[AntonioLao]

96% of the mass of the universe cannot be accounted for. This discrepancy was discovered about 70 years ago by careful observations done by Fritz Zwicky (see http://en.wikipedia.org/wiki/Fritz_Zwicky), a Swiss astrophysicist at Caltech. He theorized that although the universe is expanding uniformly, there are still local inhomogeneous random movements embedded within the universal uniformity. For example, the Local Group http://en.wikipedia.org/wiki/Local_Group which includes our galaxy, the Milky Way, and the Andromeda galaxy are approaching each other at a speed of 130 kilometers per second. However, redshift measurements seem to indicate that most galaxies are moving too fast over the speeds allow by law of gravity if only the visible mass were inserted into the equations. This is also true for the motions of stars within a galaxy. So, why do the galaxies remain stable? There must be invisible stuff that holds them together.

On the other hand, Einstein’s theory of general relativity asserts the existence of two distinct masses separately defined by different equations. These are the inertial mass and the gravitational mass. Taking Mach’s principle in consideration, these masses are equivalent for any two-body system such that a local acceleration of gravity (g) exists and g=F/m, where m is the inertial mass and F is the inertial force. However, by the principle of equivalence http://en.wikipedia.org/wiki/Equivalence_principle g=GM/r, where M is the gravitational mass, G is the universal constant of gravitation, and r is the absolute distance. Therefore, the masses can be expressed as functions of the other parameters: M=gr/G and m=F/g. From these, it is clear that if the local acceleration of gravity is zero, g=0, then M=0 but m becomes infinity or undefined even if F is constant or zero. If g is nonzero, M increases without bound with square of distance, while m remains practically a constant and m=0 if and only if F=0.

In conclusion, these demonstrated that gravitational mass as a continuous field is directly proportional to the square of distance while inertial mass as a quantum of particle remains unchanged. Since fields are difficult to detect unless they interact, for example: the Higgs field, gravitational mass are then the missing mass of the universe.