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103-529: Features common across versions of the Copenhagen interpretation include the idea that quantum mechanics is intrinsically indeterministic , with probabilities calculated using the Born rule , and the principle of complementarity , which states that objects have certain pairs of complementary properties that cannot all be observed or measured simultaneously. Moreover, the act of "observing" or "measuring" an object

206-454: A stochastic process , or sometimes random process, is the counterpart to a deterministic process (or deterministic system ). Instead of dealing with only one possible reality of how the process might evolve over time (as is the case, for example, for solutions of an ordinary differential equation ), in a stochastic or random process there is some indeterminacy in its future evolution described by probability distributions. This means that even if

309-487: A Swiss citizen (in 1896, he renounced his German citizenship, and remained officially stateless before becoming a Swiss citizen in 1901), declined his invitation to attend the conference and publicly renounced any German citizenship again. Because anti-Semitism had been on the rise, Einstein accepted the invitation by Dr. Chaim Weizmann , the president of the World Zionist Organization, for a trip to

412-488: A clear criterion for when each kind applies. Why should these two different processes exist, when physicists and laboratory equipment are made of the same matter as the rest of the universe? And if there is somehow a split, where should it be placed? Steven Weinberg writes that the traditional presentation gives "no way to locate the boundary between the realms in which [...] quantum mechanics does or does not apply." The problem of thinking in terms of classical measurements of

515-416: A contradiction and thus impossible. Complete lack of order is itself a sort of order. The position he advocates is rather that there are in the universe both regularities and irregularities. Karl Popper comments that Peirce's theory received little contemporary attention, and that other philosophers did not adopt indeterminism until the rise of quantum mechanics. In 1931, Arthur Holly Compton championed

618-472: A crucial factor in the general explanation of things. And he does so on conceptual grounds: chance events are, he thinks, by definition unusual and lacking certain explanatory features: as such they form the complement class to those things which can be given full natural explanations. Aristotle opposed his accidental chance to necessity: Nor is there any definite cause for an accident, but only chance (τυχόν), namely an indefinite (ἀόριστον) cause. It

721-402: A light source, such as a laser beam, illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate. The wave nature of light causes the light waves passing through the two slits to interfere , producing bright and dark bands on the screen – a result that would not be expected if light consisted of classical particles. However,

824-499: A much more satisfied state of mind than I could have been at any earlier stage of science. If the statements of the laws of physics were assumed correct, one would have had to suppose (as did most philosophers) that the feeling of freedom is illusory, or if [free] choice were considered effective, that the laws of physics ... [were] unreliable. The dilemma has been an uncomfortable one. Together with Arthur Eddington in Britain, Compton

927-539: A new way, as series of not-linear causes. He wrote in Essai sur les fondements de nos connaissances (1851): "It is not because of rarity that the chance is actual. On the contrary, it is because of chance they produce many possible others." Tychism ( Greek : τύχη "chance") is a thesis proposed by the American philosopher Charles Sanders Peirce in the 1890s. It holds that absolute chance , also called spontaneity,

1030-410: A pair of particles prepared in what later authors would refer to as an entangled state . In a 1935 paper, Einstein, Boris Podolsky , and Nathan Rosen pointed out that, in this state, if the position of the first particle were measured, the result of measuring the position of the second particle could be predicted. If instead the momentum of the first particle were measured, then the result of measuring

1133-562: A person has had the opportunity to make a character-forming decision (SFA), he is responsible for the actions that are a result of his character. Mark Balaguer , in his book Free Will as an Open Scientific Problem argues similarly to Kane. He believes that, conceptually, free will requires indeterminism, and the question of whether the brain behaves indeterministically is open to further empirical research. He has also written on this matter "A Scientifically Reputable Version of Indeterministic Libertarian Free Will". In probability theory ,

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1236-439: A quantum system becomes particularly acute in the field of quantum cosmology , where the quantum system is the universe. How does an observer stand outside the universe in order to measure it, and who was there to observe the universe in its earliest stages? Advocates of Copenhagen-type interpretations have disputed the seriousness of these objections. Rudolf Peierls noted that "the observer does not have to be contemporaneous with

1339-510: A result, many turn to a notion of probabilistic causation . Informally, A probabilistically causes B if A 's occurrence increases the probability of B . This is sometimes interpreted to reflect the imperfect knowledge of a deterministic system but other times interpreted to mean that the causal system under study has an inherently indeterministic nature. ( Propensity probability is an analogous idea, according to which probabilities have an objective existence and are not just limitations in

1442-412: A revision to the basic concepts of classical physics . However, it was not until a quarter-century had elapsed that the revision reached the status of a coherent theory. During the intervening period, now known as the time of the " old quantum theory ", physicists worked with approximations and heuristic corrections to classical physics. Notable results from this period include Max Planck 's calculation of

