gas swirling in these spiral arms to a more central region of brighter light and so that's our Milky Way galaxy now until a hundred years ago astronomers thought that was it that was our entire universe that was the edge nothing beyond it and actually it was this measurement this discovery of Leavitt of this relationship that allowed this guy Edwin Hubble to figure out that there was actually something beyond because a hundred years ago there were these astronomers had seen that in the sky they had the stars of the Milky Way but there was this smudges of light that no one we knew what they were they're called nebulae clouds basically of light and they weren't identified and then Edwin Hubble Edwin Hubble it's hard to find a pitch from without a pipe he was he was working at the Mount Wilson Observatory in California doing incredibly heartened backed back then telescopes were much harder work than they are now because you would have to track stars kind of all night from the telescope following and then with your telescope now it's all automated in the telescope kind of follows something for you but back then you had to kind of painstakingly track a star anyway he he looked at these smudges of light and he realized that there were some of these magic Cepheid variable stars in those smudges of light pulsating and he used the fact that he knew then if he could measure how quickly they pulsated to figure out how bright they were he realized that they were far far far too dim they couldn't possibly be in our galaxy they had to be much further away so if for example our if as we figured out that the galaxy is a hundred thousand light years across these were millions of light years away much much further and so this was this this huge opening up of our horizons that he demonstrated that there are indeed these other galaxies far beyond our own and we can now he wouldn't have been able to take these pictures at the time but now we have these magnificent images of actual galaxies that are different from ours and so this is that this is a real picture of a galaxy far far away and again you can see that this beautiful spiral disk so it would actually it would be the shape of a disk what we're seeing it like we're seeing it like that right with most of the stars in the middle and these these arms of stars spiraling into them incident into the center and so if we now look out again these these these are maybe millions of light-years away from us or then even further they're what we step out and we see the kind of building blocks of the universe and these things tend to clump together a little bit so if we have a bunch of galaxies they tend to like to group together could have been small groupings but like cosmic towns or cities with with hundreds thousands of galaxies together so this isn't a nice example of a galaxy cluster taken by the Hubble Space Telescope named after Edwin Hubble and here what you're seeing is a grouping together of galaxies where every one of those spots of light is an entire galaxy each of those with perhaps a hundred billion stars and these are this is one of the largest of objects in the universe a galaxy cluster and I think it's extraordinary and so you might have hundreds to thousands of galaxies all joined together and for these we're now we're now on scales of hundreds of millions of light years these giant objects in the in our universe and and then if we look out further still we find more of these we find our universe full of galaxies grouped together into these clusters of galaxies and in fact there's an even one level still up which is maybe unimaginative Lee called a super cluster which is where again gravity the gravity local gravity kind of draws some of these big clusters together into a grouping and so we live in one of those two we live we live in in terms we don't actually live in a big galaxy cluster big a nice Agusta we live in a small group the local group which is only three big galaxies and some little ones as well we live in a relatively small we're in a small town but we kind of we're pulled together without the clusters of galaxies around us and we thought for a while we're part of the Virgo supercluster but then quite recently some astronomers said actually there's more that's been kind of pulled gravitationally by gravity towards us which is the larger super cluster called Lanning archaea we're not quite sure which we're part of its might be Virgo might be lani archaea it's quite hard to tell because gravity is kind of pulled pulling stuff in but other things which I'll come to you later a pushing stuff away but then we stepped out really to thee we can step out now to the edges of the observable universe so if we look at any direction in the sky beyond if we try knocking a gap in this guy and don't look at a star we just see galaxies as far as we can see so this is just a snapshots from the Hubble Space Telescope of a tiny piece of sky where every one of those spots of light is a galaxy and so we we can see out to this incredible distance but it is actually a finite distance so we do there is this thing that we call the observable universe and it's a funny concept because the idea is that there is actually only a finite part of space that we can actually access and that's because we actually think that the universe is a finer has a finite age it hasn't been around forever and we'll get to that but the fact that it has a finite finite age which is now we think is about 14 billion years old means that there's an edge to what we can see we can only see things now on earth that light has had time to travel from since the beginning of time so anything that's further that's so far away that in 14 billion years like couldn't have reached us it's beyond our horizon it's beyond and we call it a cosmic horizon it's beyond