10. The Universe and Three Examples MIT 8.224 Exploring Black Holes

welcome to exploring black holes we're very pleased this evening to have Professor Alan Guth of MIT to speak to us about cosmological models Professor Guth is an alumnist of MIT he did both his undergraduate and graduate degrees here as a student in particle physics he re-entered MIT after re-entering after entering the subject of of cosmology with his invention and discovery of the inflationary Universe model having presented one model for the universe Professor Guth will tonight present three in it talk universe and three examples uh the reason for three examples by the way is that three sounds so much better than two that Universe in two example sounded so dumb so anyway the the main part of talk will in fact be about two examples namely the conventional Big Bang model without inflation and the inflationary model uh but if we have time at the end just to be true to the title uh I will talk a little bit about the possibility of creating a universe in laboratory so a man-made universe or a woman-made universe uh will be the Third Kind see if this works yeah okay uh so I want to begin by describing uh the conventional Big Bang Theory uh which really began with the work of of Albert Einstein uh Einstein invented his theory of general relativity in 1916 and then immediately set out to uh try to figure out the consequences of general relativity for the universe and he immediately discovered uh that he ran into trouble when he tried to build the kind of model of the universe that he believed was the right one namely a static model uh throughout history I guess from at least going back to Newton I guess maybe the Greeks as well uh people had thought the universe was static there was no evidence yet at this time that the Universe was expanding this was before Hubble's work uh so Einstein made the same assumption as everybody else who looked up in the Sky Stars seemed stationary uh decided we were living in a static Universe uh but when he applied his equations of of gravity he discovered something which at first surprised him although later he realized it was really true in newtonium mechanics as well but uh Newton had actually considered this question but had talked himself out of the right answer uh the point is simply though that gravity is attractive so if you try to build a model where Point masses are suspended uniformly in space going all the way out to infinity or a finite model either way uh you have the problem that everything attracts everything else and it doesn't remain static everything collapses uh and Einstein found this to be an unavoidable consequence of the original form of his theory of general relativity but he was still convinced the universe was static and he figured out a way to uh to modify it uh and he introduced what he called the cosmological term uh which was an extra term in the equations that described how the Einstein field equations the equation that described how gravitational fields are created by matter and by adjusting the coefficient of this term which he called the cosmological constant to have just the right value uh he could create a repulsive force that would suspend the universe uh against the collapse that it would otherwise undergo and he was then able to succeed in constructing a static model of the universe now all this disappeared really uh in 1929 uh with the discovery by Hubble uh that the Universe was in fact not static but was expanding uh it's probably a little unfair to give credit only to Hubble slier for example had measured a a red shift for a large number of galaxies before Hubble uh got into it but Hub was the one who codified it uh who codified this expansion pattern into what we now know as Hubble's Law the statement that on average distant galaxies are receding from us uh with a velocity which is equal to a number which we call hubbles constant he didn't um times the distance to the Galaxy now this number H is uh not really a constant uh I've always thought the astronomers call it a constant because it's essentially constant over the lifetime of an astronomer um but it certainly changes as the universe evolves uh this transparent is actually a little bit old I think now we we probably have a better idea of of what it is than the somewhat large R 60 to 80 although I guess that's probably a two standard deviation estimate of there or something like that uh the best astronomical value comes from the uh Hubble Space Telescope key project which came up with a number of 72 Plus orus 8 kilometers per second per Mega parac uh this number is now largely confirmed by U precise measurements of the cosmic background radiation which can also be bit to the value of Hubble constant come up with numbers there are very much in the same range uh once you discover that everything seems to be moving away from you uh it it gives you something of the feeling of a Tomic Universe where we're at the center and everything is moving radially outward from us uh but as you're probably aware that's not the way modern cosmologists look at the world uh instead there's a much simpler and more uniform explanation for Hubble's Law how did that happen um and that is the idea of homogeneous expansion uh what I've shown here uh is an attempt to represent a part of the universe and three successive snapshots uh where each snapshot is a photographic blow up of the previous snapshot and that's essentially How the Universe expands uh now if you think about it in a in a photographic blowup uh all distances increased by the same percentage so you can imagine yourself living on any one of the dots in this picture which are supposed to represent galaxies in some crude way uh and what you would see is you would see all the other galaxies moving away from you because all distances are increasing and you consider yourself to be at rest and furthermore you directly get out Hubble's Law that the velocity is proportional to the distance uh because all distances increase by the same percentage as you go from one picture to the next that means the bigger the original distance the bigger the change the distance and going from one picture to the next hence the bigger the velocity uh so this hubbles law gives rise very naturally to this picture of a homogeneous expanding Universe uh the easiest way to describe such a universe as you may have already discussed in this class I don't know is to introduce a scale factor so you just pick one of these pictures and call that the map of the universe uh and you put coordinates on it and I've shown coordinates on all of them the coordinates expand with the picture which is what we have in mind uh so you can just look at one picture forget the others they're all copies of each other's anyway uh and you could describe the expansion uh just by changing the scale factor of the map uh so you say that the physical distance is equal to a scale factor which changes with time times the number of notches that You' measure on on the map uh and that way you can use one map and all of the expansion is taken care of just by the scale factor and that of course allows you to write simple equations to describe how that scale factor evolves uh if want to extrapolate this picture backwards uh one finds concludes immediately that the early Universe must have been extraordinarily dense and you know that when you compress a gas it gets hotter uh and that means that the early Universe was much much hotter than the present universe and one can infer that the gas that filled the early Universe was extraordinarily hot if you went back far enough uh and if that's the case you'd expect to see some kind of a glow of this hot matter from the Earl Universe uh surviving in the universe today and and you know back in the middle part of the 20th century um people were debating between the steady state model and the Big Bang model uh and one of the predictions of the Big Bang model although not everybody understood it at the time uh was that if the Big Bang was right there should be a gas of radiation uh filling today's universe and that gas should be uh have a spectrum representing a black body uh because the early Universe would have been dense enough uh that the radiation and the matter will would have equilibrated would have come to a uniform temperature and radiation at a uniform temperature is what we call black body radiation it has a very different distinctive Spectrum what I've shown here is the first really accurate measure measurement of the spectrum of the cosmic background radiation uh from the Kobe satellite uh this data was released in 1990 very shortly after the satellite was actually launched and the data itself was actually only based on nine minutes of running of the satellite uh and as you see it's extraordinar good the data point points have very very small a bars and fit the theoretical curve amazingly um and this got much better still um