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Philosophers

Mortimer Adler
Rogers Albritton
Alexander of Aphrodisias
Samuel Alexander
William Alston
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Louise Antony
Thomas Aquinas
Aristotle
David Armstrong
Harald Atmanspacher
Robert Audi
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J.L.Austin
A.J.Ayer
Alexander Bain
Mark Balaguer
Jeffrey Barrett
William Belsham
Henri Bergson
George Berkeley
Isaiah Berlin
Richard J. Bernstein
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Robert Bishop
Max Black
Susanne Bobzien
Emil du Bois-Reymond
Hilary Bok
Laurence BonJour
George Boole
Émile Boutroux
F.H.Bradley
C.D.Broad
Michael Burke
C.A.Campbell
Joseph Keim Campbell
Rudolf Carnap
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Ernst Cassirer
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Roderick Chisholm
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Cicero
Randolph Clarke
Samuel Clarke
Anthony Collins
Antonella Corradini
Diodorus Cronus
Jonathan Dancy
Donald Davidson
Mario De Caro
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Jacques Derrida
René Descartes
Richard Double
Fred Dretske
John Dupré
John Earman
Laura Waddell Ekstrom
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Herbert Feigl
John Martin Fischer
Owen Flanagan
Luciano Floridi
Philippa Foot
Alfred Fouilleé
Harry Frankfurt
Richard L. Franklin
Michael Frede
Gottlob Frege
Peter Geach
Edmund Gettier
Carl Ginet
Alvin Goldman
Gorgias
Nicholas St. John Green
H.Paul Grice
Ian Hacking
Ishtiyaque Haji
Stuart Hampshire
W.F.R.Hardie
Sam Harris
William Hasker
R.M.Hare
Georg W.F. Hegel
Martin Heidegger
Heraclitus
R.E.Hobart
Thomas Hobbes
David Hodgson
Shadsworth Hodgson
Baron d'Holbach
Ted Honderich
Pamela Huby
David Hume
Ferenc Huoranszki
William James
Lord Kames
Robert Kane
Immanuel Kant
Tomis Kapitan
Jaegwon Kim
William King
Hilary Kornblith
Christine Korsgaard
Saul Kripke
Andrea Lavazza
Keith Lehrer
Gottfried Leibniz
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Michael Levin
George Henry Lewes
C.I.Lewis
David Lewis
Peter Lipton
C. Lloyd Morgan
John Locke
Michael Lockwood
E. Jonathan Lowe
John R. Lucas
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Alasdair MacIntyre
Ruth Barcan Marcus
James Martineau
Storrs McCall
Hugh McCann
Colin McGinn
Michael McKenna
Brian McLaughlin
John McTaggart
Paul E. Meehl
Uwe Meixner
Alfred Mele
Trenton Merricks
John Stuart Mill
Dickinson Miller
G.E.Moore
Thomas Nagel
Friedrich Nietzsche
John Norton
P.H.Nowell-Smith
Robert Nozick
William of Ockham
Timothy O'Connor
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David F. Pears
Charles Sanders Peirce
Derk Pereboom
Steven Pinker
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H.A.Prichard
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Josiah Royce
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Paul Russell
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Kenneth Sayre
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Moritz Schlick
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Wilfrid Sellars
Alan Sidelle
Ted Sider
Henry Sidgwick
Walter Sinnott-Armstrong
J.J.C.Smart
Saul Smilansky
Michael Smith
Baruch Spinoza
L. Susan Stebbing
Isabelle Stengers
George F. Stout
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Peter Strawson
Eleonore Stump
Francisco Suárez
Richard Taylor
Kevin Timpe
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Manuel Vargas
John Venn
Kadri Vihvelin
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R. Jay Wallace
W.G.Ward
Ted Warfield
Roy Weatherford
William Whewell
Alfred North Whitehead
David Widerker
David Wiggins
Bernard Williams
Timothy Williamson
Ludwig Wittgenstein
Susan Wolf

