The Copenhagen Interpretation is an explanation of quantum mechanics formulated by Niels Bohr and Werner Heisenberg in 1927 when the scientists were working together in Copenhagen. Bohr and Heisenberg were able to improve the probabilistic interpretation of the function formulated by M. Born and tried to answer a number of questions that arise due to wave-particle duality. This article will consider the main ideas of the Copenhagen interpretation of quantum mechanics, and their impact on modern physics.
Problems
Interpretations of quantum mechanics called philosophical views on the nature of quantum mechanics as a theory that describes the material world. With their help, it was possible to answer questions about the essence of physical reality, the method of studying it, the nature of causality and determinism, as well as the essence of statistics and its place in quantum mechanics. Quantum mechanics is considered to be the most resonant theory in the history of science, but there is still no consensus in its deep understanding. There are a number of interpretations of quantum mechanics, andtoday we will get acquainted with the most popular of them.
Key Ideas
As you know, the physical world consists of quantum objects and classical measuring devices. The change in the state of measuring instruments describes an irreversible statistical process of changing the characteristics of micro-objects. When a micro-object interacts with the atoms of the measuring device, the superposition is reduced to one state, that is, the wave function of the measuring object is reduced. The Schrödinger equation does not describe this result.
From the point of view of the Copenhagen interpretation, quantum mechanics does not describe micro-objects themselves, but their properties, which manifest themselves in macro conditions created by typical measuring instruments during observation. The behavior of atomic objects cannot be distinguished from their interaction with measuring instruments that fix the conditions for the occurrence of phenomena.
A look at quantum mechanics
Quantum mechanics is a static theory. This is due to the fact that the measurement of a micro-object leads to a change in its state. So there is a probabilistic description of the initial position of the object, described by the wave function. The complex wave function is a central concept in quantum mechanics. The wave function changes to a new dimension. The result of this measurement depends on the wave function, in a probabilistic way. Only the square of the modulus of the wave function has physical significance, which confirms the probability that the studiedthe micro-object is located in a certain place in space.
In quantum mechanics, the law of causality is fulfilled with respect to the wave function, which varies in time depending on the initial conditions, and not with respect to the particle velocity coordinates, as in the classical interpretation of mechanics. Due to the fact that only the square of the modulus of the wave function is endowed with a physical value, its initial values cannot be determined in principle, which leads to some impossibility to obtain accurate knowledge about the initial state of the quantum system.
Philosophical basis
From a philosophical point of view, the basis of the Copenhagen interpretation are epistemological principles:
- Observability. Its essence lies in the exclusion from the physical theory of those statements that cannot be verified by direct observation.
- Extras. Assumes that the wave and corpuscular description of the objects of the microworld complement each other.
- Uncertainties. Says that the coordinate of micro-objects and their momentum cannot be determined separately, and with absolute accuracy.
- Static determinism. It assumes that the current state of the physical system is determined by its previous states not unambiguously, but only with a certain degree of probability of the implementation of the trends of change laid down in the past.
- Matching. According to this principle, the laws of quantum mechanics are transformed into the laws of classical mechanics when it is possible to neglect the magnitude of the quantum of action.
Benefits
In quantum physics, information about atomic objects obtained through experimental setups is in a peculiar relationship with each other. In the uncertainty relations of Werner Heisenberg, there is an inverse proportionality between the inaccuracies in fixing the kinetic and dynamic variables that determine the state of a physical system in classical mechanics.
A significant advantage of the Copenhagen interpretation of quantum mechanics is the fact that it does not operate with detailed statements directly about physically unobservable quantities. In addition, with a minimum of prerequisites, it builds a conceptual system that exhaustively describes the experimental facts available at the moment.
The meaning of the wave function
According to the Copenhagen interpretation, the wave function can be subject to two processes:
- Unitary evolution, which is described by the Schrödinger equation.
- Measuring.
No one had doubts about the first process in the scientific community, and the second process caused discussions and gave rise to a number of interpretations, even within the framework of the Copenhagen interpretation of consciousness itself. On the one hand, there is every reason to believe that the wave function is nothing but a real physical object, and that it collapses during the second process. On the other hand, the wave function may not be a real entity, but an auxiliary mathematical tool, the only purpose of whichis to provide the ability to calculate the probability. Bohr emphasized that the only thing that can be predicted is the result of physical experiments, so all secondary issues should not be related to exact science, but to philosophy. He professed in his developments the philosophical concept of positivism, requiring that science discuss only really measurable things.
Double slit experiment
In a two-slit experiment, light passing through two slits falls on the screen, on which two interference fringes appear: dark and light. This process is explained by the fact that light waves can mutually amplify in some places, and cancel each other out in others. On the other hand, the experiment illustrates that light has the properties of a flow part, and electrons can exhibit wave properties, while giving an interference pattern.
