I successfully explained Quantum Electrodynamics in Science of Pursuit, Please visit http://www.geocities.com/unifytruth By replacing negative action with the corresponding pursued quantity, universe can be explained as a system pursuing happiness, profit or knowledge. So sciences about largest negative action pursuit, largest happiness pursuit, largest profit pursuit and largest knowledge pursuit can be unified into one: Science of Pursuit. From least action principle in physics, universe pursues negative action the best, so it is a perfect pursuit system. Result of pursuit is system expanding, just like universe expansion, economic development and knowledge progress. Expanding velocity is decided by methodology and mathematical expression of the pursued quantity. Relation between mathematical expression, methodology and expanding velocity is invariant with dimension and unit of the pursued quantity, so they are a priori and ultimate truth. So, although researchers and society are bad pursuit systems, they can perfect themselves by "Imitating Universe".