Dark Matter's Not Enough - with Andrew Pontzen

thank you science is all about predictions it's about making predictions and it's about testing predictions and in 1885 the king of Sweden Oscar the second said that he would award a prize to the first physicist who was able to predict with certainty for him the far future of the solar system because king oscar was worried that the solar system which consists of you know the earth that we live on and the Sun and all the planets he was worried that it might somehow fall apart that a couple of the planets might collide or something like that and then that man is fair enough it's it's a worry that we've all had from time to time just think of the terrible sci-fi movies you'd have to sit through so he wanted a physicist to show him what the far future of the solar system would be like now in 1888 a physicist called aji panca hae won that prize and the committee deciding on the award must have been pretty open-minded because he won it by submitting an explanation which went something like this you stupid Swedish man it is impossible to predict the future of the solar system I have shown using my mathematic that no one will ever be able to do that Oh sir my beard is better as annulus and what is going on with your hat it's ridiculous now the important thing to remember is that only Poincare a had a better French accent than mine so it would have been even more frightening when he said that but he got the prize and even today we still can't predict exactly what's going to happen to all the planets in fact we don't know there is a chance that one day one of the planets might just wander off or a couple of planets really might collide or Pluto being really annoyed that it's no longer a planet might launch a vicious attack on the earth now even even though any of those things could happily the last one couldn't happen but even though either of those first two things could happen I don't want you to worry I mean we do know that the solar system is pretty stable out for about a billion years or so but beyond that we genuinely don't know and the Sun we think will last for around five billion years so it's fair to say that we have no idea in a meaningful way whether the solar system is actually stable and that raises for me some questions how is it that we're able to talk with such confidence about say the past of the universe or the contents of the wider universe or the future of the universe and we do tend to make very confident statements about things like that when we're not even able to say with certainty what's going to happen to our own solar system and that's the question that I want to explore with you tonight and I'm going to do it by drawing on some of the strangest ideas known in the universe things like dark matter things like dark energy and probably to my mind the last thing that I'll draw on will be the weirdest thing in all of existence and it is of course the global economy I am going to ask you a few times throughout the evening for your opinion on things so we should just practice make sure that you're happy giving your opinion for instance do you believe in fairies even a few people undecided over there all right do you believe in the Loch Ness monster ah all right do you believe in yourself yes yes self-motivation through physics okay I want to start with my favorite physics experiments of all time it's a pendulum like you might have seen in an old-fashioned clock and it's absolutely delightful what this thing does if I just if I just give it a bit of a knock okay or let it go from over here what it does you can probably guess what it's going to do swings backwards and forwards you can see why this is my favorite experiment it's it's pretty exciting it does even more than this if you if you'll believe me if I give it a really really hard knock does anybody want to guess what's going to happen yeah it's going to go round and round okay let me do that yep there it goes round round okay but there's one more thing if I give it lots of energy it goes round and round if I give it a small amount of energy it just goes backwards and forwards there's one more thing that this pendulum will do and not all pendulums do this it's because it's got this joint in the middle here so some pendulums are sort of rigid they just go back and forth like this but it's got this joint in the middle and that means there's one more thing that this pendulum will do and if you haven't seen this before then you really are in for a treat now so let's put the lights down because I've put a light on that on the end of the pendulum here okay here we go it's alive it's just going to keep going all right so it's gone back to swinging that lit loses energy over time so it goes back swinging I do I deal one more time because it really is good honestly I could watch this all day well thank you very much good night it's hard to follow that I love this thing but it's demonstrating something that crops up all over physics it's demonstrating this motion that seems so unpredictable this is known mathematically as chaos and we find it all through physics but the first person to spots that this might happen was in fact re Poincare Hey when he was thinking about the solar system he realized that motions within the solar system could be chaotic which isn't really our normal way of thinking about the solar system because normally we think whether all the planets there and they're feeling the pull of the Sun and that's keeping the planets from flying off and it's all fairly predictable but what plunk our hey realized is that you have every now and