Theory of interstellar trade, Paul Krugman, july 1978
This paper extends interplanetary trade theory to an interstellar setting. It
is chiefly concerned with the following question: how should interest charges
on goods in transit be computed when goods travel at close to the speed of
light? This is a problem because the time taken in transit will appear less to
an observer traveling with the goods than to a stationary observer. A solution
is derived from economic theory, and two useless but true theorems are proved.