Also look at this article from The Futurist:
One of the most popular dinner party conversation topics is the possibility that the United States will be joined or even surpassed as a superpower by another nation, such as China. China has some very smart people, a vast land area, and over four times the population of the US, so it should catch up easily, right? Let's assess the what makes a superpower, and what it would take for China to match the US on each pillar of superpowerdom.
A genuine superpower does not merely have military and political influence, but also must be at the top of the economic, scientific, and cultural pyramids. Thus, the Soviet Union was only a partial superpower, and the most recent genuine superpower before the United States was the British Empire.