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The game of prediction and retrodiction A constructivist perspective on the notion of time in science Radical Constructivism (Ernst von Glasersfeld): 1: Knowledge is learnt through active construction by the knower,
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The game of prediction and retrodiction A constructivist perspective on the notion of time in science Radical Constructivism (Ernst von Glasersfeld): 1: Knowledge is learnt through active construction by the knower, not through passive "reception and storage" of data in the mind. 2: The purpose of knowledge construction is to organise the experiential world of the knower – it does not (and cannot) reflect any "objective truth" about the world.
Prediction: Eclipses and weather – modern magic..? Science: description of observed regularities in the world ↓ controlling the future Prediction and retrodiction: require a theoretical framework
A perspective on time • classical physics - empty stage (absolute time) • special relativity - space-time (relativistic time) • general relativity - space-time (dynamic time) • quantum physics - stochastic location in time Space and time: experiential categories (Kant) Object permanence: displacements in time and space Prediction / retrodiction: Time
The timeline Past------------------------------> Now------------------------------->Future “already happened" “happening" “not yet happened“ | | looks back in time<-------the learner -------->looks forward in time | | memory <------------ consciousness ------------> expectation | | retrodiction <-------------- science ---------------------> prediction | | history <---------- the scientist / teacher ---------> scenario
Determinism future totally determined by past: vs free will (the world is pre-set) solipsism:vs shared experiential world (the world has no effect) Both rejected: logically irrefutable, but existentially irrelevant..! Radical constructivism: we have freedom to act Construction of knowledge: interplay between free will and nature unfolding in time
Motion in Time 1: stationary observer – moving events Past ------------------------------------|Now|------------------------------------ Future … o o o o o… …o… … o o o o o … 2: moving observer – stationary events Past ------------------------------------|Now--------------------------------- Future … o o o o o … …o… …o o o o o … 3: timelike worldline – point events Past--------------------------------- |Now| -------------------------------- Future … o o o o o … …o… … o o o o o …
Time windowsin the perspective of prediction and retrodiction: long short short long range range range range Past<-----------------|---------------|Now| --------------|----------------->Future | | | | (inferred) (experienced) (verifiable) (unverifiable)
Retrodiction and Prediction tp tn tf Past -------------|-------------- |Now| ---------------|--------Future | | | | ? | ? | (past <--- (present ---> (future state) state state) + theory)
Classical physics Solar system orbits(eclipses):prediction, and retrodiction Sliding on a horizontal plane: prediction, but no retrodiction __________________________________________________ Geophysics– continental drift: hypothesising the past (weak retrodiction) Weather– chaotic systems: forecasting the future (weak prediction) Cosmology – the beginning and end of the Universe, prediction and retrodiction on a grand scale!
Quantumphysics Dynamics described by Schrödinger equation: time evolution ofprobability distribution Predict probable future states, not the actual state Collapse of the wave function: one state is "realised", the others "disappear"! State selection is probabilistic: frequency ~ probability, Example – beta decay: how does the atom "know"..?
Probability: In classical physics, a "makeshift strategy": tossed coin, statistical mechanics. In quantum physics, not so: no hidden variables (Einstein) (Bell inequalities, Aspect experiment…) Hence: no prediction, and no retrodiction!
Predictedknowledge - epistemic status (radical constructivism) Constructed in the Now based on theory, on present observations, and (possibly) on additional assumptions In the short-range future window: verifiable by observation ---> support of the theory In the long-range future window: verification not possible Construction of knowledge: compatible with present-day theory and experience
Retrodiction – a historical perspective Retrospective sciences: plausible hypotheses about what may have happened in the past Using: data observed in the present. Past <--> present: must then be compatible.
Retrospective sciences: Social sciences: psychology, sociology, political science, law, … History: the chronicling of human society Evolutionary biology: living organisms Geological sciences: geology, geophysics,… Cosmology: the past Universe
Retrodictedknowledge - epistemic status (radical constructivism) Prediction: the future is indeterminate Retrodiction: the past is fixed | ? True knowledge of the past: what "really happened"…? Short-range time window: memory, written records, legal proceedings, … Problematic: memory failure, false testimony, filtering, …
We construct our own past (short-range and long-range) in the present Now, by: recollections (of past events) perceptions (of present events) recorded information application of theory in a continual process of reflection: filtering selection interpretation (analysis)
Conclusion: a relativist epistemology Knowledge (of future and past) is constructed, based on: • present-day perceptions / reflections, • available recorded information • choice of theoretical framework, Must be viable in this context. No conception of "true knowledge" of the past! Meaningless to ask: "what really happened back then"..!
