In the twenties, Niels Bohr performed experiments with electrons: He fired electrons through two small slats in a wall; depending on which opening, upper or lower, that the electrons passed through, they hit the upper or lower part of the final wall that stopped them. So: can you picture a machine that fires electrons, fired through two slats in one wall, to travel through a space, and then stop at a second wall?
Next, he closed the bottom slat; the electrons went through the upper slat and hit the upper portion of the wall.
Next, close the upper slat, and see the electrons pass through the bottom slat, to hit the lower portion of the wall.
Then, just for fun, he fired the electrons through both slats, and after they had passed through the slats, he closed the upper slat. There is no way for the electrons to have known this. Yet, they hit the lower portion of the wall. He tried it again, by closing the lower slat AFTER the electrons had passed. Again.
He determined that observation determines reality.