Science

The positron is the electron’s positively charged antiparticle, central to antimatter physics, particle collisions, and positron emission tomography.

Potential energy is energy associated with a system’s configuration, including the relative positions and interactions of its components.

Powder diffraction characterizes crystalline materials by measuring radiation scattered from many differently oriented crystallites, revealing phase composition, crystal structure, and microstructural properties.

Pressure is normal force per unit area, governing fluid equilibrium, gas behavior, and mechanical energy transfer.

A prokaryote is an organism whose cells lack a membrane-bound nucleus, encompassing bacteria and archaea.

A promoter is a DNA region that directs the initiation of transcription and helps determine when, where, and how strongly a gene is expressed.

Proteins are amino-acid polymers whose structures and interactions enable biological catalysis, transport, signaling, defense, and structural support.

The Protein Data Bank is a global archive of three-dimensional biological macromolecular structures, associated experimental data, and descriptive metadata.

Protein folding is the process by which a polypeptide acquires its three-dimensional structure, governed by its sequence, physical interactions, and environment.

A proton is a positively charged composite subatomic particle found in every atomic nucleus, whose number determines an element’s identity.

Quantum chromodynamics is the quantum field theory of the strong interaction, describing how quarks and gluons form hadrons and behave at different energy scales.

Quantum electrodynamics is the relativistic quantum field theory describing electromagnetic interactions between charged particles and photons.

Quantum entanglement is a property of composite quantum systems whose joint state cannot be expressed as a mixture of independent subsystem states.

Quantum field theory describes quantum fields and their interactions, providing the framework for elementary particle physics and many quantum many-body systems.

Quantum gravity seeks a quantum description of gravitation and spacetime, extending general relativity into regimes where quantum effects become essential.

The quantum Hall effect is the quantization of transverse electrical conductance in two-dimensional systems, revealing integer and fractional quantum states.

An exactly solvable quantum system with a quadratic potential, equally spaced energy levels, and nonzero ground-state energy.

Quantum mechanics describes matter and radiation through quantum states, probabilistic measurement outcomes, and laws governing their evolution and interactions.

A quantum number labels a quantum state or a measurable property, helping classify states, distinguish energy levels, and express symmetry and conservation laws.

Quantum superposition is the coherent combination of quantum states, whose probability amplitudes can interfere and determine measurement outcomes.

Quantum tunneling is the transmission of a quantum system through an energy barrier that would prevent passage under classical mechanics.

A quark is an elementary particle with fractional electric charge and colour charge, forming the constituents of protons, neutrons, and other hadrons.

Quark–gluon plasma is an extremely hot state of strongly interacting matter in which quarks and gluons are no longer confined within individual hadrons.

A quasiparticle is an emergent excitation of a many-body system that can be described as a particle with effective properties.

Radiation therapy uses ionizing radiation to destroy cancer cells, control tumor growth, or relieve symptoms, with delivery methods designed to limit injury to healthy tissues.

Radioactivity is the spontaneous transformation of unstable atomic nuclei, accompanied by the emission of particles or electromagnetic radiation.

Radiology is the medical specialty that uses imaging to diagnose disease, monitor treatment, and guide diagnostic and therapeutic procedures.

Radiometric dating determines the ages of materials and past events by measuring radioactive isotopes and their decay products.

The reaction quotient measures a reaction mixture’s composition and, when compared with the equilibrium constant, indicates its thermodynamically favored direction of change.

A reading frame specifies how a nucleotide sequence is divided into consecutive three-base codons during protein synthesis.

A reciprocal lattice represents the spatial periodicity of a crystal in wave-vector space and provides the geometric framework for diffraction and crystal-wave analysis.

Cosmological recombination is the formation of neutral atoms in the cooling early universe, which enabled cosmic microwave background photons to travel largely freely.

Redshift is an increase in radiation’s observed wavelength caused by relative motion, gravitation, or cosmic expansion.

Optical reflection is the return of light into its original medium after interaction with a surface or interface.

Refraction is the redirection of a wave caused by changes in its propagation speed across an interface or within a nonuniform medium.

A dimensionless optical quantity describing phase propagation in a medium and governing refraction, dispersion, and related optical effects.

Relative atomic mass is the dimensionless ratio of an element’s average atomic mass in a specified sample to one twelfth of the mass of a carbon-12 atom.

Renewable energy comes from naturally replenished sources, including sunlight, wind, flowing water, geothermal heat, and biomass.

Renormalization relates physical theories across scales and absorbs regulator-dependent quantities into parameters, enabling finite predictions and explanations of universal behavior.

The renormalization group describes how effective physical theories change with scale, explaining running couplings, critical behavior, and universality.

Reproducibility is the capacity to obtain consistent research results by repeating documented procedures, particularly computations using the same data and methods.

Resonance describes delocalized chemical bonding through multiple contributing structures that collectively represent a single electronic state.

Reticular chemistry designs and constructs crystalline frameworks by connecting molecular building blocks through strong bonds, enabling systematic control of structure, pores, and chemical functionality.

A reversible process is an ideal thermodynamic transformation that can be reversed while restoring both the system and its surroundings exactly to their initial states.

Ribosomal RNA forms the structural and catalytic core of ribosomes, enabling protein synthesis and providing markers for evolutionary and microbial studies.

A ribosome is an RNA–protein complex that translates messenger RNA into proteins by decoding genetic instructions and catalyzing peptide-bond formation.

A ribozyme is an RNA molecule that catalyzes a chemical reaction, demonstrating that RNA can function as both an information carrier and a biological catalyst.

A rigid body is an idealized object whose internal distances remain constant, allowing its motion to be described entirely by translation and rotation.

RNA is a nucleic acid that carries genetic information, enables protein synthesis, regulates gene expression, and can catalyze chemical reactions.

RNA polymerase is an enzyme that synthesizes RNA from a nucleic-acid template, enabling transcription, gene expression, and the replication of many RNA viruses.

RNA sequencing identifies and quantifies RNA molecules in biological samples, revealing gene expression, transcript structure, and cellular diversity.

RNA splicing removes introns and joins exons in RNA transcripts, helping produce mature RNAs and regulate gene expression.

Robert Hooke was an English experimental scientist and architect known for Micrographia, his law of elasticity, and his work for the Royal Society.

Rothamsted Research is a British agricultural research institute founded in 1843, known for its long-term field experiments and contributions to crop nutrition, ecology, and statistics.

The Royal Society is the United Kingdom’s national academy of sciences, founded in 1660 to advance scientific knowledge through research, publication, and international cooperation.

An independent Swedish scientific academy founded in 1739 that promotes research and selects Nobel laureates in physics, chemistry, and economic sciences.

Scattering is the redirection of waves or particles through interactions, used to investigate matter and explain the propagation of radiation.

The Schrödinger equation governs the evolution of quantum states and determines the allowed energies and wave functions of quantum systems.

The scientific method is a set of procedures for building knowledge about nature. It relies on observation, testable hypotheses, controlled experiments and critical review by other researchers.

The second is the SI base unit of time, defined by an exact frequency of the unperturbed caesium-133 atom.