Questioning Newton and Einstein

welcome to the second part of question in Newton and Einstein and I'll be talking about extra dimensions as a way to modify this this theories so about 300 years ago Newton came up with the first person understanding how apples fall on earth and the motion of planets within the solar system since then there's been a lot of development and we know that although the theory of gravity by Newton works very well on some skills after a while you need to modify it a little bit and the theory of gravity by an Einstein came in and I works extremely well he works so well that we are now trying to look at the probing in the distance between the moon here and the earth through with a laser with a precision of one millimeter so since the Apollo missions they put a mirror on the moon and we're really able to reach this precision in looking at the distance between the moon and the earth with such an incredible precision and that works beautifully with the theory of general relativity and if we continue in this direction that will allow us to to give us some tests of modification of gravity or tests of gravity but before I go there in the third part of this talk let me try to understand a little bit what the universe is doing right now and how that works out with our understanding of particle physics and the quantum world so let's start with a thought experiment let's think we we're in this room and we're going to take everything out of this room so slowly we're going to take all the people out of the room and all the molecules and all the atoms and all the quarks and the electrons every particle that you heard of out of the room completely out of the room so you say well that room is actually not very empty yet because you can have photons going through you can have cosmic rays you can have new trainers if you heard of them all of that goes through this room so there's non-stop things through this room so what we're going to do is take this room put it in the middle of in out there in outer space where there's nothing around it we can achieve it in such a way that there's nothing that can penetrate this room and we take in everything out of this room and yet so this is what we call the vacuum this is the best vacuum we can think of to vacuum than anything we can produce on earth and yet this vacuum will still be filled we still be filled with energy the vacuum the absence of any particle and the photon any light that we can think of is still filled of energy this energy we can think of it as the energy that comes in because out of nothing we can suddenly produce a pair of particle or a pair of particle antiparticle they can be out of nothing and I think you've seen heard some talks by by Glenn or by cyrus out of nothing all of a sudden a particle and an antiparticle or a pair particle can get produced for a little time just a short period of time and then they just annihilate a very short period of time in this process we call loops or pair productions of particles it's extremely well understood it's not something I just came up out of my imagination and you just say oh the vacuum has been filled with this energy and loops of stuff it's something nice is extremely well understood when we think of what we do at certain and I'll explain a little bit more what people are doing at CERN later on but if they take particle and they collide them against each other and then there's that a lot of stuff that comes in and then all the particles come out and knowing what the particles are coming out we can understand what happened in the middle and see what kind of process what kind of physics happen in the meantime and this is extremely well understood with this pair production in this kind of loops that that can happen in the vacuum and I can be attached to this process so out of nothing out of the blue out of the middle of nowhere you can have this production of particle antiparticle of loops of particles coming in and that that means that the vacuum is filled with energy and it doesn't matter where you are in space locally the production of these loops is exactly the same everywhere in space and it doesn't matter what the universe is doing it doesn't matter how universe is evolving locally the production of this pearl particles is the same no matter what when you do it no matter whether you close to a black hole or you're in the middle of nowhere and no matter if you're in this class or if you are somewhere else it's exactly the same and it's exactly the same as the universe of all if the universe is expanding or if the universe is collapsing it's exactly the same everywhere so the the vacuum must be filled with an energy which density is constant in space and in time it's a constant energy density fluid that fills the whole universe so that sounds very much like a cosmological constant and a cosmic is concerned for those of you who were there last week it's something which I can actually explain the acceleration of the universe but that's not the way it was introduced in the first place a cosmic R constant was first introduced by Einstein in his Einstein equation here he probably didn't call it the Einstein equation but that's his equation and this T here T menu corresponds to all the stuff that we know of all the matter or the light all the black holes the planets whatever you can think of this is the matter and the energy which is in this ancient equation and that equation tells you how any stuff is going to affect the structure of space-time this corresponds to the curvature of space-time the structure of space-time and so our journey when Einstein wrote this equation he realized what he thought at the time that the universe was static and so he thought well if you put some stuff