the satellite remained up in the air uh taking data until I don't know 96 97 96 I suppose uh and in 1996 uh they released their was probably I guess their final measurement of the spectrum and the errors are reduced by a factor of 200 relatives to this picture uh and it still fit the black Body Curve essentially perfectly so it really is amazing how accurately uh this can be measured and how beautifully it fits what you expect from it's really very simple theory on right um okay let's say a few more words now about sort of how the standard Big Bang Theory uh Works um the theory basically says that the Universe uh as We Know It uh began some 10 to 15 billion years ago and now actually we think we know this number even more accurately than that it's now said to be 13.7 plus or minus point2 billion years uh the qualification that I put in here as We Know It uh is uh I think an important one um the cosmologists have to cover their bets um as you extrapolate the universe backwards uh the universe gets hotter and hotter and denser and denser and you get to be further further away from the kind of uh situations in which you really understand the laws of physics uh so if you naively extrapolate this conventional Big Bang Theory back to Time Zero uh you find a singularity at time zero and before that you find nothing space and time essentially began at at Time Zero in the simplest mathematical form of the model uh but there's not really any good reason to trust the extrapolation of the model back to such extraordinary Early Times uh and there are in fact many other possibilities for what might have happened at T equals zero uh and in fact even inflation itself I'll probably talk about later a little bit uh makes a rather different uh statement about what probably happened at T equals z uh in inflationary models it it looks like uh what we call the big bang was really just our local Big Bang where local refers to something that's larger than the size of our visible Universe uh but still small in the inflationary context to what we would think of as the size of the entire universe which would be vastly larger uh than what we can observe uh the initial state of this big bang was a hot dense uh uniform soup of particles uh that filled space uniformly um you're probably aware already so but I'll say it anyway just in case uh there's a common misconception about the Big Bang uh which is sort of popular in cartoons and in some popular science writing uh namely the idea that that the Big Bang was uh uh an egg of matter that existed in an empty space and the Egg exploded spewing matter out to fill the empty space uh that's not the way the Big Bang Theory works at all uh as far as I can tell it's just as logical as as the theory that we call the big bang um but observationally it doesn't work nearly as well because um if you did have an isolated explosion spewing matter out into empty space then you would think that if you're out here someplace uh even if it was somewhat after the explosion you expect to see something that looks somewhat different if you look toward the source of the explosion than if you looked in the opposite direction uh but when we look around the universe uh what we see is that the Universe looks essentially the same no matter what direction we look as long as you average over a big enough region it's identical and this this uniforming that we see is even most striking in the cosmic background radiation which really is the earliest thing that we could see and what you expect to give as the best uh description of of the explosion itself and that radiation is actually known to be uniform in old directions to an accuracy of of one part in 100,000 uh which is really an extraordinary amount of uniformity which you would not expect if you had an isolated pocket of explosion here and we were out here looking at it uh so it's a uniform explosion from the beginning you have to assume that the matter filled the space now the basic evidence for this Big Bang Theory is Hubble's Law the fact that when we look at we do see the universe expanding we see all the galaxies on average moving away from us and the further away they are the faster we see the move uh second important piece of evidence for the Big Bang Theory uh is the cosmic background radiation the graph that I just showed you showing this marvelous black body Spectrum uh showing that indeed uh the radiation looks just like what you expect uh from the glow of hot matter in the early Universe I might mention something about the the Precision of that measurement and the implications of that you might think that since thermal radiation is thermal things always thermalize eventually um that the there might be a lot of different explanations for why we could have radiation that's thermal that's filling the universe uh but it isn't really true um in order for gas to come to thermal equilibrium it has to be in in thermal contact with things uh and the radiation that's filling the universe now is not really in thermal contact with anything uh the universe is effectively empty as far as the radiation is concerned the density of the universe is extremely low uh so the fact that we're seeing such a perfect thermal Spectrum does not merely mean that the Universe has been around a while and has had reached Thermo equilibrium it really is a strong indication that the Universe was at one time extremely dense nothing like what it is now and I guess the sort of numbers that people put on that is that uh the the degree to which the radiation resembles a a back body really indicates that there could not have been uh that the Universe really had to have thermalized in the first year of its existence and since then if anybody had put any kind of a bump in the Spectrum it would have survived they would not have had time to uh to iron itself out uh the other very important success of The Big Bang Theory uh is the synthesis of the light chemical elements the important Point here is that the early Universe was so hot uh that even the nuclei of atoms uh would not have been stable they would have just been ripped apart by the thermal energy uh so the fact that we see nuclei in the universe today uh implies that those nuclei must to formed after the big bangang uh if if the theory is right at all uh now the theory really is quantitative uh it's not just a cartoon image of an explosion um it's even not even all that difficult to calculate how fast the universe would have been expanding in any given time uh what the temperature would have been in any given time what the density would have been at any given time and so on uh it really is just a calculation involving the expansion of a gas in thermo equilibrium being by the pole of gravity and you can even do it by Newtonian methods and you get essentially the right answer uh so with this quantitative picture of how the universe expanded and cooled uh one can combine that with what we know about nuclear physics and actually calculate the rates of nuclear reactions that would have happened in the Earl universe and that means that it's possible to calculate the expected abundances uh of the different nuclei uh this story has a peculiar history uh because the idea of doing these calculations really began back in the 1940s with George gof and his collaborators and they pursued these calculations for a while and then became very frustrated because they could not find any way to synthesize uh any significant amount of nuclei heavier than lithium uh so they gave up and and discussed uh but in fact we now think they were entirely right uh the elements heavier than lithium we now believe were not produced in the big Bank uh but were produced much later in the history of the universe in the interior of stars uh and then when stars explode they spew these heavier elements out into space are ready to recollect into later generation stars like our sun so essentially all the stuff that we're made out of which is all almost all heavier than lithium um is material that was synthesized in some other star uh but nonetheless the latest chemical elements uh which make up about 98% of the bionic matter in the universe even though there's only a few of them uh were produced primarily in the Big Bang and the Big Bang Theory allows us to calculate the expected abundances of those nuclei and it really works very well uh and provides a rather remarkable test of The Big Bang Theory uh the other thing that's remarkable about this nucleosynthesis calculations uh is that the processes that produced these light chemical elements uh began about 1 second after the a big bang so even in the 1960s and70s cosmologists were exploring the history of the universe all the way back to 1 second after the big bang and they had real observational tests of what they were talking about and now we're trying to go back even further uh despite these big successes let's see hold on I didn't get to the bottom of that