Simulating the universe: Supercomputers in astrophysics

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and it and yeah so thank you so much for the kind of intro and it's really an honor to be here on stage Republican with such luminaries like Alexander guessed at the astronaut we heard the girl yeah

of Cory Doctorow i it's a pleasure to talk to you today about some of the great mysteries of the universe and under the talking to you about simulating the universe I and I honestly I have find that a little bit less scary than giving a talk today on on stage following and some of the great had so I'm going to start out by just giving you a little overview of our best understanding of the universe as it is and there's an astrophysics we call the concordant cosmology basically are agreements as to you the best description of the cosmology that we have today no white is cosmology well cosmology is the science theory of the universe as an ordered whole and of the general walls which government and are concordant cosmology incorporates general relativity the big bang expansion inflation and cold dark matter as well as a cosmological constant by the end of this talk will be able to describe at a cocktail party many of these things here's a little diagram of the history of the universe so we have the big bang than quantum fluctuations or so I be a inflation to a cosmic scale and this provided the seeds of structure that we see today and we have in fact a photo of baby photo of the universe about 300 thousand years after the Big Bang is diagram that's that after grow light patterns on and we can actually see the matter distribution at the beginning the universe then things a little bit dark until the 1st stars begin to form from those there's over densities in the early universe and these stars come together in a hierarchical fashion on dark matter clumps merging and we'll see this in the simulation later I until we get but galaxies themselves and later clusters of galaxies and in the late time on at the present day we actually see that not only an expansion of the universe are coming from the Big Bang itself but the accelerated expansion which will see later that we explained by this cosmological constant so when I get to actually simulating the universe on something important to remember from this I picture is that to simulate the university need some place to start from an initial conditions we actually take a from this baby baby photo the cosmic microwave background radiation is at the initial conditions for a simulation and then making of all these forward with our best physical models to actually see our galaxy themselves moving structure formed in a way that we as human beings we wouldn't be able to otherwise in our art small sure existence and were

able to observe the universe with with telescopes and Comparison relations on to actual observations and refine our understanding as well as motivate and show those people who are actually doing the hard work of of observing a analyzing data from telescopes out where and what they should be looking for so

let's start out with the universe didn't I with the big bang in the big bang was 1st observed by by Hubble of theories by Hubble when

he observed that galaxies farther from us were receding faster from lots of which if you trace this back in time puts galaxies closer together and leads us to infer that things were closer in the past now are moving apart from each other In addition this baby photo they'll keep on going back to you on the cosmic microwave background radiation was discovered i in the fifties in a radio telescope at Bell Labs by a couple of radio

astronomers if you weren't looking for this at all and they saw all a in the radio telescope which

at 1st they blamed on changes its on and I actually got to hear the story of from 1 of the nobel prize winners later Nobel Prize winner about how an after them at that pigeons were taken away i in the noise still existed they realize that this could actually be a physical phenomenon and they consulted some theorists at Princeton and the the theorists that will actually predict this and then later this was observed in in very great detail arm with several satellites 1st W map and then later we actually can see that for a large corpus on this original part of the universe was homogeneous and isotropic that is it looks the same in every direction and we theorized because we don't think that's a we on the Earth are in the milky where in a particularly special place in the universe that it probably looks the same on every patch of the sky and in fact so far this matches very well with observations i had to other parts in in almost a million and if you actually look at a blown-up version of this photo you'll see that I divide accentuate the differences on the site is actually observe some large-scale correlations that is large regions that actually have some causal connectivity to each other and small fluctuations that it's not all the same color there are small differences and I I'm the if the universe was small and everything had enough time to

come into thermal equilibrium then there would be no structure at this point it would be all the same temperature would be all the thing that the however we theorize because of quantum mechanics that in the very early stages of the universe fraction of fraction of fractions of fractions of a 2nd after the big bang of the universe was small enough that quantum physics would still dominate and at the quantum scale things are weird as I'm sure you've heard of and there are fluctuations their differences that are coming into account up because

