Clock of the Long Now
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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. If I hurry I should finish the clock in time to see the cuckoo come out for the first time.
The Clock of the Long Now, also called the 10,000-year clock, 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.
The project was conceived by Danny Hillis in 1986 and 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, to ring in the "third millennium". That prototype, approximately two meters tall, is currently on display at the Science Museum in London.
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[edit] Design
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 (such as jewels, expensive metals, or special alloys) 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.
- Transparency: The clock should be understandable without stopping or disassembling it; no functionality should be opaque.
- Evolvability: It should be possible to improve the clock over time.
- Scalability: To ensure that the final, large, clock will work properly, smaller prototypes must be built and tested.
Obviously, no clock can have a guaranteed lifetime of 10,000 years, but some clocks are designed with guaranteed limits. (For example, a clock that shows a four-digit year date will not display the correct year after the year 9999.) With continued care and maintenance the Clock of the Long Now could reasonably be expected to display the correct time for 10,000 years.
Whether a clock would actually receive continued care and maintenance for such a long time is debatable. Hillis chose the 10,000-year goal to be just within the limits of plausibility. There are technological artifacts, such as fragments of pots and baskets, from 10,000 years in the past, so there is some precedent for human artifacts surviving this long, although very few human artifacts have been continuously tended for more than a few centuries.
[edit] Power considerations
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, atomic energy 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. This may seem an odd choice, but the clock design already assumes regular human maintenance.
[edit] Timing considerations
The timing mechanism for such a long lasting clock needs to be reliable and robust as well as accurate. The options considered but rejected as sources of timing for the clock included:
[edit] Self-contained clocks
Most of these methods are inaccurate (the clock will slowly become less correct) but reliable (the clock will not suddenly stop working). Others are accurate but opaque.
- pendulum (inaccurate over the long term, and requires lots of ticks, which creates wear)
- torsion pendulum (less frequent ticks, but even less accurate)
- balance wheel (more inaccurate than pendulum)
- water flow (inaccurate and wet)
- solid material flow (inaccurate)
- wear and corrosion (very inaccurate)
- rolling balls (very inaccurate)
- diffusion (inaccurate)
- tuning fork (inaccurate)
- pressure chamber cycle (inaccurate)
- inertial governor (inaccurate)
- atomic oscillator (opaque, difficult to maintain)
- piezoelectric crystal oscillator (opaque, difficult to maintain)
- atomic decay (opaque, difficult to measure precisely)
[edit] External events that the clock could track or be adjusted by
Many of these methods are accurate (some external cycles are very uniform over huge stretches of time) but unreliable (the clock could stop working completely if it failed to track the external event properly). Others have separate difficulties.
- daily temperature cycle (unreliable)
- seasonal temperature cycle (imprecise)
- tidal forces (difficult to measure)
- Earth's rotating inertial frame (difficult to measure accurately)
- stellar alignment (unreliable because of weather)
- solar alignment (unreliable because of weather)
- tectonic motion (difficult to predict and measure)
- orbital dynamics (difficult to scale)
- human ritual (too dependent on humans).
Hillis concluded that no single source of timing could meet the requirements. As a compromise 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.
[edit] Displaying the time and date
Many of the usual units displayed on clocks, such as hours and calendar dates, may have little meaning after 10,000 years. However, every human culture counts days, months (in some form), and years, which are based on lunar and solar cycles. There are also longer natural cycles, such the 26,000-year precession of Earth's axis. On the other hand, the clock is a product of our time, and it seems appropriate to pay some homage to our current arbitrary systems of time measurement. In the end, it seemed best to display both the natural cycles and some of the current cultural cycles.
The center of the clock will show a star field, indicating both the sidereal day, and the 26,000-year precession of the zodiac. Around this will be a display showing the position of the Sun and the Moon in the sky, as well and 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 as in a format like "02000" instead of the more usual "2000" (to avoid a Y10K problem). Hillis and Brand plan, if they can, to add a mechanism whereby the power source generates only enough energy to keep track of time; if a visitor wanted to see the time displayed, they would have to manually supply some energy themselves.
[edit] Time calculations
Options considered for the part of the clock that converts time source (for example, a pendulum) to display units (for example, clock hands) include electronics, hydraulics, fluidics, and mechanics.
A problem with using a conventional gear train (which has been the standard mechanism for the past millennium) is that gears necessarily require a ratio relationship between the timing source and the display. The required accuracy of the ratio required increases with the amount of time. (For instance, for a short period of time the count of 29.5 days per lunar month may suffice, but over 10,000 years the number 29.5305882 is a much more accurate choice.)
Achieving such precise ratios with gears is possible, but awkward; similarly, gears degrade over time in accuracy and efficiency due to the deleterious effects of friction (which is to say, they get smaller. Smaller gears move faster, throwing precise calculations seriously out of joint). Instead, the clock uses binary digital logic, implemented mechanically in a sequence of stacked binary adders (or as Hillis, their inventor 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 uses a 28-bit number representation, 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 absolute time, like a stopwatch; to convert from absolute to local solar time (that is, time of day), a cam subtracts (or adds) from the cam slider, which the adders move.
Another advantage of the digital computer over the gear train is that it is more evolvable. For instance, the ratio of day to years depends on Earth's rotation, which is slowing at a noticeable but not very predictable rate. This could be enough to throw the phase of the Moon, for example, off by a few days over 10,000 years. The digital scheme allows the number to be adjusted if the length of the day changes in a different way than expected.
[edit] Location
The Long Now Foundation has purchased a mountaintop near Ely, Nevada, surrounded by the Great Basin National Park, for the permanent storage of the full sized clock, once it is constructed. It will be housed in a series of rooms (the slowest mechanisms visible first) in the white limestone cliffs, approximately 10,000 feet up the Snake Range. The site's dryness, remoteness, and lack of economic value should protect the clock from corrosion, vandalism, and development. Hillis chose this part of Nevada because it is home to a number of dwarf bristlecone pines, which the Foundation claims are nearly 5,000 years old.
[edit] Support
The project is supported by the Long Now Foundation, which also supports a number of other very long-term projects, including The Rosetta Project (to preserve the world's languages) and the Long Bet Project.
Alexander Rose was Hillis's primary collaborator on the first prototype clock. The other members of the design team for the first prototype were David Munro, Elizabeth Woods and Chris Rand. Musician Brian Eno gave the Clock of the Long Now its name (and coined the term "Long Now"); he has collaborated with Hillis on the writing of music for the chimes for a future prototype, a CD of which is currently being sold. [1]
[edit] See also
[edit] External links
- Pictures of the prototype and various parts can be seen at http://www.longnow.org/
- Main page for the Clock on the Long Now Foundation website
- Progress on the 10,000-year Clock a talk by Danny Hillis in September 2004 available in mp3 and Vorbis
- Discover Magazine article on the clock, November 2005
[edit] References
- Stewart Brand, "The Clock of the Long Now: Time and Responsibility". Basic Books, 2000, ISBN 0-465-00780-5.
