What is energy in reality, is it PHOTON?? When mass is annihilated, two photons or light is produced. That light has very high(or highest) energy level. As the energy of light depends on it's frequency and wavelength it means that photons are not energy themselves but just energy carrier(guage boson for electromagnetic force). Now the question automatically arises that if it is just about not being mass that even a graviton or gluon does not have mass but are energy carriers but they are not produced as energy. what is energy in reality then. I don't think the classical definition are right:"The ability to do anything" There must be some REAL form of energy than kinetic, potential or others. It is even said that energy can bend the river of time(i mean to say time out of the space-time fabric) and it is also discovered that high energy can from one side grow and from other side shrink the spacetime fabric, making faster-than-light travel possible. Than what is PHYISICAL existence of energy And last thing, why two high energy photons can not produce mass?