again a little kick as two planets come close to each other because this gravity force that's pulling the planets towards the Sun is also pulling all the planets towards each other so although that's a quite weak because the planets are small compared to the Sun over time the effects can build up and a little kick now and again over a whole billion years can build up into something that's really really hard to predict and in fact Poincare Hey said it's impossible to predict and a bit later on I'll show you why he thinks it's impossible to predict why we still think today it's actually impossible to predict but I want to show you more in space I mean this stuff doesn't just apply to the solar system and to pendulums we see it throughout space and to show you it applying elsewhere in space at a I need to show you what's in space if you look up to the sky in a dark place on a dark night and you have some normal vision then you'll see maybe a couple of thousand stars but if you've got a telescope start to see there are far far more things than you can actually see the things that you see are just the nearest and brightest starts that a list stars if you like the the night sky itself is actually crammed with far more than that much more distant stars and dimmer stars and gas and dust and it's quite hard to see that with your naked eye but if you have a telescope then you start to pick it up and our best estimates today savor in our own galaxy there is something like a couple of hundred billion stars in total so our galaxy really is crammed with stuff but that's not the end of the story that's not the end of space if you know where to look if you've heard of something called the Andromeda constellation and you look at the Andromeda constellation on a really dark night then as well as stars you'll also see a faint smear of light it's about the size of the moon but it's just a faint smear of light and here is a picture taken with a telescope of that faint smear of lights made to look quite nice and bright so we can see it properly and this smear of light is actually another galaxy beyond our own it's called the Andromeda galaxy and it seems that that also has about 100 or 200 billion stars in the Andromeda galaxy and that's not the end of the story either in fact a few years ago astronomers took the hubble space telescope which is an incredibly sensitive instrument and they decided to point it at a tiny patch of the sky maybe about a tenth of the diameter of the moon and that patch of the sky was thought to be completely blank and if you take something that's really sensitive and ask it to point at something that's tiny and completely blank then what happens is it says with just ridiculous look I took this picture and I took this picture and I took this picture and you want me to point at something that's completely black well all I'm saying is it's not no it's fine it's fine no obviously you're in charge you're the astronomers I was absolutely fine if you want me today it's fine but all I'm saying is when we get back into the boardroom if Alan raises it if he says then I'm not taking responsibility I've already told my talents lie taking pictures of things not in pointing a blank bits of the sky by anyway once they'd finished having their little tiff the astronomers won they got the Hubble Space Telescope to point at this bit of the sky and over about a week leaving it pointing at that same bit of the sky this it's a picture that built up it's not blank at all if you stare at it long enough collect as much light as you possibly can find it's actually crammed with stuff just in that tiny patch and every dot of light in this picture isn't a star it's another galaxy all in that tiny amount of space so if we if we take that and imagine that we could search over the whole sky using Hubble to find all there is no way we could do this it would just point-blank refused to do it but if you could then we think you'd find at least a hundred billion galaxies in the universe each with their own hundred billion stars so the universe got quite a lot of stuff in it but we're still not done yet because suppose we go to just one of these galaxies oh I could have picked any one but I've picked this one happens to be called the m81 galaxy catchy name and we try and work out where how much stuff is actually in this galaxy well there are a few different ways you could imagine doing that the obvious way is just to see where how much light is coming from the galaxy and from that you can go how many stars must there be and you can get a bit more detailed you can say well what are the colors as the gas in there and you can just see what what can I actually see there and make an estimate how much stuff you think is there lots of people have done that over many years we're now very good at trying to work out how much stuff there is in a galaxy that's where these numbers of you know 100 billion stars and so on come from but there's another way that you can find out how much stuff there is in a galaxy it turns out that galaxies are spinning and they're spinning for the same reason that the earth is going around the Sun it's because of gravity so if you measure how fast a galaxy is spinning then that tells you something about how strong is the gravity within that galaxy and if you know how strong the the gravity is within a galaxy then you can say well how much stuff do you need to make that much gravity because gravity is just generated by stuff the reason we feel gravity here on the earth is because the earth is so big and it's creating gravity and the Sun also is creating gravity and so on so