Science
Physics, chemistry, biology and space, explained from first principles.
Featured in Science
Start with these, then follow the links inside each article wherever they lead.
Theory of relativity
The theory of relativity comprises two physics theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and 1915, respectively. Special relativity applies to all physical phenomena in the absence of gravity.
Quantum mechanics
Quantum mechanics, also known as quantum physics, is the fundamental physical theory that describes the behavior of matter and of light; the behaviors it models typically occur at and below the scale of atoms, and have often been described as counterintuitive. Its concepts and methods have been applied across many disciplines, including quantum chemistry, quantum biology, quantum field theory, quantum technology, and quantum information science.
Periodic table
The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows and columns ("groups"). An icon of chemistry, the periodic table is widely used in physics and other sciences.
Big Bang
The Big Bang is a physical theory that describes how the universe expanded from an early state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including the abundance of light elements, the cosmic microwave background radiation, the redshift of galaxies and the large-scale structure of the universe.
DNA
Deoxyribonucleic acid is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses.
Evolution
Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as genetic drift and natural selection act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations.
Photosynthesis
Photosynthesis is a system of biological processes by which photopigment-bearing autotrophic organisms, such as most plants, algae and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabolism. The term photosynthesis usually refers to oxygenic photosynthesis, a process that releases oxygen as a byproduct of water splitting.
Black hole
A black hole is an astronomical body so compact that its gravity prevents anything, including light, from escaping. Albert Einstein's theory of general relativity, which describes gravitation as the curvature of spacetime, predicts that any sufficiently compact mass will form a black hole.
Electromagnetism
In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature.
Thermodynamics
Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of thermodynamics, which convey a quantitative description using measurable macroscopic physical quantities but may be explained in terms of microscopic constituents by statistical mechanics.
Plate tectonics
Plate tectonics 'pertaining to building') is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3-4 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century.
Germ theory of disease
The germ theory of disease is the currently accepted scientific theory explaining the cause of infectious diseases. It states that microorganisms known as pathogens or "germs" can cause disease.
Vaccine
A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified.
Atom
Atoms are the basic particles of the chemical elements and the fundamental building blocks of matter. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons.
Standard Model
The Standard Model of particle physics is the theory describing three of the four known fundamental forces in the universe and classifying all known elementary particles. It was developed in stages throughout the latter half of the 20th century, through the work of many scientists worldwide, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks.
Climate change
Present-day climate change includes both global warming, the ongoing increase in global average temperature, and its wider effects on Earth's climate system. In a broader sense, climate change also includes previous long-term changes to Earth's climate.
Scientific method
The scientific method is an empirical method for acquiring knowledge through careful observation, rigorous skepticism, hypothesis testing, and experimental validation. Developed from ancient and medieval practices, it acknowledges that cognitive assumptions can distort the interpretation of the observation.
Genetics
Genetics is the study of genes, genetic variation, and heredity in organisms. It is an important branch in biology because heredity is vital to organisms' evolution.
Neuron
A neuron, neurone (British English), or nerve cell, is a cell that is excitable, firing electric signals called action potentials. Neurons form neural networks in the nervous system, mainly in the central nervous system.
Antibiotic
An antibiotic is a type of antimicrobial substance which is active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of such infections.
Higgs boson
The Higgs boson, sometimes called the Higgs particle, is an elementary particle in the Standard Model of particle physics produced by the quantum excitation of the Higgs field, one of the fields in particle physics theory. In the Standard Model, the Higgs particle is a massive scalar boson that couples to particles whose mass arises from their interactions with the Higgs field, has zero spin, even (positive) parity, no electric charge, and no color charge.
Gravitational wave
Gravitational waves are waves of spacetime curvature produced by the relative motion of gravitating masses and which propagate away at the speed of light. They were first predicted by Albert Einstein as a consequence of his general theory of relativity, appearing as "ripples in spacetime curvature".
CRISPR
CRISPR is a family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea. Each sequence within an individual prokaryotic CRISPR is derived from a DNA fragment of a bacteriophage that had previously infected the prokaryote or one of its ancestors.
Speed of light
The speed of light is the speed of electromagnetic waves. Light travels at slower speed inside materials like glass or water; its highest speed is in a vacuum.
Entropy
Entropy is a thermodynamic state variable that quantifies the probabilistic distribution of accessible microstates in a system. The term and the concept are used in diverse fields, from classical thermodynamics, to the microscopic description of nature in statistical physics, and the principles of information theory.
Cell (biology)
The cell is the basic structural and functional unit of all forms of life or organisms. The term comes from the Latin word cellula meaning 'small room'.
Protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another.
Newton's laws of motion
Newton's laws of motion are three physical laws that describe the relationship between the motion of an object and the forces acting on it. These laws, which provide the basis for Newtonian mechanics, can be paraphrased as follows: A body remains at rest, or in motion at a constant speed in a straight line, unless it is acted upon by a force.