our horizon and it's outside what we call our observable universe so we have this sphere centered on ourselves and with us in the middle of it which is the observable universe and that doesn't mean that we're at the middle of the universe right it's very important we're just at the middle of the part we can see and and the distance of that edge the the size of that you you might have thought that the size about the distance of the edge of that would be 14 billion light-years it turns out to be actually further about three times further because space has actually been growing during that time which will which will come back to you that's about four is about nearly 50 billion light years to the edge of the observable universe and this is kind of remarkable aspect of doing astronomy and looking out that far which is that it's kind of like this time machine aspect of astronomy which is that the further you look out into space the further you see back in time so we sit here at the middle of our observable universe and we look out through increasing but we the further we look back the further we look out the further back we're seeing to the part of the universe we can see nearby us we're seeing quite recently as it was quite recently but the more distant bits were seeing as they were quite a long time ago and the most distant parts were seeing as as they were billions of years ago so it's a bit confusing but very useful because we can't see we kind of think that everywhere in the universe is evolved kind of the same so if we could see like the very far away right now we think that it's doing the same as we are more or less but we see it as it was in the past and it's frustrating because we can't see how the whole universe looks like today we just can't do that but it's really useful because we get to see how different parts of it were in the past and so by seeing how different parts of it were in the past we can kind of piece together how we have come to be here now because we can see things as they were it's a bit like if you were to see if you were to be an alien coming from a different planet and you wanted to understand how humans have grown then if you give them a room full of eight-year-olds they might be able to figure out like what humans look like but they wouldn't have a good sense of how they were to evolve but if you gave them a room full of a whole diverse range of people he gave them some babies and some kids and some grown-ups and some older people then you would actually be able to reconstruct much better how humans evolve and grow so actually this idea that we can get to look at distant parts of space as they were a long time ago is really useful for us we can kind of build our picture ok so we have this is the kind of the tour of like the things that we've that we can account for most easily in the universe but soon we should be driven to ask a question or this is not the universe well it is in the universe we should ask the question which is is the stuff that we're seeing these galaxies is that all there is because if we look at this picture this is an image of the United States what you see there and if you were astronauts flying high in the sky looking down on earth at night what you would see if the earth is two bright lights you would see where there's people living where there are cities and towns what you wouldn't see is the darkness of the land underneath where there's where there's no significant amounts of light and so the question should surely calm well I'm looking at into space and I'm only seeing the bright lights what else is there and it turns out that there's quite a lot and it's been 50 years since actually we've had some idea that there's more to the universe than meets the eye and a big part of this discovery came from this great astronomer Vera Rubin who is pictured here looking at some observation of using this thing called a spectrograph to look at galaxies she's a she's an amazing astronomer she sadly died a couple of years ago but she made this great discovery about the contents of our universe so she's kind of an interesting she's an interesting character she's a great she was a great leader of of both astronomy but also promoter of women in astronomy she had a pretty hard time starting out because she well challenging time she did her degree in physics or astronomy and wants to go and do risk graduate work and so she applied to do a PhD my current University Princeton University in the late 1940s but she wasn't accepted because she was a woman and they didn't take women at the time so undeterred she went to Cornell and and successfully study there but then she moved to follow her husband to Washington to Georgetown and she had to complete her studies while looking after young children so she would go and go to lectures at night after looking after her young kids during the day and but nonetheless that was fine and she then her next her big project that she wants to work on was to look at the motion of galaxies to understand how they move and she realized that to look at them in great detail she would need to be able to use a big enough telescope to observe the fine details within distant galaxies and to do that you need something you need a telescope with a really big mirror the bigger mirror you have the higher resolution you can see and at the time the best ones one available was at the Carnegie observatory so the Palomar Observatory in California and so in 1965 she applied to use it but they said no only men can use the telescope but she persisted and one of the reasons she was given was there were no women's there were no facilities no bathrooms women she's like this is ridiculous and so she cut out a triangle of paper a skirt and pasted it on one of the men's bathroom doors like her bathroom so she was