Ripples From The Big Bang: Listening to the Beginning of Time

[Applause] thank you welcome to tonight's program in the beginning said Douglas Adams the universe was created and this made many people very angry and is widely regarded as a bad move now whether or not that's your view of our universe it was created we are stuck with it and many of us want to figure out how it actually began and that is what the subject of tonight's program tonight's discussion will be all about and what I'm going to do here in just the first few minutes of the program a kind of prologue if you will is just give you an overview of the basic idea is the basic language in our thinking about the origin of the universe that will then set us up for our discussion in which we'll have some of the leading thinkers the prime movers the architects of our understanding of cosmology joining us on the stage and we will take this initial discussion much further ok so to understand the origin of the universe it turns out that you need to have an understanding of that force which is most relevant on large distances cosmic scales that is the force of gravity so let's begin just by way of things that I think most of us are quite familiar with the first attempt to understand gravity which of course takes us to this picture here right it's Isaac Newton late 1600s writes down the famous universal law of gravity that we are all familiar with you can say with me f equals G m1 m2 over R squared thank you and with that little equation Newton is able to predict the motion of objects planets the moon terrestrial objects and the predictions coming from that little equation are borne out by observation which gives a sense that gravity is now understood but then something pretty dramatic happens early part of the 20th century if you fast forward a new thinker comes on the scene of physics and this thinker is unwilling to accept Authority accept the notion that all issues that had been viewed as solved by a previous generation perhaps they need to be rethought and in this particular case of course I'm talking about Albert Einstein and when he focused on Newton's law of gravity there was kind of a puzzle that immediately occurred to him which is how does how does gravity actually exert that force that we call gravity right if you have the Sun over here you got the earth over there there's basically empty space between them what's the mechanism by which the Sun affects the Earth's motion right so this was a deep puzzle Einstein naturally thought that he should go back to the writings of Isaac Newton to get a sense of what he was thinking about in terms of the mechanism underlying the force of gravity so he goes back to the Principia you know all the results that Newton found during his lifetime he looks up gravity right you know letter G finds you know F equals G m1 m2 over R squared the universal law of gravity he looks underneath subheading M for the mechanism by which gravity operates in there Newton says I don't know how gravity works in fact in his own words he said so the answer of that important question the mechanism by which gravity operates he said I leave it to the consideration of the reader now most readers would read that in read on right but this is Einstein who's reading at this moment and he sees this as a grand challenge to figure out the underlying mechanism by which gravity is transmitted from one place to another so he spends 10 long years trying to figure it out and finally he comes to an answer which is kind of the most simple answer you could imagine in a sense because if you got the Sun here the earth here if there's empty space in between them then somehow it must be space itself that is the medium for transmitting the force craft somehow space must be exerting the force that we usually attribute to gravity and indeed that is the idea and here's how it goes so Einstein imagines here is 3d space kind of grid like image a little hard to think in full 3d so let's go to a two-dimensional version which captures all the ideas and here's the key idea space is flat if there's nothing there but according to Einstein if the Sun appears the fabric of space curves it warps and in fact if you look in the vicinity of the earth the earth curves the environment around it - and now focus your attention on the moon because here is the main point the moon is kept in orbit because it's rolling along a valley in the curved environment that the earth creates that is how gravity works and if you pull back the earth is kept in orbit for the same reason rolling along a valley in the curved environment that the Sun creates that's the basic idea of Einstein's general theory of relativity of course that's an artist's rendition an animation of the basic ideas there's an equation underlying this picture to write the equation that takes the place of Newton's equations again you can say it with me right arm you knew minus 1/2 G me nu R cos 8 pi G over C to the fourth T mu nu right so that is the new equation of Einstein's general theory of relativity Nativity now this is a spectacularly interesting idea how do you test it how do you know if it's correct well Einstein himself realized that if space actually curves to communicate the force of gravity then imagine the following light from distant stars as that light passes by the Sun the curvature of space will cause the trajectory of the light to be curved which means if you look at distant stars when the Sun is between us and the star the star light will curve as I just mentioned but six months later when the Sun is on the other side the trajectory of the star light will not Bend and therefore the position of the stars in the sky should shift between those two observations now how can you see distant stars when the Sun is between us well you need a solar eclipse to block out the Sun temporarily making those distant stars appear so this was the idea in 1919 two teams of astronomers go out to measure the positions of stars during a solar eclipse to see if they shift and the manner predicted by Einstein's theory of general relativity and the amazing thing is as we see here they found lights are all askew in the heavens men of science more or less a goggle results of eclipses observation Einstein's theory triumphs stars not where they seem to be orbit calculated to be but nobody need worry Einstein's theory was confirmed through this prediction giving rise to an observation that agrees with it story goes that Einstein received telegram telling him about these results and he was asked professor Einstein what would you have said but you've thought if the observations didn't agree with the predictions of general relativity and Einstein is purported to have said I would have been sorry for the dear Lord because the theory is correct now I don't think that he actually really would have said that but it shows how the power of a theoretical idea can almost in some sense emanate a sense of truth but ultimately that must be confirmed by observation now this results made Einstein famous worldwide theory attained great fame and that led people to start to think about using the general theory of relativity to try to solve various problems applied in various ways and this fella over here Belgian priest Georg lament he took Einstein's idea his equations and applied those equations to the entire universe and found something very unexpected he found that the math was showing that the universe couldn't be static it couldn't be unchanging it had to either be stretching or contracting the fabric of space who would be growing or shrinking over time now this was a very unfamiliar heretical idea he took this idea and told Einstein about it 1927 and Einstein said your mathematics is correct but your physics is abominable what he meant by that was you can't believe all mathematics right you have to have good sense Einstein was saying you have to know which mathematics to trust because if it gives an implication that's manifestly wrong you can't believe it right I some is saying he was parroting the philosophy of the time that on the largest of scales the universe is static eternal unchanging you look out there nothing on the largest of scales is happening so he just thought this is wrong now the reason why he said your math is correct was actually because of this guy over here Alexander Friedmann who I should say looks just like an accountant I used years ago and in fact right around tax time he would look at me just like that but anyway so this is a gender freed Mont and even earlier even before lumetri he had also undertaken a similar calculation shown at Einstein Einstein at first said your math is wrong but then he was convinced by Friedman that Einstein was wrong I um had to retract that criticism but he never thought I never thought that the math was telling us anything about reality and all that changed with this guy over here Edwin Hubble Hubble used the powerful telescope at Mount whistle Observatory to look at distant galaxies and found that the galaxies were all rushing away from us right the universe is expanding and you know it sounds amazing you know Hubble was an Oxford trained lawyer who turned his attention to astronomy which to me proves there's hope for absolutely everyone but there we had it so the data was showing that the math was right the universe was expanding of course this gave rise to the picture yes the universe is today expanding and the idea is ever earlier back in time the universe is smaller and smaller and smaller until way back in the beginning it was really small as we just showed and underwent a rapid swelling that we are still witnessing the aftermath of today by seeing those distant galaxies all rushing away the Big Bang Theory was born and that of course is a great triumph but the Big Bang Theory itself has a number of problems some of which we are going to focus on in the discussion in just a few moments but let me just raise one of them right here just to give us a sense of where we're going an unanswered question in the Big Bang Theory it turns out is well what is it that drove the outward swelling of space what force was pushing everything apart now this is a question that people struggle with in one form or another for for many years but thankfully in our age these gentlemen over here Alan Guth Paul Stoddard Andrei Linde andreas Albrecht as well as contributions for many other scientists came up with an answer to that question I sort of love this imagery right here because like if you compare the right side to the left side you see that modern cosmologists are so happy now what they found and what we're going to be talking about here tonight is the inflationary theory what they found is we're going to discuss is that well we're used to gravity being an attractive