I love articles like this. I read it 4 times, followed all the links, and still have no idea exactly what they’re talking about or what it would look like.

A tweak to the iconic double-slit experiment could reveal if quantum mechanics is incomplete, and maybe lead to a theory of quantum gravity.

The well-known physics experiment may be hiding more than we ever realized about the nature of reality. The classic “double-slit” experiment reveals the strange duality of the quantum world, but it may behave more strangely than we thought – and could challenge one of the most closely held assumptions of quantum mechanics.

Revisiting it could help unify quantum mechanics with the other pillar of theoretical physics – Einstein’s general relativity – a challenge that has so far proven intractable.

To calculate the probability that a photon will arrive at some location on the screen, physicists use a principle called the Born rule. However, there is no fundamental reason why the Born rule should hold. It seems to work in all the situations we’ve tested, but no one knows why. Some have attempted to derive it from the “many worlds” interpretation of quantum mechanics, which proposes that all the possible states of a quantum system could exist in different, parallel universes – but such attempts have been inconclusive.

That makes the Born rule a good place to look for cracks in quantum theory. To unite quantum mechanics, which governs the universe on minute scales, and general relativity, which holds at immense scales, one of the theories must give way. If the Born rule falls over, it could clear a path to quantum gravity.

“If the Born rule is violated, then a fundamental axiom of quantum mechanics has been violated, and it should point to where one needs to go to find quantum gravitational theories,” says James Quach at the Barcelona Institute of Science and Technology in Spain.

Quach shows that if you account for interference between all three paths, the probabilities will be different from what the Born rule predicts.

He suggests testing this with a double-slit experiment that allows for a third path, a wandering zigzag in which the particle goes through the left slit, over to the right slit, then heads towards the screen. If that third path interferes with the two more straightforward ones, the results should deviate from what the Born rule suggests.

I did look up the Born Rule and you can see that it made it much clearer-

Well, duh! 

Source: Classic quantum experiment could conceal theory of everything | New Scientist