Well, thank you so much fine It's certainly an honor for me to give a talk here at the Royal institution. I'm well aware of the many fantastic lectures that you've had here going back to Faraday in 1856 so it's an honor for me to be here And thank Martin very much for his Introduction I can say that working with Martin has been one of the great privileges of my life and And so it's a particular Pleasure for me that he's able to be here today and as you'll see Martin plays an important role in the story I'm going to tell tonight. It's a story about the cold war it's a story about a high school science project and It's a story about how a generation of astronomers both theoreticians and observers together finally one hard-Won understanding of how the Galaxies in the universe are arranged what the architecture of the universe is and this story starts with Edwin Hubble, and this is a picture of the Rosette Nebula, this is a gas cloud in our own galaxy It's five thousand light years away, so lights them coming to us at 300,000 kilometers a second For five thousand years. It's forming stars here in the middle. I put the eclipsed Moon here in the foreground It doesn't go anywhere near this but I just put this in the foreground to show you the angular scale of this you say Why didn't I notice this thing in the sky? Bigger than the moon well, it's very very faint as an answer, okay next. Oh This is another nebula. This is the andromeda Nebula It's also bigger than the moon in the sky you can see this with your naked eye Is the Central brightest portions in a really dark night? this many people thought this might be a just another gas cloud in our galaxy, but hubble found very Faint variable stars of A known types if it variables in this galaxy Which proved that it was very very far away? much further away So that it was outside of our own galaxy and in fact Given its angular size and the distance of it It was actually similar in size to our own galaxy So this was no little gas cloud this was an entire Galaxy of hundreds of billions of stars Just like our own, and it has two satellite galaxies as well, so this opened our eyes to the to the world of galaxies and there was of course other other spiral nebulae like this that were smaller an angler size it must be further and farther away, so hubble started measuring and this is this is our best picture today taken with a hubble space telescope named after him and this is the hubble Ultra deep field and again superimposed the Moon and Mars And saturn in front of him. So what a tiny region of the sky we're looking at here And this whole ultra deep field is about ten thousand galaxies in it everything you see in here is a Galaxy and the little Faint ones the tiny ones here these are about 13 billion light years away, and So the if you multiply the area of the sky that we're seeing here To cover the whole sky you can see that the within the range of the hubble space telescope Are about a hundred and thirty billion other galaxies and the question is will hire those galaxies arranged Now hubble was not finished he discovered something else he discovered that the further away galaxies were the faster they were moving away from us and You can tell the velocity of a galaxy by looking at the shift of its spectral lines if it's moving away Those lines are going to be redshifted you can measure that and you could determine the velocity? So he found that the red ships he found that the red shifts of these Galaxies were getting larger and larger as he was going further and further away and in fact me and Humiston in 1931 found galaxies moving away from us at 20,000 kilometers a second which is an extraordinarily high speed. This is a uniform expansion it's like Raisins raisin bread baking in the oven as the bread gets bigger the raisins move further apart and a more distant raisin From your raisin is going to be moving away from you faster, because there's more bread in between the two of you So this is a linear homogeneous Expansion that hubble has discovered and it's this figure in 1931 that caused Einstein convinced Einstein that the universe was really expanding Now there was a ready explanation for this at the time in 1922 Friedman had published a solution of exact solution of Einstein's equations of General relativity his theory of Curved space-time to Explain gravity and this was a universe model It looked like a football and it started with a big bang at the bottom and then we're plotting one dimension of time this way and Space is one dimension around the circumference of this and the only thing that's real here is the pigskin itself Forget the outside and forget the inside This is a curved surface and the galaxies world lines are going to follow the seams in the football they're going as straight as they can in this curved surface and Their mass is causing the curvature in the football shape and it's causing them to slow down and eventually Collapse of the big crunch you do not want to be around this to big crunch But we'd be living here in this model where the universe is expanding and so This is because the space is stretching. It's not expanding into anything, but it's just getting bigger George Gamow in 1948 Pointed out that If you extrapolated this back to the past the universe would become very dense and very hot and there's hot radiation should still be bouncing around in the universe today and He and his students Herrmann and Alf Herrmann and alpher so said that you should still be able to see it today and this in fact was discovered by penzias and Wilson in 1965 and it proved that the universe started with the early hot big bang and I worked for penzias and Wilson as a graduate student and I got to run the telescope that detected this Background radiation and found its temperature to be two point seven degrees And so I would run the telescope at night by myself And I would occasionally go and look at the moon And I could see I could see the thermal radiation coming from the moon I could measure the temperature of the moon so the this discovery of the Microwave background radiation really proved that we started with a with a hot big bang model now How are the galaxies arranged in space well people knew that they were in? Clusters and here's fritz ZWicky I knew him at Caltech he's probably the premiere investigator of