force pull of thing together but in the hands of Einstein with general relativity in the hands of these gentlemen over here they realized that if you had a kind of exotic source for gravity not not the earth of the Sun the usable usual sources for gravity I should say instead if you have the universe being filled with a kind of energy filling space that energy can give rise to a repulsive gravity that pushes everything apart that can fuel the Big Bang itself that's a beautiful idea but again how do you test it you don't believe anything until you can test it and you can at least according to certain ways of looking at that we're going to talk about here tonight test these ideas the test for this makes use of the cosmic microwave background radiation one of the most important features of the observable universe to gain insight into the earliest moments of creation so what is the microwave background radiation well it's heat left over from the Big Bang kind of afterglow of creation now it was calculated by a number of theorists going back to George Gamow Alpher Herman others people like Bob Dicke and Jim people so a number of theorists calculated that there should be this heat filling the universe something like 400 photons and every cubic centimeter rushing through space but again that's calculation what about confirmation what confirmation did come from these fellows over here Arno Penzias Robert Wilson working at Bell Labs New Jersey we're working with a horn shaped antenna to communicate with satellites through radio waves and that they needed to do is eliminate all sources of interference so they could perform those calculations so they got rid of you know radar interference radio broadcast they cooled it to get rid of the thermal interference but still they found a noise that the detector kept showing that couldn't get rid of the noise they even wondered whether the noise might be coming from bird dropping some birds had nested in the horns they cleaned out the bird droppings but still the noise was there and of course what they found was the hiss of creation the cosmic microwave background radiation and indeed it was 50 years ago this week that the discovery happened the two gentlemen won the 1978 Nobel Prize in Physics and we are honored that in the audience here tonight is Robert Wilson you take a stand here so again it's a beautiful story of prediction and conformation and I raise it here this will now lead into our broader discussion because the inflationary theory suggests that there is additional information hidden in that radiation that could give us insight into whether the inflationary theory itself is correct what's the basic idea we'll come back to it the basic idea is early universe they're quantum fluctuations in homogeneity that get stretched by the rapid swelling of space coming from this repulsive gravity and that yields tiny temperature differences in this radiation sprinkled all across the sky so the prediction then is that there is something that looks like this these little speckles represent slight temperature variations in space that are in principle detectable in fact have been detected let me now show you a comparison between the theoretical prediction and the observations so let's take a quick look here the curve theoretical predictions for statistical features of the temperature variations these now are the observations and I'll just sort of stand back holy cow right is your sense that theorists know what they're doing that we have some sense of what things were like in the early universe and we're going to talk a little bit more about this in the discussion a moment let me conclude though with the following final point which will drive our discussion the theory claims that there should be even a more subtle imprint in the microwave background radiation that might in some sense be the true final smoking gun at least according to some for this theory Hill dissenting voices in the conversation but some would say that if we could find the signal about to describe that would really seal the case what's the signal I'm talking about well those quantum tuition as I was mentioning they also affect not just stuff in space but space itself so space itself can undergo quantum ripples quantum jitters right now this is at the microscopic scale if inflation actually happened these guys would be stretched out into longer ripples gravitational waves rippling through the fabric of space and when the temperature variations in the microwave back when are laid down these ripples can have an impact on that relic radiation giving rise to a swirling pattern in something known as the polarization in the microwave background radiation and in March there was an announcement that the swirling pattern had been found and we're going to be talking about that here tonight generated much excitement a lot of controversy we'll try to sort it all out with some of the great experts on the planet today all right so let's bring them on our first guests groundbreaking discovery of the inflationary theory changed the game on how we look at the Big Bang and we've all been playing on his field ever since the prime mover in our modern understanding of cosmology Alan Guth our next guests took Alan goose discoveries a step further when he proposed a new version of inflation even suggested that our universe might not be the only universe one of the most influential cosmologists in the last thirty years please welcome Andrei Linde along with Alan Guth and Andrei Linde our next guest is one of the architects of the inflationary model he also has developed alternative models motivated in part by issues that he has identified with the inflationary theory please welcome from Princeton University Paul Steinhardt our next guest leads Columbia University's experimental cosmology group and has had great impact on understanding of the microwave background radiation please welcome the first dean of science of Columbia University professor of physics amber Miller all right at our final guests for two decades has been designing deploying and operating telescopes at the South Pole and one of them may have found evidence confirming how the universe began certainly has ignited a spirited discussion on the Big Bang and inflation please welcome from Harvard University John Colvin all right so talking a moment we're going to talk about what it is that you announced in March but just to set a little bit of context I just want to get really quick thoughts on how important the discovery of say these ripples in the fabric of space from the Big Bang would be so amber fellow observer of the universe how exciting would it be to confirm that these ripples in the fabric of space have been found Carrie all right good good science right Allen thoughts on that from a theoretical perspective well I agree very important in particular it is very strong confirmation that inflation took place it also allows us to determine for the first time the rate of expansion of the universe at the time of inflation which is a very important number which we otherwise don't know now Andre we sort of know what your reaction is because there's this viral YouTube video which caught your reaction when you first heard this news I almost don't have to ask you but exciting it would be it is one of the confirmations of general theory of relativity at quantum level so it is a next stage it's not just a general theory of relativity but it's quantization and the energies which are spectacular larger than energies which can be reached the highest of all the most powerful accelerators on the earth right now a Paul you know I know that you have somewhat differing views on the inflationary theory today and we're going to come to that but putting that aside for a moment just the actual observation of gravitational waves from the beginning of the universe scale one to ten how cool would it be Oh a hundred hundred there we go be extraordinarily important I don't think we can you jump to the conclusion that it's a comes from inflation yeah I think that's something that that needs to be proven I think there are various possible sources of gravitational ways including things that we might not get of thought of so but it will be it would be an extraordinary gift that Nature gave us a cosmic signal that Nature gave us that will eventually enable us to determine what no where the history of the universe originated from where we're going yep absolutely a very important all right so with that sort of as the context of the importance let's turn to John Kovac and just want to get a sense of the experiment and and what you found so even just to set what it's like how many people work on bicep2 which is the name of the experiment so we've had a very talented team about 45 people of that order working at different institutions lead institutions Caltech Stanford the University of Minnesota my own institution Harvard a lot of the people young people students and postdocs have really dedicated their careers to this and this telescope see a picture of it here it's a very it's a very unusual and very custom-built telescope it's good really doing one thing measuring the polarization of the Cosmic Microwave Background on the specific angular scales in which this theory predicts that gravitational waves would arise and it's a it's a crazy outlandish theory from an experimentalist point of view that we could imagine what's happening at energies so extreme and times so early so the idea that this theory gives us a target something that we can build a machine to go out there and look for and see whether it's there or not motivates you know my team motivates lots of teams that are doing similar work right I'm asking a second to explain some of the terms that that you used and I've been using gravitational waves polarization but what did you find in fact I think we can even show the graph one of the key graphs from your paper right so that's it huh that's it yeah and compare it to the graph that you showed just a minute ago of the beautiful measurements so that the temperature speckles across the sky and how they match up in the theoretical curve you can see the the the level of the data at this stage that we've extract so the so the bump in that curve is the bump in the curve the the excess of the points the black data points yep above the red curve which is below there shows the excess of this swirling pattern in that map above the simplest expectation so can we see the swirling again just to have that picture in mind I think it's C that's right so this is actually slightly different colors than you're used to but the same the same yeah same swirls yep so so those swirls are indicating the polarization that you're talking about and it comes from gravitational waves that have an