Inflationary Cosmology: Is Our Universe Part of a Multiverse?

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Inflationary Cosmology: Is Our Universe Part of a Multiverse?
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ladies and gentlemen good morning I hope you can all find a seat there still some left on the side of the room welcome again it's my great great pleasure to welcome you to this new edition of the physics full also open conference and as always you have flocked in great numbers effective surpassed the 2000 mark this year which is an all-time high on your physics physicists from all walks of off while physics really some of your physicists the reveals adjust or chemists for mathematicians were astronomers or engineers or computational scientists or materials scientist or geophysicist and some of you maybe developers of state-of-the-art instrumentation advanced computer codes for analysis methods that use massive amounts of data and some of you are inspired by a possible use of your work and others are proud to say that as of yet there is no possible use of that appeared on arises that you would probably not object if it turned out that infect your work would would put turnout at To be fundamental for something that ends up in a house or telephone cleaner cars a faster computer we're just save the world from famine or energy scarcity cancer work yes you are a varied lot but it is that these valves holding conferences more clear than ever that within that variety we are also with community not a very large 1 but a very tight fighting it and we had formed take pride in thinking knowing that the formal organization has contributed to being instrumental in building that sense of community there's a reason why I bring that up this it is because we are going through a troubling time as you will know divisional scientists is that the discovery of the cabinet was published last year November 26 and it says a couple of nice things about the importance for society of science and how it is essential that we nurture our young talented scientists and it also has a page on the National Science Council MW all of which fall the physics branch and that page says that and we'll will have to be reformed and well I won't bore you with the lingo of the policymakers but many of you will know that Beijing particular has induced a shower of reactions in the press on the radio in letters from very respectable organisations led us to the ministry and the water places and that was because there was a general consensus that the fuel lines about the structure of individual might just be enough to kill signs in the Netherlands as we know it while at the same time also consensus that NW all could infect your reorganized could be organized more efficiently more transparently and with easier ways to fund cross-disciplinary research so good I know that many of you are acutely aware of the situation so that the address is briefly here is this the last physics at full physics at felt over I don't think so Is there a serious possibility that formerly eventually cease to exist as we know it will eventually is always the possibility that the proposal is certainly on the table Is it generally seen and appreciated that fall is a very low functioning organization and contributed to the extremely high level physics in the Netherlands yes very much so a lot of external parties are saying that all the time that's very helpful in the way of working in informal and SEW is set as an example 4 the entire and of the organization and so on thank you continue to send an application for projects and programs and the like yes absolutely true that use our organization that we are going to a troubling until we live in a historic time if you want and NW will the NW will change and full will change for the better off or worse we are doing our best to this process we must always remind the policymakers in The Hague that Dutch physics is at the dazzlingly high levels measured by impact it's the highest in the world so there are many ways to deteriorate and only few to improve yet this can never be a reason for speculation we have to think about ways to further improved we can actually benefit from funding for collaborative projects that already in the face of disciplines yes we do a funding scheme the very similar to but very slightly different from those in chemistry and that would benefit from harmonization and yes subjects like material science or what medical do sometimes suffer from falling in between those 2 funding pressures from the view that can be improved so things are going to change we're right in the middle of the proxy if I tell you to keep and carry all you'll probably get very worried if I had said nothing about the end of your situation you would has gotten even more more probably please don't get worried do get excited and do as a community stand up for physics for science when and for just these 2 days however use all that energy and enthusiasm to make this the best most sparkling most inspirational also conference ever meet new people make new friends let go twitter about their experiences and Please Please do not confine yourself to the box of your specialization this is your chance to think out of the box big-time make books entirely deny its existence or invent another books Donald boxes and trying the inside and outside the reach of think of these days as physics and boxes it's your present to you enjoyed conference and was that I should like to ask not to go continues to pursue the beans and fish it's a pleasure and an honor to introduce speaker today angle 2015 and 15 is the International year of of light it is also a hundred years of general relativity and 1st cosmologists it's also marks the 50th anniversary of the discovery of the the cosmic microwave background which has you know has been really fundamental in our understanding of the universe and around the time when the cosmic microwave background was being discovered and let me remind you