the first woman to ever use this magnificent telescopes five meter telescope and she worked with a colleague kent ford to build this spectrograph what does that mean it means they were looking at light from galaxies but they were breaking it up into the rainbow of different colors from red to purple to look at the light in different wavelengths they wants to see how fast galaxies were spinning and in particular how fast stars were moving around in the galaxies and you can do that so let's imagine again this is my galaxy it's spinning around and I want to see the gallop that stars on one side if you see it edge on will be moving towards you and the Stars the other side moving away and if you want to know how fast it's spinning around then you can go and use you can use the Doppler effect which you probably come across with a siren from a police car from example if something is moving away from you the signal coming from it be it sound or lie has its wavelength lengthened as it moves away from you so the signal but the the pulse rate or the the length the distance between the peaks of a signal the wavelength increases as something moves away so for sound that lowers the pitch that's what you hear with applet when a police car goes past you hear it lower pitch and with light that that lengthens the wavelength and it shifts the color more towards the red end of the rainbow which has a longer wavelength and than blue or purple and conversely if something's moving towards you it squeezes the wavelength shorter and moves it more to the blue or purple and so with us with a spectrograph you can break the light up from a galaxy into its different colors and you can figure out how fast it's moving around now why is that interesting well the speed at which something moves around is just connected to how much gravity there is in this thing how much masterís so for example the reason why we orbit the Sun is because it's got mass and and if we made it more massive we'd orbit it quicker so the faster the heavier something is the faster something orbits so she went to look at all these galaxies and she measured very carefully how fast the Stars and them were rotating and what she found was incredibly surprising she initially in Kent Ford and she found that they were rotating much too fast and particularly the ones at the edge of the galaxy stood about here they were really going much too fast and the only way that you could make sense of it going that fast was if there was actually some extra mass in the galaxy that you couldn't see and it turned and it looked as if actually the galaxy was actually many times bigger than the visible disk of light was showing up and with maybe 10 times as much mass as you could see from the Stars and so the picture of a galaxy turned into something that looks a bit like this we're in the middle of there is a tiny little blue disc of the visible stuff that that beautiful swirling disk of stars that we think we maybe thought was the whole galaxy and what Rubens work showed was that actually it seems to be so rounded by an enormous sphere or halo of completely invisible matter whose effect it is is to make it all spin around faster but is completely invisible and Ruben actually realized that this idea had been brought up thirty years before by this astronomer called Fritz Zwicky he was notoriously combative but very clever astronomer working in California and he had looked at this galaxy sorry there's a cluster of galaxies and he'd also seen this behavior of galaxies inside the cluster moving too fast around and he'd actually written a paper about it in German bringing up the idea that maybe there was invisible matter and he called it in German Dunkel materia which translates to dark matter and so Rubin realized made the connection that this this is what had Vizards wiki had seen and now Sheehan can't for was seeing it in all of the galaxies they were looking at many many galaxies same thing and and this became established that there is invisible matter surrounding all our galaxies it's not just surrounding our galaxies it's in them it's in here this it's in this room right now and and it seems that there's about five times as much of it as there is the stuff that we're made of and we have no idea what it is it's quite worrying we kind of hope so so the and I say that this happens you know 50 years ago now but the understanding of it of where it is and how its behaving has just advanced significantly since then and we're now just even more convinced that it's there and perhaps even less sure about what it is we would hope that it might be a part new particle a particle that that acts the gravity acts on but it doesn't really interact with stuff much at all so a part a particle of it would fly through your body without stopping and again probably some of it is right now don't worry though and but we hope that it was something that we kind of call a weekly interacting particle which means doesn't interact much but it interacts just a bit just enough that we could find it in a detector and the word great hopes that we could actually create some of these particles at the Large Hadron Collider in CERN but but we haven't and it's possible that we may still might but it hasn't happened yet so some of our kind of most favorite ideas about what it could be have not shown up to be true so now we're kind of with it's one of our it's one of our outstanding mysteries it's there but we don't know what it is so maybe one of you can figure it out so who so we kind of this descent I'm doing I sort of there's the visible parts of the universe and this is a big invisible part but there's another invisible part that's that's very exciting which is which is planets until 30 years ago we didn't know if there were any planets around the stars in the sky