The Age of the Universe - Sixty Symbols

kind of a good pop quiz question how old is the universe people might know it 13.8 billion years why does that number come from and there's a little bit of a interesting difference emerging that might stand the test of time and if it does stand the test of time it either means we're not understanding what we're doing or there's perhaps some new physics out there that we've not really accounted for yet and that of course is the latter would be very exciting so how do you measure something as vast as the universe like where do you start so we think of our universes evolving in time and there are these special sections and we're living in part of it and for large distances they're distant galaxies will be actually moving apart if you can figure out you know how far is that thing and how fast is it moving away from me and then rewind time then you can figure out how long the universe is been expanding for so it essentially it boils down to sort of speed equals distance over time really I mean there's a lot more of complications in there because we actually know that the universe is accelerating expanding and not just expanding it's getting faster all the time and then also the sort of effects of general activity when you bring in really really distant objects but basically is speed equals distance over time we can either measure it by looking at galaxies that are not that far away from us and determining how they're evolving with respect to one another and we these we do these music well I said when I say not that far away from those I have to be a little bit careful some of these galaxies were looking at about seven billion years old so they are a hell of a long way away from us so to measure this you obviously you can't just use one object you need a lot of them he justit just takes to be good so let's start with distance okay so how do you measure the distance of an object again it uses a concept that people might be quite familiar with so use this idea of apparent brightness so if you're crossing the street at night left right Green Cross code all that but you'll see a car headlights coming towards you and you'll know whether it's safe to cross because you know how bright color headlights normally are when they're right near you and you'll say okay well it's not that bright and so I can figure out that it's far enough away that it's safe for me to cross so our numbers basically use the same concept and they say okay we need to find something that we know what brightness it should be and how bright it appears can tell us how far away it is by looking for what we might call standard candles in them and these are the supernovae and they're typical ones type 1a supernovae in type 1a you have a binary star system one of them will have reached the end of its life and have got normal supernova okay and what it will of left behind is its core which we call the white dwarf I'll probably still be glowing somewhat well that white dwarf is sort of held up by is this thing called electron degeneracy pressure that the whole thing is held up by the fact that the electrons don't want to pushed any closer together the other star though meanwhile is sort of still orbiting around it okay still in it's sort of normal life cycle but eventually it will start to run out of hydrogen and it will swell to what we call the red giant and then that's probably going to come in to sort of the sphere of influence of this little white dwarf and that white dwarf is gonna start sort of accreting that material from that other star and then it's gonna keep building up mass and building up its mass until it reaches the point where those electrons being pushed together can't support it anymore and then it will go supernova in this type warning okay again yeah supernova twice Wow pretty cool the thing is because of that electron degeneracy pressure because electrons are the same across the entire universe that mass that it reaches one point four times the mass of the Sun is the same everywhere therefore it's always going to explode with the same energy so from that you can calculate the distance quite easily knowing that their brightness is doing so much over that distance yeah good question so you know all the type one is have a very dislike distinctive signature in their spectra so not just that all of the light we receive if we take that light and split it through a prism and we look at its constituent parts it'll have a very specific signature in its elements so first of all you have to be able to recognize what type it is and then you can say okay so how bright does that appear now so it's all about because these things happen really quickly and start to fade really quickly you have to have sort of like really quick response times for telescopes to be able to figure out what these things are so you see a type 1a go off in a galaxy you know how bright it should be you know how bright it looked and that tells you how far away that whole galaxy is exactly yeah it's really difficult to tell the distance to galaxies themselves because you have no idea what size the galaxy could be you know it could be the same size as the Milky Way it might not be it might be bigger it might be smaller and so when you have a supernova that's then bright enough to outshine that entire galaxy you can then put a distance on that