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Concepts
Every concept examined, from the second law of thermodynamics to the frame problem.
logicAbduction and inference to the best explanationAbduction is reasoning from an effect to a cause that would explain it. A patient has a fever; pneumonia would account fcontrolAdaptive controlAdaptive control is the branch of control engineering in which the controller changes its own parameters while running. economicsAdverse selection and stale pricingIn any exchange where one side knows more, the better-informed party chooses when to trade. That choice is not neutral: historyAir traffic controlAir traffic control is the practice of maintaining a continuously updated positional belief about every aircraft in a voinformationAlgorithmic randomness and incompressibilityKolmogorov complexity measures a string by the length of the shortest program that outputs it. Most strings have no shorbiologyAllostasisAllostasis is regulation by anticipation. Classical homeostasis describes a system holding a variable near a set point bcomputationAmortised complexityAmortised complexity is a way of pricing an operation by spreading its cost over the whole sequence of operations it belcognitionAnchoringAnchoring is the tendency for a first number, first hypothesis or first framing to exert lasting pull on later judgementbiologyAntigenic driftAntigenic drift is the slow accumulation of point mutations in the surface proteins of a pathogen — for influenza, haemacomputationAnytime algorithmsAn anytime algorithm is one that holds a valid answer at every moment of its execution and refines that answer if allowecontrolAshby's law of requisite varietyW. Ross Ashby's law of requisite variety states that only variety can destroy variety. Variety is the count of distinguicognitionAttention as a scarce resourceAttention is the fraction of perceptual and cognitive capacity a person can direct at one thing at one time. It is finitbiologyAutopoiesisAutopoiesis names what distinguishes a living cell from a crystal or a clock: its components are produced by a network ocomputationBackpressureBackpressure is the signal a slow consumer sends upstream to a fast producer: stop, or slow down, or I will drop what yocontrolBang-bang control and chatteringBang-bang control drives an actuator to its extremes and nothing between: full on, full off, switching at moments chosencomputationBatch versus stream processingBatch processing collects records into a bounded set, then computes over the whole set at once: payroll runs at month enepistemologyBayesian updatingBayesian updating is a rule for changing your mind by degree. You hold a belief with a strength — a prior probability. EeconomicsBounded rationality and satisficingHerbert Simon's correction to the economics of perfect choice. Real agents cannot enumerate all options, price all consephysicsBrownian motionIn 1827 the botanist Robert Brown watched pollen grains in water jitter without cause. The jitter is molecular bombardmecomputationCache invalidationA cache is a fast copy of something slow to fetch. Caches are easy to fill and hard to keep honest. The difficulty is nostatisticsCalibration and proper scoring rulesA forecaster is calibrated when events assigned 70 per cent probability happen about 70 per cent of the time. CalibratiomathematicsCantor's diagonal argumentIn 1891 Georg Cantor showed that no list of infinite binary sequences can contain them all. Given any enumeration, read metaphysicsCausal inference and interventionsCausal inference asks what would happen if the world were pushed, not merely what tends to accompany what. Observation ycognitionChange blindnessChange blindness is the failure to notice a large alteration in a scene when the alteration coincides with a disruption statisticsChange-point detectionChange-point detection is the branch of statistics concerned with locating the moment a data-generating process altered:informationChannel capacityChannel capacity is the maximum rate at which information can be sent through a noisy channel with arbitrarily small errbiologyCircadian entrainmentNearly every organism carries an internal oscillator with a period close to, but not exactly, twenty-four hours. In humacognitionCognitive load and triageCognitive load is the demand a task places on working memory, which holds perhaps four to seven chunks at once and degralanguageCommon ground in conversationCommon ground is the body of belief two speakers treat as mutually held: known to both, and known to be known. It is notmathematicsCompactnessA space is compact when every collection of open sets covering it contains a finite sub-collection that also covers it. statisticsConcept drift detectionConcept drift is the change over time in the statistical relationship a predictive model was fitted to: the joint districognitionConfirmation biasConfirmation bias is the tendency to seek, weight and remember evidence that fits a belief already held, while under-samstatisticsConjugate updating and sufficient