that this is the oldest light in the universe and its light was emitted about 13 and a half a billion years ago also the around this time and ruthless rolling an MIT where he was going to be there for 7 years between 64 and 71 he got his bachelor's who got his masters he got his PhD but he wasn't thinking about cosmology in those days he was much more focused on particle physics helped the cosmic microwave background brought us of course the heartbeat and model it basically established this model of the universe beyond any reasonable doubt but it also brought a number of issues or should I say it was clear that it was incomplete in the sense that it required extremely fine tuned initial conditions somehow the temperature of the cosmic microwave background is identical whether you in whichever direction you look at it and this is a natural because the Regions Way was emitted could not have been in constant contact something they never had time to talk to each other and it could affect another problem is that we live in a Euclidean John treatment of three-dimensional space clearly like told us and this is also very unnatural from the point of view of the hot and so and I think animal certainly operate on all these points but I think it is it said at the time after MIT he started doing various postal he was Princeton he wasn't Columbia was in Cornell and it would still have to go to Stamford after that before he founded permanent position at MIT where he has been since and around the time when he was in Cornell here he realized and he was thinking in terms of the grand unification theory is and how those would be in the early universe things like the production of magnetic monopoles was collaborating with him retired the time and then he had this amazing insight that is space where to expand exponentially and really fast 1st of expansion would immediately explain why the universe is so flat and why the cosmic microwave background is sold even from all directions and this is not a very far-fetched because all it would take was for the University of Sydney and some sort of supercooled and state just long enough to do this burst of expansion and the rest will follow immediately and so that was the birth of what we call today cosmic inflation now there were many people thinking along related lines at the time the original model turned out not to work and that's so there will a corrections and so on and so namesake Linda's stabbing sky and Albrecht to Steinhardt Mohan of cheap itself and there's a lot of players and certainly Stephen Hawking also but the most important thing perhaps about inflation is that it gives to predictions and 1 is a prediction that there should be a background all density fluctuations in the early universe and the other 1 is a background levitation weights everything that we know about the statistics of the fluctuations in the cosmic microwave background is completely consistent with the idea that they were generated during inflation and what is amazing about this idea is that it gives the quantum origin and a very clear connection with quantum processes the 1st fraction of a 2nd after the Big Bang and so it allows us to do particle physics by looking up the telescopes and none of this would have happened without commenting but so enough to to cut a long story short he has many a distinctive many prices and then we just name a few he has various the Franklin Medal the direct price I would certainly and emphasize the Gruber took 2004 priced in cosmology which is the most prestigious prize in cosmology nowadays which is shared with the unveiling the he also has the fundamental physics prize 2012 is 1 of the inaugural recipients the prices by Milner which is called a breakthrough prize in physics and he has the Kathleen 2014 priced in which he also shared with and instead of Urbanski just awarded by the Norwegian Academy of Sciences he is of course a member of the inner his been elected to the National Academy of Sciences in the U.S. and the American Academy of Sciences and Arts and Sciences and a nowadays he is the victor myself professor at MIT and a number for those of us who take inspiration from him let me mention last but not least that he also holds the price for the messiest office in MIT which is a source of great inspiration to some of us so ladies and gentlemen on and off be fair can I thank you very much ,comma for that very generous introduction I don't know I take issue with 1 point which was not stated quite correctly this messiest office award was given by the Boston Globe for at office in Boston not just MIT said was this really really much more impressive on and on and on indicate that I am very proud of itself this is actually the this meeting is the 1st time I have given visits talks in the Netherlands last evening I had use 1 of these master classes at last to about 25 of the URA graduate students and I just wanna say that that was a wonderful experience and the graduate students who I met were just incredibly enthusiastic and intelligent and that's wonderful questions and from my point of view is really just a great session that I will always remember that that so far my experience in the Netherlands is just break up this morning I would like to talk about inflation has an indicated and flesh out some of the many of the things that described briefly and I will try to describe what inflation is and how it works outright also describe what are the key pieces of evidence that cause many of us to believe that the universe actually underwent this process called inflation and in the end I like to say a few words about how inflation does not literally implied that does suggest there universe is not the only universe but is in fact 1 of many universes forming what we call a multipurpose so begin might flies to they were before the scheduled to land on the moon program you have someone begin by talking about the conventional Big Bang theory that by by which I mean the Big Bang theory as it was known
before inflation to set the stage for inflation to this conventional big-bang theory is a theory that the the universe as we know it began some 13 to 15 billion years ago and now in fact we have a very accurate estimate that number according to the plonk satellite analysis the age of the universe is 13 . 8 2 plus 2 minus 0 . 5 billion years the initial stage which gave rise to this big bang it was a hot dense uniform soup of particles that according to this conventional Big Bang Theory film spaced uniformly from the very beginning you may have seeing the cartoon image of the Big Bang as an explosion of some out spewing matter out into empty space and that never was a scientific version of The Big Bang Theory in order to explain the uniformity that we see in the universe of the Big Bang theory simply assumed that the matter from the very beginning of filled the space uniform but the Big Bang theory describes a number of things and very successfully it describes how the universe expanded and cooled and describes how the light chemical elements formed in particular this big name description begins with the universe so hot that even the nuclei of atoms would not have been stable but so the nuclei that we see in the universe today how active forms during the evolution of the universe and the latest of these nuclei we believe were formed primarily in the big-bang explosion itself and 1 can use the Big Bang theory to calculate the expected abundance is of these like nuclei and they'd be very well with what is observed so this is 1 of the classic successes of Big Bang theory and finally the Big