you can work out how much stuff is there just by going through how much gravity that seems to be now it just so happens that when you do this for every single galaxy we've done it for the numbers just do not agree when you do it using the spinning method you find an answer that there's five times more stuff than the stuff that we can actually see directly in other words six times as much stuff in total and because we haven't got a clue what's going on we invent a cool name for the extra stuff and call it dark matter the thing about dark matter is it's not just in galaxies that we find it if we go to a cluster of galaxies so this is where in the universe sometimes you don't just find a single galaxy sitting there on its own like the ones I've shown you so far sometimes there are lots of galaxies that are close together when that happens gravity gets very strong indeed and it actually starts bending light so we normally think light travels in a straight line but when gravity is strong enough can actually pull light round in the same way that stuff like us you know pulled down towards the earth light can actually be pulled around by gravity as well so if you go to something really big really heavy like a cluster of galaxies that starts to happen you can actually see that the light has been bent in this picture and then you can do the same trick you can say well how bright is all this stuff and from how bright it is you work out how much stuff do we think is there and then you can measure how bent all of these images appear and from how bent it is you get how much gravity there is and from how much gravity there is you get how much stuff there is and you end up with the same answer that there seems to be five times more stuff in what we now call dark matter then there is stuff that you can see directly and these are the kind of things that have convinced us that Dark Matter exists so now I want to check with you do you believe in dark matter oh I actually know in my notes I put the the audience will be friendly but skeptical so that's a failed prediction right perhaps say just to just to keep it on track maybe you could be friendly but skeptical I try go do you believe in dark matter I sound a bit skeptical there but I have to tell you I mean that in a sort of off-the-cuff joke moment I am I have to tell you that 5/6 of the audience are very convinced it's just that you can't see them so now that most of the audience is in fact convinced Dark Matter exists we can start asking things like well what is it made of if there's extra stuff out there that we can't see directly we'd really like to know what it's made out of and for inspiration we turn to the familiar world round I've stood the world of you know desks and seats and floors and lights and the Sun and things that we understand pretty well and what we know about things like that is that if you zoom down if you if you look closer and closer you get a big microscope really good microscope you look on a smaller and smaller and smaller scales eventually you find everything is made out of what we call particles which are just sort of tiny chunks of stuff that we can't actually divide up any further and as far as we know all matter is made out of these particles so we go well I suppose suppose Dark Matter must be made out of particles then we could call them dark dark dark matter particles it sounds nice and technically bad that's literally the level of thought that's gone into that bit but then of course we want to know how did dark matter particles behave and again we look at the familiar world around us and say well you know what do we know about the particles so we're used to the main thing that we know about particles is they feel forces so for instance why am i attracted to the earth it's because all of the different particles that make me up are pulled down by the force of gravity to walk towards the earth and then you can ask well ion why don't why don't I fall through the floor if I'm being pulled down towards the center of the earth and actually we think that's because of another force I don't really have time to go into it today but there's a force called electromagnetism and when I stand on the floor like this the only reason I don't sink through it is because there's another force pushing up on me where my shoe is making contact with the ground that comes from this electromagnetic force between particles and that's why we don't fall through things now it turns out that electromagnetism the electromagnetic force is also the reason why we can see things light itself is a sort of aspect of that force so when we go over to dark matter particles we go well alright they were they've got a feel gravity right they've got to create gravity and respond to gravity otherwise they don't do the thing that we invented them for but on the other hand we can't see them so that probably means that they don't feel the force of electromagnetism like we do and that is pretty much as far as we've got with working out the properties of dark matter we haven't got much further than that but it does allow us to work out some pretty fundamental things about diameter like where is it in the universe I mean for a really convincing demonstration that dark matter definitely exists I think the best thing we could do is actually find some actually get our hands on some and we can make predictions for how much of it is say in this room if you wanted to build an experiment that could actually find that matter the first thing you'd want to know is where how much is in this room and you might think there'd be quite a lot after all that