statisticsIn Bayesian statistics, a prior is conjugate to a likelihood when updating it on new data returns a distribution of the physicsConservation laws and Noether's theoremIn 1918 Emmy Noether proved that every continuous symmetry of a physical system's action corresponds to a conserved quanphilosophy of scienceConsilience of inductionsWilliam Whewell's term for a particular kind of evidential force. An induction drawn from one class of facts is tested acomputationContinuous integrationContinuous integration is a discipline of software production: every developer merges work into the shared mainline manycontrolControllabilityIn control theory, a system is controllable if some sequence of inputs can drive it from any starting state to any desirmetaphysicsCounterfactual reasoningA counterfactual is a claim about what would have happened had things gone otherwise: had the valve stayed shut, had theeconomicsCreative destructionCreative destruction is Joseph Schumpeter's name for the process by which economic growth destroys the arrangements thatcontrolDead time and transport delayDead time is the interval between a change at a system's input and the first observable movement at its output. It is noepistemologyDefeasible reasoningDefeasible reasoning is inference that licenses full commitment to a conclusion while leaving that conclusion open to wilanguageDeixisDeixis is the property of expressions whose reference cannot be fixed without knowing the circumstances of their utteraneconomicsDepreciation and amortisation of knowledgeIn accounting, a durable asset is not expensed when bought; its cost is spread across the years it earns. Physical assetphysicsDetailed balance and irreversibilityDetailed balance is the condition that, in true equilibrium, every elementary transition and its reverse occur at exactlstatisticsDistribution shift and covariate driftDistribution shift is the condition in which the data a model is tested on is drawn from a different joint distribution epistemologyDogmatism and belief perseveranceBelief perseverance is the tendency to keep holding a proposition after the evidence that produced it has been withdrawnhistoryDouble-entry bookkeepingDouble-entry bookkeeping records every transaction twice: as a debit in one account and a matching credit in another. ThsystemsDrift and Lyapunov stabilityA system is Lyapunov stable if small disturbances stay small: perturb the state a little and the trajectory stays near tmetaphysicsDuration and BergsonHenri Bergson distinguished two times. There is the time of clocks and graphs: a line of interchangeable instants, spatilogicDynamic epistemic logicDynamic epistemic logic is the branch of modal logic in which the semantics describe changes to information, not merely systemsEmergence and downward causationEmergence names the appearance of regularities at one level of organisation that are not stated in the laws governing thmetaphysicsEmergent noveltyEmergent novelty is the thesis that the world produces genuinely new kinds of thing: properties, entities and laws that physicsEntropy of mixingWhen two gases at the same temperature and pressure are allowed to interpenetrate, the total entropy rises even though nhistoryEpidemiological surveillance since John SnowEpidemiological surveillance is the continuous, systematic collection of health events, tied to place and time, used to epistemologyEpistemic humility and calibrationEpistemic humility is the disposition to hold beliefs no more firmly than the evidence warrants. Calibration is its measepistemologyEpistemic luckEpistemic luck is the gap between being right and knowing. A belief can be true, and even well justified, yet owe its trphysicsErgodicity and time averagesErgodicity is a property of a system, not a fact about nature. A system is ergodic when the average of a quantity taken informationError-correcting codesAn error-correcting code adds structured redundancy to a message so that a corrupted copy can be repaired without askingcomputationEvent sourcingEvent sourcing is a way of storing data in which the durable record is not the current state but the ordered sequence ofcomputationEventual consistencyEventual consistency is a guarantee offered by distributed data stores: if writes stop, every replica will converge on tepistemologyEvidentialismEvidentialism holds that whether a belief is justified depends wholly on the evidence the believer possesses at that mombiologyEvolvabilityEvolvability is a lineage's capacity to generate useful heritable variation — not its current fitness, but its ability tstatisticsExchangeability and de FinettiA sequence of observations is exchangeable if its joint probability is unchanged by any reordering: the third draw and tcognitionExpertise and deliberate practiceDeliberate practice is the specific kind of effort that produces expertise: tasks chosen just past current ability, perfbiologyExtinction debtExtinction debt is the number of species that a habitat is already committed to losing but has not yet lost. Cut a