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so much we already learned it's about space about the universe and about our place in the universe also a system but the next speakers will exploit us how we can use computationally methods to simulate the universe and actually. role planets the speakers will be an up in scene she is a ph d. student in computationally astrophysics into being and calmly in cambridge she is physics must a student at hyperbaric university and the talk is entitled grow your own. planets hollow simulations help us understand the universe it.

i felt hi everyone. the. a it's a cool animation right and they're really cool thing is that there's actually physics going on there said this object could really be out there in space but first created on a computer said this is how a star is forming how our solar system could have looked like him. the beginning. thank you for being here and that you're interested in how we make such an animation and and i am research is an astrophysics and we're concentrating on how planets form and them all he is doing her ph d. into being and doing my masses in had a beck.

and in this talk we want to show you a little bit of physics and how we can chart translate that in such a way that a computer can calculate it. so let's ask a question first what is the owners awards in the universe the most part of the universe is something we don't understand yet its stock matter and dark energy and the don't know what it is yet and that everything we can not see in this picture here.

what we can see our stars and galaxies and that's what you want to concentrate on the historic. but if we can see why would we want to watch a computer.

well everything and asked for astronomy takes a long time so each of these tiny speck says see here are galaxies just like ours this is how the milky way looks like reliving in this tiny spots year and as we all know our earth takes one year to orbit around the sun not think about how long it.

takes for the sun to orbit around the center of the galaxy its four hundred million years and even the stuff of nation this ten million years we cannot wait ten million years to watch our stars forming right that's why we need computationally methods or it simulation. is on a computer to understand these processes.

so when we watch to the night sky what do we see of course is the stars and do most beautiful nebulas. they are gas and dust and all of these images are taken with hubble space telescope all. so this one image to does belong in their own. but it looks very similar write this gives us the idea that we can describe the gases in the only worries as a fluid it's really complicated to describe the gas of us in every single particle so we can attract every single molecule in the gas that moves. the around its way easier to describe it as a fluid so remember that for later we will need that but first let's have a look how his stars forms a star forms from the giant cloud of dust and gas everything moves in that clout so eventually more dense regions of. her and they get even denser. and. these clams scam eventually collapsed one star so this is how his star forms they collapsed due to their own gravity and in this process a disc forms and in this disc planets can form so why a disc. as i said everything moves around in the cloud so it's likely that the cloud has a little bit of an initial rotation. as it collapses dissertation gets larger and faster and now you can think of making a pizza so when you make a pizza and spin your dollar your finger you get a flat just like a star like a disco around the star that's the same procedures actually. i see in this disc we have dust and gas from this dust in a disk the planet can form but how do we get from tiny little dust particles to a big planet. well it somehow has to grow and grow even for them compactor we have rocks and even grow further until we reach planets how does it grow well that just grows we know that if least that's what i have surfed when it took those images in my flat. well so dust can grow and grow in fort for that and compact but when you take two rocks were now at this in this state when you take two rocks and throw them together you don't expect him to stick right to expect him to crash and crack and. two thousand pieces so. we're standing on the proof that plassnik six exist how does this happen. and it's not quite solved in in research so this is a process that it's really hard to observe because planets are very very tiny compared to stars and even stars are only small dots in the night sky. also this as said planets form in the disk and it's hard to look inside the disc. so this is why we need computationally to understand the process the how planets form another astronomical processes so let's have a look at how the simulated on a computer. it's. ok so it somehow we have the scene nature it's beautiful and it just like the tank of water in a bubbly fluid we already have so now we have this bubbly fluid in here in the middle demonstrated but now we have to teach our computer to deal with. the bubbly fluid and that's way too much same year old molecules to simulate them as we already said so that two ways to describe ties it in a way that we just look at smaller pieces one as the raunchy in description just like taking as small bubbles all. no balls at of material that have a fixed miles they have a certain velocity that varies between each particle and they have of course and mentally because they have in the last thirty animals and we've created a number of those particles and then just see how they move around and how they collide. but with each other that would be one way i'm and that was described last year in a very good talk i can highly recommend to hear this talk if you're interested in this method however this a second way to also described this not just going with the flow of the particles spot we're bit lazy we just fox it so weak. created ritz. and as you see the on here in the script you have a certain feeling level a bit of slowpokes so what's what's the trend there and then on we just look fours each box what flows in what flows out through the surfaces of the sparks and then we have a wall you. and or in mass food within the spokes and this is how we describe ties board is going on in the disk and actually use and we're usually in the system of a disc we do not do it in as nice as a box way like this but we use boxes like those because they are already almost. like a disc and we just keep exactly the same boxes all the time and energy just measure what goes through the surfers in these boxes so.

