Nasa scientists claim to have discovered evidence of a parallel universe where time moves backwards.
A cosmic-ray detection experiment has found particles that just could be from outside our universe.
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The Antarctic Impulsive Transient Antenna (Anita) researchers used a giant balloon to get electronic antennas high into the cold, dry air above Antarctica to identify cosmic-ray showers.
They discovered particles may be moving backwards in time, indicating there is a parallel universe, where the rules of the standard model of physics do not apply.
"What we saw is something that looked just like a cosmic ray, as seen in the reflection of the ice sheet, but it wasn't reflected," Peter Gorham, a physics professor at the University of Hawaii, told Times Now.
"So we published a paper on that, we just suggested that this was in pretty strong tension with the standard model of physics. Not everyone was comfortable with the hypothesis."
He said the discoveries suggested signals came from upward-moving particles that tunnelled through the Earth before erupting from the ice.
The simplest explanation for the phenomenon is that at the moment of the Big Bang 13.8 billion years ago, two universes were formed.
But not everyone is convinced.
"There are a number of potential candidate particles that could account for the results from Anita," Geraint Lewis, an astrophysicist at the University of Sydney, told CNET.
"While parallel universes sound exciting and sexy when discussing the Anita signal, alternative ideas are still on the table."
Scientists say the unusual Anita events have been discussed since 2016.
Pat Scott, an astroparticle phenomenologist at the University of Queensland, said that while the theory was "plausible" there were myriad other theories that could account for Anita's detections.
"There's nothing that necessarily makes it a detection of a parallel universe," Scott told CNET.
Others say that if the Anita team's findings aren't the result of a bizarre experimental error, the implications are incredible.