Reference

Glossary

Key terms from our papers, in plain language. A living reference that grows with the papers.

2,3-bisphosphoglycerate (2,3-BPG): A small molecule abundant in red blood cells that binds deoxygenated hemoglobin and lowers its oxygen affinity, tuning how much oxygen is delivered to the tissues.
Accumulation of advantage: The process by which early recognition brings better positions, students, and funding, which generate further recognition — widening gaps between equally talented scientists.
Adaptive optics: A technique that corrects for the blurring of the Earth's atmosphere by deforming a flexible mirror hundreds of times a second, sharpening ground-based telescope images to near-space quality.
Aetiological diagnosis: Diagnosing based on the underlying cause of a condition, rather than on its observable symptoms alone.
Aleph-null: The cardinality of the natural numbers — the 'smallest' infinity, denoted ℵ₀, and shared by every set that can be put into a single infinite list.
Allele: One of the alternative versions of a gene; the model tracks two, with frequencies p and q.
Allele frequency: The proportion of a given allele in a population's gene pool.
Allostery: Regulation of a protein's activity by a molecule binding at a site other than the active site, shifting the protein between functional states.
Anchoring: A cognitive bias where an initial piece of information (such as a first symptom) disproportionately shapes later judgments.
Aromaticity: The special stability of certain flat ring molecules whose shared electrons are spread evenly around the ring rather than fixed in alternating double bonds.
Asymmetric synthesis: Chemistry designed to produce predominantly one enantiomer rather than a 50:50 mixture — work recognized by the 2001 Nobel Prize in Chemistry.
Atomic number: The number of protons in an atom's nucleus; Moseley showed in 1913 that this, not atomic weight, is the table's true ordering principle.
ATP: Adenosine triphosphate, the cell's spendable energy currency; breaking its bonds powers almost any cellular process.
BCS theory: The 1957 Bardeen-Cooper-Schrieffer explanation of conventional superconductivity, in which Cooper pairs lock into a single coordinated quantum state.
Behavioural inhibition: An early temperament marked by wariness toward unfamiliar people or situations, linked to later anxiety and introversion.
Bell inequality: A ceiling on how strongly two distant observers' results can correlate under any local hidden-variable theory; experiments routinely measure correlations above this ceiling, in line with quantum mechanics.
Bell's theorem: John Bell's 1964 result showing that any theory based on local hidden variables must obey a specific mathematical inequality, while quantum mechanics predicts correlations that violate it — turning a philosophical dispute into a measurable one.
Benzene: A ring of six carbon atoms (formula C6H6) that is far more stable and unreactive than its hydrogen-poor formula would suggest.
Bereavement exclusion: A former DSM-IV rule preventing a depression diagnosis shortly after a major loss. Its removal in DSM-5 was among the manual’s most contested changes.
Beta-lactamase: A bacterial enzyme that cuts the beta-lactam ring at the heart of penicillins and related antibiotics, destroying the drug before it can act.
Big Five Model: The dominant five-factor framework describing personality across openness, conscientiousness, extraversion, agreeableness, and neuroticism (OCEAN).
Blackbody: An idealized object that perfectly absorbs and re-emits radiation, whose glow depends only on its temperature and not on what it is made of.
Bohr effect: The fall in hemoglobin's oxygen affinity when pH drops or carbon dioxide rises, so oxygen is released where active tissue has made the blood more acidic.
Brønsted-Lowry acid and base: An acid is a substance that donates hydrogen ions; a base is one that accepts them. 'Strong' means it dissociates fully, 'weak' means only partly.
Buffer region: The gentle plateau in a weak-acid titration where a mix of the acid and its conjugate base resists pH change; at its midpoint the pH equals the acid's pKa.
Calibration: Correcting raw radiocarbon ages against independent records such as tree rings, because the atmospheric level of carbon-14 has varied over time.
Calvin cycle: The second stage, in the stroma, that spends ATP and NADPH to fix carbon dioxide from the air into sugar; it does not directly require light.
Camouflage (crypsis): Coloration that helps an organism avoid being seen by predators; the selective pressure behind both the moth and the finch examples.
Cantor's diagonal argument: Cantor's 1891 proof that the real numbers cannot be listed: from any proposed list, he constructs a real number that disagrees in the n-th digit with the n-th listed number, so cannot appear anywhere on it.