this is how these two methods look like if your computer with both of them so they one was stunned by me i'm usually using this boxing method and the other was stunned by my colleague and you see these like when you look at them at the color us that the structures q you have the slope in what.

you have the same slope in woods here you have you even this silly structure year the same year but what you notice you have this and large thoughts that are really these are really the mosque particles we sold before these bubbles and here you have this in our capital this is because when you create. this grit you have a very it in a region at the in a part of the digits disc where the box become a tiny and tania and well we can compute that so we have to cut out at some point in a pod so hewitt when you go to low density stays above. as blow up and distribute them as over large areas so it's not very accurate for these areas and here we have the problem we conquer a cure lately in the area so both methods have the the pros and cons and and are well it the but no foremost we will focus on this. one just an so we have is nice actually use stream the features so again going back to the boxes i'm we have to measure the flow between the boxes this flow in and.

physics because of flux and we have the density row one density wrote to end the flax is the description of what mas moves for the surface year from one box to the next so if we write this and monmouth terms it looks like this. this says. the in the time devoted to have the density meaning the change in the this dude the change over time so how much foster those low you go that level also to you would be a change in time and then this. it's really weird triangle simple it's called not love is a the positional derivative as so it's like a slope so how much how to reach change our position am actually so if we change look at the density over time it should occur. late to what the room inflow we have over position that is what the s.s. so and then we haven't physics and few principles that we have always too bad because that it's just all most common sense one of them as well have we have mosque in a bog.

six. well it like this the mosque should not go anywhere and less someone takes it out so if we have a close box and mohsen that books nothing should disappear magically we should stay it should also stay in this box so even if these particles jump around and our box with a certain. t. it's the same number of particles in the end that's again the same equation just them told in math so when the second very rudimentary principle as if we have energy in it in a completely closed box so for example the size. chemicals here and we have a certain temperature so in this case our temperatures lol maybe like outside of dumb the around to reduce greet his cell this and then we have this nice chemical stone year and at some point they react very heavily we suddenly and i have with me. much less chemical energy and a lot more thermal energy but over all the complete energy as some up you like the thermal and the chemical energy also the the energy of the movement and the energy of the potential. the ended up to this variable you that should not change over time if you sum up everything because our energy is conserved with in our clothes box and then the third thing is i think you all know this and if you have. like a small mosque as in with a certain that also at the very high velocity in this case and bombs and to someone very large what happens well you get a very small the last thirty in this large body and this morning a must stop us and the principal he is. is that in momentum is conserved meaning that the velocity times that the markets have one object is the same as then later for the other one but since it's lodger this product has to be the same that doesn't change and we have also to go. unlike in our simulations to obey these rules and we have to to code that in so that we have physics in them so you say ok this is really simple of these rules right but actually well it's not quite us and so this is an area stocks equations a very complicated equations not completely solve. of and we have here all that is marked let other riveted here we have our conservation all that was does denies and simple pod but now we have to take other the physical things in the into accounting for low pressure accounting for this cause a tea. the four compression so squeezing and like how a sticky is our fluid and also gravity so we have a lot of additional factors additional physics we also have to get in somehow and all of these also depend somehow on the change of position.

or the change of time and these derivatives aren't really nice have for our computers because they well they don't understand this triangles so we need to find a way to read another rhythm so that the. can some will relate with these modern formula in a way that the computer likes and one of the in a way to do this is in his well this simplest solution actually is just we say ok we have now distant it's not just the.

in the river tips and we want to get rid of them so if we look just at one box now and we say that in this box the new well you for the density in this box would be the previous. density plot us the flax in and out times the time step all of which we measured this flux buy it or lose so and we have to somehow get to this flax and we just say ok this flax now is the if we start.

year. slow of this curve the trend so to say they were this curve is going right now said would look like this so in our next ted time step we wouldn't have a density don't hear it in and well then we do this again we again look at this point west trend going with the line. the going and then we end up here same here so again i'm. we just try to find this flax and this is the trend at this position in time so this goes up here and then if we are here now look at this point it should go up here so this is what our next trend would be and we do this over all that. times and this is hell our simulation then would cut your late the density and a four one box over a different time steps so that kind of work so the blue curve with the analytical won the red kerr was its kind of stimuli was good works but. can we do better its it's not perfect it right so on.

