Filling the Big Gap in Einstein’s Theory | Paul Steinhardt | TEDxCLESalon

a hundred years ago Einstein presented his general theory of relativity for the first time before the Prussian Academy of Sciences and at the time it wasn't clear that there was a big gap in the theory to be filled two years later he applied his general theory of relativity for the first time to the cosmos trying to present a new theory of the universe and that theory also didn't reveal any kind of gap according to Einstein's idea the universe had a uniform density of matter and energy and it was never changing the universe was static so everything was well behaved there was no problem or gap in the theory the only problem is the theory turned out to be wrong a few years later Alexander Friedmann and George Lemaitre came along and they showed that using Einstein's same equations you could have other possibilities for the cosmos you could have a universe which was expanding with time and now the big gap became apparent because if you take that theory of an expanding universe and you extrapolate it back in time according to Einstein's theory of general relativity you reach a time a finite time ago when the temperature and the density become infinite this is what mathematicians would call a breakdown or a singularity it means there's something wrong with your theory it may have been good at later times but going back to this earlier time there's a gap in the theory something that needs to be filled with a new idea now George Lemaitre I had the idea that if you extrapolate back in time all the matter and energy in the universe would compress into what he called a primeval atom that idea never got very far no one else picked it up however it had an element in it the idea that what replaced the gap was some kind of beginning and that idea does have a descendant in the current Big Bang Theory the idea of the bang is if you like a descendent of the primeval atom idea of George Lemaitre Friedman had a different idea he had the idea the natural thing that would happen is he went back in time that the universe would bounce so in other words going forward in time it would have gone through some kind of contraction and then a bouncing took expansion and these two ideas were both around in the early days of cosmology and the early days of general relativity but the first issue to be decided was was Einstein static theory right or was the idea of an expanding universe right and that was decided by experiment so here's a picture from the early 1930s when the issue had been recently decided it had been decided by the measurements of the fellow in the middle Edwin Hubble who had first shown that there exist galaxies that fill space and then had shown that those galaxies are receding away from us most of them are except for our neighbors are receding away from us at a speed which is proportional to their distance from us and that is the characteristic signature of the Freedman Lemaitre expanding universe picture so that split the that split off the static model is simply being wrong a nice idea but wrong and revealed the big gap now Einstein had a decision to make which of these ideas would he favor the George Lemaitre idea the primeval atom were beginning or the Freedman idea of the bounce and actually if you look at the literature and the archives it's not completely clear but if you look around this time I mean this picture has taken the 1930s at that time there was a clear decision on his part to favour the idea of the bouncing universe in fact not just the universe that bounced once but Friedman's idea of the universe that bounced at regular intervals us what he what Friedman called a periodic universe Einstein worked on it lectured about it but didn't publish on it because by the time he had thought about a little bit further he realized it was a problem with this idea which is that if you took Hubble's measurement of the expansion rate of the universe and put that into this theory of the periodic universe you ended up with a theory which said that the time interval between these bounces was shorter or too short was shorter than the ages of the stars and planets so he saw a contradiction and so he didn't write further about it other than to point out the contradiction now it turns out that this problem with Hubble's measurement was not a problem of the theory it turned out to be a problem of Hubble's numbers and not so much Hubble's measurements but the number the number is measured by other astronomers which Hubble was using its input to get his expansion rate there was a problem there but it took decades to settle it it was until the 1950s but before it got settled and by that time we have no further opinion from Einstein on which idea he favored in fact by that time we understood a lot of new things about physics we had a much better understanding of quantum physics by that time and the protagonist's had changed now the debate was between the steady state model as represented by Fred Hoyle and the Friedman Lemaitre picture as represented by George gamma and there was a famous set of radio debates debates on radio between these two protagonists about the two theories and oil was a very charismatic radio personality and he decided to introduce a term to belittle the opponent's theory the I dream in Lemaitre theory and the term he introduced was big bang he referred to it as the Big Bang Theory figuring that if he could belittle it in this way people would take it less seriously now unfortunately the name had stuck and it's is still the idea that we use today it's rare to have a theory named by an opponent but that's what happened in this case but what's especially bad about it is that it tagged the theory the Friedman Lemaitre idea with just one idea the big the beginning idea it lost the idea the possibility of a bounce even though Friedman and gamma off would have perfectly allowed that possibility and were open-minded about it the to the idea of a bang being associate with Friedman Elektra became they became merged together and if you may merge together up until the present time so that when most people talk about our understand the universe today they think about the universe having to have a beginning having to have a bang at the start now that's not something that's proven it's something that simply guessed at one of the guest possibilities and it immediately leads to a problem if the universe began had a beginning now that we understand the laws of quantum physics it would have begun in a sudden quantum violent start a sudden random process which would have left the distribution of matter and energy very non-uniform and because with Einstein's theory space can curve you would have space which is curved in warped and they would if that's all it happened in the theory and it simply expanded from that point onward when you would look out the universe today would be apparent that it was very non-uniform look