Ramaparticles | a small universe to play with

Hundreds of particles fall towards the pointer. They swing past, loop back, collide with the walls and settle into orbits that never quite repeat. With a mouse, a click fixes the centre of gravity in place and another click sets it free to follow the pointer again. On a phone or tablet, a tap places the centre of gravity and a drag carries it around.

Ramaparticles began as a BBC BASIC program written many years ago. This new version keeps the original physics and adds trails that fade, a choice of colour schemes, a steady downward pull and the freedom to rewrite the law of gravity itself.

Photosensitivity warning: Ramaparticles shows fast-moving, flashing and pulsing light with bright colour changes. For a small number of people, patterns like these can trigger seizures. Please do not play if you have photosensitive epilepsy, and stop at once if you feel dizzy or unwell.

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Ways to play

• Roll the dice. The dice button creates a random new universe, with its own mix of settings, colours and effects. When one is special, the restart button replays it from the very beginning, and the share button keeps it for good.
• Watch it breathe. Leave the pointer still in the middle and let the particles find their own orbits. Turn on fading trails for long, looping light paintings.
• Change the universe. The Universe slider sets how quickly gravity weakens with distance. At 2 it follows the inverse square law of our own cosmos. Slide towards 1 and the pull reaches right across the screen, so the particles breathe in and out together. Slide towards 3 and the pull gathers close to the centre, flinging anything that passes near it out towards the walls. Every other setting is a universe that never existed.
• Push instead of pull. Repulsion turns gravity inside out and the particles flee to the walls. Switch it back and watch them pour home.
• Let it rain. Down adds a steady pull towards the floor. With soft walls the particles pile up, bounce and slosh like water.
• Play with light. The Effects panel turns the universe into something new. Kaleidoscope mirrors every movement into a living mandala. Glow lets dense clusters blaze like a nebula. Speed colour shows every slingshot in red-hot colour, Stretch draws particles out like long-exposure photographs, and Twinkle, Colour drift, Constellations and Pulsing each add their own life. Particles can also become squares, stars, hexagons or tiny yin-yang symbols. The effects combine freely, and some combinations are remarkable.
• Keep a picture. The camera button saves the screen as a PNG image, ready for a wallpaper or a post. When sharing pictures on social media, please add #ramaparticles, so we can all find each other's universes.
• Share a universe. The share button creates a link that carries every setting, so a friend opens exactly the same world.

Keyboard

P or Space to pause, N for a random new universe, B or Esc to restart the current one, R to switch between attraction and repulsion, S and F for slower and faster, T for trails, W for walls, G for the downward pull, U for pulsing, K for the kaleidoscope, H to change shape, + and − to zoom, C to save a screenshot, X to fix or free the centre of gravity, O for settings and Z for full screen.