Consider the cat in the box. Is it alredy dead OR alive (classical interpretation) or is it both at the same time (quantum mechanics) before you open the box an

Consider the cat in the box. Is it alredy dead OR alive (classical interpretation) or is it both at the same time (quantum mechanics) before you open the box and look? The classical interpretation needs so-called hidden variables which determine the state of the cat. In the quantum mechanics interpretation the state is determined when the interaction (measurement, looking at it) takes place. Before that there are several parallel realities of what could be. In the case of the cat we cannot actually determine which interpretation is correct. We need a different kind of experiment: As far as I understood (no physicist here) they use two entangled objects. E.g. two photons which are generated by a special process so that one polarized one way and the other one polarized the other way but we don't know which is which before the measurement. Then you need to measure both photons separately and determine (statistically) which has which polarization. These measurements need to be spaced out far enough such that faster than light speed communication would be required for the photon measured first to tell the second photon what was happening. So far it still doesn't help to exclude the possibility of hidden variables since the measurement setup is static. Another trick is needed. They use a random generator to determine at both ends what to measure (which polarization direction) shortly before doing the actual measurement. So, when the photon is generated it doesn't know what would be acutally measured. When you tabularize the all the possible combinations of how the photons could be measured and calculate the possible probability for the measurement results, there is a difference between what we would expect from classical physics when the status is determined at photon generation and stored inside the photons in a hidden variable and the result we would get from quantum mechanics without a hidden variable but with (faster than light) spooky entanglements. The experiments show that there is no hidden variable. This is a BIG thing because this means that classical physics are not enough to explain the universe.