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The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological...

The theory of relativity comprises two physics theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and...

Energy (from Ancient Greek ἐνέργεια (enérgeia) 'activity') is the quantitative property that is transferred to a body or to a physical system, recognizable...

In classical thermodynamics and kinetic theory, temperature reflects the average kinetic energy of the particles in a system, providing a quantitative...

Light, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum...

An X-ray is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays...

Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to...

Unsolved problem in physics What is dark matter? How was it generated? More unsolved problems in physics In astronomy and cosmology, dark matter is an...

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word...

In quantum mechanics, Schrödinger's cat is a thought experiment concerning quantum superposition. In the thought experiment, a hypothetical cat in a closed...

The degree Celsius is the unit of temperature on the Celsius temperature scale (originally known as the centigrade scale in English), one of two temperature...

A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities...

Plasma (from Ancient Greek πλάσμα (plásma) 'that which has been formed or moulded or the result of forming or moulding') is a state of matter that results...

The dew point is the temperature that air, of a constant absolute humidity and pressure, must be cooled to in order for the relative humidity to rise to...

In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called...

Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable...

When two fluid layers move relative to each other, a friction force develops between them and the slower layer acts to slow down the faster layer. This...

A proton is a stable subatomic particle, symbol p, H+, or 1H+ with a positive electric charge of +1 e (elementary charge). Its mass is slightly less than...

Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify...

The joule (/dʒuːl/ JOOL, or /dʒaʊl/ JOWL; symbol: J) is the unit of energy in the International System of Units (SI). In terms of SI base units, one joule...