1545-548: A series of invited lectures at the University of Chicago explaining the new field of quantum mechanics. The lectures then served as the basis for his textbook, The Physical Principles of the Quantum Theory , published in 1930. In the book's preface, Heisenberg wrote: On the whole, the book contains nothing that is not to be found in previous publications, particularly in the investigations of Bohr. The purpose of

1648-450: A single inevitable effect. Indeterministic (or probabilistic) causation is a proposed possibility, such that "everything has a cause" is not a clear statement of indeterminism. Interpreting causation as a deterministic relation means that if A causes B , then A must always be followed by B . In this sense, however, war does not always cause deaths (see Cyberwarfare ), nor does a singular moment of smoking always cause cancer . As

1751-471: A square and then (deterministically) interpreting a relatively large subsquare as the more probable outcome. A distinction is generally made between indeterminism and the mere inability to measure the variables (limits of precision). This is especially the case for physical indeterminism (as proposed by various interpretations of quantum mechanics ). Yet some philosophers have argued that indeterminism and unpredictability are synonymous. The oldest mention of

1854-441: A subject's knowledge). It can be proved that realizations of any probability distribution other than the uniform one are mathematically equal to applying a (deterministic) function (namely, an inverse distribution function ) on a random variable following the latter (i.e. an "absolutely random" one ); the probabilities are contained in the deterministic element. A simple form of demonstrating it would be shooting randomly within

1957-658: A system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then there exists an element of reality corresponding to that quantity". From this, they inferred that the second particle must have a definite value of position and of momentum prior to either being measured. Bohr's response to the EPR paper was published in the Physical Review later that same year. He argued that EPR had reasoned fallaciously. Because measurements of position and of momentum are complementary , making

2060-482: A theoretical concept. The Born rule is essential to the Copenhagen interpretation. Formulated by Max Born in 1926, it gives the probability that a measurement of a quantum system will yield a given result. In its simplest form, it states that the probability density of finding a particle at a given point, when measured, is proportional to the square of the magnitude of the particle's wave function at that point. The concept of wave function collapse postulates that

2163-442: A very informal poll (some people voted for multiple interpretations) conducted at a quantum mechanics conference in 1997, the Copenhagen interpretation remained the most widely accepted label that physicists applied to their own views. A similar result was found in a poll conducted in 2011. The nature of the Copenhagen interpretation is exposed by considering a number of experiments and paradoxes. This thought experiment highlights

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2266-730: A wave). Such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through. According to Bohr's complementarity principle , light is neither a wave nor a stream of particles . A particular experiment can demonstrate particle behavior (passing through a definite slit) or wave behavior (interference), but not both at the same time. The same experiment has been performed for light, electrons, atoms, and molecules. The extremely small de Broglie wavelength of objects with larger mass makes experiments increasingly difficult, but in general quantum mechanics considers all matter as possessing both particle and wave behaviors. This thought experiment involves

2369-550: Is a necessary but insufficient criterion for free will. It is necessary that there be ( metaphysically ) real alternatives for our actions, but that is not enough; our actions could be random without being in our control. The control is found in "ultimate responsibility". What allows for ultimate responsibility of creation in Kane's picture are what he refers to as "self-forming actions" or SFAs — those moments of indecision during which people experience conflicting wills. These SFAs are

2472-419: Is a real factor operative in the universe. It may be considered both the direct opposite of Albert Einstein 's oft quoted dictum that: " God does not play dice with the universe" and an early philosophical anticipation of Werner Heisenberg 's uncertainty principle . Peirce does not, of course, assert that there is no law in the universe. On the contrary, he maintains that an absolutely chance world would be

2575-405: Is a sufficient cause of y , then the presence of y implies that x may have preceded it. (However, another cause z may alternatively cause y . Thus the presence of y does not imply the presence of x , or z , or any other suspect.) It is possible for everything to have a necessary cause , even while indeterminism holds and the future is open, because a necessary condition does not lead to

2678-622: Is a thought experiment intended to make that of Schrödinger's cat more striking by involving two conscious beings, traditionally known as Wigner and his friend. (In more recent literature, they may also be known as Alice and Bob , per the convention of describing protocols in information theory .) Wigner puts his friend in with the cat. The external observer believes the system is in state ( | dead ⟩ + | alive ⟩ ) / 2 {\displaystyle (|{\text{dead}}\rangle +|{\text{alive}}\rangle )/{\sqrt {2}}} . However, his friend

2781-653: Is certain and the entire outcome of anything is probabilistic . Heisenberg's uncertainty principle and the " Born rule ", proposed by Max Born , are often starting points in support of the indeterministic nature of the universe. Indeterminism is also asserted by Sir Arthur Eddington , and Murray Gell-Mann . Indeterminism has been promoted by the French biologist Jacques Monod 's essay " Chance and Necessity ". The physicist-chemist Ilya Prigogine argued for indeterminism in complex systems . Indeterminists do not have to deny that causes exist. Instead, they can maintain that