what we can do is be refined as a bit taking a few more steps making a bit more computationally heavy but trying to get a bet there is a delusion so first we start with the same thing as before we go to this point to find the trend in this point that. the point that the line would go up in this direction from this point and then we go out just hof a step knol so great and. now we look at this house a step to this point now and do it again the same saying ok where's the trend going now and then we take where this point would go and i'm added to this trend so that would be that the average of. this trend of this exact point and this trend. it is dark orange color of and then we go back to the beginning with this trend now and say this is a better friend and of one we had before we know you start and go up again and and search the point at the four it hard for time step and and then again we do the same thing now we are. the again try to find a truly the trend an average of with a barrel before so it's not accepting the trend is a bit below the trend because we average did with the era before and now we take this averaging trend from the beginning to the top like this decade. this is already quite good but we can still do a little bit better if we ever rigid with our ending points so we go here look where's the trend going to would go quite up like this and the average this and this together and then we end up with a line like this this is so much better than. what we had before it's a bit more complicated to be fair but actually the it's almost on the line so this is what we wanted it so if you compare both of them we have here our analytical curve so over time in one box this is how the dense. but you should increase and now with a blue both of the numerical method the difference look like this so we have seen the smaller and smaller time steps even the oil markets closer and closer to the curve. but actually the room that could to the this for step and process works much better and much pasta however it's a bit more computationally with and difficult. when we simulate objects a nest on me we always want to compare that to objects that are really out there so this is a giant telescope well consisting of a lot of small telescopes but they can be connected and used as a giant telescope and the takes four.

photos of dust in the sky and this is used to take images of discs around stars and these discs look like this so these images were taking last year and they're really cool before we have those images we only had images with lesser.

resolution the so they were just blurred blogs and we could say yeah that might be a disc but now we really see the discs and reduce the ring see a thin rings and with see the thicker rings over here and even some spiral the structure is here and also some future. is that i'm not really radio the symmetric like this are key year. it's and that's not completely solve how these structures formed. and. to to find that out of a colleague of mine took this little it as an object with with the asymmetry here and so this is dimitry just saw and this is his simulation so this is how this looks like in the beginning.

probably him and he put him three planets and let the simulation run and so what we see here is that the stars cut out as an asset we have to said the great cells in the in the inner part are very very small and it would take a lot time to come all so that's. why the year of computer relieving out that spot in the middle and what we see here is three planets. interacting with the material in the disk and we can see that these planets can have a can that can make this thing here appears so that that to me and we have something looking very similar to what we want to have or what worries. what would review the observe so we can say is three planets could explain how the structures formed in this disc. it's a little bit elliptical you see that that's because it's tilted from our side of climate it would be around if he watched added face on but it's a little bit too that that's why it looks a pickle. so we are the sole we can put planets in the gas and and create structures and one very exciting thing that we found in the last year or two years ago it started but been far more is this system pedia.

this seventy in this system for the very first time we found a planet that was still in bed with completely with in the disk so the gas and dust and usually because the the gas and dust is the main thing that creates. the signal some radiation because a feat that we only observe that and then we conduct served the the planet embedded but in this case the plan was large enough and in the right position that we actually were able to observe some signature of accretion on this planet that was prior then the the rest. of the disc and the than later just this year just a few months ago we actually found out well this is not the only object year this is a very clearly a planet but actually like this thought here is also something so it's we can see it in. different and grains like every picture here is a different set of grains observed and we can see those in follow for different.

five different kinds of observations so there is a planet here and then there's also something we don't know what it is yet but it's the point like and actually creates the future that we reproduce and different kinds of observational bands or eight different kinds of the. i'm seeking the it's here that this is very interesting for the first time we actually see the planet forming right now with in the disk am so a colleague of mine also is very interested in the system and and started to simulate how does it is how do you two planets in a disk. change the dynamics of the disc and so here we have have cost us discuss it into to it because it's not stays on its it's like forty five degree still don't like not like this but like this and so he had to face on this is what is.

it looks like so there are two planets that these blocks year again as in a simulation as you have we have a close up you can actually see this little boxes are actually are some relation boxes and which we have our densities and then he just looked at how.

