Inflation & the Universe in a Grapefruit - Sixty Symbols

inflation is not the Big Bang inflation is not the Big Bang no the Big Bang is inflation if you like gives the initial conditions for the Big Bang well the Big Bang by itself is that initial singularity which we don't understand no one can go back to the very beginning and anyone who tells you they can is there's a little bit of mystique going on in to say the least so what we normally think of as the Big Bang Europe is you're thinking of just a few nanoseconds after the actual initial singularity the Big Bang has certain assumptions in it I'm going to come to inflation why you need inflation and what it is the Big Bang has certain assumptions in it is based on what was called the cosmological principle which is something I'm Stein introduced in solving his equations the cosmological principle states that the universe on large scales is homogeneous that means we're in no unique place in the universe we're just representative of the whole universe and it's isotropic that means it looks the same in all directions once you've got those initial that initial principle in place and once you've got something that's expanding out with the particles are expanding out then you can begin to work out what the temperatures of the universe how rapidly the universe should expand what it should look like today and you can make all sorts of predictions and they worked really well it gives you concepts it gives you time scales like when does nuclear synthesis occur when did the first nucleus occur after about three minutes it tells you when the microwave background radiation emerged about 300,000 years after the Big Bang it tells you when radiation matter had the same density and when we moved into a matter-dominated universe and structures would begin to form and so it gives you all of these nice results it does not tell you where did structures come from in the first place what provided the initial seeds for structures it does not tell you why in the very early universe it should be so homogeneous and isotropic why did that happen and it does not tell you how to get rid of objects that could have formed in phase transitions in the early universe in objects called monopoles which could form in grand unified theories and if you can't get rid of these mana poles they're so massive that they would have caused the universe to collapse very quickly so there are these issues which the Big Bang has associated with it that need explaining earlier it was to try and understand why the universe was as it is so flat is especially incredibly flat homogeneous and isotropic that led to people like in particular Alan Guth from MIT and then Soviet physicists like Alexis Terra bin ski and Andrei Linde came up with these ideas to provide you if you like with the initial proceeding dynamics which would then feed into what we now call the Big Bang and that was called inflation inflation and here we go an inflation corresponds to a period where the universe actually accelerates the size of the universe actually grows exponentially quickly and so it and the reason it and it's a very short period of time in the early universe this occurred for about you know about 10 to the minus 30 seconds that's all you require in order to satisfy all these conditions it could have spent much much longer but the amount you we require to explain the observed universe is about this amount it's it's it's not very long at all you have an initial very small patch of the universe that was represented by the gap there okay and that initial small patch is such that all the radiation that's present in there has had time to interact with each other it's in what's known as causal contact so light has had a chance to propagate from one side to the other side that in other words you expect this bit of the universe to be at the same temperature now this piece of the universe just then begins to grow really rapidly it just gets stretched by the expansion the expansion stretches it exponentially rapidly for this short period of time but it grows so rapidly that within it it's now easy to have a piece of which becomes our observable universe within this huge huge humongous piece it's now easy to have as much smaller patch which becomes our observable universe and because it's begun from this region which was causally connected and is nice and smooth and homogeneous it emerges has this smooth homogeneous isotropic region which is what we now see and so you have an explanation of how you can go from the universe which is on huge scales smooth and hope and isotropic and homogeneous from a region which was much smaller earlier on just blowing up a photo if you take a photo of your family and blow it up and put our cameras on the wall it's going to be the same picture it's just bigger it's it's it's much bigger yeah and but the difference is that the that the universe that you might correspond to might just be the ear of one of those of that of that photograph it doesn't have to be the whole thing anymore I should explain when when we look at the uniform nature of the this microwave background right it's it's got this beautiful smooth temperature it's about 2.75 Kelvin today and it was much hotter earlier on but it's 2.75 and it's incredibly small deviations on either side of it a few parts in 100,000 so it's almost uniform throughout and that's our whole observable universe okay now this radiation was was released about 300,000 years after the Big Bang it's when the Cosmic Microwave Background was released when the when the the first electrons began to bind with it with the protons to form and here hydrogen atoms if you look at the size of the universe at that point 300,000 years after the Big Bang and say right let me compare that size of the universe to what we see now it turns out that there is simply no way that one region of the sky that we can see today which has this temperature of 2.75 degrees Kelvin could have communicated with this region of the sky which also has a temperature of 2.75 degrees coming you know each of these patches couldn't have grown took to meet each other and so this is again another motivation for having the idea of inflation those two patches which today look completely distinct from wandering actually came from the same initial small connected patch which then grew exponentially rapidly this seems like what we all know that we all know that everything was really really small and then expanded yeah we know it's like a balloon no you see the the the standard cosmology it does have things expanding but not at the rate at which you require so if you just solve your equations for a universe full of radiation or full of matter it will expand you're quite right and but when you work out the rate at which it will expand it's not enough to then account for these this observation of the uniformity of the Cosmic Microwave Background so this isn't like a car rolling down a hill someone has pressed an accelerator yes yes someone's pressed that accelerator and so something has got to provide that initial energy energy density energy per unit volume in order to cause the universe to do this and this is where we once again and introduce the cosmologists for particle cosmologies favorite friend which is a