My question is why do we even need dark matter to make things work ? E=mc2 so if ENERGY AND MASS are the same thing if MASS creates gravity why can energy not also create gravity can someone explain this to me? if Under general relativity any form of energy couples with space time to create the geometries that cause gravity why are we even looking for dark matter all the energy in the galaxy should be enough to make up for the lost gravity right? or am i missing something? i mean really microwaves x rays gamma rays LIGHT ITSELF i mean thats ALOT of energy so shouldn't that also be alot of gravity?