clusters of Galaxies and This is his catalog of clusters of galaxies he was quite a character as maybe you've guessed and I would tell you that when the Colloquium speakers came to caltech there were there were two people in the audience they feared one was Richard Feynman and the other was fritz zWicky Simon might raise his hand at the end of the can say oh, but that's all its energy conservation doesn't it and as lucky as Lucky would might raise his hand and say I did this already in a paper in 1934 and here's the reference and you know and You'd go look up that paper, and he did your paper on that 1934 so Ricky studied the Coma cluster this is a Every point. This is Likies own drawing. This is Every point in here is a galaxy. It's a centrally condensed relaxed cluster of galaxies It looks rather like a global, er Cluster of stars this whole cluster is moving away from us at several thousand kilometers a second part of the expansion of the universe but there are differences in velocities between Galaxies here due to their and measures looking measured by the doppler shift To show you their orbital motions around the center of mass of the cluster and from this he could determine the mass of the cluster And he found to his surprise That it was several times larger than the mass that could be accounted for by the galaxies So he called this extra Mass Dark matter and we know today that this dark matter must be made of not Ordinary Materials Ordinary Matters made of Protons neutrons and electrons and This has to be made of something else some new form of elementary particle. We haven't yet detected and we know it's there because we can see it in the mass of the cluster of Galaxies and we can also detect it by its gravitational lensing properties of background galaxies, and you know zWicky wrote a paper on that in 1937 So we know that dark matter is there and Ricky discovered that in? 1933 So how is so so here is a cluster of galaxies? This is a picture from the sloan digital sky survey The perseus cluster of galaxies, so we know galaxies are in clusters This is a picture. How do they form this is actually a picture from Martins and my paper 1975 and it's in the book and this is the This is what's going on you have a slight density perturbation in the early universe Tiny fluctuation, and there's excess density because there are excess density in the fluctuation It's going to it's going to be more gravitational attraction and average in the universe so it's going to decelerate More than the whole universe does that would be out here out here So it's going to be start expanding slower than they do and therefore It's going to get denser still than the rest of the universe eventually it's going to turn around stop expanding collapse back down and relax and form a cluster and then later stuff will fall in and fall and make the Envelope this is time going up this way and spaced this way And then it's very late times even at the present day you may see something falling in now And this is exactly what andromeda is doing. We live in a local group a small cluster and and drama has been decelerated by our galaxy and the two of them are falling back together, so this is a coming back here so Galaxy clusters can form from small fluctuations in the early universe and the American school of cosmology Led by Jim Peebles So this is what's happening clusters are forming a first galaxies formed by the same mechanism of fluctuation forms decelerates collapses and then a Galaxies will cluster into clusters and then clusters themselves will cluster into Super clusters So you have this hierarchical pattern of clustering and so this is like meatballs in a low density soup and and then these are stacked like vacuum cleaners drawing additional material in so you get this meatball soup a picture of how the Of how the galaxies are clustered and this was the this is the picture that the Americans was entertaining Meanwhile over in the soviet Union Zell dovish and his colleagues were spending a completely different picture Zold Ovitch Said okay well if you had a perfectly spherical reason that could collapse and form a cluster But suppose it was irregular suppose suppose. It was a flattened Sort of a flattened sphere here, how would it collapse it would collapse into pancake first, and he believed that as a gas Collapsed into a pancake the density would go way up and as it Dissipated energy you could trigger Galaxy formation so he believed that galaxies were formed in pancakes that you formed the structures first and then the galaxies in the pancake and And so how would the pancakes be arranged in space? geometrically well they would form a giant honeycomb Pattern here there'd be big empty voids here and in fact Bob Kirchner and his colleagues had found a Big we're finding a big empty void in the constellation bootes, so so though It's believed that galaxies formed on these pancakes there'd be denser filaments in the edges and then the clusters would be at the at the corners of these were several of these plates came together and so this was the picture that the soviet School had now Why did - why did two schools develop, okay? Well? even with Modern communications the the Sometimes you just have to travel and pour your ideas right into the other person's ear to convince and so Zukie I mean I was looking but zell dovish was was not able to travel outside the soviet union Because he'd worked on the nuclear program there and soviet scientists in general did not get to travel outside Reunion so you develop these two schools now? however Martin rees did travel back and forth he was so like Marco polo to me and and and so when he invited me to come over to Cambridge University as a postdoc he told me excitedly all the things that the Russian school of Cosmology were were coming up with and in our paper We tried to marry some of those best ideas from the Russian school and the American school Together that's what we were trying to do So this is the this is the opposing school now in 1983 Though dovish and shunned on and an astro road this important paper they let me go back and show you this if you take a Of this universe you're expected to show a cellular structure Okay, and and let me mention that of course. This is in a way exactly the opposite of the American school In this picture the high-density