Einstein’s Theory of Relativity.
According to the conventional model of particle physics, protons and neutrons comprise smaller particles known as quarks, which in turn are bound by gluons.
The odd thing is this: the mass of gluons is zero and the mass of quarks is only five percent. Where, therefore, is the missing 95 percent?
The answer, according to the study published in the US journal Science on Thursday, comes from the energy from the movements and interactions of quarks and gluons.
In other words, energy and mass are equivalent, as Einstein proposed in his Special Theory of Relativity in 1905.
The e=mc2 formula shows that mass can be converted into energy, and energy can be converted into mass.
Well, I hope that clears everything up.