History of the Cyclic Universe

"The notion of a cyclic universe is not new. People have considered this idea as far back as recorded history.

"The ancient Hindus had a very elaborate and detailed cosmology based on a cyclic universe. It is a time-honored eastern philosophy that time has neither a beginning nor an end, and that the universe is locked in a perpetual cycle of formation and disintegration.

"The cyclic notion has also been a recurrent theme in western thought. Edgar Allan Poe and Friedrich Nietzsche each had cyclic models of the universe. So many people have found the cyclic idea to be appealing because when you have a universe with a beginning, you have the challenge of explaining why it began and the conditions under which it began. If you have a universe which is cyclic, it is eternal, so you don't have to explain the beginning.

"In the 1930s, Richard Tolman of the California Institute of Technology wondered what would happen if a closed universe—in which all matter and energy are ultimately compacted in a big crunch—were to survive its closure and burst forth again. Tolman realized the universe would gather entropy during each new cycle and to compensate, it would have to grow every time like a runaway snowball. And just as a snowball has to begin at some point in time, so, too, would such a universe. You would be able to calculate the 'beginning.'

"Then in the 1960s, physicists proved that a big crunch must culminate in a singularity—a point stuffed with infinite matter and heat. This is where Einstein's general relativity breaks down. The laws of physics are thus up for grabs.

"The idea of a cyclic universe has been around for a long time but has been plagued by a fundamental problem: What physics causes the collapsing universe to bounce back into the expanding phase?

"This is where String Theory steps in."

See also, An Introduction to String Theory.

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