foresstatisticsExtreme value theoryExtreme value theory is the branch of statistics concerned with the behaviour of maxima and rare exceedances rather thanepistemologyFallibilismFallibilism is the position that no belief is immune to revision. Not that all beliefs are equally doubtful, nor that knphilosophy of scienceFalsifiabilityFalsifiability is Karl Popper's criterion for demarcating empirical science from other kinds of talk. A theory counts assystemsFeedback loops and system archetypesSystems thinking holds that structure produces behaviour, and that structure is made of loops. A balancing loop resists biologyFitness landscapes and their movementSewall Wright's 1932 image: arrange all possible genotypes on a surface whose height is reproductive success. PopulationmathematicsFixed points and iterationA fixed point of a map is an input the map returns unchanged: f(x) = x. Iteration means applying the map repeatedly, feephysicsFree energy and dissipative structuresThermodynamics distinguishes total energy from the portion available to do work: free energy. Systems held far from equicontrolGain schedulingGain scheduling is a way to control a system whose behaviour changes with its operating point. Engineers linearise the pcomputationGarbage collectionGarbage collection is the automatic reclamation of memory a running program can no longer reach. The collector traces frmathematicsGodel incompletenessIn 1931 Kurt Gödel proved that any consistent formal system strong enough to express basic arithmetic, and whose axioms statisticsGoodhart's lawCharles Goodhart observed in 1975 that statistical regularities relied upon for control tend to collapse once pressure imetaphysicsGranger causalityA statistical criterion proposed by the econometrician Clive Granger. One series Granger-causes another if the past of teconomicsHayek and the use of knowledge in societyIn 1945 Friedrich Hayek asked how an economy allocates resources when the knowledge needed is scattered across millions metaphysicsHeraclitus and the riverHeraclitus of Ephesus, writing around 500 BC, held that things persist only by changing. The surviving fragments say youepistemologyHigher-order evidenceFirst-order evidence bears on a question: the barometer falls, so rain is likely. Higher-order evidence bears on your habiologyHomeorhesisHomeorhesis is the stabilisation of a trajectory rather than a value. Homeostasis defends a set point: body temperature biologyHomeostasisHomeostasis is the maintenance of an internal state within survivable bounds by continuous corrective action. Claude BerphysicsHysteresisHysteresis is the lag between cause and effect in systems whose response depends on history. Magnetise iron, then removecomputationIdempotence and replayAn operation is idempotent when applying it twice leaves the same result as applying it once. Setting a value to 7 is idbiologyImmune memory and affinity maturationVertebrate adaptive immunity keeps a library of hypotheses about what might harm the body. B cells display receptors gencognitionInattentional blindnessInattentional blindness is the failure to see a fully visible object because attention was engaged elsewhere. The eyes fcomputationIncremental computationIncremental computation is the discipline of producing an updated answer from a small change to the input by doing work languageIndexicalityIndexicals are expressions whose reference shifts with the circumstances of utterance: 'I', 'you', 'here', 'now', 'todayeconomicsInformation asymmetryInformation asymmetry describes a transaction in which one party knows something material that the other does not. AkerlinformationInformation bottleneckThe information bottleneck, formulated by Tishby, Pereira and Bialek in 1999, asks a precise question: given an input X philosophy of scienceInstrumentalism versus realismTwo answers to what a scientific theory is for. Realism says a successful theory describes what exists: electrons are reeconomicsInsurance and the pricing of tail riskInsurance prices a promise against events that mostly do not happen. The premium is an estimate of expected loss plus loepistemologyInternalism versus externalism about justificationTwo rival answers to a single question: what makes a belief justified? Internalism says justification is fixed by what iepistemologyJustified true belief and the Gettier problemSince Plato, knowledge was analysed as justified true belief: you know a proposition if it is true, you believe it, and controlKalman filteringA recursive estimator, published by Rudolf Kálmán in 1960, for tracking a hidden state from noisy measurements. It carriepistemologyKnowledge as a standing state versus an actIn ordinary usage, "know" behaves as a state verb, not an event verb. You can be learning, forgetting or checking; you cinformationKolmogorov complexityKolmogorov complexity measures the information in an object by the length of the shortest program that outputs it. A strphysicsLandauer's principleIn 1961 Rolf Landauer showed that logical irreversibility carries a