transparency just push the button by mistake uh okay uh so the Big Bang Theory can describe how the early Universe expanded and cooled it can describe how the light chemical elements formed as we just discussed uh and it does also give us a at least a a framework for describing how the matter conial to form stars and galaxies and clusters of galaxies and so on uh this of course as you might guess is a very complicated story and people are still working on it but certainly our general picture uh that matter collected through the force of gravity uh seems to be holding up very very well uh in spite of these big successes of the conventional Big Bang Theory there are certain topics uh which The Big Bang Theory really just says nothing about uh in particular in spite of the fact that for over 50 years now it's been called The Big Bang Theory uh the one thing that really says essentially nothing about is is the Big Bang itself uh the what what what cosmologists called The Big Bang Theory uh really is very strictly only a theory of the aftermath of some kind of a bang uh the bang happened before the theory starts uh so when the theory starts all the matter is already in place it's already expanding uniformly and all the Big Bang Theory describes is how that expansion was slowed by the force of gravity and how it continued through the force of inertia uh but the Big Bang Theory says nothing about what caused the explosion uh says nothing about what banged why it banged or what happened before it banged um and there also says nothing about where all this matter came from uh in the conventional Big Bang Theory all of the matter that's I mean for every particle that's in the universe today there was some precursor particle that was there right at the beginning when the theory started to describe nature uh so no explanation whatever of where the matter may have come from uh inflation uh offers a possible explanation uh to each of those two questions where the matter came from and what started expanding uh the secret behind inflation uh is the realization that modern particle theories uh actually predict that at very high energies uh we should expect to find forms of matter uh which literally turn gravity on its head and cause gravity to become repulsive uh the way this works uh is that as you probably have learned in general relativity it's not just matter or energy that can create a gravitational field it's the whole what is often called the energy momentum tensor that contributes to the source of gravity and in particular that includes pressures uh so pressures can affect gravitational fields pressures can create gravitational fields uh and it works more or less the way you probably notely guess uh the kinds of pressures we're familiar with are positive pressures uh and the kind of gravity we're familiar with is attractive gravity so you might guess that positive pressures would cause attractive gravity and that's right um but pressures don't have to be positive uh there are forms of matter that have negative pressures uh and that's what I'm talking about here if the pressure is sufficiently negative it can create more repulsive gravity than the mass density associated with that material uh creates attractive gravity uh so you can have net repulsion uh and that is the secret behind inflation um so the inflationary theory proposes that at least a small patch of this I see the thing in the bottom that's what's do it uh inflation proposes that there's at least a patch uh of the early Universe not necessar all of it uh that was filled with this very peculiar repulsive gravity kind of material uh and that patch does not have to be very large at all uh if we assume although we don't know for sure that inflation happened at the energy scale associated with what particle physicists call Grand unified theories uh then we can make estimates of the numbers that go with some of these Concepts uh and the patch would only have to be about a billion times smaller than the size of a single prot on to be big enough to start inflation happening and once inflation happens uh the result is that the region that's inflating um starts to grow exponentially uh and it grows exponentially with an extremely short time constant again taking numbers typical of grand unified theories uh the time constant of the exponential expansion uh would be a short is about 10 the minus 37 seconds uh which of course is an unbelievably small number uh these numbers that I'm using which I'm attributing to Grand unified theories maybe I should take out of a minute or here to say something about where where Grand unified theories get these crazy numbers from um the idea that underlies the grand unified theories is the idea that the three kinds of interactions that we observe in nature other than gravity namely the weak interactions the strong interactions and electromagnetic interactions are all really different manifestations of the same underlying Force law uh but at low energies the energies that we exist at well by the standards of modern particle physics uh these three interactions behave very differently um electromagnetic interactions are much stronger than weak interactions strong interactions are much stronger than electromagnetic interactions um so it doesn't look at all like these can really be just different aspects of the same Force but within the standard model of particle physics you can calculate how the strengths of these interactions uh vary with energy and you could extrapolate upward and what you discover is that if you extrapolate upward to an energy of about 10 to the 16th gev million electron volts uh in other words 10 the 16th times the mass of a proton uh all three of these interactions have the same strength uh and that is the underlying uh principle behind Grand unified theories the idea is that there's a fundamental interaction which at the energy scale of 10 to the 16th gev uh would look like was just one kind of interaction with the weak strong and electromagnetic interactions all being the same uh if that were the case by the way uh quarks electrons and neutrinos would all look the same also uh but at that energy scale there's a something that happens that we call spontaneous symmetry breaking which causes the different kinds of interactions to appear different at lower energies uh but that's what determines this extraordinar high energy scale of grand unified theories question just where the strength of the interactions meet when you extrapolate upward uh and that's what gives all these crazy numbers associated with inflation uh inflation by the way though does not really care much about Grand unified theories inflation could happen at a significantly lower scale uh but nonetheless it would still have to be higher than anything that we're accustomed to it have to be at least the scale of say the what we call the Electro scale a th000 gev um the only thing that sets the lower Bound for the energy that scale that inflation can happen at uh is the fact that at the end of inflation one has to be able to produce the Barons that we see in the universe today and one doesn't know any way to do that except at pretty high energies so continuing with the story sorry for the aside I hope I didn't confuse you uh back to the story we we now we now have this small region that's undergoing exponential expansion uh with a time constant of 10 - 37 seconds uh now we come to the first very very surprising fact I guess repulsive gravity is maybe the first surprising fact now surprising fact number two is that this peculiar material has the unusual feature that unlike any normal stuff that we know of which would thin out as it expands uh this repulsive gravity material actually maintains a completely constant density uh as it expands so it really is essentially creating new energy as the expansion takes place uh Now new energy doesn't sound very consistent with all that we've learned about conservation of energy all these years uh it is consistent maybe I didn't maybe it's a bit wrong to call it new energy um certain deposits that's going on here is completely consistent with conservation of energy uh but it takes advantage of of at least what before inflation was a fairly little known loophole in the principle of conservation of energy uh namely we're usually accustomed to thinking of energies as always being positive and if energies are always positive and you look around the world and see that has lots and lots of energy uh the only way that energy could have gotten here if it's conserved is if it was here from the start um but energies are not always positive and in fact uh the energy density of a gravitational field uh is not positive but negative uh and that means that as the expansion of this region is going on and more and more energy is appearing in the form of this peculiar material that fills the region uh that energy is positive uh at the same time more and more