electricity, that had once pervaded the entire universe. As gravity piled on the pressure, denser regions got denser, their cores got hotter, and gravity began to re-create the high energies of the early universe. At roughly ten million degrees Celsius, protons have so much energy that they can collide violently enough to overcome the repulsion of their positive charges. Once pushed across this barrier, protons began to link up in pairs, bound together by the strong nuclear force, which operates only over tiny distances. Proton pairs formed helium nuclei as they had done, briefly, once before,
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