Physical world and mathematics

Inequality (mathematics)

An inequality, or mathematical inequality, is a mathematical relation stating that one quantity is greater than or less than another, written with the symbols , ≤, and ≥.

An inert gas is a gas that does not react chemically under particular conditions; examples include nitrogen at ordinary temperatures and the noble gases helium, neon, argon, krypton, xenon, and radon.

Inert gas blanketing

Inert gas blanketing maintains a nitrogen or argon atmosphere over vessel contents to protect air- and moisture-sensitive materials, using tools such as Schlenk lines and glove boxes.

Inertia

Inertia, also called the principle of inertia, is the tendency of an object to keep its state of motion unless a force acts, measured by mass.

Inertia tensor

The inertia tensor is the symmetric 3×3 matrix relating a rigid body's angular momentum to its angular velocity; diagonalized about its principal axes, it gives three moments of inertia.

Inertial confinement fusion target

An inertial confinement fusion (ICF) target is the millimeter-scale assembly of fuel capsule and hohlraum that a laser compresses to thermonuclear conditions in a single brief implosion.

Inertial frame of reference

An inertial frame of reference, or inertial reference frame, is a reference frame in which Newton's laws hold, such as one moving at constant velocity relative to it.

Inertial fusion power plant

An inertial fusion power plant is a proposed electric generating station that ignites fusion fuel capsules repeatedly with a high-power driver and converts the released energy to electricity.

Inertial wave

An inertial wave is a transverse oscillation propagating through the bulk of a rotating fluid, restored by the Coriolis force, arising in oceans, gaseous planets, and stellar interiors.

Sep 21, 2026

Inez Fung

Inez Y. Fung, born 1949, is a Hong Kong-born climate scientist who models the sources and sinks of atmospheric CO2 and dust, and professor emerita at UC Berkeley.

Inference

Inference, also known as logical inference, is the process of deriving a conclusion from premises with certainty, as in deduction, or to a lesser degree, as in induction and abduction.

Inference engine

An inference engine is a software module that applies the stored knowledge of an expert system to problem facts, deriving new facts and deciding which actions to take.

Oct 21, 2026

Infiernillo

Infiernillo (GVP 357041) is a late-Pleistocene to Holocene basaltic andesite volcanic field in Mendoza, Argentina, along the Río Salado near Malargüe; last eruption 6890 BCE at Volcán Hoyo Colorado; distinct from Mexican and Salvadoran places named Infiernillo.

Infiltration (hydrology)

Infiltration, also called water infiltration, is the movement of water from the land surface into soil through pores, feeding the root zone and recharging aquifers.

Infiltration capacity

Infiltration capacity, also called infiltrability, is the maximum rate at which soil can absorb water at its surface, a concept introduced by Robert E. Horton in the early 1940s.

Infimum and supremum

The infimum and supremum, also called the greatest lower bound and least upper bound, generalize the minimum and maximum of a set of real numbers.

Infinitary logic

Infinitary logic, also called an infinitary language, is a family of extensions of first-order logic allowing infinitely long formulas; the best-studied case, L(ω₁,ω), permits countably infinite conjunctions and disjunctions.

Infinite divisibility (probability)

Infinite divisibility, also called an infinitely divisible distribution, is a probability distribution representable as a sum of n independent, identically distributed variables for every n.

Infinite mixture model

An infinite mixture model is a Bayesian mixture model with a prior over infinitely many components, so the number of clusters is inferred from data.

Infinite monkey theorem

The infinite monkey theorem states that a monkey typing random keys forever will almost surely type any text; a 2024 study showed real monkeys never could.

Infinite product

An infinite product is a product of infinitely many factors, defined as the limit of its partial products, and is the multiplicative analog of an infinite series.

Infinite set

An infinite set is a set that is not finite, so its elements cannot be counted with a natural number; Cantor showed in 1874 that infinities come in different sizes.

Infinite-layer nickelate NdNiO2

Infinite-layer nickelate NdNiO2 is a neodymium nickel oxide structurally matching the cuprate CaCuO2; its 2019 discovery of superconductivity in doped films launched a cuprate-analog family.

Infinite-layer nickelates

Infinite-layer nickelates are rare-earth nickel oxides with formula RNiO2 whose superconductivity, discovered in 2019 in doped NdNiO2 films, makes them the closest cuprate analogs outside copper chemistry.

Infinitene

Infinitene is an infinity-shaped polycyclic aromatic hydrocarbon made of 12 consecutively fused benzene rings, first reported in 2021 and named Molecule of the Year by Chemical & Engineering News.

Infinitesimal

An infinitesimal, or infinitesimal number, is a nonzero quantity smaller in absolute value than every positive real number, realized rigorously in the hyperreal numbers introduced by Abraham Robinson in 1960.

Infinitesimal generator (stochastic processes)

The infinitesimal generator of a Markov process is the linear operator giving the instantaneous rate of change of expected values, and it determines the process via the Hille–Yosida theorem.

Infinitesimal strain theory

Infinitesimal strain theory, also called small strain theory, is the branch of continuum mechanics describing solid deformation when displacement gradients are small compared with unity.

Infinity

Infinity is the condition of being without any finite bound in size, extent, or quantity, appearing in mathematics as both endless process and completed infinite objects.