# Why are the gravitational mass and the inertial mass of an object same?

Discussion created by Mitsuru Yamada on Oct 15, 2014

Here I would like to present you three elementary questions.

Q1.  What is the origin of inertial mass of an object?

Q2.  What is the origin of gravitational mass of an object?

Q3.  Are there any relationships between the above two?

In the last chapter of John Gribbin's book "Schroedinger's Kittens", the author introduces his idea about the equality of the inertial mass and gravitational mass.  Using the concept of feedback from the entire universe, he seems to be satisfied with his conclusion that "Thus, the inertial mass and gravitational mass are same."

But I still do not see his point.  I do not understand what he means.  Can you understand and accept his discussion about the equality of the two, Sir?

Sir Isaac Newton discovered the inverse squared law of gravitational force exerting on the two masses.  But his law seems to be empirical finding, and there is no theoritical derivation calculation from more foundamental laws even now in the 21st century.  Albert Einstein presented us the theory of spacetime geometry in his general theory of relativity.  His argument is appied to movements of celestial objects.  Particularly important finding of Einstein is the equality of energy and mass.  But it is unclear whether the mass m in his famous equation E=mc^2 represents the inertal mass or gravitational mass.

Thus neither Newton nor Einstein found what an inertial mass or a gravitational mass is all about.  So I would like to ask you what the origin of the inertial mass is, what the origin of the gravitational mass is, and why are they same for an object.