There is no certitude ...

 A particle’s straight-line path through space can be understood as the sum of all its possible paths.

Kristina Armitage/Quanta Magazine

Is it a wave or is it a particle? Duality reigns supreme as seen in the extraordinary double slit experiment originally done by Thomas Young back in 1805. As the Beatles said in Strawberry Fields Forever, nothing is real ... until you "measure" it. :)

The most powerful formula in physics starts with a slender S, the symbol for a sort of sum known as an integral. Further along comes a second S, representing a quantity known as action. Together, these twin S’s form the essence of an equation that is arguably the most effective diviner of the future yet devised.

The oracular formula is known as the Feynman path integral. As far as physicists can tell, it precisely predicts the behavior of any quantum system — an electron, a light ray or even a black hole. The path integral has racked up so many successes that many physicists believe it to be a direct window into the heart of reality.

“It’s how the world really is,” said Renate Loll, a theoretical physicist at Radboud University in the Netherlands.

In the double-slit experiment, a wave passes through both slits at once and interferes with itself on the other side. The wave represents a particle’s possible locations; white shows where it’s most likely to be detected. Alexander Gustafsson

In closing ...

The approximations work well enough that intrepid physicists like Loll are now pursuing the ultimate path integral: one that blends all conceivable shapes of space and time and produces a universe shaped like ours as the net result. But in this quest to show that reality is indeed the sum of all possible realities, they face deep confusion about which possibilities should enter the sum.

And so it goes - K. Vonnegut