To elaborate on "interesting things", at least as I understood it from a seminar by one of the authors...

- The distribution of wealth naturally forms an exponential distribution. It takes effort/energy/negentropy to depart from this situation where there will always be many more poor people than rich.

- Unlike particle energy, wealth can be negative. When this is accounted for (allow for debt), the rich inherently get richer. This is not even accounting for interest being paid by the debtors to the (presumably rich) debtees.

- At a certain point, money begets more money. This results in a power law tail and identifies the "upper class".

Physicists have gotten very good at the statistics of interacting particles. This paper asks, what if instead of a bunch of particles exchanging energy, one interprets it as the theory of many agents randonly exchanging money. Interesting things happen even in this over-simplified model.