so now we need the speed okay so we need to know the speed that this galaxy that the supernova is residing in is moving away from us again we use a handy little phenomenon called redshift okay so people might have heard of this before it's this idea that because the universe is expanding the light that's given off by that supernova will be stretched as it travels across that space okay and it will be shifted and lengthened to longer wavelengths or to redder wavelengths since redshift because it is being stretched we can then say okay we can convert that into a speed at which that is moving away from us similar to a Doppler shift so we can turn shift of say 0.5 into a recession velocity and again you're gonna need the spectra of that supernova not just to identify that it is a type 1a but actually look at the light see how much it's been shifted by and therefore calculate the speed that it's moving away from us so basically what we gonna end up with I'm gonna draw this is very exciting and you can end up with a nice plot of your distance gonna be in a really weird unit that astronomers like called a mega parsec which is a distance not a time thanks star wars and then you're gonna have it against basically redshift which will be in be translated into a speed in kilometers per second and what you end up with you're gonna measure this for as many supernova as you can and you can end up with them all sort of dotted like this give me up to draw a nice best-fit line through them okay because what you'll see is that your velocity that your receding out is gonna be proportional to your distance there's a nice correlation there so actually what we end up calling this proportional constant is the Hubble's constant or H naught here like that and this H naught is going to basically be in kilometers per second per megaparsec okay so you'll notice this is a distance and this is the measure of distance so really if we put those in the same units and we cancel them out it'd really be in 1 over seconds and so if we do 1 over H naught I'm gonna end up with something that's in seconds which will give us the age of the universe at a time there is a lot of uncertainty in this method how do you know also that you're getting the right value what you ideally need is another method to be able to confirm whether that value you're getting is right or not with supernovae the current supernovae camp is saying that the Hubble's constant is seventy three point two four kilometers per second per megaparsec and then there's another way there are there a number of ways but the second way which I think is particularly interesting is by looking at the very early universe I'm looking at the fluctuations in the temperature of the universe due to events that occurred at the very beginning of the universe maybe due to inflation repetitive motions and and you can look at the hot and cold spots and and look at the the radiation that's emitted in the turn and it reaches us in the microwave background microwave range so it's called the cosmic microwave background radiation now you can fit the hot and cold spots the distribution of these temperature fluctuations with a given cosmological model you pick your cosmological model and you see how well it fits the debt and the best fitting cosmological model is called the lambda-cdm model lambda as in the cosmological constant it gives you a value of H not today which is about 66 kilometers per second per megaparsec so you think oh come on they're close enough one's measuring the universe as a result of physics that we're seeing that have occurred three hundred thousand years 380,000 years after the Big Bang one is you know much more recent 7 billion years or so after the Big Bang and you within no percent the issue is this that the each of the sets of people that have been doing these measurements of working very hard to understand the uncertainties in their measurement and the uncertainties both in their experiments their systemic concern T's and they've both now reached a stage where they error bars over each don't overlap with one another anymore so there's been a lot of contention for a very long time about what value is actually right for Hubble's constant and ideally what you want is a completely independent measure we didn't have that for a very long time until 2017 so in 2017 there was a neutron star a neutron star collision detected by the LIGO and Vega collaboration and the really cool thing about it was that there was also an optical detection of the same event ok so not only did you check the gravitational waves we detected it in optical and gamma and x-ray and all of these different electromagnetic spectrum radiation which is really exciting but it also meant that it became what's known as a standard siren so notice that a candle or a standard ruler but standard siren so something that you know how Lau it should be and then you can compare it to how loud you observe it to be so from the gravitational waves we got how loud is it supposed to be compared to what I model it to be and then from the light that we detected we again got a redshift and therefore we could know its distance so but you're dying to know what value they found yeah yeah and if they solved the whole mystery yeah okay so here's the paper gravitational wave standard siren measurement of the Hubble constant and this is what people