astronomers thought that probably were be kind of weird if we were the only solar system to have planets but they're really hard to find because they're very dim they don't give out much light no visible light it's a bit of kind of warm warm infrared light and and they're very tiny so they're mostly invisible to us but we've recently with better telescopes and better techniques have managed to find them so in the 1990s the very first planet was found orbiting an entirely different star to us just the first one and now today we found thousands we've now and many of those have come from this wonderful satellite called the Kepler satellite and what I'm showing you here is a still shot and I encourage you afterwards to go and look it up online of a selection of the solar systems that have been found around other stars are the stars out in the sky each one of those circles represents a whole solar system around a different star in the sky and each of the dots on the circles is a planet and they found them in this really neat way which is that they were using transits of planets if a planet transits in frontof paused in front of its host star then it will slightly dim the light of the star while it passes and then the star will go back to normal again once it's gone and so Kepler managed to look for this very subtle dimming of light and has found thousands of planets this way and using what they've seen so far they assessed that probably what a good fraction of the stars in the sky have their own solar systems and the most extraordinary diversity had been found you know there are planets that orbit their Sun in hours or days with their star in hours or days compared to our you know 365 days there are planets where there are systems that orbit two stars at once for example or multiple stars and one of the most exciting places that's going to be their subject of enormous future study is this place called Trappist one which this is just an artist impression of we haven't taken these images yet which is found by the Kepler satellite it's a solar system with seven rocky planets only 40 light-years from Earth it's still quite far but it's in terms of observing stuff that's not that far it's one of our nearest stars and and the planets again these are just analysis impression of what they look like we have not got these images yet but they're there and some of them are thoughts have water on them and and it's ideal target for future observations with telescopes coming up in the next 10 years it's it's incredible and there are many coming there are many coming they're designed to be able to study these in more detail and look for potential signatures of of life so they're there this is a kind of whole invisible part of this of this bigger home we live in which is all of these rich planets are going around the stars and just because they're tiny doesn't mean they're not of course fascinating we on earth are much tinier than our Sun but I think we'd argue that we are probably more fascinating than our Sun maybe we're a bit biased but it's to me that that wealth of what we could find out quite soo the next 10 about what's out there in terms of different planets is really exciting so that's it so that those are the things that are in our universe but then we can come to thinking about the story that brought us here and I'm gonna focus on the big story which is it are things changing in a big way at all because if we look out beyond again out into this bigger universe full of galaxies has it always been there and 100 years ago this familiar guy on the left Albert Einstein was absolutely convinced that it was that the universe was unchanging that it is as it is that nothing was chain as it is now is as it always has been there could be no beginning for example and no end to the universe but he clashed with this go and the right George Lemaitre who was an astronomer and also priest in Belgium who argued against him and said actually I think the universe could be changing and let's go and find out how and and actually this guy on the right George Lamech sure the reason he thought that maybe the universe on a whole could be changing and could have a beginning at she arose from studying carefully Einstein's new theory of gravity the theory of general relativity which told which which explained how space should behave and and so and the idea here is if you sprinkle galaxies throughout space they shouldn't just stay there stay still if you just sprinkle the minister in and just plunk them down then the gravity of all those galaxies should actually tend to want to pull things all back together again and actually shrink the universe down or if it's already growing through some means that we don't know yet then it should still be moving outwards and and I want to demonstrate just quickly what we kind of mean we talked about an expanding or a shrinking universe and I'm gonna use my my universe here this is a universe by the this is a one-dimensional universe when imagine now that you're an ant living in a one-dimensional space which is this piece of elastic and I want you to imagine that you are living in one of these blue stickers which is your one dimensional what's two-dimensional think of it as only living wrong that's nine that that's a galaxy each of these blue stickers are a galaxy or a marker in this ant space and I'm gonna model what I mean by a universe that grows in this space by simply stretching the elastic stretching it apart okay and a shrinking universe I would bring it back down again grow it again like this shrink it back down now what what happens when I stretch a piece of elastic as it grows everywhere it doesn't grow from one central place the whole thing expands or the whole thing shrinks and so when we talk about an expanding space is space growing we're talking