Carbon fixation: The moment an inorganic carbon dioxide molecule is attached to an organic molecule and becomes part of a living thing's substance.
Carbon isotopes: Slightly different forms of the carbon atom (e.g. ¹²C, ¹³C, ¹⁴C); the isotopic signature of atmospheric CO₂ has shifted in step with fossil-fuel burning, fingerprinting the source of the rise.
Carbon-14: A rare, unstable form of carbon created in the atmosphere and taken up by living things; once an organism dies, its decay measures the time since.
Cardinality: The 'size' of a set, generalised to infinite sets by pairing rather than counting: two sets share a cardinality if their members can be matched one-to-one with none left over.
Carrier: An individual with one copy of a recessive allele who does not show the trait but can pass it on; the equation can reveal how many carriers are hidden in a population.
Carrying capacity: The population size an environment can sustain; absent from the basic Lotka-Volterra model and added in more realistic versions.
Cas9: The DNA-cutting protein of the system; guided by a matching RNA, it clamps onto a target sequence and slices through both strands.
Catalyst: A substance that speeds up a chemical reaction without being consumed by it; in Haber-Bosch, an iron-based catalyst weakens nitrogen's triple bond enough for hydrogen to attack.
Catalytic ozone destruction: The process in which a single chlorine atom destroys on the order of a hundred thousand ozone molecules before it is finally removed.
Cellular respiration: The controlled, staged breakdown of glucose that captures its energy as ATP, using oxygen in the later stages.
Chemiosmosis: Peter Mitchell's mechanism in which a proton gradient across the inner mitochondrial membrane stores the energy that ATP synthase uses to make ATP.
Chirality: The property of a molecule that makes it non-superimposable on its mirror image, the way a left hand cannot be laid onto a right.
Chlorofluorocarbons (CFCs): Stable, non-toxic chemicals once used as refrigerants and propellants, whose very stability lets them reach the stratosphere, where ultraviolet light frees ozone-destroying chlorine.
Chlorophyll: The green pigment that absorbs red and blue light to drive the light reactions, reflecting green, which is why leaves look green.
Citric acid cycle (Krebs cycle): The central cycle that strips electrons from acetyl-CoA, capturing them as NADH and FADH2 and exhaling the carbon as carbon dioxide.
Cognitive map: An internal mental representation of the layout of an environment, allowing flexible navigation rather than mere stimulus-response; first proposed by Tolman and given a neural basis by O'Keefe.
Colonization resistance: The way resident microbes occupy space and consume resources, making it harder for harmful pathogens to gain a foothold.
Comorbidity: The presence of two or more conditions in the same person — for example, the popularised “AuDHD” pairing of autism and ADHD.
Competitive inhibitor: A molecule resembling the substrate that competes for the active site, raising the apparent Km while leaving Vmax unchanged.
Completeness: The (unattainable) property that every true statement is provable from the axioms — the dream the first theorem destroys.
Confirmation bias: The tendency to seek, weight, and recall evidence that supports an existing hypothesis while discounting evidence against it.
Consistency: The property of a formal system that it never derives a contradiction; the second theorem shows a system cannot establish this about itself.
Constrained plasticity: This paper's conclusion that personality follows broad trajectories yet retains room to change within limits.
Continental drift: Alfred Wegener's 1912 hypothesis that today's continents were once joined and have since moved apart — vindicated and refined by plate tectonics half a century later.
Continuum hypothesis: Cantor's conjecture that there is no size of infinity strictly between that of the whole numbers and that of the real numbers; Gödel and Cohen proved it neither provable nor disprovable from the standard axioms.
Cooper pair: A loosely bound pair of electrons, coupled through vibrations of the atomic lattice, that moves through a superconductor without scattering.
Cooperativity: When binding a ligand at one site of a multi-subunit protein changes the affinity of the remaining sites — producing hemoglobin's S-shaped (sigmoidal) oxygen-binding curve.
Correlation versus causation: The distinction at the heart of interpreting microbiome studies: a difference in gut bacteria between sick and healthy people may be a cause, a consequence, or neither.
Countable set: An infinite set whose members can be listed in correspondence with the whole numbers — including the integers and even all the rational fractions; its size is aleph-null.
CRISPR: A bacterial immune system that files away snippets of viral DNA between repeated sequences and uses them to recognize and destroy the same virus on a later attack.