had been waiting for in cosmology for years and I guess you want to see the plot this blue line is what they got from the baryon acoustic oscillations with the standards rulers this is what you got from standard candles of supernovae and then this line here is the likelihood of the Hubble constant being that value given this stock this one neutron star collision can you see right where it falls right in the middle at about 70 kilometers per second per megaparsec yeah I know it's so annoying because though people were waiting for so long as soon as people heard that this happened they were like constant we're finally gonna know and it was just right down the middle of so far as one measurements of course and so I'm sure I assume they think there's some big error bars on it for it to become a significant player then you've got to have lots and lots of neutron star mergers from which you can then build up the statistics from what I recall for the next few years they're not expecting to see very many we've order one a few a year well that means you're going to be waiting 10 20 30 years to build up significant statistics on it we're basically in a waiting game now to see what happens with this and whether we can actually be sure of what the Hubble's constant is or not the equation to work out when the time when it began is trivial it's a really terrific Utley quotient it only consists of two terms in it and one it but one of them is the evolution of the Hubble parameter H naught is its value today but it evolved in time and the way it evolved in time depended on what's in the universe and that's the thing people are trying to pin down you know how much of it is matter how much you is called out matter how much it is dark energy how much is in the curvature the space-time and different combinations of those three will give me a different edge to the universe try to calculate it yeah okay yeah let's do it t what's your time of your universe is going to be 1 over your measurement for the Hubble's constant and so the Hubble constant that the LIGO team found was 70 plus 12 minus 8 because it wasn't very precise kilometers per second per megaparsec we're gonna have 1 over 70 basically so one mega parsec is three point zero eight six times 10 to the 22 meters that value is burnt on your brain if you've done and I strongly degree ok so what we're actually gonna do is we're gonna do 1 divided by 70,000 put through made it into meters okay so that's meters per second and then divide that by three point zero eight six times 10 to the 22 meters okay and then you'll be thankful to him that I did that calculation before and it was four point four one times 10 to the 17 seconds so let's turn that into years okay so if we divide it by 60 we get it in minutes if we divide that by 60 again we get it in hours we do that by 24 we get it in days and we divide that by 365 point two five we get it in years and you don't know what that comes out as mm-hmm thirteen point nine seven billion yes so that means if I mean that's so exact that means if we like to use a calendar and go back we can find out if the Big Bang happened on a Wednesday yeah you really want to do that would be really cool actually we should do that thirteen point nine seven billion obviously you can't quote it to that accuracy because Lycos estimate was seventy plus 12 minus 8 so really we could only say fourteen billion years but it's pretty close to sort of the thirteen point eight that people always quote that obviously is from one of those two camps but it obviously varies so people take a nice average okay so at Brady's request okay considering the fact that the detection was made on the 17th of August 2017 and using the numbers published in the paper and using these numbers here we have calculated that the Big Bang happened on a Tuesday it's either a Monday or a Tuesday and March 6 minus 6 is my birthday I mean it's pretty clear that that's when it was yeah if you enjoyed this video can I also recommend our astronomy channel deep sky videos which features a lot of the same people you see on sixty symbols in addition to some really cool videos about telescopes the main thing we're doing is making a hundred and ten films about the so called Messier objects this is a list of a hundred and ten things in space that were listed by an astronomer called Charles Messier he was interested in comets and these hundred and ten objects he knew weren't comets they were smudgy on the sky like a comet but they never moved so it was kind of like an anti list avoid these things it was only many years later when telescopes got better we realized Messier list wasn't boring stuff you should avoid but was in fact an incredible bunch of things including galaxies clusters of stars nebulae things Messier probably hadn't even thought of now we've done more than half of the 110 I think we must have done about 60 we're not doing them in order we're sort of jumping all over the place but if you'd like to watch them I'll put a link on the screen and in the video description that's deep sky videos but in the meantime thanks for watching sixty symbols and we'll see you here again saying

Channel: Sixty Symbols

Views: 202,716

Rating: 4.9502687 out of 5

Keywords: sixtysymbols, hubble, hubble constant, universe, big bang

Id: R30ratQanWw

Length: 16min 26sec (986 seconds)

Published: Fri Feb 02 2018