of quantum effects and because we see these large-scale correlations on if we didn't have something to blow the universe up but faster than it might otherwise I these correlations would not exist because essentially if you were to calculate the speed of light these areas of the sky wouldn't have had enough time at that point to have come into cover contact so due to this and many other reasons the physicist Alan Guth 1 of my former professors at MIT theorized that there was this aspect that we call inflation that in the very early universe blue the universe up I took cosmic scale at a much faster rate than 1 would expect otherwise and this also solves several other puzzles theoretical puzzles in cosmology namely the horizon the flatness problem essentially are how the large-scale correlations came to exist and how the universe is as flat as we observe it to be today and so as I was saying no we can see in pictures quantum fluctuations are grown to a cosmic scale and these fluctuations are exactly those that later incorporate overdensities that an evolve into structure that is stars galaxies clusters of galaxies that we see today OK so the next picture of the

concordant cosmology the next piece of the puzzle is general relativity in their understanding of gravitational

physics on in the modern era started out with Newton's and was refined by Einstein and in a way that says that space time tells matter how to move and matter tells spacetime how to curve Einstein in

1916 discovered that while Newtonian physics

describes the everyday regime at very high energies higher masses extreme regimes of the theory was a bit more refined and we have these equations on which look a little bit complicated but it basically writing out mathematics what I said in words on the left hand side we have a space time telling matter how to move on the right hand side we have matter telling spacetime how to curve and the people side is telling me in that phrase so essentially if you change 1 you get a a change in the other this is observed arm

actually in let's go back sorry about that that it yeah yeah this is observed in a phenomenon called gravitational lensing where we can actually see this on the sky this extremely theoretical concept of a relationship that swing space time and energy essentially we have here on a galaxy cluster that actually bends light it tells us that matter light how to move and we can observe these blends objects on the sky and calculate from that lensing the mass the intervening mass it

so let's move on to the final portion of the puzzle and 1 of the last things we need to understand the basic ingredients to do a simulation of the universe and then I'll go into some unresolved questions as well because if we knew everything about the universe there would be no need add to try to discover more so cold dark matter it was 1st theorized by Fritz lady his actually swiss astronomer who migrated to Tech in later days in Fritz Zwicky observed that and in particular galaxy clusters clusters of nebula I his day is unclear that these objects

called lower also galaxies on that the velocity on the outskirts of the cluster was higher than was expected on given our understanding of gravitational physics and this phenomenon was noticed by Zwicky and he theorized that there was some extended by the elements of of dark matter of nonluminous material that was causing messing with those calculations he was able to predict how much of that under the material there would be a as well as the velocity in his predictions matched on observations In this kind of went up by the wayside for some years and so of your Rubin and forward in 1970 so the same phenomenon

in and i in the andromeda nebula and Rubin and word saw the same thing on the outskirts of the galaxy but this particular 1 being andromeda the velocity is much higher than you would expect calculating on the mass from a light alone and the idea of dark matter was further confirmed by 1 of the 1st examples of a simulation being used effectively I to in tandem with period and observation were flying our understanding and OSHA ca and people's did an N-body simulation of a galaxy essentially simulating it's on with and without some dark matter component and without the dark matter component they got on things which didn't match observations galaxies that worked stable on as we observed the so here's 1 example from the plot of ribbon and forward I'll show you a few plots throughout this talk but on just to give you an idea of the type of data that we're actually dealing with here we have a velocity in the y axis we have radius from the x axis and you see a very flat per here if there was not too dark matter what 1 would expect is this to rock at the outer radius on and that's not in fact what we observed in in modern galaxy clusters with modern observations and it

it this is well matched and this is an observation of large-scale structure on and by simulations show these filamentary arm elements which forms and this prediction from gravitational N-body simulations match very well

observations from a large-scale structure surveys additional evidence came from gravitational lensing where you can compute the lensing of light and infer that matter map from matter and compute the amount of luminous matter vs . material and again this show the

need for some dark component finally some evidence that there are many more pieces the velocity upper presented today is a recent observations of a pair of colliding galaxies in what is called the bullet cluster and incorporates on smoking gun evidence for dark

matter namely we have X rays from gas that is lim material does not match the gravitational map from the dark matter so we can see that there are 2 different mediums medium that are interacting directly from observations

