Says a team of three Canadian physicists:
The Big Bang didn’t just result in our familiar universe, according to a mind-bending new theory – it also generated a second “anti-universe” that extended
backwards in time, like a mirror image of our own…
This new theory is compelling, according to a news release about the new theory, because it would mean that the universe is filled with “very massive sterile neutrinos” that could explain dark matter, a mysterious material that is believed to make up much of the universe. By the researchers’ own admission, according to Physics World, many details of the new theory still need to be hammered out. Jon Christian, “New Paper: A ‘Mirror Image’ of Our Universe Existed Before The Big Bang” at ScienceAlert
The theory is “compelling” because a mirror universe is an entirely natural idea, perhaps an old one. It’s neater and cleaner than the multiverse and does not entail absurdity. On the contrary, it creates symmetry where before there was asymmetry. But if a mirror universe is not something we can determine or study in this universe, it’s not science. That doesn’t mean it’s a bad idea but we need to be careful how we invoke it.
Abstract:We propose that the state of the Universe does not spontaneously violate CPT. Instead, the Universe after the big bang is the CPT image of the Universe before it, both classically and quantum mechanically. The pre- and postbang epochs comprise a universe-antiuniverse pair, emerging from nothing directly into a hot, radiation-dominated era. CPT symmetry selects a unique QFT vacuum state on such a spacetime, providing a new interpretation of the cosmological baryon asymmetry, as well as a remarkably economical explanation for the cosmological dark matter. Requiring only the standard three-generation model of particle physics (with right-handed neutrinos), a Z2 symmetry suffices to render one of the right-handed neutrinos stable. We calculate its abundance from first principles: matching the observed dark matter density requires its mass to be 4.8×108GeV. Several other testable predictions follow: (i) the three light neutrinos are Majorana particles and allow neutrinoless double β decay; (ii) the lightest neutrino is massless; and (iii) there are no primordial long-wavelength gravitational waves. We mention connections to the strong CP problem and the arrow of time. (open access) – Latham Boyle, Kieran Finn, and Neil Turok Phys. Rev. Lett. 121, 251301 – Published 20 December 2018 More.
See also: Did Stephen Hawking Discover A Means Of Detecting Parallel Universes Just Before He Died?
Claim: Evidence, maybe, for parallel universes
Cosmologist: Parallel universes are pushing physics too far?
New Scientist: How Far Away Are Our Parallel Selves?
and on time travel:
Would backwards time travel unravel spacetime?
Economist: Can time go backwards?
Astrobiologist: Why time travel can’t really work
Carlo Rovelli: Future time travel only a technological problem, not a scientific one. Rovelli: A starship could wait [near a black hole ] for half an hour and then move away from the black hole, and find itself millennia in the future.
Rob Sheldon’s thoughts on physicists’ “warped” view of time An attempt to force complete symmetry on a universe that does ot want to be completely symmetrical
At the BBC: Still working on that ol’ time machine… BBC: “But using wormholes for time travel won’t be straightforward.” Indeed not. Unless everything is absolutely determined, some wise person from the future has already gone back through a wormhole and altered the present so that we can’t go anywhere.
Is time travel a science-based idea? (2017)
Apparently, a wormhole is our best bet for a time machine (2013)
and
Does a Time Travel Simulation Resolve the “Grandfather Paradox”?