scale of field and in up until March of this year we used to say scalar field but no one's ever seen a fundamental scalar field of course we've now got the Higgs it's got Nobel Prize associated with it so we can all proudly talk about scalar fields and this is another example it's a different type of scalar field it's not a not necessarily a Higgs field it's a but it's a it's an object that's just got a value and magnitude and it has a potential energy associated with it and in the early universe this potential energy dominates over everything else all the energy and the radiation and any matter that's there it's much less than the potential energy of this scalar field and that is enough to drive this period of of acceleration and then eventually as the universe is expanding Excel you know growing exponentially quickly this field it doesn't stay on the top of this hill you can imagine the field as if it's on it on it on a very on a hill there it's got a very flat region and then it drops down right it's going down to its minima the field is gradually rolling down this hill and as it's up at the top here it's it's fairly stationary this energy is constant it's this potential energy is constant and then eventually it begins to experience the steeper part of the hill and the field quickens up and at that point as it quickens up this natural period of inflation this acceleration stops and you you leave that accelerating period the universe then has to go into what's called the reheating all of that energy is stored in this field has to get transferred over into the particles that you and I are made of because that they've all been diluted away during this period of expect exponential expansion anything in the universe has just been diluted away as the universe expands so rapidly so we've got to re re energize the universe we've got to create the particles again and this process is called reheating and it's a very difficult process to actually understand because it's in the sense of the field has to couple to lots of other particles and we have to understand how they're created and that's an ongoing area of research trying to understand how efficiently this is done but the universe reheats it creates the particles that you and I are made of and that that then enters a radiation-dominated era and that if you like is what we would call the beginning of the Big Bang so the inflation before the big in that in the sense I think of if you think of the Big Bang has been based on the idea of the cosmological illogical principle being satisfied and an expanding universe as its initial conditions then inflation will give you that it doesn't inflation still hasn't addressed this bit about the very beginning right I've avoided it again because I don't know the answer to that I don't know what actually bank to give me the big to even to spark off that period mystery toilet we don't understand with this you know you can give error to you yeah yeah Big Ben one people inflation then inflation then Big Bang to Big Bang one is being the initial what happens at that very easy catch you showed me with your hand yeah inflated yeah where did that come from that was Bob viously band out of the mystery yeah the creation of space-time has to create yes so what ever managed to launch the universe I'll create space-time wherever that energy initial energy some people would argue it is inflation that for example quantum mechanics allows things allows you to because of the Heisenberg uncertainty principle which tells you you can trade off energy for a fraction of time you can you can grab a lot of energy for a short period of time for example in the Heisenberg uncertainty principle and and that energy could be the energy stored in this field and so some people would say that's what happened that energy was it was enough to trigger the creation of space-time and then off it went so in that sense inflation does it for you that passions lated whatever was there like that became diluted hmm what was in there did it will have had it will have had radiation yet will have had some energy in there but not atoms no not a turn we're too high we're too high an energy for that there is so if an atom was to try and thought you know what is an atom an atom of hydrogen is where an electron is bound to a proton and and and proton itself is made up of quarks okay but if you if you increase the energy of that electron bound into the proton if you in fact it takes relatively little energy to for you to rip the energy rip the electron off again and so the early universe had way way more energy than that so in fact everything that would be present in the early universe would have been in their most basic fundamental form we wouldn't be able to form structures like protons even at that stage is it valid for me to ask how big these things were well how big was how big was the universe before and after inflation so this yeah of course it's valid so for example a patch and that is about 10 to the minus 20 I think it's about 10 to the minus 27 centimeters and would have grown would have been enough a big in at work yeah 10 to minus 27 centimeters at about 10 to the minus 30 seconds after the Big Bang would have been enough to then grow to easily encompass our observable universe which at the end our observable universe at the end of a period of inflation would be probably about the size of a grapefruit and then it could carry on growing after that but it would have done enough expansion to then account for the observed o sub P that we see today then we went from very small to a grapefruit through a grapefruit myself yeah by the end of the period of inflation that we require there could have been much more I mean nobody there are models of the universe because they require these scalar fields you can change this potential that's the thing that you can play around with and get different predictions there's a very key thing about inflation which I need to discuss in a second but different models will give you different periods of announce of inflation and but we require fixed amounts in order to account for the observed uniformity of this radiation and the observed flatness special flatness of the universe but isn't there also an upper bound to the inflation could isn't there a point where you guys will say my life inflation lasted that long that wouldn't work I mean have you got it you tell me this lower bound is this 10 to the minus 13 is there an upper bound well there's an upper bound no I mean you can have there are models of what we call an eternal inflation these are models where inflation has been going on in some part of the universe forever it's just not happening here I mean well actually it is happening right now with dark energy but it's at a different energy scale and so there isn't enough about in that sense I mean there are there are models of inflation where you're it's constantly popping off different regions of space growing exponentially quickly that but they're just not the regions that we live in it's it's important our region inflation did end because if inflation carried on then structures could never form matter would always be ripped apart rather than it being allowed to clump together so we know inflation how to end it could have gone on for