Critical temperature: The temperature below which a given material becomes superconducting; raising it has been the central quest of the field.
CUDOS norms: Robert Merton's four norms of science — communalism, universalism, disinterestedness, and organized skepticism — that the scientific community informally enforces on its members.
Deep brain stimulation (DBS): A treatment that uses targeted electrical stimulation of specific brain regions — explored for otherwise treatment-resistant depression.
Delocalization: The spreading of electrons over many atoms instead of being pinned between two, which gives benzene its uniform bond lengths and reluctance to react.
Dennard scaling: The companion trend, broken around 2005, by which shrinking transistors also allowed higher clock speeds at the same power.
Diathesis-Stress Model: The idea that a predisposition produces an outcome only when triggered by environmental stress.
Digital signature: A cryptographic mark made with one's private key that anyone can verify with the matching public key, proving a message or update genuinely came from the claimed sender.
Double-slit experiment: A demonstration in which particles sent one at a time through two slits gradually build up a wave interference pattern, exposing quantum superposition.
Double-strand break: The cut Cas9 makes across both DNA strands; how the cell repairs it — sloppily or from a template — determines the edit.
DSM: The Diagnostic and Statistical Manual of Mental Disorders — the primary classification system used in Western psychiatry, published by the American Psychiatric Association.
Eccentricity: The changing shape of Earth's orbit, from nearer-circular to more elliptical, on cycles of about 100,000 and 413,000 years.
Efflux pump: A membrane protein that expels antibiotics from a bacterial cell before they reach a lethal concentration, sometimes against several drug classes at once.
Eka-element: Mendeleev's name for a predicted but undiscovered element — for example eka-silicon, later found and named germanium — described in detail before anyone had seen it.
Enantiomers: The two mirror-image forms of a chiral molecule, identical in ordinary bulk properties but potentially very different in how they interact with the chiral molecules of life.
Entropy: A measure of how many microscopic arrangements of a system look the same at the large scale; systems drift toward high-entropy states simply because there are vastly more of them.
Enzyme: A biological catalyst, almost always a protein, that speeds up a specific chemical reaction without being consumed by it.
Eponymy: Naming a discovery, law, unit, comet, or disease after a scientist — in Merton's account, the highest denomination of scientific recognition.
EPR paradox: Einstein, Podolsky, and Rosen's 1935 argument that the spooky correlations of entangled particles showed quantum mechanics was incomplete and that the particles must carry hidden, pre-set instructions.
Equivalence point: The point in a titration where the added reagent exactly neutralizes the substance being measured, so their moles are equal.
Eutrophication: Over-enrichment of waterways with nutrients — often agricultural nitrogen runoff — that fuels algal blooms whose decay strips oxygen from the water and creates aquatic dead zones.
Event Horizon Telescope: A global network of radio observatories linked by very-long-baseline interferometry to act as a single Earth-sized telescope, capable of resolving the shadows of supermassive black holes.
Exoplanet: A planet orbiting a star other than the Sun; the first around a Sun-like star was confirmed only in 1995, and thousands are now known.
Exponential growth: Growth by a constant factor each period, which appears as a straight line when plotted on a logarithmic scale.
Fecal microbiota transplant: Transfer of stool from a healthy donor to restore a functioning microbial community; strikingly effective against recurrent Clostridioides difficile infection.
Fibonacci sequence: The sequence 1, 1, 2, 3, 5, 8, 13, 21... in which each term is the sum of the two before it.
Formal system: A fixed set of axioms together with strict rules for deriving theorems from them — the object Gödel's theorems are about.
Genotype frequency: The proportions of the genotype combinations — p² for AA, 2pq for Aa, and q² for aa — predicted at equilibrium.
Geomagnetic reversal: An episode in Earth's history when the magnetic field's north and south poles swap; cooling basalt records each reversal as a stripe in the seafloor's magnetisation.
Germline editing: Editing of embryos or reproductive cells, which makes heritable changes passed to all future generations; subject to a near-total moratorium.
Glycolysis: The first, oxygen-independent stage, in the cytoplasm, that splits glucose into two molecules of pyruvate for a net gain of two ATP.
Gödel numbering: Gödel's method of encoding statements and proofs as numbers, so that arithmetic can express claims about its own formulas.
Golden angle: The turn of about 137.5° between successive plant parts that packs them most evenly, derived from dividing a circle by the golden ratio.
