Quantum Mechanics 3

Under the many-worlds interpretation, the Schrodinger equation, or relativistic analog, holds all the time everywhere. An observation or measurement of an object by an observer is modeled by applying the wave equation to the entire system comprising the observer and the object. One consequence is that every observation can be thought of as causing the combined observer-object’s wavefunction to change into a quantum superposition of two or more non-interacting branches, or split into many “worlds”. Since many observation-like events have happened, and are constantly happening, there are an enormous and growing number of simultaneously existing states.

If a system is composed of two or more subsystems, the system’s state will be a superposition of products of the subsystems’ states. Once the subsystems interact, their states are no longer independent. Each product of subsystem states in the overall superposition evolves over time independently of other products. The subsystems states have become correlated or entangled and it is no longer possible to consider them independent of one another. In Everett’s terminology each subsystem state was now correlated with its relative state, since each subsystem must now be considered relative to the other subsystems with which it has interacted.

— Wikipedia on Many-worlds interpretation

This is insightful, but incorrect. Please refer to my previous post “Single-world interpretation, 7” for details.

The main theme is that the macroscopic reality can never be an eigen-quantum-state. Instead, the macroscopic reality is the resultant effect of the superposition of eigen-quantum-states. For example, without quantum superposition, there would be no Principle of Least Action in classical mechanics.

— Me@2012-12-28 12:52:12 PM

In particular, Sidney explains that our world is a quantum world and any phenomena that look classical are approximate or derived. So it’s really nonsensical to ask for an “interpretation of quantum mechanics”. Instead, one should really discuss the “interpretation of classical physics” and its derivative appearance from the quantum framework.

Of course, Sidney was well aware of the fact – and made this fact explicit – that the people who have problems with these concepts have those problems simply because they believe that underneath quantum mechanics, there is still some classical physics operating.

— Sidney Coleman: Quantum mechanics in your face

— Lubos Motl

2012.12.28 Friday (c) All rights reserved by ACHK