all the planets would change the structure in the gas and also how the gas would interact with the planet's shifting them around. and it's that's interesting so the planners tend to pier oddone area open a gap and within the disc a block a lot of gas around here so you have a brighter in here again and then the hearing out more and more and at some point in a simulation you saw they get a bit. the jump he says. so who very nice you also see that the planets and use in the whole this some kind of future us like like spiral features and so it is single planet were changed the symmetry and the appearance of a whole disc. said a reason why the planet is staying at this point is that because we're rotating with the planet so it's actually going around the disc but the like camera is rotating with the planet at staying at the fixed place we put it in six. so but there's more because as i already said in an obvious those equations we have a lot of different kinds of physics that we all have to include in our simulations one of the things of course as we maybe don't have just to star in it does we have planets in there and maybe two stars in their in all of the.

these larger bodies have also an interaction between each other so that we have a star every plan and will have an interaction with the star schools but also the plans between each other they have also an intake can write so in the end you have to take in. into account hoops the all. and if all of these these interactions and also we have accretion just looking like this and then know so many increase in means that the gas is bound by some objects can be the disc the planet on the star that. it takes out and the mosque the dust or the gas and and pounds it to this object and then its loss to the the discord this and the other structures because is completely bond to that so. but the principle of this would be as malaysian i did last year and published we have here binary star so these to spot the dots are a starts i kind of kept them in the same spot they've but the in every picture will be one orbit of the. this binary but since we have interactions you actually see them rotating because of the interactions which is another and then also we have here a planet and hear a plan and and interesting thing was that these to plan is indirect in such a way that they end up on they expect the the same orbit. so. one star as for the out the orange one and then very fast they go in and they end up on exactly the same orbit with know what the plainest be the only. once the book. so. another thing is with the accretion here we actually see clouds from above dropping down onto the new forming star here so all of this what you see here of would be god is a gas hydrogen and it's a very. the only face so that this is not completely flat it has a lot of material and we actually have this in full from above two boards to star in and the start keeps the mouse and we have to take this also into account in our simulations.

another thing we have to take into account up to now we just cared about monsters and then cities but of course i am what we actually see is that stars are kind of warm hopefully otherwise temperatures he would also not be nice and and different the. nichols have different and condensation points and this is also true in the system so we restart with his star temperature of over at the surface of the star we have to temperature around four thousand kelvin and then we go a bit into the disc and there's a.

point where every for the first time reach a point where we have any material at all because it starts to condensate and we actually have something solid like iran for example add the thousand five hundred kelvin and and if we go further in reach a point where we have as solid water as. and this is added to the hundred kelvin this is what we then would need actually to have a plan and that also has water on it because we don't get the water in in the summit state it will not fall into a terrestrial planet and be bone that right. so this is important for our earth actually and then if we go even further alec we have also other gases and condensate team to sol it's like c o two or methane of things like that. and since we only get water on a planet when we have a temperature that is low enough so that the water actually the farms as solid and it's important for us to think about and whether this in our forming disc where do we start to have a planet like earth. if that could have some water right but it's not just the simple picture where we have all these nuys rings fractures where we have a clear line actually it gets more complicated because we have pressure and shocks and thermodynamics as a lot like pogo dance.

singh rights you crash into each other and it's all about collisions so against temperature is determined by the speed of your gas molecules like you bond thing and crashing into each other exchanging momentum so there's two ways to heat up such sets or. the dance for thing is you get a large amount of velocity from the outside like the huge cake a shock into your system as second way would be a we have a higher pressure it like more molecules that also you of course have more conditions and then a higher temperature so if you change. change because you have a planet no in his system. the pressure at some point you actually get a higher temperature so that is not then we lose does nuys line because suddenly we have different and. the difference and the the precious at different locations and the colleague of mine also simulated this so its size also ninth so this is the initial condition we just assumed ok if we have noticed terrapins whatsoever we have our nice planets year and one a use so same distance as earth to the sun. and here too but here we assume that lot less as in the less heat gets transferred from the surface of the disc and here we have a planet far out like jupiter or something and now we actually let this planet change the structure. of the disc and what happens is that we phoned the spirals and within this prior its we change pressure and with this actually if you see these aren't everywhere weds orange it's hotter than the islands' so we don't have water where it's our image and.

waits blue we can have water and interesting thing is even if you put a planet out here like to patel we still form this region's in in a system where we have less water. the moon.

