The Clock of the Long Now is a proposed mechanical clock designed to keep time for 10,000 years. The project to build it is part of the Long Now Foundation, a private organization that seeks to become the seed of a very long-term cultural institution. The project was conceived by American inventor Danny Hillis in 1986: ‘I want to build a clock that ticks once a year. The century hand advances once every one hundred years, and the cuckoo comes out on the millennium.I want the cuckoo to come out every millennium for the next 10,000 years.’
The first prototype of the clock began working on December 31, 1999, just in time to display the transition to the year 2000. At midnight on New Year’s Eve, the date indicator changed from 01999 to 02000, and the chime struck twice. That prototype, approximately two meters tall, is currently on display at the Science Museum in London. The first full-scale clock’s manufacture and site construction is being funded by Jeff Bezos, who has donated $42 million, and is located on his Texas land.
The clock is one of several projects through which the foundation intends to promote long-term thinking. In the words of Stewart Brand, a founding board member of the foundation, ‘Such a clock, if sufficiently impressive and well-engineered, would embody deep time for people. It should be charismatic to visit, interesting to think about, and famous enough to become iconic in the public discourse. Ideally, it would do for thinking about time what the photographs of Earth from space have done for thinking about the environment. Such icons reframe the way people think.’
The basic design principles and requirements for the clock are: Longevity (the clock should be accurate even after 10,000 years, and must not contain valuable parts that might be looted); Maintainability (future generations should be able to keep the clock working, if necessary, with nothing more advanced than Bronze Age tools and materials); and Transparency (the clock should be understandable without stopping or disassembling it; no functionality should be opaque).
Many options were considered for the power source of the clock, but most were rejected due to their inability to meet the requirements. For example, nuclear power and solar power systems would violate the principles of transparency and longevity. In the end, Hillis decided to require regular human winding of a falling weight design because the clock design already assumes regular human maintenance.
The clock will use an unreliable but accurate timer to adjust an inaccurate but reliable timer, creating a phase-locked loop. In the current design, a slow mechanical oscillator, based on a torsional pendulum, keeps time inaccurately, but reliably. At noon the light from the Sun, a timer that is accurate but (due to weather) unreliable, is concentrated on a segment of metal through a lens. The metal buckles and the buckling force resets the clock to noon. The combination can, in principle, provide both reliability and long-term accuracy.
The center of the clock will show a star field, indicating both the sidereal day and the precession of the zodiac. Around this will be a display showing the position of the Sun and the Moon in the sky, as well as the phase and angle of the Moon. Outside this will be the ephemeral dial, showing the year according to our current Gregorian calendar system. This will be a five-digit display, indicating the current year in a format like ‘02000’ instead of the more usual ‘2000’ (to avoid a Y10K problem).
Gears degrade over time in accuracy and efficiency due to the deleterious effects of friction. Instead, the clock uses binary digital logic, implemented mechanically in a sequence of stacked binary adders (or as their inventor, Hillis, calls them, serial bit-adders). In effect, the conversion logic is a simple digital computer (more specifically, a digital differential analyzer), implemented with mechanical wheels and levers instead of typical electronics. The computer has 32 bits of accuracy, with each bit represented by a mechanical lever or pin that can be in one of two positions. This binary logic can only keep track of elapsed time, like a stopwatch; to convert from elapsed to local solar time (that is, time of day), a cam subtracts from (or adds to) the cam slider, which the adders move.
Musician Brian Eno gave the Clock of the Long Now its name (and coined the term ‘Long Now’) in an essay; he has collaborated with Hillis on the writing of music for the chimes for a future prototype.
The Daily Omnivore 
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