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 Bois-Reymond Hilary Bok Laurence BonJour George Boole Émile Boutroux Daniel Boyd 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 Tom Clark 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 Tim Maudlin James Martineau Nicholas Maxwell 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.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 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 Marcello Barbieri Gregory Bateson Horace Barlow 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 Jean-Pierre 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 Bernard d'Espagnat 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 Benjamin Gal-Or Howard Gardner Lila Gatlin Michael Gazzaniga Nicholas Georgescu-Roegen GianCarlo Ghirardi J. Willard Gibbs James J. Gibson 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 Jeff Hawkins John-Dylan Haynes Donald Hebb Martin Heisenberg Werner Heisenberg John Herschel Basil Hiley Art Hobson Jesper Hoffmeyer Don Howard John H. Jackson William Stanley Jevons Roman Jakobson E. T. Jaynes Pascual Jordan Eric Kandel 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 Pierre-Simon Laplace Karl Lashley David Layzer Joseph LeDoux Gerald Lettvin Gilbert Lewis Benjamin Libet David Lindley Seth Lloyd Werner Loewenstein Hendrik Lorentz Josef Loschmidt Alfred Lotka Ernst Mach Donald MacKay Henry Margenau Owen Maroney David Marr Humberto Maturana James Clerk Maxwell Ernst Mayr John McCarthy Warren McCulloch N. David Mermin George Miller Stanley Miller Ulrich Mohrhoff Jacques Monod Vernon Mountcastle Emmy Noether Donald Norman Alexander Oparin Abraham Pais Howard Pattee Wolfgang Pauli Massimo Pauri Wilder Penfield Roger Penrose Steven Pinker Colin Pittendrigh Walter Pitts Max Planck Susan Pockett Henri Poincaré Daniel Pollen Ilya Prigogine Hans Primas Zenon Pylyshyn Henry Quastler Adolphe Quételet Pasco Rakic Nicolas Rashevsky Lord Rayleigh Frederick Reif Jürgen Renn Giacomo Rizzolati A.A. Roback Emil Roduner Juan Roederer Jerome Rothstein David Ruelle David Rumelhart Robert Sapolsky Tilman Sauer Ferdinand de Saussure Jürgen Schmidhuber Erwin Schrödinger Aaron Schurger Sebastian Seung Thomas Sebeok Franco Selleri Claude Shannon Charles Sherrington David Shiang Abner Shimony Herbert Simon Dean Keith Simonton Edmund Sinnott B. F. Skinner Lee Smolin Ray Solomonoff Roger Sperry John Stachel Henry Stapp Tom Stonier Antoine Suarez Leo Szilard Max Tegmark Teilhard de Chardin Libb Thims William Thomson (Kelvin) Richard Tolman Giulio Tononi Peter Tse Alan Turing C. S. Unnikrishnan Francisco Varela Vlatko Vedral Vladimir Vernadsky Mikhail Volkenstein Heinz von Foerster Richard von Mises John von Neumann Jakob von Uexküll C. H. Waddington John B. Watson Daniel Wegner Steven Weinberg Paul A. Weiss Herman Weyl John Wheeler Jeffrey Wicken Wilhelm Wien Norbert Wiener Eugene Wigner E. O. Wilson Günther Witzany Stephen Wolfram H. Dieter Zeh Semir Zeki Ernst Zermelo Wojciech Zurek Konrad Zuse Fritz Zwicky Presentations Biosemiotics Free Will Mental Causation James Symposium |
Arthur Holly Compton
In 1923, Arthur Holly Compton discovered that radiation (high-energy X-rays) could collide with electrons, exchanging energy with them as they were scattered. This was the first solid evidence for Albert Einstein's "light-quantum hypothesis," proposed in 1905. Sadly, he did not think that his work supported Einstein's hypothesis, which was not fully accepted until after the "founders" of quantum mechanics reluctantly accepted it.