thermodynamic cost. Erasing one bit of information isystemsLatency as an architectural parameterIn systems engineering, latency is the interval between an event happening and a system being able to act on knowledge ocognitionLearned helplessness and stale models of controlIn 1967 Steven Maier and Martin Seligman found that animals given inescapable shocks later failed to escape when escape mathematicsLimits and the concept of a supremumA sequence of numbers may approach a value it never reaches: 0.9, 0.99, 0.999 climbs towards 1. The supremum is the leashistoryLloyd's of London and continuous risk revisionLloyd's of London is not an insurance company but a marketplace, grown from Edward Lloyd's coffee house on Tower Street physicsMaxwell's demonIn 1867 James Clerk Maxwell imagined a tiny being stationed at a shutter between two gas chambers. It watches individualcognitionMetacognitionMetacognition is cognition about cognition: the monitoring and control of one's own knowing. Psychologists split it in tinformationMinimum description lengthMinimum description length treats learning as compression. A model is good to the extent that describing the model, thenmathematicsMonotone convergenceIn the real numbers, a sequence that never decreases and never exceeds some fixed ceiling must converge — and it convergeconomicsMoral hazard and unobserved actionMoral hazard names a specific failure: one party takes an action the other cannot observe, and the unobserved action is informationMutual information decayMutual information measures how much knowing one variable tells you about another, in bits. When a system evolves and yobiologyNatural selection as an online algorithmNatural selection does not compute an optimum in advance. Each generation, a population's variants meet an environment acontrolNegative feedbackNegative feedback is the practice of measuring what a system actually does, comparing it to what was wanted, and drivingsystemsNetwork cascades and contagionA cascade is a failure that spreads through a network because each node's state depends on its neighbours'. One bank caneconomicsNetwork effects and tippingA network effect exists when a good becomes more valuable to each user as more people use it: telephones, payment rails,biologyNiche constructionNiche construction is the process by which organisms modify the conditions that select them. Earthworms alter soil chemilogicNon-monotonic logicClassical logic is monotonic: once a conclusion follows from a set of premises, adding premises can never take it away. statisticsNonstationarityA process is stationary if its statistical properties do not depend on when you look: the mean, the variance, the correlphilosophy of scienceNovel prediction versus accommodationIn the philosophy of science, a theory accommodates a fact when the fact was already known and available while the theorcontrolNyquist samplingA signal containing no frequencies above B can be reconstructed exactly from samples taken at any rate above 2B. Below tcontrolObservabilityObservability is a property of a system paired with its sensors. Rudolf Kálmán defined it in 1960: a system is observablcomputationObservability versus monitoring in softwareMonitoring watches a system through questions decided in advance: a fixed set of metrics, thresholds and dashboards, eacphilosophy of scienceObservation is theory-ladenThe thesis that no observation is neutral. What a person registers, and what they count as a datum at all, depends on thstatisticsOnline learning and regret boundsOnline learning studies decisions made in sequence, where each choice is committed before its consequence is known. PerfcontrolOpen-loop versus closed-loop controlAn open-loop controller acts on a plan without measuring the result. Set the toaster dial, wait, hope. A closed-loop coneconomicsOpportunity cost of delayed noticingOpportunity cost is the value of the best option foregone. Delayed noticing gives that idea a clock. If a fact becomes teconomicsOption value and irreversibilityWhen a decision cannot be undone, committing now destroys the ability to act differently later. Economists price that lologicParaconsistent reasoningClassical logic contains a rule with a violent consequence: from a contradiction, anything follows. Accept both P and nophilosophy of scienceParadigm shifts and normal scienceThomas Kuhn distinguished two modes of scientific work. Normal science operates inside an accepted framework, solving pustatisticsParticle filters and sequential Monte CarloA particle filter represents uncertainty about a hidden state with a cloud of weighted samples — particles — rather thansystemsPath dependence and lock-inPath dependence names a class of systems whose end state cannot be derived from present conditions alone. Small early evcognitionPerceptual constancyPerceptual constancy is the fact that objects look stable while the signal arriving at the senses does not. A sheet of psystemsPercolation thresholdsIn a random medium, connectivity does not grow smoothly with density. Add links