regions where the galaxies live you'll notice are all in one connected piece The Honeycomb, but the Voids now are the ones that are that are isolated from each other, so there's one High-Density region in many isolated loW-density regions So it's the exact opposite of the American view so here's a slice of two slices that in a still made Of this observational data here's clusters of galaxies here and and you know you can see the cell Here and so oh when people looked at this. This was a big support for the for the This picture and so though which also noted that our own virgo Supercluster nearby seemed to have a sort of pancake geometry so this was the the picture of the from the Russian school Now at this time a new theory came along This was a guth proposed the theory of inflation And he proposed that instead of starting with a singularity at the beginning of the universe that was the big bang He wanted to start it off with a with a brief period Of accelerated expansion which he called inflation and This gave you a little extra time in here for different regions to get in causal contact with each other over what the big bang could offer and and when the universe was tiny so different regions could communicate with each other and this helped to explain did explain the Uniformity of the temperature of the microwave background we see when we look in different directions something the big bang wasn't able to do in a natural way, so This this period of accelerators could start it with a very small circumference here. Maybe 10 to the minus 27 centimeters, and then it had this very rapid accelerated expansion this was powered by something we call vacuum a high degree of vacuum energy What's vacuum energy um? a vacuum is when you take We take first all the people out of the room then we take all the ar out then we take all the light beans going Through the room and we just have totally empty space here you would figure that that would have a zero density But we've discovered now the Higgs particle Which is associated with a higgs field and the Higgs field permeates all of space it's what gives particles their mass and the higgs field is capable of producing a Nonzero vacuum energy as well as other fields are capable of producing a Vacuum energy we sometimes call this dark energy today, so um The the vacuum itself might have a Nonzero positive energy density now in special relativity One of the properties you wanted for the vacuum was that it had no unique standard of rest So if you had two rocket ships going through this vacuum state at different speeds It would be nice if the rocket ships measured equal energy density so you couldn't tell the difference you couldn't tell anything about whether you were at rest or moving or not, so but if that's true by the logic of special relativity the only way that that would be possible for rockets moving at different speeds to measure the same amount of energy density would be if The Energy Density was accompanied by a negative pressure of the same magnitude but but opposite inside Now this negative pressure is sort of like a universal suction But it's uniform so it produces no Hydrodynamic effects as you know it takes pressure differences to make the wind blow and knock you over So we have in this room 15 pounds per square inch of air pressure, but we don't notice it because it's uniform and so it has no hydrodynamic effects, but according to Einstein's equations pressure has a gravitational effect as well as energy density and So it's a negative pressure So it is a negative or repulsive gravitational effect and it operates in three dimensions two horizontal dimensions front back left right and the vertical dimension up down So the pressure is operating three dimensions the energy density therefore is the the repulsive effect of the negative pressure the gravitational repulsive effect of the negative pressure is three times as potent as the gravitational attractive effect of the energy density so the overall effect of this dark Energy is Repulsive and it causes the universe to start to expand so even if you started it statically it would start to Expand and it doubles and doubles and doubles in size once every 10 to the minus 38 seconds or so So you know how that goes 1 2 4 8 16 32 64? 128 512 1024 if I did that again We'd be up to a million so the universe expands by an extremely large factor in a very short period of time this can explain why the universe is so big it's one of the attractions of the inflation theory, so inflation was a theory that could explain lots of things and We we believed in inflation because it explains very well the fluctuations that we see in the cosmic microwave background and We also believe in inflation because we can see a low grade inflation starting to occur at the present epoch two teams of astronomers discovered that the the expansion of the Universe is accelerating today and It's accelerating such that it's doubling in size it was going to be doubling in size about once every 12 12.2 billion years, so this is a very low grade inflation There's a very low amount of vacuum energy and in fact it's about Corresponds to about 7 times 10 to the minus 30 grams per cubic centimeter it's tiny but it's not enough to have this dynamical effect and that we can measure and they won the Nobel prize in physics for this so we see a low grading form of inflation going on right now Now now I realized that the theory of inflation one of the other nice things that it has is that Things are so small First let me mention though let me mention a problem that guth had to solve Guth wanted the inflation to and right here uniformly and and then turned that energy into thermal particles to start a hot big bang So what he wanted to have happen here was like you have this Inflating see high density inflating see it's like you'd like to put the pot on the stove And have it turn to steam all at once. It's the whole pot turn to steam and that would make our big bang I'm universe that we saw, but he knew that what would happen instead was just what happens when you put your Your pot on the stove that you you will form bubbles of steam in the in the expanding sea So it would form Bubbles of steam and a uniform high density see this was a highly non-Uniform distribution Not what we thought the universe would look like so