I did say that there's five times more of this stuff than there is of the familiar matter that we're actually made out of but actually in this room you'd be wrong about that because the earth is formed out of normal matter and and what's really important about that is these extra forces that I've been talking about so if you if you imagine in the in the early days before the earth existed there were just lots of bits of rock and dust strewn about and then what happens is that rocks can sort of bump into each other and when they do bump into each other they're a bit so they kind of stick together and more dust comes on it all sticks together and it gets bigger and bigger and eventually you left with a big lump of rock and that's the the earth and that that's the limit of my knowledge of geology so other any geologists in the dark as a geologist ooh the back with would you agree that that's pretty much all you need to know about geology yeah she's nothing she's nothing that's all you need to know about geology good so that's dealt with geology so the reason that there's so much stuff normal stuff here on earth is because stuff is sticky dark matter we think can't be sticky because it doesn't feel any of these forces it needs to be sticky so although there's five times more of it on average here on earth we've got a big lump of normal stuff so actually that means the normal stuff can outweigh the dark matter by quite a lot so if our calculations are right then in this room right at the moment what's happening is that dark matter particles are arriving so they're coming from the northwest which i think is over this depends on on the time of day in the time of year by the way but right now I think they're coming from the northwest which i think is probably over there quite high up in the northwest at this time of day and they're coming at a hundred kilometers a second that's pretty fast and because they don't feel anything so they're streaming at us from space they're coming through the ceiling without noticing it's there they're going through your head through the seats through the floor through the whole earth and out the other side of the earth so work anyone feel the Dark Matter are you are you sure I think that wasn't that wasn't really wise expecting to happen that I'm not sure what the correct response lattice no of course we can't feel the dark matter normally the reason we don't feel them is to feel anything there needs to be a force there the reason I can hurt myself and I hurt myself on the pendulum earlier on it's because of the forces and there isn't a force there to do that I thought it can just come through we did disappears but if you could if you could somehow freeze time I just died just totally destroyed that that just you just ruined that ah if you could freeze time and search throughout this room find all the dark matter we think there'd be something like a million particles of dark matter in this room with us right now and that sounds like quite a lot but actually particles are very very tiny so that's actually just a millionth of a millionth of a millionth of a kilogram in here and at this point you might be wondering well how on earth do you go about finding a millionth of a millionth of a millionth of a kilogram of something that's invisible and untouchable which is a great question but I'm not going to answer you can ask it later on and I can try but there's another question here which is what I really want to focus on to get back to the pendulum which is how on earth do we know how on earth have we made a calculation of how much dark matter is in here and how fast it's coming through and from what direction now we can do this using computers and I'm going to show you one of our computer simulations of the way that Dark Matter works I'm going to show you it in a very particular way what I'm going to do is I'm going to take a virtual galaxy so we've got a galaxy inside the computer and what the computer is able to do is calculate all the gravitational tugs that all the different bits of the galaxy are exerting on this one blob of dark matter that I've labeled there so that we can find out if I just drop a blob of dark matter into a galaxy and it feels all this gravity coming from all the different bits of the galaxy what happens next this is all of course on the assumption that we write that that gravity and no other forces are applicable for dark matter but we can do it nonetheless and we use computers because they're there they're required to add up all these different forces and get us a sensible answer so this is what happens there it is it's attracted mainly towards the center where most stuff is so you'll see it keeps going through the center but it sort of swings back and forth because by the time it gets to the center it's got quite a lot of speed built up so it just kind of flies through and comes out the other side now what you might have noticed about this is that it looks pretty unpredictable it looks chaotic in the same way that the motion of the pendulum looks chaotic and in fact mathematically speaking it is chaotic which means it's very hard to predict and because no it it changes its behavior quite wildly from from one moment to the next and what's really unnerving about this if you if you care about making predictions for what happens to dark matter is that I can sort of do this experiment twice on two different computers now for that for the experts I'm using 32-bit precision on the left and 64-bit precision on the right you can just think of it as like PC and Mac if you prefer these are just two different computers