negative energy is appearing in the form of the gravitational field that's filling this region so total energy is conserved uh the humongous creation of positive energy is compensated by the humongous creation of negative energy in the form of the gravitational field so the total energy remains constant therefore remains entire incredibly small because it all started out a billion times smaller than a proton uh and the energy could very well be exactly zero uh with a perfect cancellation of the energy of matter uh on the positive side and the energy of gravitational fields on the negative side uh I think I'll come back to the rest of this transparency if I have them in the right order I think yeah the next transparency has a little thought experiment uh to try to convince you that indeed gravitational energy really is negative it's a Newtonian experiment um but the same thing well the same thing is true in general ity and I guess maybe one doesn't have to think of as Newtonian experiment it's I guess the same results would would happen in general relativity pretty much uh what I want you to think about here on the top part of the slide we show a hollow shell of matter and these arrows show the gravitational field of that matter uh shown as conventional field lines where the density of the field lines is related to the strength of the field and as you hopefully know uh if we have a shell of matter uh the gravitational ins field inside is exactly zero uh it's canel from Poles in different directions uh and the gravitational field outside uh is exactly the same as what you'd have if you just had a point mass of the same total mass located at the center and all this was really discovered by Isaac Newton way back when okay now for the thought part of the thought experiment I want to imagine letting this shell of matter collapse I want to imagine is made out of something soft like soft clay uh so it's not rigid and it's every bit of is pulling on the rest so there'll be a gravitational force pulling inward everywhere on the shell and I want to take advantage of that Force to generate power uh so these little things attached to it are supposed to be little bicycle generators uh like a gra a generator light uh and I I'm imagining tying a string around each of the generators so that as the shell of matter pulls inward uh it pulls on all the strings turns all the generators lights a lot of lights uh then on the third transparency uh the third little image at the bottom uh we think about what what the net exchanges of energy were during this process and the diagram is supposed to show space in three different regions outside the region where the gravitational field where the shell originally was this circle is supposed to be the same radius as that Circle uh outside that region the gravitational field is exactly the same as it was at the beginning uh it's just the gravitational field of a point Mass uh located at the origin uh at the very center the gravitational field is zero just like it was in the original picture so the change from the original picture to this picture is the region in between the region of space that the shell moved through as it collapsed and that region is now filled with a gravitational field uh while previously there was no gravitational field there at all and that's the only change between between and the gravitational field between picture one and picture 3 A and C as they're labeled on the transparency uh so the net effect of this operation was to extract energy uh and create more gravitational field so if energy is conserved there's only one possible conclusion uh the gravitational field must contain negative energy to cancel the positive energy that was given off so that the total energy at the end is the same as the total energy at the beginning um so I think there's no doubt from thought experiments like this or from other calculations uh that the energy of gravitational field is is certainly negative uh I might mention that if you're familiar with how to calculate the gravitational field of aulum field excuse me if you're familiar with how to calculate the energy density of aulum field um then you could probably pretty immediately realize that it's the same for Newton's law of gravity uh as it is for kulum interactions they're both one over R squ Force laws uh but there is one important difference which is the overall sign uh if I have two positive charges they repel each other if I have two positive masses they attract each other uh you calculate the energy in a field by asking how much work do you have to do to push around the sources of that field to create the field uh if you imagine doing that for masses and doing it for charges uh it's exactly the same calculation uh but you have to push charges together to create a strong electric field so the electric field has a lot of energy in it you have to put energy in it to make it uh while at the same time if you're trying to make a strong gravitational field by putting masses together you actually take energy out as you put the masses together uh so the energy of the gravitational field was negative okay back to where I was um so we have this region of space undergoing exponential expansion at essentially uniform density uh and we have to get out of that somehow we don't want to keep doing that forever because that's not what our universe looks like now uh but that turns out to be natural too because this repulsive gravity material that I was talking about with the negative pressure is unstable uh so it decays um and it decays very much like a radioactive substance it has a half life essentially um and when it decays it like a radioactive substance it doesn't disappear when it decays it means it turns into other kinds of materials and releases energy in the process uh so it converts to ordinary matter uh with extra energy so the matter heats up this is often called reheating uh and what you're left with is a hot hot gas of ordinary particles after inflation uh and that turns that of course is just what you want because it's essentially reproducing the uh starting point of the conventional Big Bang Theory uh it doesn't have to go very long to succeed in creating everything that we see uh it turns out that it only takes about a 100 e-foldings of this exponential expansion uh to go from something more than a billion times smaller than the size of a proton to something which the end of inflation will be about the size of a marel which sounds awfully small but at these extraordinary densities that in fact is the Nason form of our universe continues expanding coasting uh for another 14 billion years and becomes large enough to accompass everything that we see uh so the bottom line then is that uh inflation does nothing to change the Big Bang Theory the entire Big Bang Theory gets kept intact uh but inflation serves the very nice purpose of uh setting up the initial conditions uh which previously just had to be assumed okay well so far I imagine uh I've got ACR gotten across the point that that inflation is sort of a nice story about how the universe might have been created uh uh on this transparency in the next I'd like to say a few words about uh why we think it's actually pretty likely that our universe uh actually did undergo inflation in its early period uh so I want to talk about some of the signs that our universe has some of the traits that it has uh that seem to point towards an inflationary beginning uh and there are three of them I want to talk about two on this transparency and one on the next uh so the first is the large scale uniformity uh I think I mentioned earlier uh that the uh that when we look at the cosmic background radiation uh it appears to be uniform in all directions to this extraordinary accuracy of one part in 100,000 uh now if we ask what that says about the early Universe uh we have to ask a little bit about what the history of this cosmic background radiation was uh it has a fairly simple history uh during the first approximately 3 or 400,000 years of the history of the universe uh according to our calculations the universe was sufficiently hot uh that the gas in the universe would have been ionized and it turns out that photons have a very short mean-free path when they're going through a plasma and ionized gas uh the free electrons of the plasma have a very large cross-section for scattering the electrons uh so during the first 3 or 400,000 years of the history of the universe the photons were at every given instant moving at the speed of light but nonetheless they didn't go anywhere because they were constantly being scattered in different directions so they were doing a a random walk with a very short step size uh and the net result was essentially no no Transportation during that first time period but then at about 3 or 400,000 years after the big bang the universe cooled enough so that the gas neutralized and became a neutral gas like