He was astonished to learn that this sum total of mass is different from a separately computed estimate. This other value was obtained by analyzing the sum total of galaxies and the brightness of the Coma cluster. Juxtaposing this value with the periphery computation he observed that there was a discrepancy of at a minimum four hundredfold. Since the galaxies were insufficiently massive to cause the computed orbital velocities there must be some other mechanism to explain this phenomena. This conundrum became in the scientific lexicon the missing mass problem. Zwicky had established the need for the existence of an invisible source of mass hitherto unknown which must provide the necessary gravitational effect for the cluster.

Thus, it is a fact of the current state of cosmology that the greatest set of evidence for dark matter comes from this galactic gravitational data. Scientists have even made galactic curves describing the rotational properties of stars versus the distance from the galactic center. When the gravitational data is plotted it can be shown that only a small portion of the observed speeds are explicable by classical computations. In other words, there is a scarcity of visible mass in the observed galaxies to attribute the sum total of gravitational effects to visibly observable stars planets and galaxies. Thus, the simplest way to explain this galactic mystery of insufficient mass is to hypothesize a non-detectable type of mass known as dark matter which can be the cause for the gravitational effects.

As more and more data is collected on these and other aspects of the universe, formulae and cosmological postulates are generated describing the results so obtained. Fulfilling the requirements of the aforementioned aspects leads some scientists to propose several different types of dark matter. The four main types of dark matter are called 1- baryonic dark matter; 2- warm dark matter; 3- cold dark matter and 4- hot dark matter. Dark matter ranges from the known to the predicted, from black holes to brown dwarfs to the massive compact halo objects (MACHOs), the neutrino, axions, WIMPS or weakly interacting massive particles and the esoteric neutralino. However, there is an alternative explanation for the gravitational effects which originally created the dark matter concept.