Where do particles come from? - Sixty Symbols

well Brady I thought today um we discuss where do the particles come from in the universe there's a period that went on in the very early Universe which we've discussed before which solves lots of problems but it leaves us with one little problem it's emptied the universe of all the particles but here we are right this beautiful sunny day we've got particles all around us we've got radiation we've got matter that's clumped into galaxies we know what the standard model of physics is and all these particles are there but they weren't there at the end of this period which we needed early on so I thought I would try and just spend a few minutes explaining where we think these particles have come from all right so where does the story start we live in the universe which we Christen the hot big bang and the hot big bang is we had some particles that that are expanding out because the universe is expanding and when we look at the universe it's very flat it looks like it if you're on the you know the surface of the earth when you look across it you you barely see any evidence of curvature it looks really flat and now Universe might be slightly curved but it looks beautifully flat what do you mean by flat cuz the universe is three-dimensional like what do you mean by the universe is flat so there are these ways of of talking about the spatial curvature of the universe yeah indeed we could be living on a sphere the spatial curvature of that in terms of the the overall space time is especially flat that and so that's got a positive curvature there's a there's a thing with the negative curvature which is the universe espcially would look like a saddle that you put on a horse you know that that sort of can curve up that's got a negative curvature the universe could have a slightly negative curvature slightly positive curvature or it could be the special sections themselves are flat we think that they're consistent with being flat at the same time when we look out at the at the sky and we look at the the radiation that comes to us from the cosmic microwave background that was emitted about 300,000 years after the universe began the r ration is the same in all directions it's got the same temperature it looks exactly the same in all directions when we look on really large scales in the universe the universe looks what we call homogeneous that we're clearly not homogeneous you and I although we're both incredibly fit and we do lots of exercise we don't look the same the planets don't look the same the Stars don't look the same but if you go to large enough scales then on average the distribution of matter looks the same that's called homogeneity you wear in no special place and then finally there are no obvious huge what we call topological defects monopoles in the universe these are objects which if they were around would have caused the universe to have collapsed because of their abundance and their mass and they're not there this is the universe we live in but all of those aspects the fact that universe is beautifully flat the fact that it's so isotropic the fact that it looks homogeneous the fact that there are none of these what we call topological defects present these are all an issue they all have to be fine-tuned in the standard hot big bang in order for us to explain why they are what they are today because the universe is 13.7 billion years old and for example the flatness if you had a little bit of curvature in the universe and you evolved it for 13.7 billion years it would become really curved and we don't see it we see it flat so it must have been incredibly close to being flat early on so this is what then led to the idea of of inflation inflation was a came before what we would call the hot big bag and inflation was this idea that if you had a small enough patch of of the universe where everything was causally connected so light could have interacted with all the regions of it and then for some reason or other it grew exponentially rapidly for a very short period of time but it grew by a factor of about a billion billion billion times 10 to the 27 times so some huge region over the time scale of I think it's a millionth of a million of a millionth of a millionth of a second then that would be enough to have caused the universe to be incredibly close to being flat isotropic so it looks the same in all directions and and it would crucially have given you one extra ingredient it would have given you the small fluctuations which then would have led to galaxis forming so that's probably the biggest thing from inflation but that's before the Big Bang Yes but but it's but it's already banged no something else happened to lead to inflation which we don't know so that's where a lot of research is in what what led to this period of inflation what's that called the thing that triggered inflation well some people would call it sort of the initial Singularity what happened sort of that then led to the universe to emerge in the first place but what we tend to call that hot big bang where the US is full of radiation that has to come at the end of this period of inflation if you're not happy to accept these initial conditions of the hot big bank and you want to explain them you want something that can explain them and that's what inflation was there so the when the Big Bang happened I know that we're not talking about the big bang but when the Big Bang happened the universe was already had quite some size to it the region that actually would turn up into to be our universe wasn't that big but it was a v sometimes people talk about it being like the size of a melon or the size of a basketball or something that billion billion and million million stuff you were blowing my mind with because the start was so small it's still not very big yeah yeah in fact the region that we require was was incredibly small that then didn't hadn't grown to such a big scale for for our universe that we live in but the actual whole region of that that was affected grew much much bigger and so that could be ginormous and we haven't experienced that bid yet we're