Niels Bohr regarded the “complementarity principle” as the most fundamental principle of Quantum Mechanics, He introduced the concept of “complementarity” in his Como Lecture in 1927. The formal presentation [1] was given in his book “Atomic theory and the description of nature” (Cambridge University Press) in 1934. In his 1958 paper “Quantum physics and Philosophy: Causality and Complementarity” [2] Bohr explains the “complementarity principle” as follows.
“Within the scope of classical physics, all characteristic properties of a given object can in principle be ascertained by a single experimental arrangement, although in practice various arrangements are often convenient for the study of different aspects of the phenomena. In fact, data obtained in such a way simply supplement each other and can be combined into a consistent picture of the behaviour of the object under investigation. In quantum mechanics, however, evidence about atomic objects obtained by different experimental arrangements exhibits a novel kind of complementary relationship. Indeed, it must be recognized that such evidence which appears contradictory when combination into a single picture is attempted, exhaust all conceivable knowledge about the object. Far from restricting our efforts to put questions to nature in the form of experiments, the notion of complementarity simply characterizes the answers we can receive by such inquiry, whenever the interaction between the measuring instruments and the objects form an integral part of the phenomena.”
Specifically, what “novel kind of complementary relationship” is Bohr talking about? One often cited example is the complementarity of “particle” and “wave” views. Some experiments detect the wave nature of the elementary particles and other experiments detect the particle nature. Bohr is saying that both views are valid and complementary.
The “complementarity principle” is a very useful principle but I don’t think that it implies the view that elementary particles do not have intrinsic properties independent of the measuring device or measuring base. The theoretical physicists who constructed the Standard Model (SM) of particle physics, and the experimental physicists who built the Large Hadron Collider (LHC) and its many detectors would not agree with this view either. The reason for their rejection would be that charge, spin and mass of elementary particles are measurable in a very consistent way across many different local environments (measuring bases) very different from the atomic environment.
All electrons are identical because they all exhibit the exact same charge, spin and mass. It is true that one experimental setup may extract the wavelike behavior of electrons and another experimental setup may extract the particle behavior but the intrinsic properties known as charge, spin and mass are still needed to explain the wavelike behavior as well as the particle behavior.
[1] Neils Bohr, “Atomic theory and the description of nature.” Cambridge University Press (1934)
[2] Neils Bohr, “Essays 1958-1962 on Atomic Physics and Human Knowledge.” Wiley (1963)
Suresh Emre
Renaissance Universal 