and there is stuff in the universe well it's gonna make the universe evolved and since he thought the universe was static he so well there must be something there to balance to counteract this effect from the matter so as to keep the universe static and that's how he introduced the cosmic are constant then a few years later Hubble came along and said well actually the universe is not static the universe is evolving and that's when he removed this cosmic scale constant and what people know it as it's greater blunder not to realize that the universe actually wasn't static and that was evolving but the truth is a cosmological constant would not have been able to make the universe static it's not something which is Nikola Libya and it's not it's it's something which wouldn't happen for four fundamental times the the idea behind a cosmic are constant is that you won't like to make the universe expand more and anything any kind of matter would lemon actually attracts it each other and would like to make the universe contract and so the idea behind having a cosmological constant would be to balance the two effects effects but if you had a tiny little bit more of matter then it wouldn't be the cosmological constant wouldn't be enough to contrive this effect and the universe would wreak elapsed so you wouldn't have been stable if you add a little bit more of a cosmic Arkenstone it would have gone the other way so a cosmological constant is actually not able to make the universe static it's not a stable solution rather what a cosmic arkinson does is make the universe accelerate so they can be at the tongue they didn't know what exactly evolution of the universe was there could be different scenario it could be like if the universe is very much dominated by a lot of matter eventually it will win out if the universe starts evolving after a while all the gravitational attraction will win out and the universe will start collapsing again so that would be one of these scenario and that could happen in it doesn't need to necessarily rekha lapse it might not be quite enough matter to make it red collapse or it can be in any of this configuration if you have a cosmic scale constant on the other hand what you would like to do is really make the universe expand more one more and this is a cartoon way to think of it but since because Montecarlo constant its energy density is the same locally it's exactly the same no matter how the universe is evolving so if the universe is expanding if it's the effective volume of the universe is bigger but the density remains the same in the cosmic are constant overall there's more of it and so the more the universe is expanding in the more dark energy there are the more cuz much constant days overall and so relax it very much so it in such a way that he really wants to make the universe expand more and more in such a way they would accelerate at the end and that that's what a cosmic scale Callister will do eventually we will make the universe accelerate well this is actually very convenient because this is precisely what we observing and so these are the different case scenario that I just mentioned if you have a lot of matter the universe was start evolving but then eventually will rech elapsed and then there's some critical scenario where it will not quite wreck elapsed and just continues its evolution but what we observe through the measurement of the observation of supernovae which is an explosion of star what we observe through that is that the universe is actually in a configuration where it will continue accelerating it looks like and this is something that has been observed about 15 years ago actually and is the reason of its the winning of the Nobel Prize two years ago from these three gentlemen for the discovery of the accelerating expansion of the universe through observation of distant supernovae so it seems like everything is good a priori we have the vacuum energy which can lead to a cosmological constant because the energy density present in the vacuum energy is completely constant in space and in time and a Cosmo jacquard constant can actually make the universe the expansion of the universe accelerate which is exactly what is being observed so a priori everything is good in the best of the world now we'll see if this works out well in the next part of this talk we'll estimate the amount of energy density present in the vacuum energy and compare it with the amount needed to explain the acceleration of the universe what is observed and we'll see if that works out if that works out there'll be the end of the talk if that doesn't then we'll need to work a bit better the empty empty space energy what wheeler called space phone right now we understand particle physics very well we think and this energy that I'm talking about is just related to the energy related to these particles but not to the energy of what makes the space-time itself and that's more related to to gravity itself and to how how to sink of it at the quantum level but I'm not I'm not going there yet so does the energy in the vacuum satisfy equals mc-squared it is indeed a relation between you can think of it as a relation between the mass of whatever particle you can think of and that leads to an energy present in this vacuum so it is it is definitely a relativistic concept like that anyway we will see that it does relate to the notion of the mass of whatever particle with an energy which is what are the e equal MC squared is yeah what's the methodology for measuring the energy in the vacuum and if there is a vacuum would the Box collapse okay so that's a very good question the energy of the vacuum itself is just the energy in the vacuum the we can't probe it it is just a pair production which is