The "Compton effect" provided real support for the wave-particle duality of radiation (which Einstein had proposed as early as 1909) and matter (proposed by Louis de Broglie in 1924. Compton himself initially denied that his experiment supported Einstein's idea of light quanta (later called photons). Compton was awarded the Nobel Prize in Physics in 1927 for this "Compton effect," the year that Werner Heisenberg discovered quantum indeterminacy.
Compton scattering is "inelastic," because the energy hν (or hc / λ) of the incident photon is different from that of the scattered photon hν' (or hc / λ').
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λ' - λ = ( h/mc ) (1 - cosθ )
The wavelength shift λ' - λ varies from nothing to twice h/mc, which is known as the Compton wavelength. For a derivation, see Compton scattering on Wikipedia.
Wolfgang Pauli objected to Compton's analysis. A "free" electron cannot scatter an electron, he argued. A proper analysis, confirmed by Einstein and Ehrenfest the same year (1923), is that scattering should be interpreted as a two-step process, the absorption of a photon of energy hν followed by the emission of a directed photon hν', where the momentum of the photon hν' / c balances the momentum of the scattered electron mv.
In later years, Compton championed 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. He attached sticks of dynamite to his amplifier, anticipating Schrodinger's Cat
Compton argued against biologists who claimed that cells were so large that they behave with statistical regularity, leaving no room for chance.
In Science1 magazine in 1931, Compton published a short note, "The uncertainty principle and free will."
In his very excellent presentation of the uncertainty principle, published in a recent number of SCIENCE,2 Professor Darwin concludes with a comment regarding the significance of this principle in connection with the problem of "free will," which should not be allowed to pass without comment. He may be correct in his view that "the question is a philosophic one outside the thought of physics." Yet the reason that he offers to show that the uncertainty principle does not help to free us from the bonds of determinism is inadequate. Darwin's argument is that "physical theory confidently predicts that the millions of millions of electrons concerned in matter-in-bulk will behave .. . regularly, and that to find a case of noticeable departure from the average we should have to wait for a period of time quite fantastically longer than the estimated age of the universe." He apparently overlooks the fact that there is a type of large-scale event which is erratic because of the very irregularities with which the uncertainty principle is concerned. I refer to those events which depend at some stage upon the outcome of a small-scale event. As a purely physical example, one might pass a ray of light through a pair of slits which will so diffract it that there is an equal chance for a photon to enter either of two photoelectric cells. By means of suitable amplifiers it may be arranged that if the first photon enters cell A, a stick of dynamite will be exploded (or any other large-scale event performed); if the first photon enters cell B a switch will be opened which will prevent the dynamite from being exploded. What then will be the effect of passing the ray of light through the slits? The chances are even whether or not the explosion will occur. That is, the result is unpredictable from the physical conditions. Professor Ralph Lillie has pointed out3 that the nervous system of a living organism likewise acts as an amplifier, such that the actions of the organism depend upon events on so small a scale that they are appreciably subject to Heisenberg uncertainty. This implies that the actions of a living organism can not be predicted definitely on the basis of its physical conditions. Of course this does not necessarily mean that the living organism is free to determine its own actions. The uncertainty involved may merely correspond to the organism's lack of skill. Yet it does mean that living organisms are not subject to physical determinism of the kind indicated by Darwin.
In his 1931 Terry Lectures at Yale and the 1935 book, The Freedom of Man, and again in the 1940 book The Human Meaning of Science, Compton developed this idea of the amplifier and added a daemon
Imagine a faint ray of light passing through a tiny hole, which then spreads by diffraction into a broad beam. In the path of this broad beam we may place two photoelectric cells, A and B, each connected with an amplifier. These will be made so sensitive that the entrance of a single photon, i.e., particle of light, into either cell is recorded. A shutter in the path of the light ray remains open long enough to transmit a single photon. Into which cell will the photon fall ?
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Compton's Demon
According to modern physics, we thus live in a world of chance.
