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 Barrett William Belsham Henri Bergson George Berkeley Isaiah Berlin Richard J. Bernstein Bernard Berofsky Robert Bishop Max Black Susanne Bobzien Emil du BoisReymond Hilary Bok Laurence BonJour George Boole Émile Boutroux F.H.Bradley C.D.Broad Michael Burke Lawrence Cahoone C.A.Campbell Joseph Keim Campbell Rudolf Carnap Carneades Nancy Cartwright Gregg Caruso 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 Austin Farrer Herbert Feigl Arthur Fine John Martin Fischer Frederic Fitch Owen Flanagan Luciano Floridi Philippa Foot Alfred Fouilleé Harry Frankfurt Richard L. Franklin Bas van Fraassen 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 Frank Jackson William James Lord Kames Robert Kane Immanuel Kant Tomis Kapitan Walter Kaufmann Jaegwon Kim William King Hilary Kornblith Christine Korsgaard Saul Kripke Thomas Kuhn Andrea Lavazza Christoph Lehner Keith Lehrer Gottfried Leibniz Jules Lequyer Leucippus Michael Levin Joseph Levine George Henry Lewes C.I.Lewis David Lewis Peter Lipton C. Lloyd Morgan John Locke Michael Lockwood Arthur O. Lovejoy 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 Otto Neurath Friedrich Nietzsche John Norton P.H.NowellSmith 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 JeanPaul Sartre Kenneth Sayre T.M.Scanlon Moritz Schlick Arthur Schopenhauer John Searle Wilfrid Sellars Alan Sidelle Ted Sider Henry Sidgwick Walter SinnottArmstrong 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 C.F. von Weizsäcker William Whewell Alfred North Whitehead David Widerker David Wiggins Bernard Williams Timothy Williamson Ludwig Wittgenstein Susan Wolf Scientists David Albert Michael Arbib Walter Baade Bernard Baars Jeffrey Bada Leslie Ballentine Gregory Bateson John S. Bell Mara Beller Charles Bennett Ludwig von Bertalanffy Susan Blackmore Margaret Boden David Bohm Niels Bohr Ludwig Boltzmann Emile Borel Max Born Satyendra Nath Bose Walther Bothe Jean Bricmont Hans Briegel Leon Brillouin Stephen Brush Henry Thomas Buckle S. H. Burbury Melvin Calvin Donald Campbell Sadi Carnot Anthony Cashmore Eric Chaisson Gregory Chaitin JeanPierre Changeux Rudolf Clausius Arthur Holly Compton John Conway Jerry Coyne John Cramer Francis Crick E. P. Culverwell Antonio Damasio Olivier Darrigol Charles Darwin Richard Dawkins Terrence Deacon Lüder Deecke Richard Dedekind Louis de Broglie Stanislas Dehaene Max Delbrück Abraham de Moivre Paul Dirac Hans Driesch John Eccles Arthur Stanley Eddington Gerald Edelman Paul Ehrenfest Manfred Eigen Albert Einstein George F. R. Ellis Hugh Everett, III Franz Exner Richard Feynman R. A. Fisher David Foster Joseph Fourier Philipp Frank Steven Frautschi Edward Fredkin Lila Gatlin Michael Gazzaniga Nicholas GeorgescuRoegen GianCarlo Ghirardi J. Willard Gibbs Nicolas Gisin Paul Glimcher Thomas Gold A. O. Gomes Brian Goodwin Joshua Greene Dirk ter Haar Jacques Hadamard Mark Hadley Patrick Haggard J. B. S. Haldane Stuart Hameroff Augustin Hamon Sam Harris Ralph Hartley Hyman Hartman JohnDylan Haynes Donald Hebb Martin Heisenberg Werner Heisenberg John Herschel Basil Hiley Art Hobson Jesper Hoffmeyer Don Howard William Stanley Jevons Roman Jakobson E. T. Jaynes Pascual Jordan Ruth E. Kastner Stuart Kauffman Martin J. Klein William R. Klemm Christof Koch Simon Kochen Hans Kornhuber Stephen Kosslyn Daniel Koshland Ladislav Kovàč Leopold Kronecker Rolf Landauer Alfred Landé PierreSimon Laplace David Layzer Joseph LeDoux Gilbert Lewis Benjamin Libet David Lindley Seth Lloyd Hendrik Lorentz Josef Loschmidt Ernst Mach Donald MacKay Henry Margenau Owen Maroney Humberto Maturana James Clerk Maxwell Ernst Mayr John McCarthy Warren McCulloch N. David Mermin George Miller Stanley Miller Ulrich Mohrhoff Jacques Monod Emmy Noether Alexander Oparin 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 Henry Quastler Adolphe Quételet Lord Rayleigh Jürgen Renn Juan Roederer Jerome Rothstein David Ruelle Tilman Sauer Jürgen Schmidhuber Erwin Schrödinger Aaron Schurger Sebastian Seung Thomas Sebeok Claude Shannon David Shiang Abner Shimony Herbert Simon Dean Keith Simonton B. F. Skinner Lee Smolin Ray Solomonoff Roger Sperry John Stachel Henry Stapp Tom Stonier Antoine Suarez Leo Szilard Max Tegmark Libb Thims William Thomson (Kelvin) Giulio Tononi Peter Tse Francisco Varela Vlatko Vedral Mikhail Volkenstein Heinz von Foerster Richard von Mises John von Neumann Jakob von Uexküll John B. Watson Daniel Wegner Steven Weinberg Paul A. Weiss Herman Weyl John Wheeler Wilhelm Wien Norbert Wiener Eugene Wigner E. O. Wilson Stephen Wolfram H. Dieter Zeh Ernst Zermelo Wojciech Zurek Konrad Zuse Fritz Zwicky Presentations Biosemiotics Free Will Mental Causation James Symposium 
Albert Einstein  Autobiography (Excerpts)
Comments on Quantum Mechanics
Before I enter upon the question of the completion of the
general theory of relativity, I must take a stand with reference
to the most successful physical theory of our period, viz., the
statistical quantum theory which, about twentyfive years ago,
took on a consistent logical form (Schrödinger, Heisenberg,
Dirac, Born). This is the only theory at present which permits
a unitary grasp of experiences concerning the quantum character
of micromechanical events.