Bang theory describes although it's still a work in progress but that the Big Bang theory describes ultimately have the matter in the universe congenial to form stars galaxies and clusters of galaxies and so on and and although that is a work in progress it certainly has so far been very successful astrophysicists feel they have a very good understanding of how galaxies form up while on talk about next is what the classic Big Bang theory does not describe because that's where the entree for inflation lies I should maybe same right here that there is nothing that I know of that classic Big Bang theory describes incorrectly it's just that it leaves a number of questions unanswered but so in particular the traditional Big Bang theory says nothing about what caused the expansion even tho it's called The Big Bang Theory it really affects is nothing about the banning of the traditional Big Bang Theory it is really only a theory of the aftermath of the bank I like to say that it says nothing about what banged and wide-angle or what happened before paying to those kind of questions that are still open In addition the classic Big Bang theory says nothing about where all the matter came from in the context of the traditional Big Bang theory for every particle that exists in the universe today it was at least some precursor particles that existed from the very beginning the origin of matter is not even attempted to be explained so inflation comes in as possible answers to the east questions that the classic Big Bang theory leaves unanswered so next what is government inflation and how does it work well I only told you that the traditional Big Bang Theory get everything that it describes correct so when does not want to In anyway destroying the successes of the possible big bank there so possibly for that reason that inflation plays a role which I think is best described a word that was probably invented by Hollywood the word frequent inflation serves as a prequel to the traditional Big Bang description of inflation happens 1st and sets out the initial conditions that otherwise had to be assumed to make the trip to the traditional Big Bang Theory work what inflation can you that's very new is inflation offers a possible explanation of vote for what I like to call the bank of the Big Bang and by that I mean that inflation can explain the actual propulsion mechanism and that drove the universe into this period of tremendous expansion that we call the Big Bang and inflation explains this propulsion mechanism in terms of a feature that I like to refer to as a miracle physics none of his sister not supposed to talk about miracles I think that what would I use the word miracle here I am not trying to describe anything supernatural but I use the phrase miracle physics to indicate a feature of laws of physics which has 2 properties but 1 is officially saddles so that it was not talk when I was in graduate school and Tutu officially profound so they can really affect our view of the universe and from mining way of thinking that inflation is based on 2 of these miracles of physics and the first one is the 1 that describes the propulsion mechanism that inflation proposes which is gravitational repulsion no we all learned about gravity 1st presumably by learning the Newtonian theory of gravity and a Newtonian gravity gravity is always attractive but in the context of general relativity it turns out that that's no longer true from the very beginning it was realized that general relativity oversees the possibility of repulsive gravity and this comes about because in general relativity it is not just mass density is or densities that create gravitational fields but in general relativity pressures it also act as a source of gravitational field and by the way it works of positive pressures produce attractive gravitational fields of the fact that we're used to but pressures can be negative and by extrapolation or by actual calculation in general relativity 1 sees that a negative pressure actually produces a repulsive gravitational field and that is the underlying secrets of the propulsion mechanism of cosmic inflation the service negative pressure can produce impulsive ground and helped negative pressure come about the answer to that is very simple in the context of present-day particle physics but it turns out that any state for which the energy is dominated by the potential energy of a scalar field all will produce a negative pressure Sue the models of inflation that we deal with them today are principally of 2 general types although there are many complications that have been introduced in different models of inflation but basically they're still I think to primary types which would propose very early on was what was originally called International sometimes called small fueled inflation illustrated on this diagram but outweigh the potential energy function for the scalar field but has a bump it very
similar by the way to the potential energy function that we believe that the heat shield obeys but inflation takes place when the scalar field is perched on the top of the hill just balanced and unstable configuration it will force eventually fall off due to fluctuations quantum fluctuations of nothing else but the primary arranged so that that takes a long time by early universe standards and so for a period as long enough for inflation to happen the scalar field is essentially trapped at the top of the sale and the energy densities just dominated by the potential energy associated with the field but the other common class of models of inflation are what was originally called chaotic inflation or sometimes large fueled inflation and these models can deal with much more general class a potential energy functions which in many ways makes it look much more plausible and here was noticed by 180 in 1983 that for almost any potential if the scalar field starts off high enough on the Hill as it rolls down there can be a long enough period where the energy is dominated by the end year that scalar field the potential energy that's your field so that inflation could take place and those are basically the 2 schemes for how inflation can happen In terms of the sequence of events the scenario of inflation basically proposes that at least a small patch of the early universe of contained in this negative pressure kind of material a scalar field in 1 of these peculiar states and if inflation happens at the energy scale of grand unified theories which is very plausible energy scale for inflation although we really don't know what energy scale inflation and act but it is at this scale grand unified theories use that for sample numbers so we're talking about an energy scale of 10 to the 16th GVT but then the patch I need only be as large as 10 to the minus 20 centimeters