Golden ratio: The number close to 1.618 that ratios of consecutive Fibonacci numbers approach, and to which the golden angle is tied.
Graphene: A single-atom-thick sheet of carbon atoms arranged in a hexagonal honeycomb lattice — the first true two-dimensional crystal, isolated by Geim and Novoselov in 2004.
Graphite: The familiar form of carbon in pencil leads — stacks of graphene layers held together by weak forces between layers and strong bonds within each one, which is why graphite cleaves easily.
Gravitational redshift: The stretching of light to longer (redder) wavelengths as it climbs out of a gravitational well — a prediction of general relativity, confirmed near Sgr A* by observing the star S2 at closest approach.
Grid cell: A neuron in the medial entorhinal cortex that fires at multiple locations forming a regular triangular lattice across the environment, providing a built-in metric for distance and direction.
Guide RNA: A short RNA whose sequence directs Cas9 to a chosen spot in the genome; change the guide and you change the target.
Gut microbiota: The bacteria and other microbes of the intestine, which digest fibers the body cannot, make certain vitamins, and help train the immune system.
Gut-brain axis: The proposed two-way communication between gut microbes and the brain — a real area of study often overstated in popular coverage.
Haber-Bosch process: The industrial reaction that combines atmospheric nitrogen with hydrogen over an iron catalyst at high temperature and pressure to make ammonia — the basis of modern nitrogen fertiliser.
Habitable zone: The range of distances from a star where a planet's temperature could allow liquid water to exist.
Half-life: The fixed time for half of a radioactive sample to decay; carbon-14's is about 5,730 years.
Halting problem: Turing's undecidable problem of whether an arbitrary program will ever stop — a computational cousin of incompleteness.
Hardy-Weinberg equilibrium: The state in which allele and genotype frequencies stay constant from generation to generation, holding only when a specific set of assumptions is met.
Hardy-Weinberg principle: A description of the genotype proportions a population shows when no evolutionary forces act on it — the baseline against which evolution is detected.
Hayflick limit: The roughly 40-60 division limit of normal human cells, discovered by Leonard Hayflick and counted down by shortening telomeres.
Head-direction cells: Neurons that fire when an animal's head faces a particular direction, acting as an internal compass that feeds the brain's positioning system.
Heritability: The share of variation in a trait across a population attributable to genetic differences; estimated at roughly 40–50% for personality.
High-temperature superconductor: A material — notably the copper-oxide cuprates — that superconducts above 77 K, the temperature of cheap liquid nitrogen, by a mechanism still not fully understood.
Hill coefficient: A number summarising how cooperative a protein's binding is: 1 means the sites act independently, higher values mean stronger coupling (around 2.8 for hemoglobin).
Hippocampus: A curled structure in the temporal lobe essential for forming new memories of events and for spatial navigation; home of place cells.
Homochirality: The phenomenon whereby living organisms use exclusively one enantiomer of chiral molecules — L-amino acids and D-sugars — rather than a mixture of both mirror forms.
Honeycomb lattice: The hexagonal arrangement of atoms in a graphene sheet whose symmetry causes its electrons to behave as if they were massless, racing through the sheet by the equations normally used for light.
Horizontal gene transfer: Movement of genetic material between organisms other than by parent-to-offspring inheritance; in bacteria, via conjugation, transformation, or transduction.
Hückel's rule: A rule predicting which ring systems gain aromatic stability, based on the number of shared (pi) electrons they contain.
Incompleteness theorems: Gödel's 1931 results: any consistent system strong enough for arithmetic contains true statements it cannot prove, and cannot prove its own consistency.
Individualism vs. collectivism: A cultural dimension that shapes how traits like extraversion are valued and expressed.
Industrial melanism: The rise of dark-colored forms of organisms — most famously the peppered moth — in soot-darkened, polluted environments.
Information is physical: The realization, following Landauer, that a stored bit is a real configuration of matter, so destroying it has consequences measured in heat and entropy.
Insolation: The amount of solar radiation reaching a given place and time; northern-summer insolation is the controlling lever in Milankovitch's theory.
Interference pattern: The bands of reinforcement and cancellation produced when waves — or quantum probability amplitudes — overlap; their appearance is the signature of wave behavior.
Keeling Curve: The continuous record of atmospheric CO₂ concentration measured atop Mauna Loa since 1958 — a seasonal sawtooth riding a steady upward trend, the foundational dataset of climate science.
