Cosmology: Galileo to Gravitational Waves - with Hiranya Peiris

I have to say it's amazing to be here I was a kid you know watching the Christmas lectures growing up and this is just amazing it's very very much an honor to be here and I'm hoping to take you through how we know what we know about our own universe and like Jason said maybe briefly even beyond it and I want to start here so I'm a cosmologists cosmologists study the origin the evolution and the fate of our universe you know just a small stuff so for the very longest time cosmology was a speculative subject it's one of the oldest branches of science so you can see here this is the Flammarion woodcut a medieval person trying to pierce through the dome of the sky to try to figure out what makes the University what is behind all of these lights we see in the sky and cosmologist today are still doing that it's a different kind of science than all the other experimental sciences where you can actually go and make experiments and try to see directly how the universe works but I think you'll probably agree it's a good thing that we can't make a universe in the lab we can't make one pop into existence poke at it change a little bit see what's going on we can't do that so we have to become detectives we have to look for the clues that the universe itself left us and it seems that Nature has been very kind to us Nature has left us clues that expressed themselves in the language of mathematics and display themselves to us in the data that we can obtain by looking out into space and one of the reasons that this is possible is a quirk of nature which is that light has a speed limit so you know this is a bane of science fiction writers everywhere light has a speed limit it's very fast but it's finite so this means that even the nearest stars when light from the nearest stars reach us you know several years have gone by for that light to travel to us so we see those stars as they were in the past and this works further and further away as well as we look out into the depths of space we see the universe as it was when he was older and eventually it starts to look quite different from the modern day universe it starts to look simpler darker and you can roll back time in this sort of time travel to the very earliest light you can see in the universe we call this the Cosmic Microwave Background so I'm going to start our story by rewinding all the way back to 13.8 billion years ago when this light came into being it's Super Tuesday today so let's start with the Dawn's ancient light so reminding ourselves that we live inside a galaxy so we live in a spiral arm of galaxy and many of the maps of the universe that I'm going to show you in this microwave light is going to look like taking a whole sphere and projecting it into this sort of elliptical projection so when I show you maps like that it's going to be the whole sky so our galaxy looks different as you go to longer and longer wavelengths here eventually get to the microwave wavelengths and then you turn up the contrast by a factor of 100,000 and the universe looks like that so you see this red band across this picture that's emission from our own galaxy gas in our own galaxy in the microwave bands but if you look above and below this band see these little models of blue and green these tiny patches indicate variations in the temperature of the universe and hence its density at one part in 100,000 at a very very early time so early that it's a baby picture of the universe this light comes to us from when the universe was only 380,000 years old is the earliest light we can see and these little patches these little mortals actually form the seeds of all of the structure that appears in our universe today everything that we see from a galaxy to a person to planet somehow came from the fact that the very early universe was very slightly uneven in its density from one place to another it all grew under the action of gravity into what we have seen today I'm going to lead you through the history of this light and how we can learn about the universe from it and I want to start at the beginning with its discovery so it's discovered in 1964 by these two blokes so Arno Penzias and Robert Wilson they were working at at Bell Labs in New Jersey and they built this experimental radio telescope to to do something far more mundane they wanted to look at the radiation from gas in interstellar space between the stars and they came to find that there was a funny kind of hiss in this instrument and it was coming from all over the sky and they thought they've got something wrong there's some noise in the instrument and they started getting very obsessed with pigeon droppings they called it very delicately a white dielectric subject and they started getting into the telescope's grouping this stuff out and eventually they found that that didn't work I recently learned that there is an actual murder mystery here you know pigeons they they home so you can take them away but did they come back home so sadly the pigeons were shot and the hiss continued and the pigeons gave their lives in vain it is very sad however these guys walked down the road to Princeton University and met some of their colleagues who had actually been actively looking for this hiss this this noise in their instrument and basically it was the afterglow of the Big Bang it had been predicted in the 1940s was discovered by accident in 1964 the pigeons didn't get anything but these guys won the Nobel Prize for their trouble so I'm going to fast-forward through a lot of blood sweat and tears to 1992 by this time our instruments had improved enough that we could put a satellite in space to measure this radiation very accurately the afterglow of the Big Bang and if you actually look at this satellite this is called cosmic background Explorer Kobe it made a map like this and showed that this light this very uniform light all over the sky was very cold it was at about three degrees above absolute zero extremely cold in space and on top of that it did something remarkable so it's great that you see this light coming from everywhere it's it's in this room and it's a very uniform temperature that tells you the the very early universe verse was very homogeneous