which I probably don't need to point out is more than a billion times smaller than the size of a single proton actually are talking about the universe emerging from an unbelievably small volume I now because this patch is going to be fantastically enlarged by inflation the initial density of such patches can be very low and the probability of such patches forming in the 1st place can also be very low as long as it can happen the belief is that inflation will that magnify those regions and everything else was becoming the and irrelevant compared to the regions that happened to contain this negative pressure repulsive gravity material once we assume that a patch of this sort exists everything else really follows automatically from what we understand about the laws of physics once we imagine a patch filled with a stellar field of this peculiar state the gravitational wave motion created by this negative pressure then becomes the driving force of the Big Bang within that actually could have many places it many times our big Bang might just be 1 of many but the pact she is driven by this gravitational repulsion into a period exponential expansion and if we are talking about the introduce children theories then the time constant for this exponential expansion is about 10 to the minus 38 seconds incredibly short in order for the model to work the patch has to expand exponentially by a factor of at least 10 to the 28 so it started at 10 to the minus 28 7 years ago in the end it has to be at least a centimeter across these tendencies to ultimately expand to become the universe that we see today that expansion requires 65 time constants but which is not a huge number of and as long as inflation continues for at least 65 time constant this mutual initial region will grow to be something big enough to produce our entire observed universe if inflation continues longer than that that's OK there's no need to fine-tune mountain inflation under just the minimum needed to make the model work the this your field will eventually rolled down the hill either roll off the plateau in the case of new inflation or discontinue rolling down the hill and the case of chaotic inflation and little reaches the bottom of the hill the energy that had been stored in the potential energy of the field it's released and that Kennedy produces a host of other particles which then start colliding with each other and the assumption that very quickly collaborates producing a hot soup of ordinary particles with attractive gravity and that's the starting point of the conventional Big Bang theory so we still feel rolls down the held that the end of the people and the start of the sense of the main feature of the conventional Big Bang theory Standard cosmetology begins but now an important feature of this inflationary process is that as this tremendous amount of expansion is going on but it's the energy density thinned out accordingly you really have nothing left by the time inflation was over but we're talking about increasing the one-year size by a factor of 10 to the 28 the volume increases by Cuba that if the energy density went down like 1 over the volume which is something you might expect and that would be a disaster it would mean that you end up with a completely in the universe and inflation would not be any possibility for explaining the universe that we see so there's a pewter thing that happens here that that even know this fantastic expansion is taking face of Wallace taking place the energy density of the universe actually does not go down at all so it means that this exciting material is very different from the kind of materials that we deal with today in our own experience that sounds like this on violate conservation energy because we have more and more energy appearing in the form of a scalar field which is now occupy a larger and larger volume with the same energy density however it turns out that this actually does not violate conservation and packaging which is sound a bit strange probably elements that possible is the 2nd miracle physics that I alluded to earlier said that inflation seems to realize on to miracles of physics and the southern Europe will is the fact that although energy is rigorously and served as far as we know we have know anyway get around that however it turns out not to be true that energy is always wasn't which we usually I think in the back of our minds and you have to be positive about the fact that the energy of a gravitational field is and this is true even in the context of Tony Abbott it's not really a novel that fact that people have not pay too much attention to over the years Seattle what's going on during inflation is that the positive energy of the scalar field is being compensated but the negative energy and gravity to the tunnel energy of universe is constant during inflation and the system being exactly 0 there might be a perfect cancelation between the positive energy in the matter and negative energy in the gravitational field which could be shown schematically where this picture which
is intended to kind of drive the point home are very likely the total energy universes 0 with a large contribution in the black positive of matter and radiation and equally large contributions in the red negative coming from gravity no there may not be surprising to you that the energy of gravitational field is negative but I I can give you a simple argument that I think most of you will be ready to buy if United calculated the energy density of a old which is part of most standard undergraduate and classes columns love attraction you know this is exactly the same as the law of gravity toward lost workforce except there is assigned difference positive charges repel each other to positive masses attracted to Sudan's law has the opposite sign cooling but so when you calculate the energy of an electric field which exactly by asking how much work you have to do with charges around to create an electric field you end up with a formula that says that the Butterfield has energy density which is a constant Times Square field positive constant I need to do exactly that same calculation for low gravity the initial sign differences the beginning just carries through to give you a sense I'm difference in the end and discovered that the energy density of Newtonian gravitational field is just a negative constant Times Square of the gravitational acceleration little G squared and so you immediately concluded that the energy of a gravitational field is negative but actually get this where spring to work and matters 0 I think you really need to think about realistically what I try to describe here but it does work inflation allows the universe to expand by an arbitrary amount with fixed energy density and no consolation was that it's perfectly consistent