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The American Association for the Advancement of Science sounds like a feet-on-the-ground organization. But in a recent meeting in Boston some scientists took flight, at least in imagination. They talked about physically possible step-ups in the speed of travel that might make it conceivable to reach a near star. Alpha Centauri, our neighbor, is 4.4 light-years from the sun, which means 6 trillion miles times 4.4. We learn that if a cave man 11,000 years ago had launched something at the pace of Voyager, it now would be only one-fifth of its way to the nearest star.