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On Problems with Near-light-speed Travel


Dave Thomas

Volume 29.5, September / October 2005

Forget Star Trek-style warp-speed (greater than the speed of light) travel and its attendant problems (like the possibility of warping through a sun). Just traveling at near-light speed could bring a host of serious problems. Take a grain of interstellar dust, for example. A tiny grain of silicon dioxide (quartz, or sand) just one micron wide (a millionth of a meter, fifty times smaller than the width of a hair) would present no problem to travelers at normal speeds. But if a spacecraft were going along at 90 percent of light speed, the innocent sand grain would appear like a high-energy missile. In fact, the relativistic calculation of the micron-sized grain’s kinetic energy, as viewed by the approaching craft, would be close to 170 joules, which is about the energy of a 22-caliber bullet (40 grains, 64.8 mg/grain) traveling over the speed of sound (about 1,200 feet per second, or 366 meters per second). At such energy levels, the sand particle might even explode into a shower of protons and neutrons when it collides with the spacecraft. And a proton, traveling at 0.9c, can penetrate a stainless steel hull about 74 cm (about 2 and a half feet) thick. I don’t want to bum out all the Trekkies out there, but it’s worth pondering: near-light-speed travel is going to be hard.

Dave Thomas

Dave Thomas, a physicist and mathematician, is president of New Mexicans for Science and Reason and a fellow of the Committee for Skeptical Inquiry. He is currently a scientist/programmer at IRIS/PASSCAL in Socorro, New Mexico, and also teaches classes in physics, psychology, and critical thinking at New Mexico Tech.