there for a little while and then it's not there the only way the only effect he has that we know of at the moment is through its effect on the structure of space-time and so through its gravitational pull back on on the geometry and so what and because if it looks like a cosmic are constant what you will do actually is make that box expand and accelerate rather than a collapse it's it's a it's an energy density which looks like a cosmic arkanstone which really like to have the Box expanding and accelerate when the pairs collide and annihilate one another does that create the energy for the emergence of another pair at another time sometimes they can do yeah so this is just a cartoon where you just have a production a pair production and any tiny leads maybe it only relates in and produce something else or maybe before any elated annihilating it creates something else yeah that's just the simplest scenario and that I can think of but a lot of much more complicated thing can happen has a nonzero expectation value does it contribute to the cosmological constant and itself with what sign positive or negative we would think it's a positive one but it that's that's a very good point that the discovery what we think is the discovery of the higgs particle is absolutely crucial in our understanding of particle physics and the most it gives us some information about the existence of a vacuum energy there so let me go to the second part of this talk where we'll take the vacuum energy from particle physics and then we'll see how well he does against observations so elated Lee's Theory versus observations another way I could have labeled it is the standard model of cosmology which we understand extremely well and as I mentioned this has led to a Nobel Prize two years ago for the discovery of the acceleration of the universe it has also led to many other Nobel prizes throughout their history so we think we understand the model of cosmology and by that I mean how the universe is evolving what it is made of to some extent and how gravity affects it to a very good accuracy and we think we understand we think that University is accelerating right now so there is one standard model of cosmology on one side and on the other side there's a standard model of particle physics where we think we understand with an extremely good accuracy what matter is and not only what matter is but what the forces are all the forces but the gravitational force so out of matter we have atoms which are made of some electrons spinning around some nucleus I just realized this is in French actually I hope you can understand so one the electron and other particles like the electrons are fundamental particles Y corresponds to the nucleus of the atom is not a fundamental particle but it's made out of protons and neutrons which themselves are made out of quarks and the quarks are the fundamental particles and we understand the course and all the other particles like that extremely well we also understand the particles that carry the force that want to make the alux on spin around the necklace and I want to make the quirks make a proton or neutron and I want to make the proton a neutron stick together all of that is related to some forces you know about the electromagnetic force and there's also some weak and some strong forces in the game we think we understand the standard model of particle physics with an extremely good accuracy nevertheless when we put weak we put them against each other when we try to confront them we see a huge discrepancy so I mentioned before that from the cosmetic own point of view it looks like everything is amazing I mean it's just won another prize two years ago for the discovery of the acceleration of the universe and this seems to be confirmed by many other observations things to be very much recording towards a standard model in the particle Theory side the same thing is going on and there was a huge excitement last year for what we think is the discovery of the Higgs at the LHC this is a huge excitement because it really corresponds to the oops that should have gone the other way to the last piece of the puzzle of the standard model so all of these particles are mentioned about they can be nicely categorized in this box and then there was just one little particle missing out of this this whole box which was the Higgs and the fact that we discovered the Higgs more or less exactly where we should have done really confirms that we have a very strong understanding of the standard model of particle physics the hey the mass of the Higgs till last year was known till then the most massive particle in the standard model was the Tao the top quark and you can't quite see maybe it's 171 Giga electron volt and now since last year we've seen from experiment at CERN in Geneva and in particular to experiments the CMS which is so this is you can see the mountain see this is the lake of Geneva black limo and this is where CERN is that's where protons spinned and collide against each other and there's different detector the CMS which is located here this is to give you the scale of this detector and then located here is Alice which is just as big and both of them underground like that and both of them they confirmed the existence of something a particle hopefully fundamental particle at the same mass which is at about a hundred and twenty-five jjigae electron volt tako give a little bit do you correct revolt is a notion of mass or a notion of energy thinking of the relativistic concept for us we'll take the energy as being something like a mass we don't we don't are not going to distinguish them right now and so the mass of that particle is given in terms of an energy this is just a unit of energy if you want to convert that