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Philosophers

Mortimer Adler
Rogers Albritton
Alexander of Aphrodisias
Samuel Alexander
William Alston
Anaximander
G.E.M.Anscombe
Anselm
Louise Antony
Thomas Aquinas
Aristotle
David Armstrong
Harald Atmanspacher
Robert Audi
Augustine
J.L.Austin
A.J.Ayer
Alexander Bain
Mark Balaguer
Jeffrey Barrett
William Belsham
Henri Bergson
George Berkeley
Isaiah Berlin
Richard J. Bernstein
Bernard Berofsky
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
Carneades
Ernst Cassirer
David Chalmers
Roderick Chisholm
Chrysippus
Cicero
Randolph Clarke
Samuel Clarke
Anthony Collins
Antonella Corradini
Diodorus Cronus
Jonathan Dancy
Donald Davidson
Mario De Caro
Democritus
Daniel Dennett
Jacques Derrida
René Descartes
Richard Double
Fred Dretske
John Dupré
John Earman
Laura Waddell Ekstrom
Epictetus
Epicurus
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
Leucippus
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
Lucretius
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
Parmenides
David F. Pears
Charles Sanders Peirce
Derk Pereboom
Steven Pinker
Plato
Karl Popper
Porphyry
Huw Price
H.A.Prichard
Protagoras
Hilary Putnam
Willard van Orman Quine
Frank Ramsey
Ayn Rand
Michael Rea
Thomas Reid
Charles Renouvier
Nicholas Rescher
C.W.Rietdijk
Richard Rorty
Josiah Royce
Bertrand Russell
Paul Russell
Gilbert Ryle
Jean-Paul Sartre
Kenneth Sayre
T.M.Scanlon
Moritz Schlick
Arthur Schopenhauer
John Searle
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
Galen Strawson
Peter Strawson
Eleonore Stump
Francisco Suárez
Richard Taylor
Kevin Timpe
Mark Twain
Peter Unger
Peter van Inwagen
Manuel Vargas
John Venn
Kadri Vihvelin
Voltaire
G.H. von Wright
David Foster Wallace
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
Vlatko Vedral
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

Presentations

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Mental Causation
James Symposium
 
Decoherence
Decoherence is a broad explanation for the lack of uniquely quantum effects in macroscopic objects. Decoherence theorists say in particular that it explains the absence of superpositions of live and dead Schrödinger Cats.

The "decoherence program" of H. Dieter Zeh, Wojciech Zurek, and their colleagues is an attempt to describe the "appearance" or "emergence" of a classical world from the microscopic quantum world.

Decoherence theorists trace the emergence of classical properties to the interaction of quantum systems with the environment, generally the exchange of photons between quantum systems and the environment, but also the collisions of particles (which are mediated by virtual photons). No physical system is ever completely isolated from the environment. A perfectly isolated system is by definition unobservable and thus of no interest to an experimental physicist, though theoreticians often work with such ideas. Although isolation is one of the fundamental principles of all physics experiments, it is the case that it is practically impossible to prevent high-energy particles and photons from passing through any experiment.

Denials of Standard Quantum Physics
Most decoherence theorists subscribe to what they call a "universally valid quantum theory." Despite the name, this theory denies one of the basic hypotheses of standard quantum physics, namely the collapse of the quantum-mechanical wave function (Dirac's projection postulate), which is the ultimate source of chance, indeterminism, free will, and creativity.

"Universally valid" refers to the Wheeler-Everett-DeWitt-Wigner view that replaces the wave-function collapse with a splitting of a universal wave function Ψ into separate branches or components, each of which contains all the material of the universe just before the quantum event, typically a quantum measurement. Where standard quantum theory predicts the probabilities of the measurement yielding two or more eigenvalues of the physical observable being measured, the "Many Worlds" theory assumes that new worlds are created with each world realizing one of those eigenvalues, all other things about the new worlds being the same as before the measurement.

John Bell described the many-worlds theory as "extravagant." We find it extremely so, since it blatantly violates the most fundamental conservation laws of physics. In order to create another parallel universe, it must double the amount of energy, mass, charge, etc. And the new universe must be as large as our observable universe. All this because they find the idea of the collapse of the wave function non-intuitive, which in some respects it is. But in other respects it is simply the actualization of a single outcome from among many alternative possibilities.

Some of the decoherence theorists appear to share a dislike of indeterminism, exemplified by Albert Einstein's famous dictum "God does not play dice." Einstein objected to determinism, even more strongly, he objected in his famous EPR paper to the non-local character of quantum reality, which suggested to him that "influences" are traveling faster than the speed of light, violating his theory of special relativity.

And if Einstein disliked the measurement of one quantum particle instantly altering the properties of another particle a significant distance away (in this universe), what would he have thought about duplicating the entire observable universe contents in an unobservable parallel branch of the universal wave function Ψ?

Decoherence in Standard Quantum Physics
Decoherence can be separated from the "many worlds" and "no-collapse" theories. The core idea is that classical macroscopic properties depend on decoherence of quantum properties, especially the interference of different components of a coherent quantum system. We can endorse that view and show that it is not classical properties that "emerge" under conditions of decoherence, but quantum properties that show up when we look at sufficiently isolated systems small enough to exhibit coherence.

Paul Dirac described the breakdown of classical mechanics as "an inadequacy of its concepts to supply us with a description of atomic events." (Dirac, p.3)

The early Greek philosophers Democritus, Leucippus, and Epicurus argued that large objects were made from smaller objects, but there comes a size when something is absolutely small. Quantum mechanics defines the absolutely small as objects that cannot be seen without disturbing them. Decoherence says that the very act of looking at a quantum system destroys the coherence that reflects its fundamental quantum nature.

Dirac defined an object to be "big" when the disturbance accompanying our observation of it may be neglected, and "small" when the disturbance cannot be neglected. There comes a size when every attempt to minimize the disturbance fails. Dirac says "there is a limit to the fineness of our powers of observation and the smallness of the accompanying disturbance - a limit which is inherent in the nature of things and can never be surpassed by improved techniques or skill on the part of the observer.."

An important consequence of absolute smallness is that we must revise our idea of causality. If a system is small, we cannot observe it without producing a serious disturbance and hence we cannot expect to find causal and deterministic connections connections between our observations. There is an unavoidable indeterminacy in measurement of quantum systems, so that we can only calculate the probability of various possible measurements.

Under pressure from Niels Bohr, Werner Heisenberg modified his original idea that indeterminacy is always a result of observations (see Heisenberg's Microscope). Indeterminacy is an intrinsic property of quantum objects in space and time and does not depend on observations by conscious observers (with Ph.D.'s, as John Bell quipped).

Note that quantum systems can make information-generating measurements on themselves, which the decoherence theorists accept.

A Two-State Example of Coherence and Decoherence
Consider the famous Two-Slit Experiment.

We can label the probability-amplitude wave function passing through the left hand slit in the figure ψleft and the waves passing through the right-hand slit ψright. These are coherent and show the characteristic quantum interference fringes on the detector screen (a photographic plate or CCD array). This is the case even if the intensity of particles is so low that only one particle at a time arrives at the screen.

In a dramatic experimental proof of decoherence, Gerhard Rempe sent matter waves of heavy Rubidium atoms through two slits. He then irradiated the left slit with microwaves that could excite the hyperfine structure in Rb atoms passing through that slit. As he turned up the intensity, the interference fringes diminished in proportion to the number of photons falling on the left slit. The photons decohere the otherwise coherent wave functions.

The Quantum-Classical "Boundary"
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Chapter 6.8 - Reason Chapter 6.10 - Triads
Part Five - Problems Part Seven - Afterword
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