Relativity of quantum superpositions

Understand

In modern physics only relative quantities are considered to have physical significance.

• For example, position assigned to a system depends on the choice of coordinates, and only relative distances between different systems have physical relevance.
• On the other hand, in quantum theory the scenario where one system, A, is localised around certain position while another system B is in a spatial superposition is considered to be physically different from the scenario where A is in a superposition, while B is localised.
• Different physical effects are anticipated in the two scenarios especially when the two systems have widely different masses.