a long long time in terms of the amount of doubling of the size of the universe but we know that we require the as a fixed amount at the end of the inflationary period in order to account for what we see today you talk about a time when the observable universe was a sizable break the universe no the observable universe but the universe that we saw they you know in flesh and leads to the size of the universe way bigger than our observable one and so we don't know what's going on out in those regions and it's in those regions that we could it could still be inflating there could still be regions of the universe influencing out there and spawning more expansion accelerated expansion there's a good whole group of people don't particularly like the idea of inflation and there's a and they would myth and I've worked on both both both of these and sides of the argument and and and one of the reasons is the question of you know how fine-tuned do you have to be in order to get inflation in the very in the early universe and there is a big question about this using this argument over this initial patch for example why should it have been uniform at this epoch where we expect quantum fluctuations to be so big that it could spoil it all for you and so there is it there is a question about the fine-tuned aspects of these inflationary models and that's one way you you argue about how how how likely it is that inflation actually occurred and that's enough that's still a debate going on as to the and there are different models in the others there are models called the cyclic universe right where the universe undergoes a series of expansions and collapses and each each time it collapses and bounces back these are usually brains that are bouncing out of string theory or bouncing back out you'd call that your Big Bang but there are issues there as well concerning how you actually deal with the bounce itself and all of these models where you end up dealing with regions of high curvature where singularities conform you always ending up because the mathematics usually is breaking down on you a degree of speculations required to to actually unfelt inner them or not speculation but but but you need to acknowledge that that we may not have full control of the mathematics and that we need to try and understand that better it's a it's an amazing idea it's so now let me come to the bit I said I needed to talk about which many people would say it places it on really solid ground which is in many ways the big key breakthrough or the key result out of inflation isn't necessarily this fact that it provides me with a naturally and natural where to get a smooth homogeneous isotropic universe that's not the key thing the key thing is that it provides me with a way of obtaining the initial fluctuations in the matter content in the universe it provides me with those seed primordial fluctuations with which galaxies can then begin to grow which the microwave background anisotropies can be observed to be what they are and the reason inflation does this for me is this input on this scale of field again do you remember I drew the picture in over here where I said imagine the field is on a potential which is flat and then getting steeper okay so and it's evolving down and I drew it very smoothly just evolving down but in reality what's happening is this field is a quantum field it's not a classical field like a ball rolling down it's got this a quantum object quantum objects inherently have fluctuations just through the Heisenberg uncertainty principle so as its mean value is indeed going down it's wanting to just fall down all the time it's fluctuating backwards and forwards backwards and forwards backwards and forwards these fluctuations mean that in some regions of the universe it's slightly higher up the potential in other regions it's slightly lower down the potential that means it's got slightly more energy here in this region slightly less energy in this region so now in different parts of the universe I've got these slight deviations in energy those feed into the equations they affect how gravity works where it's slightly more energy in the particles slightly less energy in the particle and it provides you with this small fluctuations in the pull of matter towards matter from this region to this region photons of light experience slightly different gravitational pulls as they go through and they lead naturally to the onset of these fluctuations which is the macro Cosmic Microwave Background and our satrapies which we discussed with about Planck and then later on from those fluctuations you seed the structures of the universe what inflation seems to do quite remarkably is when you look at the distribution of these fluctuations of the microwave background and you look at these Doppler Peaks okay and then they can now pick out about seven of these Doppler peaks and you fit it to your inflationary scenario it just works like a dream it just Maps all of them there are some slight issues in some regions which people are homing in on because they're desperate to try to find something that might be wrong with inflation but the odds that we don't yet understand about it but the general feature seems to be there that the inflationary prediction due to these fluctuations of this field seem to map brilliantly over to the Cosmic Microwave Background I know so but and so there's a whole group of people would say inflation is RIT is on really firm footing I'm not quite there because I see inflation as this wonderful paradigm that works really well that make the idea works really well but where did this in photon field come from where did this scalar field come from it's got some from from some fundamental theory and there we begin to struggle actually if you try to and that's where I've sort of been doing the bulk of my work if you try and incorporate inflation in the world of particle physics and in our in string theory it's actually not that easy it's quite difficult to get a scalar field which does everything you want it to do in terms of the Cosmic Microwave Background and yet also fits very nicely into the dynamics of the universe from the world of string theory is it gone it the bulk of its energy is gone yes and there are some models of the of the universe remember I said there are many models of their simpler time so in the majority of them is gone that the field has has decayed and that's the reheating process at the end of inflation and it's declared its energy has gone into creating all the particles but there are some models called one particular set models called quintessential inflation where that that M photon energy hasn't yet all gone and some of it is still driving the current acceleration of the universe the universe is accelerating again today at a much lower energy scale than it was accelerating in the early universe but it still it is accelerating and some models have that energy there but the majority of the models would say it's something else causing that acceleration today emit and that in photon energy has indeed gone

Channel: Sixty Symbols

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Keywords: sixtysymbols, inflation, universe, big bang

Id: m7C9TjdziPE

Length: 24min 7sec (1447 seconds)

Published: Tue Dec 17 2013