Quantum mechanical interpretations

Main participants in the discussion of interpretation

Schrödinger

Born

Everett

An interpretation of quantum mechanics is a set of statements dealing with the completeness, determinism, or way in which the results of quantum mechanics and related experiments should be understood. Although the basic predictions of quantum mechanics have been extensively confirmed by very precise experiments, some scientists consider that some aspects of the understanding that it provides are unsatisfactory and require additional explanations or interpretations that allow a more intuitive recognition of the results of quantum mechanics. experiments.

The problems about how certain aspects of quantum mechanics should be understood are so acute that a number of alternative schools exist, differing for example as to whether the theory is underlyingly deterministic, or whether or not some elements have objective reality, or whether the theory provides a complete description of a physical system.

The measurement problem

The big problem is the measurement process. In classical physics, measure means to reveal or make manifest properties that were in the system before we measured.

In quantum mechanics, the measurement process uncontrollably alters the evolution of the system. It is a mistake to think within the framework of quantum physics that to measure is to reveal properties that were in the system before. The information provided by the wave function is the probability distribution, with which such a value of such a quantity can be measured. When we measure, we start a process that is indeterminable a priori, which some call chance, since there will be different probabilities of measuring different results. This idea was and is still the subject of controversies and disputes among physicists, philosophers, and epistemologists. One of the great objectors to this interpretation was Albert Einstein, who, regarding this idea, said the famous phrase about him & # 34; God does not play dice & # 34;.

Regardless of the problems of interpretation, quantum mechanics has been able to explain essentially the entire microscopic world and has made predictions that have been successfully tested experimentally, making it a unanimously accepted theory.

Problem formulation

The measurement problem can be informally described as follows:

1. According to quantum mechanics a physical system, either a set of electrons orbiting in an atom, is described by a wave function. Such wave function is a mathematical object that supposedly describes the maximum possible information contained in a Pure state.
2. If no one outside the system or within it observed or tried to see how the system is, quantum mechanics would tell us that the system's state evolves in a way determinist given by the Schrödinger equation. I mean, it could be perfectly predictable where the system will go.
3. The wave function informs us what are the possible outcomes of a measure and its relative probability, but does not tell us what concrete result will be obtained if an observer effectively tries to measure the system or find out something about it. In fact, the measure on a system is an unpredictable value of the possible results.

That raises a serious problem, if people, scientists or observers are also physical objects like any other, there should be some deterministic way of predicting how, after putting together the system under study with the measuring device, we finally arrive at a deterministic result. But the postulate that "a measurement destroys the coherence of an unobserved state and inevitably remains in an unpredictable mixed state after the measurement", seems which only leaves us 3 outputs:

• A) Or we just got to understand. process of decoherence Therefore a system passes from having a pure state that evolves predictably to have a mixed or unpredictable state (see chaos theory).
• B) Or we admit that there are some non-physical objects called "conscience" that are not subject to the laws of quantum mechanics and that solve the problem.
• C) Or we try to invent any exotic hypothesis that makes us reconcile how on the one hand we should be observing after a measure a state not fixed by the initial state and on the other hand that the state of the universe as a whole evolves deterministly.

The previous statement, "a measurement destroys the coherence of an unobserved state and inevitably after the measurement it remains in an unpredictable mixed state, it seems that it only leaves us 3 outputs ", is too risky and untested. If we start from the fact that the fundamental entities that constitute matter, precisely, and contrary to what (B) deduces, are not aware of themselves, and without any preference for determinism or absolute chaos, they can only find equilibrium behaving according to laws of probability or what is the same by laws of "determined chaos". In practice, any defense or denial of quantum theory does not respond to deductive mathematical reasoning but to impressions or suggestions originating in totally arbitrary philosophical axioms. It should be noted that e.g., the word "balance" in this paragraph may or may not make sense and the value of reality that is granted to it is not subject to any mathematical demonstration.

Interpretations

Commonly there are various interpretations of quantum mechanics, each of which in general addresses the problem of measurement in a different way. In fact, if the measurement problem were fully resolved, some of the competing interpretations would not exist. In a way, the existence of different interpretations reflects that there is no consensus on how precisely to pose the measurement problem. Some of the most widely known interpretations are as follows:

• Statistical interpretation, in which a quantum state is supposed to describe a statistical regularity, the different results of the measurement of an observable attributable to stochastic factors or fluctuations due to the environment and not observable. Statistical electrodynamics is a theory of electrons in which the apparently random quantum behavior of electrons in a system is attributable to fluctuations in the electromagnetic field due to the rest of the electrons in the universe.
• Copenhagen Interpretation is the traditional interpretation of quantum mechanics, universally accepted at its beginnings by being supported in proven principles, to which most traditional quantum mechanics manuals have adhered. Initially due to Niels Bohr and the group of physicists working with him in Copenhagen around 1927. The principle of uncertainty and the principle of complementarity of ondulatory and corpuscular descriptions are assumed.
• Participatory interpretation of the antropic principle.
• Interpretation of consistent stories.
• Target collapse theory. According to these theories, the superpositions of states are destroyed even if no observation occurs, diffusing the theories in what physical magnitude is that which causes destruction (time, gravitation, temperature, non-linear terms in the evolution operator...). That destruction is what prevents the branches that appear in the theory of the multi-universes or parallel universes. The word "objective" comes from that in this interpretation both the wave function and the collapse of it are "real" in the ontological sense. In the interpretation of the many-worlds, collapse is not objective, and in Copenhagen it is an ad-hoc hypothesis.
• Interpretation of the parallel universes. According to this hypothesis, after a measure all possible results are performed in some way, although a concrete observer only observes one of the results (the other results would occur in replicas of our universe, which does not interact with the perceived universe of the first observer).
• Interpretation of Bohm It is an interpretation that precludes the principle of locality and postulates a model of hidden variables in which the apparent randomness is due to the unknown value of such hidden variables. According to Bohm if the value of the hidden variables were known the result would be completely deterministic.