| Copenhagen Interpretation |
Article Index for Copenhagen |
Limousines in Copenhagen |
Website Links For Copenhagen |
Information AboutCopenhagen Interpretation |
| CATEGORIES ABOUT COPENHAGEN INTERPRETATION | |
| fundamental physics concepts | |
| interpretations of quantum mechanics | |
| quantum measurement | |
| university of copenhagen | |
|
The Copenhagen interpretation is an Interpretation Of Quantum Mechanics formulated by Niels Bohr and Werner Heisenberg while collaborating in Copenhagen around 1927 . Bohr and Heisenberg extended the probabilistic interpretation of the Wave Function , proposed by Max Born . Their interpretation attempts to answer some perplexing questions which arise as a result of the Quantum Mechanics , such as Wave-particle Duality and the Measurement Problem . OVERVIEW There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.Aage Petersen paraphrasing Niels Bohr , ''Quantum Reality'' by Nick Herbert There is no definitive statement of the Copenhagen InterpretationIn fact Bohr and Heisenberg never totally agreed on how to understand the mathematical formalism of quantum mechanics, and none of them ever used the term “the Copenhagen interpretation” as a joint name for their ideas. Bohr once distanced himself from what he considered to be Heisenberg's more subjective interpretation Stanford Encyclopedia of Philosophy since it consists of the views developed by a number of scientists and philosophers at the turn of the 20th Century. Thus, there are a number of ideas that have been associated with the Copenhagen interpretation. Asher Peres remarked that very different, sometimes opposite, views are presented as ''the Copenhagen interpretation'' by different authors."There seems to be at least as many different Copenhagen interpretations as people who use that term, probably there are more. For example, in two classic articles on the foundations of quantum mechanics, Ballentine (1970) and Stapp(1972) give diametrically opposite definitions of “Copenhagen.”", A. Peres, ''Popper's experiment and the Copenhagen interpretation'', Stud. History Philos. Modern Physics 33 (2002) 23, preprint Principles # A system is completely described by a wave function , which represents an observer's knowledge of the system. ( Heisenberg ) # The description of nature is essentially probabilistic. The probability of an event is related to the square of the amplitude of the wave function. ( Max Born ) # Heisenberg's Uncertainty Principle ensures that it is not possible to know the values of all of the properties of the system at the same time; those properties that are not known with precision must be described by probabilities. # (Complementary Principle) Matter exhibits a wave-particle duality. An experiment can show the particle-like properties of matter, or wave-like properties, but not both at the same time.( Niels Bohr ) # Measuring devices are essentially classical devices, and measure classical properties such as position and momentum. # The Correspondence Principle of Bohr and Heisenberg, saying that the quantum mechanical description of large systems should closely approximate to the classical description. THE MEANING OF THE WAVE FUNCTION The Copenhagen Interpretation denies that the wave function is real, or is at least non-committal about its reality. There are some who say that there are objective variants of the Copenhagen Interpretation that allow for a "real" wave function, but it is questionable whether that view is really consistent with Positivism and some of Bohr's statements. Niels Bohr emphasized that Science is concerned with the predictions of experiments, additional questions are not scientific but rather meta-physical. Bohr was heavily influenced by positivism. On the other hand, Bohr and Heisenberg were not in complete agreement, and took different views at different times. Heisenberg in particular was prompted to move towards Realism ."Historically, Heisenberg wanted to base quantum theory solely on observable quantities such as the intensity of spectral lines, getting rid of all intuitive (anschauliche) concepts such as particle trajectories in space-time This attitude changed drastically with his paper [3 in which he introduced the uncertainty relations – there he put forward the point of view that it is the theory which decides what can be observed. His move from positivism to operationalism can be clearly understood as a reaction on the advent of Schr¨odinger’s wave mechanics {Link without Title} which, in particular due to its intuitiveness, became soon very popular among physicists. In fact, the word anschaulich (intuitive) is contained in the title of Heisenberg’s paper Kiefer, C. ''On the interpretation of quantum theory – from Copenhagen to the present day'' Even if the wave function is not regarded as real, there is still a divide between those who treat it as definitely and entirely subjective, and those who are non-committal or agnostic about the subject. An example of the agnostic view is given by von Weiszacker, who, while participating in a colloquium at Cambridge, denied that the CI asserted: "What cannot be observed does not exist". He suggested instead that the CI follows the principle: "What is observed certainly exists; about what is not observed we are still free to make suitable assumptions. We use that freedom to avoid paradoxes." John Cramer on the Copenhagen Interpretation The subjective view, that the wave function is merely a mathematical tool for calculating probabilities of specific experiment, is a similar approach to the Ensemble Interpretation . THE NATURE OF COLLAPSE All versions of the Copenhagen interpretation include at least a formal or methodological version of adherents do.) An adherent of the subjective view, that the wave function represents nothing but knowledge, would take an equally subjective view of "collapse", as nothing more than an observer becoming informed about something that was previously ambiguous. The existence of collapse as an ''objective'' process, with obvious implications about the reality of the wave function, is more contentious. Some argue that the concept of collapse of a "real" wave function was introduced by John Von Neumann and was not part of the original formulation of the Copenhagen Interpretation"the “collapse” or “reduction” of the wave function. This was introduced by Heisenberg in his uncertainty paper and later postulated by von Neumann as a dynamical process independent of the Schrodinger equation"[http://arxiv.org/PS_cache/quant-ph/pdf/0210/0210152v1.pdf Kiefer, C. ''On the interpretation of quantum theory – from Copenhagen to the present day'' . ACCEPTANCE AMONG PHYSICISTS According to a poll at a Quantum Mechanics workshop in , throughout much of the twentieth century the Copenhagen interpretation had strong acceptance among physicists. John Gribbin Gribbin, J. ''Q for Quantum'' describes it as having fallen from primacy after the 1980's. CONSEQUENCES The nature of the Copenhagen Interpretation is exposed by considering a number of experiments and paradoxes. 1. Schrödinger's Cat - A cat is put in a box with a radioactive source and a radiation detector. There is a 50-50 chance that a particle will be emitted and detected by the detector. If a particle is detected, a poisonous gas will be released and the cat killed. The wave function is in a 50-50 mixture of alive cat and dead cat. How can the cat be both alive and dead? | ||
| 2 ''' | "http://wwwinformationdelightinfo/information/entry/Wigner's_Friend" class="copylinks">Wigner's Friend ''' - Wigner puts his friend in with the cat The external observer believes the system is in the state <math>(dead
angle + alive
angle)/\sqrt 2</math> His friend however is convinced that cat is alive Ie for him, the cat is in the state <math>alive></math> <i>How can Wigner and his friend see different wave functions</i> |
|
|