Why this universe? Maybe not special – just possible

Cosmologists have spent For decades you’ve struggled to understand why the universe is so amazing. Not only is it smooth and flat as far as we can see, but it’s also expanding at an ever-increasingly slow pace, when naive calculations suggest that – out of the Big Bang – space should have been gravitationally collapsed and imploded by repulsive dark energy.

To explain the flatness of the universe, physicists have added an intriguing opening chapter to cosmic history: They propose that space rapidly inflated like a balloon at the start of the Big Bang, flattening any curvature. To explain the bland growth of space after that initial spell of inflation, some have argued that our universe is just one among many less welcoming universes in a giant multiverse.

But now two physicists have turned conventional thinking about the vanilla universe on its head. Following a series of papers begun by Stephen Hawking and Gary Gibbons in 1977, the duo have published a new account suggesting that the blurring of the universe is to be expected, not rare. Our universe is what it is, according to Neil Turok from the University of Edinburgh and Latham Boyle from the Perimeter Institute for Theoretical Physics in Waterloo, Canada, for the same reason that air spreads evenly throughout a room: Weirder’s options are conceivable but highly improbable.

The universe “may seem very subtle, very improbable, but [they’re] Saying, “Wait a minute, this is my favourite,” he said Thomas Hertogcosmologist at the Catholic University of Leuven in Belgium.

“It’s a new contribution that uses different methods compared to what most people do,” he said. Stephen Gillencosmologist at the University of Sheffield in the UK.

The provocative conclusion is based on a mathematical trick that involves switching to a clock ticking imaginary numbers. Using an imaginary clock, as Hawking did in the 1970s, Turok and Boyle were able to calculate a quantity, known as entropy, that appears to correspond to our universe. But the imaginary trick of time is a roundabout way to calculate entropy, and without a more rigorous method, the meaning of the quantity remains hotly debated. While physicists have puzzled over the correct interpretation of the entropy calculation, many see it as a new clue on the road to the fundamental quantum nature of space and time.

“In a way, it gives us a chance to see the microstructure of space-time,” Gillen said.

imaginary paths

Frequent collaborators, Turok and Boyle are known for coming up with creative and unconventional ideas about cosmology. Last year, to study how likely our universe is, they turned to a technique developed by physicist Richard Feynman in the 1940s.

With the goal of capturing the probabilistic behavior of particles, Feynman imagined a particle exploring all possible paths connecting a beginning and an end: a straight line, a curve, a loop, to infinity. He devised a way to give each path a number related to its probability of existence and sum all the numbers. The Path Integral technique has become a powerful framework for predicting how any quantum system is likely to behave.

Once Feynman began announcing the integral path, physicists discovered a strange connection to thermodynamics, the venerable science of temperature and energy. It was this bridge between quantum theory and thermodynamics that enabled Turok and Boyle to calculate it.

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

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