that was a problem that needed to be solved in inflation And so I wrote a paper in 1982 saying that The solution of this problem was that we lived in one of the bubbles and if our whole universe Were a bubble universe that we lived in then seen from inside one of the bubbles remember you're looking back in time You've just seen the uniform inflating fee that occurred before that from inside one of the bubbles your view was Uniform and so this would solve a goose problem Very shortly after my paper appeared There was a paper by linda and an independent Paper by Linda and another independent Paper by Albrecht and Stein art proposing basically the same thing and they Had a detailed particle physics scenarios that could make this work And this was called new inflation, and it solved a goose Problem so let me show you this this is a space-time picture of how this would work Time is going this way you start with a tiny inflating region here It's inflating seeing that bubbles are forming in this You know these are bubble universes and then the galaxies world lines are going to fan out Here these bubbles are going to expand forever and the whole thing is going to keeps expanding forever And we're living in one of these bubble universes and the space between us, and other bubble universe is stretching so fast that the light from them is not getting over to us, so this is a picture that we have of What we now call the multiverse and so while we can't see these other bubble universes It seems that we've got a lot of evidence in favor of inflation, and it seems like almost an inevitable consequence of inflation that you would form a Multiverse at the end so this could go on forever, and you create an infinite number of these bubble universes now I realized that One of the nice things that inflation did for you was that? It started off so small and so rapidly expanding that the uncertainty principle told you that you would have random quantum fluctuations and these could start the fluctuations that were going to eventually grow up into clusters of galaxies by the present day, so Inflation predicted though that these were random quantum fluctuations that meant that that you just put random what uncorrelated waves through the universe and you could put these on your computer with a random number generator and here's the thing if you if you had a series just imagine sine waves going every which lengths uncorrelated with each other different different wavelengths and things and The thing it was true about this was if you had a positive fluctuation over here and a negative Fluctuation over here this would be above average in density. This would be below average in density if you simply flip the sign of your random number generator at the beginning that you told the computer to use it would switch all the negative density Fluctuations from positive density ones and so it would just reverse the two reasons this part would now be the high density part and that Part would be below average density so one thing that must be true with random Fluctuations which inflation predicted was that the initial conditions? The high the regions that were above average in density and the reasons that below average in Density had to be Geometrically similar had to be geometrically changeable with each other this was not true in the American Model we had isolated clusters in one low density part it was not true in the Russian model Where he had one high density part and many isolated low density parts. They were both cases geometrically dissimilar well, I knew there was a third way a Sponge-like Topology because I had done a High-school Science project Now here are the five regular polyhedron? These have been known since the time of the ancient Greeks And they're the only ones that you can have that are regular faces and all the vertices look the same So so here's one. Here's the cube it's You'll notice that it's three squares arranged around the point You can think of this as a surface made of squares. I mean, I don't have anything inside here this is just made out of squares, so The there's a 90 degree angle here and here and here where the top and the two sides need so you've got three ninety degree Angles so the Angles around this point are 270 degrees that's less than the 360 degrees you expect in a plane so all of these Polyhedrons have less than 360 degree angle around a vertex. Here's another one This is an octahedron. It is four triangles around the point So that's four times sixty degrees. That's also less than 360 degrees These are and so so this is a property that all of these have And this is the only way you can do it three triangles around 2.45 Triangles around the point and three pentagon's around the point those are the only possibilities But Mr. Kepler the Man, who? Invented the laws of Planet planetary motion which are so helpful to Newton he thought that you could also count as regular polyhedron the Well-known three regular planar networks these were Surfaces met regular Sir is made of polygons there were just as good as a polyhedron it just had an infinite number of faces Okay, so here's here's the checkerboard it is four squares around a point that is 360 degrees here is the six triangles around the point that's 360 degrees and Here's three hexagons around the point that's 360 degrees, so if you broaden your definition of a regular polyhedron You could get this You could get this three additional regular Polygon Networks now this is a Illustration from my high school science project I submitted to the west now science talent search The science Town search still goes on today It's run by regenerated said Several sponsors over the years, but then it was sponsored by Westinghouse it was one of the most prestigious Science contests for high school students in the United States and my project was on relating space-Filling packings of Polyhedrons, this is a this is a semi-regular polyhedron. It's a truncated octahedron You just cut the corners off the octahedron, and it has square faces here And it has hexagons here two different kinds of faces. This is a Truncated Octahedron roll box and you stack them here and you get this space filling Body centered cubic pattern you can fill up a whole warehouse of these and so my my project was on relating these stockings of polyhedrons to the