the air in this room and it's not always safe to extrapolate from the room to the universe uh but this particular extrapolation actually works that is just like the air in the universe is transparent to photons it turns out that since 4,000 years after the big bang the gas that fills the universe has been transparent to photons uh and that means that the photons that we observe in the cosmic background radiation today uh have for the most part been traveling on straight lines uh since 400,000 years after the big bang now just like when photons travel from my face to your eyes they allow your eyes to form an image of what my face looks like uh we are actually seeing when we look at the cosmic background radiation an image of what the universe look like uh at 3 or 400,000 years after the big bang uh so since the radiation is so incredibly uniform uh that implies that the universe itself must have been incredibly uniform one part in 100,00 uh at this very very early time now we know that things tend to come to a uniform temperature uh so it's a fair question to ask could the universe have come to this uniform temperature uh just because things always come to the uniform temperature you take a slice of pizza out of the oven and cools down to the temperature of the room uh but you can ask was there enough time for that and you might at first think you have to figure out about thermal coefficients and things like that uh it turns out to be much easier it's just a simple kinematics problem uh a simple calculation shows that for the universe to even itself out by such an early time if it did not start out uniform uh it would require that energy and information could be transmitted Across the Universe uh at a speed that would have to be about 100 times the speed of light okay if the universe started out non uniform you'd have to be able to get energy from one end of the visible Universe to the other by 300,000 years after the big bang and you can't you miss by a factor of about 100 uh so we do think that nothing travels faster than light and that means that within this conventional Big Bang Theory uh there simply was not enough time for the universe to smooth itself out and the only way you can make the conventional Big Bang Theory work is to just assume that the Universe started out completely uniform for reasons unexplained uh inflation has a very nice way of of getting around this problem uh because with inflation uh what has this Spurt of accelerated expansion and what that spur of accelerated expansion allows you to do is to start with a model of the universe which was Far Far smaller uh than you ever could have imagined in conventional cosmology uh and that means that this spec that existed before inflation started uh was small enough so it could have easily reached a uniform temp tempature and uniform density by the same kind of mundane processes by which the air in the room spreads itself out uniformly and comes to uniform temperature uh and then after that uniformity is established inflation can take over and stretch that tiny region uh to become large enough to include everything that we see so inflation gives a very natural explanation uh for How the Universe got to be so amazingly uniform and it really is an amazingly uniform universe that we're living in uh by the way it's perfectly okay with me if you want to ask ask questions during the talk uh I think that that' be fine any questions yeah particle creation occurred after inflation was over as well um well I guess what I should have said is that after inflation is over this uh conversion of gravitational energy into matter energy has ended uh but one still has the conversion of energy from one kind of particle to another uh so the particles that are associated with the this repulsive gravity material that I'm talking about um Can Decay into other kinds of particles which then still Decay into other kinds of particles so it has ordinary particle interactions going on after inflation and gradually uh rather actually rather quickly uh we believe that the matter in the universe uh reached a kind of a thermal equilibrium uh where every particle was uh had an abundance that was pretty much determined by the energy necessary to produce that particle any other questions where did the come from ah any other easy questions um well of course we don't know um there are speculations however uh which you know are worth talking about um you know I think you know some years ago the idea of of actually creating a universe by scientific processes probably sounded completely absurd uh now sounds at least sensible enough so that uh resp respectable journals do publish papers on the subject um the uh the sort of class of ideas that I think are are most prevalent in in physics literature uh and in thinking of most cosmologists are ideas that combine uh Notions from quantum gravity uh Notions from quantum theory with Notions of gravity or quantum gravity uh we don't really have a very successful quantum theory of gravity yet uh string theory is supposed to be in principle a successful quantum theory of gravity and my guess is that it probably is uh but people still don't don't understand String Theory very well so really for all of the almost all of the questions uh that people had been hoping would be answered by quantum gravity string theorist still don't have any anything to say about it in particular they don't really have anything to say about the creation of the universe yet uh but the vague ideas that people have had have uh centered from the idea that um that in the quantum theory everything is probabilistic you can always undergo Quantum jumps from any state to any other state if they have the same values of conserved quantities it's essential for all this by the way that we believe that all of the conserved quantities of the universe are zero uh which may seem surprising at first but if you think about it it's it's probably true um the the the subtle ones are energy uh and you know years ago people thought the universe had tremendous m of energy so and that energy is conserved but now now now people realize that gravity has negative energy and total energy of the universe is very likely zero uh another conservation law that's uh subtle in its implications is conservation of barion number uh the number of protons plus neutrons minus the number of antiprotons minus the number of anti- neutrons there other particles that contribute to that list uh that are more shortlived uh that that number is experimentally conserved and in the 1960s when I was in Graduate School uh that was considered a firm conservation law of nature the conservation of Baron number and certainly as well confirmed experimentally as any conservation law we know of I think uh but uh nonetheless starting really in the 70s and 80s uh physicist realized that uh conservation of Baron number almost certainly is not an exact conservation law of nature um the first glitch that people discovered uh was that when when tried to build these Grand unified theories that I spoke about uh the grand unified theories never conserved bar on number uh but we're still consistent with observation uh because their most novel predictions occur at these extraordinarily high energy scales uh they're still consistent with the idea that low energies uh bar on number seems to be very accurately conserved even though very high energy bar on number would be very VI very badly violated by gr unified theories it was then later discovered that there are in fact subtleties associated with the quantization of what we call the standard model of particle physics which is much better confirmed and much uh much more mundane than Grand unified theories uh so now physicists are are well convinced on theoretical grounds that even the standard model of particle physics does not exactly consider a bar on number even though the violations are again extremely small unless you go to very high Energies uh so the dep picture now is that barion number is not believed to be conserved and it's believed that at high energies it can be violated quite badly and we believe that the excess of Barons over anti Barons that we see in our universe uh was the result of barion non-conserving processes in the early Universe uh so that the fact that the Universe appears to have a that Baron number is again not not a statement that we have a conserved quantum number uh that the Universe has a non-zero value for uh other conserved quantities you can think about charge uh as far as we could tell the universe is perfectly consistent with having zero electric charge uh angular momentum as far as we can tell the universe is perfectly consistent with having zero angular momentum uh so it really does look like we have a zero quantum number universe so if that's the case coming back to how you might create a universe from nothing uh you could then imagine that in the full quantum theory of general