into something more that you can think of a bit better that corresponds to ten to the minus twenty five pounds it's not very heavy and both of these both of these experiments have confirmed the presence of something at the same scale so this is in here or in here and there that would be what would you would have expected if they hadn't been a particle there and the presence of that little bump here has been zoomed here the little bump little bump here and there that confirms that lipid bump is the confirmation of a particle and this energy funny enough this energy is smaller than the top quark I mentioned before so this Higgs particle is has a much smaller than what another particle that we had detected before but it was much harder to detect it and than the top quark so the top quark and the Higgs field the two most massive particle that we know of and that have been detected and as you raised the notion of mass is the same in relativistic it's related to the notion of energy and so if you have a particle present in your universe which has a given mass it actually contributes to the vacuum energy which is which with an amount proportional to its own mass and we're dealing here with our energy density we want to think of the energy density or the vacuum energy which this is what we said was constant and so that's a mass per unit volume and in our language that just corresponds to something which has a unit of energy to the power of four rather than mass per volume that's just the way we we put it so thinking of this massive particles present in the Sun and model will we expect from the standard model of particle physics that the vacuum energy will be filled with an amount proportional to around the mass of the Higgs to the four and that's going to be the most complicated formula in this talk that corresponds to about 125 g electron volt to the four which corresponds to that amount so don't worry too much about the details here this is the result and if you want to put that into something which is a little bit more understandable still that corresponds to 10 to the 23 kilogram per centimeter cube I chose the Higgs you could have done the same thing with the top quark you wouldn't have mattered too much so this is the amount of vacuum energy at least that would expect from particle physics maybe if they are all the particle out there which we haven't detected yet with a larger mass maybe they could contribute with a even greater amount to the vacuum energy but we don't know so this is even being a little bit conservative almost and saying this is what we would expect so now let's see how this amount of energy density present in the vacuum compares with observations with the amount of vacuum and with the amount of energy density that you will need to explain the acceleration of the universe so to explain that curve here and I'm now going to go the calculation of that trust me or trust the people have done it to explain this curve here to exceed supernova data and not only that when since then there's been a multitude of other observation you will need an energy density of that order of magnitude 10 to the minus 48 the minus here is not a typo so when you compare what you think should happen from cosmology or if you really believe in action theory of general relativity from your observations you would expect to have vacuum energy which is of the order of 10 to the minus 48 electron volt now from the particle physics side what you expect is that amount of vacuum energy this is a huge discrepancy this is 56 orders of magnitude discrepancy this is not just a little typo that we did in our calculation and we can just forget about it and move on this is the biggest difference Percy in the whole history of physics this is a huge embarrassment it's a huge embarrassment because he lies at the interface of two fields which are really we thought extremely well understood and and they work extremely well in their own region but we put them together and we have this company what we think is complete nonsense so clearly our intuition from either the gravitational side cosmological side or from the particle physics and quantum sides is wrong or there is something when we put them that doesn't quite work out when we put them the two of them together to give you a sense on how ridiculous this discrepancy is let me just tell you what correspond to what corresponds to would have an energy density which is of that amount if you take an ounce and you put that out in a volume of 10,000 miles to the cube which would be enough to fit the entire USA in in that area here if you put a volume of that size if you put an ounce where the whole mass of the ant in total would corresponds to one ampere for this unit volume will correspond to that amount of energy density so it's really ridiculously small if you are within if you are within the solar system if you are within the galaxy this amount of energy density is ridiculously small compared to anything else it's because the universe is between the clusters of galaxies is because the universe is so big and has nothing else but only that vacuum energy that eventually that energy density wins over and that makes the universe accelerate but within this room the amount of observed what we think observed cosmic are constant energy density present is ridiculously small is and would have absolutely no impact on the evolution of this room at this scale if you want to compare this amount of vacuum this amount of energy density necessary to explain the acceleration of the universe with what you would expect to have from particle physics that would correspond to take in the whole mass of the moon and trying to fit it in a cube of one centimeter size that whole energy the whole mass in