Issac Newton's Theory of Universal Gravitation

Issac Newton's theory of universal gravitation states that every single point mass attracts every other point mass by a force heading along the line combining the two. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses.

My thought:

Although, I agree with Newton's theory and believe it possesses some truth, I believe there isn't enough proof to make his theory universally correct. I believe that it's sufficient, but is only used in general descriptions of gravity. Newton's theory seems to overlook the precession of perihelion or apsis of the earth, among several other planets. There is also no way of identifying the mediator of gravity. Newton "felt" and "assumed" there was an universal example of doing just so, but there wasn't. I also feel this theory may be limited to only smaller and lower limitations. I will write about this more in the future.