relativity uh there would be a a Quantum state that corresponds to nothingness uh the absence of space absence of time absence of everything uh I if geometry is described by this Theory uh then you know for every possible geometry there's a state in the theory and one possible geometry is the geometry of no points the geometry of nothingness uh so if that's the case then you could imagine a Quantum jump from nothingness to somethingness uh and of course you only need to make a very small Universe by this Quantum jump because that inflation can take over and turn it into a big universe um so I think there's a very valid line of speculation there uh we certainly don't yet have a quantitative Theory or any general agreement about about how such a quantiative theory might work I'm also uncurious to why um you said when it got to about the size of a marble why the expansion would have quit being exponential uh yeah the question was uh that the the questionnaire wasn't clear why when the universe reached the size of ble marble that the uh expansion would no longer be accelerating um the what see first of all I should maybe specify that uh it doesn't have to stop when it reach when it reaches marble size uh what I meant to say but probably wasn't quite as precise as I should have been is that at the end of inflation uh the region that will evolve to become the presently observed Universe was about the size of a marble so the actual thing could have been much bigger so if it expands well beyond marble size and then expansion stops the acceleration stops that's fine so there's no need for any fine-tuning here you just need to have enough inflation now what causes it to stop is the fact that this repulsive gravity material that I'm talking about is fundamentally unstable uh so it's a metastable state uh and with some finite life time uh So eventually it will Decay and uh the detailed particle physics of this repulsive gravity material is not actually something that we know about um you know a typical Theory gives rise to such materials but the detailed properties of those materials can vary from Theory to Theory okay I'll go on but feel free to interrupt anytime um so item two on my list uh in terms of pieces of evidence that our actual Universe very likely underw inflation uh is What's called the flatness problem uh which is related to the mass density of the universe and the geometry of the universe uh cosmologists always talk about the mass density of the universe in terms of a ratio called Capital Greek Omega uh which is the actual mass density divided by a number called the critical density and this critical density is determined by the geometry of the universe uh the universe is expanding as we've already said and this critical density will depend on that expansion rate uh but according to general relativity space bends and it bends in response to the matter that fills the space and homogeneous universes are actually the most simple example really of the consequences of general relativity uh if the mass density exceeds a certain critical value uh the universe will curve back on itself forming what's called a closed Universe uh this closed Universe uh really is a very good analog of the surface of a sphere surface of a sphere is two-dimensional the space of our universe is three-dimensional but otherwise uh the properties of a closed Universe are essentially ident IAL to the properties of the surface of a sphere um on the surface of a sphere first of all the total area of the surface of a sphere is finite simly the total volume of a closed Universe would be finite if you travel on the surface of a sphere you never encounter any Edge you just go around and around and around same with the closed Universe you never encounter any Edge to a closed universe but if you keep traveling in what you thought was a straight line you come back to where you started from go around and around and around uh in both cases the axioms of ukian geometry are violated uh for example if you follow two parallel lines on the surface of a sphere imagine starting with the equator following two longitude lines upward those longitude lines will meet when you get to the North Pole uh so lines that look parallel on the surface of a sphere will eventually meet uh same thing in a closed Universe lines which look parallel if you extend them far enough will converge um another feature of standard feature of ukan geometry is the sum of angles of a triangle uh according to ukan Geometry it's always 180 de but if you draw a triangle on the surface of a sphere you could probably see it sort of bulges outward and the total of the angles is always a little more than 180 degrees depending on how big the triangle is and same thing in a Clos Universe uh if you look at a triangle in a closed Universe the sum of the three angles is always a little bit more than 180 degrees now if the mass density is just a little bit less than this critical density um then you have what's called an open Universe uh and an open Universe all the properties are exactly the opposite of what we just said so the space is not finite it's infinite uh if you follow two parallel lines in an open Universe they will start to diverge uh if you look at a triangle in an open Universe the sum of the angles will always be a little bit less than 180 Dees and if the mass density is just right you get idian geometry and that's called that's the critical density it's that precise density which you Idan geometry instead of an open or a closed Universe now uh to uh to appreciate the story I'd like to go a little bit back in time to say five years ago or 10 years ago or 20 years ago uh at at those times any one of them you can take your pick uh the best we knew about Omega was that it was equal to one to within about a factor of 10 during most of the time people thought Omega was somewhere between 1/10 and 3/10 of of the oh which means the mass was 1/10 or 3/10 of the critical density now it turned out that turns out that even if that's all you know it's already incredibly shocking that it's so close to one even though one1 doesn't sound all that close to one it sounds like it's off by a factor of 10 which usually isn't that close uh but the reason why a factor of 10 is close in this case uh is you see by extrapolating backwards the numbers that I'm quoting are numbers or estimates for the present Universe uh if you look at the evolution of Omega it turns out that Omega and the number one um evolve in a way that's uh a close analog of a pencil balanced on its tip uh if pencil is perfectly balanced on its sharp tip uh it won't know which way to fall and will stay there forever if you don't have any wind and you're using classical mechanics to describe it uh but as soon as the pencil leans just a tiny bit in any direction it will rapidly start to fall in that direction uh same thing with Omega and one it's an unst Omega equals 1 is an unstable equilibrium point and what that means is that if Omega in the early Universe were just a tiny bit less than one it would have rapidly fallen off to zero and if Omega in the early Universe were just a tiny bit more than one it would have rapidly risen up towards Infinity um so the fact that Omega is anywhere near today which is pretty late in the history of the universe uh indicates that at Early Times Omega must have been extraordinarily close to one uh so in particular plugging in numbers uh at one second after the big bang even if all you knew was that Omega was within a factor of 10 of being one today you would still know that at 1 second after the big bang Omega must have been one to 15 decimal places uh so I always like to say that the value of the mass density of the universe at one second after the big bang is actually the the best known number in physics uh and it gets even worse if you try to extrapolate back earlier if you go back to the plump time 10 Theus 43 seconds which is the time at which we think the quantum effects of gravity become important uh at that time Omega if you just extrapolate the conventional model Omega must have been equal to 1 to 58 decimal places which is absolutely of course absurd um inflation gets around that and the way that inflation gets around that is it reverses the evolution of Omega dramatically uh inflation turns gravity on its head and causes it to become repulsive and that also changes the way Omega evolves uh so instead of Omega being driven uh away from one uh during inflation Omega is driven prop L towards one uh so with inflation you could start out with Omega being 10 or 1/10th or a million or a millionth um and inflation will drive Omega to one uh to the extraordinary accuracy that you need uh it drives Omega to one exponentially and in fact the exponential has half the time constant of the exponential of the expansion so it drives it twice as strongly to towards one as as the space expands uh so inflation gives a very natural explanation