2884-427: Is convinced that the cat is alive, i.e. for him, the cat is in the state | alive ⟩ {\displaystyle |{\text{alive}}\rangle } . How can Wigner and his friend see different wave functions? In a Heisenbergian view, the answer depends on the positioning of Heisenberg cut , which can be placed arbitrarily (at least according to Heisenberg, though not to Bohr). If Wigner's friend

2987-492: Is himself adding a factor not supplied by the physical conditions and is thus himself determining what will occur. That he does so is known only to the person himself. From the outside one can see in his act only the working of physical law. It is the inner knowledge that he is in fact doing what he intends to do that tells the actor himself that he is free. Compton welcomed the rise of indeterminism in 20th century science, writing: In my own thinking on this vital subject I am in

3090-449: Is independent of a subjective observer or measurement or collapse, which relies on an "irreversible" or effectively irreversible process, which could take place within the quantum system. Another issue of importance where Bohr and Heisenberg disagreed is wave–particle duality . Bohr maintained that the distinction between a wave view and a particle view was defined by a distinction between experimental setups, whereas Heisenberg held that it

3193-473: Is irreversible, and no truth can be attributed to an object except according to the results of its measurement (that is, the Copenhagen interpretation rejects counterfactual definiteness ). Copenhagen-type interpretations hold that quantum descriptions are objective, in that they are independent of physicists' personal beliefs and other arbitrary mental factors. Over the years, there have been many objections to aspects of Copenhagen-type interpretations, including

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3296-504: Is just in existence itself? Perhaps he is by chance thrown in some point of this terrestrial surface without any how and why ". In his Anti-Sénèque [ Traité de la vie heureuse, par Sénèque, avec un Discours du traducteur sur le même sujet , 1750] we read: "Then, the chance has thrown us in life". In the 19th century the French Philosopher Antoine-Augustin Cournot theorized chance in

3399-580: Is never a collapse of the wave function. The transactional interpretation is also explicitly nonlocal. Some physicists espoused views in the "Copenhagen spirit" and then went on to advocate other interpretations. For example, David Bohm and Alfred Landé both wrote textbooks that put forth ideas in the Bohr–Heisenberg tradition, and later promoted nonlocal hidden variables and an ensemble interpretation respectively. John Archibald Wheeler began his career as an "apostle of Niels Bohr"; he then supervised

3502-417: Is no different from quantizing the electric current in a superconductor while neglecting the atomic-level details. You may object that there is only one universe, but likewise there is only one SQUID in my laboratory. A large number of alternative interpretations have appeared, sharing some aspects of the Copenhagen interpretation while providing alternatives to other aspects. The ensemble interpretation

3605-427: Is obvious that there are principles and causes which are generable and destructible apart from the actual processes of generation and destruction; for if this is not true, everything will be of necessity: that is, if there must necessarily be some cause, other than accidental, of that which is generated and destroyed. Will this be, or not? Yes, if this happens; otherwise not. The philosopher Sextus Empiricus described

3708-412: Is positioned on the same side of the cut as the external observer, his measurements collapse the wave function for both observers. If he is positioned on the cat's side, his interaction with the cat is not considered a measurement. Different Copenhagen-type interpretations take different positions as to whether observers can be placed on the quantum side of the cut. In the basic version of this experiment,

3811-464: Is possible to reformulate quantum mechanics to make it deterministic, at the price of making it explicitly nonlocal. It attributes not only a wave function to a physical system, but in addition a real position, that evolves deterministically under a nonlocal guiding equation. The evolution of a physical system is given at all times by the Schrödinger equation together with the guiding equation; there

3914-461: Is similar; it offers an interpretation of the wave function, but not for single particles. The consistent histories interpretation advertises itself as "Copenhagen done right". More recently, interpretations inspired by quantum information theory like QBism and relational quantum mechanics have appeared. Experts on quantum foundational issues continue to favor the Copenhagen interpretation over other alternatives. Physicists who have suggested that

4017-422: Is sometimes asked: "Could quantum mechanics be extended by adding so-called "hidden variables" to the mathematical formalism, to convert it from an epistemic to an ontic theory?" The Copenhagen interpretation answers this with a strong 'No'. It is sometimes alleged, for example by J.S. Bell , that Einstein opposed the Copenhagen interpretation because he believed that the answer to that question of "hidden variables"

4120-422: Is the idea that events (or certain events, or events of certain types) are not caused , or are not caused deterministically . It is the opposite of determinism and related to chance . It is highly relevant to the philosophical problem of free will , particularly in the form of metaphysical libertarianism . In science , most specifically quantum theory in physics , indeterminism is the belief that no event

4223-525: The Dogmatists , it is necessary to suspend judgment about the existence of causes, too, saying that they are no more existent than non-existent Epicurus argued that as atoms moved through the void, there were occasions when they would "swerve" ( clinamen ) from their otherwise determined paths, thus initiating new causal chains. Epicurus argued that these swerves would allow us to be more responsible for our actions, something impossible if every action