Kepler's third law: The classical relation between an orbiting body's period and the size of its orbit, which fixes the mass of whatever it is orbiting — used here to weigh Sgr A* from a single star's loop.
Key distribution problem: The classical difficulty that two parties wanting to exchange secret messages first need a way to deliver a shared key in secret, which is itself a secret to protect.
Km (Michaelis constant): The substrate concentration at which the rate is half of Vmax; a small Km signals high affinity, a large Km low affinity.
Landauer's principle: The rule, established by Rolf Landauer in 1961, that erasing a single bit of information must dump at least a fixed minimum of heat into the surroundings.
Le Chatelier's principle: A principle of chemical equilibrium stating that a system at equilibrium shifts to partially counteract any change in conditions (temperature, pressure, concentration) imposed on it.
Length contraction: The shortening of a moving object, or of the distance it crosses, along the direction of motion, as measured by an observer it moves relative to.
Life-Course-Persistent vs. Adolescent-Limited: Moffitt's taxonomy contrasting antisocial behaviour that persists from childhood into adulthood with behaviour confined to the teenage years.
Light curve: A plot of a star's brightness over time; the depth and spacing of its dips reveal a transiting planet's size, year, and distance.
Light reactions: The first stage, in the thylakoid membranes, that captures light and stores its energy as ATP and NADPH while splitting water and releasing oxygen.
Local hidden variables: The proposal that entangled particles' correlated outcomes reflect predetermined instructions set at creation, with no faster-than-light influence — the picture Bell's theorem and experiment have ruled out.
Longitudinal study: Research that follows the same individuals over a long period to track change.
Loophole-free Bell test: An experimental setup that simultaneously closes the locality, detection, and freedom-of-choice loopholes; first achieved in 2015, putting Einstein's local-realist picture beyond reasonable rescue.
Looping effect: Ian Hacking’s idea that naming a human category changes the people in it: as a label circulates, individuals shape their experience around it.
Lorentz factor (gamma): The quantity 1/√(1 − v²/c²) that sets how much a moving clock slows and a moving length contracts — almost exactly 1 at everyday speeds, soaring toward infinity near light speed.
Lotka-Volterra model: A pair of coupled equations describing how predator and prey populations rise and fall together, the founding model of mathematical ecology.
Mass hierarchy: The unresolved question of how the three neutrino mass states are ordered from lightest to heaviest, which oscillation experiments can probe but have not yet settled.
Mathematical ecology: The use of mathematical models to describe how populations change and how species interact.
Matilda effect: Margaret Rossiter's term for the systematic under-crediting of women's scientific contributions, often reassigned to male colleagues or simply forgotten.
Matthew effect: Merton's term for the way recognition flows disproportionately to already-eminent scientists, so an early lead in reputation compounds over a career.
Mauna Loa Observatory: A high-altitude weather station on the Hawaiian volcano Mauna Loa, deliberately remote from cities and vegetation, where Keeling began the continuous CO₂ record in March 1958.
Maxwell's demon: An 1867 thought experiment in which a tiny intelligence sorts fast from slow molecules through a frictionless door, seemingly lowering entropy for free and violating the second law.
Mechanical exfoliation: Geim and Novoselov's method of peeling graphite into ever-thinner flakes with adhesive tape until a single graphene layer remains — the famous 'sticky-tape' discovery technique.
Meissner effect: The active expulsion of magnetic fields from a superconductor's interior — a property distinct from zero resistance, and the reason a magnet can hover above a superconductor.
Michaelis-Menten equation: The relation v = Vmax[S]/(Km + [S]) describing how an enzyme's reaction rate depends on substrate concentration.
Microbiome: The community of microbes living in and on the body — and, more meaningfully, the millions of genes they collectively carry.
Mid-ocean ridge: A continuous undersea mountain range running through the world's oceans where mantle material rises and solidifies into fresh oceanic crust.
Milankovitch cycles: Slow, regular variations in Earth's orbit and axial tilt that pace the ice ages by changing how much sunlight reaches the high northern latitudes.
Mirror life: A hypothetical synthetic organism built entirely from the opposite chirality — D-amino acids and L-sugars — raising both medical opportunities and biosafety concerns.
Monozygotic twins: Identical twins who share virtually all their genes; comparing them, especially when reared apart, helps estimate genetic influence.