finally In recent years and this was also recently awarded the nobel prize there's a concept of a cosmological constant as an explanation for observations that began in the late eighties it is shown that our universe is not only expanding but it's accelerating and expansion as alluded to before yeah and essentially so that you can

observe remote supernova explosions and particularly a type of supernova

Type 1 and I have a very regular armed explosion pattern and eating precisely infer art very precisely and for the distance at which these these explosions occur and we've observed several of these us we of these in the modern era and with these distances with the explosions with the

ages of the stars we can infer on the expansion rate of the universe and show that it is in fact only standing but accelerating and its expansion we can as well so I predicts that from the cosmic microwave background radiation that the universe the geometry of it I connecting the geometry of spacetime how matter of functions in the universe is flat in calculate the amount of matter energy that would be necessary I to create such a flat universe in and realize that there's a bit missing so these 2 came together and and need explanation for what could be causing the accelerated expansion of the universe namely the cosmological constant that is in this complicated equations that I showed you before relating to the geometry of space time to matter energy there's a freedom of freedom to add an additional constant term and Einstein originally are played around with this these equations are given to us on by some data given to us by by nature itself so fundamentally on efficient match nature and it seems like nature has dictated that there's this extra constant term and when we do incorporate that we get things that match quite neatly with the observations and produced in late time accelerated expansion of the universe yeah

so I've talked to you about are concordant cosmology I'll touch a a little bit about discordance cosmology and this basically on it is to give you a flavor for were not taking

as astrophysicists these things is given by data given by nature and not every puzzle has been solved so so I'll go over some perhaps alternatives to cold dark matter and and some perhaps alternatives to cosmological constant on it to the cosmological constant and then I'll close with how simulations or

exploring both predictions that are concordant cosmology in convincing ourselves that concordant cosmology is actually the right 1 by actively exploring scientific alternatives so cold dark matter

from simulations have aren't with how problem and here are the 4 horsemen of the cold dark matter apocalypse namely missing satellites because core problem too big to fail and the angular momentum bail problem not going to go into all of these in exquisite detail on I will mention that 1 of the angular momentum bailout problem but is no longer considered a problem and that goes to show that some things out with increased observation quality with increasing 1 quality some problems art problems for all time they're just horrid problems they go away on and I'll go over I in particular the missing satellite problems so that issue is that N-body simulations simulations of cosmic structure formation predicts more

satellites of a galaxy such as the milky way then we observe on if you do dark matter simulations only it's uh some people have said well maybe we don't understand gravitational physics What if we modify our general relativity theory of Newtonian mechanics on in a way such that we get that flat what's curves without resorting to dark matter the and so far none of these have held out i in cosmological simulations context they

produce more problems than they fix on another alternative might be well what if dark matter behaves in a slightly different way what if it has a slightly different velocity with the particle is slightly different and people have managed to do simulations of cold dark matter warm dark matter and hot dark matter and that's not necessarily important that we understand all the results of of these simulations together but it can be heuristically see that in the hot dark matter simulation it doesn't have as much of this filamentary structure that we observed in the universe itself so it's quite clearly ruled out whereas the warm dark matter has less structure and it's in these nodes that look a bit like like neurons and that the galaxies themselves form we see that in the warm dark matter situation it has more potential of matching reality and some papers indicate that might solve some but not all of these issues particularly in the 1 that I went into it in detail the missing satellite problem all warm dark matter particle has a smearing effect on cosmic structure so that means that you're satellites are formed on however since this doesn't fix all problems here and there is no indication that just simulating Dark Matter Physics alone is not enough and I'll go into on the physics that are being incorporated into modern simulations by cold dark matter is still the favorite paradigm however physicists actively explore alternatives and that's 1 of the joys of being a physicist and being a simulator is that you can come up with an idea I calculate its expected effects are roughly and then actually simulate as expected effects and role in or out of a model so

