Scientific theory

A scientific theory is an explanation of some aspect of the natural world that has been repeatedly tested and is supported by a substantial body of corroborating evidence gathered through accepted scientific methods of observation, measurement and experiment. It differs from a scientific fact, which is a direct observation, and from a scientific law, which is an empirical description of a regularity, such as Newton's law of gravity, without itself explaining the underlying mechanism. In everyday language theory often implies an unproven guess, but within science the word denotes an explanation that has already been tested and is widely accepted, a distinction the paleontologist Stephen Jay Gould summarized by noting that facts and theories are different things rather than rungs on a ladder of certainty. A theory's strength grows with the range of phenomena it explains and its simplicity, and it can be refined or abandoned if it conflicts with new evidence, though a small number of well tested theories, among them evolution, heliocentrism, cell theory, plate tectonics and germ theory, are considered extremely unlikely to be overturned.