Quantum mechanics has introduced a new fundamental property of any collective of quantum entities: indistinguishability. That property has not any analogy in classical mechanics, physics or in any other branch of the contemporary science. It is formulated absolutely rigorously mathematically. Nevertheless, it may be represented clearly enough and quite understandably by common language:
Quantum indistinguishability means that no experiment can distinguish between a state of a quantum collective and any other state of the same collective where any two or more individual members of it have exchanged their individual states (or roughly speaking, their “places” in the collective), e.g. their space positions.
Quantum indistinguishability implies still one extraordinary property of quantum individuals in collectives: they can be two, fundamentally different types: bosons and fermions. Arbitrarily many individuals of the formers or only two individuals of the latters can share the same quantum state.
The definition of quantum distinguishability (the former paragraph) refers to a collective: it turns out to be the same from the empirical (experimental) viewpoint if two or more individuals in it exchange their states, respectively their position in the collective order.
The definition of bosons or fermions (the latter paragraph) refers to individuals in a collective.Entanglement :
There is still one exceptionally extraordinary property of certain collectives of quantum individuals: entanglement. It was theoretically forecast in 1935 independently by Einstein, Podolsky, and Rosen ( Can Quantum-Mechanical Description of Physical Reality Be Considered Complete? ) and Schrödinger ( Die gegenwärtige Situation in der Quantenmechanik ). The formers deduced it as a reductio ad absurdum , i.e. as a formal proof that quantum mechanics should be incomplete for its completeness would imply entanglement as a nonsense. However, John Bell (1964) suggested a real experiment to be tested the hypothesis of entanglement.Clauser and Horne (1984), Aspect, Grangier, and Roger (1981, 1982), and may many others after them demonstrated convincingly that entanglement is a real physical phenomenon, and even the basic state of any real quantum collective.
Entanglement consists in the “ghost action at a distance” (in Einstein’s words): the measurement of any quantum individual of any quantum collective sharing a common past influences the states of all others no matter how remote they are from the measured individuals.
Entanglement explained by quantum indistinguishability :
A certain individual is measured according to the experimenter’s prejudice drawn from everyday experience. However, all individuals of the collective at issue are measured simultaneously no matter how far they are from each other according to the principle of quantum indistinguishability as it is defined above:
Indeed, if arbitrarily many individuals of the collective exchange their “places” with the individual alleged as the only measured single one, the collective will remain unchanged, absolutely the same. Though, the experimenter according to common sense measures only an individual, the whole of the collective turns out to be what is measured really because of quantum holism.
In a sense, the experimenter measuring (in his or her opinion) only an individual, measures all individuals of the collective in fact, and thus influences any other individuals no matter how remote they are.
Partial entanglement as both partial distinguishability and partial indistinguishability:
Anyway, the influence onto all individuals of the collective no matter which is measured is equal initially. This initial state corresponds to maximal entanglement and absolute indistinguishability from each other. A process of individuation called decoherence begins gradually. It is due to the environment, in which the quantum system is situated, and especially to its heterogeneity: the environments consists of different parts interacting differently with the quantum collective. That decoherence causes gradually the diminishment of entanglement within the system corresponding to the increase of distinguishability. Anyway, there exists partial entanglement and partial indistinguishability in the course of decoherence, but both decrease.
The end point is the practical absence of entanglement and absolute distinguishability of all individuals of the collective. They feature all entities in our everyday experience, classical physics and science founded on macroscopic phenomena.
The bigger than the Planck constant the physical interactions are, the faster the process of decoherence takes place. It takes place even as to quantum entities such as atoms or electrons for nano- or microseconds.
Nevertheless, the theoretical and philosophical meaning of quantum indistinguishability and entanglement is huge.
A few main philosophical conclusions from quantum indistinguishability and entanglement :1. The concepts of indistinguishability and entanglement meditate those of individuals and
collectives.
2. The individuals cannot be accepted as primary unconditionally, and even they should be considered as secondary at least in a certain physical sense and from a viewpoint corresponding to the process of decoherence of any quantum system.
3. A circle between individuals and the whole of their collective takes place permanently as a physical process consisting of two phases: (1) the appearing of new and new coherent quantum systems originating from the whole of the collective; (2) their individuation to absolutely distinguishable individuals in the process of decoherence originating from the environment consisting of distinguishable heterogenetic parts.
4. Quantum indistinguishability offers a model for the problem about the relation of individuals and collectives including the concepts of quantum indistinguishability and entanglement, as absolute as partial, as a mediator between their polar opposites. That model is realized in nature and can be considered as consistent and true in that sense.
No comments:
Post a Comment