some alternatives to this cosmological constant and the so called red dragon of the cosmological constant and so the Four Horsemen 1st there's the cosmological constant problem so this is good news and bad news the good news is that unlike dark matter which is its predicted by any of the best candidate of of particle physics namely it's not predicted by the Standard Model of particle physics on the cosmological constant is projected however it is predicted to be much much larger than the cosmological constant that we observe from us nature itself so there's a desk discrepancy of almost 100 orders of magnitude and there's also a coincidence problem namely this is the fact that the universe has always been dominated by this accelerated expansion phase of previously the energy distribution that dominated were other components such as matter or radiation and it's only in the current epoch in which we

happen to live in as humans on where the cosmological constant is beginning to dominate so usually when we assume that were some or special in the universe this is a incorrect assumption so the coincidence problem leads us to think that perhaps I we aren't at so I so much of a special place arm and maybe think that maybe there could be another explanation so 2 alternative explanations are 1st you can have

some sort of a scalar field permeating the universe perhaps a different type of particle or field than those predicted by standard physics war on here's a funny cartoon about how Einstein on is wrong and currently conducting an experiment which may

prove prove Einstein wrong you exciting it's impossible to find a good thing which in this town said I'm signed in 1947 and this was disproven so this is just to say that of course Einstein was right about everything and there are many could be a as I mentioned before that these equations are given by a data given by nature and maybe they're more complicated in a way on that is different than a cosmological constant perhaps it has more mathematical terms functions of things rather than constant and so these are to propose alternatives that people are myself included have explored actively in simulations so far it looks like the cosmological constant is the simplest explanation for the observation however and it's a beautiful thing to be able to try

out into a universes different consequences and convince yourself that at the dark energy

that the cosmological constant is the correct explanations OK it so 1 thing that I'll mention I won't go into my research in detail but if you try to work in the field to develop alternatives alternatives to the cosmological constant because all our observations match it so well you have to tweak the equations such that they match observations on the cosmic scale and on a local scale very well and often this is done via mathematical chameleon effect essentially designed a mathematical function that high it's modifications of gravity locally and only on comes to light in in reproducing things such as the cosmological acceleration as well some additional observables because of course you want in the end be able to differentiate between your theories in finance arm and alternatives that the observational level philosophically if you can't actually scientifically differentiate

between 2 theories what difference do they actually have so it remains to be seen whether any of these alternatives to slay the dragon but 2 dates are at most physicists work with the concordancer cosmology and there is a community that explorers alternatives and most of that community remains convinced nevertheless of the concordant cosmology so I told you about on some puzzles that physicists are working to address what is the nature of dark matter and what is the nature of dark energy in what is

causing cosmic inflation and the cosmological constant is something else the horizon problem the cosmological problems and there are many more in astrophysics also give you a few other puzzles that I will talk about in in detail but the reason why there are more there's more matter than in China in our in our universe is unclear how the 1st super massive black holes formed they form very early after the Big Bang and it's unclear how they were able to feed of grows so quickly and how all stars actually explode at the fundamental level we observe exploding stars all over the universe the why is

producing ultrahigh energy cosmic rays that we observe a very high energetic particles that are observed on Earth unification of quantum mechanics and general relativity there are many more in astrophysics I mentioned is because we have a good understanding but we're trying to explore on the solution and the very nature of even those things that we think that we do you understand yeah so some ways to address this Army historically this is Einstein's new book and you might see

some i indication of the notation that we saw before I'm not a physicist would calculate a theoretical physicist would calculate and then there would be people who looked at the stars

on themselves and later we built Earth-based telescopes and also

space-based telescopes yeah

and the there wasn't really anything in

between here and here is calculating or you were an observer observing nature as it was and you're trying to match these 2 and I knew supercomputing as us something in between the 2 so 1st you are theorist because you take your theory is you discretize them you put them in a language that the computer can understand in simulation and evolve and for the also an observer and that you're generating huge datasets on observing those datasets and creating predictions that on can and should be verified by people who are looking at the universe directly in the dream would be that your theory is not the universe so well that you're convinced that the right

and this is just an example of 1 supercomputer in the West there's supercomputers all over the world are many modern nation-states have it as part of the scientific and national defense infrastructure and they're very fast and the use of a largely and for a large part physics i in the academic community on here this is a supercomputer in Texas is called constant and its use 41 % for physics and I 1 example useless side to explore 1 of those unresolved questions that I said before how on stars actually explode what is the supernova mechanism how to better understand it so now

