A question from Yahoo! Answers:
In the future (hypathetically) what would be Earth’s main export?
Great question, albeit the one without an answer.
The theory of comparative advantage predicts that goods that end up as exports are those that can be produced at a comparative advantage. In other words, if on Earth one unit of good A sells for the same price as one unit of good B, while on another planet one unit of good A sells for the same price as five units of good B, Earth will export good A and import good B. So it is impossible to say what the Earth’s main exports are going to be without first looking at the economies of its trading partners.
Also, comparative advantage must be large enough to cover transportation costs. If interstellar cargo hauling turns out to be prohibitively expensive, there will be no trade.