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Philosophers
Mortimer Adler Rogers Albritton Alexander of Aphrodisias G.E.M.Anscombe Anselm Thomas Aquinas Aristotle David Armstrong Augustine J.L.Austin A.J.Ayer Alexander Bain Mark Balaguer William Belsham Henri Bergson Isaiah Berlin Bernard Berofsky Susanne Bobzien Emil du Bois-Reymond George Boole Émile Boutroux F.H.Bradley C.D.Broad C.A.Campbell Joseph Keim Campbell Carneades Ernst Cassirer Roderick Chisholm Chrysippus Cicero Randolph Clarke Samuel Clarke Anthony Collins Diodorus Cronus Donald Davidson Democritus Daniel Dennett René Descartes Richard Double Fred Dretske 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 Carl Ginet Nicholas St. John Green H.Paul Grice Ian Hacking Ishtiyaque Haji Stuart Hampshire W.F.R.Hardie R.M.Hare Georg W.F. Hegel Martin Heidegger R.E.Hobart Thomas Hobbes David Hodgson Shadsworth Hodgson Ted Honderich Pamela Huby David Hume Ferenc Huoranszki William James Lord Kames Robert Kane Immanuel Kant Tomis Kapitan William King Christine Korsgaard Keith Lehrer Gottfried Leibniz Leucippus Michael Levin C.I.Lewis David Lewis Peter Lipton John Locke Michael Lockwood John R. Lucas Lucretius James Martineau Hugh McCann Colin McGinn Michael McKenna Paul E. Meehl Alfred Mele John Stuart Mill Dickinson Miller G.E.Moore Thomas Nagel Friedrich Nietzsche P.H.Nowell-Smith Robert Nozick William of Ockham Timothy O'Connor David F. Pears Charles Sanders Peirce Derk Pereboom Steven Pinker Plato Karl Popper H.A.Prichard Hilary Putnam Willard van Orman Quine Frank Ramsey Ayn Rand Thomas Reid Charles Renouvier Nicholas Rescher C.W.Rietdijk Josiah Royce Bertrand Russell Paul Russell Gilbert Ryle T.M.Scanlon Moritz Schlick Arthur Schopenhauer John Searle Wilfrid Sellars Henry Sidgwick Walter Sinnott-Armstrong J.J.C.Smart Saul Smilansky Michael Smith L. Susan Stebbing George F. Stout Galen Strawson Peter Strawson Eleonore Stump Richard Taylor Kevin Timpe 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 Alfred North Whitehead David Widerker David Wiggins Bernard Williams Ludwig Wittgenstein Susan Wolf Scientists Michael Arbib Bernard Baars John S. Bell Charles Bennett Margaret Boden David Bohm Neils Bohr Ludwig Boltzmann Emile Borel Max Born Leon Brillouin Stephen Brush Henry Thomas Buckle Donald Campbell Anthony Cashmore Eric Chaisson Jean-Pierre Changeux Arthur Holly Compton John Conway E. H. Culverwell Charles Darwin Abraham de Moivre Paul Dirac John Eccles Arthur Stanley Eddington Paul Ehrenfest Albert Einstein Richard Feynman Joseph Fourier Michael Gazzaniga GianCarlo Ghirardi Nicolas Gisin Thomas Gold A.O.Gomes Joshua Greene Jacques Hadamard Patrick Haggard Augustin Hamon Sam Harris Martin Heisenberg Werner Heisenberg William Stanley Jevons Pascual Jordan Simon Kochen Stephen Kosslyn Rolf Landauer Alfred Landé Pierre-Simon Laplace David Layzer Benjamin Libet Josef Loschmidt Ernst Mach Henry Margenau James Clerk Maxwell Ernst Mayr Jacques Monod Roger Penrose Steven Pinker Max Planck Henri Poincaré Adolphe Quételet Jerome Rothstein Erwin Schrödinger Claude Shannon Herbert Simon Dean Keith Simonton B. F. Skinner Henry Stapp Antoine Suarez Leo Szilard William Thomson (Kelvin) John von Neumann Daniel Wegner Steven Weinberg Norbert Wiener Eugene Wigner E. O. Wilson Ernst Zermelo |
Schrödinger's Cat
Erwin Schrödinger's intention for his infamous cat-killing box was to discredit certain non-intuitive implications of quantum mechanics, of which his wave mechanics was the second formulation. Schrödinger's wave mechanics is more continuous mathematically, and apparently more deterministic, than Werner Heisenberg's matrix mechanics.