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4326-459: The Pyrrhonist position on causes as follows: ...we show the existence of causes are plausible, and if those, too, are plausible which prove that it is incorrect to assert the existence of a cause, and if there is no way to give preference to any of these over others – since we have no agreed-upon sign, criterion , or proof, as has been pointed out earlier – then, if we go by the statements of

4429-482: The Schrödinger equation was as a tool for calculating probabilities . Quantum mechanics cannot easily be reconciled with everyday language and observation, and has often seemed counter-intuitive to physicists, including its inventors. The ideas grouped together as the Copenhagen interpretation suggest a way to think about how the mathematics of quantum theory relates to physical reality. The 'Copenhagen' part of

4532-570: The blackbody radiation spectrum, Albert Einstein 's explanation of the photoelectric effect , Einstein and Peter Debye 's work on the specific heat of solids, Niels Bohr and Hendrika Johanna van Leeuwen 's proof that classical physics cannot account for diamagnetism , Bohr's model of the hydrogen atom and Arnold Sommerfeld 's extension of the Bohr model to include relativistic effects . From 1922 through 1925, this method of heuristic corrections encountered increasing difficulties; for example,

4635-436: The special theory of relativity . The idea was originated by Nuel Belnap . The equations of general relativity admit of both indeterministic and deterministic solutions. Ludwig Boltzmann was one of the founders of statistical mechanics and the modern atomic theory of matter . He is remembered for his discovery that the second law of thermodynamics is a statistical law stemming from disorder . He also speculated that

4738-402: The time reversibility of the laws in question, particles could also head inwards, unprompted by any pre-existing state. He calls such hypothetical particles " space invaders ". John D. Norton has suggested another indeterministic scenario, known as Norton's Dome , where a particle is initially situated on the exact apex of a dome. Branching space-time is a theory uniting indeterminism and

4841-768: The "actual," is absolutely necessary here and cannot be omitted from the interpretation of quantum theory. In the 1970s and 1980s, the theory of decoherence helped to explain the appearance of quasi-classical realities emerging from quantum theory, but was insufficient to provide a technical explanation for the apparent wave function collapse. In metaphysical terms, the Copenhagen interpretation views quantum mechanics as providing knowledge of phenomena, but not as pointing to 'really existing objects', which it regards as residues of ordinary intuition. This makes it an epistemic theory. This may be contrasted with Einstein's view, that physics should look for 'really existing objects', making itself an ontic theory. The metaphysical question

4944-448: The 1920s. However, no such text exists, and the writings of Bohr and Heisenberg contradict each other on several important issues. It appears that the particular term, with its more definite sense, was coined by Heisenberg around 1955, while criticizing alternative "interpretations" (e.g., David Bohm 's) that had been developed. Lectures with the titles 'The Copenhagen Interpretation of Quantum Theory' and 'Criticisms and Counterproposals to

5047-677: The 29 attendees were or became Nobel Prize winners, including Marie Curie who, alone among them, had won Nobel Prizes in two separate scientific disciplines. The anti-German prejudice that had prevented Einstein and others from attending the Solvay conferences held after the First World War had melted away. Essentially all of those names who had contributed to the recent development of the quantum theory were at this Solvay Conference, including Bohr, Born, de Broglie, Dirac, Heisenberg, Pauli, and Schrödinger. Heisenberg commented: "Through

5150-570: The Bohr–Sommerfeld model could not be extended from hydrogen to the next simplest case, the helium atom . The transition from the old quantum theory to full-fledged quantum physics began in 1925, when Werner Heisenberg presented a treatment of electron behavior based on discussing only "observable" quantities, meaning to Heisenberg the frequencies of light that atoms absorbed and emitted. Max Born then realized that in Heisenberg's theory,

5253-498: The Copenhagen Interpretation', that Heisenberg delivered in 1955, are reprinted in the collection Physics and Philosophy . Before the book was released for sale, Heisenberg privately expressed regret for having used the term, due to its suggestion of the existence of other interpretations, that he considered to be "nonsense". In a 1960 review of Heisenberg's book, Bohr's close collaborator Léon Rosenfeld called

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5356-423: The Copenhagen interpretation. Heisenberg spoke of the wave function as representing available knowledge of a system, and did not use the term "collapse", but instead termed it "reduction" of the wave function to a new state representing the change in available knowledge which occurs once a particular phenomenon is registered by the apparatus. Because they assert that the existence of an observed value depends upon

5459-419: The Copenhagen tradition needs to be built upon or extended include Rudolf Haag and Anton Zeilinger . Under realism and determinism , if the wave function is regarded as ontologically real, and collapse is entirely rejected, a many-worlds interpretation results. If wave function collapse is regarded as ontologically real as well, an objective collapse theory is obtained. Bohmian mechanics shows that it