different Crystal structures in this case metallic Crystals and this was like the metallic crystal structure you got for sodium So that that was my science project for the western half and it it went on to win the second place in that contest that year and Glenn Seaborg was one of my judges he was of course as element named after him sabor game as well as winning two nobel prize, so this was a quite exciting for me Many years later I was asked to be the chair of the judges for this contest and so I served in that capacity for 14 years and the Well, I think the best science project. I saw into my 14 years in that contest was by Jacob Lorry it was a math project. What was the number one winner that year and This was on surreal numbers. It was really amazing project and He went on to recently quite recently when the three million Dollar breakthrough prize in Mathematics The most famous person to go through the contest in my years is no doubt Natalie portman. She was one of the 300 semi-finalists in the contest that year and It was it was it was my job as chair of the judges to take a ranked list of the 300 best projects that have been selected as semi-finalists by a team of evaluators and to winnow that list down to 120 to go on to the next stage of judging and I actually remember her project because I really really liked it It was a project about how you might get an enzyme to digest waste paper and Produce hydrogen fuel So it had this environmental thing going on, and I really liked it and I put it in Susie asta cle into the top hundred and Twenty pile, so She's known for being one of the 300 semi-finalists, but actually she did two and a half times better than and When they published her paper on the internet, I had no idea she was an actress I remember it was a it was it was a woman's project from New York, but I had no idea of that she was an actor sir who she was so it was judged entirely on its scientific merit and Later her paper was published on the internet, and I recognized it immediately this project that I actually particularly liked so um Instead of winning a nobel prize she wanted oscars She turned out all right so it was it was a thrill for me to work with all these fantastic students during the years and I think contests like this are very important because they encourage people to try Scientific research early in their early in their career see if they like it Now the the I won the second place of scholarship has paid for half of my harvard education but the most important thing to happen was something I noticed when I looked at the plastic model of This that I was building I had I had made a lot of Plexiglas hexagons and and I was gluing them together, and I noticed that there was a full butterfly Pattern of four hexagons that came together around the point which you can see there and I've Replicated this here today. This is what they looked like and I've got four hexagons around the point. How can you do that? Well? Is it? It's a saddle shaped surface This is a negatively curved surface in mathematics and these are positively curved surfaces like the sphere and the plane is in between so these have more than 360 degrees around the point and and not only that whether this one configuration but it can be it could be continued and in fact I noticed that if I just took all my squares and threw them away The boxes would all open up, and I would have one continuous Sponge-like Pattern of Hexagons that was all related and the divided space into two equal parts and so this was a a different polyhedron that was had more than 360 degrees around the point this is my high school science project for that which I entered in the National Science Fair international at the time this is now the International science and engineering fair you can enter that from Britain and countries around the world and these I made models of these Polyhedrons that I had found and here's a close-up of them Here's your squares six around the point here's pentagon's five around the point These are ones that I had found and when I got to harvard I submitted this into the American Mathematical monthly and The referee pointed out that the three of these had been discovered by Petry and coxeter in 1926 but these four were new so it was publishable and and since my paper came out a crystallographer names well as Discovered as discovered three three three more of these so these are sponge-like networks Well now years and years later when I was confronting this problem in astronomy I knew that there was something that would divide space into two equal parts of sponge so here's a picture that squares six around the point and It divides space into could be a high density part here and a low density part here that are interlocking and so if you have a marine sponge Here's your Marine sponge it has it has water passages going through it bringing nutriments tall insides of the sponge and if you poured concrete in those passages You could that could solidify and then if you took acid? And you dissolved away the poor sponge then then that would be gone and you'd be left with a concrete sponge, so That also would have air passages going through it so the insides and the outsides of a sponge Can be the same and so this is just what the initial conditions and inflation should like? interlocking sponge like Topology So I got together with Millat who was a n-body simulator and Dickinson who was an observer? and we wrote a paper called a sponge like Topology of large-scale structure and Millat made a simulation. This is initial conditions based on inflationary initial conditions, so these are slight density fluctuations their ever so slightly above average and The the above-average regions of these random initial conditions look like a sponge you can see the holes here And you can see this all in one piece and here's the other half of this cube This is the low-density parts and these are Also a sponge you can see the holes over here, and this is all in one piece as well So that was our initial conditions Then we evolved it on the computer up to the present epoch and then we're going to smooth this Data because we don't care that the Galaxy's are individual points We want a census of galaxies like you take I want to know how the population goes on the scale of counties so you can hear so we smooth the