given exactly the same piece of computer code and asked to solve exactly the same problem and I'm just going to show you what happens when we set them going so at first everything looks fine the dark matter goes round sort of the same and looking a bit boring but if you watch really carefully you might start to notice there are slight differences between the two sides and then whether you can see that and overtime those differences get bigger and bigger until eventually the thing on the right is doing something that is just completely different from the thing on the left and that's kind of worrying because we've got two different computers and they give us two different answers to our question about what dark matter is doing now to understand the reasons for this you can just launch a calculator app or something if you've got one on on your phone you can you can calculate along to this by the way if you if you want to have a go it's it's fun for all the family if you if you open a calculator app and type in one point two three four is a very serious calculation five six seven eight nine and you divide it by a billion so I divide it by one zero zero zero zero zero zero zero zero zero American billion and then multiply it by a billion one zero zero zero zero zero zero zero zero zero you should get back to what you started with but you don't write you started with one point two three four five six seven eight nine and you end up with one point two three four five seven computers are rubbish the one thing they're supposed to be able to do is numbers and and they can't and you might think well that's okay because you know you you can just increase the level of precision because what's gone wrong here is a the computers just not storing the numbers accurately enough it's not keeping a record of these numbers accurately enough to be able to go back to what you first started with so you might think well yeah that's that's okay what we just need to turn up the precision in fact that's what you do when you go to 64-bit you're just making it more precise but the trouble with that idea is that then if you go to an even better computer that's got 128 bits then you find it's completely different again what this dark matter ends up doing and if you go then from 128 bits to 256 it changes again and that is what re Poincare a realized would be true of the solar system it doesn't matter how accurately you try and keep track of all the numbers you need to work out what's going to happen to the solar system your calculation is going to go wrong because you would need an infinite number of digits on your numbers in order to get this right and for a start nobody can measure the position of everything in the solar system to an infinite number of digits and secondly it would just take too long to write any of them down and now we're seeing it elsewhere in the universe we're really serious about trying to make predictions about dark matter and you yet the computers kind of scupper us the computers just are not good enough to be able to do that and the real thing is that computers are sorry it's um that's not meant to happen so it's like so I'm what can we I am I'm not sure right okay that's oh no no no no that's that's um that's what I thought he would complain about right and later on I'm going to be giving you a memory card with some pictures on you can import them into iPhoto if you like when I when I said it was sensitive this is not what I meant it's a it's a brand new 64 gig memory card with extra speed all right should we do that satellite right good all that sat out the way um where was I 32-bit six four yeah right okay so the problem that we've got is that these systems these systems that we call chaotic are just far too sensitive to what we do I mean every time I start this pendulum it does something slightly different because I just can't start it accurately enough in the same way and the same problem applies to dark matter if you just lose the tiniest bit of accuracy on your calculation it ends up doing something completely different and this is a massive problem right how can we possibly claim to be able to calculate what's coming through this room at the moment if we can't work out what happens to a single blob of dark matter now to answer that I've actually invented a brand new experiment to show you how this works out this is called I wait for it this is this is going to be the world's first long exposure selfie all right this is this is going to be worth it I'm going to take this this is just a normal camera and it's got a long exposure mode where it's able to keep recording the light that's arriving at it for 20 seconds is what we're going to do and that's going to help us keep track of exactly what this pendulum does over quite a long period of time 20 seconds so I'm going to give this a go I'm going to stand next to it at a safe distance and if we can have the lights down again then we will do the world's first long exposure selfie here we go all right it's just twiddling around at first but of course when it loses a bit of energy it's a this is a selfie 20 seconds is quite a long time actually you know maybe I should do less it's a very long time ah okay that was it that was it you just witnessed it now if I take out the memory card so that we can see what we just recorded I'm just going to pop it in here err er okay oops here is oh it's good it's good there it is now you can see one thing has gone slightly wrong with this in that the right hand side looks very dim that's slightly unfortunate because it makes it look a bit hard harder to look at it's actually