go a little bit more into simulation details how you might actually simulate the universe on a computer to try to address some of these questions and in ancient times Aristotle but that there might be 4 elements earth fire water and air

perhaps a 5th element called contestants and all I had to see this is a little analogy of some select elements of astrophysical simulations of course there can be of different ingredients depending on what physical phenomena and you're trying to simulate whether that planet formation or whether that are structure the cosmic scale whether that's a supernova a black hole a single galaxy clusters of galaxies the clusters and of of other objects and so here's some select elements we have of course gravity on which would be simulated with and body numerical relativity equations we have gasses that i which would be simulated with hydrodynamics essentially can model the non dark matter component of our cosmic on structure as influence there's magnetic fields and photons which would be modeled by the equations of radiation and magnetohydrodynamics and the subgrid physics that is physics that is perhaps but lower resolution but we

try to model heuristically on on to match observations in the best way possible and that could be and depending on the simulation what is below your resolution will change that could be stars had to be black holes that could be cooling chemistry physics etc. and I actually briefly flashed the equations here some of them but we won't go into detail but it does did you and tastes on that's and body and numerical relativity equations we have the way the equations for gasses that we have the equivalent of 4 magnetohydrodynamics yeah radiation transport equation and we have each researcher depending on the equation or the the type of physics they're trying to model we have a difference on set of of subgrid models so for some problems gravity may dominate in which case you can say within the error bars and can just include 1 portion of the equations and ignore the others on however as we're always trying to refine our our understanding always trying to incorporate as much of the physics of the universe as we can afford to honor supercomputers and we had progressing abilities here and I'll show

you another plot this should be my last slide again so here on the y axis I have the resolution of the simulation on the X. axis I have over time and then here on various numerical schemes so there are different ways of discretizing of representing these equations are computationally hands on different sorts of physics Some include just cooling in star formation others include stellar feedback and black hole feedback on top of the

basic and body and gas dynamic equations and then here we have many academic after physicists and the take away from this plot is that there is more resolution and more physics that were able to address over time and this is a this is allowing us to have more confidence in our our simulations and make new and novel predictions in areas where we were previously not able to simulate so that the higher resolution you have your simulating on on the cosmic scale that basically means and if you can imagine the universe pixels but it used to be that the universe would look more like a big game where each individual components in our simulation was on to very poor resolution and now able to simulate things with the resolution that were able to see I'm not quite that the hair on on the black hole on 10 the joke Wykle's are about to have no hair on the you won't see the hair on the black hole but were able to see and more exquisite detail the actual nature of the effect of our equations again so under close with some amazing movies on and I'll start out at a

smaller scale will get up to the scale of the universe of some of these examples of of equations in action so the the black hole I on my my collaborator and colleagues Christian Rice Lake is actually not here in Berlin at the Albert Einstein institutes make a pilgrimage to see him on in here hopefully if the new sets and to black holes that are being simulated and will see that they orbit each other and they'll eventually merge and the equations of general relativity predicts a phenomenon called gravitational waves radiation essentially from gravity and our actual detector is being built up by international collaborations to observe these gravitational waves and simulations such as this actually predict other properties of these waves of the is extremely expensive experiments that will give us a new telescope of observing the universe in the gravitational waves spectrum arm are best able to observe

and I calculate on their observation program

next of going to a little greater of of the simulations so this is actually a problem that that I started working with as well as Christian and this is the issue of perhaps I I mentioned before that 1 of the puzzles of modern physics is how the 1st super massive black holes form and 1 candidate is perhaps we have a super massive star to begin with on however the super massive stars are quite difficult to form because if you have a large gas cloud it it

more readily once to form many smaller objects you have to have the conditions under which the super massive stars and perhaps we might have as conditions in the very early universe exactly when we need these stars to potentially form super massive black holes the here's a simulation arm of these uh a super massive star actually collapsing and forming a black hole around and were able to predict the properties and eventually on predict in certain situations that the stars could explode and we would observe those explosions and the nature of those observations now to go up and scale and I this is by a colleague bookish spring at Heidelberg fear in Germany on there's a lot of great computational astrophysics going on around here in Germany in Europe my PhD at the University of