and it doesn't tell you where all the stuff in the universe today which is very inhomogeneous where where did that come from so this experiment actually discovered the primordial ripples from which everything came this is the map they made it's quite crude you can see the red band of the galaxies going through it it's got quite low resolution but this was say this was the discovery of the origin of structure in the universe without which we would not be here I want to start to show you the human face of some of these experiments as well so Penzias and Wilson a couple of people you know they built an experiment they caught the Nobel Prize now we're starting to see teams of people and this is a theme that I hope that you will capture as I go on with my with my talk about how it takes the cooperation of different people to get to these discoveries so this is part of the Kobe team I find it very enjoyable to see some of my colleagues in these 80s costumes with George Smoot he's celebrating his Nobel Prize perhaps but he also likes life a lot so maybe this is something else and this John mother who also got the Nobel Prize for this discovery and I want to show you also the culprit over there there might be people in the room that don't recognize that that's a computer computers so people have been building brilliant experiments for a long time to try to understand the universe computers now increasingly play a fundamental role in it and you can start to see the appearance of a computer along with the team that they made the discovery in 2003 we had a second generation satellites from from NASA this is the Wilkinson microwave anisotropy probe try saying that fast several times so what this satellite did it was a much bigger increase in in sensitivity and resolution from Kobe and that very crude map of the primordial ripples that Kobe made came into sharp focus so this is the map with the help of which we figured out the so-called standard model of cosmology it's a model that describes basically all of the data that we have obtained about the universe and I'll get to it in a little bit I want to show you part of the W map team as well this is a purse a very important picture for me because I'm actually there and that was during my PhD and you can see us looking very very happy because that's when me that day we got the first cosmological results from looking at this map and there's Dave Wilkinson who the satellite is named after a brilliant experimentalist so now I want to actually tell us a little bit about what we are seeing when we see this light so the early universe was very hot it was so hot that electrons were separated from their nuclei okay so the whole thing was ionized with a plasma and packets of light of photons couldn't get very far because they kept bouncing off all of the free electrons so the universe was opaque to light and eventually as the universe expanded it cooled and even though this is still very hot when it was about 3,000 degrees Kelvin you could not keep these atoms ionized any more it was cold enough for neutral atoms to form and at that time this light was released it was the universe becoming transparent that released the light and since then the light has been traveling to us through space so one of the most remarkable things about these journeys of these photons from this very early time room they were released at 380,000 years after the Big Bang and they have been travelling to us for over 13 billion years and during that time before they were eaten by our detectors they have mostly never encountered any other matter the universe is extremely empty and what you're seeing here is the pristine image of this light so why is it in the microwave so in the very early universe when it was very hot they were not microwaves they were gamma rays x-rays very very energetic photons but as they travel through the universe it share in the in the expansion of the universe so the wavelength of this light gets stretched out and they become stretched into the microwave where we see them now so it's cooling down it's stretching and now we see it in the microwave and when you're looking at these maps what you're seeing is a cosmic tug-of-war a battle between gravity and pressure which sets up sound waves in the sea of electrons and photons in the early universe and you can see these vibrations happening at all of the different scales that we can see in the universe and at the moment that the universe becomes transparent you see the sound waves just frozen so you're hearing the sound of the universe when it was very young you can actually convert the data that we get from the microwave background into sound and listen to the structure in it so you can hear that it's not a hiss it's not uniform it has structure in it there's a scale to it so how can we actually use this data to learn anything about the universe it's because in addition to these beautiful instruments that can measure the sky we also have theories and these theories make predictions for what the sky should look like remember we can't do experiments we can make predictions though from theories of physics and we can actually compare what we get out of these theories with the data so this map is like a fingerprint and you can identify the culprit theory by comparing a lot of theories with the data and coming up with the one that fits the fingerprint here again the advent of computers is really really important so we need to calculate what this fingerprint looks like and that requires usually a huge amount of supercomputer time to analyze all of this data and when we do that what we find is something rather surprising this map that was made by W map is basically three megapixels so you know how much information there is in all of those pixels all of that information in that map is basically described by six numbers so these numbers tell us things like when did the first stars form how much atomic or baryonic matter is there in the universe how much dark matter is there in the universe what is the shape or geometry of the universe how old is it and how clumpy was this very early universe so these six things can describe all of this data that is first of all really surprising because it's simple however it tells us