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Describe the transformation of radiation into matter where followed the ‘Big Bang’ After the Big Bang… Where the big bang is recorded to begin, the first step was radiation filling the Universe. This took between 10-12 to 10-10 seconds. At this time, the universe is lying in a dense, hot and small state. As proposed by Einstein’s theory of general relativity, the expansion of the Universe can be driven by energy density in the form of matter radiation. As the radiation here was exceedingly larger than matter, it can be excluded (ie. matter doesn't exist). This radiation creates pairs of particles and anti-particles, some of which collide and annihilate back to radiation. These include quarks and anti-quarks, which averaged in number until the cooling of the Universe (and hence the radiation associated with it) which created less off these pairs, and the overall result was quarks greatly outnumbering anti-quarks. As this occurs, the amount of matter present is increasing due to the still highly abundant radiation until eventually the energy density in the matter superceeds the amount of energy density in radiation. The energy density of radiation continues to be in smaller and smaller ratios to that of matter, and so can be counted as negligible in cosmic equations and the further expansion of the Universe can be determined by the actions of matter from this point. Following this new shift in matter domination, a less efficient energy exchange between matter and radiation is created. Accretion of the stars and galaxies The moment when the expansion began was roughly 14 billion years ago. The universe began in a very hot, dense state, then cooled as it expanded. As distances increase, the average density of the universe decreases. Since matter cools down as it expands (think of the outer layers of an expanding red giant, for instance), the universe is going from a hot dense state to a cool low-density state.
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