Chemical reaction
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated.
Radioactive decay
Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
Energy
Energy 'activity') is the quantitative property that is transferred to a body or to a physical system, recognizable in the capacity to do work and in the form of heat and light. Energy is a conserved quantity, the law of conservation of energy states that energy can be converted in form, but not created or destroyed.
Gravity
In physics, gravity, also known as gravitation or a gravitational interaction, is a fundamental interaction, which may be described as the force that draws material objects towards each other. The gravitational attraction between clouds of primordial hydrogen and clumps of dark matter in the early universe caused the hydrogen gas to coalesce, eventually condensing and fusing to form stars.
Mathematics
Mathematics is a field of knowledge concerned with abstract concepts such as numbers, geometric shapes, sets, functions, and probabilities. It uses logical reasoning and proof to study and establish their properties, often expressed as theorems, formulas, and equations.
Pi
The number π is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle's circumference to its diameter. It appears in many formulae across mathematics and physics, and some of these formulae are commonly used for defining π, to avoid relying on the definition of the length of a curve.
Prime number
A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number.
Calculus
Calculus is the branch of mathematics that studies continuous change, and is the principal precursor of modern mathematical analysis. Originally called infinitesimal calculus or the calculus of infinitesimals, it has two major branches, differential calculus and integral calculus.
Guides in Science
The cell: the unit everything living is built from
What is inside a cell, what each part does, and the difference between the two great classes of cell.
DNA, RNA and how a gene becomes a protein
The structure of the molecule, the code it carries, and the two steps that turn instructions into working machinery.
Evolution by natural selection
The mechanism in four conditions, the evidence behind it, and the misconceptions that cause most exam mistakes.
Human body systems, and how they cooperate
A tour of the major systems, what each one solves, and the principle that links all of them.
Ecosystems: energy, matter and why food chains are short
How energy moves through living systems, why it runs out quickly, and how matter differs by cycling.
Atoms and the periodic table
What atoms are made of, why electrons sit where they do, and why the table is shaped the way it is.
Chemical bonding and why substances behave differently
Ionic, covalent and metallic bonding, intermolecular forces, and how structure explains properties.
Reactions, equations and the mole
Conservation of mass, balancing, reaction types, and the counting unit that makes calculations possible.
Acids, bases and the pH scale
What makes something acidic, why the scale is logarithmic, and how buffers hold a solution steady.
Motion and forces
Newton's three laws, what they actually claim, and the reasoning habits that make mechanics problems tractable.
Energy, work and power
Conservation, energy transfer, efficiency, and why energy is never really used up.
Waves, sound and light
Wave behaviour, the electromagnetic spectrum, and why light stubbornly behaves as both wave and particle.
Electricity and circuits
Charge, current, voltage and resistance, with the analogies that help and the ones that mislead.
Plate tectonics: why continents move
The evidence for drifting plates, the three boundary types, and what each one builds or destroys.
Climate and weather: the system that moves heat
Why weather happens, how climate differs from it, and the physics behind the greenhouse effect.
The solar system, stars and the life cycle of matter
How the solar system formed, how stars work, and why almost every atom in you was made inside one.
Algebra: what the letters actually mean
Expressions, equations and functions, plus the rearrangement habits that stop most algebra errors.
Geometry and trigonometry
Angle reasoning, similarity, the Pythagorean theorem and the trigonometric ratios, tied together.
Probability and statistics, and how they get misused
Averages, spread, probability rules, and the reasoning errors that appear constantly in real arguments.
How to solve a problem you have not seen before
A general method for unfamiliar questions, and why practising retrieval beats rereading worked examples.
Genetics and inheritance
From Mendel's peas to the human genome: how traits pass from parents to children and why siblings differ.
Viruses and bacteria
Two very different kinds of microbe: how each lives, how they cause disease and why they need different treatments.
States of matter
Solids, liquids, gases and plasma, what holds each together, and what happens when matter melts, boils or freezes.
Organic chemistry basics
Why carbon forms the backbone of life, how organic molecules are named and grouped, and where they show up every day.
Sound and hearing
How vibrations travel through air, why sounds have pitch and loudness, and how the ear turns waves into signals.
Magnetism
Why magnets attract and repel, how electricity and magnetism are linked, and how Earth's magnetic field protects life.
Volcanoes and earthquakes
Why the ground shakes and mountains erupt, how scientists measure them, and how people reduce the danger.
The water cycle
How water moves between oceans, air, ice, rivers and underground, and why the cycle is changing as the planet warms.
Numbers and number systems
How people learned to count, where zero came from, and the growing family of numbers from integers to irrational and imaginary ones.
Statistics in everyday life
Averages, samples, correlation and misleading graphs: the statistical ideas that help you read the news critically.