Mass is defined in terms of inertia - the need for a force to make something alternate its direction or velocity of motion. Mass and energy are below some occasions interconvertible, as expressed in the equation E = mc^2 however various conditions ought to be satisfied for this to occur big scale. For example, you can't turn an electron into pure power, but an electron and the positron will react to generate energy in the form of a pair of gamma rays (challenge situation for readers: why do you want TWO gamma rays, no longer only one?). The reference to Higgs was once spot-on. This is all very much physics. No person really is aware of, but we've not given up and mustn't quit of finding out fairly a bit of more. BTW, a neutron weighs moderately greater than a proton, and roughly 2000 times as a lot as an electron. That you can calculate the vigour released in a nuclear response by using subtracting the mass of the products from the mass of the dad or mum, and utilising Einstein's system. The mass of a proton involves the mass of the quarks, of the gluons conserving the quarks collectively, and the energy worried.