We might connect one of our amplifiers with an electrical device which will explode a stick of dynamite, and the other amplifier with a switch which will open the circuit. Now what will happen when the shutter transmits a photon? If it enters one cell the dynamite will explode, and the apparatus will be blown to bits. If the photon enters the other cell, the switch will be pulled and the apparatus is no longer in danger. Both events are equally probable. Similarly any event which depends at some stage upon the outcome of a small-scale event is essentially unpredictable on the basis of previous history.
Compton's Demon
A daemon controlling the shutter might be conscious of their qualities. The daemon controlling the shutter might consider a photon which would enter the photoelectric cell that would result in exploding the dynamite a "bad" photon, and one which would enter the cell where it would prevent the catastrophe a "good" photon. Being directly conscious, of these nonphysical characteristics which will determine their direction, the daemon may then close the shutter to all approaching "bad" photons until a "good" photon has passed through and saved the day. Has the daemon in this way contravened any physical laws?
The point is that the event under consideration is really an individual act, to which, since it can be performed but once, the laws of statistics do not apply. Whether the switch is opened or the dynamite exploded by the first photon, in either case the experiment is complete. This corresponds closely to human action, considered in the light of habit. An experiment involving deliberation can be performed on a person only once; for afterwards his condition is not the same. Habit will now enter into the determination of his action. Thus deliberate actions likewise are individual events, and are not therefore predictable from laws of probability. Faced by the necessity for an individual decision, all one's physiological structure, his environment, and previous history determine what Warren Weaver describes as a "spectrum of action probability," within which "spectrum" it is possible for any action to be chosen. There will be greater probability for certain modes of action than others; but these probabilities do not specify the choice of the individual act.
It would be easy to outline a closely parallel scheme whereby consciousness could select the desirable brain current, even though the undesirable one might be equally probable from statistical considerations, thus leading to the performance of the desirable act rather than its alternative. It is not necessary to elaborate any particular brain mechanism for performing the selection, for the example just given shows that it is possible to select one of a number of physically possible acts without violating or modifying any physical law. In this way the determination of a man's actions by his will is, I believe, shown to be consistent with the principles of physics is they are now understood.
In the late 1950's Compton revisited these ideas in an Atlantic Monthly2 article.
TODAY'S PHYSICS HAS ROOM FOR FREEDOM The fault in the theory of mechanical determinism was not discovered until about thirty years ago. It was then found that the laws of Newton do not describe what happens to the atoms of which matter is composed. It was found instead that the properties of these atoms are such that prediction of what happens to them can only be made within certain limits. The amount of this uncertainty is fixed in the very nature of matter itself. On my laboratory desk I have two simple devices. The first is a freely swinging pendulum. Its beats are regular, repeating themselves uniformly at equally timed intervals. This pendulum is typical of the objects with which the physicists of Laplace's time were familiar. The second device is a Geiger counter, responding with a click to each ray that enters it from a nearby capsule of radium. The clicks occur at irregular intervals. It may be that about 100,000 clicks will occur each day. But several seconds may pass without any clicks, while during the next second two or three will occur. Whether in the following second a ray will be counted cannot be foretold. This device responds to the action of individual atoms. Nothing of this kind was known until near the end of the nineteenth century. The pendulum swings back and forth according to a precise law. The clicks of the counter occur at random. If such a pair of experiments had been known in Newton's time, it is doubtful whether the idea that events must happen according to precise laws would ever have been formulated. It would have been evident that only under special conditions can one predict definitely what will occur. These conditions are that what we observe shall be the average of a very large number of individual events. Consider what happens when an atom of radium disintegrates. This event can be recorded by such an instrument as a Geiger counter. The average life of a radium atom is about two thousand years. That is, in any one year from the time the radium atom is first formed, the chance is about one in two thousand that it will disintegrate. It may disintegrate during the present year, but there is roughly one chance in eight that it will remain unchanged six thousand years from now. What the physicists of the twentieth century have shown is that there is no kind of observation that can be made which will tell in what particular year the radium atom will disintegrate. If the atom was in existence six thousand years ago, it was then identical