Good question...here is my theory: Music is the harmonic representation of mathematics. After all, it is said that mathematics is the language that God used to create the universe.
Once the mathematic code has been broken down by way of computations or via a musical arrangement of audible chords you then have the weapon or instrument required to create your rift in the physical world. In this case, the safe itself has now become the point in which a controlled local event horizon has been manifested. Thus, allowing Loeb to transfer his hand through the wall of unstable atoms thus retrieving the apple.
Side Note: Nikola Tesla (creator of the electric age and the Father of Physics) created a concept in which a machine could be created that would mimic and increase the harmonic signature of any object. Known as “The Multiple Wave Oscillator”. Thus, braking down the molecular components of the object. Someone could have taken his idea to another level to manifest the creation of a harmonic distortion field (aka Event Horizon) to create such an outcome. Tesla was also noted as delving into what was known then as “pseudoscience” which is known today as Fringe Science.