5562-656: The Copenhagen tradition, have expressed frustration at how it took the mathematical formalism of quantum theory as given, rather than trying to understand how it might arise from something more fundamental. ( E. T. Jaynes described the mathematical formalism of quantum physics as "a peculiar mixture describing in part realities of Nature, in part incomplete human information about Nature—all scrambled up together by Heisenberg and Bohr into an omelette that nobody has seen how to unscramble".) This dissatisfaction has motivated new interpretative variants as well as technical work in quantum foundations . Indeterminism Indeterminism

5665-474: The PhD thesis of Hugh Everett that proposed the many-worlds interpretation. After supporting Everett's work for several years, he began to distance himself from the many-worlds interpretation in the 1970s. Late in life, he wrote that while the Copenhagen interpretation might fairly be called "the fog from the north", it "remains the best interpretation of the quantum that we have". Other physicists, while influenced by

5768-701: The Solvay Conference on Chemistry. The 1st Solvay Conference on Biology titled "The organisation and dynamics of biological computation" took place in April 2024. Hendrik Lorentz was chairman of the first Solvay Conference on Physics, held in Brussels from 30 October to 3 November 1911. The subject was Radiation and the Quanta . This conference looked at the problems of having two approaches, namely classical physics and quantum theory . Albert Einstein

5871-1306: The Solvay archives 1948: (scientific committee – present) Sir Lawrence Bragg , Niels Bohr, Théophile de Donder , Sir Owen Willans Richardson , Jules-Émile Verschaffelt , Hendrik Kramers (scientific committee – absent) Peter Debye , Abram Fedorovich Ioffé , Albert Einstein, Frédéric Joliot-Curie (speakers) C. F. Powell, P. Auger, Felix Bloch, Patrick Blackett , Homi J. Bhabha , Marie-Antoinette Tonnelat on behalf of Louis de Broglie , Rudolf Peierls, Walter Heitler, Edward Teller , R. Serber, Léon Rosenfeld (additional participants) H. Casimir, J. Cockroft, P. Dee, Paul Dirac , Ferretti, O. Frisch, Oskar Klein , Leprince-Ringuet, Lise Meitner , Christian Møller , Francis Perrin , J. Robert Oppenheimer , Wolfgang Pauli , P. Scherrer, Erwin Schrödinger (auditeurs) J. Timmermans, G. Balasse, J. Errera, O. Goche, P. Kipfer, L. Flamache, M. Occhialini, Marc de Hemptinne (secrétaires) E. Stahel, J. Géhéniau, Miss Dilworth, Ilya Prigogine , L. Groven, Léon Van Hove, Yves Goldschmidt, MM Van Styvendael, Demeur, Van Isacker (administrative commission) Jules Bordet, Ernest-John Solvay, Dr F. Héger-Gilbert, E. Henriot, F. van den Dungen. The following Nobel prize-winning scientists either attended Solvay Conferences before 1934 or were recipients of

5974-590: The United States to raise money. The fourth Solvay Conference on Physics was held in 1924. These conferences, supported by the King of Belgium, had become the leading international gathering for the discussion of the very latest developments in physics. The subject was "The electrical conductivity of metals and related topics". Scientists based in Germany and Austria were not invited to this Solvay meeting due to

6077-471: The book seems to me to be fulfilled if it contributes somewhat to the diffusion of that 'Kopenhagener Geist der Quantentheorie' [Copenhagen spirit of quantum theory] if I may so express myself, which has directed the entire development of modern atomic physics. The term 'Copenhagen interpretation' suggests something more than just a spirit, such as some definite set of rules for interpreting the mathematical formalism of quantum mechanics, presumably dating back to

6180-604: The cat is actually both dead and alive until the box is opened to check on it. But the cat, if it survives, will only remember being alive. Schrödinger resists "so naively accepting as valid a 'blurred model' for representing reality." How can the cat be both alive and dead? In Copenhagen-type views, the wave function reflects our knowledge of the system. The wave function ( | dead ⟩ + | alive ⟩ ) / 2 {\displaystyle (|{\text{dead}}\rangle +|{\text{alive}}\rangle )/{\sqrt {2}}} means that, once

6283-406: The cat is observed, there is a 50% chance it will be dead, and 50% chance it will be alive. (Some versions of the Copenhagen interpretation reject the idea that a wave function can be assigned to a physical system that meets the everyday definition of "cat"; in this view, the correct quantum-mechanical description of the cat-and-particle system must include a superselection rule .) "Wigner's friend"

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6386-399: The choice to measure one excludes the possibility of measuring the other. Consequently, a fact deduced regarding one arrangement of laboratory apparatus could not be combined with a fact deduced by means of the other, and so, the inference of predetermined position and momentum values for the second particle was not valid. Bohr concluded that EPR's "arguments do not justify their conclusion that

