What will be the world language?

Today at lunch, a kid said that he should’ve taken Spanish, because that will someday be the world language. Another kid agreed, saying that America will eventually fall, like all great civilizations (Rome, for instance).

That actually got me thinking - what would be the world language if there ever was one? Spanish is spoken by more than half the countries in the western hemisphere - English has America, Australia, and England on its side, as well as most of Canada - French is spoken by France, Quebec, and Morocco - Italian is primarily spoken only in Italy (as far as I know) - insert any other language you feel needs to be included here.

Anyone have any ideas/thoughts/comments?