with what it is today. The possibility of disintegration has always been there. Whether it will in fact disintegrate in this particular year is, as far as physics is concerned, a matter of chance—a likelihood of one in two thousand. There is something comparable with this example in the case of every atomic or molecular event. Thus when light falls on a photographic emulsion, under its stimulus there is a certain chance that any particular grain of silver bromide will be changed so that it can be developed to silver. With a given light exposure, this chance may be one in ten, so that on the average about one-tenth of the grains will be transformed. But which particular grain will thus be changed is by the very nature of the process unpredictable. These examples illustrate a point of critical importance in today's interpretation of the physical world. Nature provides nothing whose precise measurement would make possible the exact prediction of an atomic event. On this limitation that nature sets on our knowledge both experiment and theory are agreed. The average of large numbers of atomic events does indeed follow exact laws. In a large lump of radium in one year almost precisely one part in two thousand will have disintegrated. In a square inch of the photographic emulsion, almost exactly one tenth of the silver bromide, after the light exposure, will be reduced to silver. The number of atoms in my laboratory pendulum is huge, roughly a million billion billion. The statistics of the action of such numbers of particles are very precise — even more so when one observes the moon's regular revolution around the earth. Not all large-scale events, however, are thus precisely predictable. If at any stage the big event depends on some atomic process, the end result shares in the uncertainty of this small event. A typical large-scale event of this kind is the explosion of an atomic bomb. Such an explosion is triggered by the appearance of a neutron during the particular fraction of a microsecond when the chain reaction must be started. But this neutron comes from a radioactive process, which cannot be precisely foretold. If the chances were only even that during the critical time interval a neutron would appear, there would likewise be only even chances that the bomb would explode. In order that the bomb shall be sure to fire, it is arranged that during the critical time interval some thousands of neutrons will probably be present. Thus the chance of failure becomes practically zero. Now most of life's processes are like such an atomic chain reaction. They begin with some very small event and grow. They are in fact chemical chain reactions. What starts these reactions in living organisms is not known in detail, but we do know that the beginning is on a molecular, or in certain cases on a submolecular, scale. Thus when I touch something hot and quickly withdraw my finger, the nerve currents that stimulate the muscular contractions are themselves small-scale reactions. The events that are involved when choices and decisions are made have so far defied physical identification; but in all probability they are reactions involving such small numbers of particles that definite prediction on a physical basis is by the nature of things impossible. As far as physics is concerned, a person's actions which we think of as free would thus appear to occur simply according to the rules of chance. We find nevertheless that in practical life such actions can be predicted when we know the person's intentions. This implies that something additional to the physical phenomena is involved. What we actually note is that in such a case the person has a kind of firsthand knowledge of his own situation that is not gained from any physical observation. This additional knowledge is the awareness of his own intentions. When he acts he feels that he is acting freely. That is, his action corresponds with what he intends. Thus, for example, I told the editor that I would have this article prepared in time for the present issue of the Atlantic. How could I confidently give him this assurance? Was it on the basis of physical data? Only to the extent that it appeared physically possible that the article could be prepared in time. As a physical event an immense number of other possibilities were equally likely to occur. Was not the primary basis of my prediction rather that I knew my own intention? And this I knew, not through any kind of observation, but by an inner awareness; not through a deduction from data, but because of a choice that I was making from among the various possibilities before me. After thousands of years of discussion among scientists and philosophers, the place of free acts in a world that follows physical law has thus become clarified. There is nothing known to physics that is inconsistent with a person's exercising freedom.
Compton's work was closely read by Karl Popper, who gave the first Arthur Holly Compton Memorial Lecture in 1965. Can we read Compton's remarks above and find the two-stage model of free will advocated by Popper? Compton says:
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 is himself adding a factor not supplied by the [random] physical conditions and is thus himself determining what will occur.We can see Compton's quantum randomness contributing to the "range of possible events," which he says Warren Weaver called the "spectrum of action probability," within which "spectrum" it is possible for any action to be chosen. For Teachers
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