Time travel Accidentally, we are all traveling at the same rate into the future. But suppose it were possible and not too pricey to travel further either forwards or backwards. What madcap paradoxes await the careless traveler? * Antigravity An antigravity field, let’s say, could be created by small spinning tori beneath us. Unless the energy it takes were greater than the potential it produces, this device would violate thermodynamics, not to mention Einstein’s relativity, so we’re looking for a loophole. Otherwise, it’s off the table. * Teleportation They say the energy it would take exceeds the energy in our solar system, but we don’t need to actually transport each atom from the ship to the surface of a planet; instead, we find and gather atoms that are available for reconfiguration at the destination. I know this means we can reproduce ourselves or anything else into a sufficiently dense environment, but for the time being we are in it for pure science. * Parallel worlds Who’s to say we don’t already slip from world to world? What you mean when you say it, isn’t necessarily the same as what I think when I hear it.