OK that's what I want to say that how inflation works when where I hope to have the good explained so far that is how inflation works and what kind of a scenario it gives us or how the early universe may have behaved during his early period I should maybe emphasized that inflation is not a theory of the actual origin of the universe inflation starts with the universe already existing inflation supposedly that we can find aspect of the universe that's filled with scalar field with a negative pressure but but then inflation describes a period revolution which essential properties of the universe come into being and it's the properties that I will talk about them what features does are actually universe have that suggests that it really came from this process of inflation and went up about 3 features are maybe for different intelligence last after the 3 very Labor salad our our 1st of all this is something I alluded to in her introduction of the uniformity of the universe With we look around the universe is very large scales astronomers discovered that the universe is amazingly uniform this uniformity shows up most definitively but in the cosmic background radiation are radiation that we view as the left-over heat out of the big-bang explosions and astronomers have dominated this cosmic background radiation rather extraordinary precision and what they found is that to an accuracy of 1 part in 100 thousand the intensity of the effective temperature this radiation that is exactly the same in all directions of the staff even when you look opposite directions I know that turns out to be very very hard to understand in the context of this conventional thinking theory without inflation and explain why the radiation that we see in the cosmic background radiation we believe was "quotation mark released but at a time of about 380 thousand years into the history of the universe I'm where that number comes from is that according to our calculations prior to 380 thousand years after the universe hot enough so that the gas that killed the universe was in the form of plasma and plasma turned out to be very opaque very non-transparent to radiation so during this early period during this 1st 380 thousand years of the photons that make up the cosmic background radiation were present and they were traveling at speed of light that there constantly being scattered off of the free electrons of the plasma ,comma so because they're constantly changing directions even know they are always moving at the speed of light up during that early plasma period photos really didn't go anywhere were changing direction so frequently that the net progress was essentially 0 and then add 380 thousand years according to our calculations of the universe cooled enough so that the plasma neutralize became a neutral gas like air in this room and just as the air in this room it is very transparent of photons the gas that filled the universe from that time onwards there has been very transparent to from Thailand's so we believe that the photons that we're seeing today the present background radiation have literally been traveling on straight lines are from 380 thousand years after the Big Bang until now and that means that these photons are really carrying an image of what the universe look like at 380 thousand years just like the photons travel in a straight line from my face theorized that allow you to figure out what I look like and so the implications is that the universe by 380 thousand years after the Big Bang was somehow already smooth presumably in both mass density and temperature up to an accuracy of 1 part 100 thousand and that's the question that were trying to understand what happened we count this tremendous amount of uniformity but nevertheless we do not know that there's something that we sometimes call this year with all of thermodynamics which simply says that things tend to come to thermal equilibrium to the area in the sector alters the film lecture hall uniformly and if we were all and things like that have come to uniform temperature but also those classes happen and and that could explain the uniformity of the universe made a behalf to think a little bit about how long that takes in 1 way or another there was enough time to explain the uniformity by 380 thousand years and it turns out that it only takes a short calculation to convince oneself but that there's is no way that that could have happened but within the conventional bank was not the time and the reason why it's so obvious is that all you need to know the speed of light to get the the answer in order for the universe to smooth itself out by 380 thousand years if you assume it's not start out and you would have to acquire the movement of energy and also information and about 100 times the speed of light to make that happen and says nothing that we know of physics violates the speed of light means that within physics as we know it if the universe did not start out completely uniform there's no way I could become uniform by 380 thousand years in the context of conventional however in inflationary cosmology of everything changes in the very simple and easy to explain away inflation simply inserts into our description of the history of the universe this period of
humongous exponential expansion and that means that if we follow the
universe backwards in time when we go through this period of inflation going backwards he gets smaller and smaller and smaller but so it means that it for inflation in the region that's going to become the observed universe today was vastly smaller there ever could have imagined in the context of conventional cosmology without inflation so while the universe was so tiny before inflation but there was plenty of time for it to become a uniform and both mass density and temperature in the same way as air in this room spreads itself have acquires an approximate uniform temperature and then once this uniformity is established on this incredibly small in scale inflation simply takes over and stretches this tiny patch of space so that today is large enough to include everything that we sit on giving us a very natural explanations for why the universe looks so uniform so this is 1 of the important pieces of evidence were inflation without inflation we have no way of understanding the uniformity of the universe maybe I should add here that you could always just assume if you like that the universe started Tlalnepantla uniform and that doesn't work out the since it's just an unjustified assumption that has no physics behind most of us would like to have a more physical explanation for how the universe got to be some uniforms and if 1 wants such a physical
explanation than inflation is really the only game in town for an answer that question the 2nd item