evolving gradually encompassing more and more of it we've currently inflated and we're like a melon so the universe is it's created these small fluctuations as well which has then led to the structures that we see much later on but and so one thing that drives inflation I should just mention is we we have these things called scal of fields we're all beginning now to hear about scal of fields we've heard about the Hig field right these are fields are mathematical quantities which fill space and time and their vibrations are what lead to particles so when particles are created there's lots and lots of vibrations of the scal of field the higs field is the most famous one but each particle has its own field associated with it so there was one that's postulated called the scale of field for inflation called the inflaton field the energy stored in that inflaton field is what drove this this acceleration okay so where's the problem here's the problem any particles were around before inflation started inflation drives this acceleration so rapidly that the particles just get diluted away the any curvature that was present gets stretched imagine you have a a rubber sheet and you pull it rapidly and then all the fluctuations rubber sheet just get flattened out it becomes effectively flat and the particles that were in there they all just get pushed to the side so we end up with a universe which is very big but it's very cold the temperature of any radiation that's present goes as one over the size of the universe and that size is gone has grown by what did I say a billion billion billion times so the temperature of any radiation has effectively dropped to zero zero all the particles have gone so we've ended up in a universe which is going to be our universe which has got no particles effectively no radiation because it's all at almost zero temperature is empty and there's no structures there Welcome to our world nice so I've got to reheat this is called the process I'm going to describe is reating and we're here at the board because as it happens it's it's an area of active research so I've got some project students working on this and then I'm doing some work with a postto here Swagger Mishra who did a video as well and with some of his colleagues from from India um but I just have this little diagraph here this is in funny funny units it's like the size of the universe it's it's sort of one over it so it shrinked rapidly during this period here which we call inflation can it shrinking I thought it expands in inflation one over the size ah one over the size of course then why use those unit so this is shrinking and then the standard hot big bang which is expanding is this this bit of it here so that's shrinking you're one over so that's shrinking at that point then right so these are called okay it's a bit more subtle these are called co-moving coordinates um during inflation this parameter H is a constant this is the Hubble parameter and oh it's here this is effective of the size of the universe a the scale factor the Hubble parameter is is the derivative a DOT over a god you're letting me do some maths in a 60 simpol video I don't believe it so it goes one over T So during radiation uh and matter this decreases during radiation radiation domination a universe that's full of radiation and in fact this is the solution when it's full of matter it goes a t to the 2/3 so H decreases so but so one over H is here so that goes as T from the one/ h a is going as t to the 2/3 so this grows this quantity which I'm pling grows in that period so even though that line goes down and then up yeah even though that line goes down and then up yeah it's always getting bigger it's yeah the size is getting bigger it's just the rate at which the size gets bigger is important here so so this is this frean Robert oh so that line represents a rate not a size well it's affect it's it's a rate really yes if if I think of a is still having any Dimension this isly a rate it we been put so we have the inflationary bit here we have the standard universe that we're living in here it's coming down a bit here because of dark energy dark energy is causing the universe to accelerate again today when we've done videos on Dark Energy but we there's this bit here which connects the end of the inflation to the start of the hot big bag and that's the bit we now I'm just going to talk about that's the reheating that's where we've left this bit here as we've left inflation the universe is flat it's got no monopoles we've got fluctuations that have been created we've got it's isot Tropic fantastic initial conditions but there's no particles so now we've got to create the particles Big Bang still hasn't happened Big Bang hasn't happened really yet for me the big bang is going to be when we've created those particles and then the universe can start expanding in that D okay that's for me the sort of what I'd call The Big Bang so where's the Big Bang on that line oh I guess I'd do it here just after just after that okay okay so we're we're reheating so what is the Catalyst for the end of inflation and the start of reheating fantastic I can draw a picture draw a picture of course you can so the inflation is driven by what we call the scal of field so we the names five so this we call the inflaton field this has associated with it two terms if you if I was to write down the energy of the FI it's got a derivative it's kinetic energy half mv^ s we learned at school this is the kinetic energy of the field what's that that dot there's important is that's that's that means okay right is Define the rate of change of fire with respect to time the velocity okay veloc in the okay plus and then we have his potential energy so the energy is the kinetic energy and then actually it's got some Brant energy but it's this term I want to concentrate on so a typical form for vfi would might look something like this it would go up to some constant type thing as a function of F so in this region here where for large values of fire can you see it's very flat you like skiing you remember oh you was you wouldn't have done sledging very much okay imagine