already three things that we don't think that we expected which is that there's dark matter this dark energy and the early universe was clumpy so something made all of the structure in the early universe those three ingredients are not in our standard theories of physics it's already telling us that there's a lot we don't know it's simple and yet it's bizarre and strange so before we go on I'm going to now rewind this story that we have learnt about the universe and show you the the history as we understand it following W map so we're going to go into a cold spot it's an over density so there's extra gravity there extra mass there and it attracts other matter towards that the early universe is dark but then eventually the first stars turn on and they light up the universe with their UV light and eventually all of these structures form long filaments of dark matter and you see clusters of galaxies dotting the universe it's not a uniform distribution of galaxies they're cluster and it's this turbulent history through which we are actually looking all the way back at the very pristine early light that brings us to this decade so this is the third generation CMB satellite is called Clank it's actually a European satellite so I was also privileged to work on this experiment and it's measured the Cosmic Microwave Background with extreme sensitivity and resolution and it recently made this map you can see the size of the team this is their two teams and here's part of one team this is what it takes to reach this level of precision and accuracy it's a lot of people working together and it is an example I think of the value of European cooperation because all of these different countries came together to do this amazing experiment get the data and figure out something about our universe which is deeply profound so Planck operates way out beyond the orbit of the moon and it has exquisite instruments that can actually measure temperature variations from point to point on the sky of a millionth of a degree and that's like if you are on earth and there's a rabbit on the moon trying to measure the temperature of that rabbit so this requires Plax detectors to be cooled to 0.1 degrees above absolute zero it's done with liquid helium so obviously the mission has a finite lifetime because the helium eventually boils off into space and runs out so that's what happened to plank but while it was cooled it made this pristine map I'm going to show you the level of improvement that we got basically once a decade so that's Kobe and this w map and there's plank so there is this amazing increase in precision with which we can measure the parameters of our standard model of cosmology so ee map figured out the basic story but now we can say things like this the age of the universe is 13.8 to plus or minus point zero five billion years that sub percent position so this sort of data is what is needed to try to answer one of the more audacious questions that we asked at the beginning of the talk what is the origin of everything in the universe so now I will move to to that subject so where did everything come from well the precision of Planck allows us to rewind time back to so this is a decimal point followed by 32 zeros and a one a tiny fraction of a second after the beginning of time and at this time we think that quantum fluctuations in something called a scalar field we call it the in photon produced all of the structure we see in the universe which got stretched back out by the expansion of the universe into everything that we see today this is a really really bizarre science fiction like idea everything in the universe arose in tiny little quantum fluctuations it was especially audacious till a couple of years ago of course when we didn't actually know what their any scalar fields in nature at all and then the Higgs field was discovered so we know nature can do this but inflation is a big extrapolation in physics so the basic idea is that you know there's this here be dragons regime at the dawn of time T equals zero we don't know what happened there but it's very shortly after that we think that all of this structure in the universe came from these quantum fluctuations and then 380,000 years later you see the imprint of those fluctuations in the Cosmic Microwave Background and then we had the story of the universe that I described earlier from that point on so when you extrapolate physics this much and you can't actually do an experiment to test it which is probably a good thing as I keep saying it's you know it's a little bit you know how do you figure out whether this is correct or not is it it sounds so speculative the virtue of this theory is that it makes very precise predictions for what you should see I'll give you one example again using the analogy of sound so the information in these maps are hard to visualize or present in an intuitive way but you can actually think about it as listening to a piece of music and trying to figure out whether the music has more power in the base frequencies or the treble frequencies okay so the very largest scales in the universe are the long wavelength or base fluctuations and the short scales are the treble fluctuations and you can see is there more power in the base or the treble okay and inflation makes a very detailed prediction for this so imagine there was more power in the treble then the universe would sound like this or if there was more power in the base it might sound like this oh it was nice and roughly balanced it might sound like this Thank You mr. Bach and booted mr. Disney because I usually use Star Wars music for this there wasn't allowed to use it here so the universe actually sounds roughly balanced a little bit bass-heavy and that's exactly what inflation predicts so this bizarre theory was not the only theory it wasn't the only culprit in town for what caused everything in the universe to come into being there were other theories there was cosmic strings these are defects in space-time one-dimensional just stretched out across the whole of space or there are things called textures which are like little swirls of space these are things called phase transitions you're actually very familiar with phase transitions if you have seen water turning