about something like this where all of the galaxies in the universe sprinkle through it I'm moving apart from each other and a shrinking space would be one where they were all moving together like this and that's very different from the idea of maybe something bursting out from a point in space we think a space that grows is a space that grows everywhere now this is just a one-dimensional universe we think that we might be living in a universe that's like this in three dimensions a bit like a stretchy elastic in three dimensions and an analogy for that is a bread dough full of raisins imagine you take a small bread dough that the raisins and yeast and let it rise the raisins will all move apart from each other in that in that race in that dough universe and that's kind of what we think of when we think of an expanding universe is everything moving apart from everything else so this guy George de mettre who was brilliant but he he made one error which was that he wrote about his predictions and his interesting findings in a really obscure belgian journal in french that none of the relevant read so he wrote this fantastic paper where he where he said I think the universe is growing and here's how we could go and figure out if it's growing and oh I have actually gone to figure it out and oh I think the universe is growing and it starts in a big bang and huge news really important results all no one read it and it wasn't until like four years later they got translated into English and was read by the wider community but he he made this predict prediction that was that was that others did too which is that in such a universe okay let's imagine that's dudes all together right imagine I live in this and back in this and I'm in my stretchy universe my universe is growing and I want to know if I as an ant living in one of those blue spot galaxies how I can tell whether the universe is growing or not and as an aside I'll say that the reason that these are blue spots are not not drawn on with blue pen is that we don't think in an expanding universe that a galaxy itself will expand we think the gravity and that's too strong compared to how we now how fast we now do think space is growing so when we think about expanding space anything inside a galaxy is not growing so even if space is growing like this room is not growing right now right that's nerds okay so if you're an ant in one of these galaxies and you want to know if your space is growing you can look out a galaxies around you and they all should appear to move away from you if space is growing if you picked any one of these galaxies and looked out you'd see space you'd see that everything around you sorry moving away and actually you'd see something even more specific than that which is that they're galaxies very close to you wouldn't move very far in something the time I take to stretch it but the galaxies very far from you move further and how that can be seen is that distant galaxies should be expected to be moving away faster from you than ones close by so this very specific prediction of a next Bandon universe which I'm showing here let's talk through it which is if we have along here the distance of a galaxy from the Milky Way and the speed that it appears to be moving away from us then if the universe is growing all the galaxies in it should approximately lie along this line where the nearer galaxy should be moving away from you slower and the further one should be moving moving away from you faster and if the universe is not growing at all then there should be no pattern but they shouldn't follow a pattern and so both la Mettrie and then with better data Edwin Hubble in the late 1920s went to look at all these galaxies that they just discovered were actually separate galaxies beyond their own and they measured how fast or they appeared to be moving away from us and they found that it was in fact true that almost all of the galaxies around us in the sky are in fact moving away from us and they followed this trend that the ones further away from us are moving away from us faster again that doesn't mean that we are at the middle of the universe with everything moving around us if you hopped over to another galaxy you would see the same thing happen everywhere you jump to in space you would see galaxies moving away from you and so this was this was big news this said that the universe is growing and actually by work by measuring how fast things are going you can do something even better you can work out when in the past that growth should have started and when the growth started when imagine in your heads you can whine back now when I shrink down my elastic I can't get it to stop I can't get it to let's say I'm out here if I wind back time in my head I shrink back down the elastic it stops there because my elastic has a finite thanks but imagine if you will that the elastic could keep shrinking down and down and down and down and further until all those spots were on top of each other that would be what we call the Big Bang the beginning of time when everything that's now stretched apart was right back on top of each other and so actually just by looking at how galaxies are moving away from us how fast you could imagine even just doing this with a simple you know if you know the speed that something's moving and how far it is away I'm pretty sure we can all figure out what time it set off from me right that's a that's a no that's a evaluation that we can do and so by looking at the galaxies all around us that we were able to make astronomers could make the first estimates of how old the universe is now Edwin Hubble and George Lemaitre are both showed that the universe was growing and they had this pattern but they actually got their distances wrong by it about eight times wrong and so they actually