From Reader Clifford the Big Red Dog :-)

By Rafi Letzter

A series of viral articles claimed that NASA had discovered particles from another parallel universe in which time runs backward. These claims were incorrect. The true story is far more exciting and strange, involving a journey into the Big Bang and out the other side.

The sensational headlines had muddled the findings of an obscure 2018 paper, never published in a peer-reviewed journal, which argued that our universe might have a mirror reflection across time, a partner universe that stretches beyond the Big Bang. If that's the case, and a series of other extremely unlikely and outlandish hypotheses turn out to be true, the paper argued, then that in turn could explain a mysterious signal hinting that a completely new particle is flying out of the ice in Antarctica.

The claim that NASA discovered a parallel universe seemed to have been first dreamed up by British tabloid The Daily Star, and the story was then picked up by British and American outlets, including The New York Post.

Our universe's "mirror"

In order to understand how The Daily Star arrived at its bizarre, viral claim, it's necessary to understand the claims of two separate papers from 2018.

The first paper, by Latham Boyle, a physicist at The Perimeter Institute in Ontario, Canada, and his colleagues, proposed a mirror universe — a reflection of our universe across time. It was published December 2018 in the journal Physical Review Letters (after an appearance on the arXiv server in March that year).

"I think nobody else understands the full sweep of what they have composed," said John Learned, a University of Hawaii astrophysicist and the co-author of a second paper, which builds on Boyle's theory.

Boyle's work is a kind of expansion pack meant to plug holes in the theory that tells the dominant origin story of the universe: Lambda-Cold Dark Matter (ΛCDM).

ΛCDM explains the cosmos using two key ideas: An unknown dark energy causes the universe to expand. Rewind that expansion far enough backward in time and the whole universe occupies a single point in space. Second, an unseen dark matter gravitationally tugs on stuff in the universe, yet emits no light. This dark matter, the idea goes, accounts for the vast majority of the universe's mass.