Decoherence...

• is a consequence of quantum theory that affects virtually all physical systems

• arises from unavoidable interaction of these systems with their natural environment

• explains why macroscopic systems seem to possess their familiar classical properties

  No additional classical concepts are required for a consistent quantum description

• explains why certain microscopic objects ("particles") seem to be localized in space

  There are no particles

• explains why microscopic systems are usually found in their energy eigenstates (and therefore seem to jump between them)

  There are no quantum jumps

• thus explains why there appeared to be contradictory levels of description in physics (classical and quantum)

  There is but ONE basic framework for all physical theories: quantum theory

• explains also how the Schrödinger equation of general relativity (the Wheeler-DeWitt equation) may describe the appearance of time in spite of being time-less

  There is no time at a fundamental level

• is a direct consequence of the Schrödinger equation, but has nonetheless been essentially overlooked during the first 50 years of quantum theory

Decoherence is the theory of universal entanglement. Generically, it does not describe a distortion of the system by the environment, but rather a disturbance (change of state) of the environment by the system. This may nonetheless affect the system itself because of the fundamental quantum aspect of kinematical nonlocality.

The process of decoherence is based on an arrow of time in the form of a special (ultimately cosmological) initial condition.

Decoherence can not explain quantum probabilities without (a) introducing a novel definition of observer systems in quantum mechanical terms (this is usually done tacitly in classical terms), and (b) postulating the required probability measure (according to the Hilbert space norm).