different in different directions and that's not what we see we see the opposite we see them you markedly smooth the universe a universe which looks the same in all directions with it tiny except for tiny tiny little variations and so in order to hold on to this idea of the Big Bang we've had to immediately introduce an amendment and that amendment is what we know as inflation so the idea of inflation is that after this violent beginning for some reason a new form of energy took over the universe that we might just call inflationary energy and this had the characteristic of speeding up the expansion of the universe instead of slowing it down and stretching the universe so fast that any curves and warps in the universe were smoothed out and the distribution of matter and energy would smooth out and it would remain that way throughout the inflation except at the end when inflation ends it ends by this energy decaying into ordinary matter and radiation and this decay process like any decay process in nature is influenced by quantum physics quantum physics doesn't allow things to end everywhere at the same time it would force some regions randomly chosen to end earlier their inflation than others so that instead of getting a universe which is smooth everywhere you'd get a universe that had a kind of speckly pattern of distribution of temperature and distribution of matter and radiation much like the picture that is shown here which is taken from Linux an experiment the Planck satellite experiment so seeing a universe which is smooth with this speckly pattern is in most common discussions about cosmology viewed as evidence some even argue proof of this inflationary Big Bang hypothesis but maybe you should raise some questions about this idea for example a reasonable question to ask is coming out of this quantum beginning what are the chances of inflation occurring after the Big Bang even if you put in the ingredients needed to have inflation are you guaranteed that inflation begins well you might guess that's not going to be the case but would it disturb you if I told you the answers were only one in two that inflation would begin well you might say one out of two isn't bad are willing to accept those odds but what if I told you the answer is the chances was less than one in a hundred then you might feel a little uncomfortable 99 times out of a hundred you wouldn't get the right universe you'd get something else but what if I told the answers were more like you know one in a million or one in a billion then there's only one chance in a billion that I can get the universe that we see now you might wonder whether or not this theory is really working is really satisfactory if most the time I would get something that looks quite different than we observe and what if I told you the answer is more like this okay one in well that huge number is one followed by a hundred zeroes but some of you might know has a name it's called a Google and so what if I told you the chances were less than one in a Google now you might be very uncomfortable that this is really an idea which is explaining the universe as it is when the chances of getting what we observe is so tiny but actually the answer is much less than that the answer is more like one in the Googleplex and one in the Googleplex is one followed by a Google zero okay so an extremely small number one in the Google it's one of the smallest numbers that have names to them and the probability of getting inflation to come out from a quantum beginning like this by the simplest by the most rational ordinary measures we use to measure other probabilities is that it's at least that small and maybe smaller still so that's bad news now suppose that we happen to live in the lucky region that's one in a googolplex even then that doesn't necessarily mean we're going to end up with the universe that looks smooth and flat and simple the way we observe the universe to be and the reason is because again those quantum fluctuations begin to become important the same ones that are produced in the little speckling pattern well every now and then produce a huge deviation in the process of inflation causing inflation to keep going while in other places it's ended now those will be in some sense rare events but when they occur they produce huge volumes of universe much more volume than the universe part of the universe that ended the inflation so in fact most of space would be this stuff which is continuing to inflate and then it would produce quantum fluctuations that continue the inflation further well maybe producing other patches where inflation ends and this would continue literally eternally and we call this eternal inflation and one of the consequences when you combine quantum physics with gravity and you add inflation to it that you is that you end up with eternal inflation and with eternal inflation most of space is always inflating at any given time there are patches where inflation has ended but those patches don't look necessarily like us again due to quantum fluctuations some look like us but some don't and what I should really say as an infinite number might look like less but an infinite number do not so we end up in fact with a multiverse what we call a multiverse of possibilities where literally what we mean literally is anything that can happen physically happen given the ingredients will happen and they will happen an infinite number of times so some of these patches will be flat and smooth some of will not be flat some of them will not be smooth someone will have the speckled pattern we observe some not and there'll be an infinite number of anything so you can ask the question what are the chances then in this multiverse of getting a patch with the properties we actually observe and the answer is either ill-defined or less than one in a googolplex extremely tiny now this has led some to suggest that maybe that's just what we have to accept the idea that we live in the universe that's set by random chance but for others of us it suggested that maybe we need to be rethinking our idea about the beginning of the universe and this has been further pushed forward as a result of the recent events resents of the last year and a half or so involving attempts to try to measure another so-called prediction of inflation the production of gravitational ways of cosmic wavelengths in March of 2014 the bicep2 group working in Antarctica this is the experiment that you're looking at they claimed to have seen a signal that would be a signal of these cosmic gravitational waves and those would be waves that were character supposed to be characteristic of inflation in fact some even argued this was the final proof of inflation but then we discovered a few months later that this was a mistake that in fact what they were observing was not cosmic gravitational waves from the early universe but a pattern there was being produced by light passing through the dust