It can be assumed that the experiment is carried out with a stream of photons (or electrons) of such low intensity that only one particle passes through the slots each time. Nevertheless, when adding the points where photons hit the screen, the same interference pattern is obtained from superimposed waves, despite the fact that the experiment concerns supposedly separate particles. This is because we live in a "probabilistic" universe, in which every future event has a redistributed degree of possibility, and the probability that something completely unforeseen will happen in the next moment of time is rather small.
Questions
Slit experience puts suchquestions:
- What will be the rules for the behavior of individual particles? The laws of quantum mechanics indicate the location of the screen in which the particles will be, statistically. They allow you to calculate the location of light bands, which are likely to contain many particles, and dark bands, where fewer particles are likely to fall. However, the laws that govern quantum mechanics cannot predict where an individual particle will actually end up.
- What happens to the particle at the moment between emission and registration? According to the results of observations, the impression can be created that the particle is in interaction with both slits. It seems that this contradicts the regularities of the behavior of a point particle. Moreover, when a particle is registered, it becomes a point.
- Under the influence of what does a particle change its behavior from static to non-static, and vice versa? When a particle passes through the slits, its behavior is determined by a non-localized wave function passing through both slits at the same time. At the moment of registration of a particle, it is always fixed as a point, and a blurred wave packet is never obtained.
Answers
The Copenhagen theory of quantum interpretation answers the questions posed as follows:
- It is fundamentally impossible to eliminate the probabilistic nature of the predictions of quantum mechanics. That is, it cannot accurately indicate the limitation of human knowledge about any latent variables. Classical physics refers toprobability in those cases when it is necessary to describe a process such as throwing dice. That is, probability replaces incomplete knowledge. The Copenhagen interpretation of quantum mechanics by Heisenberg and Bohr, on the contrary, states that the result of measurements in quantum mechanics is fundamentally non-deterministic.
- Physics is a science that studies the results of measuring processes. It is wrong to speculate about what happens as a result of them. According to the Copenhagen interpretation, questions about where the particle was before the moment of its registration, and other similar fabrications are meaningless, and therefore should be excluded from reflection.
- The act of measurement leads to an instantaneous collapse of the wave function. Therefore, the measurement process randomly selects only one of the possibilities that the wave function of a given state allows. And to reflect this choice, the wave function must change instantly.
Forms
The formulation of the Copenhagen interpretation in its original form has given rise to several variations. The most common of these is based on the approach of consistent events and such a concept as quantum decoherence. Decoherence allows you to calculate the fuzzy boundary between the macro- and microworlds. The remaining variations differ in the degree of "realism of the wave world."
Criticism
The validity of quantum mechanics (Heisenberg and Bohr's answer to the first question) was questioned in a thought experiment conducted by Einstein, Podolsky andRosen (EPR paradox). Thus, scientists wanted to prove that the existence of hidden parameters is necessary so that the theory does not lead to instantaneous and non-local “long-range action”. However, during the verification of the EPR paradox, made possible by Bell's inequalities, it was proved that quantum mechanics is correct, and various hidden variable theories have no experimental confirmation.
But the most problematic answer was Heisenberg and Bohr's answer to the third question, which placed measurement processes in a special position, but did not determine the presence of distinctive features in them.
Many scientists, both physicists and philosophers, flatly refused to accept the Copenhagen interpretation of quantum physics. The first reason for this was that the interpretation of Heisenberg and Bohr was not deterministic. And the second is that it introduced a vague notion of measurement that turned probability functions into valid results.
Einstein was sure that the description of physical reality given by quantum mechanics as interpreted by Heisenberg and Bohr was incomplete. According to Einstein, he found some logic in the Copenhagen interpretation, but his scientific instincts refused to accept it. So Einstein couldn't stop looking for a more complete concept.
In his letter to Born, Einstein said: "I am sure that God does not throw dice!". Niels Bohr, commenting on this phrase, told Einstein not to tell God what to do. And in his conversation with Abraham Pais, Einstein exclaimed: “You really think that the moon existsonly when you look at it?”.
Erwin Schrödinger came up with a thought experiment with a cat, through which he wanted to demonstrate the inferiority of quantum mechanics during the transition from subatomic to microscopic systems. At the same time, the necessary collapse of the wave function in space was considered problematic. According to Einstein's theory of relativity, instantaneity and simultaneity make sense only for an observer who is in the same frame of reference. Thus, there is no time that could become one for all, which means that instantaneous collapse cannot be determined.
Distribution
An informal survey conducted in academia in 1997 showed that the previously dominant Copenhagen interpretation, briefly discussed above, was supported by less than half of the respondents. However, it has more adherents than the other interpretations individually.
Alternative
Many physicists are closer to another interpretation of quantum mechanics, which is called "none". The essence of this interpretation is exhaustively expressed in David Mermin's dictum: "Shut up and calculate!", which is often attributed to Richard Feynman or Paul Dirac.