I won't talk about it is often called the flatness problem which is the question of why it is university so flat and especially when I was the early universe so flat to set the language for talking about this but I want to tell you I remind you that if we assume that because knowledge is due at least political universe the universe we see is homogeneous the same in all places and has attracted the same in all directions if we assume that degree of uniformity than there are only 3 possible geometries shown here as a close geometry open geometry or flat geometry of each of these pictures says a triangle which illustrates an important feature of these 3 geometries in the close geometry Every triangle has more than 180 degrees in the open geometry Every triangle has a total of less than 180 degrees and only in the flat geometry which is the borderline cases there's a triangle have exactly 180 degrees as you could told us so this is the Euclidean geometry and that we all learned about high school and you could on certainly very accurately describes our universe the question is why now according to general relativity the flatness of the universe is related to its mass density and seismologists talk about quantity that we call Omega Capital Greek which is just the actual mass density divided by the critical mass density with a critical mass density is really just a finding that density that makes the universe geometrically flat I should add the critical density is not universal constant it depends on the expansion but granted expansionary there's a certain density that would make the the universe geometrically flat out so with this definition of Made equals 1 is the fact case by the by construction of major bigger than 1 is close universal meant less than 1 would be an open universe now if we
think about the evolution of the universe years where the situation becomes part of dramatic but it turns out that or maybe was 1 which is certainly what were very near the town of omega equals 1 is an unstable equilibrium point which means that it's like a pencil bouncing step up the pencil starts out exactly straight up and we using classical physics only stated up forever will know which way to fall With its lending just the tiniest found in any direction it will a fairly short amount of time fall over in that direction and that's the same as a manager it'll make it in the early universe where exactly exactly equal to what would stay exactly exactly equal 1 forever but for just a little bit less than 1 the early universe rapidly trail after 0 and was just a little bigger than 1 in the early universe of rapidly rise toward infinity which means that the universe would reach a maximum volume in turn around and collapse In easier these 2 cases if you were a major travel off rapidly to 0 4 or shot rapidly tourism Infiniti galaxies would not have a chance to 4 form so in order for galaxies to form at all the initial value of America you have to be in the alliance and be quantitative incredibly it means that if you consider a time of 1 2nd after the Big Bang is an example but in saying this I should maybe highlight that 1 2nd after the Big Bang is the beginning of these processes of nucleosynthesis by which the likened elements for 1 or 2 at a time in which a possible cosmologist and they have a very good understanding of how the university hated that time you about to 1 2nd after the Big Bang Omega must have an equal to 1 . 215 desolate places to avoid either of these states and get a universe that looks like what we see today now in the conventional Big Bang theory there is nothing literally nothing whatever that controls the initial value of America is just a free parameter of the theory so wide that free parameters somehow got people want to an accuracy of 15 or more deaths lessons Peter is a big mystery in the context of conventional cosmology it's the very severe fine-tuning problem inflation gets around that however but because during the period of inflation the evolution of the universe has dramatically changed gravity is repulsive during inflation stays attractive that was completely changes the equations that describe how the universe evolves and in particular it also changes the way lamented behaves with time so during all eras in the history of the universe except for inflation Omega is driven away from 1 exercise unstable equilibrium phenomenon but during inflation Omega driven Towards One and 7 Towards One doubly exponentially fast so Omega minus 1 gets suppressed by the square of the expansion factor which is itself growing exponentially but so inflation drives that make it 1 an incredibly quickly so with inflation would no longer have to assume that the initial value of Omega was by some mysterious process fine-tuned to be people who 1 to Italy's 15 decimal places with inflation American start off being too were 10 or even 100 or 110 1 100 the further you start from 1 of the more inflation you need to drive inflation to 1 but because an exponential process you don't need much more inflation the start with the method very far away from 1 so the flatness problem is solved and not only is the finest problems solved but this mechanism of driving amounted to 1 essentially always over sheets but you could if you wanted to fine-tune inflationary models starts at just the right time so amazing gets very close to 1 but still noticeably on equal to 1 of the requires a lot of fun to do that so the assumption is that any inflationary model will generically driver made it 2 1 and give me a prediction that today on occasion ones that use 1 of the predictions of reflection for medication you want to add that hold up well until 1998 was in fact a serious problem press inflationary enthusiasts but because until 1998 the astronomers were telling us that metal is not 1 it was more like . 2 0 . 3 and initially that was With the favored value was for astronomers but there was pretty much uncertainty as time went on the uncertainty tended to go down in the interview that astronomers talked about and the numbers seem to converge pretty succinctly to 0 . 2 to 0 . 3 now I should add a personal note here that this caused a a fair amount of discomfort to me especially on nights when I found myself having dinner with a bunch of astronomers the astronomers with service here have been saying well yet inflation certainly a pretty theory that but obviously can actually be writing this inflation predicts a many as long as the data seemed to show very clearly that America is not .period 2 . 3 so fortunately for inflation but that turned out not to be the final story although the astronomers were right about the matter that they were looking at the ordinary matter in the dark matter but now that we think the Omega really is 1 and the latest terrible value coming from plant satellite team analyzed and jobs to some of the data is that the president best experimental value from and there is 1 . 0 0 0 0 blob of Lott and other words currently we think that about half of the century have really verified the maggot is 1 that important difference is that the ingredient that has gotten added to the equation starting in 1998 and something that we call the dark energy the bombshell discovery in 1998 was a discovery made by 2 independent groups of astronomers hope who discovered that the universe is not slowing down under the influence of gravity which is what everybody including me I should confess expected but in fact the universe today is actually accelerating due to apparent a form of inflation that's happening today that is today we leave the universe in fact is dominated by this new ingredient to the energy will be called dark energy which is a material that we presume has negative pressure of producing repulsive gravity exactly the type that I talked about in the
