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A mirror universe might tell a simpler story: Neil Turok

By

Rose Simone

Dark matter and other key properties of the cosmos could be explained by a new theory describing the big bang as a mirror at the beginning of spacetime, says Perimeter’s Director Emeritus

November 8, 2023

Neil Turok was frustrated. Over the decades, physicists had developed numerous models to explain the birth of the universe. There was the big bang model. The big bang plus inflation. Models of universes with extra dimensions and new particles and forces. Multiverses. Even Turok’s own cyclical universe model, which he has now abandoned.

None of them seemed quite right.

They all needed embellishments like inflation to make them fit the universe we see around us.

These complications seemed, to Turok, to stand in sharp contrast with the data gathered so far. Giant microscopes and telescopes used to probe the universe on subatomic and cosmic scales have not yet yielded signals of any new particles or forces. Instead, they point to a highly economical description of the universe and its basic laws.

Turok wondered whether a new perspective might explain dark matter, the stuff that clumps galaxies together, and the cosmological constant (or “dark energy”) that pushes the universe apart.

Perhaps what was needed was just a new way of looking at things.

“It seems that nature has worked out a simpler way of being consistent than theorists had anticipated,” Turok says.

That thought attracted him and his collaborator, Latham Boyle, to a new idea: the mirror universe.

“It’s an approach that was born out of a certain sense of frustration with previous approaches. In my view, they had all become rather complicated and contrived, including my own approaches,” Turok said during a recent Perimeter Public Lecture titled, “Secrets of the Universe: Hiding in Plain Sight?”

Turok served as Perimeter’s Director from 2008 to 2018 and now holds the Higgs Chair of Theoretical Physics at the University of Edinburgh. He also holds the Carlo Fidani Roger Penrose Distinguished Visiting Research Chair at Perimeter, a role that brings him back to the Institute regularly for conferences, collaborations, and public events like the recent lecture.

Boyle and Turok began to develop the mirror universe idea when both were faculty members at Perimeter. Boyle recently joined Turok at the University of Edinburgh while continuing his association with Perimeter as a visiting fellow.

Together with their collaborators, they have co-authored a number of papers outlining their new theory of the universe, including “The Big Bang as a Mirror: a Solution of the Strong CP Problem” (preprint), “A Minimal Explanation of the Primordial Cosmological Perturbations” (preprint), and “CPT-Symmetric Universe,” which was published in Physical Review Letters.

During his public lecture, Turok showed the audience an image of the famous fresco, The School of Athens, painted by the Italian Renaissance artist Raphael in the early 1500s. It depicts a congregation of philosophers, mathematicians, and scientists from Ancient Greece. In it, we see, to one side, the figure of Anaximander looking over the shoulder of Pythagoras and scribbling notes as Pythagoras works out his mathematical theorems. Turok thinks they were on to something.

The School of Athens. https://en.wikipedia.org/wiki/The_School_of_Athens[/caption]

“The universe is literally telling us its laws,” Turok says. “We have to look at the incredible array of data we now have, figure out which parts of that data are telling us something fundamental, and learn how to correctly interpret them.”

The mirror universe idea is inherently simple, Turok says. It evokes a geometrically symmetrical universe that one can imagine looking like an hourglass on its side. On the right is a universe flowing forward in time; on the left, a universe flowing backward in time. In the middle is the singularity, where the wavelength of the radiation in the universe becomes smaller than the unimaginably tiny Planck length, about 10−20 times the diameter of a proton.

L. Boyle/Perimeter Institute for Theoretical Physics https://physics.aps.org/articles/v11/s147[/caption]

But no, sorry, it wouldn’t be like the mirror universe in Star Trek. No one can transport to the other side to meet the mirror versions of Kirk and Spock with opposite personalities from their counterparts.

“I think of it more as a sort of mathematical device to do something sensible with the singularity. You have a picture of an extended spacetime and impose a symmetry on it, so you can flip it around,” Turok explains.

In this model, the universe respects a specific kind of symmetry known as CPT. CPT stands for charge (C), parity (P), and time reversal (T). CPT symmetry means particle interactions should look the same if you flip the...