because we we tried to get this sorted out but clearly not especially because the LED sometimes looks a bit dimmer Oh on this side of the camera that on that side of the camera but nonetheless if you slightly ignore that you can see the kind of patterns that it's made and now the thing is that we can actually understand quite a lot of these patterns although the specifics of what happens when we set this thing going are quite complicated you know that the actual path it it went through looked very unpredictable there are certain things when you look at it like this that you can predict so for a start you've got the fact that at the top here there's not not very many lines so going through the top in fact if I go all the way up here you can see not very much up there another thing you can see is that it never goes outside this circle right never never outside there and the final thing you can see is it tends to come back towards the centre quite a lot if you look over here it's coming back towards the centre quite a lot there and we can actually understand all of these features so for you know why why is it that it never goes outside a circle well that one's pretty obvious it's because this thing is only a certain length so if I take it round you know just cannot get any further unless the thing flew off and hit me in the face but that would not be good so that's what means that it's got to be within a circle so that's the first thing we can understand then the second thing that I mentioned is that it doesn't tend to go above about this height we can understand that too that's to do with energy so I give it a certain amount of energy at the start and over time because of friction and so on that energy kind of seeps away and at anytime if it's got a certain amount of energy it can't get above a certain point if it's got lots of energy it might be able to get all the way up there if it's only got a tiny amount of energy then it can only be down here so as the energy runs down in this thing increasingly it just cannot it can't get high enough to to form a streak going up towards the top of this picture right so energy tells us something and then there's the final thing about it returning to the middle can actually see a lot of streaks going towards the middle there and this one's a bit more subtle this is something that we call degeneracy in physics it's basically because if I'm near the middle there are a lot of ways I can reach it so imagine I want if I want the light to be here then it doesn't really matter where this bit of the pendulum is it can it can be over there and I can still get the light roughly into that position or it can be up there and I can still get the light into that position or it can be you know all the way over there and I can get the light into that position near the center you've got lots of different ways that the whole thing can be arranged just to get the light into it like lighting for its position further further out that's no longer true if I want the light to be over here then the only thing I can really do is have the pendulum looking like that or there's one other possibility which is that the pendulum looks like that but there are only two ways of getting it in most places there are only two ways of getting it in the center there are many ways of getting it we call that degeneracy and it means that it seems like it's being attracted towards the center but it's just a sort of statistical effect there's lots of different ways for it to get to the center so there are lots of things about the long-term behavior of this thing that we actually understand very well without having to be able to calculate exactly what it does every time that we said it going and in fact that means that if I take now I can't see there we are so earlier on I actually made a calculation of what I would expect this pitch to look like now unfortunately we've lost half the picture but I can still compare the other half if we do that you can see the kind of patterns that you get out of my prediction which was based on the maths of all the different forces acting within this pendulum actually looks not too bad I mean the details aren't the same but all these kind of general features like it doesn't go near the top very much it's attracted towards the center and so on and there are more you know you can go on forever finding more and more subtle things those general patterns are reproduced now that's the key thing that means we're actually able to get somewhere with this all right the fact is that okay we can't predict exactly what's going to happen to the pendulum and we can't predict exactly what's going to happen to one given blob of dark matter in the universe but what we can do is understand why although the predictions in detail break down the kind of patterns that come out are going to be the same from from from from one version to another so that applies to the dark matter in the computer as well yes the details go wrong but the basic patterns that come out are still consistent between our two computers that I showed you earlier on and in fact that really is one of the reasons why we do take dark matter see well that and the fact we don't have any better ideas but the that is one of the reasons we take dark matter seriously because we can do calculations with it if we just sort of you know ignore the fact that we're talking about patterns rather than about specifics in fact these galaxy simulations that I'm talking about even go as far as showing us how galaxies form in the real universe so this is a more complete galaxy simulation which has started