PlanetPhysics/Quantum Paradoxes 2

Quantum `Paradoxes'
A paradox is a statement which has either an apparent or a real self-inconsistency (such as "A and non-A"), thus contradicting the logical principle of excluded third (`tertium non datur')

In the early stages of quantum theory development there were at least two suggested paradoxes, one reported by Schr\"odinger and the other reported by Einstein-Podolsky-Rosen. These quantum `paradoxes' are as follows:

1. The `Schr\"odinger cat paradox' in a thought (or `gedanken') experiment that supposedly shows that a "cat is neither alive nor dead" but in a superposition of the so-called `live' and `dead' states. A related version of this `paradox' is the two-slit experiment in which, for example, `an electron passes through two slits at the same time, thus interferring with itself and resulting in a diffraction pattern at the detector behind the two slits'; however, if the electron position is determined before reaching the two slits the diffraction pattern, of course, disappears, as only one electron possible state exists--that which was already measured or observed.

The wave-particle duality proposed by Louis deBroglie, and readily accepted by Albert Einstein, is thought to remove this type of quantum `paradox', although it simply shifts the argument to the quantum logic realm where quantum micro-entitites such as an electron or any other quantum `particle' can simultaneously possess an associated wave (or `character'); the existence of the associated wave of a quantum particle was later elaborated in quantum field theories (QFT) in the form of `virtual photons' that mediate the electromagnetic interactions between charged quantum particles such as electrons, protons, ions, etc.

2. The Einstein-Podolsky-Rosen (or EPR) `paradox' is a thought experiment that reveals the non-local character of quantum theory, and was presented initially as `proof that Quantum Mechanics' is incomplete, because quantum non-locality was proposed to contradict both Special and general relativity theories.