this little cube that would correspond to what you would naively expect from a particle physics this seems to be we should really have observed that by now this is a huge energy density and that's what we'd expect but clearly that's not what is present if we think that that has an effect on the curvature of space-time as we would be from a pure general relativity so since there is such a discrepancy between what we see from particle physics and why we see from cosmology or from the gravity side we really have to ask ourselves do we really understand these theories as well as we thought we did could it be that they break down at some scale could it be that they doing very well up to a given scale but after that we really need to start changing things a little bit and there's many different ways people have tried to change the particle physics ID or to change the gravitational side or to change the interaction between the two and I'll just present one exciting way one can think of it which is at tackling more the cosmological side and tackling the mutation aside and introducing the notion of extra dimensions to tackle this discrepancy between particle physics and cosmology so in summary there's a huge discrepancy between what we expect would be the amount of acceleration from particle physics and what we observe from a cosmos get a point of view how to emphasize this is usually sold in a different way you've probably seen this picture before when you see that here about 5% of the matter is what we know of it's everything we made of its all the planets is all the black holes it's all the light it's everything that we need then we know of it corresponds to this 5% of ordinary matter on top of this ordinate or there's something else some other kind of matter which we're not interacting with but which is not fundamentally so different than ours we just don't interact with but the way it acts on gravity is the same than than our kind of matter and we think the universe is filled with about 27% of that in total energy budget not energy density and now in this picture we see that the total amount of energy present of any verse in this dark energy which is cosmological constant or vacuum energy is the biggest amount of energy present in our universe corresponding this is results from the Planck satellite corresponding to 68 about 68% I might change a little bit with something like that so for my cosmic our point of view this works very well from all the observation and we sing but still he relies on the fact that the universe is filled with some dark matter and some dark energy which is something we never seen before and this seems to be a problem but an even bigger problem than that is actually we would know what this dark energy is if it was just the vacuum energy from particle physics but in that case it's not like he would just dominate the amount of energy present in the universe with that amount of 68 or 70 percent it would really completely dominate the whole amount of energy present universe up to 99.9999% a huge amount and this is the real discrepancy between particle physics and cosmology so in the second part of the talk I'll see if extra dimension could help tackling this discrepancy and how and then how what would be the observational signatures of extra dimensions if we went back to your initial black box in space and since we're going by supposition we can't go out and measure it if that box were filled with dark matter would it remain constant or expand under either of these two theories if the box had started to expand initially and you had some dark matter then it will make the the box continue to expand for a little while if you had just dark matter there maybe eventually it will contract and it make the universe we contract if you also have some dark energy present in your box and if it has enough of that then maybe eventually the the the dark matter wouldn't be relevant and what a vacuum energy or dark energy present that would win over and we'll make the expansion of that box even accelerate so it depend a little bit on how much there is dark matter versus dark energy present in your box you squeeze the moon into this little box there once um no that wouldn't be enough to give you a black hole no no you would need the Schwarzschild radius of the moon is so for the earth is a centimeter of the order of centimeters so for the moon its I would expect a few dozen magnitude as maybe it's a few me a fraction of a millimeter in the shorter radius that you will need to do squeeze it into if you squeeze the mass of the Sun into that little box so it gives you a black hole would you ever be able to attain absolute zero in that box without those particles or how would that work if this particle didn't exist if we didn't have any of these particles so we if we gave up our notion of the sender model of particle physics it could be then I don't know yeah what I don't know what the the remaining theory would be but it's if we if we believe in particle physics we don't think we can it's not like we can take these loops out of it they really they really they're and we can't we can't interact directly with we can't interact but we can't take them off it's it's it's it's something which exists by by itself is not we can't remove them wait so we can never achieve a perfect vacuum with no energy density present in it if our current understanding of particle physics is correct but the alternate theory that we explored last week would be that there really isn't dark energy or dark matter there is simply a lack of understanding on the gravitational forces the theory which is mommed I believe that you explore last week that would tackle dark matter that would not tackle dark energy so you still need dark