from quite early on in the universe and shows how we think galaxies build up now we've got everything in here we've got gas and stars and dust and we've got Dark Matter as well which you can't actually see the way I've drawn it here I'm trying to draw it as though this is what a telescope would see if it could see the the universe evolving but what we see over time is that you start with lots of little galaxies and over time they merge together they're actually being pulled together by their Dark Matter they merge together they form bigger and bigger things and if you skip forwards through 14 billion years which is how old we think the universe is and you end up with a big whirling pool of gas and stars and you can even fly into it and have a look at what would it be like to live inside this thing and in fact it turns out that we're able to build something that looks very much like our own galaxy this is what a good picture of the night sky looks like so despite dark matter being based on some pretty wacky ideas and despite the fact that actually we can't calculate exactly what happens to dark matter we can take the ideas that we've come up with and just kind of use them anyway hope for the best and we end up with a virtual universe inside a computer that looks very much like our own so so that brings me on to the final example that I wanted to go through of how you can get away I suppose with the fact that things are really quite unpredictable and I promised I would talk about the economy right as I am actually going to talk about the economy it turns out that physicists we're thinking about the economy they thought hey we can do this we can do the economy can't be that hard so they came up with a model for how the economy works and the model of the the physics model of the economy works like this so you start out the day you're at your in your house and all your money that you own in the world is all just in piles of cash around you and then you pick up all of your piles of cash and then you go out the door and once you get out into the street with your wads of cash when you see somebody passing you by with their wads of cash you just throw some at them you way they are there somebody there's some money that's somebody you just throw the money round and also if somebody throws some money at you then you take it obviously I mean you're not stupid so so inside somebody throws some money at you you take it and then at the end of the day having gone around throwing money around you go home you loosen your tie you go home you get home and you stash your money that is the physicist model for the economy that's it now it sounds a bit stupid right a little bit but it makes some predictions one prediction you can get out of this model is how how which should people be in general so if I take all the different families in a country and I find out how much money they have after they've been doing this for a few years then I can plot it on a graph if you don't like graphs it's okay this bit won't last very long this is this is the prediction okay that you get from this physicist view of the economy is saying that that a few a few people over on the right-hand end make lots and lots and lots of money it keeps going you know off there and probably for about a mile in that direction into the city and then down at the left-hand end you have quite a lot of people in fact the vast majority of people making not very much money and it's just based on that simple idea that's all it is and so having done that you then go okay let's get let's get some data because that's what you do with predictions right you compare them to data about the real world so let's get some data by the real world these guys took the census data from the United States to find out well how much money are people actually making and you can plot that on this graph bang it's really it's absolutely amazingly close I love the fact that the world's most advanced economy is basically modeled by a bunch of three-year-olds playing Monopoly it just and it's it's mind-blowing and I think the thing to take away from this is that you can take ideas which are clearly not very sensible and you can still learn something from them you can still find out something about the world from ideas that are a bit wacky not of course you couldn't use this to work out how much money does here of course you couldn't do that but you can find out things on average about what goes on on average so similar to the idea about the dark matter and the idea about the pendulum now finally I did promise I'd say something about dark energy so this is the last thing I'll bring out it's a perfect topic actually just to bring up in the last two minutes because dark energy is a whole new thing it's not the same as dark matter it's totally separate and it's based on the following fact the universe is expanding that's been known for for quite a long time that just means all the different galaxies that I've shown you in the universe they're all getting further away from each other over time but not only is it expanding it's actually expanding at an accelerating rate so that means if two galaxies are flying apart at a given rate today then tomorrow they'll be flying apart just a little bit faster and that is pretty weird to be to be honest I mean for a start you can imagine that really requires you to find some energy somewhere if you want to make things go faster you need to add some energy in and so physicists sat down they thought right okay well we kind of did ok with the dark matter thing I think we got away with that so yeah which means it's