Cosmologists spent decades of trying to understand why our Universe is so amazingly vanilla. Not only is it smooth and flat as far as we can see, but it is also expanding at an ever-increasing speed, when naive calculations suggest that space should be plagued by gravity and coming out of the Big Bang. burst apart by a dark repulsive energy.
To explain the flatness of the cosmos, physicists added a dramatic opening chapter to cosmic history: They propose that space rapidly inflated like a balloon at the start of the Big Bang, smoothing out any curvature. And to explain the gentle growth of space after that initial period of inflation, some people have argued that our Universe is just one among many less hospitable Universes in a vast universe.
But now the traditional thinking about our vanilla Universe has been turned on its head by two physicists. Following a line of research started by Stephen Hawking and Gary Gibbons in 1977, the duo published a new calculation that suggests the clarity of the cosmos is expected, rather than rare. Our universe is the way it is, according to Neil Turok of the University of Edinburgh and Latham Boyle of the Outline Institute for Theoretical Physics in Waterloo, Canada, for the same reason that air spreads evenly across a room: There are strange possibilities to imagine but extremely. impossible.
The universe may seem very fine-tuned, very optimistic, but [they’re] saying, ‘Wait a minute, it’s your favorite,’” said Thomas Hertog, a cosmologist at the Catholic University of Leuven in Belgium.
“It’s a new contribution that uses different methods compared to what most people have been doing,” said Steffen Gielen, a cosmologist at the University of Sheffield in the United Kingdom.
The provocative conclusion rests on a mathematical trick of converting to a clock that ticks with imaginary numbers. Using the imaginary clock, as Hawking did in the ’70s, Turok and Boyle could calculate a quantity, called entropy, that seems to correspond to our universe. But the imaginary time trick is a roundabout way of calculating entropy, and without a more rigorous method, the meaning of the quantity is still highly debated. Although physicists are confused about the correct interpretation of the entropy calculation, many see it as a new guidepost on the road to the fundamental quantum nature of space and time.
“In a way,” Gielen said, “it’s giving us a window into perhaps the microstructure of spacetime.”
Turok and Boyle, who often collaborate, are known for coming up with creative and unconventional ideas about cosmology. Last year, to study how likely our Universe could be, they turned to a technique developed by physicist Richard Feynman in the ’40s.
Aiming to capture the probable behavior of particles, Feynman imagined that a particle explores every possible path that connects start to finish: a straight line, a curve, a loop, ad infinitum. He devised a way to assign a number to each path that was similar and add all the numbers. This “true path” technique became a powerful framework for predicting how any quantum system is likely to behave.
As soon as Feynman began publicizing the central path, physicists saw a curious connection to thermodynamics, the fascinating science of temperature and energy. It was this bridge between quantum theory and thermodynamics that enabled Turok and Boyle to calculate.