impact when the CMB is formed a few hundred thousand years after the Big Bang so can you just give us a quick explanation of what polarization is just so that we all know we're talking about so light as I'm sure the whole audience knows is is a it's both a particle and a wave phenomenon so if we think of it as a wave phenomenon it's a disturbance that's in the electric and magnetic fields so as light propagates in a direction the electric field might be aligned in a particular orientation with respect to the way that that light is coming I think we have a little visual can you bring up the polarization video just to write so this is what you're talking about so an electromagnetic wave light and right here we see the the light coming towards the side of the screen and imagine the electric field is represented by the red here and the amplitude of that field is oscillating up and down on a vertical plane so a light wave likes being animated here would be described as a hundred percent polarized completely polarized in the vertical direction so if we go back to the map what we're actually seeing with our telescope is very small degrees of polarization of this early that this light that's coming to us microwave light from the sky the the patterns that we see in this map at each point express the degree of polarization that's coming to a polarization of the light coming to us from that spot on the sky so when you see a vertical bar on that map that actually represents not a hundred-percent polarization of the light but a polarization at the level of typically one part in 30 million ones Oh thirteen if you think of particles of light photons coming to us from that spot in the sky what that means is for every 30 million photons that are coming to us with a horizontal orientation that field you might see 30 million in one on average coming with the vertical orientation extremely faint effects so you need to build a very specialized telescope to be able to teach the size and and the the origin of that polarization that tiny polarization that you're talking about may have come from gravitational waves that originated with in some sense the Big Bang so just quickly gravitational waves I mentioned it briefly my introductory remarks I think we have a little image of it if you can just explain what that is and what a gravitational wave would do sure so a gravitational wow that's a wrong gravitational wave let's hold on so a gravitational wave not nearly that strong passing through the early universe that arises according to this theory of inflation that we've been that we've been given has the potential to distort space-time in the early universe when these microwave photons are being released and that distortion of space-time can be thought of as a stretching and a compression and that can impart a particular polarization to the light that comes to us from that region in space and the geometry of the stretching and compression of a gravitational wave can actually impart a specific swirling pattern to the polarized light as we look at it across the sky that kind of swirling pattern isn't expected to arise from the the other well-known physics that produces polarization of the Cosmic Microwave Background light so how long did it take you to find the state to accumulate this data so the data that you see behind you was collected by the bicep2 team over three years of relentless observations from the South Pole training our telescope on a small patch of sky and you're down there like doing this oh you're like hey turn on the telescope when I was a young student that actually did spend an entire year at the South Pole threw one winner one winner was enough for me yeah but we go down there in the summer months three months of the year you can get in and out of the South Pole Station the National Science Foundation flies us in and out on ski equipped c-130s it's really an amazing adventure and then when the last plane leaves in February we leave behind a small crew and typically one person running each telescope and that person will operate the telescope for the next nine months and we have that telescope trained on that patch of sky collecting as many of those photons as possible because you need an awful lot of them to tease out those really early small effects so three years of data went into that map all right fantastic so the excitement when you made this announcement in March was largely tied to the inflationary theory which suggests that this is the kind of result that you'd expect if the inflation theory is right so I'd like to now place it in context and head back to the discovery of the inflationary theory so Alan I'm going to start with you you you know had a fantastic great breakthrough in the late 1970s and I just want to sort of briefly walk through it so first off in the 1970s what was the state of Big Bang cosmology what were the essential problems and they're actually two that I'd like you to focus on the flatness problem the horizon problem if you just tell us what those are the flatness problem is something that I in fact just learned about almost by coincidence at a lecture I dropped in on given by Bob Dicke from Princeton this problem that has to do with the fine-tuning of the expansion rate of the early universe as Bob Dicke explained it that expansion rate if you think for example of the universe at a time of one second after the instant of creation that expansion rate had to be just right to an accuracy of about 14 decimal places if it was expanding just a little bit faster by one digit and the fourteenth definite place the universe would have swung apart so fast that galaxies would never have a chance to form and if was expanding just a little bit slower again just by one digit in the fourteenth decimal place the universe would have rapidly we collapsed before any galaxies or structures could form and within the conventional Big Bang Theory there was nothing that explained why the expansion rate was what it had to be it just had to be that or else the universe would not look anything like what it does look like and presumably we would not be here yep that's the flatness problem the horizon problem has to do with the uniformity of the observed universe no we're not that used to thinking of the universe as being that uniform we see clumps of galaxies and galaxy clusters but if you averaged over larger scales the universe starts to look amazingly uniform and this uniformity is most striking in the cosmic background radiation astronomers have now very carefully measured the temperature pattern and we've seen fluctuations which we've seen Maps up on the screen here but nonetheless the temperature is in fact uniform to one part in 100 those maps describe very very small fluctuations to men dysley exaggerated so the question is how did the universe get to be so uniform and so uniform so early this cosmic background radiation was released at about 400,000 years after the instant of creation so you can imagine that somehow things smooth themselves out but when you try to calculate you soon realize that within the parameters of the conventional Big Bang Theory that's simply not possible in particular you can imagine tracing back the photons coming from that direction in the sky and similarly to trace back the photons coming from the opposite direction and when you do that calculation you find that at the time of emission those two sources were separated from each other by about a hundred times the distance that life could have traveled up until that time and that means that there's no way that that photon could have known anything about that photon yet somehow they arranged to have the same temperature to an accuracy of one part 100,000 and nobody had the foggiest idea how that could happen and that was the horizon problem so at the risk of this sounding like a seder what was special about the night number 6 1979 it was certain the climax of about a year of my working on this very much influenced by a fellow postdoc at Cornell at the time Henry Tai who's the first person who got me into this in the first place really we were looking at the question of suppression of magnetic monopole production which I won't want to get into now but in any case we were dealing with I pollicis that the universe underwent a tremendous amount of super cooling at a phase transition that certain particle theories predicted would have taken place in the early universe and I went home that night and answered a question which Henry had raised actually which is what effect would this super cooling have on the expansion rate of the and once you write down those equations the answer is actually pretty obvious it has a tremendous effect on the expansion of the universe it drives the universe into this phase of exponential expansion which we now call inflation so this was in your own words a spectacular realization yeah amazing thing you know there's all this you know talk about the NSA and you know sometimes you know it's good stuff we actually got a hold hope you don't mind of they had footage of a nanny cam that you had said I don't mind you bring up the footage so there you are I just wonder did you think it was a breakthrough when like the equation started floating that's always on like when your pen started you know drifting you know the universe is really expanding all it was that that's sort of that's what that's what it's like yeah yeah so so this was you know an amazing moment and we actually having a shot of your notebook if we can bring that up on the screen so there we have it right spectacular realization yeah that's really all unlike the previous film yeah no no I should say the other another film was not real um it's from from a nova program but so there there is what you found and I just want to go a little bit more deeply into what it is that you found so you said the universe supercooled so basically if I understand correctly and I'm just gonna move us along here there is a field that you hypothesize which is kind of a substance that fills space and the idea was that the field was occupying a certain value that was giving an energy that would fill space in fact the energy was such that it could drive this acceleration this outward expansion of space so if we can just show a little picture maybe you can just describe if this is a good description of as I can bring that up so what are we seeing right here okay what we're sitting here is a graph where the horizontal axis is the value of this scalar field that we're studying or how prophesizing and the vertical axis is the energy density that space would have if the field had that value value on the horizontal axis and we really believe that there are very likely scalar fields in nature which behave this way the Higgs field that the standard model