Albert Einstein originated the suggestion that the superposition of Schrödinger's wave functions implied that two different physical states could exist at the same time. This is correct for so-called "entangled" states (see the Einstein-Podolsky-Rosen experiment) , but it applies only for atomic level phenomena and over limited distances that preserve the coherence of the wave functions.
Einstein wrote to Schrödinger with the idea that the decay of a radioactive nucleus could be arranged to set off a large explosion. Since the moment of decay is unknown, Einstein argued that the superposition of decayed and undecayed nuclear states implies the superposition of an explosion and no explosion. Many years later, Richard Feyman made this a nuclear explosion! (What is it about some scientists?)
Einstein and Schrödinger did not like the fundamental randomness implied by quantum mechanics. They wanted to restore determinism to physics. Indeed Schrödinger's wave equation predicts a perfectly deterministic time evolution of the wave function. Randomness enters only when a measurement is made and the wave function "collapses."
Schrödinger devised a variation in which the random radioactive decay would kill a cat. Observers could not know what happened until the box is opened.
The details of the tasteless experiment include:
What do exist simultaneously in the macroscopic world are genuine alternative possibilities for future events. This is what bothered physicists like Einstein, Schrödinger, and Max Planck who wanted a return to deterministic physics. It also bothers determinist and compatibilist philosophers who have what William James calls an "antipathy to chance."
Until the information comes into existence, the future is indeterministic. Once information is macroscopically encoded, the past is determined.
What's wrong with this picture?
Quantum mechanics claims only that the time evolution of the Schrödinger wave functions for the probability amplitudes of nuclear decay accurately predict the proportion of nuclear decays that will occur in a given time interval.
The quantum probabilities simply predict the number of live and dead cats that will be observed in a large number of identical experiments
More specifically, quantum mechanics provides us with the accurate prediction that if this experiment is repeated many times (the SPCA would disapprove), half of the experiments will result in dead cats.
Note that this is a problem in epistemology. What knowledge is it that quantum physics provides?
If we open the box at the time T when there is a 50% probability of an alpha particle emission, the most a physicist can know is that there is a 50% chance that the radioactive decay will have occurred and the cat will be observed as dead or dying.
If the box were opened earlier, say at T/2, there is only a 25% chance that the cat has died. Schrödinger's superposition of live and dead cats would look like this.
If the box were opened later, say at 2T, there is only a 25% chance that the cat is still alive. Quantum mechanics is giving us only statistical information - knowledge about probabilities.
Schrödinger is simply wrong that the mixture of nuclear wave functions that accurately describes decay can be magnified to the macroscopic world to describe a similar mixture of live cat and dead cat wave functions and the simultaneous existence of live and dead cats.
The kind of coherent superposition of states needed to describe an atomic system as in a linear combination of states (see Paul Dirac's explanation of superposition using three polarizers) does not describe macroscopic systems.
How does information physics resolve the paradox?
As soon as the alpha particle sets off the avalanche of electrons in the Geiger counter (an irreversible event with a significant entropy increase), new information is created in the world.
For example, a simple pen chart recorder attached to the Geiger counter could record the time of decay. Notice that as usual in information creation, the energy expended by a recorder increases the entropy more than the increased information decreases it, thus satisfying the second law of thermodynamics.
Even without a mechanical recorder, the cat's death sets in motion biological processes that constitute an equivalent, if gruesome, recording. When a dead cat is the result, a sophisticated autopsy can provide an approximate time ,when Schrödinger's cat died because the cat's body is acting as an event recorder. There never is a superposition of live and dead cats.
The paradox points clearly to the Information Philosophy solution to the problem of measurement. Human observers are not required to make measurements. In this case, the cat is the observer.
In most physics measurements, the new information is captured by apparatus well before any physicist has a chance to read any dials or pointers that indicate what happened. Indeed, in today's high-energy particle interaction experiments, the data may be captured but not fully analyzed until many days or even months of computer processing establishes what was observed. In this case, the experimental apparatus is the observer.
And, in general, the universe is its own observer, able to record (and sometimes preserve) the information created.
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