Looking at the moon

"Does the Moon exist when no one is looking at it?". This question was originally asked by Albert Einsten and the answer is obviously yes, but why? The Moon is a macroscopic object so it has well-defined position and momentum independently of observation. However, Einstein was concerned, at the time, about the new emerging physical theory: quantum mechanics. Its fundamental concept is the Heisenberg's indeterminacy principle which states that the more precisely the position of some particle is determined, the less precisely its momentum can be predicted, and vice versa. This means it is the act of observation that defines the position of the object!