one at a time to a large lattice and, fophysicsPhase transitions and critical pointsMatter reorganises itself abruptly at particular values of its control parameters. Water at one atmosphere is liquid at biologyPhenotypic plasticityPhenotypic plasticity is the capacity of a single genotype to produce different bodies, behaviours or physiologies depeneconomicsPrediction marketsA prediction market is an exchange where contracts pay out on the occurrence of a specified future event. A contract on cognitionPredictive coding in the brainPredictive coding holds that perception is not a passive reading of the senses but an active hypothesis. Higher levels osystemsPreferential attachmentPreferential attachment is the rule that growth follows existing advantage: a new node joining a network connects to an metaphysicsPresentism versus eternalismPresentism holds that only the present moment exists. The past has ceased to be; the future is not yet. Eternalism holdslanguagePresupposition accommodationWhen someone says "my sister is arriving on Thursday", they do not assert that they have a sister; they treat it as alreeconomicsPrincipal-agent problems in automationA principal hires an agent to act on their behalf. The agent knows things the principal does not: what it actually did, historyPrinting and the fixity of the textWhen a text is set in type and struck off in hundreds of identical copies, its wording stops moving. Scribal copying letstatisticsPrior sensitivityIn Bayesian statistics, a prior encodes what you believe before seeing data. Prior sensitivity is the study of how much metaphysicsProcess philosophyProcess philosophy holds that the basic constituents of reality are events, not things. Alfred North Whitehead's ProcesscognitionProspective memoryProspective memory is remembering to do something later. It splits in two: event-based, where a cue in the world triggerbiologyPunctuated equilibriumIn 1972 Niles Eldredge and Stephen Jay Gould proposed that the fossil record's gaps are data, not failure. Most species,historyRadar and continuous surveillanceBefore radar, air defence depended on scouting: patrols flown at intervals, observers with binoculars, reports arriving informationRate-distortion theoryRate-distortion theory measures the cheapest possible description of a source at a stated level of error. For a source aeconomicsReal options under uncertaintyA real option is the right, without the obligation, to take a physical or commercial action later: to build, abandon, exinformationRedundancy and predictability in natural languageNatural language is heavily redundant. Shannon's 1951 guessing experiments put the entropy of printed English at roughlystatisticsRegression to the meanMeasure anything twice with imperfect reliability and the extreme values will move inward. A pupil who scores top of thephysicsRelaxation timeA perturbed system does not snap back. It settles, and settling takes time. Relaxation time is the characteristic intervphilosophy of scienceReproducibility and the replication crisisReproducibility is the demand that a reported finding survive independent repetition. From roughly 2011, systematic attephilosophy of scienceResearch programmes and degenerating problem shiftsImre Lakatos held that science advances not by isolated theories but by research programmes: a hard core of assumptions systemsResilience versus robustnessRobustness is the capacity of a system to absorb a shock whose form was anticipated. A bridge designed for a hundred-yeaphilosophy of scienceRetraction and the scientific recordRetraction is the formal withdrawal of a published scientific claim, sitting alongside errata, corrections and expressiohistorySCADA and industrial telemetrySupervisory Control and Data Acquisition is the layer of instrumentation that watches an industrial process while it runeconomicsSearch theorySearch theory studies decisions made when options arrive one at a time, at a cost, and cannot all be inspected at once. historySeismic monitoring networksA seismic monitoring network is a set of instruments — broadband seismometers, strong-motion accelerometers, GPS receivesystemsSelf-organised criticalitySelf-organised criticality names the tendency of certain driven, dissipative systems to settle, unprompted, at the edge languageSemantic driftSemantic drift is the slow migration of a word's meaning away from its earlier sense. "Nice" meant foolish, then precisecognitionSemantic satiation and drift of meaningTwo related facts about words. Repeat one aloud thirty times and it goes briefly inert: the sound detaches from the senslanguageSense and referenceGottlob Frege separated two things a word carries. Its sense is the mode of presentation, the route by which a thing is biologySensory adaptationSensory receptors do not report absolute magnitudes. They report deviations from a running baseline. Step from bright sustatisticsSequential analysis and optional stoppingClassical statistics assumes a sample size fixed before data arrive. Sequential analysis does not. It