Science

The second law of thermodynamics establishes the direction of spontaneous processes through entropy increase and limits the conversion of heat into work.

A semiconductor is a material whose controllable electrical conductivity enables electronic switching, amplification, light emission, sensing, and energy conversion.

Semiconductor doping is the controlled introduction of impurities to regulate charge-carrier concentrations and the electrical behavior of semiconductor materials and devices.

Silicon is chemical element 14, a major constituent of Earth’s crust and a semiconductor used in electronics and solar cells.

Spacetime is the four-dimensional framework combining space and time in which relativity describes events, motion, causality, and gravity.

A theory of space, time, and motion based on equivalent inertial frames and the invariant speed of light in vacuum.

Speciation is the evolutionary process through which populations diverge into distinct species, often through the development of reproductive isolation.

A species is a fundamental biological grouping whose boundaries are identified using reproductive, morphological, ecological, and genetic evidence.

Specific surface area is the surface area of a material divided by its mass, used to characterize powders, porous solids, and dispersed phases.

Spectroscopy studies how matter interacts with radiation, using spectra to reveal composition, structure, energy states, and physical conditions.

The speed of light in vacuum is an exact physical constant that defines the metre and sets the local limit for transmitting matter and information.

Spin angular momentum is an intrinsic quantum property governing particles’ rotational behavior, magnetic interactions, and statistical classification.

The spin–statistics theorem connects integer spin with bosonic statistics and half-integer spin with fermionic statistics in relativistic quantum field theory.

A dynamic RNA–protein complex that removes introns from precursor messenger RNA and joins exons during eukaryotic gene expression.

Spontaneous symmetry breaking occurs when a system’s equilibrium state lacks a symmetry obeyed by its underlying physical laws.

The Standard Model is the quantum field theory describing known elementary particles and their electromagnetic, weak, and strong interactions.

A standard state is a conventionally defined reference condition used to express thermodynamic properties, activities, and chemical equilibrium constants.

A star is a self-gravitating, luminous astronomical object whose active life is powered primarily by nuclear fusion.

A state function is a thermodynamic property whose value depends only on a system’s present state, not on the process used to reach it.

Statistical mechanics explains macroscopic physical properties through the probabilistic behavior of microscopic constituents.

The strong interaction binds quarks into hadrons and, through its residual effects, holds protons and neutrons together in atomic nuclei.

A quantity describing how spatial arrangement and correlations determine scattering amplitudes or intensities in crystals, liquids, and other materials.

Superconductivity is a quantum state of matter characterized by zero direct-current electrical resistance and magnetic-field expulsion under suitable conditions.

Superfluidity is a quantum state of matter characterized by nondissipative flow, macroscopic coherence, and distinctive rotational and thermal behavior.

A supernova is a powerful stellar explosion that ejects matter, produces a luminous transient, and contributes to the chemical evolution of galaxies.

The superposition principle states that a linear combination of inputs or solutions produces the corresponding linear combination of responses in a linear system.

Supramolecular chemistry studies how intermolecular interactions organize molecules into larger assemblies with distinctive structures, properties, and functions.

Synchrotron radiation is electromagnetic emission from relativistic charged particles following curved paths, used to study matter and astronomical sources.

Taxonomy is the science of identifying, describing, naming, and classifying organisms, providing a framework for studying biological diversity and evolutionary relationships.

Temperature is a physical quantity describing a system’s thermal state and determining the direction of spontaneous heat transfer between ordinary bodies.

A framework developed by Albert Einstein that describes space, time, motion, and gravity through special and general relativity.

Thermal conductivity is the material property that relates conductive heat flux to a temperature gradient.

Thermodynamic activity is a dimensionless measure of a substance’s chemical potential relative to a specified standard state, accounting for nonideal behavior.

A state in which a system has no spontaneous macroscopic changes or net dissipative flows under its imposed constraints.

The thermodynamic limit takes particle number and volume to infinity at fixed density, providing a mathematical foundation for bulk thermodynamics and sharp phase transitions.

A thermodynamic system is a selected quantity of matter or region of space studied through its properties and exchanges with its surroundings.

Thermodynamics studies energy transfers, macroscopic properties of matter, and the constraints governing equilibrium and physical change.

A thylakoid is a membrane-bound compartment that supports the light-dependent reactions of photosynthesis in chloroplasts and most cyanobacteria.

A tide is the periodic rise and fall of sea level driven principally by the Moon’s and Sun’s gravitational influence on Earth.

Time dilation is the relativistic difference in elapsed time associated with relative motion or differences in gravitational potential.

Titration is a quantitative analytical method that determines the amount of a substance from its reaction with a measured quantity of another reagent.

Total internal reflection is the complete reflection of light at a boundary with a lower-index medium when the incidence angle exceeds a critical value.

Transcription is the enzyme-mediated synthesis of RNA from a DNA template, enabling gene expression and the production of functional RNAs.

A transcription factor is a protein that regulates transcription, usually by recognizing regulatory DNA sequences and influencing the transcription machinery.

Transfer RNA is a small RNA molecule that decodes messenger RNA codons and carries amino acids to ribosomes during protein synthesis.

A transition state is the barrier-crossing configuration or ensemble of configurations separating reactants from products in an elementary chemical reaction.

Translation is the ribosome-mediated synthesis of a polypeptide according to the nucleotide sequence of messenger RNA.

A transposable element is a mobile DNA sequence that can relocate or generate new copies within a genome, influencing genome structure, gene regulation, and evolution.

Chinese-born American theoretical physicist who shared the 1957 Nobel Prize in Physics for investigating parity violation in weak interactions.

A quantum principle placing limits on the simultaneous sharpness of certain physical quantities and on the precision of their joint measurement.

A unit cell is a repeating region of a periodic crystal structure, defined by lattice vectors and described by its geometry and atomic contents.

A universality class groups systems with different microscopic structures that share the same large-scale scaling behavior, especially near continuous phase transitions.

Vacuum polarization is the quantum modification of electromagnetic propagation and interactions by fluctuations of charged fields, producing charge screening and measurable radiative corrections.

Valence bond theory describes chemical bonding through localized orbitals, electron spin coupling, and resonance between contributing electronic structures.

Van der Waals forces are nonbonding interactions arising from permanent or induced electric dipoles, influencing molecular cohesion, adsorption, and material structure.

A virtual particle is an internal contribution to a quantum-field-theory calculation, generally off shell, rather than an independently detectable particle.

A virus is an acellular infectious agent that replicates within host cells and carries genetic information as DNA or RNA.

Viscosity measures a fluid’s resistance to deformation during flow, relating viscous stress to the rate at which the fluid deforms.

W and Z bosons are massive elementary particles that mediate the weak interaction and form a central part of electroweak theory.

Walter Pitts was an American logician whose work with Warren McCulloch established foundational mathematical models of neural computation.