energy to explain the acceleration of the expansion of the universe you wouldn't need as much maybe dark matter to explain the motion of stars within galaxies maybe within galaxies you could modify your theory of gravity so as to explain this motion of stars but you still need dark energy to explain the acceleration of the universe in the third part of this talk we're gonna move on to the extra dimensions and as it was something of a horror for Homer Simpson hopefully first you will be something positive Oh at least we can learn from it so there's different ways we can think of extra dimensions and I'll actually use one but let me present the other way because it might be a little bit more intuitive I don't know so this might be a picture that you've seen before one way to think of extra dimension so let me just start by saying that we live in our world I think we see three special dimensions three special dimensions we can go in three independent directions and that's our three spatial dimensions we have also one dimension of time that we don't have much control on but it's another dimension and so am i said that we're living in our word in four dimensions or in our word in three plus one dimension with just separating out at the time direction because it's it's a little bit different and when we think of extra dimensions we'll never introduce another dimension of time this is really a concept that we wouldn't be able to deal with when trying to unify it with the quantum world etc it really leads to a lot of pathologies that I'm happy to answer questions about later but I'm not going to go into right now so when we think of extra dimensions we're always going to think of extra dimensions of space rather than extra dimension of time so we have three dimensional space and clearly if there was another dimension of space just like ours we would observe it and we think and we will be able to say that whether or not it's there so if there are extra dimensions we need to explain why we're not seeing them and maybe one of the reason we're not seeing them or seeing it if there's just one of them it's because actually tiny they're not behaving they're not quite the same way as our three dimensions but they're very small and this is the cartoon present here where you could have something which this will correspond to our dimensions because I have to project our three-dimensional world onto here and then draw an extra dimension so it's a little bit tricky but this will correspond to one of our dimensions and is being relatively large animals we would see only one dimension only only our three dimensions there but when you go to smaller and smaller distances what you could see is the extra dimension present there and in this model with small extra dimension what you would mean is that what we see is this texture for the Apple we see that the Apple in the within this piece of paper and and we might think that this is all that we have but actually there's more to the Apple and it can go into an extra dimension and that would be the whole Apple there now it could be that is yet another dimension where I can draw because I only see three special dimensions but it could be yet another dimension where there's more to the Apple in this extra dimension but it's so small and we're not seeing it with our own eyes we're not able yet to see it and maybe we'll have to go to extremely small distances to start seeing it and be very very small and for that to happen an alternative to this very small extra dimension is large extra dimensions where we're not made out of things that can go into the extra dimension but rather we can find on a surface within this extra dimension this is the notion of surface in extra dimension of brain membranes in the extra dimensions so they will be here our dimensions we confine into these dimensions just like we would come be from confine on a piece of paper and but there would be an extra dimension present there it's a little bit like these droplets of water can find on the web of spider web or maybe a better analogy is a little bit like the soap this bubble of soup is like we confine on to this surface but yet there's an extra dimension there's more present in the surface is confined into an extra dimension but but it would be a little bit like we are this space water water water spider confining the surface of the water and we cannot this animal cannot swim within the water but yet the fact that the water is present and how deep the water is and and what actually the pond is made of it if it is water if it is honey or what it is really that this pond is made of affects the life of this animal just living at the surface of the water so you be just like us weirdly living on a given surface within an extra dimension and exactly what the extra dimension is made of and what happens in this or dimension has an influence on us and so we will need to understand this extra dimension to really understand all of physics present in our surface so within some given scale maybe within the solar system it's okay not to care too much about the extra dimension but maybe when you go to larger and larger distances and when you really want to try to describe the universe as a whole at very large distances you need to start understanding what's going on along the extra dimension to be able to see how it affects us in this model with extra dimension where you can find on our surface all the matter that we made of and all the light and all the normal forces the electromagnetic force the weak and the strong force that come in to make the the nucleus and the atom and the molecule and the bigger matter all of these things they will be confined on that surface the only thing that we know of which would be able