A lot of the value of antiques comes from the lost knowledge they represent, whether that's just sentimental "you just had to be there" experiences or more conc

A lot of the value of antiques comes from the lost knowledge they represent, whether that's just sentimental "you just had to be there" experiences or more concrete "you don't know how to make the varnish on a Stradivarius" lost knowledge. For that matter, the distances between systems creates a sort of time-travel effect. You receive their knowledge hundreds of years after the fact, making it implicitly "antique lost knowledge." So I think the point still stands that all trade would be done using photons. I would be very interested to discuss how "trade done using photons" is such a 21st-century concept and that it bears as much resemblance to interstellar trade as the black pepper trade of the 13th-century proscribes capital markets today.