Physical world and mathematics

Pseudo-observations

Pseudo-observations are rank-transformed values of a multivariate sample, scaled by 1/(n+1) so margins are approximately uniform, making them the standard input for semiparametric copula inference.

A pseudo-Riemannian manifold, also called a semi-Riemannian manifold, is a smooth manifold with a non-degenerate metric tensor of indefinite signature, whose Lorentzian case is the spacetime geometry of general relativity.

Pseudocumene

Pseudocumene is 1,2,4-trimethylbenzene, a flammable liquid hydrocarbon found in petroleum and coal tar, used chiefly to make trimellitic anhydride and as the Borexino neutrino detector's solvent.

Pseudoephedrine

Pseudoephedrine, also sold as pseudoephedrine hydrochloride, is a sympathomimetic amine used as an oral nasal decongestant for congestion from colds, sinusitis, and hay fever.

Pseudogap

A pseudogap is a partial suppression of the electronic density of states at the Fermi level, distinct from a true gap, coined by Nevill Mott in 1968.

Pseudomagnetic fields for phonons

Pseudomagnetic fields for phonons are artificial gauge fields making phonons behave as charged particles in a magnetic field, though phonons carry no charge, inspired by strained graphene.

Pseudomagnetic fields for photons

Pseudomagnetic fields for photons are strain-engineered gauge fields that make uncharged light in deformed photonic crystals act like charged particles, first realized in strained honeycomb waveguide arrays in 2013.

Pseudomathematics

Pseudomathematics, also called mathematical crankery or pseudo-maths, is purported mathematical work that fails accepted standards of logic and rigor, typically by amateurs targeting proved-impossible problems like squaring the circle.

Pseudometric space

A pseudometric space is a set with a distance function satisfying the metric axioms except that distinct points may lie at distance zero, as with functions equal almost everywhere.

Pseudopotential

A pseudopotential is an effective, usually nonlocal potential that replaces an atom's nucleus and inert core electrons in electronic-structure calculations, underpinning plane-wave density-functional theory methods for solids.

Pseudorandom generator

A pseudorandom generator is a deterministic algorithm that stretches a short random seed into a longer output that appears random to any observer who lacks the seed.

Pseudorandom quantum states

Pseudorandom quantum states, or PRSs, are keyed quantum states generated efficiently by a quantum computer yet indistinguishable from Haar-random states by any efficient quantum adversary.

Pseudorandomness

Pseudorandomness is the property of a deterministic process whose output appears random when its internal workings are hidden; cryptographic pseudorandomness means computationally indistinguishable from truly random output.

Pseudoscalar

A pseudoscalar in geometric algebra (Clifford algebra) is the product of all orthonormal basis vectors, representing a unit oriented volume and fixing the space's orientation.

Pseudoscience

Pseudoscience is a non-scientific doctrine or practice whose major proponents present it as scientific. Deciding which claims qualify is the demarcation problem, debated since antiquity and still unresolved.

Sep 29, 2026

Pseudospectral method

A pseudospectral method solves differential equations by representing the solution with global basis functions like Fourier modes or Chebyshev polynomials, enforcing the equation at collocation points, giving exponential accuracy for analytic solutions.

Pseudospectrum

A pseudospectrum is a family of sets in the complex plane attached to a matrix or operator, showing where the resolvent norm is large, which matters most for non-normal operators.

Pseudouridine

Pseudouridine is a modified nucleoside in RNA in which uracil bonds to ribose through carbon instead of nitrogen, discovered in 1951 and now used, as N1-methylpseudouridine, in mRNA vaccines.

Pseudovector

A pseudovector, also called an axial vector, is a quantity that transforms like a vector under rotations but, unlike ordinary polar vectors, keeps its sign under spatial inversion.

Psi Andromedae

Psi Andromedae (ψ Andromedae), also cataloged as 20 Andromedae, is a yellow supergiant star in Andromeda, about 1000 light years away and recorded as a multiple star system with six pairs.

Psi Persei

Psi Persei (ψ Persei, HD 22192) is a Be star in the constellation Perseus, a hot B-type star with a circumstellar gas disk and the brightest radio-emitting Be star.

Psi4

Psi4 is a free, open-source electronic structure program for quantum chemistry that implements Hartree–Fock, density functional, and coupled-cluster methods, written as a hybrid of C++ and Python.

PSJ Cobre Mendocino

PSJ Cobre Mendocino, formerly the San Jorge project, is a copper-gold porphyry mining project in Uspallata, Mendoza Province, Argentina, developed by Minera San Jorge S.A.

Psoralen

Psoralen is a plant-derived furocoumarin found in celery, figs, and parsley that becomes phototoxic under UVA light and is used in PUVA therapy for psoriasis and vitiligo.

PSPACE

PSPACE is the complexity class of decision problems decidable using polynomial memory regardless of time; it contains P and NP, and Savitch's theorem shows nondeterminism adds nothing.

PSR B0329+54

PSR B0329+54, also cataloged as PSR J0332+5434, is a bright radio pulsar discovered at Cambridge in 1968, the brightest below 1 GHz in the northern hemisphere and a standard target for pulsar studies.

PSR B0355+54

PSR B0355+54 is a middle-aged radio pulsar about 3,400 light-years away in Perseus, whose supersonic motion has produced one of the most extensively studied pulsar wind nebulae in X-ray astronomy.

PSR B0525-66

PSR B0525-66 is a pulsar in the Large Magellanic Cloud, inside the supernova remnant LHA 120-N 49. It is associated with the gamma-ray event of March 5, 1979.

PSR B0525+21

PSR B0525+21, also cataloged as PSR J0528+2200, is a slowly rotating radio pulsar in Taurus near the Crab Nebula, with a spin period of about 3.7 seconds.