looks something like that so what the little ball shows is the possibility that the scalar field could have the value at the bottom of that hill and if it did classically it would stay there forever because it can never have enough energy to get over the hill to get to the lower energy quantum mechanical you can tunnel can tunnel through the barrier I think we can show us this guy there goes right through the barrier so when it turns through then that would be the end against inflation so we just just see it again so the process would be then something like this the fields hanging out at that value and then it tunnels through and that happens very quickly and that's the end of this rapid phase of expansion of the early universe good so you know just to sort of see this in a little bit more detail those of you who don't like equations can't ignore this but so this is the basic math behind this right so what's that equation we're looking at up there that's one of the famous equations derived by Alexander Friedmann in 1922 and if maybe 24 and if what we have on the right hand side if if the energy density and the pressure satisfy that relation then then what happens is a double dot which represents the acceleration of the expansion change the sign normally it's positive normally that equation is dominated by the first term there which is the Greek letter Rho which means mass density but if the pressure is negative which it is for this peculiar state then that quantity Rho plus 3 P over C squared becomes negative and the force of gravity is reversed it magically becomes repulsive instead of attractive and that gives us a solution is equation that any undergraduate or high school kid could work out where the expansion goes faster and faster over time and that then gives rise to the bang so that's the way we want to think about that okay so this was the beginning of the inflationary theory let's just quickly describe for us how to solve the problems that you started off with for why we would look for an alternate theory at all so how does this address the flatness problem okay well there you have some video some some stills that might be useful okay he didn't show me these in advance especially because this came from your book okay but there are multiple explanations some of which are not in my book okay welcome to the one from my book the equations of general relativity themselves which we haven't written entirely here link this expansion rate to the curvature of the universe and the prediction from inflation is that the expansion rate is going to be just the right rate to correspond to a flat universe and given that it's now pretty obvious to see what this next picture is gonna be the sphere is going to get bigger and bigger which is what inflation does assume we're gonna have that and as it gets bigger and bigger or if you look at a fixed size of the image it gets to look flatter and flatter so it's just like the basic reason why the surface of the earth looks flat to us even though we know perfectly well these days that the earth is actually round but as long as you look at a small patch of it it looks flat and for the same reason our patch of universe looks flat to us because we're basically looking for at a very small part of something which on a much larger scale may be curved we really don't know okay for horizon problem we have another little image over here which basically just sets up the problem you're talking about two distant regions in the universe having temperatures that were very very close but if they try to communicate by sending a signal between them you said that if a photon starts to travel say from the patch on the left and it's traveling outward doesn't have enough time to reach the region way over there how therefore till they correlate their temperatures how does inflation address that problem basically idea is very simple inflation inserts into the scenario of the universe a period of gigantic expansion which is just not there in the conventional model without inflation and that means that if you imagine thinking about the region of the universe that we see today and tracing it backwards in time when it goes through this period of inflation it's now contracting rather than expanding this we're following it backwards it means that before inflation the region was vastly smaller than we ever would have thought in the context of conventional cosmology and that means that before inflation there's plenty of time for the universe to smooth out those in density and temperature in exactly the same way as the air in the room smoothes itself out across the lecture hall acquiring an approximately constant temperature constant density those guys are so close that it's easy for them to communicate early on and then then you put and emotion takes over yep and magnifies this tiny region to become large enough to include everything that we currently see so that's the basic idea and just quickly the aftermath of this discovery so here's your paper okay describe this and then we have also here a cool little magazine article Copernicus Galileo Hubble and now Guth I love that right what was that like so this changed everything yeah no it certainly changed everything from my career at before the discovery inflation I had been a postdoc for nine years at four different places and I had a job for one more year after that that had been lined up but beyond that who knew yep and something I was getting offers from all over the full story is that I got an offer from essentially all over accept from MIT which is where I wanted to be I had been a graduate student there and liked it so I finally actually on the advice of a fortune cookie to call him IT and ask if maybe maybe they'd be interested hiring me too since that's of other places seen today and they said yes and I went to MIT and they've been there ever since wow I didn't know that story it's fantastic all right so Andre and Paul in Alan's original version of inflation all these good things happen but they're even Alan had pointed out that there was some some issues and that's when both of you come into the story what was the main issue that needed to be addressed to make this theory fly as far as one would like it to yeah well one can explain it in the following way in Alan's theory the skill field seats in the minimum over the potential and does not move so this looks like exactly like an empty space and when you are talking about empty space then the question is how do you even know that this empty space expands because there is nothing there so the notion of expansion becomes kind of questionable on the form of level this means that there is no preferable coordinate system and in some system actually the universe collapses and then it expands and then when it decays when a tunnels it tunnels in different regions totally inherently and as a result even though the idea how inflation exponential expansion smooth as the universe you need to explain what it's smooth it if it's already smooth if it's vacuum and how it decays simultaneously everywhere so the same problem of simultaneous decay requires some marks on what expands to say that it is simultaneous so this is the basic reason why you have a problem with this simply so what it say you came up with a way of addressing this yeah it was actually it was like that you know you have this minimum like Allen and then the question was do you really tunnel directly to the absolute minimum or not and at that time I was just running my computer and checking how it goes and I have seen that actually sometimes you're tunneling almost horizontally and then for wool for a long time you are rolling down and then when you are rolling down then the universe continued expanding almost exponentially somewhat like we're saying here yeah can we run that one again right rather than having it sitting in some yeah little minimum you're imagining a shape more like this yes and that addresses the issues all right and at that time when I first realized that this is possible I thought that maybe I'm just dreaming making a mistake because it could not be real so a cold at night and this was in summer 81 I counted at night one of my colleagues and I asked him we whether you thought about anything like that and because I was afraid to wake up my family I was colleague sitting at night in the restroom with the telephone calling so had to wake up the children and I asked him and he said nope I didn't think about it I say oh well then I hang up and they waked up my wife and totally I know how the universe was born [Laughter] so Paul you also were inspired to work on inflationary ideas around the same time what did you find something similar to this in mind yeah well first of all I should say that the whole reason why I entered cosmology was because I was privileged to hear a talk by Alan one of the first talks he gave on inflationary cosmology I walked in the room as a as a young postdoc never having taken a course on cosmology never having studied it but in the course of one hour I was converted it was I always described it as the most inspiring and most depressing talk I ever heard because for most the talk Alan was telling this wonderful story just how he described how there were these fundamental problems to be solved and and and how inflation could potentially solve them but then in the very last five minutes of the talk he explained how the idea failed that although you managed to get the field trapped in this minimum that you did that was shown there although would occasionally tunnel it would only tunnel out in a tiny region a tiny bubble of empty space nothing that would contain the stars and galaxies that we would see and that occasionally maybe these bubbles would collide but that would not lead produce enough stuff to make the universe that we observed so he began the solution of the problem but there was a sticking point how do you ever end this inflation in a what we now call a graceful way in a smooth way that leaves a universe which is filled with the matter and radiation that we see so I remember sitting in the room after everyone I just was stunned by this talk I just sat and I think I was like the third or fourth row back and everyone was leaving and I was just thinking oh there's got to be a solution to this problem this is too sweet an idea to let's us stand there so so I thought well I'll spend a few weeks working on you know learning a little bit of cosmology and doing this and I can go back to what I normally do but in fact they haven't stopped working on cosmology ever since and I guess my inspiration was I was trying to look for different solutions to get around this problem of getting caught by this energy barrier and the process of reading about phase transitions supercooling