eppstein@garfield.columbia.edu (David Eppstein) (10/13/86)
Ok, so FTL communications violate causality. Can anyone give me a coherent explanation of why this is such a big problem? Seems to me it might even have advantages; for instance with time loops you might be able to build a working alternating Turing machine. But anyway, let's assume for the moment that tachyons exist. At "rest" they are supposed to move with "infinite" velocity; that implies to me that they are line-like rather than point-like (or equivalently point-like particles in a dual space to the three dimensions we all know and love). Can anyone come up with descriptions of time and motion for such an object that make sense (e.g. geodesics dualize and we have some equivalent of the speed of light)? If we had Newtonian physics it would be easy. Time is trivial and geodesic motions could just be rotations about fixed points possibly including a fictional point at infinity. But we don't (sigh)... p.s. does anyone know why I can't post to both net.physics and sci.physics? -- David Eppstein, eppstein@cs.columbia.edu, seismo!columbia!cs!eppstein