About
A hobby project about
the nature of randomness.
In April 2025, I started wondering: if I shuffled a deck of cards continuously, how long before I saw the same shuffle twice? The answer, it turns out, is longer than the age of the universe, and by many orders of magnitude.
So I wrote a script. Between April 27, 2025 and September 14, 2025, it ran 11 sessions across roughly 142 days, recording 12,300,339 arrangements to a database. Every one of them has since been compared against every other, and not a single pair matched.
That's not surprising. A standard deck of 52 cards can be arranged in 8.07 × 10⁶⁷ different ways, a number so large it makes the number of atoms on Earth look small.
The Algorithm
Shuffles are simulated using the Gilbert-Shannon-Reeds model, the standard mathematical description of a riffle shuffle. Each shuffle cuts the deck asymmetrically near the center, then interleaves the two halves with drops weighted by remaining card count. 75% of shuffles end with a final cut.
What's Next
More shuffles. Every one recorded here is checked against the entire archive before it, not just against the shuffle that came immediately before, and the result is kept so it can be checked again by anyone later. If two ever match, that pair will be the first documented repeat of a shuffled deck. Nobody expects it to happen. That is the point.
Who Builds This
ShuffleArchive is built and run by Clotfelter Data & Design, a Chicago-area software firm that builds websites, web applications, databases, and integrations.