tests after every philosophy of scienceSevere testingSevere testing is Deborah Mayo's refinement of Popper. A claim is not credible because evidence agrees with it; it is crinformationShannon entropy of a sourceClaude Shannon defined the entropy of a source as the average number of bits needed to encode each symbol it emits, givecognitionSignal detection theorySignal detection theory models any yes/no judgement made under noise. Two quantities govern performance and they are indstatisticsSimpson's paradoxSimpson's paradox occurs when an association present in every subgroup of a population reverses, or vanishes, once the scognitionSituated and embodied cognitionSituated and embodied cognition holds that thinking is not confined to symbol manipulation inside a skull. It is an actisystemsSmall-world topologyA small-world network combines two properties that usually pull apart: high local clustering and short average path lenglanguageSpeech acts and performativitySome sentences report; some sentences do. Saying "I accept", "you are dismissed", "the court finds for the plaintiff" dohistoryStatistical process controlStatistical process control is a method for deciding, from measurements taken as work proceeds, whether a process is behsystemsStigmergyStigmergy is coordination without direct communication. An agent modifies its environment; the modification changes whatcomputationStreaming joins and windowingIn stream processing, a join combines records from two or more unbounded sequences that refer to the same thing — an ordinformationSurprisal and self-informationSurprisal is the information content of a single outcome: minus the logarithm of its probability under some model. An evstatisticsSurvivorship bias in corporaSurvivorship bias is the distortion that arises when a sample consists only of the cases that made it through some unrecbiologySymbiosis and horizontal gene transferSymbiosis is durable partnership between unlike organisms; horizontal gene transfer is the movement of genetic material logicTemporal logicTemporal logic is the formal study of statements whose truth changes with time. Where classical logic asks whether a senlanguageTerminology churn in technical fieldsTechnical fields rewrite their own vocabularies while using them. Standards committees rename genes, reclassify bacteriaepistemologyTestimony and epistemic dependenceTestimony is knowledge acquired from others' say-so rather than from one's own perception or reasoning. Epistemologists logicThe AGM postulates for belief revisionIn 1985 three logicians set out axioms for rational change of belief. Given a set of accepted sentences closed under conhistoryThe Apollo guidance computer and state estimationApollo could not navigate by dead reckoning alone. An inertial measurement unit integrates accelerations from a known stphysicsThe arrow of timeMost fundamental physical laws run equally well backwards and forwards. Newton's equations, Maxwell's, the Schrödinger ecognitionThe availability heuristicNamed by Amos Tversky and Daniel Kahneman in 1973, the availability heuristic is the mental shortcut of judging how likebiologyThe Baldwin effectIn 1896 James Mark Baldwin proposed that what an organism learns during its own lifetime shapes what natural selection cstatisticsThe bias-variance tradeoff over timeAny estimate carries two kinds of error. Bias is systematic: the estimator points at the wrong target. Variance is jittecognitionThe binding problemIn perception, separate channels process separate attributes. Colour, motion, orientation and pitch are handled by diffemetaphysicsThe block universe and the problem of changeIn the block universe, all times exist alike. Past, present and future are regions of a single four-dimensional whole, ncomputationThe CAP theoremA distributed store cannot simultaneously guarantee consistency, availability and tolerance of network partitions. SincehistoryThe chronometer and the longitude problemLatitude can be read from a single observation: measure the sun's height at noon, consult tables, done. Longitude cannotepistemologyThe closure principleIn epistemology, the closure principle says knowledge is closed under known entailment: if you know p, and you know thathistoryThe Cuban missile crisis and reconnaissance cadenceIn October 1962, American knowledge of Soviet missile construction in Cuba arrived in discrete parcels: a U-2 flew, filminformationThe data processing inequalityIn information theory, if X produces Y and Y alone produces Z — a Markov chain X → Y → Z — then the mutual information Iphilosophy of scienceThe demarcation problemThe demarcation problem asks what separates science from non-science. Logical positivists proposed verifiability; Popperphilosophy of scienceThe Duhem-Quine thesisPierre Duhem argued that a physicist never tests a single hypothesis. A prediction follows only from a hypothesis plus aeconomicsThe efficient market hypothesisFormulated by Eugene Fama in the 1960s, the efficient market hypothesis holds that asset prices reflect available