""This is an exceedingly long short book, stretching at least fifty thousand years into the past and who knows how many into the future."" So begins Visions of the Future, the prophetic new book by eminent economist Robert Heilbroner. Heilbroner's basic premise is stunning in its elegant simplicity. He contends that throughout all of human history, despite the huge gulf in social organization, technological development, and cultural achievement that divides us from the earliest known traces of homo sapiens, there have really only been three distinct ways of looking at the future.