estimate an age of age of the universe that was only two billion years and after that there was this subsequent kind of years of understanding exactly how to use these pulsating stars in an accurate way until in 2001 this is random a Wendy Freedman American astronomer led a team that used the Hubble Space Telescope to measure these pulsate pulsating stars even better and managed to get a really good estimate of how fast the universe is growing and it was her team's measurements that gave us one of our best current day estimates of the age of the universe which is about 14 billion years there's another way you can do it too which is actually what I do which is I look at look at distant light from the Big Bang itself and we can use that to infer the age of the universe in a slightly different way and it gives us an even a slightly more precise measurements but the measurements agree broadly and they point to this this time in the deep past the Big Bang when everything started so when we look around so this big picture of of our story is that the universe is growing galaxies are moving apart from each other that there was a beginning some big bang something quite strange is happening now that 20 years ago we went out to measure we thought right the universe is growing this some initial energy set off this initial expand but you know the stuff throughout space filling it and the gravity of all the galaxies still in space sure tend to slow down the growth of space and sure it eventually either just slow and slow and slow it down you know getting slower and slower forever or maybe slow down enough to turn around to stop the expansion and to reverse and start shrinking again this was genuinely a interesting question 20 years ago it's still interesting but it seems to be no longer the right question because astronomers went to measure very distant galaxies and looked at how far away fast they are moving away from us and they did this clever trick of comparing how fast the universe is growing in the past to how fast it's growing now and they thought they'd see that it was growing faster in the past and not as fast now slowing down but they saw the exact reverse they saw that the universe is growing faster today than it was in the past it's speeding up the galaxies are flying apart from each other faster and faster and this is as strange as if I threw a ball in the air and instead of coming back down or in the most crazy example I throw it so hard that it just kind of coasts off up into space slowly unlikely instead this is as weird as if I threw the ball in the air and it sped up away from my hand away from the gravity gravity's full of the earth and and again this is long with dark matter it's one of our big mysteries right now in in astronomy and into cosmology which is that there appears to be something in the universe that is making the whole of space grow faster and faster and again we don't know what it is we call it dark energy and that really means we don't know what it is it might be the energy of empty space itself it might be that as space grows and grows that every box of empty space has its own energy and as space gets bigger and bigger this becomes that a more dominant and it can make space expand faster and faster but it could be something else this is the one of the big things we want to find out just as I finish I just wants it I've I've had time to talk about the big story there's also our more our local story which is you know us our son has not been around forever and we think that it was born about five billion years ago in a place a bit like this not this place this is the Eagle Nebula this beautiful image of of a stellar nursery the place where stars are born and so within the galaxies that I talked about these galaxies have these spiraling discs of stars but they also have these clouds of gas and debris from older stars and this is an example of them these beautiful clouds of dust and gas and inside those are where new stars are forming where balls of gas are condensing into new stars and drawing around debris desks of kind of rocks and other things that will eventually form into planets and so we think that our Sun itself was born about four five billion years ago with with some planets that coalesced around it and it was born from the remnants of older stars older stars are where our ingredients were work created everything we're made of was created in the core of a star not everything the only thing that's not creating the Korus star is hydrogen and helium at the beginning of the universe that's all there was nothing else and so everything all the oxygen nitrogen carbon everything that's in our bodies was made in the furnace of older stars that then exploded and sent out their material out into space into some of these stellar stellar nurseries where new stars were born with planets around them that were made of the kind of things we're made of so we really are made of stars and seas and so and so there's this this story of there's the cycle of of the stars that create us and is the bigger story of the whole of how the whole of the universe is growing and so you know we have we've really found out so much and so quickly about a magnificent universe that's happened really in the last decades our knowledge has advanced so much but there are still tons of fascinating interesting questions and what is true is that today's astronomers and and I won't get to answer them all but happily someone else will maybe some people in this room thanks [Applause]

Channel: The Royal Institution

Views: 162,738

Rating: 4.6928 out of 5

Keywords: Ri, Royal Institution, universe, multiverse, jo dunkley, physics, astrophysics, cosmic inflation, cosmos, astronomy, big bang

Id: bFobsse_dZk

Length: 56min 5sec (3365 seconds)

Published: Wed Jun 12 2019