Happy trillionth birthday, universe

Give or take a few billion years, anyway. At least, it’s one way of explaining the cosmological constant.

The cosmological constant represents the energy of empty space, and is thought to be the most likely explanation for the observed speeding up of the expansion of the universe. But its measured value is a googol (1 followed by 100 zeroes) times smaller than that predicted by particle physics theories. It is a discrepancy that gives cosmologists a real headache.

In the 1980s, physicists considered the possibility that an initially large cosmological constant could decay down to the value measured today. But this theory was abandoned when calculations showed that it would take far longer than 14 billion years – the time since the big bang – for the constant to reach the level seen today.

According to Steinhardt and Turok, today’s universe is part of an endless cycle of big bangs and big crunches, with each cycle lasting about a trillion years. At every big bang, the amount of matter and radiation in the universe is reset, but the cosmological constant is not. Instead, the cosmological constant gradually diminishes over many cycles to the small value observed today.

This version of the universe always appealed to me; a perpetually cycling universe makes more sense than a big-bang-out-of-nothing followed by an eternal expansion and cold death.

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