one problem investor physical of simulations us that we don't always know how to how to shape our boxes are how to omar how hoyer small these boxes have to be so we use a trick to reshape the boxes we need them it's called that at the firm. fresh and this is a simulation of direct flowing through it flowing in this direction and the blue fluid and the other one so at the boundary it shaped the the two fluids sheer and they mix up somehow and we don't know how in advance so we started simulation. but as the simulation starts we reach a peak those boxes here so in the middle we don't need much free v. shape because it is not that complicated two years just the flow but at the boundary b.c. those mixing up of the two fluids and so the. reshape the cells as we meet them. this is done in the some him in the program in astrophysical program called at the port vote later show you some more programs to to used for simulations. but another simulation i want to show your first is also done with people and it's a simulation of the universe of from here to hear it's very big its fifth thirty million light years so each of these thoughts you see here is the size of a galaxy or even more and he. you can actually see that at some regions it's very empty so we would view of rotating around this is you and your neighbors to simulated universe years and these regions year are empty and we don't need a lot of boxes steered the big boxes are enough year but in this dense regions where we have a lot of. the tyrol we need smaller boxes and this is a disc method i showed you were really reshape the boxes as we need them this used for this simulation. a. to actually use the years whole the gloom beginning of the universe they're basically the initial mosque collapsing to the first galaxies and furs supernovas starting i'm very beautiful and simulation.

. the start that different programs as i already mentioned in leicester physics three of them in those three are all open source so you can download them and use them on your own machine if you like and that they're more a lot more. some of them open source some of them are not it's sometimes it's hard to get them. we will look in the following will present the tool fargo three d. and pollution and the detailed version or a more detailed wind and other people because yeah we usually get the usually use the those two for our simulations. what i want to show you with this slide is that it depending on what you want to simulate you need to choose a different program and one thing is that in astrophysics is sometimes called a the whole program coated so if i use the word code sorry about that it's i mean the whole program. so let's have a look at fargo three deem that's a hydra dynamics code and what you see here is an input parameter five a day you define how to disclose like what how much mass does it have how big is it and. what planet so here it to put to do see that jupiter's put in. and we also define how our how big are boxes are. this program is written in see which is quite nice because a lot of astrophysical programs are still written in fortune so this is good for me because i don't know any fortune. but we can run this. and what's typical for fargo said that the compilation. actually on my computer so i don't need a fancy computer i just did it on my small leapt up. and now we run it and now a typical for fargo as you will see are a lot of dots so here it will print out a lot of dots. and it will create at certain times some outputs and these outputs huge files containing numbers so if you look at them they're not really interesting they just aren't numbers in something like a text file so big part of astrophysics is also to visualize the data not only. the two created but also to make images so that we can make movies of them for that i prefer to use piven but their lot of tools umpires my platoon of a but there are a lot of different tools to to visualize the data so this is actually that output did farce. one was just saw jupiter planted in the disc that die defined in this parameter file and it's already started to do some spirals and if i would have led have let it run for that and the the spirals were more prominent and. yeah. now we have a planet here on our computer. i. and so.

we also have to do produce somehow was the in has a bit more set up five so what i need is three five c. year looks a bit complicated to break it down this fi and defines my grid and initial where you some and this simulation times here we him put. actually what physics do we want to need what does our can know coordinate system so to be one to have a disc or just like says and spiric are boxes or like squared boxes and how is the time to find and here we then actually ride a bit of. code to say ok now how do i want to gravitational potential so what's the source and of gravity or or what would happen at the in a region where we have this dark spot we have some hard to define what happens if cars reaches despond reid is it just falling in. this is bouncing back or something or says looping through the one end to the next and this is also something we then just have to code in and if we even make it and that run it looks like this so the in.