Zurich which also has a fantastic Computational Astrophysics Group and here's a single galaxy forming and I the very 1st galaxy-formation simulations did necessarily forming in a beautiful spiral structure but we saw that by adding increase resolution by adding up more explicit physics we are able to observe and predicts are properties that galaxies like our very own Milky way might have I find this be extremely beautiful and I have something interesting to note is that these user the time is given in mega years so not just a year but making use of OK so here's dark matter

on cosmological scales so this is a dark matter only simulation and as I mentioned before and if you have a problem for which gravitational physics dominates and since the majority of the physical matter in the universe is in fact composed of dark matter in our own galaxy has a hundred times more got more dark matter then baryonic matter and so it is in fact for

many universal questions such as the nature of cosmic structure had to match observations it's very well predicted by Dark Matter Physics alone and this is from the Millennium simulation which was done around them in the Millennium and its has since been done on in increased resolution by the same group with the Millennium to run excetera and we can see a tour of the universe very much like our own and the large-scale properties

the distribution of where expect galaxies to be of matter in the universe matches very well with others and finally I have found a simulation on the cosmic scale that incorporates many of the ingredients of our most of the ingredients of fats as earth water air and fire diagram I showed you before namely this has 5 dark matter and body physics and has hydrodynamics it has on many models of star formation arm as accurately as possible gas clean it has black hole physics on so this simulation is done by the illustrious collaboration are out of Harvard and we can see on just how beautiful our universes arm and see how we might in fact to simulated in the Super here OK so just

to recap on we started out with the initial conditions we simulated by the evolution of these initial conditions of that cosmic migrate background radiation the density given by that armed with a variety of physical methods and we have predictions to compare 2 near present-day observations and this work is done by a variety of physicists throughout the world and helps to inform our understanding of the universe on a philosophical and human level are the ability to created designing experiments and observations in a

way that's as efficient as possible and actually probing is fundamental conditions not randomly looking but looking in a very efficient way what are the questions that we can ask I had to spend the telescope our scientific budget in the most ideal manner possible and finally these large-scale supercomputing techniques have really prototype the away from any other fields of soul that 41 % of supercomputing time i is is physicists in natural sciences and other big portion is chemist in computational chemistry both of these areas have to protect develop algorithms that are

now extending into biology and there are many computational biologists and computational narrow scientists that are you using the techniques that we were really forced to use very early on to address problems in astrophysics that we now have access to and also being forced to use in in problems such as biology etc. yeah so I'd like to thank you very much on and I'll leave you with that and I'll take a few questions thank you pH it was so cool just raise yeah and 0 yeah and what the role plays a arch and artistic expression and the construction of these visualizations

some so I think there's a great deal that art can play out particularly if you look at our multiplying modal data data that

comes from a variety of different sources are from the astrophysics scale you might have come from the actual observations data from different wavelengths that the human eye can even perceive and so it's a manner of art and usability to construct an image that a scientist to make the most sense of honor in this data

that are not even able to see with the their i in addition in these cosmological simulations you might have data that comes from the body component the Dark Matter Physics the baryonic physics in you might want to represent this in the same visualization in a way that a scientist and the and that of a person or a funder or the public can appreciate the effects and I think there's a great deal of both parts and also usability in that you want to be able to actually pick out the features that are important and not highlight things there's various for the site I it but all Molière of the yeah yeah I have a question not quite sure how to phrases because I'm I don't know enough about it but I was interested in the way you like highlighted this disk and 2 aspects and

