Law, theory, and hypothesis do not constitute a body of knowledge. In other words, a theory is not just made up of rules or hypotheses. These phrases also denote the degree of rigor or theoretical or empirical validity that a concept possesses.
- A hypothesis is a best-guess explanation offered for a particular physical phenomena. It is intrinsically falsifiable since one may begin to gather evidence to support or contradict the hypothesis. One idea is that gravity is essentially the atmosphere pulling us downward. In this instance, it seems appropriate. But it disintegrates when someone asks what holds the planet's atmosphere to it, and so on.
- Law: A law is an explanation of an observation that is more empirical in character. It is a picture of how things seem to work rather than an explanation of how they function. The same was true of Newton's law of gravity. It was developed from Johannes Kepler's rules of planetary motion, which were were illustrations of Kepler's (and Tycho Brahe's) painstaking studies of planets and their trajectories around the sun. Neither of those systems of laws provided an explanation for how gravity operated. They involved looking for a mathematical pattern in the data or a suitable curve to fit the data display. Laws may not be accurate representations of natural phenomena. However, laws become facts if they are viewed as "rules of nature," such as the fact that the earth revolves around the sun, which in turn revolves around the galactic center.
- A theory is a complex thought construction that is used to explain observations, including their causes and mechanisms. It has its origins in a hypothesis, which is then evaluated against observations for validity, amended, and ultimately shaped into a formal construct. When a collection of hypotheses adequately explains the majority of the recorded data, it is fair to refer to it as a theory, from which predictions can be made. A theory needs to be able to predict the future and be falsifiable. When given input data, a theory must be able to forecast consequences that can be empirically verified. Since string theory offered few to no predictions that could be independently verified, this has plagued string theorists for a time. General Relativity is a theory that attempts to explain the origins and operation of gravity.
In the same way that this iPad I'm typing on is solid or that birds can fly, gravity is a known truth or a rule of nature. Theories include efforts to describe its dynamics, such as general relativity, loop quantum gravity, string theory, etc.
Thanks,
Eddie