6489-403: The classical variables of position and momentum would instead be represented by matrices , mathematical objects that can be multiplied together like numbers with the crucial difference that the order of multiplication matters. Erwin Schrödinger presented an equation that treated the electron as a wave, and Born discovered that the way to successfully interpret the wave function that appeared in

6592-441: The concept of chance is by the earliest philosopher of atomism , Leucippus , who said: "The cosmos, then, became like a spherical form in this way: the atoms being submitted to a casual and unpredictable movement, quickly and incessantly". Aristotle described four possible causes (material, efficient, formal, and final). Aristotle's word for these causes was αἰτίαι ( aitiai , as in aetiology ), which translates as causes in

6695-408: The discontinuous and stochastic nature of the "observation" or "measurement" process, the difficulty of defining what might count as a measuring device, and the seeming reliance upon classical physics in describing such devices. Still, including all the variations, the interpretation remains one of the most commonly taught. Starting in 1900, investigations into atomic and subatomic phenomena forced

6798-408: The event"; for example, we study the early universe through the cosmic microwave background , and we can apply quantum mechanics to that just as well as to any electromagnetic field. Likewise, Asher Peres argued that physicists are , conceptually, outside those degrees of freedom that cosmology studies, and applying quantum mechanics to the radius of the universe while neglecting the physicists in it

6901-443: The existence of alternative possibilities (or the agent's power to do otherwise) is a necessary condition for acting freely, and (2) determinism is not compatible with alternative possibilities (it precludes the power to do otherwise)". It is important to note that the crux of Kane's position is grounded not in a defense of alternative possibilities (AP) but in the notion of what Kane refers to as ultimate responsibility (UR). Thus, AP

7004-418: The idea of human freedom based on quantum indeterminacy and invented the notion of amplification of microscopic quantum events to bring chance into the macroscopic world. In his somewhat bizarre mechanism, he imagined sticks of dynamite attached to his amplifier, anticipating the Schrödinger's cat paradox. Reacting to criticisms that his ideas made chance the direct cause of our actions, Compton clarified

7107-421: The implications that accepting uncertainty at the microscopic level has on macroscopic objects. A cat is put in a sealed box, with its life or death made dependent on the state of a subatomic particle. Thus a description of the cat during the course of the experiment—having been entangled with the state of a subatomic particle—becomes a "blur" of "living and dead cat." But this cannot be accurate because it implies

7210-495: The imprecision of how the boundary between quantum and classical might be defined. This boundary came to be termed the Heisenberg cut (while John Bell derisively called it the "shifty split"). As typically portrayed, Copenhagen-type interpretations involve two different kinds of time evolution for wave functions, the deterministic flow according to the Schrödinger equation and the probabilistic jump during measurement, without

7313-402: The initial condition (or starting point) is known, there are many possibilities the process might go to, but some paths may be more probable and others less so. The idea that Newtonian physics proved causal determinism was highly influential in the early modern period. "Thus physical determinism [..] became the ruling faith among enlightened men; and everybody who did not embrace this new faith

7416-417: The intercession of the observer, Copenhagen-type interpretations are sometimes called "subjective". All of the original Copenhagen protagonists considered the process of observation as mechanical and independent of the individuality of the observer. Wolfgang Pauli , for example, insisted that measurement results could be obtained and recorded by "objective registering apparatus". As Heisenberg wrote, Of course

7519-428: The interpretation include the following: Hans Primas and Roland Omnès give a more detailed breakdown that, in addition to the above, includes the following: There are some fundamental agreements and disagreements between the views of Bohr and Heisenberg. For example, Heisenberg emphasized a sharp "cut" between the observer (or the instrument) and the system being observed, while Bohr offered an interpretation that

7622-404: The introduction of the observer must not be misunderstood to imply that some kind of subjective features are to be brought into the description of nature. The observer has, rather, only the function of registering decisions, i.e., processes in space and time, and it does not matter whether the observer is an apparatus or a human being; but the registration, i.e., the transition from the "possible" to

7725-409: The light is always found to be absorbed at the screen at discrete points, as individual particles (not waves); the interference pattern appears via the varying density of these particle hits on the screen. Furthermore, versions of the experiment that include detectors at the slits find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would

7828-499: The mathematical formalism of quantum mechanics, and Bohr distanced himself from what he considered Heisenberg's more subjective interpretation. Bohr offered an interpretation that is independent of a subjective observer, or measurement, or collapse; instead, an "irreversible" or effectively irreversible process causes the decay of quantum coherence which imparts the classical behavior of "observation" or "measurement". Different commentators and researchers have associated various ideas with

7931-423: The momentum of the second particle could be predicted. They argued that no action taken on the first particle could instantaneously affect the other, since this would involve information being transmitted faster than light, which is forbidden by the theory of relativity . They invoked a principle, later known as the "Einstein–Podolsky–Rosen (EPR) criterion of reality", positing that, "If, without in any way disturbing

