What is the theoretical Schrodinger's Cat problem?
One of the key components of quantum mechanics states that waves, which have no mass, are also particles and particles, which have mass, are also waves. Simultaneously. And in contradiction to each other.
One can observe wave characterisics (interference) in particles, and one can observe particle characteristics (collisions) in waves. The key word here is "observe".
Contradictory quantum states exist in parallel, in some sense waiting to be observed. Shroedinger's cat is a graphic example of this.
Inside a covered box, for a non-quantum observer, a cat is either alive or dead. For a quantum observer, however, the cat is BOTH alive AND dead. Simultaneously. Two parallel quantum states, both equally probable.
Only when the box is opened and "observation" of the cat takes place, can we verify one state over the other. In quantum mechanics, therefore, "esse est percipi" -- in other words, "to be is to be perceived".