context of inflation and the early universe and this part of the story the key thing is that when you add in the dark energy that we infer from the expansion it brings an end up from the point 2 . 3 that was about to now being almost exactly wants sports we can tell so that becomes what used to be a major stumbling block for inflation observation might now a wonderful success inflation OK the 3rd item that I want to talk about what is the small-scale non-uniform agrees that we see in the universe the structure of the universe now earlier I emphasize how incredibly uniform the university is when we look on large-scale also and that's true of and again here is the constant background radiation gives us the most precise measurements of this uniformity or non uniformity in the cosmic background radiation is uniform its intensity to 1 part in 100 thousand credible although what is perhaps even more incredible is that now astronomers can devise instruments which can measure the temperature too much better accuracy the map and when the temperature patterns as measured to better accuracy than that we find that there are no these we expect that because we knew that non-uniform means were necessary at some point in order to explain how galaxies formed if everything were completely uniform galaxies never would happen but now these fluctuations have been seen in measured a very high degree of accuracy and that can lead to the important question of where these fluctuations come from but in the context of conventional cosmology there was never an explanation for the uniformity in the 1st place so certainly never an explanation for the violations of the uniformity so in the context of conventional before inflation as nology these fluctuations if a person wanted described the universe at that level of detail which put in by hand ahead of the there's so little but in some fluctuations but no no attempted an explanation for I want to be there but in the context of inflation if we 1st think of inflation using purely classical physics which historically is how it all started inflation just stretches the universe out by this enormous racial and that is to lose everything now so the classical level of inflation would produce a universe that would be essentially completely smooth and galaxies would have no chance of forming because you initial seeds of some sort of so there was a period of about a year in the early history of inflation where I the number of other people worried about that it seemed to be a tragic flaw of inflationary models that day I could not explain why these non-uniform agrees but they don't realize that quantum theory comes to arrest you if we treat inflation .period mechanically instead classically then the very probabilistic nature of quantum theory tells us that instead of predicting a completely uniform Marston today I wouldn't have lasted until they will be slightly higher in some places and slightly lower in other places that's exactly the kind of ripples on top of the uniform background which exactly describes what we see in the cosmic background radiation so once we take into hell quantum theory and we expect fluctuations and furthermore contrary really does allow us when we put that into the legal description inflationary models realize its Cafe the properties of these non-uniform means that we expect and it turns out that we don't know enough about the underlying physics of inflation at the present time to be able to predict the amplitude of these fluctuations after that we need to know more about the potential energy function for the actual still feel we've actually drives inflation and for the time being really speculating about the existence of the scalar field so we don't know any of its detailed properties its overhead and detailed modelling to calculate everything but without a detailed model we cannot calculate the expected amplitude with these observations by it turns out nonetheless last that almost all inflationary models under the same predictions for the spectrum of the fluctuations in by spectrum I mean how the intensity varies with wavelength it's pretty much the same use of the word spectrum when we talk about the spectrum of a sound waves would break the sound wave up into definite way once about how big is the intensity each way of the same thing to the pattern of hotspots in cold spots in the sky it's equivalent to measures designed to adjusting the patterns that we're really saying something we can measure would rule out to astronomers have done that and this is the most recent data from the plant satellites but the gasps from data points With Arab origin will use a small The Odyssey and the Green Line is effect to inflationary model with a few free parameters but it's basically the prediction of inflation united States just gorgeous said indicating that inflation is a wonderful a wonderfully accurate accounting for the fluctuations that we actually see In the cosmic background radiation actually clear about what's been on here on the vertical axis this piece of disability case where there is the intensity the fluctuations and a given and were scale measures Michael Calvin squared off on the horizontal axis is the multiple number of these measurements are actually made by expanding and spherical harmonics gives the concept of a circle monarch is not obvious that can be translated into a just angular scale in a new way of life which is what shown on top to the numbers of properties the equivalent annual once for a given multiple number and with the longest wavelengths once of left the shortest way once at the right hand as he she gets very complicated patterns and that pattern is predicted by inflation plus the evolution happened after inflation should be mentioned that the inflationary prediction itself is really very simple inflation index was called scale and inspectors essentially straight line what parts of the bumps mingles come about from residences that happen as universe evolves out those residences will not occur at all if you do not have inflation said up the initial uniform pattern Khalid over very large distance scales so we are seeing here is the very direct effects of inflation and the fitting beautifully with what the observations are but the