Montreal Protocol: The 1987 international treaty phasing out ozone-depleting chemicals, ratified by every country and widely called the most successful environmental agreement ever.
Moore's law: Gordon Moore's 1965 observation that the number of transistors on a chip doubles at a regular cadence — later settled at about every two years.
MRSA: Methicillin-resistant Staphylococcus aureus — strains carrying the mecA gene, whose altered penicillin-binding protein (PBP2a) resists nearly all beta-lactam antibiotics.
Muon: A heavy, short-lived cousin of the electron; cosmic-ray muons reach the ground only because time dilation stretches their brief lifetime in our frame.
Natural selection: The process by which heritable traits that improve survival and reproduction become more common in a population over generations.
Nature–nurture: The broader debate over how far biology versus environment shapes who we are.
Neutrino: A nearly massless, electrically neutral elementary particle that interacts only via the weak force and gravity, passing through ordinary matter almost undisturbed.
Neutrino oscillation: The quantum-mechanical phenomenon in which a neutrino produced as one flavour (electron, muon, or tau) is later detected as another, possible only if the flavours mix and the underlying mass states differ.
Nitrogen fixation: The conversion of unreactive atmospheric N₂ into reactive nitrogen compounds (such as ammonia or nitrate) that plants and other organisms can use to build proteins and nucleic acids.
Nomothetic: An approach that seeks general, law-like findings across many people, contrasted with idiographic study of the individual case.
Obliquity: The tilt of Earth's axis, varying between about 22.1° and 24.5° on a ~41,000-year cycle, which sets how extreme the seasons are.
Off-target edit: An unintended cut at a site that resembles the target sequence — a central safety concern in turning CRISPR into medicine.
Operant conditioning: Learning in which behaviour is shaped by its consequences, such as reinforcement (Skinner).
Organized skepticism: The scientific norm that every claim, however authoritative or politically and religiously sensitive, is open to critical scrutiny.
Over-diagnosis vs. better recognition: Two readings of rising diagnostic rates: either we are labelling normal variation as disorder, or we are finally identifying conditions previously missed.
Oxidative phosphorylation: The final stage, where harvested electrons drive proton pumping and ATP synthase makes most of the ATP, with oxygen as the final electron acceptor.
Ozone hole: The severe seasonal collapse of stratospheric ozone over Antarctica each spring, first reported in 1985, far larger than models had predicted.
Ozone layer: A thin band of ozone (O3) in the stratosphere that absorbs the Sun's most damaging ultraviolet radiation, shielding life on land.
Paradigm shift: Thomas Kuhn’s term for a fundamental change in the assumptions and methods of a field — here, shifts in how disorders are conceived.
Parts per million (ppm): A unit expressing how many molecules of a gas are present per million molecules of air; preindustrial CO₂ sat near 278 ppm, the 2024 average near 422 ppm.
Path integration: Continuously updating an estimate of one's position by integrating self-motion (speed and direction) over time — a form of dead reckoning the grid system performs even without visible landmarks.
Pattern recognition receptors: Immune-system receptors (PRRs) that detect microbe-associated molecular patterns (MAMPs); because these interactions are stereospecific, mirror-chirality microbes might evade them.
Peppered moth: Biston betularia, whose pale and dark forms tracked industrial pollution up and then back down, making it a textbook case of selection observed in real time.
Periodic law: The observation that the chemical properties of the elements recur at regular intervals when the elements are listed in the right order.
Periodic table: The arrangement of the chemical elements, in order of atomic number, into rows and columns that place elements with similar properties together.
pH: The negative base-ten logarithm of the hydrogen-ion concentration; each whole unit is a tenfold change, with 7 neutral in pure water at room temperature.
Phase lag: The quarter-cycle delay by which the predator peak trails the prey peak, the signature that lets the cycle sustain itself.
Photosynthesis: The process by which plants, algae, and some bacteria use light energy to turn carbon dioxide and water into sugar, releasing oxygen as a by-product.
Phyllotaxis: The arrangement of leaves, seeds, or florets on a plant, whose spiral counts frequently come out as consecutive Fibonacci numbers.
pKa: A measure of a weak acid's strength: the pH at which exactly half of it has given up its hydrogen ions.
Place cell: A hippocampal neuron that fires when an animal is in one particular location of its environment, encoding position by which cells in the population are active.