Einstein's concern about nonlocality is that it may violate his principle of relativity.
This theory, on the one
hand, and the theory of relativity on the other, are both considered
correct in a certain sense, although their combination
has resisted all efforts up to now. This is probably the reason
why among contemporary theoretical physicists there exist entirely
differing opinions concerning the question as to how the
theoretical foundation of the physics of the future will appear.
Will it be a field theory; will it be in essence a statistical theory?
I shall briefly indicate my own thoughts on this point.
Physics is an attempt conceptually to grasp reality as it is thought independently of its being observed. In this sense one speaks of "physical reality." In prequantum physics there was no doubt as to how this was to be understood. In Newton's theory reality was determined by a material point in space and time; in Maxwell's theory, by the field in space and time. In quantum mechanics it is not so easily seen. If one asks: does a ψfunction of the quantum theory represent a real factual situation in the same sense in which this is the case of a material system of points or of an electromagnetic field, one hesitates to reply with a simple "yes" or "no"} why? What the ψfunction (at a definite time) asserts, is this: What is the probability for finding a definite physical magnitude q (or p) in a definitely given interval, if I measure it at time t? The probability is here to be viewed as an empirically determinable, and therefore certainly as a "real" quantity which I may determine if I create the same ψfunction very often and perform a q measurement each time. But what about the single measured value of q? Did the respective individual system have this qvalue even before the measurement? To this question there is no definite answer within the framework of the [existing] theory, since the measurement is a process which implies a finite disturbance of the system from the outside; it would therefore be thinkable that the system obtains a definite numerical value for q (or p), i.e., the measured numerical value, only through the measurement itself. For the further discussion I shall assume two physicists, A and B, who represent a different conception with reference to the real situation as described by the ψfunction.
According to Einstein's "objective reality," a system variable has a single determinate value between measurements. The only possible measurement is the actual measurement.
A. The individual system (before the measurement) has a
definite value of q (i.e., p) for all variables of the system,
and more specifically, that value which is determined by a
measurement of this variable. Proceeding from this conception,
he will state: The ψfunction is no exhaustive description
of the real situation of the system but an incomplete
description} it expresses only what we know on the
basis of former measurements concerning the system.
The Copenhagen Interpretation asserts that there are at every instant multiple possible values for a system variable. One of these becomes actual in a measurement.
B. The individual system (before the measurement) has no
definite value of q (i.e., p). The value of the measurement
only arises in cooperation with the unique probability which
is given to it in view of the ψfunction only through the
act of measurement itself. Proceeding from this conception,
he will (or, at least, he may) state: the ψfunction is an exhaustive
description of the real situation of the system.
We now present to these two physicists the following instance: There is to be a system which at the time t of our observation consists of two partial systems S_{1} and S_{2}, which at this time are spatially separated and (in the sense of the classical physics) are without significant reciprocity. The total system is to be completely described through a known ψfunction ψ_{12} in the sense of quantum mechanics. All quantum theoreticians now agree upon the following: If I make a complete measurement of S_{1}, I get from the results of the measurement and from ψ_{12} an entirely definite ψfunction ψ_{2} of the system ψ_{2}. The character of ψ_{2} then depends upon what kind of measurement I undertake on ψ_{1}. Now it appears to me that one may speak of the real factual situation of the partial system S_{2}. Of this real factual situation, we know to begin with, before the measurement of S_{1}, even less than we know of a system described by the ψfunction. But on one supposition we should, in my opinion, absolutely hold fast: the real factual situation of the system S_{2} is independent of what is done with the system S_{1}, which is spatially separated from the former.
If we measure the zcomponent of S_{1} electron spin, then the zcomponent of S_{2} must be found to be in the opposite direction, to conserve total spin = zero.
