For the last two weeks, readers of the social news site Reddit have been obsessed with "The Button." It's an April Fools' Day prank and social experiment, and it's very simple: Users who go to reddit.com/r/thebutton will find a button and a countdown, going from 60 seconds to 0. Registered users can press the button once (and only once) if their Reddit account was created before April 1 — and doing so resets the counter to 60.

13 days later, the countdown still hasn't reached zero.

Whenever it drops too low, Reddit users can't help but click the button. The time at which a user pressed the button is indicated by a coloured "flair" by their name, and a sprawling, eccentric culture has already sprung up around it. A rarer colour is highly valued, and an indicator of status, splitting users into a bizarre virtual caste system.

However, with users only able to press once and new accounts ineligible to press, it can't last forever. And one Reddit user thinks they know when it will finally end: November 27, 2015.

"ezeeetm" has crunched the numbers on The Button, and thinks that the late-Autumn date is the latest point at which the countdown could reach zero. When the experiment first launched, it was rare that the button ever got past the 55-second mark; already, it's regularly dropping down to 30-odd seconds.

For a real-time look of button-presses, check out this graph. The visualisation below shows button presses over the course of around two hours on April 13.

This second graph, via spuz, shows how seconds reached before the button is pressed in dropping over time:

By looking at the average spacing between clicks of the button, coupled with the number of eligible people left who still haven't pressed the button, "ezteem" estimates a maximum length of time before the button reaches zero as November 27. But other factors could speed this process — including users pressing in faster succession than anticipated. ezteem anticipates the minimum possible life of the Button as April 18 (though this is very unlikely).

The mystery of The Button has captivated the world's attention. But at some point, it will reach zero. And then? No-one knows.