4th and there was talk about that now rarely talked about large-scale homogeneity flatness and density perturbations in a seen CMA I have Mike with background on uninhabited will that gravity way is although this is a story that's very much up in the air but many of you are probably aware that last March March 17 to be exact the group called Sept to announce that they had seen no evidence for a polarization patterns in the cosmic background radiation which are viewed as being a direct indication of gravity waves in the early universe which are in turn 1 of the predictions of inflation inflation predicts that quantum fluctuations in scalar fields are stretched out by inflation to become very visible in the density perturbations but inflation also predicts that if gravity really is quantized very small scales there fluctuations of the gravitational metric itself which also gets stretched to reduce possible gravity waves and those interned practicing on the CMB which we can see today in the form of these so-called it have been the polarization of cosmic background radiation so it is a scene it's a very important new piece of evidence for inflation and it also has the important property of pinning down the energy scale inflation because the intensity of the predicted the gravitational waves depends directly on the energy scale at which inflation happen but as you probably have also heard since the initial announcement other groups have looked at the data and the nature of the experiment and realize that there's enough uncertainty about the effects of dust in our own galaxy so that the dust might account for the entire signal to this point we don't really know it by Sept you did see a genuine single from the early universe or not we are waiting the wings for her 2 papers that come out any day now we're expecting the paper from the plunks satellite team describing their own measurements of polarization of possible sky which could perhaps find the modes and were also waiting for a joint analysis by the plant team and the bicep to team pooling their data in a small patch of sky the prices to look at to try to use the phone to infer how much just there is to be able to decide whether by subduing really seen any single from the early universe or not but this could end up going you away it will probably not be very decisive in way that the good news is that more experiments are under way the bicep to chain themselves are starting by Sept 3 and something called the cabaret which will be returning more data later this calendar year and the other experiments as well so if gravity waves really do exist at the intensity range that 552 claimed that we should know for sure within a year or 2 other is however a good chance that the actual intensity gravity ways might be much weaker and then we have to wait much longer inflation is range actually with possible intensity of the gravity waves that can come from inflationary models but addressing the bottom and if a signal is confirmed it really will open a hole in the window on the early universe and incredibly important discovery so now and talking
about the evidence for inflation in getting into the finale of my talk had a steady slide against discussed this issue multiverse which I find fascinating you could certainly be interested inflation not paying attention to the idea of a Moldova's that's viable but inflation does seem to vary significantly suggests the possibility of a more diverse and the real estate is that almost all detailed models of inflation lead to what is called eternal inflation which means inflation that once it starts never stops but rather inflation goes on for ever using more and more of what in this context "quotation mark pocket universes universe would they that 1 of them I will call upon the universe just indicate that's not the entire existence that were talking about so roughly speaking this happens because inflation is driven by a peculiar state of distillate fuel which can be viewed as a matter stable state which decays with some kind of a half-life Our and the important feature is that this half-life is generally long compared to the exponential expansion rate which is going on at the same time government and so on so what that means is that if you wait for 1 half-life of the decay but after the region that you're looking at would have decayed may become normal matter where inflation has ended up with the have that's continuing to inflate won't act occupy vastly larger volume there when you started with so even while this that stable status it's growing and growing exponentially and there doesn't seem to be any way of stopping this so most models inflation goes on forever producing an infinite number of these pocket universes and we would be living in 1 of those pocket universes the cost that money have time so I wouldn't let me just finish by a short discussion I have to try to get across the question of how seriously office's really take this idea of Moldova's I think in general multiverses fast now almost every seismology conference where there are people who are enthusiastic about it people skeptical about it a few years ago there was a conference where some reporter was taking notes about what people were saying and Martin Rees said the Astronomer Royal of Great Britain and the former president of the Royal Society also former Master of Trinity College ignited furious and every possible honor you can imagine the radioactive waste but he said that he has worked with on the role the worst part he said that he sufficiently confident about the multiverse talked about his love life I'm now at the same meeting Monday when they were much closer colleagues who were other pioneers of inflationary seismology I was present when he's lost a lot on the idea of the Moldova's initially John using that he was confident that he would you bet is only on the existence of molten fortuitous specify what evidence would be required to settle this bad but that's what he says but no Steve Weinberg at this meeting but heard about these quotes and commented on them elsewhere heightened regards the wonder the ultimate source of reasons and almost all subjects on Wednesday said on that I have just enough confidence about Moldova's today bed gets was coming out but the city has just enough problems that was above 108 and 1 recent loss of about 100 theft