into ice for example you know something that can change phase space can do that too and it can create structure however these theories also made very precise predictions for what you would see in the Cosmic Microwave Background and it's not like the data so you know obviously many people worked on different kinds of theories for many years sometimes entire careers and then the data came in and told us the answer and some of those theories were just wrong here I want to make a really important point which is that looking and not finding is not the same as not looking you can make theoretical predictions but you have to test it with the data and if the theory that you worked on is not the one that the data tells you is right your time has not been wasted because you have learned something you have learned that the universe works a certain kind of way and not another kind of way that is extremely valuable information to the cosmological detect now I want to move to the dark side of the universe and again you can see that there's a lot of dark stuff that we cannot see in the universe by looking at the Cosmic Microwave Background so basically as these photons travel towards us from the very early universe they're very slightly deflected by massive cosmological structures that they encounter on the way this is called gravitational lensing so just like a magnifying glass will focus rays of light rays of light are deflected by massive structures where gravity acts as a lens not glass and you can measure this effect using the precision of Planck's data so you can see a very very tiny difference I hope in these maps that's what we're trying to measure its percent level changes in the map in the shapes of these hot and cold spots that we see in the sky and by inverting this effect you can make a map of where all the matter is in the universe this is integrated through 13 billion years of cosmic time where all the stuff is so will you look at this map it doesn't look so interesting because it doesn't have all this intricate precision that you saw in Planck's map of the Cosmic Microwave Background this is like Kobe now this is the start of a new field it's a new window into the universe that allows us to map matter that is not visible this is not their only evidence for dark matter of course but it is a strong piece of evidence and that brings me back to the very very bizarre fact that the universe is actually mostly stuff we cannot see so visible matter matter made of stuff like us everything you test at the Large Hadron Collider like five percent of the universe eighty percent of the matter in the universe is dark matter but matter is not the main part of the universe at all it's it's it's dark energy so it might sound like we don't know what we're talking about and so we're calling things dark you might be mostly correct actually if you say that we have more idea about what dark matter could be then what dark energy could be so dark matter there are many extensions to the standard model of particle physics that might give us candidates particles that interact very weakly with normal matter and therefore very hard to detect but dominate the matter content of the universe dark energy is a different beast I'm not going to really touch on it in this talk but it forms the majority of the energy budget in the universe it's making the expansion of the universe accelerate it's been doing that for a billion years it's not going to stop and it's going to lead to a very sad end to the universe many billion years from now and we don't know what it is we can measure its effect we know what it's doing to the universe but we do not have a physical understanding of that so that's here be dragons but we can learn a lot in coming years about dark matter so I'm going to move to that so how can we see dark matter we can't actually see that matter right we can see light why can we see light we evolved to see light because the Sun emits a lot of visible light and similarly stores and therefore galaxies out in the universe emit visible light and so we can see them we went and built instruments to measure that and since the 1990s we have been making massive maps of the universe in terms of the light from galaxies this is part of the Sloan digital Sky Survey and this is this is not an animation each one of these galaxies is a real object placed into a big animation and these are real galaxies there's about 400 thousand galaxies here I could stare at this for hours it's like a swarm of fireflies and flying through the night and you can see they're clustered they congregate they're not scattered around space why do they congregate it's because they're attracted to big filaments of dark matter that you can't actually see so these four hundred thousand galaxies is a tiny fraction of the Sloan Digital Sky Survey other Sky Service I'm currently working on will map hundreds of millions of galaxies far out into the history of the universe and in the 2020s something called the large synoptic survey telescope will start this is a ten year survey of the entire universe but so far the pictures of the universe I've shown you are static they're frozen in time lssd will actually map what the sky looks like repeatedly every night and we'll make a movie of the universe of the changing universe that's the window we have not had yet and that is humming so when you see these galaxies it should perhaps remind you of seeing a picture of the earth at night now this is a simulation which is you know a sensitizing do you remember that so for a very long time before the invention of electricity I guess if you looked at the earth at night from space you wouldn't really know whether there were oceans whether they were continents etc so now that we do have cities and we have electricity you look at the Earth from space at night and you can see the outline of the continents you can see that there are land masses and this is a biased measure of course of where the land is because you know you won't see Antarctica you see where people live similarly gal these trace the underlying dark matter in some kind of biased way that we can simulate here is such a simulation and again you can see the the utility of computers this is a simulation of the form of