informlogicThe frame problemPosed in formal logic, the frame problem asks how a reasoner represents what an action leaves alone. Describe a robot licognitionThe free energy principleThe free energy principle, formulated by Karl Friston, holds that any system that keeps its identity over time must resicontrolThe good regulator theoremIn 1970 Roger Conant and W. Ross Ashby proved a result about control: the simplest optimal regulator of a system is necemathematicsThe halting problemIn 1936 Alan Turing proved that no general procedure can decide, for every program and input, whether that program eventcontrolThe internal model principleA result from control theory. If a feedback controller is to drive the error to zero against a persistent external signastatisticsThe likelihood principleIn statistics, the likelihood principle holds that all the evidence a dataset carries about an unknown quantity is contaeconomicsThe Lucas critiqueIn 1976 Robert Lucas argued that the statistical relationships economists estimate from historical data are not structurlanguageThe map and the territoryIn 1931 Alfred Korzybski put a constraint on representation: the map is not the territory. Any account of something is msystemsThe Markov blanketIn a probabilistic graph, a node's Markov blanket is the minimal set of variables that, once known, makes everything elsinformationThe noisy channel coding theoremIn 1948 Claude Shannon proved that every noisy communication channel has a number attached to it: a capacity, measured isystemsThe observer in a complex systemIn complex systems theory, the observer is not outside the thing observed. Measurement consumes resources, occupies chanphilosophy of scienceThe pessimistic meta-inductionA historical argument about scientific belief. Look back at the theories once held by competent, well-evidenced scientisepistemologyThe preface paradoxAn author writes a book, checks every claim, and believes each one. In the preface she writes: some errors surely remainepistemologyThe problem of inductionHume's problem: no amount of past observation logically guarantees anything about the next case. That bread nourished yebiologyThe Red Queen hypothesisIn 1973 Leigh Van Valen noticed something odd in the fossil record: the chance a genus goes extinct barely depends on hoepistemologyThe regress of justificationAsk why a belief is justified and you receive another belief. Ask again and the chain continues. Either it runs on forevphysicsThe second law of thermodynamicsThe second law states that in an isolated system entropy does not decrease: differences flatten, gradients dissipate, ancontrolThe separation principleIn control theory, the separation principle says that for a linear system driven by Gaussian noise and judged by a quadrmetaphysicsThe specious presentThe present we actually perceive is not a knife-edge instant but a short stretch of time with duration. E.R. Clay named physicsThe speed of light as an information boundNothing that carries information travels faster than light in vacuum: 299,792,458 metres per second, about one nanoseconhistoryThe telegraph and the collapse of news latencyBefore 1844, news moved at the speed of the fastest horse, ship or train. Prices, orders and reports all travelled at thhistoryThe Toyota production system and jidokaJidoka is one of the two pillars of the Toyota Production System, alongside just-in-time. Usually rendered as "autonomatphysicsThe ultraviolet catastropheIn 1900 classical physics predicted how much light a hot object should emit at each wavelength. Equipartition gave everyeconomicsThe value of informationIn decision theory, the value of information is the price a rational actor should pay for a signal before receiving it. economicsThe winner's curseIn a common-value auction, bidders estimate the same unknown worth and bid their estimates. The winner is not the best-iphysicsThermal noise and the fluctuation-dissipation theoremA resistor left alone produces a small random voltage. Nyquist gave it in 1928: mean square voltage equals 4kTRΔf. The seconomicsTransaction costsTransaction costs are the costs of using a market rather than doing something yourself: finding a counterparty, discoverlanguageTranslation and untranslatabilityTranslation moves a text between languages. Untranslatability is what resists the move. Some resistance is stylistic, buphilosophy of scienceUnderdetermination of theory by dataAny finite body of evidence is compatible with more than one explanation. Ptolemaic epicycles and Copernican orbits bothhistoryWeather forecasting and data assimilationWeather forecasting stopped being extrapolation from charts and became state estimation. A numerical model integrates thcognitionWorking memory versus long-term memoryCognition distinguishes two operations on information. One is maintenance: holding a small number of items live, availabcomputationWrite-ahead logging and the event logA database that overwrites a record in place has destroyed the evidence of what it once held. Write-ahead logging invert