Scientists

Michael Arbib
Bernard Baars
Gregory Bateson
John S. Bell
Charles Bennett
Ludwig von Bertalanffy
Susan Blackmore
Margaret Boden
David Bohm
Niels Bohr
Ludwig Boltzmann
Emile Borel
Max Born
Satyendra Nath Bose
Walther Bothe
Hans Briegel
Leon Brillouin
Stephen Brush
Henry Thomas Buckle
S. H. Burbury
Donald Campbell
Anthony Cashmore
Eric Chaisson
Jean-Pierre Changeux
Arthur Holly Compton
John Conway
John Cramer
E. P. Culverwell
Charles Darwin
Terrence Deacon
Louis de Broglie
Max Delbrück
Abraham de Moivre
Paul Dirac
Hans Driesch
John Eccles
Arthur Stanley Eddington
Paul Ehrenfest
Albert Einstein
Hugh Everett, III
Franz Exner
Richard Feynman
R. A. Fisher
Joseph Fourier
Lila Gatlin
Michael Gazzaniga
GianCarlo Ghirardi
J. Willard Gibbs
Nicolas Gisin
Paul Glimcher
Thomas Gold
A.O.Gomes
Brian Goodwin
Joshua Greene
Jacques Hadamard
Patrick Haggard
Stuart Hameroff
Augustin Hamon
Sam Harris
Hyman Hartman
John-Dylan Haynes
Martin Heisenberg
Werner Heisenberg
John Herschel
Jesper Hoffmeyer
E. T. Jaynes
William Stanley Jevons
Roman Jakobson
Pascual Jordan
Ruth E. Kastner
Stuart Kauffman
Martin J. Klein
Simon Kochen
Stephen Kosslyn
Ladislav Kovàč
Rolf Landauer
Alfred Landé
Pierre-Simon Laplace
David Layzer
Benjamin Libet
Seth Lloyd
Hendrik Lorentz
Josef Loschmidt
Ernst Mach
Donald MacKay
Henry Margenau
James Clerk Maxwell
Ernst Mayr
Ulrich Mohrhoff
Jacques Monod
Emmy Noether
Abraham Pais
Howard Pattee
Wolfgang Pauli
Massimo Pauri
Roger Penrose
Steven Pinker
Colin Pittendrigh
Max Planck
Susan Pockett
Henri Poincaré
Daniel Pollen
Ilya Prigogine
Hans Primas
Adolphe Quételet
Juan Roederer
Jerome Rothstein
David Ruelle
Erwin Schrödinger
Aaron Schurger
Claude Shannon
David Shiang
Herbert Simon
Dean Keith Simonton
B. F. Skinner
Roger Sperry
John Stachel
Henry Stapp
Tom Stonier
Antoine Suarez
Leo Szilard
William Thomson (Kelvin)
Peter Tse
Heinz von Foerster
John von Neumann
John B. Watson
Daniel Wegner
Steven Weinberg
Paul A. Weiss
John Wheeler
Wilhelm Wien
Norbert Wiener
Eugene Wigner
E. O. Wilson
H. Dieter Zeh
Ernst Zermelo
Wojciech Zurek

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H. Dieter Zeh

H. Dieter Zeh is one of the founders of the idea of decoherence.

Zeh taught a course on the direction of time over the past few decades at Heidelberg University. The course has been published in a textbook, The Physical Basis of the Direction of Time, that has gone through five editions.

Zermelo's Recurrence Objection to the H-Theorem

In the latest edition of his text, Zeh discusses Ernst Zermelo's recurrence objection to Ludwig Boltzmann's H-Theorem and suggests that the time-dependence of the size of the whole universe prevents such a recurrence.