data on a distance of 24 Million Light-Years and then we counted the density of galaxies and and so this is the how the regions look today, the Contrast has been greatly enhanced But you'll notice that this we took the median density contour that would divide space into two equal volumes and you'll notice that the high density Parts here are exactly where the low the high density parts were in the initial conditions They've just grown up and become higher and higher density and the low density parts also are Mimicking what they had in the initial conditions small scale fluctuations will grow in place becoming bigger and bigger without moving in the standard picture, so we discovered that if you looked at the Universe today, and you smooth bit you could get this is also smooth with the same smoothing length You could you could get a picture of what the initial conditions look like and see whether they resemble a sponge which Inflation would predict so here's an observational sample that we looked at a tiny one and here's the earth here Here's the Virgo Supercluster Up here and the high density reasons all in one piece and here's the low density region It's all in one piece here, and this is that you can see a hole over here. We measured it these these have sponge-like Topology This is what a honeycomb would look like we do that. We smooth the data We looked at one of these old overage honeycombs and and it The high Density region is all in one piece this looks exactly like swiss cheese We call this a swiss cheese Universal equivalent the Honeycomb and the isolated voice if you look at the low dense they have of this picture You can see them. They look like You can see them They're separated from each other as happens the isolated regions with with positive Curvature on them on those surfaces So so this is looking quite different for example as to what we're actually seeing in that even that first observational sample So here. I am with David weinberg who worked on this project There I am another I worked on time travelers a little time travel to the past for me so as I looked then And we're looking at some of this data And we used the stereo glasses you know that we made were red blue stereo pictures So we look like we're looking at some old science fiction movies and About this time they'll operon geller and hooke reproduce this picture This is a slice picture of the universe it has the earth here. You're looking into narrow slice they're measuring distances out here by using the doppler shifts of the galaxies and hubble's expansion law and this is a complete sample, so there's no question about you're missing any galaxies and They found these incredible structures you can see cells here and this looked quite like the Anasta picture only more spectacular and many people looked at this picture and And said this this is like the the honeycomb picture and in fact geller and hooker Described this as a froth of bubbles which is geometrically equivalent to honeycomb isolated bubbles with the walls all connected so this picture looked like it favored the picture of the Russian School now they kept taking data and they made a thicker slice a Thicker slice put together three slices here and one of these filaments here Became more prominent they call this the great wall because it reminded them of the great wall of China, and this was about 750 million light Years long it was an extraordinary of large structure now Park and I did a simulation This is parks. Thesis. He did the simulation. I told him to make them sequencing so What he did was to make a simulation that that had a 4 million particles in it to simulate for the first time a region as large as the as is this observational Sample by of a geller and hooker and so this was made using people's new idea of What's called cold Dark matter? so people's proposed that there was that the dark matter of Ricci was made up of weakly interacting massive particles and that the the nice thing that and also blumenthal bagels and premack produced the same idea around the same time independently and the wonderful thing that this did for you was that the the normal matter was coupled to the hot thermal radiation because in early days The atoms are ionized and we had positive and elem negatively charged particles So they were stuck to the radiation which had a pressure which resisted collapse But the cold Dark Matter could start growing Earlier than the matter could and this helped you in particularly its small scales this helped to be able to make galaxies early and so it helps people to make the galaxies first which he wanted to do and this was quite a breakthrough and a park simulation is based on the on the cold dark matter model of Jim people's and when we first looked at this cube that he made and there was a giant Filament in it and so he just made a slice of that and the agreement this is just what's extraordinarily like the stuff that that geller and hooker were seen and these long fill in life is it proved that cold dark matter could make structures as big as this and It also proved that it can make things that look like this, but we knew for a fact that This simulation had a sponge-like topology because we could see it in 3D So we knew that a simulation whether sponge-like Topology could look like the geller hooker sample Meanwhile, but we had to wait until they got a complete 3D sample of that Meanwhile we were looking to other 3D samples that were complete. This is the Juvenalian Haynes Observations this is the high density half this is the low density half of their survey This is the perseus cluster in here. Which I showed you this is the perseus pisces super cluster which is a giant filament of Galaxies and You can see the hole here the high density part is all in one piece This is the complimentary low-density part and you can see the holes here, and you can see that This is all in one connected piece, so this is a sponge-like Topology Juvenalian hain Now later when the the governor had completed their 3D survey By any more and more slices. This is their final results the earth is here. This is the Northern hemisphere This is the this is the great wall in here. This is the southern hemisphere which they added to their survey and Here you can see that the great wall is Actually a filament connecting clusters of Galaxies