I've discovered there was a different kind of phase transition that people that was not so well known certainly not in the highness G or cosmology community which isn't the kind that occurs by this tunneling but it's what's called Aspen nodal transition has a technical name it's known in the metallurgy literature quite a bit but it was not known in in even most condensed matter physicists don't know if that thoroughly and and that turns out to be a picture in which the phase transition occurs that in such a way that as you supercool the barrier disappears and you can end up with this flat plateau that we saw here and that was the I swear the idea came from that there was this alternative phase transition I have to say that III was not quite as excited as Andre was when I when I made this so you weren't in the bathroom when you did in the bathroom but there was there was there was a feature there was a feature that bothered me then and continues to bother me now which is to have this special kind of phase transition you have to tune the parameters in the theory rather specially so your goal is to explain naturally why certain things occur but you're doing it at a price of arranging this phase transition sort of dialing the knobs that make that curve it's just so away and that's one of the problems that remains with us today now Andre you've thought about this this problem of Tony you've you have argued that they're more general shapes that can still give rise to inflation and so tell us a little bit about chaotic inflation well that was a continuation of the story so this was a first Allen's model than our model of new inflation and then this model of new inflation survived for about a year and then we had some problem even with this new model and the problem was well with many different aspects of it but it stamped in particular from our assumption that first there was this hot Big Bang then were these phase transitions then there was a super cooling the end of this tunneling etc and all of this set of things it was very difficult to much together and what happened later is that I realized that you don't necessarily need it because instead of all of these strange potential withstanding etcetera you can just have simplest parabolic potential and then the scale yeah right oh my god well so the scalar field in these potential and interestingly in normal kind of previously studied models where the field stuck and the minimum for a while then here there's maybe not even minimum you may have it temporarily does not matter and you may not need any phase transitions and supercooling anything but what happens is that when you are solving Einstein equations together with the equation for the scalar field and explaining universe you find out that there is a strong friction which stops the field from rapidly running down it's like the universe helps the scalar field please stay here for a while no no I want to go down please stay here forever so when the scalar fields a base then it stays for a while at approximately the same height without any need to some support like that just like that on the wall and during this time because the amplitude of the scalar field almost does not change then the universe expands almost exponentially now this thing almost doesn't change is extremely important if the shape of the potential such that it's very very curved no inflation rolls down too fast if it is very very flat there is an opposite danger the speed of the motion of the field becomes very slow like in the original model way just totally flat and then what happens is that perturbations of density which wait just a moment in the beginning they are too large so you must be just the golden medium between that not too steep not the flat just right then the universe gives you well galaxies which you want to do them now another feature which which both it I think all of you have played a part in is that we have these models of inflation so you've got this field filling space energy is giving rise to this repulsive gravity pushing everything apart but it's very hard to get it to fully end which suggests that there may be other realms other regions that are undergoing this expansion to which in poetic language can be spoken of as other universes so tell anybody wants to jump in on that one well I can say a little just using this one potential which shown here so naturally you would expect that this is what you go you just go down you go down you go down straight forward but you'll notice that maybe you can hear it again you see that potential you know she notices that this dot was jumping here so what this jump means well during expansion of the universe there are tiny tiny quantum fluctuations of the skill field they are tiny but the universe expands them and then the universe expands new quantum fluctuations are produced and a new quantification sometimes not always not everywhere this quantifications bring the scale field upwards again and then the universe expands scale Hill Goes Down and in some places it is brought back again and when it happens in those parts of the universe where the scalar field jumps back again the speed of expansion becomes as large as it was initially and then this part becomes separate exponential large part of the universe so it looks like the universe self reproduces itself this is like if you think about what Greeks told us here is our universe and this is perfect sphere at least we'll try to understand why it is perfect so now that we understood that it is perfect this quantum fluctuations make it slightly imperfect and it's like imperfections sometimes produce galaxies as we will learn later and sometimes it produces new pieces of the universe which are also expanding and the universe becomes a fractal so it is eternally growing fractal tree consisting of new universes and new universes producing like we have a little bit in that can you skip ahead to the eternal inflation video just to give a sense of what the universe would look like that'd be a single Big Bang that's the decay of the inflation in one place so each of these bubbles here floating in this background of Lin photon field would be one of the universes that you're talking about with our universe just being one in this big vast collection so that's the place that we've gotten to with these ideas of inflation and to bring in the observers as I'd like to do in a moment I want to turn now to the evidence that we have for these ideas where the argument usually comes from the microwave background radiation and these fluctuations so I want to turn to it just a quick discussion of that all of you guys have had a hand in this Allen and Paul I think there was this famous workshop right what was it called enough field workers have a definite one so tell us what was going on there okay this was the summer of 1982 shortly after this new inflationary model is invented by Andhra and Paul and Andy Albrecht and people were beginning to think about the question of how uniform should the universe be and for a while a number of us were very worried that inflation because it just stretches everything to make it smooth we produce a universe that would be completely smooth and if it started out completely smooth there'd really be no way that galaxies perform so eventually the idea started circulating around the community in my local group that kind of started with Stephen Hawking although I later learned the idea goes all the way back to Andrei Sakharov much earlier but the idea was that maybe quantum theory can be responsible for these fluctuations and at first that idea sounds very weird because we always think of quantum theory is describing things that are very very small now we're trying to describe the Galactic structure of the universe but nonetheless when you think about it carefully it certainly initially had the germ of working because sensation has this wonderful property of stretching these tiny quantum fluctuations from very small scales to bring them up to macroscopic and cosmological scales and at this Nuffield workshop was for different groups I guess were working on the question of how to actually calculate these density perturbations and that the beginning of the conference I think maybe stair Vince key knew the right answer the rest of us didn't but during the course of the conference we gradually came up with answers compared them a lot of them disagreed with each other we were arguing like mad for it was a three-week conference but finally by the end we all agreed on the picture and then we all published our separate papers with basically the same conclusions and all you were you're oh yeah our group was one of them we were trying to use a method a special method that was developed by Jim bar Dean of what's called a gauge invariant method and there was an important contribution because I think it was the the method that's the most reliable sure method of doing a calculation in general relativity there's this subtlety that when you're looking for a lump or an excess your the question we're trying to address is where are there lumps of energy or lumps and temperature yep and just distinguishing that from simply a course of coordinates it reach a different choice of coordinates and general relativity is a is a difficult mathematical challenge that it was solved by Jim and and having that powerful method and have all having that method get the same results and converge with these other results to give the same numerical answer I think made us all really excited at the end of the conference that we had actually nailed the question that we came into the conference worrying that the quantum fluctuations could destroy the inflationary theory it could be that you did the calculation found the quantum fluctuations and found that they gave us variation with space that was incompatible with things we knew instead what we found was something in between we found that the initial models that we were thinking of had the right shapes of hot spots and cold spots but the amplitudes the degree of hotness and coldness was way too strong and but by the end of the meeting once we understood how this mechanism worked for producing the fluctuations we knew what to do we knew how to change those inflationary potentials to inflate change it in order to now makes it which would give them not only the right number of hot spots and cold spots not just the right distribution but also the degree of hotness and coldness it came at a price again that we have to still live with today which is you again needed to do even more additional fine-tuning of the parameters than before so even Andres favorite model of that cut potential has to be super fine-tuned by 15 orders of magnitude in order to we're going to come back come back don't answer