to do with energy so we'll call it dark energy that's good it's a good start and and we need to be able to get energy out of nowhere does anyone do anybody have any ideas you could write you could rub your hands together you would need an awful lot of people rubbing their hands together throughout the universe to generate the required amount of energy and then they'd all need to be eating food and the and the food would have energy in it already so unfortunately that doesn't actually create the energy out of nowhere so the solution that physicists came up with to this is is to look again to something relatively familiar something that we all know about bits quantum mechanics let's do quantum mechanics that does weird things in the quantum mechanical world it turns out that a vacuum like there is pretty much in the deepest parts of space isn't totally empty whatever that means there's there's a sort of trace of energy left over even in a vacuum and we call it the vacuum energy say what you see ah and so physicists well I always thought it is probably that isn't it let's um I think we're done oh that's fabbi Bobby so so I are you all convinced by dark energy this is about two people who are everybody else isn't I think I'm with everybody else the thing is what's going on here what happened with Dartmouth and what's going on with dark energy is we're seeing something strange happening in the universe and then we're reaching for whatever we can to try and explain it so in the case of dark matter we reached for what we know about particles and we kind of applied that as best as we could and we came up with some ideas and now we're applying then they seem to be sort of working in the case of dark energy we did something pretty similar it's just that the thing that we reached for happened to be quantum mechanics so it's it's it's even weirder but I suppose the reason that I chose the title for tonight is because I think it's a fair criticism that people make certainly of dark energy that the reality of what's going on here could be vastly weirder it could be much much weirder why do we think that nature is really just doing stuff that we're basically quite familiar with even though this quantum mechanic stuff is weird it's all been measured in the laboratory and so we're just taking something that we've done before and scaling it up to the size of the universe you could say the same about dark matter we know quite a lot about particles because we can deal with them here on earth and so we take that idea and we just scale it up to the size of the universe and it seems like a pretty damn stupid thing to do so might seem naive almost but on the other hand what happens is that we then take those ideas we run with them we I suppose you know we take we take ideas that might just be totally wrong and then we do calculations that might be totally unreliable and then we come up with numbers that might mean nothing I spill like Tesco's accountancy I suppose but then we go and compare with the real universe and we do find that despite all of these problems if we're interested in sort of averages then quite often we are able to get those things right but I suppose my point is that you can turn that around you can say all right we understand why some of these things come out about right on average where things go wrong is when we're interested in something very very specific like if you're interested in is the solar system stable we just don't have an answer we can we can we tell you on average would solar systems typically be stable and you're probably not so interested in the answer to that question it's the same as the weather forecast right they can say oh well you know is your house likely to flood tomorrow well on average this many houses will flood you're not really to be fair that interested in that question you're more interested in whether your house is going to flood tomorrow so the questions that we ask are ones that are deliberately made quite broad and so it could be that the reality of what's going on is something much weirder and that we're getting the right answers just because we're asking questions that are broad enough that you know think things work out anyway but I suppose I have an optimistic view of that that sounds quite pessimistic I have an optimistic view of that it means that when we do finally find out what's really going on in the universe and it probably is much weirder than we realize at the moment then all of the work that we're doing at the moment which might be based on very wrong ideas might still come out and be very very useful indeed because it's all about patterns it's not really about specifics and that's all I wanted to say thank you very much for listening I think we have time for questions now could you just tell me what the difference is if there is any difference between dark matter particles and neutrinos

Channel: The Royal Institution

Views: 653,802

Rating: 4.5008173 out of 5

Keywords: Science, Ri, Royal Institution, Science Communication, Education, dark matter, physics, lecture, talk, event, Andrew Pontzen, space, cosmos, dark energy

Id: GFxPMMkhHuA

Length: 54min 4sec (3244 seconds)

Published: Wed Nov 19 2014

Reddit Comments

[u/zxxx]

Q&A

[u/MarquisNoir]

Old lady fell asleep near the end, bless her.

[u/thankfuljosh]

This guy is like a cartoon of a physicist. Could not bear it.

[u/Lawls91]

This lecturer was super cringey and the lecture was really watered down, would not recommend.

[u/[deleted]]

nobody is even encouraging these antics but he goes on and on trying to put on a big performance. alarming and gross.