Planck's constant: The very small fundamental constant that sets the size of energy quanta; the energy of a packet of light equals this constant times the light's frequency.
Plasmid: A small, often circular loop of DNA separate from the chromosome that can carry several resistance genes and be passed between bacteria by conjugation.
Plate tectonics: The theory that Earth's rigid outer shell is broken into plates which move over a softer mantle beneath, producing earthquakes, volcanoes, and mountain ranges where they meet.
Polygenic: Shaped by many genes of small individual effect rather than a single gene.
Precession: The slow wobble of Earth's tilted axis, on a ~19,000-23,000-year cycle, which changes the time of year at which Earth is closest to the Sun.
Predator-prey cycle: The perpetual oscillation the model produces, in which neither population settles and the two chase each other around a loop.
Public-key cryptography: A system using two mathematically linked keys per user — a public key for encryption and a private key for decryption — so that strangers can exchange secrets over an open channel without first sharing a password.
Quantum: A discrete packet of energy; Planck's assumption that light is emitted and absorbed only in such packets cured the ultraviolet catastrophe and launched quantum physics.
Quantum entanglement: A joint quantum state of two or more particles in which their measured properties are correlated more strongly than any classical mechanism allows — so measuring one fixes the other's outcome instantly, no matter the distance.
Quantum tunneling: The leakage of electrons straight through barriers that should stop them, which makes very small transistors unreliable and limits further shrinking.
Racemate: A 50:50 mixture of both enantiomers of a chiral compound; thalidomide was unknowingly sold as a racemate, exposing patients to its teratogenic mirror form.
Racemic mixture: A 50:50 mixture of both enantiomers of a chiral compound.
Racemization: The interconversion of one enantiomer into its mirror image; thalidomide undergoes this readily in the body, so a pure enantiomer does not stay pure.
Radiometric dating: Determining the age of a sample from the steady, unchangeable decay of unstable atomic nuclei within it.
Rank-order stability: How well people keep their position on a trait relative to others over time; it tends to rise with age.
Rayleigh-Jeans law: The classical formula for blackbody radiation that fit the data at long wavelengths but predicted the ultraviolet catastrophe at short ones.
Reactive nitrogen: Forms of nitrogen (ammonia, nitrate, nitrous oxide, etc.) that are biologically and chemically active, in contrast to inert atmospheric N₂; modern agriculture has roughly doubled how much circulates.
Reliability vs. validity: Reliability is whether a measure gives consistent results; validity is whether it actually captures the thing it claims to. A diagnosis can be reliable yet not valid.
Replicative aging: Decline that arises as cells exhaust their capacity to divide — one side of the trade-off telomeres help manage.
Resistome: The full collection of antibiotic-resistance genes present in a microbial community or environment — much of it ancient and predating clinical antibiotics.
RSA: The 1977 public-key system by Rivest, Shamir, and Adleman, whose security rests on the difficulty of factoring the product of two very large prime numbers back into those primes.
RuBisCO: The enzyme that fixes atmospheric carbon dioxide onto an organic molecule; thought to be the most abundant protein on Earth, and notoriously inefficient.
Sagittarius A*: The compact radio source at the centre of the Milky Way, identified as a supermassive black hole by tracking the orbits of nearby stars and later imaged by the Event Horizon Telescope.
Seafloor spreading: Harry Hess's 1962 idea that new oceanic crust forms at mid-ocean ridges and spreads outward, carrying the continents away from the ridge like material on two opposing conveyor belts.
Seasonal cycle of CO₂: The annual rise and fall in atmospheric CO₂ driven by the Northern Hemisphere's land plants taking up carbon in spring/summer and releasing it through autumn/winter decay.
Second law of thermodynamics: The principle that the total entropy of an isolated system never decreases, which is why heat flows from hot to cold and broken things do not reassemble.
Seesaw mechanism: A theoretical proposal that links the unusually tiny masses of the known neutrinos to the existence of much heavier, as-yet-undetected partner particles.
Self-organization: The emergence of ordered patterns from simple local rules; the Douady-Couder experiment produced Fibonacci spirals from physics alone, with no biology involved.
Senescence: The permanent non-dividing state a cell enters when its telomeres grow critically short.
Shor's algorithm: A quantum algorithm devised by Peter Shor in 1994 that would factor large numbers efficiently on a sufficiently capable quantum computer — breaking RSA and motivating today's post-quantum cryptography.
