Physical world and mathematics

Hochschild Mining

Hochschild Mining plc is a London-listed precious metals mining company producing silver and gold in South America, rooted in a trading group founded in 1911.

Hockey stick graph

The hockey stick graph is a reconstruction of Northern Hemisphere mean temperature over the past millennium, showing 900 years of gradual decline followed by a sharp twentieth-century rise.

Hodge conjecture

The Hodge conjecture is an unsolved problem in algebraic geometry, posed by W. V. D. Hodge in 1950 and one of the Clay Millennium Prize Problems.

Hodge star operator

The Hodge star operator, also called Hodge duality, maps a p-form on an oriented inner product space to its complementary form, underpinning the Hodge Laplacian and Maxwell's equations.

Hodge structure

A Hodge structure is an algebraic structure on a real or rational vector space recording a decomposition into (p, q) pieces, introduced by W. V. D. Hodge.

Hodge theory

Hodge theory is the branch of mathematics that studies the topology of manifolds through harmonic differential forms, created by W. V. D. Hodge in the 1930s.

Hodgkin–Huxley model

The Hodgkin–Huxley model, also called the Hodgkin–Huxley equations, is a set of four differential equations published in 1952 that describes how action potentials are generated in nerve cells.

Hodograph

A hodograph, also called a hodogram, is a plot of horizontal wind at successive heights, representing the vertical wind profile; meteorologists use its curve to judge storm types and rotation.

Hoeffding's inequality

Hoeffding's inequality, also called the Hoeffding bound, bounds the probability that a sum of bounded independent random variables deviates from its expectation using only the summands' ranges.

Hofmann elimination

Hofmann elimination is an organic reaction in which a quaternary ammonium hydroxide, on heating, gives an alkene, a tertiary amine, and water, favoring the least substituted alkene.

Hofmann rearrangement

The Hofmann rearrangement, also called the Hofmann degradation, converts a primary carboxamide into a primary amine with one fewer carbon, first reported by August Wilhelm Hofmann in 1881.

Hofmann–Löffler–Freytag reaction

The Hofmann–Löffler–Freytag reaction (HLF reaction) is an organic reaction forming pyrrolidines from N-haloamines in strong acid, described by Hofmann in 1883 and expanded by Löffler and Freytag from 1909, an early example of directed C–H functionalization.

Hofmeister series

The Hofmeister series is an empirical ranking of ions by their ability to salt out, or precipitate, proteins from solution, first reported by Franz Hofmeister in 1888.

Hofstadter butterfly

The Hofstadter butterfly is the self-similar fractal energy spectrum of electrons in a two-dimensional crystal lattice under a perpendicular magnetic field, computed by Douglas Hofstadter in 1976.

Hofstadter's butterfly

Hofstadter's butterfly is the fractal energy spectrum of electrons in a two-dimensional crystal lattice in a magnetic field, predicted by Douglas Hofstadter in 1976 and first observed in graphene in 2013.

Hofstadter's butterfly in graphene/hBN moiré superlattices

Hofstadter's butterfly in graphene/hBN moiré superlattices is the fractal electron energy spectrum that appears when graphene aligned on hexagonal boron nitride sits in a strong magnetic field.

Hohlraum

A hohlraum is a small hollow metal cavity, typically gold-lined, that converts laser energy into x rays to compress fusion fuel; NIF's 192-beam shots achieved ignition in 2022.

Hoi-Kwong Lo

Hoi-Kwong Lo is a quantum information scientist and professor at the University of Toronto known for QKD security proofs, the decoy-state method, and co-inventing MDI-QKD in 2012.

Hölder condition

A Hölder condition is a continuity requirement on a function, |f(x) − f(y)| ≤ A|x − y|^α with 0 < α ≤ 1; the case α = 1 is Lipschitz continuity.

Hölder's inequality

Hölder's inequality is a bound in analysis relating the integral of a product of functions to the product of their norms; it generalizes the Cauchy–Schwarz inequality.

Holdridge life zones

Holdridge life zones are a climate classification system naming regions by the vegetation their climate can support, proposed by Leslie Holdridge in 1947 and still used for mapping.

Hole spin qubit

A hole spin qubit is a quantum bit that stores information in the spin of a hole, a missing electron, confined in a quantum dot in silicon or germanium.

Holevo's theorem

Holevo's theorem, also called the Holevo bound, is a result in quantum information theory proved by Alexander S. Holevo in 1973 that limits how much classical information measurements can extract.

Oct 10, 2026

Holger Bech Nielsen

Holger Bech Nielsen, born in 1941, is a Danish theoretical physicist at the Niels Bohr Institute in Copenhagen, counted among the fathers of string theory and known for the Nielsen–Olesen vortex.

Sep 20, 2026

Holger Braunschweig

Holger Braunschweig is a German inorganic chemist at the University of Würzburg whose boron compounds bind and reduce dinitrogen like transition metals, work honored with the 2009 Leibniz Prize.

Holger F. Bettinger

Holger F. Bettinger, born 1970 in Nördlingen, Germany, is a German organic chemist who has held the organic chemistry chair at the University of Tübingen since 2008.

Holger Frey

Holger Frey is a polymer chemist and professor of Organic and Macromolecular Chemistry at Johannes Gutenberg University Mainz, known for hyperbranched polyglycerols and degradable polymers.

Holger Müller

Holger Müller is a UC Berkeley experimental physicist, on the faculty since 2008, known for atom interferometers, the 2019 laser phase plate for electron microscopy, and biophysics.

Hollis Dow Hedberg

Hollis Dow Hedberg (1903–1988) was an American petroleum geologist who led exploration at Gulf Oil, taught at Princeton, and chaired the International Subcommission on Stratigraphic Classification.