According to the type of measurement which
I make of S_{1}, I get, however, a very different ψ_{2} for the second
partial system ( Ψ_{2}, Ψ_{2}^{1},... ). Now, however, the real situation
of S_{2} must be independent of what happens to S_{1}. For the
same real situation of S_{2} it is possible therefore to find, according
to one's choice, different types of ψfunction.
Schrödinger says that ψ_{12} is a single wave function describing the two particles. A measurement anywhere collapses both particles into singleparticle Ψ_{2} and Ψ_{2}. Both are measured, e.g., in zdirection, conserving all properties for both.
(One can escape
from this conclusion only by either assuming that the measurement
of S_{1} ((telepathically)) changes the real situation of
S_{2} or by denying independent real situations as such to things
which are spatially separated from each other. Both alternatives
appear to me entirely unacceptable.)
If now the physicists, A and B, accept this consideration as valid, then B will have to give up his position that the ψfunction constitutes a complete description of a real factual situation. For in this case it would be impossible that two different types of ψfunctions could be coordinated with the identical factual situation of S_{2}. The statistical character of the present theory would then have to be a necessary consequence of the incompleteness of the description of the systems in quantum mechanics, and there would no longer exist any ground for the supposition that a future basis of physics must be based upon statistics.    It is my opinion that the contemporary quantum theory by means of certain definitely laid down basic concepts, which on the whole have been taken over from classical mechanics, constitutes an optimum formulation of the connections.
In his final remarks, Einstein said any future theory will probably incorporate quantum theory!
I believe,
however, that this theory offers no useful point of departure for
future development. This is the point at which my expectation
departs most widely from that of contemporary physicists. They
are convinced that it is impossible to account for the essential
aspects of quantum phenomena (apparently discontinuous and
temporally not determined changes of the situation of a system,
and at the same time corpuscular and undulatory qualities
of the elementary bodies of energy) by means of a theory which
describes the real state of things [objects] by continuous functions
of space for which differential equations are valid. They
are also of the opinion that in this way one can not understand
the atomic structure of matter and of radiation. They rather
expect that systems of differential equations, which could come
under consideration for such a theory, in any case would have
no solutions which would be regular (free from singularity)
everywhere in fourdimensional space. Above everything else,
however, they believe that the apparently discontinuous character
of elementary events can be described only by means of an
essentially statistical theory, in which the discontinuous changes
of the systems are taken into account by way of the continuous
changes of the probabilities of the possible states.
All of these remarks seem to me to be quite impressive. However, the question which is really determinative appears to me to be as follows: What can be attempted with some hope of success in view of the present situation of physical theory? At this point it is the experiences with the theory of gravitation which determine my expectations. These equations give, from my point of view, more warrant for the expectation to assert something precise than all other equations of physics. One may, for example, call on Maxwell's equations of empty space by way of comparison. These are formulations which coincide with the experiences of infinitely weak electromagnetic fields. This empirical origin already determines their linear form; it has, however, already been emphasized above that the true laws can not be linear. Such linear laws fulfill the superpositionprinciple for their solutions, but contain no assertions concerning the interaction of elementary bodies. The true laws can not be linear nor can they be derived from such. I have learned something else from the theory of gravitation: No ever so inclusive collection of empirical facts can ever lead to the setting up of such complicated equations. A theory can be tested by experience, but there is no way from experience to the setting up of a theory. Equations of such complexity as are the equations of the gravitational field can be found only through the discovery of a logically simple mathematical condition which determines the equations completely or [at least] almost completely. Once one has those sufficiently strong formal conditions, one requires only little knowledge of facts for the setting up of a theory; in the case of the equations of gravitation it is the fourdimensionality and the symmetric tensor as expression for the structure of space which, together with the invariance concerning the continuous transformationgroup, determine the equations almost completely. Our problem is that of finding the field equations for the total field. The desired structure must be a generalization of the symmetric tensor. The group must not be any narrower than that of the continuous transformations of coordinates...
A Brief Note on Completeness
Now it would of course be possible to object: If singularities
are permitted at the positions of the material points, what justification
is there for forbidding the occurrence of singularities
in the rest of space? This objection would be justified if the
equations of gravitation were to be considered as equations of
the total field. [Since this is not the case], however, one will
have to say that the field of a material particle may the less be
viewed as a pure gravitational field the closer one comes to
the position of the particle. If one had the fieldequation of the
total field, one would be compelled to demand that the particles
themselves would everywhere be describable as singularityfree
solutions of the completed fieldequations. Only then
would the general theory of relativity be a complete theory.
[So for Einstein, even his fourdimensional field theory is not yet complete. Completeness would eliminate possibilities in favor of a single determinate actuality; if only one possibility, there are no probabilities. All is certain. No new information is possible in the universe. Note that Einstein's views about quantum mechanics in 1949 were essentially unchanged from his views in 1930. See his explanation of how field theories came to be a part of our description of reality  alongside material particles  as a result of Maxwell's equations in his 1931 article "Maxwell's Influence on the Evolution of the Idea of Physical Reality." And Einstein arguably grew pessimistic about the possibilities for deterministic continuous field theories (by comparison with indeterministic and statistical discontinuous particle theories) in his later years:
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