you're on a hill okay but and you're on a sledge or you're on skis and if the hill is very flat you're not going to move very much you can you might move a little bit because perhaps it's got a little bit of a slot but unless you actively kick it but really go for it you're not going to move and that's what happens early on the field stays up here and so all this this energy here in this potential energy is a constant and it dominates everything it dominates and so this is what causes inflection this bit but the field is beginning to go down here slowly slowly slowly but eventually can you see it begins to feel the curvature here it begins to go a bit quicker so now you're going down the steeper bit but now You' real oh I I'm on the black row this term now becomes important all the time V is dropping because it's going down this term becomes important and so inflation ends say here when that term becomes as important into that toe it's called Slow Roll breaks down but we to go so inflation ends so so now the universe has stopped inflating we're here on this plot and what this field does it'll be symmetric and the it begins to oscillate this field now begins to oscillate around the minimum backwards and forwards oscillating backwards and forwards this is the only energy we've got we've lost all the particles we lost all the radiation this is the only energy we've got in the whole universe to play with and what happens is this field f is coupled to other fields and as it oscillates it begins to Decay fire begins to to Decay to other fields maybe fermium fields which then give us things like the electron or maybe other fields like this Kai which eventually perhaps give us the h and what happens is it as it couples it decays and there are two modes of Decay and I just want to tell you about them both because one of them is familiar to you and you have no idea why it's familiar the one that isn't particularly familiar is called perturbative Decay that's where this field f is only very weakly coupled to this F very weakly so each time it ulates it thinks I can't be bother to Decay can't be bother to Decay but eventually it decays just very slowly so oscillates backwards and forwards it's not a very efficient way of heat reheating but it is decaying to create these and also of course it will create photons which is what you and the light the Hermes here but it's not very efficient there's another way which is called parametric resonance preheating is the technical T and the way it works is you're familiar with you been on a swing you've taken your sun to a swing I guess and you know it you push a swing if you push totally push a swing at random it won't do very it'll go up a bit and then it'll go a little judder a bit but if you hit with a resonant frequency magic point that magic point it goes from and after about two or three Cycles it's going well right up and then you're a bit worried about this so you your TR stop it for old cars those of us who used to be in old cars the mirror of a car would if it hit about 45 to 55 M hour it would start vibrating because the the mirror the natural frequency of the connecting part of the mirror onto the onto the window exactly matched the frequency of rotation of the car at that speed and so it would the the resonance effect would cause this to go go in like crazy and you'd lose you actually you couldn't see out in the back very well that's help is sorted now but I remember that with what that well that's what he taught me so what happens then the alternative way is this thing has a what's we call parametric resonance it actually just goes maybe one or two cycles and it decays and it decays into so the the syon field is decaying and it first of all so this is the parametric resonance this is active where areas of research okay and it's that that prompted me to try and mention it so five it decays and it decays into what we call condensates it forms a condensate it and these condensates um are like because F wants to be together condensate is like something that sort of wants to be a bigger entity together and in particular they can form a thing called osons and I'm I'm particularly um like these because I I wrote one of the first papers on osons in 1995 with ph Marcel glyer my friend we wrote a paper on osons and these are fantastic objects these are objects that have no right to exist okay they they they form these this the upid out size they just exist on energetic grounds there's nothing that no conserve charge they have no winding number like you would get with a cosmic string or a monopole they just exist on this because the energetics of them allows them and whereas they should decay in the in the space of say one cycle of this field that which bounces up and down these last a billion cycles and so what's of interest is these can be relevant for this effect and so these osons one of the things where they're investigating is the formation of these osons and how long they've survive as the universe is reheating and it reheats a lot more efficiently through parametric resonance because of this aspect where if you hit the right frequency the thing decays very rapidly and you produce lots and lots of these particles in fact of these ones very very very quickly and that can lead to a really hot Universe um quite quickly which then eventually totally reheats VI the the perturbative effect at the very end but that's basically the idea of of the reheating that this INF on field which has led to his understanding the density perturbations which are the fluctuations of this field leading to structures which has allowed us to understand the initial conditions of the hot big bang that it's that energies that's stored in that field that then gets converted through this oscillations into the particles that we see today that then reheat the universe and that then takes it to this point here and that's what I would then say is a start of the hit back so the inflaton field kind of shook itself to Pieces it shakes itself to pieces and the debris is particles and these this is part of the debris the osons that condensate actually it breaks up into these