An Explanation for the Equality between Inertia and Gravitational Mass

The mechanism causing the equality of inertia and gravitational mass of a body, which was demonstrated experimentally by Eotvos in 1909 is still unexplained although this equality is the basis of Einstein's General Theory of Relativity (GTR). Using consequences of GTR, this paper explains why the inertia mass is equally to the gravitational mass. The two masses are equal because the ‘mechanism' that produces the inertia ‘force' of a body is the same with the 'mechanism' that produces the gravitational ‘force' of the same body.