formation of a cluster of galaxies a cluster of galaxies one of the biggest assemblages of stuff that you can see in the universe hundreds thousands of galaxies they're blowing out huge plumes of gas as they form and eventually these assemblages will start to look like objects that we can see in the universe so how can we use this to test dark matter so again it's a little bit like how we figured out the standard model of cosmology we have different models for what the Dark Matter particle should do both in terms of interacting with each other but also how they would affect the baryons the gas the the stars as these kinds of structures form and as we get more and more precise maps of where galaxies live what they look like we can compare our models again with this data to figure out which of these theories are correct and which are not and to do that you need computers so you might remember that when I showed you the Kobe detectives there's a little funny desktop computer sitting behind them you know that's what that's what I use it's a supercomputer and so you need hundreds of cores to run your very very big computer codes and you make very precise simulations of what the universe should look like but on top of that our data is now getting so big that we are starting to for example collaborate with companies like Google to actually extract information out of that data because it's got getting beyond the Guil where a human being could sit there and spend a career looking at even a fraction of that data so it is big data and it needs big algorithms so I showed you the universe in microwave light I showed you the universe in visible light and something that's starting to happen in cosmology now is looking at different wavelengths so here you can see the universe in gamma rays and x-rays optical we saw so you go longer and longer wavelengths you eventually get to the radio and we're starting to make surveys of the universe in all of these different frequencies so here what you see is that it's a little kind of clip out piece showing the galaxies again along the middle line and you can see that there's different information at different wavelengths and by looking at that different information we can build a much more careful and complete picture of the universe in the last part of my talk I want to turn back to the origin of structure and how it relates to black holes because everybody loves black holes so do I so remember this theory this bizarre theory called inflation where the universe created all of the structure in it while quantum fluctuations this theory makes an extra prediction which is that it should have said the whole universe ringing like a bell with gravitational waves and there are many kinds of different types of evidence that we can seek as cosmology detectives there is the absence of evidence which rules out theories there is circumstantial evidence that's the sort of evidence that we could now start to think that inflation or dark matter are good ideas about how to describe the parts of the universe which are not described by stand-up standard models of physics in their smoking guns as definitive proof and if we could discover gravitational waves from the very early universe produced by inflation that would be a primordial smoking gun so that's very exciting there's an avenue to find that and that's because the Cosmic Microwave Background is polarized that means that the light that comprises the microwave background has a handedness to it vibrates preferentially in certain directions the textures on these maps which I love it's like the the van gaal color scheme they actually try to give a hint of what this polarization would look like and if there were gravitational waves in the primordial universe that would imprint a faint signature into this polarization now it's really really difficult to observe you have to do it from very cold dry places on the planet such as Antarctica I have friends who winter over working at telescopes in Antarctica in the dark for so many months because they wanted with the first to see this gravitational wave signature so till last year until this year for many of us we didn't know whether the universe could make gravitational waves and that's where black holes come in so what you're seeing here again it's not an animation it's not something anybody dreamed up in a computer game this is a real simulation of two black holes in spiraling together and merging so what you see here is this red and green part that's how time is slowed down near the potential wells of the black holes the arrows are the swirls of space into the hole roles created by the deep gravitational wells of these black holes it's gonna slow down a little bit to show you the final merger of the event horizons of the two black holes into one and this creates a sort of burst of gravitational waves called the chirp and these gravitational waves then spiral out into the universe from the black holes where a very lucky human being might actually detect them so you know this is the story and of course this happened so a pair of black holes each about thirty times the mass of the Sun did this they did it a billion years ago about a billion light years away and the universe vibrated and so you know we have seen the universe we have heard the universe but we can also feel the universe by measuring this so as they merged about three times the mass of the Sun got turned into energy in a fraction of a second that bursts of gravitational waves arrived at the earth on the 14th of September last year and it made a tiny tiny tiny change in the position of a mirror in an observatory which is one of the most amazing things that humans this is a really amazing thing to have done so these observatories so you can see there two of them and I'll explain a little bit why so LIGO is a gravitational wave observatory except that it was conceived a very long time ago decades ago has been operating for 25 years or more and till that time it wasn't an observatory it was an instrument for measuring noise can you imagine spending 40 years of your life measuring noise better and better and better and better and better till you can detect waves crashing on the rocky beach till you can detect the engines of