again our nuys the in the thing we hopefully put in all wanted to put in the time steps of what our boundaries were a pair are metres of the physics out fully the right ones and then nice the we start with our time steps and with see this its who ray it. i heard it to leave because it's actually not quite simple usually to set up a run in program running problem because you have to really think about what should be the physics what's the as scale of your problem was the time scale of your problem and and specify this in a good way but in. in simple this is how it works as their few test problems have you actually want to play around with this am to make it easy for the beginning and and this is how we do you simulations so as i read said we can just start them on our laptop so here this is my laptop and ages. the tide the dots less fargo three d. and that should run right and then i just wait for ten years to finish the simulations of five hundred times that source of and like five hundred on outputs well that's not the best ideas so we need more power and the in the. of us for example are using. in clusters are for bad and britain back and and that takes to know or computationally time by a lot is usually like a defector of. maybe twenty which is a lot sooner i i would need on my computer may be a year and then i just need maybe you've five hours a few days the or a week on this cluster which is usually the simulation time about a week for me i'm so any easy. here is that we use cheap use the us but we don't know that are mostly not use them for gaming be used them for actually its actual science. nice to play on that great but yeah i think that just just set. so back to earth actually so. can we now we wanted to grow our own planet we can do that yes of course can we grow earth well earth is a very special planets we have a very nice temperature here right and we have not to crashing atmosphere like to peter like a huge planet that we could not live under we have a magnetic. if you that she uses from in. the radiation from space and we have water but just enough water so that we still have land on this planet where we can live on so even if we find tuna simulations the probability that we actually hit earth and have all the parent is right sex. the tiny it's not that easy to simulate in earth so and there are a lot of open questions to how did we actually managed to get just as sip of water on our sofas how did we manage to collide enough mas or take rogate enough modest to farm.

the stress free a planet without jupiter as sweeping up all the mosque in our system how could we be stable in this are but when there are seven and other planets swirling around and interacting with us.

none of this is the open in our field of research actually and not completely understood this is the reason why we still need to do extra physics and even in all our simulations there's no planet be and the earth is quite unique and perfect for the human life so. the piece take care of the earth and take care of yourself and have all the others people on the congress and thank you for listening and thank you to everyone who helped us make this possible and to the people who actually coated the our programs with which we simulate. thank you have.

the good for the beautiful talk and sold the message at the end the papers open for discussions lloyds you you guys have any questions please come to the microphones.

some i asked my signal angel nolde questions right now bots microphone to please are you think you're going much really beautiful talk i can agree and i have to question and the first as a mutual if you are using of your stocks the creation but i'm you have all on the one hand you have seen. just the disc and on the other hand you have a toilet planet in it and so will you do things the same description for both was that high quite made it did it very much depends like it did this is one of the things a short year that for people to rewrite this see fire had that specify seven things in the about every physics.

this has somewhat his or her own where shun of things and sews some big usually the planet's if they're not much they will be put in as and gravity source and possibly one that connect create and paddles i usually then put in in a different. and way however also pebbles the are or at the moment a bit complicated their special group specializing in understanding pebbles because and this we set in the beginning and when they could like usually they should be destroyed if you hit two rocks very hard together the order to rocks together they don't stick of year. hit them hard together this planet around and we don't it up with to explain your help havel's are a small rocks are very like makes sense stones are something like that yes a bigger bigger rocks but not very big yet. so is so it depends on which could you use its youth a very shortly one the author me to into trouble to the statistics was a completely a lot of them it's a good question and mostly you if you have this in solar type system.

a year in a range where it does is not necessary for example though with a binary see if they could very close together the than at the inner part of these that is something we could consider and actually i know for to do it has more years to include relativistic physics to us. and who can we have quite some questions will keep them shorts number one please the thank you thank you very much for your interesting talk and i think you had it on your very first lights it's about seventy percent of the universe consists of dark matter and energy.

is set some whole considered a new simulation sore and handles this well in the simulations we make every they're doing planets and discs around stars it's not considered their own in this simulation we showed you about the only were is at the beginning the bluish things.

where all dark matter so that was included in their own thank you. ok michael's all three of i think i'm sorry he talked about three different programs i think the role for three years third on during so you're a complete beginners which program would you suggest is like you more use like you want to learn more which one is user friendly are good public were so just park or first it's the kind of user friendly.

he has the somewhat could support and they are always also always very the painful for actually commons and the additions if people actually are engaged and trying to improve on that because we are physicists we're not perfect programs and where have all also happy to learn more so.

fr why would i would suggest that has some easy ways of testing some systems and getting something done and it also has a very good documentation and also will end the yet emanuel how to make the first steps on the internet so you can look that up are some things you. let's go to one question from all sorts from was signalling group that you to talk and this one question from bias.

how do you know your model is good and when you can only have so of snapshots that's a good question.