And you can you can swim from this void around into that void and so this is a sponge-like Topology in a sponge-like Topology the great clusters of Galaxies are connected to filaments by filaments to make one connected piece At the high density part of the sponge and then the the voids are connected by Tunnels to form the Complementary piece so this is indeed a sponge-like topology. You look at it over here We've smoothed it at a larger scale a low lower resolution version You can clearly see here that the the great wall is the filament connecting clusters of galaxies? There's there's a hole in the distribution here. I want to looking closely at this part of the survey we're going to turn it upside down and Here it is and Michael boldly who's working on this This is the Earth here There's a big void in here, and you put a light in this here, and you can see the red light shining through Tunnels to other Voids through two other tunnels This is the high Density part It's all in one piece and here's the low density part And there you can see this big void here, and you can see the tunnels leading through to the other Void so this is sponge-like where this is a paper by bond in 1995 They showed this computer simulation His colleague and there were colleagues here too. They showed a computer simulation bun by clipping They studied something different they studied the velocity flows in the initial conditions and if you have if you have a filament like this connecting Filament like this in the initial conditions Then there'll be velocity it'll pull stuff toward it with velocity flows that are coming in from two Directions here if it was a pancake. It'd only be pulling things in from along one axis here So they analyze these velocity flows and they were getting flows that that were produced by filaments in the initial conditions Characteristically and so this confirmed what we've said all along Which was that the filaments are present in the initial conditions? They're part of the sponge like nature of the initial random conditions And of course what happens is that after the filament is formed then gravity continues to pull it together? So by by late times you're going to get it's going to be narrower filaments connecting these clusters of Galaxies, and so it looks like a web they call this the cosmic web. This is the first paper to use that word and And that word has stuck to describe this structure, so this confirmed what we were saying earlier Later we've done the sloan digital sky survey and Mario Yurich and I found this large Filament here Which we called the sloan great wall and we measured its length to be one point three seven billion light-years It was about twice the size of the great wall of geller and hooker We were looking at a bigger volume of space This got Mario Eurasian myself Into the guinness book of world records, and we didn't even have to eat a teapot dogs in ten minutes the But let me speak up for this record because there's a lot of largest things in the guinness book of world records There's the largest Ball of twine There's the largest there's a largest building But of although, this is the largest structure in the universe We through the previous record-Holder was the great wall of gallon hooker um? Of all the largest things in that book, this is the largest of the largest Okay, so so anyway, we're continued to find Filaments Let me go back to this picture This is I'm going to show you a close-up of this end of the sloan great wall And this is a picture made by my student Lauren hofstetter And what he's done here is we put the actual pictures of the galaxies from the survey at exactly the right Locations or right distances from the Earth in the picture and and and you can see all these Galaxies here in this rich Eastern and uh but they're fifty times enlarged So you could see them in other words if the galaxies were this size this picture should be fifty times larger Showing you the vast distances between these galaxies and the tremendous size of this sloan Great wall now in the in about 2005 of the the Europeans, Led by Springle did a giant computer simulation of structure formation in this inflationary Big bang model with coal Dark matter and They used a ten billion particles that shows how computer simulations had gone since the time part did his and They found this wonderful picture of the sponge-like Topology with with all these filaments connecting the clusters of galaxies beautiful pictures now They also did slices Of their survey to compare with various observational ones so here's here's the the to sloane great wall and the Great wall geller and hooker They made a slice just like this and their observational set and they found this great wall here Which is quite as long as the one that we're seeing here And then one that looked quite like the closer one that we see of geller and hookers, so these simulations were able to Reproduce as we've Gotten bigger and bigger simulations They've been actually better and better able to agree with the bigger and bigger observational samples that we're seen which Indicates that maybe we're on the right track here's how the Beast things have progressed the first little cube. I showed you was this tiny thing and this is the great wall of Geller and Hooker here in 1994 and then in 2006 We made this is to large survey regions from the sloan Digital sky survey The great wall the sloan great wall is down here, and you can clearly see this as this is the habitants They have this is a sponge-like Structure so every survey that we've done is shown a a sponge-like structure of the high density region We invented a statistic called the genes-- here - which measures the number of holes - the number of isolated regions and in that Density contour Surface, and we were seeing about 50 60 70 about 80 holes in this sample and the the Jagged Line is the Observations here and the the the dashed line, which follows it so closely is the twelve Catalogs that we made from N-body simulation that used the exact random initial conditions an entire spectrum of fluctuations you expected from inflation and This fit perfectly explained the number of holes and these are different density contours Now this is the medium density condor these are higher and lower density condors It's it's that all the density contours. This is