Sam Geen, CEA Saclaywith thanks to Romain Teyssier, Yohan Dubois, Emma Geen, the pynbody team

● Research-level astrophysics on your home or school computer● Learn about astronomy and computing by building your own galaxies...● … then blowing them up with powerful cosmic explosions!

Mare Nostrum Supercomputer

What is it ?

The science case

● Galaxies form from gas and dark matter collapsing under gravity● When the gas cools, condenses and fragments, it forms stars● Rotational energy in the collapsing gas gives galaxies a disk structure● Spirals and bars are formed by waves building up in the rotating disk● Grains of dust block light, making dark ripples in the spiral arms● Radiation from big, bright stars, exploding dying stars and supermassive

black holes can blow galaxies apart!● Galaxies can collide together or swallow smaller galaxies whole

➔ The goal is to teach people how astrophysics works by doing the same experiments we do in real astrophysics laboratories

➔ Aimed at children 13+, or just curious players!

Simulations ? Simulations !

This film came out 15 years ago and I should probably stop referencing it

● Uses RAMSES (Teyssier 2002), developed at CEA Saclay

● Uses adaptive meshes and N-body particles to simulate anything in astrophysics you can think of (nebulae, planet formation, galaxies, or the whole universe, why not)

The grid structure around a single galaxy forming through galaxy collisions and streams of cold gas spiralling in under gravity

● If teams of highly-trained astronomers can do it, why not you ?

What does it look like so far ?

● Real-time interactive 3D interface with OpenGL + shaders● Fun, cartoony graphics trick you into thinking science is fun ! (it is!) (really!)● Prototype follows one galaxy in real-time, showing dark matter, stars and gas

Art by Emma Geen

What's the story ? (Morning Glo-OK Oasis is also old)

● Evil Octopoids from another galaxy have taken over the Milky Way● Humanity needs to build a new galaxy to escape their invasion● A cast of friends and colleagues advise you on what's happening● Learn through doing through defeating goofy space aliens

Program Design

● Challenge #1: Maximise simulating power of ordinary home computer● Challenge #2: Render simulation results as fast & efficiently as possible● Challenge #3: Rewrite Fortran code to work nicely with Python● Challenge #4: Make all of this fun!

RAMSES (Fortran → F2Py)

Thread #1 Thread #2 Thread #3

Data ReaderMain Program

Renderer User InputWritten in Python + Pyglet with OpenGL + GLSL

Uses Wiican for prototype Wiimote interface3D Graphics 2D GUI

Render Pipeline1) Render billboarded particle splats in vertex shader2) Draw to floating-point framebuffer3) Use reduction shader to find max/min of image4) Take logarithm of image to bring out dynamic range

Where to go from here?● Modify RAMSES Fortran code to allow real-time

user interaction – select stars to blow up, gas clouds to turn into stars, etc

● Create more scenarios – make a pretty nebula, discover the cosmic web, make a solar system

● Discoverable educational tips – create a journey of discovery in astronomy and computing

● Make a telescope view – learn how telescopes see the real universe and their limitations

● Give the player goals:● Guide a civilisation through your galaxy● Collect new powers inside the simulation● Collide your galaxy with your friend's galaxy

● Export your galaxies to put in your own projects● Add more graphics, sound, user controls, etc● Add user avatars, personalisation, sharing● I really want to get Oculus Rift working!● Test on real members of the public!

Thanks for your time!