Quantum mechanics — know the present, and the next moment is still not fixed
Physics has two great branches. People often divide them by name, Newton on one side and Bohr on the other, but that soon snags — Einstein stands on both sides. He was the one who opened the door to the quantum with the photoelectric effect, and he opposed its conclusions all his life. The division lies not in the people but in the question.
The first board — one at a time
The wall in the middle has two slits. Particles are fired from the left one at a time and a dot marks where each lands on the screen at the right. Nobody can say in advance where one will land. So the only thing to do is fire a great many.
That stripes appear when the particles are fired one at a time is a strange thing. It means a single particle went through both slits. Yet switch on “which way did it go” and the pattern vanishes, leaving just two clumps. The moment it becomes possible to find out which path it took, the two paths stop overlapping.
The misunderstanding that leaks in here most often. “It happens because a person looked”, “consciousness affects it” — these explanations are widespread, and they are wrong. What matters is not who looks but whether information about which path was taken is left in the world. Even if no person reads that record, even in an empty room, the pattern vanishes just the same. Why that information erases the pattern — the interpretation is still argued over.
The second board — the box
The device in the box goes off within the hour with a probability of one half. Until we open it, we do not know. But are not knowing and not being settled the same thing? Schrödinger brought up this cat story to say “this is absurd”.
Open it many times and it comes close to half and half. So far it is like a coin. The difference is that a coin is already settled under your palm. The two-slit pattern above showed that the quantum cannot be seen that way. The point is not the cat but the difference between “not known” and “not there”.
It is right that this feels strange. The very people who produced these results could not accept them to the end. It is not that you fail to understand; it is closer to say that nobody yet understands it completely.
On the classical mechanics bench, leaving the sliders in the same place gave the same result. Here, leaving them in the same place gives something different every time. Yet that difference piles up into an exact pattern. Each one unknowable, the whole exact — that the world is made this way we learned only a hundred years ago.
These are the names for the scenes you handled here. The library has a five-part series that tells this story in order — from why energy comes in lumps to entanglement.