Particle Mirror

2017, Karl Sims

This playful exhibit allows visitors to interact with computer simulations of particles as they move and generate sounds. A virtual mirror is created by displaying a video image of the room on a large wall, which is augmented with special effects to give the impression that the participants are in the same environment as the particles. A depth sensor detects the shapes of people in front of the display so they can push the particles around with their movements. The exhibit cycles through various simulation modes with different visual and audio effects, each lasting about one minute.

Particle Mirror is on display at the Museum of Science, Boston in the Blue Wing next to the entrance of the Theater of Electricity. If you visit the museum, please also check out the Reaction-Diffusion Media Wall in the main lobby.

Particle Mirror rays
Photo © Ashley McCabe
Visitors at the Museum of Science in Boston see a mirrored image of themselves augmented with interactive particles and special effects.

A physics simulation determines the behavior of each particle. Gravity, swirling motions, collision avoidance forces, and air friction are combined with the interactive forces from the shapes of people in front of the display. These forces allow your motions to push the particles and trigger their sounds. The results can resemble bouncing balls, fireflies, falling snowflakes, sparkling glitter, foamy bubbles, or even molecules.

Particle Mirror snow

In this "snow" simulation, you can collect the falling particles, toss them around, or sweep them off the floor as they accumulate.

Particle Mirror sticky balls

These sticky colored balls are attracted to each other and tend to form clumps, but you can break them apart with your motions or try to capture one.

Particle Mirror sparkles

These "sparkles" generate pleasant bell sounds when they bounce off you. Flickering and glint effects are applied to the particles to give a "pixie dust" look.

Particle Mirror blue sparks

A "trails" effect is applied to these particles to make them look as if they are swimming through some kind of swirling fluid. The particles on the top and bottom of the screen generate different musical chords when you push them.

Particle Mirror small balls

These bouncy balls repel each other and tend to spread out so they are evenly spaced.

Particle Mirror fireflies

When you push these "firefly" particles they leave bright glowing trails and generate musical chords.


Karl Sims developed the particle simulation and visual effects software for this exhibit using C, OpenGL and OpenCL which runs on a Linux computer with an NVIDIA GTX1080 graphics card.

Bill Gardner of Wave Arts provided the audio software and sound design. The particle audio software was written in C++ using the JUCE application framework.

Jesse Gray of IF Robots developed the Kinect camera and depth sensor interface.

Thanks to the Museum of Science team including: Chris Brown, Katie Gilligan, Michael Horvath, Malorie Landgreen, Roxanne Lashley, Alexander Lussenhop, Bobbie Oakley, Boob Rayle, Chris Whiting and Ben Wilson. Thanks also to Chris Brown, Malorie Landgreen, Kristen Orr and Felix Sims for demonstrating Particle Mirror in the photos shown here.

Particle Mirror balls

These larger colored orbs each generate a specific note when bumped.

Particle Mirror strings

In this effect, chains of particles are attracted to each other by simulated spring forces. If you break them apart with your motions they will attempt to reform. A light-rays effect is also applied to the shapes as they move.

Particle Mirror bubbles

These particles are attracted to each other to create a bubbly effect. Your motions can generate waves that propagate through the particles, somewhat like sound waves passing through air molecules.

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© 2017, Karl Sims, All rights reserved.