just now we have something to look for right so you guys have now made predictions and thank you he's never done that so amber so now now there's something to look for and just give it a sense before these ideas what was the state of observational cosmology and people sort of know what to look for is this sort of a turning point now there's something to shoot for well before inflation you still we still have this idea of the hot Big Bang YUM so there is something to look for there so the idea is if the universe started hot and dense however we got to the hot and dense point if it started hot and dense we should see this Cosmic Microwave Background so that's what Brian was talking about at the beginning where Penzias and Wilson discovered that there is in fact the Cosmic Microwave Background that had been predicted in advance and then following that initial discovery the COBE satellite then demonstrated that not only was the hot Big Bang correct but in fact the statistical properties of what you would expect to see in that data were also correct and in particular the hot plasma emits as a what is called a blackbody it's a type of emission that depends only on the temperature of the plasma so it's an enormous ly simple system it's not difficult and you can go and predict what you should see and you can measure it and it turned out that what Kobe measured was that the prediction and the measurement were so close to each other that if you draw the theoretical curve and you plot the data on top of the theoretical curve unlike the data that Brian for the fluctuations that temperature alone you can't even tell the difference between the theoretical curve and the actual measurement so this was this was the first spectacular demonstration right track so that that was spectacular discover the next step then it did look for the fluctuations and how do you how do you how do you do that you go out and you observe the Cosmic Microwave Background and at every step here we're just trying to get better at doing that so we're trying to measure it more precisely and the game is that you're always trying to develop the latest technology you're pushing the boundaries this is a hard thing to do so you need very sensitive instruments you need very well controlled instruments so it isn't just about raw sensitivity you need to design your instruments so the signal that you see you're really really sure it didn't originate in your instrument so that's a really important point that sometimes you get lost when you're talking about this instruments really really need to be very specially designed and then the other thing you worry about is you want to make sure that when you're observing what you think is the Cosmic Microwave Background you're indeed observing the Cosmic Microwave Background you're not observing something that lives in our galaxy or between our galaxy and the microwave background remember that when you're observing the microwave background you're observing universe as it was when it was only 380,000 years old which means that the light was traveling throughout the entire history of the universe until it crashes into your detectors so if it came through anything else that could have changed the character or if anything between the microwave background and your detectors is itself emitting it can complicate that signal fortunately there are clever ways that you can design your instruments to tell the difference between the signal in the front and the signal in the back but you have to do that right - so the game is to design these instruments precisely and now analyze your data very carefully so that you're sure that what you're seeing is what you think you're seeing which are seeing in the background in these pictures is another approach so there are three primary approaches to measuring the Cosmic Microwave Background there are the ground-based telescopes like the ones that John was talking about there are balloon born experiments like the one you see here they're the satellites you saw a picture of minute ago both Kobe and W map satellites and sometimes for the gold standard they are very expensive you don't get to fly them all the time the other issue with satellites though is that you have to lock in the technology are gonna fly in a satellite years before the satellite actually launches and the technology development has been proceeding so quickly and for ground-based experiments and balloon borne experiments part of the game is you grab that technology when it is hot off the press or you're involved in developing it and testing it and then you're allowed in a balloon board an experiment or a ground-based experiment to put the technology on the experiment and try it whereas the satellite you have to be much more careful so the main difference between balloon borne and ground-based experiments as I discovered when I was a graduate student is if you're really saying you will choose to work on a ground-based experiment so I've naturally in the last several years been working on a balloon for an experiment instead if you're really brave you were gonna blow that's kind so the the goal of working on a Bloomberg experiment other than being not sane this is my experiment called ebox being launched roughly a year ago also from Antarctica so an article's the magic place to do this in in John's case because it's a really great place to observe in our case because it's a really place great place to get up over the atmosphere so these balloons fly and about 130,000 feet the reason to fly from Antarctica is not that there's anything special about the location per se but that is the only place in the world where you're allowed to go and fly for a long time and the winds are circumpolar near the poles you could do this in principle in the north but Russia doesn't like it when the u.s. flies equipment I can't imagine why they'd have a problem with that so in Antarctica you're allowed to do this so you also get down on the plains with the skis and and do something crazy like build your experiment and then this thing you've been working on for five to seven years the folks and NASA say okay science team hands off your heart goes into your throat and you know that all the stuff that on the ground that you could fix when when not if when it breaks you don't get to fix it right so this is why it's insane to do this the reason one would do it even though it's insane is that you can observe it frequencies that are very difficult to observe at from the ground so on the ground the atmosphere is transparent in some frequency bands or relatively transparent and not all frequency bands and if you want to discriminate between emission from something like dust in our own galaxy and microwave background radiation it's nice to be able to measure at a frequency where dust is the stronger thing that you expect to see as well as measure at a frequency where the microwave background is the thing that is the strongest thing you expect to see compare those two signals and then you can subtract the dust and that's something you can do from a balloon much more easily than you can do from the ground so when you put it all together through all these wondrous devices satellites balloon ground-based telescopes the relationship between the fluctuations predicted and the fluctuations measured how closely do they match you showed the data so here this is temperature flexure yes if this is actually just sort of a schematic why don't we actually move forward to the actual real graph right there so just what are we seeing here so this is a what's called an angular power spectrum but really you can think of it as how much fluctuation power you see on that map of fluctuations as you look at different characteristic scales so if you think of blobs of a big blobs how much big blob this you see is measured by what you see at the far left and as you go to characteristic separations between smaller and smaller and smaller scale fluctuations you move over there toward the right the green curve is the theoretical prediction and the red curve is what the data actually measures and what's interesting if you look down the theoretical predictions very precise on smaller scales and it's not so precise on the larger scale there's some uncertainty and that has to do with the fact that we only have one universe to observe so if you're trying to characterize what you would predict from the very largest scales you don't have enough even theoretical information to be able to say what exactly it should look like on the very largest scales so that it's called cosmic variance it's just something we we cannot measure more than that the bottom line is a pretty impressive agreement between spectacular and that's John now where you come in so this is the temperature fluctuations you go one step further and just remind us again just so we can see the next data just remind us of you can put the swirly data back on if you will so this is the experiment where you're not just looking at temperature variations but this more subtle signature the polarization the vibrational direction of the light right that's so at different spots in the sky different blobs different characteristic scales you're not just counting up how many more photons you see in that patch versus that you're measuring the alignment of the electric field and you're counting up whether you see an excess of one alignment over the other that's what these these lines on this map represents we map out a patch of the sky and in this case it's a small patch of the sky about 1% of the sky and we tease out the pattern of these alignments across that patch so this basically takes us up to March 17 2014 right so we've marched through the theory the observations and it seems like a pretty strong story but now we want to move on to the next chapter of our discussion here where we're going to examine the case a little bit more closely for the for the remainder of the time that we have here and Paul I want to now give you time to speak your mind on why don't we start with with the observation so there's been a lot of discussion in in the community and be good to just have a friendly discussion out here of are we certain that the polarization is have been found are originating with the creation event inflationary expansion or could it be something else of Paul thoughts on that and then John let you answer of course good actually I'd like to hear John's answer first because there has been a lot of discussion and I don't know what the current answer is but does want me just raise the issue because I don't know that every if you guys listen to the physics conversation probably not that my I can I can put on the table just to help your discussion what the issue is and then you can pick it up from there because I