IEEE Spectrum November, 2011 - 58

CHIME TIME: the clock's digital mechanical computer
[drawing above, prototypes at right] is a complex
system of gears, pins, and rollers that generates a
unique sequence of chimes each time it's played.
images: cLockwise from Left, Long now foundation (2); nichoLas chatfieLd-tayLor

Bezos is footing the bill for the clock's installation near the
tiny town of Van Horn. Hillis and Rose hope this clock will be
the first of several at different sites. (Small-scale prototypes
of the clock already exist, including one that's now housed at
the Science Museum in London.) Although the budget for the
Texas project has not been officially disclosed, a recent article
in Wired put it at US $42 million. Given the highly skilled staff,
the high-tech construction and machining equipment, and the
rarefied raw materials involved, that seems about right. But
Bezos bristles at the notion that his investment might be perceived as frivolous. "Symbols are important," he says.

if you Accept thAt premise, then you'll understand
why Hillis and Rose's first concern wasn't sketching out the
clock's innards. Instead, they obsessed over how people would
experience the clock. They wanted it to be as engaging as possible, "to make someone care about it in 10 000 years," Hillis says.
"We spent more time debating the aesthetics of a given part
and how humans will interact with it than any other thing,"
says Rose. "What is the day like as they walk through this
architectural-scale clock mechanism?"
For inspiration, the team looked backward-to enduring ancient monuments like the Egyptian pyramids and
Stonehenge. They also looked to the present-to theme park
rides, such as those Hillis designed during his time as vice
president of R&D for Walt Disney Imagineering. They realized that what each of these very different entities has in common is that the visitor experiences it as a rite of passage.
Hillis has spent the past seven years working with Rose and
other members of the team to design what he calls the "plotline"
of the clock. First, they wanted to ensure that visitors would be
vested in the journey. That meant building the clock in a faraway,
hard-to-reach place, somewhere requiring a real commitment to
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visit. (The site they chose indeed qualifies-for now. But it's anyone's guess what this place will be like in 10 000 years.)
Even after the intrepid explorers of the future reach the site,
the drama of their journey would continue to unfold as they
enter the mountain, snake through tunnels, and climb up the
spiral steps past the clock gears. Finally, they would arrive at
the chosen spot, where they would wind the chime generator
and hear the bells ring.
But what if you were the first person to visit the clock in centuries, or even millennia? Given the vagaries of human history,
it's reasonable to expect that people might one day forget the
clock even exists. So for the sake of the wayward traveler who
just happens upon the clock by accident, the operation had to
be obvious just from looking at it.
"Someone who looks at a part must be able to figure out what
to do," Rose says. "People need to be able to stumble across it
and understand how it works and how to maintain it." He and
Hillis call this quality "transparency."
An electronic clock was therefore out of the question:
It wasn't sufficiently transparent. Instead, they decided to
make the clock entirely mechanical-even the digital computer that generates the melody of the clock's 10 chimes. The
chime-generating computer uses a phased series of twenty
2.4-meter-diameter gears, called Geneva wheels, to produce
up to 3.5 million unique sequences of chimes.
Although much of the clockwork is similar to the workings
of a standard grandfather clock, it differs from an ordinary
analog gear-driven clock in a few key ways. For one thing, it
will be the largest clock ever built. And instead of having a
pendulum that counts off each second, the clock's pendulum
has a base of 10 seconds. So it will tick at one-tenth the speed
of a regular clock, which should help its gears, bearings, and
other components last at least 10 times as long. And rather
than having a 12-hour face, the clock will display the posispectrum.ieee.org

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Table of Contents for the Digital Edition of IEEE Spectrum November, 2011