Could Dark Matter Be Explained by an Anti-Universe Running Backwards in Time?
"A wild new theory suggests there may be another 'anti-universe,' running backward in time prior to the Big Bang," writes Live Science, citing a new paper recently accepted for publication in the journal Annals of Physics.The idea assumes that the early universe was small, hot and dense - and so uniform that time looks symmetric going backward and forward. If true, the new theory means that dark matter isn't so mysterious; it's just a new flavor of a ghostly particle called a neutrino that can only exist in this kind of universe. And the theory implies there would be no need for a period of "inflation" that rapidly expanded the size of the young cosmos soon after the Big Bang. If true, then future experiments to hunt for gravitational waves, or to pin down the mass of neutrinos, could answer once and for all whether this mirror anti-universe exists.... Physicists have identified a set of fundamental symmetries in nature.... We live in an expanding universe. This universe is filled with lots of particles doing lots of interesting things, and the evolution of the universe moves forward in time. If we extend the concept of CPT [charge/parity/time] symmetry to our entire cosmos, then our view of the universe can't be the entire picture. Instead, there must be more. To preserve the CPT symmetry throughout the cosmos, there must be a mirror-image cosmos that balances out our own. This cosmos would have all opposite charges than we have, be flipped in the mirror, and run backward in time. Our universe is just one of a twin. Taken together, the two universes obey CPT symmetry. The study researchers next asked what the consequences of such a universe would be. They found many wonderful things. For one, a CPT-respecting universe naturally expands and fills itself with particles, without the need for a long-theorized period of rapid expansion known as inflation. While there's a lot of evidence that an event like inflation occurred, the theoretical picture of that event is incredibly fuzzy. It's so fuzzy that there is plenty of room for proposals of viable alternatives.... We would never have access to our twin, the CPT-mirror universe, because it exists "behind" our Big Bang, before the beginning of our cosmos. The theory ultimately just extends the symmetry of CPT, argues the article, "from applying to just the 'actors' of the universe (forces and fields) to the 'stage' itself, the entire physical object of the universe." Thanks to long-time Slashdot reader fahrbot-bot for sharing the story!
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