>>11217151Ever heard of Schrödinger's cat? If you put a cat in a box with a poison that is released depending on a completely random event you will not know if the cat is dead already unless you look inside the box. The cat is to be considered both dead and alive until we open the box. This is called superposition. Similarly, an elementary particle's position cannot be known unless you check for it (e.g. with a very high frequency photon). Its position can only be determined probabilistically prior to measurement via the wavefunction (an imaginary probability densitiy function). Since we don't know how the wave function of a particle collapses, we can only be confident that it will be inside a certain region of space with confidence proportional to the probability at that point in space. This is why we speak of electron orbitals being a space that is occupied by an electron with (arbitrarily defined) 90% probability. An electron orbital is just the 3D wave function given by the Schrödinger equation with a certain associated potential energy corresponding to the distance from the positively charged nucleus.
So the measurement problem describes our inability to determine the outcome of events on the quantum scale. This gives rise to numerous different interpretations of quantum mechanics. For example, the many worlds interpretation is a hypothesis that claims for every wave function collapse (particle-particle interaction) the universe splits in two, which would explain the seemingly random nature of such events. Physicists measuring the spin of a particle wonder why exactly it is spin-up, even though in a parallel universe, they might be wondering precisely why it is spin-down.
Hope that was helpful. Correct me if I made a mistake.