to lick within the extra dimension with liberty probe the extra dimension would be gravity because gravity is really the theory of space-time itself and so if we have another dimension that corresponds to another direction in space and grab since gravity is a theory of space-time it better be able to see this extra dimension so it's really through the force of gravity that would be able to see what's going on beyond the surface that we confined upon so how would the notion of extra dimension help us with this huge discrepancy that we have of fifty six orders of magnitude between the observed acceleration of the universe and the expectation from the vacuum energy from particle physics it can actually help us in two different ways and it's not really one or the other in most model when we build extra dimensions the two different ways come in to make sense and to help you the first one is a little bit more tricky to understand but the comes out behind it is it's quite easy the the idea behind an extra dimension is that whatever stuff which contributes to the vacuum energy or even to the the cosmological constant would not only affect our dimensions and make our universe accelerate but it will also affect the extra dimensions in such a way that it's of effect its net effect on us it's smaller than what we would have naively anticipated if the extra dimensions were not there so really the that I'm trying to draw two extra dimensions it's a little bit tricky but we would be living in a point here and whatever vacuum energy present in that point here it could actually have an effect on the extra dimension in such a way that it doesn't have such a big effect on us anymore and this is something that can happen when you have two extra dimensions and actually with my collaborators we've seen that something like that could happen if you have more than two extra dimensions as well and it's quite natural that these kind of things happen if you have vacuum energy it could actually make you could curve the extra dimension rather than make our own universe accelerator as much another way extra dimension can help with this futures currency is still by changing the name notion of gravity and in su the fact that gravity leaks within the extra dimension so since it's able to prote extra dimension since it's able to leak within the extra dimension what is left over on our dimensions is a little bit weaker there's a bit less of gravity were present in our dimensions so this is again a cartoon trying to represent that we've been confined into this surface in the extra dimension and not only does gravity propagate within our dimension but we also need to share it with the extra dimension so you would go with in the extra dimension and be diluted more quickly and actually if we were leaving not on just on such a membrane but if you're really relieving in for space plus one time dimensional world then Newton would actually have come up with the Newton key below rather than engineering squalor that you may have heard of just because gravity would have diluted more quickly as you go to larger larger distances so in models with extra dimensions what you tackle is the gravitational side of the theory and you actually try to with extra dimension you you change the amount what a huge amount of vacuum energy height affects the geometry of your space on high-tech affects your universe and how it makes it accelerate and through the help of extra dimension it could be that you could have a large amount of cosmic scale constant as large as what you now really expect from the vacuum energy of particle physics so you keep that side of the theory intact but the effect this has on the geometry the effect this has on universe sorry is not as what you would have naively anticipated from the standard Einstein theory of gravity because you have extra dimensions there but if you have extra dimensions we better observe them one way or another that would be the exciting thing to be able to probe extra dimensions then as many different ways you can probe extra dimensions I just can I go through three of them and then I'm happy to answer questions about no extra more ways to probe extra dimensions but the first one is related to how well we understand the motion of planets and satellites within a solar system I mentioned earlier that three this is the laser red laser linear ranging experiment through this experiment we can we know the distance from the moon to the earth with a precision of one millimeter so that allows us to understand the motion of the Moon around the earth with a great precision but if we have extra dimensions there at some given distance kills it starts making the laws of Newton's law and in the nose laws of Einstein's theory of gravity slightly different and I will affect every so slightly the motion of planets and the motion of satellites within the solar system and since we can understand their motion or can't approve the motion so well we could ultimately see if it's a consistent departure or not or if we have to stick to the theory of Einstein theory Relativity so going on into probing the motion of planets and satellites in the moon within a solar system will be our way to probe for the presence of extra dimensions another way to probe for the presence of extra dimensions is something more cosmological skills after all we think of the idea of extra dimensions in here because it could have an effect on very large distances on the size of the universe this is on the right this is a picture of every point here corresponds to galaxies and that corresponds to clusters of galaxies this is something which has been observed this is measurements we are here and we'll look in some direction on the sky and at a distance away from