Another argument against the statistical interpretation of irreversibility, the recurrence objection (or Wiederkehreinwand), was raised much later by Ernst Friedrich Zermelo, a collaborator of Max Planck at a time when the latter still opposed atomism, and instead supported the 'energeticists', who attempted to understand energy and entropy as fundamental 'substances'. This argument is based on a mathematical theorem due to Henri Poincaré, which states that every bounded mechanical system will return as close as one wishes to its initial state within a sufficiently large time. The entropy of a closed system would therefore have to return to its former value, provided only the function F(z) is continuous. This is a special case of the quasiergodic theorem which asserts that every system will corne arbitrarily close to any point on the hypersurface of fixed energy (and possibly with other fixed analytical constants of the motion) within finite time.

While all these theorems are mathematically correct, the recurrence objection fails to apply to reality for quantitative reasons. The age of our Universe is much smaller than the Poincaré recurrence times even for a gas consisting of no more than a few tens of particles. Their recurrence to the vicinity of their initial states (or their coming close to any other similarly specific state) can therefore be excluded in practice. Nonetheless, some 'foundations' of irreversible thermodynamics in the literature rely on formal idealizations that would lead to strictly infinite Poincaré recurrence times (for example the 'thermodynamical limit' of infinite particle number). Such assumptions are not required in our Universe of finite age, and they would not invalidate the reversibility objection (or the equilibrium expectation, mentioned above). However, all foundations of irreversible behavior have to presume some very improbable initial conditions...

In order to reverse the thermodynamical arrow of time in a bounded system, it would not therefore suffice to "go ahead and reverse all momenta" in the system itself, as ironically suggested by Boltzmann as an answer to Loschmidt.

This agrees with the Eddington and Layzer solutions of the recurrence problem
In an interacting Laplacean universe, the Poincaré cycles of its subsystems could in general only be those of the whole Universe, since their exact Hamiltonians must always depend on their time-dependent environment.
In a 1993 response to an article by Nicholas Gisin entitled "Wave-function approach to dissipative processes: are there quantum jumps?," Zeh argued that "quantum jumps" ("collapses" of the wave function) are only "apparent." Their appearance is caused by the loss of shielding from the environment, which "continuously monitors" a quantum system.

Zeh's work seems inspired by two 1952 articles by Erwin Schrödinger titled "Are There Quantum Jumps?" (Part I and Part II) and perhaps by John Bell's 1987 article with the same title.

Max Born replied to the Schrödinger claims, defending his statistical interpretation of quantum mechanics. Here is Zeh's position:

As far as is known, all properties of closed quantum systems are perfectly described by means of wave functions in configuration space (in general, wave functionals of certain fields) dynamically evolving smoothly according to the time-dependent Schrödinger equation. However, the condition of being closed (or shielded against interactions with the environment) can easily be estimated to be quite exceptional. It characterizes very special (usually atomic) systems from which the laws of quantum mechanics were derived. When the shielding ceases, most notably during measurements, discontinuous events ('quantum jumps' or a 'collapse of the wave function') seem to occur, and particle aspects seem to be observed. Such events are also known to lead to a loss of interference between different values of the 'measured' variables - regardless of whether any result is read from the apparatus by an observer.

Macroscopic systems are very effectively coupled to their environment in this way. They cannot avoid being 'continuously measured' in the sense of losing interference. This is obvious without any calculation, since we could never see macroscopic objects if they did not continuously scatter light which thereby had to carry away 'information' about their position and shape. The effect of such interactions is often taken into account dynamically by means of stochastic terms in the evolution of the wave function of the considered system (sometimes called 'chopping' or 'kicking') - equivalent to a nonunitary evolution of the density matrix.' These terms (introduced ad hoc) are usually interpreted as representing fundamental aspects of quantum mechanics (just as the supplementary dynamics that von Neumann introduced as his 'first intervention' to augment the Schrödinger equation in the case of measurements proper).

