Time for the future

Abstract

Imagine a clock that keeps time for thousands of years. It ticks every 10 seconds, chimes once a millennium, and self-corrects for variations in Earth’s rotation. Such a clock is inventor Danny Hillis’s dream, and it’s coming alive inside a mountain in West Texas. “I got tired of only working on projects that were rush rush rush to get something done quickly. I wanted to work on something that mattered over the longer term,” says Hillis, cofounder of the research and development company Applied Minds. He says the clock is like a time capsule, in that it reaches out to connect with the future.Nestled in a 150-meter-deep shaft 3.7 meters in diameter, the clock will have a 3-meter, 110-kg titanium pendulum. It will be powered by stainless-steel bellows right below ground that expand and contract as the ambient temperature rises and falls each day. Five-ton weights that hang in the shaft are pulled upward when fed energy from the bellows; it is the weights that require such a long shaft. Visitors will also be able to hand wind the clock.The 10 000-year clock will count days with the pendulum and keep on track by noting the Sun’s highest position every clear day through a sapphire window to the sky. The clock sets itself to solar noon by checking against a specially shaped cam that encodes the calculated daily time of the Sun’s transit for the next 10 000 years. If the Sun is obscured—even for a century or more—the clock can make up for it in intervals of five minutes per clear day.“When you get into the details, it causes you to think about time differently,” says Hillis. For example, leap seconds are important “when you are designing a clock to last 10 000 years.” The clock would be off by as much as 30 days at the end of that time if the uncertainties and variability in the length of the day were ignored, he says. (See the story on page 27.) “Global climate change seems like an abstraction, but then you realize that if the worst projections are right, the ice caps will melt and the Earth will spin a little faster, and that makes a difference for how the clock reads. I have to take that possibility into account.”The clock’s roughly 10 000 parts will be made from titanium, high-molybdenum stainless steel, ceramics, and other stable materials. “We have pieces of metal, flexures, that bend. We have to make sure they can bend a billion times,” says Hillis. “We have to make windows that will stay transparent.” Aside from the materials problems, the biggest challenge is aesthetics, he says. “How do you design something that people understand and care about even when the culture changes?”To save energy, the clock will display the time only when asked by a visitor. Those who make the trip to the remote site will be able to climb a long spiral staircase along the shaft wall. They will be able to make the clock chime—a different melody every time. In another mechanical feat, the current positions of the planets and the phase of the Moon will be displayed in one of the clock cavern’s chambers; the calculations for the positions of the planets were made by Jon Giorgini of NASA’s Jet Propulsion Laboratory.Hillis’s vision of a 10 000-year clock inspired others, and in 1996 the nonprofit Long Now Foundation was formed to oversee the project. Amazon.com founder Jeff Bezos is the multimillion-dollar clock’s biggest sponsor. The shaft for the Texas clock was drilled last year, and although design problems remain, Hillis says, “we are physically constructing big pieces. Certainly the clock will be built in my lifetime. That’s my ultimate deadline.”This 2.4-meter prototype to test some mechanisms for a larger 10 000-year clock chimed at the turn of the last millennium and now stands in the London Science Museum. (Rolfe Horne, courtesy of The Long Now Foundation, http://www.longnow.org.)PPT|High resolution© 2012 American Institute of Physics.