Eternal return

Eternal return (also known as "eternal recurrence") is a concept that the universe and all existence and energy has been recurring, and will continue to recur, in a self-similar form an infinite number of times across infinite time or space. The concept is found in Indian philosophy and in ancient Egypt and was subsequently taken up by the Pythagoreans and Stoics. With the decline of antiquity and the spread of Christianity, the concept fell into disuse in the Western world, with the exception of Friedrich Nietzsche, who connected the thought to many of his other concepts, including amor fati.

In addition, the philosophical concept of eternal recurrence was addressed by Arthur Schopenhauer. It is a purely physical concept, involving no supernatural reincarnation, but the return of beings in the same bodies. Time is viewed as being not linear but cyclical.

The basic premise proceeds from the assumption that the probability of a world coming into existence exactly like our own is greater than zero (we know this because our world exists). If space and time are infinite, then logic follows that our existence must recur an infinite number of times.

In 1871 Louis Auguste Blanqui, assuming a Newtonian cosmology where time and space are infinite, claimed to have demonstrated eternal recurrence as a mathematical certainty. In the post-Einstein period researchers cast doubts on the idea that time or space was in fact infinite, but many models provided the notion of spatial or temporal infinity required by the eternal-return hypothesis.

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