鈥淚T IS the world鈥檚 slowest computer. It鈥檚 also the first computer that is
year 10 000 compliant,鈥� quips Stewart Brand. He鈥檚 not talking about a desktop
PC鈥攏othing remotely electronic, in fact. As chairman of the Long Now
Foundation, a non-profit organisation based in San Francisco, Brand is referring
to the Millennium Clock鈥攁 clockwork device as big as a good-sized building
that will keep time for the next 10 000 years.
The clock is the brainchild of Danny Hillis, a computer scientist and
engineer who invented the massively parallel architecture of today鈥檚
supercomputers. As one of the founding members of the Long Now Foundation,
Hillis talked about the clock at the Massachusetts Institute of Technology in
Cambridge, last month. Hillis is designing the clock to survive not only the
ravages of time but nuclear winters, earthquakes鈥攅ven the collapse of
civilisation itself. It鈥檚 a demanding brief. The clock must operate in a way
that will allow anyone to decipher it, even if they know nothing about it and
have never seen it before. It will have to be easy to maintain. And repairs must
be possible with tools that are no more advanced than those in use during the
Bronze Age. Hillis argues that these skills are more likely to survive into the
distant future than those developed more recently. 鈥淪emiconductor technology
could be a lost art in 100 years,鈥� he says.
The idea鈥攁nd the reason behind the Long Now Foundation鈥檚
existence鈥攊s to promote the concept of long-term responsibility by
encouraging people to think not in terms of hours, days or years but on a
timescale of thousands of years. If all goes to plan, the foundation hopes to
have the Millennium Clock complete by the end of 2001. A prototype should be
completed early next year.
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In essence, a clock is a simple device made up of four basic components.
First, it needs something that performs a regular movement in a fixed time
interval. This can be a swinging pendulum, a vibrating atom or simply the
passage of the Sun across the sky.
Next, it must have a counting device that records the number of these
movements鈥攖eeth on a cog, the frequency of infrared light that excites an
atom or even a human counting the number of times he or she turns an hourglass.
This counting device is usually linked to a display such as the hands of a clock
or figures on a computer screen. Finally, clocks need a source of power whether
from mechanical winding, chemical battery power or some other source.
The Millennium Clock has all these components. The problem is to ensure they
will be able to survive for the clock鈥檚 projected hundred-century life span. The
need for an open design means that dirt is certain to get into the works. Even
small amounts of dust and grit can dramatically change friction in most
mechanisms. However, there will be no lubrication. 鈥淲e simply assumed the
friction was going to be large and designed around it,鈥� says Hillis. Though the
clock will be large, most of its components will move slowly over short
distances. This will inevitably lead to some erosion, but again the clock鈥檚 size
comes to the rescue鈥攊t won鈥檛 matter if friction erodes large parts by a
millimetre or so over 10 000 years, says Hillis.
The timing device in this clock will be a torsion pendulum鈥攐ne that
rotates rather than swings. Made of tungsten, a metal that is 70 per cent denser
than lead, it will weigh 100 kilograms and hang from a 5-metre spring. The
weight will rotate through 350 degrees and back again once every minute.
Ensuring that the pendulum has a highly consistent period is another
challenge. Just as changes in the length of a swinging pendulum modify its
period, changes in the elasticity of the spring in a torsion pendulum have a
similar unwanted effect. The elasticity of most materials depends on their
temperature, a factor that Hillis will not be able to control over the lifetime
of the clock. So he will make the spring out of elinvar, an alloy of iron and
nickel with an elasticity that is stable over a large temperature range.
But even elinvar cannot make a torsion pendulum consistent enough to keep
time for 10 000 years. So Hillis plans to incorporate a mechanism for
synchronising the clock with the Sun. The idea is to catch the Sun鈥檚 rays at
exactly midday every day and focus them onto a metallic plate that will expand
and bend. The bending motion will adjust a cog inside the clock, rather like
nudging the hands of a conventional clock towards noon.
Counting the cycles of the pendulum will be relatively straightforward. The
device that links a pendulum to the rest of a clock, known as the escapement,
serves two purposes. It converts the back-and-forth motion of the pendulum into
a step-like motion in one direction. And it gives the pendulum the regular push
it needs to keep going. In the Millennium Clock, the escapement will drive a
series of cogs that convert the 1-minute period of the pendulum into a 12-hour
cycle. The final 12-hour wheel is the one that will be nudged back into place by
the solar synchroniser at noon each sunny day.
More difficult is converting the 12-hour period of the clock into an accurate
display of months, years and seasons. The conversion is straightforward when one
period is a whole-number ratio of another. For instance, when minutes have to be
converted to hours, a simple arrangement of cogs does the trick. But a solar
year is equal to 365.242189 days and designing a set of cogs that represent this
ratio is impractical. 鈥淐locks usually end up approximating but this won鈥檛 work
over 10 000 years,鈥� explains Hillis.
Digital design
So he is getting rid of cogs entirely and intends to calculate the time and
date using a mechanical digital computer similar to the first mechanical
computer designed by a mathematician called Charles Babbage more than 100 years
ago. Known as the bit serial mechanical adder, the computer consists of a
thousand levers that can be flipped back and forth to represent the 0s and 1s of
a digital code. Every 12 hours, the clock will feed one bit of information to
the computer, which will use it to update its calculations of the day, month,
year, the season and the phases of the Moon. It will even take into account the
precession of the Earth鈥檚 axis: this has a period of 26 000 years and so is
significant over a period of 10 000 years.
The final component of the clock is its power source. 鈥淚t would have been
very easy to make the clock automatic, by using temperature changes to wind it,
for example,鈥� says Hillis. But instead, it will have to be wound every year.
鈥淚nstitutions don鈥檛 survive without people,鈥� he explains. The clock will have to
be cleaned, maintained and possibly even repaired. To this end, all the parts of
the clock will be replaceable using skills that have been around for thousands
of years鈥攕and casting with bronze and perhaps some hammering. 鈥淲e will
also leave some spare parts,鈥� he adds.
The next task for Hillis and his colleagues is to find a site for the
Millennium Clock. 鈥淲e have lots of ideas for places but we鈥檙e still looking for
suggestions.鈥� The foundation has already considered Egypt, Jerusalem and China
as well as the peak of a 3000-metre mountain in Nevada. 鈥淭hat would make
visiting the clock a kind of pilgrimage which is an interesting idea,鈥� Hillis
says.
Will people want to make such a pilgrimage? 鈥淵ou never know until you do it,鈥�
laughs Brand. 鈥淚f it works, it becomes a kind of talisman for the long view,
which means a responsible perspective on things.鈥� But above all, Brand believes
the Millennium Clock will provide a source of inspiration for future
generations. 鈥淚t should give you a personal sense of: Wow! 10 000 years right
迟丑别谤别.鈥