I think yeah it seems like the standard

model is not ours like standard as it might in there as it might seem so um regarding more outlandish in cosmology of physics maybe I'd something like the holographic principle the the idea of a

holographic universe or something like that which sounds outlandish that from your point of view is it conceivable that something is going to happen on a massive scale like for gravitation supersymmetry something like that or even the sites at some point you have the holographic principle has a of standard model mean is not conceivable that's the foundations on standard us I I would say the things on a question on the 1 that's on certainly we don't understand how quantum

mechanics and general relativity be unified and I think that because we don't understand that that we can't necessarily expect exactly when the solution will be on what we can say historically is that even when Newtonian physics was usurped by general

relativity Newtonian physics falls out of general relativity if you do the math at CERN and the energy scales so we can say that probably theories that are currently being used on something not so well with the observations they will

still fall out of a higher level theory on it just will be that the higher level period will allow us a greater understanding and perhaps predict things that were not able to with our current theories on so I'm I don't have perfect intuition as to what that might be I would say I would not be surprised if in the next 40 years we find some something fundamentally new what that fundamentally new thing will be I'm not sure about but that even so it's very useful to work with our current theories of our current understanding on to make predictions

because there's will match at at some level of the observations it yeah yeah 0 yeah thanks for your very most

talk and the wonderful pictures and um can simulations now tell us what it's going to be the fate of the universe this is already mentioned this you going to be infinite so our current understanding is that the universe is already infants and that

because it's accelerating in the expansion that on and because it's flat but the geometry of the universe is occur back on itself so that it will continue in this accelerated expansion for the rest of time and eventually and galaxies will become farther and farther from each other and eventually will be sort of the heat death of the universe where everything just cools down and it doesn't look like it's going to come back together but that that time scale is astronomically due to its orders of magnitude larger than the universe has even been in existence today the able

questions 0 yeah so yeah you know I would like to thank you for you to play off sorry about that that I like to ask every astrophysicist items to the single question and I hope you will indulge in Douglas Adams wrote

wants that's them if the universe would be understood completely it will be replaced by something so outlandish that it defies that defies understanding would you would you agree with that statement at the very subtle statements as usual Douglas Adams in

many science fiction authors and Cory Doctorow in included have an excellent things to teach us about our reality physics of politics I want to get to the question itself I would say my intuition says that it it would be very difficult to simulate the entire universe with the entire universe so that the simulation is a proof of understanding most but if we can simulate the universe with the universe we may never be able to truly understand the universe so I kind of feel like will never reach that state arm I don't know about if we reach that state if it would be replaced by something else but my intuition would say that will never be able to completely understand things it based on whole questions you have questions was resumes we're only going to offer the great questions by the way that it's an honor to be here this is all essentially yet and you just as the universe at and in no there was consensus and this is the consensus there is a consensus that yeah and that basically comes from there many observations that might show that but you can calculate that from the structure of the cosmic microwave

background radiation it would give you on either be lumped year or less from the universe wasn't exactly flat as so essentially we can use that to calculate on how much of that the energy

balance there should be in the universe and the components of which are on the cosmological constant is as a member of thank you yeah the little

cargo yet and I could see your life think of thank you for that it's mind-blowing of they don't in Wellington to from my question is you know when it stops somewhere as another shell exploded into what is now a flat or whatever concave those matter really but what has been or what is around this nut shell you know my mind kind of goes haywire when I think about you know it started as something that what's about to where this is expanded to this day you cannot Hertz's talk about but this this is cell I feel like every physicists has a different way of

mentally understanding that it's a lot easier to understand in mathematics than it is to try to incorporate and you in everyday understanding but as I mentioned before the general it's simply give a relationship between geometry and matters and so how I like to think of it is that the on which were operating if you imagine a sheet of graph paper that has a bunch of lines in it now if you shrink the size of of book the squares in your product graph paper from large squares to smaller squares to smaller squares to smaller squares on I really fundamentally changes if you have an infinite sheet of graph paper and you're only allowed to plot that there's little point then when need shrink the infinite she everything gets closer and closer together until the point where the graphic we can even see the squares anymore it's all at 1 point but that point is still Internet sit in your conception so when the big bang happened what happens is that point expands into the squares that we see today in the squares are getting bigger and bigger of space time and now the in fact accelerating at the rate that they're getting at so that's I like the like IMO questions I'll be around for the rest the day in the conference so feel free to contact me up

and I'd love to hear about what you guys are all of you and really enjoying the conference them things like this in the

and