airplanes flying overhead you measuring noise because you want to measure for example the gravitational waves emitted by those black holes which will make a change in your mirror in your laser interferometer of a tiny fraction of the size of a proton if that is not amazing I don't know what is this is like taking the full distance to the nearest star which light takes about four years to reach and over that distance being able to measure the width of a human hair that's what this instrument does it is mind boggling and they measured this they turned it on and they were having an engineering run and they saw this why are there two it's because you know they're really really subject to these these noisy backgrounds that that exist things like the the beach or the the planes I was even told at one point although I haven't found any evidence for this that they can you know feel the alligators walk on the instrument in the Louisiana swamps but maybe that's a that's just a story so they have to so that they can be sure that when they detect this amazing signature for the first time they can see it's happening in two different instruments widely separated and they can be sure that it is coming from out there rather than from your local environment they go even further these guys are really hardcore you know so there are four people in LIGO and they will sometimes without telling anyone inject a false signal into the system that's because they don't want to fool themselves they don't want human beings to think they have detected something that is one of the biggest discoveries in human history and have that not be true so they fool the other researchers into trying to analyze fake data and they go all of the way to writing a paper and getting it ready for publication and then they tell you oh no that is not real but this time that system was not online and there was one lucky human being so this is a collaboration of hundreds of people some of the papers that have just come out have fifteen hundred people on them but there was one lucky human being who is actually a very nice Italian researcher who works in Germany not even in America who is the first human being to see the signature of the dance of these black holes as they merged that's an amazing thing to experience for the first time but you know this is an amazing instrument and it is just the beginning because gravitational waves now that they have been detected and that is an amazing discovery of course can now be regularly detected just as we have been measuring the universe through all of these electromagnetic wave bands this is a new way of sensing the universe and we can do it from space and that makes a sensitive to different kinds of sources that could be detected so you can have black holes merging of very different masses ranging from solar mass slides back holes to the monster but black holes of millions times the mass of the Sun which are at the center of galaxies and you can have dense spheres off of nuclear matter exotic matter the size of London inspire pardon me in spiraling in and create other signatures Oh to tie it back to the origin story of the universe if you wait for billions of years you can start to see the signature of the the cosmic background that's predicted by inflation of course you can't see that in a laser interferometer you would have to look for that in the Cosmic Microwave Background in the last couple of minutes I want to show you that there's even more stuff that we don't know and this again ties back to this idea of inflation so inflation looks like it is the culprit for generating all the stuff in the universe and if we measure these gravitational waves we can confirm it but if it's right it makes a big universe it doesn't just make the observable universe it makes the universe much bigger than that and even more bizarrely that's not the end of it either it will create structure on hugely large scales over the size of the observable universe including other pocket universes that is the implication of this theory that is it sounds like science fiction that is something that we have to figure out how to test if all of these clues keep falling in and pointing the finger at this theory so often when when one learns about scientific breakthroughs you know somebody's getting a Nobel Prize everything is settled everything is so certain by the time that that happens I hope that hearing about these discoveries actually you know tells a better story of what what science is like there's a lot of lead time into making those experiments and making those discoveries there can be decades that can be Korea spent working on theories which turn out not to be true there's a dassit in that that's bravery in that and it is a really important thing that we have these conceptions of this very long term strategies between you know making a prediction and getting the answer out so you know Einstein didn't actually believe in gravitational waves he predicted them you know this is the hundredth anniversary of the discovery of of general relativity by Einstein he predicted it he flip-flopped he wrote a paper saying that gravity gravitational waves did not exist and luckily the paper was not accepted because they do exist but you know so you can have doubts about what you're predicting but the scientific process itself is is self-correcting so there are many blind alleys and there are probably children in this room that can ask me questions about what I've talked about and many times I say I have to say the answer is I don't know so you know rather than being a collection of facts this is a process in which we are exploring into the unknown and by using the methods of detectives we will hopefully continue to tell the story of the universe in more extreme regimes further back in time and also into the distant future thank you do elect do gravitational waves take time and how is that compatible with instant gravity between objects

Channel: The Royal Institution

Views: 67,134

Rating: 4.8146892 out of 5

Keywords: Ri, Royal Institution, universe, cosmology, hiranya peiris, dark energy, gravitational waves, lecture, talk, newton, CERN, LHC, Big Bang

Id: 5HXOfIwl9Jo

Length: 51min 27sec (3087 seconds)

Published: Wed Aug 10 2016