How are principles created i.e. how is it decided that something qualifies as principle?

What is the difference between a principle, a law and a theory?

Were there any principles that were proved to be wrong or are principles always right? For example, the reason why Einstein proposed that the speed of light is constant is because the Principle of Relativity would be violated otherwise.

Are physical principles comparable to mathematical axioms?

Is there a list of physical principles? I couldn't find any on google.

marked as duplicate by Qmechanic♦Sep 28 '13 at 15:10

• Possible duplicates: physics.stackexchange.com/q/35660/2451, physics.stackexchange.com/q/44706/2451 and links therein. – Qmechanic Aug 27 '13 at 6:58
• There are a plethora of proposed physical principles that were eventually proved wrong, especially ones made by the ancient Greek natural philosophers since they rarely checked ideas against experiment. The first historical example we have a physical principle comes from Thales c.600 BC, who said all matter is made from water. Aristotle's first law of motion is "Everything that is in motion must be moved by something", and Aristotle thought heavier objects fall faster than lighter ones. – David H Aug 27 '13 at 13:56

Going with your example: the constancy of the speed of light is a law that motivated the more general "principle of relativity" for Einstein: the idea that the laws of physics should be the same for all "inertial" observers. This latter idea of "inertial" observers began as (1) those moving uniformly in special relativity - later generalized to (2) those moving along geodesics and whose frames are Lie-dragged by the Levi-Civita connexion: sorry to sound too technical in that last bit but I threw it in because it is a "jargon" phrase which you can do successful Google searches on: its a way of characterizing the conditions in GR that mean that if an observer carries a system of relatively stationary $x,y,z$ orthogonal rods with little vectorial accelerometers (those able to measure acceleration direction) mounted along the rods' lengths, all of those accelerometers will read nought. The "theory" was the set of deductions Einstein made from this principle: the Lorentz transformation, the Einstein field equations with their attendant calculations of the extent of precession of Mercury's perihelion and bending of light around the Sun (both confirmed by experiment) as well as many others, equivalence of mass and energy and so on and so forth.