Physical world and mathematics

Multivariate meta-analysis

Multivariate meta-analysis is a statistical method in evidence synthesis that jointly combines effect estimates for several correlated outcomes from multiple studies, typically giving narrower confidence intervals than separate analyses.

Multivariate normal distribution

The multivariate normal distribution, also called the multivariate Gaussian, generalizes the normal distribution to random vectors of correlated variables, defined by a mean vector and covariance matrix.

Multivariate probit model

The multivariate probit model is a regression model for several correlated binary outcomes, introduced by Ashford and Sowden in 1970 and estimated by simulation or Bayesian methods.

Multivariate stable distribution

A multivariate stable distribution is a probability distribution of a random vector such that every linear combination of its coordinates follows a univariate stable distribution, generalizing the Gaussian and Cauchy laws.

Multivariate statistics

Multivariate statistics is the branch of statistics analyzing several variables measured on the same subjects simultaneously, using tools like principal component analysis, MANOVA, and discriminant analysis.

Multivector

A multivector is an element of a geometric algebra formed as a linear combination of blades of different grades, mixing scalars, vectors, and bivectors in one object.

Multiverse

The multiverse, also known as multiple universes, is the hypothetical collection of all universes, including our own, proposed in inflationary cosmology, quantum mechanics, and string theory.

Multiverse analysis

Multiverse analysis is a statistical method that runs every reasonable combination of data-processing choices on one dataset, showing how robust a finding is to arbitrary researcher decisions.

Multiwavelength anomalous dispersion

Multiwavelength anomalous dispersion (MAD), or multiwavelength anomalous diffraction, is an X-ray crystallography phasing method, devised by Wayne Hendrickson, that solves protein structures from a single crystal.

Mummy brown

Mummy brown, also known as Egyptian brown, was a dark brown pigment prepared by grinding Egyptian mummies, used in oil painting from the 16th century and sold into the 20th.

Munsell color system

Munsell color system, created by Albert H. Munsell, is a color order system specifying color by hue, value, and chroma (e.g. 7.5YR 5/4); standardized in ASTM D1535 and widely used in soil science.

Muography

Muography is an imaging technique using naturally occurring cosmic-ray muons to probe the internal density of volcanoes, pyramids, and built structures, like X-ray radiography on much larger scales.

Muon (μ⁻)

The muon (μ⁻), historically called the mu meson, is an elementary particle similar to the electron but about 207 times heavier, discovered in 1936 in cosmic radiation.

Muon Collider

A muon collider is a proposed particle accelerator colliding muons and antimuons at multi-TeV energies, studied since the 1960s and led today by the International Muon Collider Collaboration at CERN.

Muon excess in air showers

The muon excess in air showers, or muon puzzle, is the observation that cosmic-ray air showers contain more muons than simulations predict above roughly 10 PeV.

Muon g−2

Muon g−2 is the muon's anomalous magnetic moment, a precision test of the Standard Model. Fermilab's 2025 measurement agrees with the lattice-based prediction, ending a former 5.2σ tension.

Muon Ionization Cooling Experiment

The Muon Ionization Cooling Experiment (MICE) at the Rutherford Appleton Laboratory in the UK demonstrated ionization cooling of muons for the first time, publishing in Nature in 2020.

Muon neutrino

The muon neutrino is one of the three known flavors of neutrino, identified by producing a muon in charged-current weak interactions. It was discovered in 1962 at Brookhaven National Laboratory.

Muon puzzle

The muon puzzle, also called the muon deficit, is a discrepancy in cosmic-ray physics in which air shower simulations predict fewer muons than experiments observe, growing with energy.

Muon radiography

Muon radiography is a passive imaging technique that uses naturally occurring cosmic-ray muons, far more penetrating than X-rays, to map the internal density of structures such as volcanoes and pyramids.

Muon spectrometer

A muon spectrometer is the outermost detector of a particle physics experiment, identifying muons and measuring their momenta from curved tracks in a magnetic field.

Muon spin spectroscopy

Muon spin spectroscopy (μSR) is an experimental technique that implants spin-polarized muons into a material and measures their precession to probe local magnetic fields and dynamics.

Muon tomography

Muon tomography, also called muography, is an imaging technique that uses naturally occurring cosmic-ray muons to see inside large opaque objects such as volcanoes, pyramids, mines, and nuclear reactors.

Muon-catalyzed fusion (μCF)

Muon-catalyzed fusion (μCF), or muon catalysis, is a fusion process in which muons shrink deuterium and tritium atoms so their nuclei fuse near room temperature, the muon catalyzing further fusions.

MUonE

MUonE is a proposed CERN particle physics experiment, first proposed in 2017, to measure elastic muon-electron scattering and determine the hadronic contribution to the muon anomalous magnetic moment.

Muonic atom

A muonic atom is a bound state in which a negatively charged muon orbits an atomic nucleus in place of an electron, orbiting about 200 times closer.

Muonic hydrogen

Muonic hydrogen (μH or μp) is an exotic atom in which a negatively charged muon orbits a proton instead of the electron, making it far smaller than ordinary hydrogen.

Muonium

Muonium (symbol Mu) is an exotic, hydrogen-like atom made of a positive muon and an electron, discovered in 1960 by Vernon W. Hughes and used for precision QED tests.