Gravity - a force
created by the presence of mass
Any two pieces of mass attract each other with a force more or less inversely proportional
to the square of their separation and directly proportional
to the product of their masses. This is Isaac Newton
's famous law of gravity,
F = Gm1
where G is the gravitational constant.
Of course, this has been proven wrong by Albert Einstein
's theory of general relativity
, which treats gravity as the result of the warping of space-time by mass. In most cases, the answers given by relativity match those of Newton's law.
Gravity is always attractive. Two pieces of mass are never repulsed from each other due to gravity.
s are one prediction of general relativity, as are gravity waves
and various other phenomena.
General relativity isn't the final word on gravity
, either. Attempts at combining GR with quantum mechanics
and the unification of the four forces (electromagnetism
, the strong nuclear force
, and the weak nuclear force
) under one unified theory
have lead to things such as superstring theory
which describe the universe in ways different from both QM and GR.