Applications of Complexity Theory Complexity theory seems to capture something fundamental about the
structure of the universe, in that it formalizes the intuitive notion
that some problems are harder than others.

Scott Aaronson predicted, "The NP Hardness Assumption will eventually be
seen as analogous to the Second Law of Thermodynamics or impossibility
of superluminal signaling."

So-called "hard problems" are the basis of modern cryptography.

Are there any other applications that utilize, depend on, or exemplify the
existence of computationally hard problems?
The most recent issue of the CACM has an article by Faliszewski, Hemaspaandra and Hemaspaandra on the use of complexity theory in the realm of social choice theory and election design in particular. One example of such a result is that while Arrow's theorem guarantees that any election system is 'hackable', it might be NP-hard to do so.