Science

Nitrogen is the chemical element with atomic number 7, the main constituent of Earth’s atmosphere and an essential component of living organisms.

The nitrogen cycle is the network of biological, chemical, and physical processes that moves nitrogen among the atmosphere, organisms, soils, waters, and sediments.

Nitrogen fixation converts molecular nitrogen into chemically combined forms, supplying essential nutrients through biological, atmospheric, and industrial processes.

The Nobel Prize in Chemistry is an international award established by Alfred Nobel’s will to recognize important chemical discoveries and improvements.

An international award established by Alfred Nobel’s will, recognizing important discoveries and inventions in physics since 1901.

Noether’s theorem connects continuous symmetries of an action with conserved quantities, explaining the mathematical origin of many conservation laws in physics.

Nuclear binding energy is the energy required to separate an atomic nucleus completely into its constituent protons and neutrons.

Nuclear fission is the splitting of a heavy atomic nucleus into smaller nuclei, releasing energy and usually neutrons that can sustain a chain reaction.

Nuclear fusion combines light atomic nuclei into heavier nuclei, powering stars and providing the physical basis for experimental fusion energy systems.

Nuclear magnetic resonance is the resonant response of magnetic atomic nuclei to radiofrequency fields, enabling molecular analysis and magnetic resonance imaging.

Nuclear physics studies atomic nuclei, their constituents and interactions, and the transformations and forms of matter arising from nuclear processes.

Nuclear power generates electricity from nuclear reactions, principally controlled fission, using reactor heat to drive turbines and generators.

Nucleic acids are nucleotide polymers that store, transmit, and express genetic information and perform structural, regulatory, and catalytic functions.

A nucleon is a proton or neutron, the two closely related composite particles that constitute ordinary atomic nuclei.

A nucleosome is the basic repeating unit of eukaryotic chromatin, consisting of DNA wrapped around a core of histone proteins.

Nucleosynthesis is the formation of atomic nuclei through nuclear reactions, explaining the cosmic origins and abundances of chemical elements and their isotopes.

A nucleotide is a phosphorylated sugar–base compound that forms nucleic acids and participates in cellular energy transfer, metabolism, and signaling.

Ocean acidification is the long-term decline in seawater pH, driven primarily by absorption of carbon dioxide released by human activities.

Ohm’s law describes the proportional relationship between voltage and electric current in a conductor whose resistance remains constant under specified conditions.

Optics is the branch of physics concerned with light, its propagation and interaction with matter, and the formation and manipulation of images.

Orbital hybridization describes atomic orbitals as linear combinations that help represent directional bonding and molecular geometry.

An order parameter is a quantity that distinguishes phases of a physical system and characterizes the type and degree of ordering.

Osmosis is the net movement of solvent through a selectively permeable membrane, driven by differences in solvent chemical potential.

Pair production is the creation of a particle and its antiparticle from energy supplied by radiation, collisions, or an external field.

Paleontology studies the history of life through fossils, reconstructing ancient organisms, evolutionary relationships, environments, and changes across geological time.

Paramagnetism is a magnetic response in which an applied field induces magnetization in the same direction, without spontaneous magnetic ordering.

Parity describes how physical quantities and quantum states transform under spatial inversion, a symmetry conserved by electromagnetic and strong interactions but violated by weak interactions.

A particle accelerator uses electromagnetic fields to increase the energy of charged particles, producing beams for fundamental research, medicine, and industry.

A particle jet is a collimated spray of particles produced in high-energy interactions, usually associated with an energetic quark or gluon.

Particle physics investigates the fundamental constituents of matter and the interactions governing their behavior.

A partition function normalizes statistical weights and connects microscopic states to thermodynamic properties and probabilistic models.

The path-integral formulation expresses quantum evolution as a sum of amplitudes over possible histories, weighted by their action.

A quantum principle forbidding identical fermions from occupying the same single-particle state, underlying atomic structure, the stability of matter, and degeneracy pressure.

Peer review is the evaluation of scholarly work by relevant experts to inform publication, funding, and research-quality decisions.

A peptide bond is an amide linkage joining amino acid residues, forming the backbone of peptides and proteins and constraining their molecular structure.

Permeability measures how readily a porous material transmits fluids through its connected pores and fractures.

Permittivity describes the relationship between electric displacement and electric field, governing a medium’s polarization response, capacitance, and electromagnetic-wave behavior.

Perturbation theory approximates a difficult mathematical or physical problem through systematic corrections to a simpler, understood problem.

The phase problem is the loss of wave-phase information in intensity measurements, which complicates reconstructing structures from diffraction data.

Phase space represents all possible states of a dynamical system, allowing its evolution to be studied through trajectories, geometry, and statistical distributions.

A phase transition is a change between distinct states of matter or collective organization as physical conditions vary.

A phenotype is an organism’s observable or measurable characteristics, arising from its genetic constitution, environmental influences, and development.

A phonon is a quantum of collective vibration in matter, central to the microscopic description of sound, heat capacity, and thermal transport.

A phosphodiester bond is a phosphate-based covalent linkage that forms the backbone of DNA and RNA and occurs in other biological molecules.

The photoelectric effect is the emission of electrons from matter after absorbing electromagnetic radiation, providing foundational evidence for the quantum nature of light.

Photolithography uses patterned light and photosensitive materials to define microscopic structures, especially in semiconductor manufacturing.

A photon is a quantum of the electromagnetic field, carrying energy and momentum and mediating electromagnetic interactions.

Phylogenetics is the study and inference of evolutionary relationships among organisms, genes, and other biological entities.

Physical chemistry uses physical laws, mathematical models, and experimental measurements to explain chemical structure, properties, equilibrium, and change.

Physics is the natural science that studies matter, energy, motion and force, and the basic interactions that govern the universe from subatomic particles to the cosmos.

Pierre Curie was a French physicist whose research established key findings in piezoelectricity, magnetism, and radioactivity.

A pion is one of three light, spin-zero mesons that play a central role in nuclear forces and the low-energy behavior of the strong interaction.

The Planck constant sets the scale of quantum phenomena, relates photon energy to frequency, and provides the basis for the SI definition of the kilogram.

Plasma is an ionized state of matter whose mobile charged particles exhibit collective electromagnetic behavior.

A plasmid is an independently replicating DNA element that commonly carries accessory genes and serves as a tool for genetic research.

Polarization describes the orientation and temporal behavior of a wave’s transverse oscillations, particularly the electric field of light.

Polyadenylation adds an adenosine-rich tail to RNA, influencing messenger RNA maturation, translation, stability, and degradation.

Population genetics studies genetic variation within and between populations and the processes that change allele frequencies across generations.

Porosity is the fraction of a material’s total volume occupied by pores or voids, whether empty or filled with fluids.

A porous material is a solid containing voids whose size, connectivity, and surface chemistry influence its physical properties and interactions with fluids.