Why this universe?  Maybe it’s nothing special – just likely

Why this universe? Maybe it’s nothing special – just likely

Why this universe?  Maybe it’s nothing special – just likely

cosmologists have issued decades of striving to understand why our universe is so amazingly vanilla. Not only is it smooth and flat as far as we can see, but it’s also expanding at an ever-so-slowly increasing rate when naive calculations suggest that — after the Big Bang — outer space should have been crumpled by gravity and by blasted apart by repulsive dark energy.

To explain the flatness of the cosmos, physicists have added a dramatic opening chapter to cosmic history: They propose that at the onset of the Big Bang, space rapidly inflated like a balloon, smoothing out any curvature. And to explain the gentle growth of space after this initial inflation, some have argued that our universe is just one of many less hospitable universes in a vast multiverse.

But now two physicists have turned conventional thinking about our vanilla universe on its head. Following a line of research begun by Stephen Hawking and Gary Gibbons in 1977, the duo have published a new calculation that suggests the cosmos’ plainness is expected rather than rare. According to Neil Turok of the University of Edinburgh and Latham Boyle of the Perimeter Institute for Theoretical Physics in Waterloo, Canada, our universe is the way it is for the same reason that air spreads out evenly in space: there are stranger options conceivable, but extremely unlikely.

The universe “may seem extremely fine-tuned, extremely unlikely, but [they’re] and say, ‘Wait a minute, that’s the favourite,'” said Thomas Hertog, a cosmologist at the Catholic University of Leuven in Belgium.

“It’s a novel contribution that uses different methods compared to what most people do,” said Steffen Gielen, a cosmologist at the University of Sheffield in the UK.

The provocative ending is based on a mathematical trick that switches to a clock ticking with imaginary numbers. Using the imaginary clock, as Hawking did in the 1970s, Turok and Boyle were able to calculate a quantity known as entropy, which appears to correspond to our universe. But the imaginary time trick is a roundabout way of calculating entropy, and without a more rigorous method, the importance of magnitude remains hotly debated. As physicists puzzle over the correct interpretation of the entropy calculation, many see it as a new signpost on the way to the fundamental quantum nature of space and time.

“Somehow,” Gielen said, “it gives us a window into which we might be able to see the microstructure of spacetime.”

Imaginary Paths

Turok and Boyle, frequent collaborators, are known for coming up with creative and unorthodox ideas on cosmology. To study how probable our universe might be, last year they turned to a technique developed by physicist Richard Feynman in the 1940s.

Aiming at capturing the probabilistic behavior of particles, Feynman imagined that a particle explores all possible routes connecting beginning to end: a straight line, a curve, a loop, to infinity. He devised a way of assigning each path a number related to its probability and adding all the numbers together. This “path integral” technique became a powerful framework for predicting how a quantum system would most likely behave.

When Feynman began publishing the path integral, physicists discovered a curious connection to thermodynamics, the venerable science of temperature and energy. It was this bridge between quantum theory and thermodynamics that made Turok and Boyle’s calculation possible.

South African physicist and cosmologist Neil Turok is a professor at the University of Edinburgh.Photo: Gabriela Secara/Perimeter Institute

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