  In this paper the reason why entropy reduction (negentropy) can be used to
measure the complexity of any computation was first elaborated both in the
aspect of mathematics and informational physics. In the same time the
equivalence of computation and information was clearly stated. Then the
complexities of three specific problems: logical compare, sorting and SAT, were
analyzed and measured. The result showed SAT was a problem with exponential
complexity which naturally leads to the conclusion that no efficient algorithm
exists to solve it. That's to say: NP!=P.