of her own galaxy its pattern being distorted so instead of having proof of gravitational waves and so-called proof of inflation they had the opposite the evidence from their most recent paper is that which just came out in the last month the evidence is that in fact the limit on gravitational waves has now quite stiff ruling out all the simplest inflationary ideas so when you add that to the mix there's lots of reasons to go back and rethink the question of the big gap where did we go wrong in this theory beginning with the bang we were forced to the idea of inflation maybe what we have to do is rethink the BET rethink the gap instead of having a big bang think about a Big Bounce instead go back to Friedman's idea and that's what some of us have been thinking about although with lots of new ideas added to it so in this kind of theory the smoothing and the flattening of the universe occur at not out of coming directly out of a bank not coming out of some random quantum origin but when the universe is going through a period much like we're observing today where physics is described well by classical physics whether random quantum effects don't play affect some don't have an effect on large scales at present don't have an active effect on large scales and if you don't have this quantum randomness prior to smoothing in that case you don't have this low probability of things starting if you put in the right ingredients they will start 99.9999% of the time giving you the smoothing and flattening that you want furthermore because the smoothing in this scenario does not occur by rapid high energy inflation but by a slow period of contraction that might begin sometime a trillion years from now if we were looking forward in time or that would have occurred a psyche maybe a hundred trillion years ago in our past before the bang because it occurred during a period of slow contraction rather than rapid expansion you end up not having a multiverse the multiverse was occurring due to random quantum fluctuations that were causing the universe to inflate eternally you've now gotten rid of that idea by having smoothing occur by contraction furthermore this kind of idea does have generic predictions of its own it gives you a smooth and flat universe it gives you a speckle pattern of hot and cold spots like what we see in the Cosmic Microwave Background but it does two other things which are generic first of all it doesn't produce that spectrum of cosmic gravitational waves those were caused during inflation because the concentration of energy during inflation is very high that's what's driving the very rapid expansion but if you're smoothing the universe by slow contraction there is no such concentration of energy to produce the source of gravitational so in this case you should not expect to see the gravitational waves so in fact at the moment that bicep2 had announced that they had seen gravitational waves that was death for these kinds of ideas when they had to come back and retract well now we're in an interesting situation where we're not sure where things are we're still trying to look for those gravitational waves but now the theory is alive again in fact the simplest theory for described kind of theory for describing the properties of the universe we observe a second prediction of the theory if it occurs if you imagine that the bounce doesn't just just doesn't occur once but that the bounce occurs at regular intervals that we live in a kind of cyclic universe which is a natural outcome of this kind of idea if that's the case then what's happening to the universe now which is that it's expanding at an accelerating rate that can continue whatever's driving that acceleration has to decay into another form of energy a lower state of energy that will cause the universe to contract and that's a second fact about a second fact that comes out of these kinds of ideas that represents a kind of prediction and the interesting thing is that these predictions are testable they aren't just ideas the things we can actually go out and try to test so for example bicep2 is now that team has gone on and improved their experiment and there are other experiments like the spider balloon experiment being shown here which runs a balloon which launched it was just launched a balloon last winter which circumnavigated Antarctica and gathered radiation from the cosmic microwave background experiments like that are trying to improve our measures of gravitational waves to see if there are these cosmic gravitational waves the ones of cosmic origin or not and they will tell us about that part of the story at the same time their experiments at the Large Hadron Collider in Geneva Switzerland which are telling us not just about the discovery of the Higgs particle which you've all heard about but the properties of the Higgs and how in how how it interacts with other matter and determines the stability or an instability of our present vacuum and the interesting situation at present is that if you take the data as it stands today and the simplest theory of the Higgs the so-called standard model at the moment it points to the idea that our vacuum is metastable or is metastable which is consistent with this idea of a bouncing universe a necessary requirement or prediction of this idea so this is a time that you should all be trying to mind the gap okay because what's going to be happening in the next few years is going to be historic it's going to determine whether or not the bang idea or a bounce idea is the right idea so it's going to be telling us where the universe came from it's also going to be indicating to us where the universe is going it's going to be telling us about the relationship between gravity and quantum physics and more than that it's going to be giving having a profound effect on our outlook on what is the ultimate reach of science and what I mean by that is the following if we live in a multiverse in which the patch of universe we see simple though it may be smooth and flat as it may be if that's not representative of the whole if that's simply due to random chance in a multiverse then what anything we observe including that tells us nothing about the universe as a whole and detaches us from understanding the fundamental physics that produce the universe we observe on the other hand if we have this bounce idea in that kind of picture everywhere in the universe has properties like what we observe and so even though our view of the universe is limited to our horizon what we observe really is representative of the universe as a whole and informs us about the fundamental laws of physics that shape the universe and I think that is a really important major profound implication of these experiments we'll be taking a place over the next few years so pay attention stay tuned and mind the gap you

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Length: 22min 31sec (1351 seconds)

Published: Wed Feb 03 2016