Physicists use fundamental constants to help determine the scale at which a theory is valid. In order for a quantity to be a fundamental constant, it must appear as a constant in a physical law, and it must take the same value in every law in which it appears. Three of the most well-known constants are Newton's gravitational constant (G), the speed of light in a vacuum (c), and Planck's constant (h).

English physicist Isaac Newton discovered the first fundamental constant with his law of universal gravitation, F = Gmm/r2 . The law of universal gravitation states that the force, F, between two masses, m and m, is directly proportional to the product of the masses, and inversely proportional to the square of the distance between them, r2 . The proportionality constant, G, sets the scale of the gravitational interaction. G is very small (G=6.67 x 10-11 Nm...