The Theory of Interstellar Trade
Any civilization that has mastered interstellar travel will almost certainly also have mastered atomic transmutation as well.  So as long as all the interesting stuff is made of atoms, and the atoms over there are the same as the ones over here (which AFAWCT they are), there are only two possible &quot;goods&quot; that could be worth transporting between star systems: information, and free (in the physical, not the economic sense) energy.  You don&#x27;t need a space ship to transfer either of those, you just convert them into photons and let Maxwell do the work.  The idea that it might be worthwhile to actually <i>ship</i> something (including ourselves) to another star system is based on very quaint notions of identity binding and what it takes to produce things.