just I just don't know what the bicep2 groups view is on things and they you should be speaking for that so the issue has been Jessica issue that amber brought up we want to make sure that the signal we're seeing that the swirly pattern is really due to something that's happening in the most distant parts of the universe the Cosmic Microwave Background and not due to say to the effects of lensing of galaxies in the foreground or dust in our own galaxy or effects in the atmosphere or even effects in the telescope which can mix which can turn a pattern which has no and any one of those things can take patterns which have no swirls and turn them into a swirling pattern so you you know part of the challenge of the team that they work really hard to do is to make sure they can't you know they've really checked all those effects and you know they're just beginning to roll out their data and their analysis and there isn't it I haven't seen you know I haven't seen for example a systematics paper that helps us analyze similars effects but one of the effects that can be analyzed from the outside is partially is you know the degree which dust would contribute a b-mode signal of its own Swilly signal of its own and so people have tried to use different kinds of data and different kinds of models of dust to estimate what that so-called foreground that dust foreground would be and and so did the bicep2 team try to do the same but the results disagree i think that you know the results of group at Princeton led by Raphael flogger for example looking at all the desk models same dust models that they that the that the bicep2 team used in their analysis concludes that actually you could account for most or perhaps all of the signals that they've observed in this in terms of swirly patterns not due to anything to do with the microwave background not due to anything to do with gravitational waves but might be due entirely to dust in the foreground so John we need to resolve yeah so the question is how do confident re where do things stand the swirls do they come from quantum fluctuations stretched by inflationary expansion and printing on the microwave background or could it be something else yeah so the answer the question as you put it originally yeah are we certain that these swirling patterns that we see on the sky are actually coming from quantum fluctuations that are telling us about the inflationary theory the answer is no we're not certain we the way that science works is we always need follow-up we need confirmation we need more data what we said in March was that we as we reported that pattern that our telescope had observed over three years and we had analyzed there were four years of the data that we were very confident looking at the statistics of our data set that that pattern is not there by random chance yes extremely confident that there was a high significance detection of --mode polarization the swirling pattern on the sky yeah and in fact that was the title of the paper that we chose a section of emote polarization at degree angular scales so we did an analysis a thorough analysis and we're looking forward to rolling out all of the papers but the analysis was actually complete and it's in the result paper on the systematics effects that we looked at in our instrument to convince ourselves that this was not a spurious effect that arose some when our instrument and we feel very confident of that statement I think it's it's it's unlikely that there is a systemic effect that we somehow missed and all the cross-checks that we've done in four years of analysis yeah this data and we analyzed the data with a great deal of skepticism when we saw a signal starting to emerge from this that was an unexpected signal for our team this this swirling pattern had a amplitude that was much larger than frankly people were expecting to see one so the the last question of what is the interpretation of this signal a likely interpretation what our team did is we compared it the signal and many ways to what the expectations were for emission from our galaxy we looked at radio emission so not dust emission and we think we can very confidently rule that out there are a lot of discussions including from the Princeton group about some contribution from from radio emission synchrotron emission we actually think that the the data from that beautiful w map satellite indicates that's really negligible so you know we think that people should look closely at that but we think people can generally agree based on the data in hand that that's not significant the galactic dust there's a lot more uncertainty so we said that when we rolled out the the the result in March but we looked at it in as many different ways as we could with the data at hand so we compared the amplitude of our signal to the expected level given historical projections of how much dust power there ought to be and our patch and I don't think that that's in dispute that all of those projections were quite a bit lower than the signal that we saw the the the recent controversy I think comes from the interpretation of what new information has been brought to this problem from the new Planck satellite and data that they're only starting to show us now on whether the the polarization of this dust emission might be higher than people have previously assumed so we look when will that data when will that Planck data be a well we'd like to know I think we'd all like to know we're very eager to see it but so far the plunk I heard three weeks actually I heard over breakfast yeah two days ago I think you were there right you were there I heard is that another thing that would be great no we're very eager to see what they have to to say about the polarization in our region because up until now what they've shown us actually blanked out that region in their published paper a few weeks ago because they said that the uncertainties were very high in their data set on what the polarized dust emission looks like there but we we looked at the data in several other ways we looked at its spatial distribution across our field there was no evidence for the kinds of unevenness that we would to see from Glock to dust we looked at the pattern of our B modes and it doesn't match the pattern of any buddies predicted pattern of dust polarization and we looked at the evidence that we have which right now is very limited in the the the color or the different frequency composition the signal that we saw and although it's not a very significant result it favors CMB and disfavors dust and we reported all of those things that I think we reported them pretty pretty carefully and pretty accurately and then that results in March was that we concluded and many people that looked at the data agreed that the most likely interpretation is that it's probably not dust that it's probably dominated by inflation air gravitational waves my favorite comments at the time of our March 17th release was from somebody who's not in our team a theorist Mark kamionkowski he said it quacks like a duck a lot of mine is whatever uncertainty there is say within a year but probably less there'll be other data that will allow us to sort it all that's right we're really excited a beleaguered about the new data that's going to be brought to bear from the Planck satellite we're looking forward to comparing our maps directly and doing a joint analysis that's going to be really powerful other groups including Amber's are working really really hard on producing more datasets and our own team already has a lot more new data that we're eager to get out there and we're eager to see the answer we're eager to see how the data breaks as much as everybody else's yep great can I ask you because you know this is this announcement really created a huge impact in the field and it had an impact on people's lives and people's careers on grants and the attitudes of the public at large so it's a really you know I think it made us a makes us appreciate that the science we do really has a huge impact and people are very interested in it all over the world I think you know but and since that announcement there has been a lot of discussion about what are possible sources of ultra alternate explanations for the same data set and I appreciate what John said but you know now that you've had this two months of experience getting some feedback what is the in March 17 there was a very clear strong statement in the paper and in the announcement that gravitational waves had been observed and there were statements about you know a lot of high confidence levels what would you say today what is the right way to characterize it fair way to characterize the situation as you see it today I think the way that we characterize the situation now is the same way that we characterized it in March and we did not say in the paper that gravitational waves had been observed we said the simplest and most economical explanation for the data that we were reporting was gravitational you know I'm sorry but the your last line in your paper was quite dramatic that the error had apparently begun so clearly that's right no no it's okay so listen I think that we as scientists don't need to dumb down the conversation for the sake of the no let's want to make sure you say qualifying it that's fine we were careful to qualify it and and I think it's important as we as we report our scientific results and that those get discussed in the public that we not pretend that things are always black or white that uncertainty is either zero or a hundred percent so as we reported the results and I think most of what I saw written about our results was actually on target in that sense that what was being presented was evidence inflation in favor of gravitational waves the confidence level with what confidence that would you express it well I wouldn't have confidence should we often express that in science in terms of percentage confidence levels or Sigma or you know and there's some statements like that in a paper so you know looking back at looking at the current situation how you see it now but you say is the same as seen then how would you express it how would you best express it I think that we express it by explaining the different lines of argument that we have in which the data right now don't match up with the expectations from dust combining those different lines of arguments quantitatively is as difficult as combining the lines of argument favoring inflation versus alternatives of inflation right now because their model dependent statements really what your preconceived notions are of what a reasonable model of dust ought to be in the absence of data so III think you know there extrapolations from regimes where we understand what the uncertainties are to regimes where