us we'll look at the distribution of galaxies present in the sky so these are the different directions in the sky we've been looking at another distance away from us so that corresponds to the structure the map of the galaxies present in our universe in some directions when we think we understand well actively well even very well how this map has has come and how the structure of the galaxies in our universe has coming through the agglomeration and through the collapse of some structure thanks to dark matter but also thanks to the normal matter in in this theory and this is a simulation which been made using the standard laws of gravity to explain this structure of the universe and you can see this is a projection was this is a different kind of projection but we can see that it looks very similar in the sense that there is this filaments structure person here and it looks more or less similar now if you introduce extra dimensions and you modify the laws of gravity that will have an effect on how matter pool itself and how the structure gets formed by that I mean how the distribution of galaxies is in our universe and so this is a simulation on how we would expect things to happen in a normal theory of gravity using Newton gravity up to some scale and then maybe Einstein gravity up to another skill compared to a theory of what would happen in a theory with one extra dimension and you see that in this case you will have a bigger pool of matter you have a slightly different distribution of galaxies in our universe and by comparing the two and by comparing this with our observations we could tell them apart and say whether or not we would live in a world with extra dimensions i've amendment both of them more or less compatible but maybe as we go more and more within the observations we'll be able to tell them apart nor and more and funnelin and you just mentioned another way we could test for the presence of extra dimensions and modifications of Garrety in general is through the idea of gravitational waves so in a theory of Einstein theory of gravity you might have heard of that we expect the existence of gravitational waves it is very much like the notion of light for a photon only here the notion of gravitational waves is for the theory of gravity we expect that if some large massive object collapse with one another or some some things happen in the gravitation sector we expect the emission of gravitational waves which would modify the structure of space-time around it ever so slightly such that if a gravitational waves is propagating here in a line perpendicular to the to the board that would deform the object around here a little bit like that and there's two different ways it could do that these are the two what we call polarizations 9 a theory of modified gravity in general in a particular in a theory with extra dimensions because you have extra dimensions you have different ways these gravitational waves can modify things around it and so you have what we call more polarizations or simply more ways they can modify things around it you can go along the line of propagation here it will go along the line of publication you can have modes like that or you can mode we have something which makes things grow for little while and then go down for a little worse so these are just extra stuff that could happen although we haven't directly detected gravitational waves yet we do really hope that is going to happen very very soon and they are a different interferometer out there that would hopefully detect gravitational very soon gravitation waves very soon and could be in principle able to tell whether they would be this extra stuff like this presence in gravity present in gravity so this is the LIGO interferometer and it will soon going to advance like which really would expect you to detect the presence of gravitational waves and potentially detect the presence of these extra polarizations as we know it and they are different other interferometer presence there so let me summarize this light pole last part it could be that there would be extra dimensions out there after all we live in our world with three dimensions why couldn't I be extra dimensions are there if there were extra dimensions are there then they need to be a little bit different because we have an observe them yet either they are small or we simply confine on a surface within the extra dimension and only gravity would be able to see the extra dimensions that could potentially help with this huge discrepancy between particle physics and cosmology or the acceleration of the universe in two different ways either it can make the vacuum energy curve the extra dimensions more than more than hours really effect the extra dimensions rather than hours and simultaneously will make gravity weaker because there's a leakage there's a dilution within the extra dimensions so we don't a large amount of vacuum energy might not affect us as much as we naively would have anticipated the good news is that there's a multitude of observational tests that we could go and look for and we could see really whether there is periods of modified gravity and theories of extra dimensions out there through either the direction of gravitational waves and the extra polarization through understanding the motion of planets and satellites within the solar system and so for instance the way mater pulls each other to create the structure and although the structure of the galaxies and the strata clusters of galaxies within our universe thank you

Channel: Case Western Reserve University

Views: 8,560

Rating: 4.6235294 out of 5

Keywords: case, western, reserve, university, science, origins

Id: LO5rxTdi9O0

Length: 51min 16sec (3076 seconds)

Published: Fri Nov 01 2013