we have we have to as he said were in theoretical astrophysics so they are theoretical models and these models cannot include everything so every single process it's not possible because then we would cut too late for use in the u.. sad to to know every model as good you have to. i usually you have a hypothesis are and an observation that you somehow want to understand with most of the necessary physics at this stage to reproduce his image so in also from the observation. can we have to take into account what our parents as kind of should be how dense says end of the simulation should be and things like this so by comparing to observe patients that's the best measure we can get is to be. kind of agree the of course if we do something completely wrong then it would just blow up or we will get the horror be high density so this is all we know them it's the physics will just go crazy and two to two large this cake otherwise we would try to compare to observations. that it actually is sensible what we did here that's one of the most complicated tasks to include just enough physics that this system as represented in in a good enough way but not yet so but not too much that our is simulation would blow up in time.

number two please i've got the question about the that the brits how does the computer decide how to that the great because the doctor where's the high density comes off to make a great deal has backed the in this is actually quite in the.

in interesting and also not quite easy to answer the question let me try to give it to do and brian the breakdown not show an insider here i am the the thing is a you measure and the evaluated the velocities or in the flex you also evaluate. the velocity and velocity goes high you know this had a lot happening so we needed in smaller group in there so we try to create more grid cells where we have a high velocity in the not show this is of course in an algorithm bit harder to to actually achieve but this is the idea. we measure the velocities at each point and if we measure the height was thousand t. we change to a smaller group saw you can predict where the moscow and by the dance these are getting high exactly step by step closer to say thanks. we stay with michael for to get out of that a bit of a classical questions i guess a lot relies on your initial conditions and have two questions related to that supers.

i guess they are inspired by observations order of the uncertainties that you hop and be them what is the impact if you change your initial conditions like the density and that this year and i write know my main the in reserves is actually you figuring out his sensible initial conditions or a pair.

meters for a disc in his view just lead to have an initial set of conditions and a sensible set of parameters and led to the run very long you expect a system hopefully to corn forced to the state that it should be in but your parent meters are of course very important and here we go. back to what we can actually understand from observational and and what we need for example is the did density for example and that is something we try to estimate from and the light we see in the east discs that you saw in this nice group with all these does we estimate. ok what's the average i'm like the what should then be the average densities of dust and gas in comparable discs. acts should be one more number two.

into portal told the one you increase the detail on the greet you are more in you have to one when you want to be paid the the on the gravitational force in one sell you have spawned the all the masses for law all the other cells so the. the complexity of the cockles groves. particularly at the square of the hold yourself that or just pour spews well that would be one way to do that that there are ways to simplify if you have a lot of particles in one direction and they are fire away from the object year.

looking at so you have so if you have several balls year in one ball here then you can include all these balls or you can you can think of them as one ball so it depends on you look at how you define define how.

how many particles you can take together is when you look at the angle of this the of of the you have the the the big or it did the many particles will have from seen from the object to looking at and you can define a critical angle and. if it's if an optic it gets smaller than this or if lot of optics get smaller than this angle you can just say ok that's one object so that's a way to simplify this method and there are some yeah i think that's the main idea or.

the the real more than one.

do you have a strategy to tech is of them the simulation of a group of valuable solution or doesn't happen lot that you wait one week for the cooperation and find out its total creche the trash ought crash and the time so that also depends on the program your using so in fargo.

good it gives this output ad after is a certain amount of calculation stamps and you can already look at those are puts before this simulation is finished so that would be a way to control if it's really be working. i think it's a simple produce so you you get every ever use sept i'm there's a difference between times that and actually output steps so and you define your output steps notes and as the whole simulation but you can look at big each outputs the the in. and as soon as it's produce so i usually get like five hundred outposts of but i already can look at the first and second after maybe half an hour's something like that but it also happens said you to start a simulation and wait and wait and wait and see you put something wrong in their and weldon you have. to do it again so this happens as well thanks ok one final question.

you're ok for him is there are a program in which you can calculate heard back works so that you don't have the start and conditioned by the the ending conditions and you can calculate how it had started and not for hydrogen.

and makes if you go to and body and that is so way to go backwards in time but for hydrogen amongst the theme is that you have to be learned the most likely arctic conditions so the buchanan really turn them back in time. i'm with anybody cannot because actually it's kind of and well it's not another tickly solve but this much closer than make the turbulence says tree means spirals and all the things you do so in this malaysians. ok i guess that brings us to the arrival of the talk of the session thank you for the discussion and of course think you guys for the presentation on.

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