I meant to say:
Even the concept of "barter" is cloudy when there is *NO* physical contact between the parties. Or when it is delayed by many human generations. I am assuming the human lifetime is not extended much beyond 80 to 100 years. I suppose there would be some physical contact. Hundreds of years after a colony is set up at Alpha centauri, there might be new groups people on Earth who want to go there, perhaps because they like the culture. They might set out on a 80-year trip, in suspended animation, or in an arc where their grandchildren arrive. - Jed