Soai reaction: A chemical reaction demonstrating that a small initial break in enantiomeric symmetry can be amplified by autocatalysis, offering a mechanism for how homochirality might have arisen.
Social Investment Theory: The view that taking on social roles such as work, marriage, or parenthood reshapes personality by rewarding certain behaviours.
Solar neutrino problem: The decades-long discrepancy between the number of electron neutrinos predicted from solar fusion and the smaller number actually detected — resolved by recognising that neutrinos change flavour in flight.
Special relativity: Einstein's 1905 theory of motion at constant velocity, built on the constancy of the speed of light, from which time dilation and length contraction follow.
Standard Model: The established theory of particle physics describing the known fundamental particles and three of the four forces; it originally assumed neutrinos were massless, which oscillations disprove.
Subduction: The process by which one tectonic plate slides beneath another at an ocean trench and descends into the mantle, recycling old oceanic crust and triggering deep earthquakes and volcanism.
Subgenual prefrontal cortex (sgPFC): A brain region involved in processing emotion, mood, and autonomic stress responses. Abnormal activity here is linked to major depressive disorder.
Substrate: The molecule an enzyme acts on; it binds in the enzyme's active site, is converted to product, and is then released.
Superconductivity: A state in which a material's electrical resistance drops to exactly zero below a critical temperature, so a current set flowing in a loop can circulate indefinitely.
Supermassive black hole: A black hole millions to billions of times the mass of the Sun, found at the centre of most large galaxies; the Milky Way's is Sagittarius A*, about 4 million solar masses.
Superposition: A quantum state in which a system occupies several possibilities at once; in the double slit, a single electron effectively samples both paths.
Symptom-based diagnosis: Classifying a disorder by the pattern of symptoms a person presents, as emphasised by the DSM-5. More reliable to apply, but its validity can be debated.
T and R states: Hemoglobin's two quaternary structures — 'tense' (low oxygen affinity) and 'relaxed' (high oxygen affinity) — that it switches between as oxygen binds and unbinds.
Telomerase: An enzyme that rebuilds telomere sequence from its own RNA template, extending the ends and resetting the division clock; active in germ and some stem cells, off in most others.
Telomere: A protective cap of short repeated DNA (TTAGGG in humans) at the end of a chromosome, shortened a little at each cell division so the genes further in stay safe.
Time dilation: The slowing of a moving clock relative to an observer it moves past, by a factor that grows without limit as the clock approaches the speed of light.
Titration: A method for finding an unknown concentration by adding a solution of known concentration a little at a time until the two exactly neutralize.
Transistor: The basic electronic switch at the heart of a chip; packing more of them onto silicon drove decades of computing gains.
Transit depth: The fractional dimming during a transit, equal to the ratio of the planet's area to the star's, which gives the planet's size.
Transit method: Detecting a planet by the small, regular dip it causes in its star's brightness each time it passes between the star and us.
Transmission spectroscopy: Reading a planet's atmospheric composition from starlight that filters through its atmosphere during a transit.
Trapdoor one-way function: A mathematical operation that is easy to compute one way but very hard to reverse — unless one knows a secret 'trapdoor' that makes the reverse easy; the basis of public-key schemes.
Two-dimensional material: A crystal essentially one atomic layer thick, with bulk properties dominated by its single plane; graphene is the archetype, and many others (e.g. MoS₂, hexagonal BN) have followed.
Ultraviolet catastrophe: The classical prediction that a blackbody should radiate ever more energy at shorter wavelengths, diverging to infinity — a clear sign that classical physics was incomplete.
Uncountable set: An infinite set strictly too large to be put into one-to-one correspondence with the whole numbers; the real numbers between 0 and 1 are the standard example.
Uranium-lead dating: A radiometric clock using uranium's billion-year half-life, locked in zircon crystals, used to date rocks and the age of the Earth.
Valence electrons: The outermost electrons of an atom, whose arrangement explains why elements in the same column of the table behave alike.
Vmax: The maximum reaction rate, approached when every enzyme molecule is saturated with substrate; set by the amount of enzyme and how fast each can turn over.
Wave-particle duality: The quantum principle that objects such as electrons display both particle-like and wave-like behavior, depending on what is measured.
Which-path information: Knowledge of which slit a particle actually took; whenever such information exists, even in principle, the interference pattern vanishes.