## A Summary of Decoherence and the Transition from Quantum to Classical by Wojciech H. Zurek

**Normie Jean B. Sajor**

Quantum mechanics is one of the most functional theories in the world of physics. It describes the workings of particles, atoms, and molecules with extraordinary accuracy and also explains the action of lasers and transistors. Yet, the debate about the relation of quantum mechanics to the familiar physical world continues.

For instance, the so-called measurement problem has been a source of continual speculation. In quantum mechanics, it is the unresolved problem of how the wavefunction collapses. The wavefunction obeys the deterministic Schrödinger equation into a linear superposition of different states. However, actual measurements always find the physical system in a definite state. But why we cannot predict precise results for measurements, but only probabilities?

The Copenhagen interpretation which is proposed by Niels Bohr was the first accepted explanation of how a single outcome emerges from the many possibilities and insisted that a classical apparatus is necessary to carry out measurements. It created a dividing line between classical and quantum. The border line must be mobile according to Niels Bohr. Classical is identified frequently as macroscopic but the insufficiency of this approach has become visible as a result of recent developments such as the cryogenic version of the Weber bar, a gravity wave detector which must be treated as a quantum harmonic oscillator even though it can weigh a ton.

There might be no boundary between classical and quantum since macroscopic systems cannot always be safely placed on the classical side of the boundary. The many-worlds interpretation claims to do away with the boundary. In this interpretation, the superpositions evolve without end according to the Schrodinger equation. Zurek stated that “Each time a suitable interaction takes place between any two quantum systems, the wavefunction of the universe splits, so that it develops ever more branches.” Hugh Everett, the author, proposed the idea that the wavefunction never collapses. The many-worlds interpretation and other post-Everett interpretations use decoherence to explain the process of measurement or wavefunction collapse.

Decoherence try to clarify the transition from quantum to classical by analyzing the interaction of a system with a measuring device or with the environment. It can be viewed as the loss of information from a system into the environment. As Stahlke said, “any interaction with the environment leads to an entanglement between the particle’s state and the environment’s state. As the entanglement diffuses throughout the environment the total state can no longer be separated into the direct product of a particle state and an environment state.”

Although decoherence does not give the solution in the measurement problem but it does bring some enlightenment. It is still unknown at which point the wave actually collapses and caught the attention of the scientific world. Environmental entanglement provides a mechanism in which wave collapse can transmit into the system from distant.

[1.] Zurek, Wojciech H. Decoherence and the Transition from Quantum to Classical. Physics Today. October,1991.

[2.] Stahlke, Dan. Quantum Decoherence and the Measurement Problem

March 8th, 2012 at 12:06 am

Quantum Mechanics is an incomplete theory and is not totally wrong.This is the stand of Einstein which I believe is right.There is a need to interpret the theory in a different light to avoid the apprent paradoxes.