Big bang Quote by Steven Weinberg

““Using the standard model of elementary particles, we know how to follow the course of nuclear reactions in the standard "big bang" theory of the universe well enough to be able to calculate that the matter formed in the first few minutes of the universe was about three- quarters hydrogen and one-quarter helium, with only a trace of other elements, chiefly very light ones like lithium. This is the raw material out of which heavier elements were later formed in stars. Calculations of the subsequent course of nuclear reactions in stars show that the elements that are most abundantly produced are those whose nuclei are most tightly bound, and these elements include carbon, oxygen, and calcium. The stars dump this material into the interstellar medium in various ways, in stellar winds and supernova explosions, and it is out of this medium, rich in the constituents of chalk, that second-generation stars like the sun and their planets were formed. But this scenario still depends on a historical assumption-that there was a more-or-less homogenous big bang, with about ten billion photons for every quark. Efforts are being made to explain this assumption in various speculative cosmological theories, but these theories rest in turn on other historical assumptions.””

— Steven Weinberg