of uh of why You' expect omeg to be so close to one and in fact this has always been considered a prediction of inflation this mechanism that drives Omega towards one drives Omega towards one a lot so unless inflation really just ends it just as Omega finally gets near one which doesn't seem very plausible at all uh you end up with inflation driving Omega exactly to one or essentially exactly to one uh so the expectation of inflationary model is that today Omega really should be absolutely indistinguishable from one and for most of the uh 20 some year 23 year I history uh of inflation that was a very bad prediction and people thought that inflation maybe wasn't exactly right because it was predicting a Omega 1 and that's not what anybody saw uh but with just within the past few years uh mainly with the Advent of what we now call Dark Energy it now looks like Omega really is one and in fact according to the um results of the W map satellite which I'll show you in a few minutes Omega is now supposed to be equal to 1.02 plus or minus 02 uh So within 2% or so uh we now think we actually have evidence observational evidence that Omega really is equal to one just like inflation predicts and that actually brings me to the next Point um while inflation explains why the universe is so uniform when you average over very large regions uh inflation also provides an understanding of the non-uniformities that we see on very small scales nonuniform is responsible for galaxies and clusters of galaxies and also for faint ripples that could be seen in the cosmic background radiation and those faint ripples are one of the easiest ways of making precise comparisons between Theory and observation because the ripples are so faint that you can use linear perturbation Theory to calculate them well we talk about galaxies it gets very complicated to calculate so it's very hard to compare what you see uh with what would be predicted by a theory about the early Universe um so astronomers have now made very accurate measurements of these non-uniformities they arise inflation in inflationary models in a very peculiar way uh they depend crucially on quantum theory uh classically inflation would just smooth everything out by this enormous expansion uh but Quantum mechanically uh everything is probabilistic so if classically it's uniform in a quantum mechanical version of that it would mean that in some places just by quantum mechanical chance the density would end up being a little bit higher than this classical average in other places it would be a little bit lower than the classical average uh so inflation leads very naturally to an almost uniform background with small Ripples and you can predict the pattern of those ripples using quantum theory and understanding it's mainly a question of understanding how inflation ends uh the main effect is that because of quantum uncertainties inflation doesn't end at exactly the same time everywhere some places inflate a little bit more and some places inflate a little bit less and that ends up producing non-uniformities in the mass density now we it turns out that we don't know enough about the particle physics of very high energies to be able to bring predict the amplitude of these fluctuations the intensity of these rieles uh so we have to take that from the data inflation right now if we knew the full particle physics inflation would predict what that should be but since we don't know the full particle physics inflation does not give us a prediction for the intensity of ripples uh but inflation does give us a prediction for the spectrum of the ripples that is how the intensity of the ripples should vary with the wavelength of the different ripples uh you should think wavelength here and not frequency when I talk about a spectrum uh but otherwise it's the same as the concept of spectrum that you're used to how the intensity varies with with wavelength and uh I have here a graph of that's now a few months old uh of theory and observation uh I don't know how I can see them but they're green data points here with eror bars and they're also red data points with error bars coming from two different observations uh Boomerang the green points uh was a balloon experiment that flew at the South Pole orbited for about two weeks I say or it made a big circle around theity of the South Pole and then came back uh and CBI cosmic background imager whoops uh this right uh CBI was a groundbased experiment uh but ground was very high ground it's on top of a high mountain in Chile uh and which shown is the Spectrum where long wave lenser to the left and short wave lenser to the right uh it's labeled what's called multiple number uh that's just a spherical harmonic expansion if you know about spherical harmonics as I imagine most of you probably do if you don't you can just think of this as a measure of the wavelength uh where the wavelength is equal to 180 degrees divided by L so high L corresponds to short wavelength it's all measuring in the angles this you're just seeing an image on the sky you don't know how far away it is so it's angular wavelength that we're talking about so anyway what's shown here is the data uh which as you see is pretty complicated has a series of bumps and Peaks um and a theoretical curve based on the inflation model which fits the data pretty well although the a bars are still quite large here and for comparison I've shown an open model a model where Omega 0.3 which is very much the favorite model five years ago uh and now we can see that it fits this data extraordinarily badly so this open model is now considered to be completely ruled out now the data has gotten significantly better since this picture uh the new ingredient is uh a data set that was released just last month uh by a satellite called W map the Wilkinson microwave anisotropy Pro uh that's David Wilkinson from whom it was just recently named uh David Wilson was a great guy he died about guess little more than a year ago now um and he was one of the leaders of the project in fact has been one of the leaders in microwave background research since its very beginning uh shown here is an artist conception of the satellite itself uh with the Earth and the moon and the sun behind it uh this lineup shown here is accurate uh this is a more detailed picture of the orbit that the satellite has it's a very peculiar orbit it lives in a place called L2 which is a lrange point uh a lrange point of the Earth Sun system and lrange point means it's essentially a stationary point in the rotating frame following the Earth around the Sun uh it's a very simple one uh L2 just lives on a line uh from the Sun to the Earth and Beyond the Earth is this point called L2 and the satellite really goes around with the Earth uh person with the screen is going to camera is going to hate me for this uh but the satellite goes around with the Earth like this this always always lying on the side of the Earth away from the Sun and that's perfect for astronomical observations because it means that it can look outward and the Sun the Earth and the moon are at all times always behind it uh and with those three objects in the sky it's you're not in a place like that uh you know one of them is almost always in the way in this case none of them are ever in the way so it's the perfect place for astronomical observations and it will soon become very crowded there are a number of missions planned for L2 uh but this U map experiment was the first one to get there the I've shown here let me skip this it's it's interesting but we're running out of time um uh this is the data uh the same spectrum that I showed you before it's on different a different scale so it doesn't look exactly the same uh but it's basically the same picture that I showed you before but this time with the data from the W map experiment which is much much more precise so these little dots really do have error bars even though you probably can't see um so the air bars are far smaller than what we had before and it still fits the theoretical curve essentially perfectly uh it's rather miraculous that you can make predictions for such obscure things and have them turn out to actually work okay I want to say just uh I'm almost finished but guess yeah this will be my last transparency since we're out of time um I have one other transparency if you I'll skip it um what makes this notion that Omega equals one suddenly the consensus while five years ago nobody believed Omega is equal to one except for True die hards who had faith in inflation uh what makes what makes the change is the discovery that today our universe is actually accelerating uh and this evidence began in about 1998 uh coming from the observations of two different astronomical teams who observed uh type 1A supern using them as standard candles uh to gauge what the expansion rate of the universe has been uh because these type 1A Supernova could be seen at such distances