quite a spectacular affirmation of the inflationary predictions This is the cosmic microwave background It's a tall sky picture taken from the w maps satellite I bought a model of this when we're at the center of this sphere. We're looking out in space no Matter which Direction We look we see the cosmic microwave background coming in from all directions in the sky all like from all over a big sphere We're looking out in space and back in time So this is we're seeing this is 13.8 billion years ago just 380,000 Years after the Big bang We're and and and that means that the the radius here the the so-called look-back time Distance out to this that we're seeing is 13.8 Billion 13.8 billion Light-years, and so this is the cosmic microwave background that we're seeing and we're seeing fluctuations in this of one part in a hundred thousand and and this is these are the fluctuations that are going to grow up to form the structure that we see and Here is a picture from Planck This is a graph of the amount of power in this in different angular sizes so a lot of spots you see are like it one degree and And the the red dots here are the experimental data from the Planck Satellite and the Green line? The Green band here is the predictions of the standard the standard now inflationary Big bang model and the agreement is just outstanding and and these these peaks here represent acoustic waves in the early universe and you can even look at the amplitudes of these and figure out the ratio of Dark matter and normal matter and so forth so this is a spectacular result now I mentioned acoustic waves if you take a Place where there's going to be an extra lump of ordinary matter here to make it's going to end up making a galaxy that's like dropping a It's like dropping a rock in a pond the sound waves will go out here They'll produce a ripple out here and this freezes in when the when the atoms When the electrons and protons recombine to form hydrogen and so you there's an extra normal matter here And you expect this to give you a slight excess chance of finding? Galaxies in this in this at this distance from where you find your starting galaxies so we can look this is our Telescope here for the sloan digital sky survey here's a picture of a typical galaxy that we use in here so if you locate on a galaxy you ask yourself a question is there an extra little bump in the number of galaxies when you get to this special radius that you can that you can calculate and the answer is that Eisenstein found this extra bump in the data and and so this is a ruler of that you can apply to the Cosmic web and the Cosmic Web Expands every time the universe expands by a certain factor the Cosmic web stretches and expands by that factor so you can use this as a Ruler to tell you about the expansion history of the universe Now as I said the accelerating expansion that we're observing today which was discovered by Supernova Absorb servation, we call this dark energy and We can we can use this detailed measurement of the expansion history of the universe which comes from Supernovae comes from this sloan digital sky survey from these measurements of this so a bump and from the Cosmic microwave background And from gravitational lensing data. Thank you again for to Azuki and you can put this all together and student of Mine Zag Slip ian Found A Nice sitting formula to fit this data, and we can measure then the ratio of the pressure to the energy density in this dark energy which makes up about 70% of the stuff of the universe today and we've got about 4% Ordinary Matter and like 26 percent dark matter and but we can measure Actually the pressure and energy ratio by using Einsteins field equations And so the answer that the best answer that we've gotten using a combining all this data these groups of people Combine teams of large number of people using this fitting formula the value. We find is minus 1.008 plus or minus 0.06 eight so within the errors of the Observation this is equal to minus one now einstein would be very pleased with this Because he invented early on so a term to add to his field equations called the cosmological constant and this was to in the hope of producing a static Universe Model but then in 1934 a La Mantra found that if you move this constant from one side of the equations to the other It could represent a vacuum energy with a negative vacuum pressure And so this is what we think we're looking at today it's not a constant for all time, but it's something that can actually vary through the history of the universe as the physics changes in the early universe we expect that some of the forces reunited and That therefore we had a high vacuum energy we have a low vacuum energy today, so this looks like If this stays one the vacuum energy in the universe is going to stay constant The universe is going to expand forever doubling in size every 12.2 billion years and eventually There will be we're talking more than 10 to 138 years from now But but maybe less than 10 to the 10 to the 34 years from math long time in the future eventually We expect to see bubbles of lower density vacuum occurring like like bubbles in an eternally fizzing champagne So this is the our view of the cosmic web today This was taken in the infrared by the 2mass survey and this is an all-sky view again Like the Cosmic microwave background picture. I showed you we're looking here toward the center of our galaxy you can see it looks quite similar to andromeda This is where we're in the plane of the Galaxy. So we're looking at the center. This is in the foreground and These dots here are all galaxies and the colors are indicating. How far away They are and so you can see the the filaments here connecting the the clusters of great Galaxies in this sponge-like Pattern and so you should realize when you look at this picture that you're seeing the fingerprint of Inflation you're seeing some of the largest things in the universe But you're also seeing the oldest things in the universe because these began as small vacuum Fluctuations made in the first 10 to the minus 35 seconds of the universe and by studying this cosmic web we therefore can learn something about the very early universe and Also by measuring it we can find out something about the future dynamics of the universe Over the next trillion years as well. Thank you you