8034-551: The moon exists only when I look at it." While Einstein did not doubt that quantum mechanics was a correct physical theory in that it gave correct predictions, he maintained that it could not be a complete theory. The most famous product of his efforts to argue the incompleteness of quantum theory is the Einstein–Podolsky–Rosen thought experiment , which was intended to show that physical properties like position and momentum have values even if not measured. The argument of EPR

8137-413: The only causes that exist are of a type that do not constrain the future to a single course; for instance, they can maintain that only necessary and not sufficient causes exist. The necessary/sufficient distinction works as follows: If x is a necessary cause of y ; then the presence of y implies that x definitely preceded it. The presence of x , however, does not imply that y will occur. If x

8240-438: The ordered universe is only a small bubble in a larger sea of chaos. The Boltzmann brain is a similar idea. Solvay Conference The Solvay Conferences ( French : Congrès Solvay ) have been devoted to preeminent unsolved problems in both physics and chemistry . They began with the historic invitation-only 1911 Solvay Conference on Physics, considered a turning point in the world of physics, and are ongoing. Since

8343-411: The outcomes of each possible measurement on a system. Knowledge of the wave function together with the rules for the system's evolution in time exhausts all that can be predicted about the system's behavior. Generally, Copenhagen-type interpretations deny that the wave function provides a directly apprehensible image of an ordinary material body or a discernible component of some such, or anything more than

8446-525: The possibility of exchange between the representatives of different lines of research, this conference has contributed extraordinarily to the clarification of the physical foundations of the quantum theory. It forms, so to speak, the outward completion of the quantum theory." The following list of participants is extracted from the proceedings of the Solvay Conferences in Physics stored in

8549-462: The quantum description turns out to be essentially incomplete." Einstein was an early and persistent supporter of objective reality. Bohr and Heisenberg advanced the position that no physical property could be understood without an act of measurement, while Einstein refused to accept this. Abraham Pais recalled a walk with Einstein when the two discussed quantum mechanics: "Einstein suddenly stopped, turned to me and asked whether I really believed that

8652-432: The second quarter of the 20th century. This lack of a single, authoritative source that establishes the Copenhagen interpretation is one difficulty with discussing it; another complication is that the philosophical background familiar to Einstein, Bohr, Heisenberg, and contemporaries is much less so to physicists and even philosophers of physics in more recent times. Bohr and Heisenberg never totally agreed on how to understand

8755-496: The sense of the multiple factors responsible for an event. Aristotle did not subscribe to the simplistic "every event has a (single) cause" idea that was to come later. In his Physics and Metaphysics , Aristotle said there were accidents (συμβεβηκός, sumbebekos ) caused by nothing but chance (τύχη, tukhe ). He noted that he and the early physicists found no place for chance among their causes. We have seen how far Aristotle distances himself from any view which makes chance

8858-605: The success of 1911, they have been organised by the International Solvay Institutes for Physics and Chemistry , founded by the Belgian industrialist Ernest Solvay in 1912 and 1913, and located in Brussels . The institutes coordinate conferences, workshops, seminars, and colloquia. Recent Solvay Conferences entail a three year cycle: the Solvay Conference on Physics followed by a gap year, followed by

8961-443: The tensions still prevailing after the First World War. So there was no Planck, Einstein, Sommerfeld or Born. Perhaps the most famous conference was the fifth Solvay Conference on Physics, which was held from 24 to 29 October 1927. The subject was Electrons and Photons and the world's most notable physicists met to discuss the newly formulated quantum theory. The leading figures were Albert Einstein and Niels Bohr . Seventeen of

9064-422: The term an "ambiguous expression" and suggested it be discarded. However, this did not come to pass, and the term entered widespread use. Bohr's ideas in particular are distinct despite the use of his Copenhagen home in the name of the interpretation. There is no uniquely definitive statement of the Copenhagen interpretation. The term encompasses the views developed by a number of scientists and philosophers during

9167-532: The term refers to the city of Copenhagen in Denmark . During the mid-1920s, Heisenberg had been an assistant to Bohr at his institute in Copenhagen. Together they helped originate quantum mechanical theory. At the 1927 Solvay Conference , a dual talk by Max Born and Heisenberg declared "we consider quantum mechanics to be a closed theory, whose fundamental physical and mathematical assumptions are no longer susceptible of any modification." In 1929, Heisenberg gave

9270-513: The term. Asher Peres remarked that very different, sometimes opposite, views are presented as "the Copenhagen interpretation" by different authors. N. David Mermin coined the phrase "Shut up and calculate!" to summarize Copenhagen-type views, a saying often misattributed to Richard Feynman and which Mermin later found insufficiently nuanced. Mermin described the Copenhagen interpretation as coming in different "versions", "varieties", or "flavors". Some basic principles generally accepted as part of

