The big bang is the preeminent theory of modern cosmology. The model is strongly supported by evidence. But if the big bang caused the Universe, what caused the big bang? Everything from God to nothing has been proposed as an answer, but there are some who think our Universe could have formed from another, earlier Universe. If that Universe also arose from an earlier Universe, then the answer could be that there truly was no beginning.
This is the idea behind Conformal Cyclic Cosmology (CCC), an idea proposed by Roger Penrose. The basic idea goes like this: our Universe began in a hot, dense state, but it was very uniform. Clumps of matter appeared in the Universe over time, which eventually became stars, galaxies, black holes and the like. At the moment our Universe is a clumpy distribution of galactic clusters, but because of dark energy and the expansion of the cosmos that will change over time. Galaxy clusters will become increasingly isolated. Supermassive black holes may capture their surrounding galaxies, but through Hawking radiation even black holes should evaporate into a sea of radiation. So our Universe should become uniform again in the distant future. Could the uniformity of the beginning of our Universe be somehow connected to the uniformity at the end of another Universe?
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