# Law of physics

A**law of physics**is a mathematical relationship between measurable quantities that describe the physical state and properties of bodies. This is a fundamental concept in physics.

Collectively, the **laws of physics** are those physical theories which
have been widely published and tested, and are considered by the
scientific community in general to be valid. They also tend to be very
general, basic theories: instead of having a large list of laws governing
many different phenomena in different circumstances, special cases are
arrived at through a particularization of basic ideas. Well-known laws of physics include
Einstein's theory of general relativity, Newton's laws of motion,
Maxwell's equations for electricity and magnetism, and the theory of
Quantum mechanics.

Interestingly, these so-called "laws" can essentially be viewed as a
series of approximations: well-established physical laws are found to be
invalid in some special cases, and the new theory created to explain these
discrepancies can be said to have generalized the original, rather than
superseded it. One well-known example is that of Newton's law of
gravity: while it described the world accurately in most normal
circumstances, such as the movement of the planets around the sun, it was
found to be inaccurate when applied to very large masses or very high
velocities. Einstein developed the theory of general relativity, which
accurately handled gravitational interactions both those extreme conditions
and in the range occupied by Newton's law. However, Newton's formula for
gravity is still used in most circumstances, as an easier-to-calculate
approximation of gravitational interaction. The same phenomena can be
observed when comparing Maxwell's Equations with the theory of
quantum electrodynamics, and in other cases. This leads to the philosophical question of whether there are any real **Laws of physics** at all, or are they all just cases where our sensory and rational apparatus generate a mathematically simple approximation, valid within the range of normal human experience, to a true formula which may be much more complicated.

Outside the scientific community, it is often assumed that the **laws of physics** have been proved beyond a doubt. It would be nice to guarantee that some law in physics is 100% correct for all possible situations. Ironically, however, what we term **laws of physics** are not proved at all, in the same fashion a mathematical theorem can be proven; it is just that no example has ever been seen where they are violated. They can always be invalidated, however, by experimental evidence should any such case be seen; or more often, be found to be a close approximation to which another term or factor must be added to cover experimental evidence from more extreme conditions, i.e. huge or infinitesimal scales of time or space, enormous speeds or masses, etc.

Other laws of physics are included in a partial list of laws in science. See also the list of differential equations of mathematical physics.