people can actually disagree on what reasonable guesses are so the best that we can do in a situation like that as a scientist is to lay out all of the evidence and to allow people to discuss it I think we did that very fairly so Paul you also have expressed some reservations even though you've played a pivotal role in the development of the inflationary theory with the theory itself you've got only about about nine minutes left but you want it do you want to have a brief conversation about some of those concerns and allow these gentlemen over here - sure sure I'll try to be brief so to help out yeah I think there are I think the major concern about the inflationary theory to me is that we've learned over the last 30 years about inflation is it's extraordinary flexibility in terms of what it can produce we originally thought of it as a theory which very simply smooth flattens the universe and leaves a very special spectrum of perturbations behind and we've discovered as it has at least three different levels of flexibility that allow you to vary what comes out arbitrarily to begin with it turns out that in its extraordinary results are extraordinarily sensitive to the initial conditions what exactly happens coming out of the Big Bang we thought that inflation would be robust and used to you know automatically take over and produce the bang as shown in your beautiful movies we've learned that it actually only works if you have rather special initial conditions go away from those special conditions and then the output changes a second degree of flexibility is you've been showing different curves of this inflationary field and there's you know some choices and how you shape that that curve and as you change that curve you change what the predictions are Andrei has recently written a paper in which he continuously changes the parameters and continuously changes the output showing that in fact you can get a whole range of possible predictions from the theory not something specific a whole range and then thirdly even if you fix it those first two things I'd love you to fix the initial conditions I allow you to fix any particular shape that you want then you end up with the third issue which is the multiverse you don't end up with a uniform universe which has all the same properties physical properties and cosmological properties you end up with the universe which is a multiverse which is a patchwork of different patches which span every conceivable cosmological possibility so yes some are flat like our universe like we were hoping for but some are not in fact an infinite number of these patches are not an infinite number we'll have a beautiful simple microwave background what we observe but an infinite number will not etcetera etcetera so in fact there's no since every combination of things can happen in this multiverse the there's no prediction in such a theory there's so much flexibility of theory which is to say there's no test you can make of the theory they would allow you to disprove it now that's an important line when you cross in science and you get to a point and then a theory reaches a point where you cannot conceive the test that would rule it out then that theory crosses from conventional science that we've planted and practice over you know the last hundred years into a different realm and some people think that's ok I'm conservative I think that from my point of view that is you know takes you past science into something that I would call metaphysics and makes the theory you know we would call scientifically meaningless because you can't just prove it all right Andre you've been extraordinarily well behaved alan run to any thoughts on that nothing speechless that was good let me start by commenting about Paul's most recent comment about testability I think anybody who's looked seriously at the history of science realizes that the old popper idea that theories are falsifiable and you test them and test them test them and then you discover an experiment that doesn't work in the medley occur then the theory is falsified that's just not the way science happen rather science is an arena of competing ideas and right now inflation is by far the most widespread idea in cosmology but if somebody comes up with another idea people will start comparing the two and it's the preponderance of evidence that ultimately determines which theory survives which theories dies and so far inflation just beautifully fits all of the day that we have so it's it's striving and as part of that confidence come from the fact that the initial calculations were done you know in a single universe and you got amazing agreement we've seen it between the data and the theory so it was really a prediction not a post diction that to me feels impressive and it means that you know I understand the issues that Paul's raising Paula I've had a lot of conversations we had a email exchange that went on I don't know like a year back and forth the battle I was looking at the other day but it still feels that this is gotta have some truth in it how can you have that agreement is that part of what drives your confidence oh yeah absolutely absolutely and maybe I should also clarify that inflation is not a unique theory which is really part of what Paul was talking about inflation is really a general idea you know we showed you these curves but those are just typical curves so it is true as Paul says that inflation is not a unique theory but a class of theories but nonetheless what we found so far is that the simplest versions of inflation are the ones that fit the data beautifully the ones that were graphing against on these graphs is that we're showing you so we haven't had to add any bells and whistles and look at extremely exotic versions of inflation in order to fit the data it just looks like a beautiful fit - beautiful I would say to have much chance of not being on the right track yes I can well not be playing directly because it would be well lengthy I will just give two citations I think that they're from Churchill something well analogy between democracy and inflation so democracy is the worst possible form of God except for all others that have been tried and then another and then another one that sometimes well people eventually come to right decision only after trying alternatives so that's exactly what is going on right now you know we're trying all the aterna give all the attorneys for quite a while many possibilities of alternative solution of all existing problems have been proposed in particular by Paul and I've studied many of them and every single one which I have been able to check everything single on which I was able to check this does not mean that every single one because there are many but all of them did not work in the end so this may be just rule I was unlucky or maybe there was something wrong in the way we're testing but this pattern repeats and repeats and repeats and every year we have another alternative which is actually encouraging on the other hand yes it sounds like something very strange is going on previously we were in the hunt of the wild goose right okay so now in the hunt of quacking duck certainly there is a lot of progress but what I can say independently of those who is going to win who is going to lose I just feel there's something in the atmosphere something happening right now that was 30 years ago all of us we're developing one kind of theories we were extremely exciting because we had this feeling very similar to what you told when talking about Einstein that Lord could not make these mistakes etcetera and I remember very vividly thinking for myself I'm not a religious person but I formulated that for me like that God would make a stupid mistake missing an opportunity like that and I just cannot believe that he would do it so that was theoretical and on the other hand at that time it was kind of unbelievable that we will come to experimental tests of all of this although this wonderful curves tested by Planck satellite it's magnificent I remember how I was boarding the airplane and coming to United States from Geneva at the time when this well perturbations have been announced it and so my wife sent me a message and I've been getting it on my cell phone which I borrowed from my wife yeah so she sent me no non-gaussian e that is something which everybody expected everybody expected that right now 99% of an inflationary theories will be dead because one satellite is going to find some specific not pleasant feature of these perturbations and she said no non-gaussian ET i am downloading 30 papers by plunk issued just right now as i am boarding well and then I am reading all of this during my flight two years and I feel myself just I'm I was almost actually I was physically crying at that time I'm looking at this this was totally spectacular now we're having different set of evidences we do not know yet in which direction it will all go we know that one way or another disagreement agreement we will eventually reach some consensus about this that's how science work is sometimes painful it sometimes really really hurt okay but but on the other hand I found myself all the time repeating what we just I just noticed that this I'm repeating when when you hear somebody else say does not matter but when you see here yourselves in fantastically interesting then I go out home I return back from the lectures i repeating well not so fantastically interesting we're living in the times when we're stimulated about all of these experimental discoveries and about theoretical development into something which sooner or later will be resolved in something beautiful I am sure I just can't congratulate everybody who participates in this because it's such a beauty contest whoever wins it it is a big way [Applause] well thank you we uh we unfortunately are at a time this has been a delightful conversation I think the point you make is a great man it is just astounding that we can sit here and seriously talk about what happened a trillionth of a trillionth of a trillionth of a second after the beginning we can talk about it observational II theoretically I mean it truly is the golden age of cosmology so please join me in thanking you [Applause]

Channel: World Science Festival

Views: 328,679

Rating: 4.7275162 out of 5

Keywords: Ripples From The Big Bang, Listening to the Beginning of Time, BICEP2, CMB, Andrei Linde, Alan Guth, Amber Miller, John Kovac, Paul Steinhardt, Brian Greene, universe, inflation, cosmological, inflationary theory, cosmic background radiation, gravitational waves, ripples in space-time, New York City, NYC, world science festival, full program, World, Science, Festival, 2014, Big Ideas Series

Id: 70Y1Dri0umI

Length: 95min 18sec (5718 seconds)

Published: Thu Jun 26 2014