> Well if you can propel something forward you can propel it backwards as well
Not necessarily - at least with currently known science. Light sails work ok transferring momentum from photons, allowing positive acceleration from a giant laser Earth. Return trip requires a giant laser on the other side.
Not necessarily - at least with currently known science. Light sails work ok transferring momentum from photons, allowing positive acceleration from a giant laser Earth. Return trip requires a giant laser on the other side.