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 BoisReymond 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. 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Klein Simon Kochen Hans Kornhuber Stephen Kosslyn Ladislav Kovàč Rolf Landauer Alfred Landé PierreSimon Laplace David Layzer Benjamin Libet Seth Lloyd Hendrik Lorentz Josef Loschmidt Ernst Mach Donald MacKay Henry Margenau James Clerk Maxwell Ernst Mayr John McCarthy 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 Max Tegmark 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 Fritz Zwicky Presentations Biosemiotics Free Will Mental Causation James Symposium 
Rolf Landauer
Rolf Landauer extended the ideas of John von Neumann and Leo Szilard, who, along with many other physicists, had connected a physical measurement with thermodynamical irreversibility, that is to say a dissipation of energy and increase in entropy.
The increase in entropy (or decrease in available negentropy, as Leon Brillouin put it), must equal or exceed the increase in information acquired in the measurement, in order to satisfy the second law of thermodynamics. Landauer studied the special case of digital computers which read and write information as part of their calculations, but have extremely small or even zero energy dissipation, especially in computations that are in principle logically reversible. Such calculations must include their input values along with their outputs, in order to allow the computer to step backward through the calculation and restore the original state. Some of Landauer's thinking assumes completely deterministic classical mechanics, in which trajectories are a known function of the forces and initial conditions. This is of course an idealization not realizable in the physical world, but can be approximated by large classical objects such as billiard balls (cf., the digital physics of Ed Fredkin). Since the introduction of quantum mechanics and the realization that we live in a universe with irreducible background noise (the cosmic microwave background radiation with a temperature of about 3°K), noise and entropyfree deterministic systems are the idealizations of mathematicians, philosophers, and computer scientists. Indeed, a major difference between Bell Labs and IBM can perhaps be seen in the observation that Bell Labs has learned to communicate signals in the presence of noise and discovered the ultimate cosmic source of entropic noise, where IBM has excelled at eliminating the effects of noise from our best computers. At Bell Labs, Claude Shannon developed information theory, with its fundamental connection to Ludwig Boltzmann's entropy. And there Arno Penzias and Robert Wilson discovered the cosmic background radiation. At IBM, Landauer and his colleague Charles Bennett are famous for logically and thermodynamically reversible computing, which ignores the effects of noise and entropy until the computer bits of information must be erased (Landauer's Principle).
Note that Landauer's work is mostly logical and does not discuss the underlying physics of irreversibility.
Logically irreversible devices do not remember the inputs. They are thus oneway processes that lose information. Logically irreversible devices are necessary to computing, says Landauer, and logical irreversibility implies physical irreversibility.
We shall call a device logically irreversible if the output of a device does not uniquely define the inputs. We believe that devices exhibiting logical irreversibility are essential to computing. Logical irreversibility, we believe, in turn implies physical irreversibility, and the latter is accompanied by dissipative effects.Landauer then goes on to describe classes of computers that can be considered logically reversible. They must not only save their inputs, but also the results of all intermediate logical steps, to provide the necessary information to perform all the steps backwards and restore the original conditions. In particular, he says, no information can be erased. That the entropy must go up on erasure is known as Landauer's Principle. Landauer's colleague at IBM, Charles Bennett, carries on the investigations of logically reversible computing. Landauer describes two examples of logically reversible machines. [The first is] a particular class of computers, namely those using logical functions of only one or two variables. After a machine cycle each of our N binary elements is a function of the state of at most two of the binary elements before the machine cycle. Now assume that the computer is logically reversible. Then the machine cycle maps the 2^{N} possible initial states of the machine onto the same space of 2^{N} states, rather than just a subspace thereof. In the 2^{N} possible states each bit has a ONE and a ZERO appearing with equal frequency. Hence the reversible computer can utilize only those truth functions whose truth table exhibits equal numbers of ONES and ZEROS. The admissible truth functions then are the identity and negation, the EXCLUSIVE OR and its negation. These, however, are not a complete set' and do not permit a synthesis of all other truth functions. For Teachers
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