“I think this is the most important thing I can work on. More than cancer. Over the long run, I think this will make more difference to more people.”Danny Hillis is building a giant mechanical clock inside a mountain in West Texas, with cash from Amazon.com founder Jeff Bezos. “Over the lifetime of this clock, the United States won’t exist,” Bezos tells me. “Whole civilizations will rise and fall. New systems of government will be invented.