9373-458: The time generally maintained the principle that the numerical value of a physical quantity is not meaningful or does not exist until it is measured. Prominent physicists associated with Copenhagen-type interpretations have included Lev Landau , Wolfgang Pauli , Rudolf Peierls , Asher Peres , Léon Rosenfeld , and Ray Streater . Throughout much of the 20th century, the Copenhagen tradition had overwhelming acceptance among physicists. According to

9476-484: The two-stage nature of his idea in an Atlantic Monthly article in 1955. First there is a range of random possible events, then one adds a determining factor in the act of choice . A set of known physical conditions is not adequate to specify precisely what a forthcoming event will be. These conditions, insofar as they can be known, define instead a range of possible events from among which some particular event will occur. When one exercises freedom, by his act of choice he

9579-515: The undetermined, regress-stopping voluntary actions or refrainings in the life histories of agents that are required for UR. UR does not require that every act done of our own free will be undetermined and thus that, for every act or choice, we could have done otherwise; it requires only that certain of our choices and actions be undetermined (and thus that we could have done otherwise), namely SFAs. These form our character or nature; they inform our future choices, reasons and motivations in action. If

9682-476: The wave function of a system can change suddenly and discontinuously upon measurement. Prior to a measurement, a wave function involves the various probabilities for the different potential outcomes of that measurement. But when the apparatus registers one of those outcomes, no traces of the others linger. Since Bohr did not view the wavefunction as something physical, he never talks about "collapse". Nevertheless, many physicists and philosophers associate collapse with

9785-429: Was "yes". By contrast, Max Jammer writes "Einstein never proposed a hidden variable theory." Einstein explored the possibility of a hidden variable theory, and wrote a paper describing his exploration, but withdrew it from publication because he felt it was faulty. During the 1930s and 1940s, views about quantum mechanics attributed to Bohr and emphasizing complementarity became commonplace among physicists. Textbooks of

9888-424: Was defined by the possibility of viewing the mathematical formulas as referring to waves or particles. Bohr thought that a particular experimental setup would display either a wave picture or a particle picture, but not both. Heisenberg thought that every mathematical formulation was capable of both wave and particle interpretations. A wave function is a mathematical entity that provides a probability distribution for

9991-462: Was deterministically caused. For Epicureanism , the occasional interventions of arbitrary gods would be preferable to strict determinism. In 1729 the Testament of Jean Meslier states: "The matter, by virtue of its own active force, moves and acts in blind manner". Soon after Julien Offroy de la Mettrie in his L'Homme Machine. (1748, anon.) wrote: "Perhaps, the cause of man's existence

10094-557: Was held to be an obscurantist and a reactionary". However: "Newton himself may be counted among the few dissenters, for he regarded the solar system as imperfect , and consequently as likely to perish". Classical chaos is not usually considered an example of indeterminism, as it can occur in deterministic systems such as the three-body problem . John Earman has argued that most physical theories are indeterministic. For instance, Newtonian physics admits solutions where particles accelerate continuously, heading out towards infinity. By

10197-445: Was likewise dissatisfied with the indeterminism of quantum theory. Regarding the possibility of randomness in nature, Einstein said that he was "convinced that He [God] does not throw dice." Bohr, in response, reputedly said that "it cannot be for us to tell God, how he is to run the world". Much criticism of Copenhagen-type interpretations has focused on the need for a classical domain where observers or measuring devices can reside, and

10300-469: Was not generally persuasive to other physicists. Carl Friedrich von Weizsäcker , while participating in a colloquium at Cambridge, denied that the Copenhagen interpretation asserted "What cannot be observed does not exist". Instead, he suggested that the Copenhagen interpretation 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." Einstein

10403-677: Was one of those rare distinguished physicists in the English speaking world of the late 1920s and throughout the 1930s arguing for the “liberation of free will” with the help of Heisenberg’s indeterminacy principle, but their efforts had been met not only with physical and philosophical criticism but most primarily with fierce political and ideological campaigns. In his essay Of Clouds and Clocks , included in his book Objective Knowledge , Popper contrasted "clouds", his metaphor for indeterministic systems, with "clocks", meaning deterministic ones. He sided with indeterminism, writing I believe Peirce

10506-452: Was right in holding that all clocks are clouds to some considerable degree — even the most precise of clocks. This, I think, is the most important inversion of the mistaken determinist view that all clouds are clocks Popper was also a promoter of propensity probability . Kane is one of the leading contemporary philosophers on free will . Advocating what is termed within philosophical circles " libertarian freedom", Kane argues that "(1)

10609-542: Was the second youngest physicist present (the youngest one was Lindemann ). Other members of the Solvay Congress were experts including Marie Curie , Ernest Rutherford and Henri Poincaré (see image for attendee list). The third Solvay Conference on Physics was held in April 1921, soon after World War I . Most German scientists were barred from attending. In protest at this action, Albert Einstein , although he had renounced German citizenship in 1901 and become

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