uh they were able to essentially measure how the Hubble constant has evolved over the past five billion years and the remarkable Discovery was that the Universe was not slowing down as we expected from ordinary gravity uh but in fact the universe today seems to be filled with this repulsive gravity with some form of repulsive gravity material uh not possibly not so different from what drove the inflation although certainly at a much lower energy level uh so today the universe is actually accelerating we now believe uh and the reason why that fits in so nicely with inflation is first of all it confirms the idea that gravity can act repulsively uh but that was never really doubted by people who understood general relativity uh the really important thing is that we can calculate how much mass density would be needed to cause the acceleration uh that's being seen and when we add that to the matter that we already was there because we saw either the matter or its gravitational effects uh it adds up to almost exactly the critical density I say here it's known to about 10% that it adds upright uh this is an old transparency now with this W map data uh the number is 1.02 plus or minus .02 which I just love um so we really have now a very consistent picture I should add that it's a very peculiar picture uh we have three totally different kinds of stuff filling our universe in our model now there's the ordinary matter the stuff that we're made of which is about 4% of the total budget uh there's what we call dark matter which is matter that we've never seen we don't know what it is uh but it's it clusters in clusters of galaxies and in galaxies and it's because of that clustering that we know it's there we see its gravitational effects uh and then there's the smooth background of matter that's causing the universe to accelerate uh and we have even less idea of what that is although it could just be vacuum energy but even if it is we don't know why why there's is vacuum energy at at anything like that energy level um so the universe is made up of 96% stuff that we don't understand at all uh but nonetheless we have a very consistent model and even though we don't understand this stuff we have a very detailed picture of how the stuff behaves uh so we have a a very successful model now uh now beginning to be called the standard model of cosmology um but it's model that certainly is built out of ingredients uh that we know very very little about if you want to come back later if you ask me questions after the class ends I'll talk about how to create a universe in the laboratory but meanwhile I'll just summarize um what I tried to convince you today was that the Big Bang Theory is is well supported by the evidence there's the Hubble expansion the cosmic backround radiation the abundances of the light chemical elements um but I pointed out that the classic form of The Big Bang Theory does not even attempt to explain the actual Bang uh but inflation does uh inflation offers a possible explanation of what started the universe expanding and it can explain the origin I usually say of essentially all of the matter and energy in the universe you have to start with the spec of this peculiar form of matter uh which by the way would weigh about a gram or so uh so inflation is not a theory of the ultimate origin of the universe uh but it does take you from something very small to something that would be much much bigger in fact than our visible Universe um the inflationary theory is supported by evidence in number number of ways it can explain the uniformity that we see on large scales it can expain explain the nature of the cosmic background radiation non-uniformities and I'll also explain why we're so close to the uh critical mass density of the universe and new observations in particular new observations of the cosmic background radiation observations of the Supernova 1A large scale Galaxy surveys also although I didn't talk about this uh are making very important new observations and so far they're all fitting in very nicely uh with this theoretical framework that we have to describe the universe thank [Applause] you questions why does the inflationary model predict um for Omega what what does it drive Omega towards one okay the question for the microphone is is why does why does inflation Drive Omega towards one uh there is actually a very simple explanation in terms of geometry uh general relativity ties geometry to the mass density so it ties geometry to Omega um and what inflation does is it simply takes a perhaps a piece of the universe it doesn't have to be the whole universe and stretches it by a fantastic Factor uh and just as the surface of the Earth looks flat to us even though we know the Earth is really round uh really any curved surface if it's not a fractal stretched enough uh will start to look smooth uh so that's what inflation does it takes a tiny Speck of the universe that's so small that even if the universe is curved that spec would not show that curvature uh and magnifies that spec to become large enough to be everything that we see and therefore it essentially necessarily looks flat and according to general relativity if it's geometrically flat uh it is also at the critical mass density your original inflation was changed in various ways is there a way to talk qualitatively about that or is it simply beond no I I I think I can I can do that um the Ed is right that the original version of inflation that I first proposed did not work um I was at least aware of that the time I published it so that the paper has all the qual all the necessary qualifications so the the paper isn't wrong even though the theory is uh it was later patched up by other people the first working version of inflation was proposed uh in independently by Andre Lind in the Soviet Union and alre and steinhart in the US uh the key has to do with the ending of inflation um from the beginning it was apparent that inflation had a wonderful mechanism for solving these cosmological problems uh but you needed to end inflation in a way that uh that didn't mess up those Solutions uh inflation Ends by essentially a phase transition uh by the decay of this repulsive gravity material and in my original proposal that phase transition would have been a first order phase transition uh very much like the way water boils and I had in mind uh that if things if I was lucky uh the water would boil forming a lot of little bubbles that would rapidly coales forming a uniform Steam and the uniformity could be maintained uh but when I and others started doing more detailed calculations of how this would work uh we found that the uh the bubbles would not merge smoothly and in fact we were even even able to show that the the bubbles would never uh undergo a process that we that's called percolation um percolation is I guess a word meant made up by either the people who inv meted coffee or condensed matter physicists uh but this in this context percolation means uh forming an infinite cluster so if you when the when the first order phase transition happens you have bubbles of the new phase forming uh and roughly speaking what happen happens is the bubbles just form a complicated horrible bubbly mess like like violently boiling water uh and the homogeneity never gets regained uh in detail what we're able to show is that when the bubbles form uh as they're forming the space is expanding around them uh we show that the bubbles would form finite clusters only would never emerge to fill the whole space that's the absence of percolation and furthermore if you looked at any given cluster of bubbles uh it would really be dominated by whatever bubble formed first because that bubble has been expanding so rapidly by the time the other bubbles form they'll be very teeny compared to the first one so each bubble Universe would really look like a bubble sheet and these bubbles by the way do have the characteristic of soap bubbles that all the energy ends up in the on the walls really uh so each bubble Universe would really look like a sheet of matter uh with with uh complications on the surface of that sheet but nonetheless it would never uniformly fill a volume uh so it ended up looking nothing like like our Universe uh the problem was solved by uh what's called the new inflationary Universe uh and the secret behind the new inflation our universe was to modify the Dynamics of the proposed phase transition uh making it a a very mild second order phase transition uh so one often says that the the decay of this material is much more like the congealing of jello than the boiling of water and that's what's needed to keep things smooth enough uh so that the end of inflation you still have a uniform Universe like inflation was able to achieve for you okay well no no further questions let's thank alen anyone wants to stick around find out how the universe made labat or anything else you want to know about inflation