osons which are smaller debris particles fall out and and do the osons then break down into something else they break down this to something else cuz they they've got a finite lifetime they they're then Decay so does do we go from the infon field direct to electrons or do we go via the osons good question you don't always go via osons if the coupling is too strong to these other fields these osons don't that's what we've been discovering okay in the last few last few weeks these assoles don't fall I don't want to go there no if Nature's been like that if it's coupled these fields very strongly to these fields that it goes directly just so I'm clear is this you you said you'd be discussing this in the last few weeks amongst your fellow researchers does that mean what you've been telling me now is not like accepted law or it is the accepted way that particles formed or is this kind of you know you and your you and your teammates have come up with this and you're hoping it becomes I wish it come up with it um the idea of reheating has been around since inflation um and that it was realized the universe is empty so how we're going to that that's a baly universe to live in right SL universe so it was realized very early on that that there had to be there was a possible mechanism the details of the calculations are very difficult because the they're called nonlinear equations they and you've got more than one field you've got this field fine but you've got these fields that they're coupled to so your equations are are long and diff difficult you can't solve them analytically so numerics play a big role and I think the progress is that the numerical scale you know that hey computers are getting larger you can do bigger simulations so you can trust your results a bit more and I'd say that's where the field is going I remember reading about this thing parametric resonance in actually remember down in the t- room at Sussex having the paper as hmer Cy about in 1994 that P that original paper came out by Lind stabinski and kofin uh so the idea has been there for a long time but what we've been able to do which I don't think people have done is um we we've new americ we've been able to actually couple these together and and seeing properly when these form we can see them forming in the simulations and so we know when they're not forming and when they are forming and we can then work out the the effect of having these objects forming as the universe decays as these fields Decay and create the particles is the inflaton field totally gone now then that's no longer exists yeah yeah the the infon field is gone today is gone there's a final bit of this process where um you know these osons are made up of the infon field so they as they fragment there's still a bit of residual infon field and that's the bit that then decays via this perturbative effect I was talking about okay redut so so we went from inflation yeah then we then the inflaton field shook itself to pieces and somehow we got all these particles and then sudden and then the particles all went bang and Scattered via the big Bank say they went bang so so that's that's the they were they were distributed by the Bang Yeah well it's not it's not a bang in that's not a singularity there that's not A Spacetime Singularity so this is a this is a smooth effect that's going on here but I I would argue that this is what we would normally call the hot big bang in the sense of it's a universe that's got all this radiation and matter in there and is expanding out that's what I would call the the hot big bang but it's it's an unfortunate term at the level of when it was first introduced we had no idea about inflation we had no idea about reheating that that there the Big Bang really was that that you'd say the universe began from this Singularity Som now or close to the old fashion big bang that everyone thinks of as being there's nothing and then suddenly there's something that's not the hot big bang that's the start of inflation I would argue that's the start of inflation and so the same issue is still there right how did that begin that's still there what's that is that a cold Big Bang the hot here is is referring to the fact you've got all this radiation that's been produced and that's got temperature what do people in your field call the point where inflation starts again start of inflation start of inflation okay right that's what I thought the Big Bang was going from zero to something yeah and and think you know you would think of the start of inflation that which I've put here on the right yeah the right it could have been anywhere along here um that the the the the main contributors to the energy of the universe is this field and I wouldn't be thinking of this necessarily as a particularly hot environment it could be but this would be this has to be dominating for this to take place if there are other contributors to this let's say this is the energy of the whole universe if there are other terms coming in here from radiation and particles and they're dominating this will never inflate you need this to be constant and to be dominating for for inflation to occur so it's a good question do would I call it a hot big bag I wouldn't probably call it a hot big bag yeah may we should introduce the cold big bag you you need a better word for the start of inflation but what don't know all right I'll leave that with you okay all right Professor Copeland and his collaborators have a new paper out on this topic just recently uploaded I'll put a link in the video description also in the description I'll put a link to the University of Nottingham's School of physics find out more about their research and also opportunities to work or study there if you'd like to see more 60 symbols videos well of course I'm going to link to those too including some really good ones with Professor Copeland some deep Dives on the sofa check them out it's emerges as this smooth homogeneous isotropic region which is what we now see

Channel: Sixty Symbols

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Length: 25min 34sec (1534 seconds)

Published: Sat Jun 22 2024