But the ANITA team have seen several of these “impossible” events.

Even as the team wrote their paper they knew the shapeshifting particle idea was a bit of a stretch.

“Not everyone was comfortable with the hypothesis,” Gorham told New Scientist.

The Big Bang should have created equal amounts of matter and antimatter – the scarcity of antimatter in our universe has been a puzzle for decades 

The simplest – and therefore scientifically the most elegant explanation is this: at the moment of the Big Bang two universes were formed – ours, and another one that from our perspective is running in reverse.

Of course if there were any inhabitants of this mirror universe, they’d see ours as the backwards one.

The team could just have discovered splinters of an anti-universe 

If the team’s findings aren’t the result of a bizarre experimental error, the implications are incredible.

Ibrahim Safa, who also works on the experiment, says: “We’re left with the most exciting or most boring possibilities.”