The Theory of Interstellar Trade

I did not think that Paul Krugman was still writing academic papers. Nor have I seen any evidence in the last decade that he still has any sense of humor.
Consequently, I was surprised to see an article written by him entitled “The Theory of Interstellar Trade,” published recently in the journal Economic Inquiry. Here is the abstract of the paper:

This article 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 the 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.

A quick look at the acknowledgments, however, clears things up. The original manuscript was written in July 1978, when Krugman was an active researcher and being a curmudgeon wasn’t part of his professional identity.