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Core Concepts

Best Explanation
Divided Line
Downward Causation
Emergent Dualism
Identity Theory
Infinite Regress
Mental Causation
Multiple Realizability
Possible Worlds
Schrödinger's Cat


Mortimer Adler
Rogers Albritton
Alexander of Aphrodisias
Samuel Alexander
William Alston
Louise Antony
Thomas Aquinas
David Armstrong
Harald Atmanspacher
Robert Audi
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
Michael Burke
Joseph Keim Campbell
Rudolf Carnap
Ernst Cassirer
David Chalmers
Roderick Chisholm
Randolph Clarke
Samuel Clarke
Anthony Collins
Antonella Corradini
Diodorus Cronus
Jonathan Dancy
Donald Davidson
Mario De Caro
Daniel Dennett
Jacques Derrida
René Descartes
Richard Double
Fred Dretske
John Dupré
John Earman
Laura Waddell Ekstrom
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
Nicholas St. John Green
H.Paul Grice
Ian Hacking
Ishtiyaque Haji
Stuart Hampshire
Sam Harris
William Hasker
Georg W.F. Hegel
Martin Heidegger
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
Michael Levin
George Henry Lewes
David Lewis
Peter Lipton
C. Lloyd Morgan
John Locke
Michael Lockwood
E. Jonathan Lowe
John R. Lucas
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
Thomas Nagel
Friedrich Nietzsche
John Norton
Robert Nozick
William of Ockham
Timothy O'Connor
David F. Pears
Charles Sanders Peirce
Derk Pereboom
Steven Pinker
Karl Popper
Huw Price
Hilary Putnam
Willard van Orman Quine
Frank Ramsey
Ayn Rand
Michael Rea
Thomas Reid
Charles Renouvier
Nicholas Rescher
Richard Rorty
Josiah Royce
Bertrand Russell
Paul Russell
Gilbert Ryle
Jean-Paul Sartre
Kenneth Sayre
Moritz Schlick
Arthur Schopenhauer
John Searle
Wilfrid Sellars
Alan Sidelle
Ted Sider
Henry Sidgwick
Walter Sinnott-Armstrong
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
G.H. von Wright
David Foster Wallace
R. Jay Wallace
Ted Warfield
Roy Weatherford
William Whewell
Alfred North Whitehead
David Widerker
David Wiggins
Bernard Williams
Timothy Williamson
Ludwig Wittgenstein
Susan Wolf


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
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
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
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
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


Free Will
Mental Causation
James Symposium

Schrödinger's Cat (and Wigner's Friend)
To understand and resolve the paradox of Schrödinger's Cat, it helps to understand that Erwin Schrödinger invented his paradox to poke holes in some implications of quantum physics that he regarded as unacceptable. Like Albert Einstein, Max Planck, and others prominent in the new physics, Schrödinger disliked the indeterminacy, the element of chance and apparent loss of strict causality, in quantum mechanics.
Schrödinger's diabolical thought experiment was designed to amplify microscopic quantum uncertainty into the macroscopic world.
The I-PHI key to dissolving the paradox is to focus on the information present at each time in the experiment.
In standard quantum theory, an isolated system is prepared in a known state at time t. This consists of making a quantum measurement on the system and finding the experimental value for some observable quantity S(t). The future development of the system is completely described by a time evolution operator H(t) which yields a complex probability function ψ(t). This is the "wave function" invented by Schrödinger, whose formulation of quantum mechanics is called wave mechanics.
Without any further observation, the best knowledge we have of the system state at later times depends on the (real) square of this (complex) probability amplitude function. If there are a finite number of states, we can calculate the probability of finding the system in each state. Schrödinger's thought experiment imagines two possible states for the cat, alive and dead. His ghoulish Geiger counter apparatus is arranged to have a fifty percent chance of detecting an unpredictable radioactive decay and releasing cyanide to kill the cat in one hour.
So what is known, what information exists in the world, at that time one hour into the experiment?
For an external observer, complete knowledge is the paradoxical superposition of the two ψ-functions for live and dead cats. If we really did this fiendish experiment many times, our estimated probabilities would agree very well with the total observed outcomes.
But what about the cat as a participant observer? For example, if the cat is killed one minute into the experiment, information will be encoded in the universe, information that can be read later in the cat's autopsy. The collapse of the wave function when the atom decayed could also have been registered on a chart recorder monitoring the Geiger counter electrical output.

More details on Schrödinger's Cat is in the Experiments section.

These are two examples of how the physical universe can be its own observer. Whenever information is encoded in information structures, we do not need the consciousness of physicists to collapse the wave function and make up the mind of the universe, as Werner Heisenberg, Eugene Wigner, John Wheeler, and others speculated.

In his "Remarks on the Mind-Body Question," Wigner imagines a friend who performs an experiment (it was a randomly generated flash of light, but it could be a Schrödinger's cat experiment) while Wigner is out of the room. When Wigner comes into the room, he learns the outcome. During the time only his friend knew, he wonders whether the state of the system is a superposition of "flash seen" and "flash not seen," or was it known at some previous point?
Clearly the most Wigner could know would be the probabilities he would calculate from the "flash seen" and "flash not seen" wave functions. But equally clearly, Wigner sees that the wave functions have collapsed, since the information has already been encoded in the mind of his friend.
He then substitutes a machine for his friend and decides that the situation is again indeterminate, with just a much larger box. Now it is his consciousness that collapses the wave function. He concludes (incorrectly) not only that mind is necessary to observe the physical universe, but also that mind is not material, a strange contribution to the classic mind-body problem.
For Scholars
Erwin Schrödinger's thought experiment:
One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.

It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a "blurred model" for representing reality. In itself it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.

Eugene Wigner's Consciousness:
When the province of physical theory was extended to encompass microscopic phenomena, through the creation of quantum mechanics, the concept of consciousness came to the fore again: it was not possible to formulate the laws of quantum mechanics without reference to the consciousness. All that quantum mechanics purports to describe are probability connections between subsequent impressions (also called ‘apperceptions’) of consciousness, and even though the dividing line between the observer, whose consciousness is being affected, and the observed physical object can be shifted towards one or the other to a considerable degree, it cannot be eliminated.
Werner Heisenberg's comments on knowledge of the observer:
The laws of nature which we formulate mathematically in quantum theory deal no longer with the particles themselves but with our knowledge of the elementary particles.

The conception of objective reality … evaporated into the … mathematics that represents no longer the behavior of elementary particles but rather our knowledge of this behavior.

Chapter Eighteen - The Sum Chapter Twenty - The Biology of Knowledge
Part Three - Value Part Five - Problems
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