 I still use this when I'm talking to people as an example of getting so much power out of a GPU. Now this is an example of a class of simulations called n-body simulations. Right. This is an n-body simulation where the gravity between all of these different bodies is being modeled and this particular algorithm interacts every body with every other single body. It's an n-squared algorithm in technical terms. Everything is interacting with everything else. That's right. We compute it one frame at a time and we do it so fast that we're able to do a million particles per second. We see, of course, this galaxy now in motion. This is 20,000 particles but because it's n-squared, that's 400 million interactions at each image. It's an enormous amount of computing power. That's something else. Okay, well that's very impressive and we surely admire the work that we've done in the past but what's the big deal now? Let's see Kepler. Let's see Kepler. Kepler. Right. This is... All right, what are we looking at here? This is a whole step up. This is instead of 20,000 bodies, 280,000 bodies. We're modeling it with the Bonsai multipole code out of the observatory of Leiden and in collaboration with Heron Boudreau and Evgeny Gabirov, we have had so much success in taking this code and applying all of these amazing kind of things to it. I recognize this. I see this. Where are we right now? Tell us. Orion is in the past of space. On the lower left, we have the Milky Way and on the upper right, we have the Andromeda Galaxy. The year is up in the top left hand corner. This is about 3.8 billion years in the future. We simulated, just pretty obvious, we simulated from present day to 3.8 billion years from now. If this is not a time machine, I don't know what is. This is a perfect example of a time machine. We've reached the moment where really interesting stuff starts to happen. The Andromeda Galaxy is heading towards us and we are going to end up merging up the first parts later on. This code is based on a thing called a tree code where instead of interacting everybody with every other body, we create this tree hierarchy of interactions. We can see the hierarchy right here. This grid that you see is showing with ever increasing intensity where we are focusing the compute power. Each box is bracketing about 16 stars and out of 280,000 stars, that makes an enormous number of boxes. We are using the dynamic parallelism that you just talked about to very efficiently prune out these boxes and generate this tree structure in a way that would not be possible before. You can see these beautiful swirls of stars just being flung around. There's a 50-50 chance the sun is going to be out there in one of those just flung out of the galaxies. In three and a half billion years, we are going to collide with Andromeda. That's right. It will sweep past us, tear all these stars away and come back for a killer blow. I guess the advice to the audience is to put our personal matters in order. In three and a half billion years, we might end up in a different galaxy. Now you know what's coming. Watch out guys. Get your will written. One of the things that's really curious to me is all these stars on the outer fringes of the galaxy don't seem to be moving nearly as slowly as I would have expected. In the center where there's greater mass, I would have expected the planets and the stars to be rotating much more quickly and outside much more slowly. Why am I not seeing that? There's something wrong with the simulation. You've actually hit one of the great mysteries of astronomy. Based on exactly these kinds of simulations and observations of stars, they realized that the stars in our galaxy and every galaxy we can see are going way, way too fast. Without a good explanation for what this was, without good computer models to show it, they spent about 50, 60 years trying to figure it out. Finally, in models approximately this size that we can now do in real time, they figured out that there is in fact only 10% of the matter in the galaxy is visible to us and 90% of it is invisible dark matter that lives in a big halo around the outside of the galaxy holding it together and driving that inner illuminated core. Ladies and gentlemen, we've identified dark matter. I need someone out of issue a paper to write up a paper quick.
 I still use this when I'm talking to people as an example of getting so much power out
 of a GPU.
 Now this is an example of a class of simulations called n-body simulations.
 Right.
 This is an n-body simulation where the gravity between all of these different bodies is being
 modeled and this particular algorithm interacts every body with every other single body.
 It's an n-squared algorithm in technical terms.
 Everything is interacting with everything else.
 That's right.
 We compute it one frame at a time and we do it so fast that we're able to do a million
 particles per second.
 We see, of course, this galaxy now in motion.
 This is 20,000 particles but because it's n-squared, that's 400 million interactions
 at each image.
 It's an enormous amount of computing power.
 That's something else.
 Okay, well that's very impressive and we surely admire the work that we've done in the past
 but what's the big deal now?
 Let's see Kepler.
 Let's see Kepler.
 Kepler.
 Right.
 This is... All right, what are we looking at here?
 This is a whole step up.
 This is instead of 20,000 bodies, 280,000 bodies.
 We're modeling it with the Bonsai multipole code out of the observatory of Leiden and
 in collaboration with Heron Boudreau and Evgeny Gabirov, we have had so much success in taking
 this code and applying all of these amazing kind of things to it.
 I recognize this.
 I see this.
 Where are we right now?
 Tell us.
 Orion is in the past of space.
 On the lower left, we have the Milky Way and on the upper right, we have the Andromeda
 Galaxy.
 The year is up in the top left hand corner.
 This is about 3.8 billion years in the future.
 We simulated, just pretty obvious, we simulated from present day to 3.8 billion years from
 now.
 If this is not a time machine, I don't know what is.
 This is a perfect example of a time machine.
 We've reached the moment where really interesting stuff starts to happen.
 The Andromeda Galaxy is heading towards us and we are going to end up merging up the
 first parts later on.
 This code is based on a thing called a tree code where instead of interacting everybody
 with every other body, we create this tree hierarchy of interactions.
 We can see the hierarchy right here.
 This grid that you see is showing with ever increasing intensity where we are focusing
 the compute power.
 Each box is bracketing about 16 stars and out of 280,000 stars, that makes an enormous
 number of boxes.
 We are using the dynamic parallelism that you just talked about to very efficiently
 prune out these boxes and generate this tree structure in a way that would not be possible
 before.
 You can see these beautiful swirls of stars just being flung around.
 There's a 50-50 chance the sun is going to be out there in one of those just flung out
 of the galaxies.
 In three and a half billion years, we are going to collide with Andromeda.
 That's right.
 It will sweep past us, tear all these stars away and come back for a killer blow.
 I guess the advice to the audience is to put our personal matters in order.
 In three and a half billion years, we might end up in a different galaxy.
 Now you know what's coming.
 Watch out guys.
 Get your will written.
 One of the things that's really curious to me is all these stars on the outer fringes
 of the galaxy don't seem to be moving nearly as slowly as I would have expected.
 In the center where there's greater mass, I would have expected the planets and the
 stars to be rotating much more quickly and outside much more slowly.
 Why am I not seeing that?
 There's something wrong with the simulation.
 You've actually hit one of the great mysteries of astronomy.
 Based on exactly these kinds of simulations and observations of stars, they realized that
 the stars in our galaxy and every galaxy we can see are going way, way too fast.
 Without a good explanation for what this was, without good computer models to show it, they
 spent about 50, 60 years trying to figure it out.
 Finally, in models approximately this size that we can now do in real time, they figured
 out that there is in fact only 10% of the matter in the galaxy is visible to us and
 90% of it is invisible dark matter that lives in a big halo around the outside of the galaxy
 holding it together and driving that inner illuminated core.
 Ladies and gentlemen, we've identified dark matter.
 I need someone out of issue a paper to write up a paper quick.