Precisely such empirically justified dynamical terms can however be derived within the well established quantum mechanics of interacting systems provided the environment is properly taken into account. Joos and Zeh have calculated that even small dust particles or large molecules must 'decohere' (that is, lose certain interference terms) on a time scale of fractions of a second, while Zurek' has estimated that for a normal macroscopic system the rate of decoherence is typically faster than thermal relaxation by an astounding factor of the order of 1040. In contrast, microscopic systems tend to decohere into energy eigenstates, since they interact with their environment mainly through their decay products. It is for this reason that the time-independent Schrödinger equation is so useful for describing atomic systems. In quantum measurements proper, microscopic properties will first become correlated with macroscopically different pointer positions, the superpositions of which must then immediately decohere in the described way...

All particle aspects observed in measurements of quantum fields (like spots on a plate, tracks in a bubble chamber, or clicks of a counter) can be understood by taking into account this decoherence of the relevant local (i.e., subsystem) density matrix. (The concept of 'particle numbers' is of course explained by the oscillator quantum numbers of the corresponding field modes - at least for bosons.)

In fact, all classical aspects (or the apparent validity of fundamental superselection rules) seem to be derivable in this way from the assumption of a global Schrödinger wave function(al). It is the unavoidable environment that determines which properties decohere (that is, become classical)...

I do not know of any apparent violation of the Schrödinger equation or the superposition principle that cannot at least plausibly be expected to be derivable in terms of decoherence. In spite of this success (which can hardly be an accident), this description is often considered as insufficient to explain the measurement process itself...

The reservations do seem sound, since decoherence is described formally by means of the density matrix of the considered subsystem of the universe, obtained by tracing out the rest (the 'environment'). The concept of the density matrix (of subsystems in this case) is however justified itself only as a means for calculating expectation values or probabilities for outcomes of further measurements, that is, for the secondary quantum jumps which would have to occur, for example, when the pointer is read. This explanation of measurements therefore seems to be circular from a fundamental point of view. In the global wave function (which is interpreted as representing 'reality' in this picture) all interference terms remain present. The universe as a whole never decoheres. The description of measurements by means of merely local decoherence - so goes the usual argument - must be wrong, since one does observe , in contrast to this global superposition of different outcomes derived from the Schrödinger equation, that only one of its components (a wave packet representing a definite outcome) exists after every measurement.

However, this latter claim is wrong, and so is the argument. For after an observation one need not necessarily conclude that only one component now exists but only that only one component is observed . But this fact is readily described by the Schrödinger equation without any modification. Whenever an observer interacts with the measurement device in a way that corresponds to an observation of the result, his own state must be quantum correlated with the macroscopic pointer position (and potentially also with other observers), and hence be decohered from the beginning. Superposed world components describing the registration of different macroscopic properties by the 'same' observer are dynamically entirely independent of one another: they describe different observers. Because of the fork-like structure of causality (the spreading in space of the retarded effects of local causes), there is no chance of their forming a superposition with respect to (or in) a local observer any more (except, perhaps, in a recollapsing Friedmann universe).

This dynamical consequence of decoherence explains everything that has to be explained dynamically in order to understand what can be observed by local observers.

John Bell called Hugh Everett's "relative states" or "many worlds" interpretation of Q.M "extravagant"
He who considers this conclusion of an indeterminism or splitting of the observer's identity, derived from the Schrödinger equation in the form of dynamically decoupling ('branching') wave packets on a fundamental global configuration space, as unacceptable or 'extravagant' may instead dynamically formalize the superfluous hypothesis of a disappearance of the 'other' components by whatever method he prefers, but he should be aware that he may thereby also create his own problems: Any deviation from the global Schrödinger equation must in principle lead to observable effects, and it should be recalled that none have ever been discovered. The conclusion would of course have to be revised if such effects were some day to be found. But as of now, there is no objective reason to expect them to exist; and even if they did, they need not take the form of the apparent discontinuities which are readily described by means of local decoherence according to the universal Schrödinger equation.
Works
There are no Quantum Jumps, nor are there Particles!, Physics Letters A, 172.4 (1993): 189-192. (PDF)
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