t the heart of a remote hill somewhere in the Texan desert, in a shaft carved several hundred metres deep into the rock, is the prototype of a clock unlike any other. With a driving weight weighing five tonnes and gear wheels two metres in diameter, the Clock of the Long Now is meant to keep time for the next ten millennia. Behind this project is the California-based foundation The Long Now, with the aim of “encouraging imagination at the timescale of civilizations”.

The foundation unveiled a first prototype, two metres in size, in 1999 and on display since then at the London Science Museum. For its second, full-scale clock, it obtained the support of the entrepreneur Jeff Bezos (the world’s second-richest person, with a fortune of 200 billion dollars).

The billionaire provided 42 billion dollars towards its construction, plus a hill situated on his 600sqm ranch in Texas – which is also where the launch site for the rockets of his company, Blue Origin, is situated. Excavation work began in 2009 and the clock’s main components were recently installed. It should be fully operational “in the next few years,” its designer, Danny Hillis, announced in an internal interview published in 2024.

This cast-bronze part is the material representation of the curve required to translate, with the help of a cam, absolute incremental time (measured by the torsion pendulum) into solar time, the latter depending on the Earth’s orbit and inclination.

Solar synchroniser

The oscillator is a torsion pendulum in titanium with a period of seven seconds. This consists of an arm nearly two metres in length with two weights the size of a football at each end. The mechanism is reliable, but not very accurate as it accumulates drift. A phase-locked loop maintains accuracy by coupling it to a “solar synchroniser”– a device with a synthetic sapphire prism set beneath the glazed cupola, several metres in diameter, that closes the shaft. It is oriented in such a way as to capture the sunlight only when the sun is at its zenith, regardless of the day of the year.

The solar synchroniser captures the sunlight when the sun is exactly at its zenith and focuses it on a metal wire. This contracts, adjusting the time measured by the torsion pendulum.

The prism concentrates the sun’s rays when the sun is at its zenith and heats a metal wire made of nitinol – an alloy of nickel and titanium with particularity of having shape memory: when it exceeds a certain temperature, it contracts and triggers a mechanical lever that adjusts the clock daily – or at least every day the sun shines. A cam undertakes the transformation required to go from solar midday, which depends on the Earth’s orbit and rotation, to the incremental time supplied by the pendulum.

View from the top of the shaft, showing the staircase at the edge and the gear wheels in the centre.

A mechanical computer

Instead of standard reduction gears, the system uses a mechanical computer to record the time that has passed. This uses binary logic based on gear wheels and levers to operate 32-bit digits (up to 4.3 billion), which are then transformed into local time by cams. This computational approach will make it possible to modify calculations without stopping the clock – for example, to take into account the slowing of the Earth’s rotation and the lengthening of days.

A cam follows the surface of the central cast-bronze part to transform absolute incremental time into solar time.

The foundation plans to display the time in five different ways in as many chambers carved into the rock. The first chamber, devoted to annual time, contains an orrery displaying the movement of the planets, the Moon and space probes. What will be displayed in the four other chambers, intended to mark the passage of ten, a hundred, a thousand and ten thousand years, is not yet decided: that will be left to future generations.

The date displayed shows the year only, in a five-figure format to avoid any “bug of the year 10,000” (the current year is therefore 02024). The clock has a 10-chime carillon controlled by a mechanical calculator made up of Geneva wheels. Programmed by the musician Brian Eno, it is capable of generating more than three million different melodies, ensuring that each sequence played in the Texan cavern is absolutely unique.

According to the inventors, the project was designed according to five principles: longevity, of course, maintainability with only simple tools, transparency to ensure that future generations can understand how the clock works without having to take it apart, evolvability to be able to adapt and improve the mechanism, and scalability to be able to transition from miniature prototypes to full-scale systems.

Musician Brian Eno programmed the tunes that this mechanical computer plays on ten tubular bells. More than 3.5 million combinations are possible.

These constraints ruled out certain solutions for supplying energy to the different mechanisms, such as photovoltaic or nuclear energy. And so they chose a simple driving weight proportional in size to the mechanism: a bronze sphere several metres in diameter, filled with concrete and weighing five tonnes.

Two mechanisms raise the weight. The first is automatic and keeps time uninterruptedly. It is fed by the difference in temperature between night and day: the solar synchroniser heats an air chamber, which moves a graphite cylinder and raises the driving weight. The second is a visitor-wound horizontal winch, or windlass, which produces the energy needed to operate the display mechanism and chimes.

Pilgrim travellers

For its inventor Danny Hillis, it should be possible one day to visit the Texas clock, not as a tourist attraction, but “more like a pilgrimage for the very determined seeker”. Led by a guide through a desert which is home to “mountain lions and rattlesnakes”, the visitor will have to follow a challenging mountain trail to an entrance in the cliff face.

He or she will have to pass through an airlock-like chamber to access the base of the shaft. Having climbed the spiral staircase, they will be able to wind the mechanism to display the date and hear a – unique – melody on the chimes. The foundation plans to build a second, more accessible clock at the top of a mountain in Nevada.

While the project of building a clock at the scale of civilisations impresses by virtue of the technical challenges to be overcome, its philosophical ambition is not without its critics. In 2020, in Wired – surprisingly, a magazine known for its techno-optimism – political expert David Karpf described the 10,000-year clock as a waste of time: a project by a billionaire for billionaires which, by focusing on the future, provides “an escape from wrestling with the dark times we are living through” and an invitation to “ignore the troubles we face today”. Will our descendants view it in the same way?