Day & Night Screensaver
Day & Night is a Conway's Life variant with the rule B3678/S34678, built so that swapping every live cell for dead and dead for live produces exactly the same rule. Starting from near-even density, light "day" regions and dark "night" regions evolve as genuine mirror-image twins.
How the Day & Night screensaver works
Every cell is alive ("day") or dead ("night"), updated each generation from its eight neighbors, just like Conway's Life.
The rule is B3678/S34678 — a dead cell is born with 3, 6, 7 or 8 live neighbors; a live cell survives with 3, 4, 6, 7 or 8.
This rule set is symmetric under inversion: flip every cell's state and the rule produces the identical next generation, just inverted.
Starting near 50% density lets you watch light and dark regions grow, ripple and collide as real structural mirror images of each other.
A worked example
Look for a light blob and a dark blob of similar shape drifting near each other — swap your eye's focus from live to dead cells and the pattern looks the same, because the rule genuinely treats both states identically.
Settings & tips
- Cell color recolours the live "day" cells against the dark background.
- Starting density is set near 45% by default so both day and night regions form clearly.
- The board reseeds once the pattern settles into stillness.
Frequently asked questions
- What does "symmetric" mean here?
- Inverting every cell — live becomes dead and dead becomes live — produces an identical rule, so light and dark patterns behave as true structural mirrors.
- Is a key needed?
- No — it's a pure local computation.
- Is it free?
- Yes — free, no download, in your browser.
- Is this related to Conway's Game of Life?
- Yes — it uses the same neighbor-counting mechanics, just with a different, symmetric birth/survival rule.