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The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic...

Voltage, also known as (electrical) potential difference, electric pressure, or electric tension is the difference in electric potential between two points...

Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measured with a thermometer. It reflects...

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

Werner Karl Heisenberg (/ˈhaɪzənbɜːrɡ/; German: [ˈvɛʁnɐ kaʁl ˈhaɪzn̩bɛʁk] ; 5 December 1901 – 1 February 1976) was a German theoretical physicist, one...

A gamma ray, also known as gamma radiation (symbol γ ), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic...

In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability...

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

Space is a three-dimensional continuum containing positions and directions. In classical physics, physical space is often conceived in three linear dimensions...

X-rays (X-radiation) are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist...

A neutron star is the collapsed core of a massive supergiant star. It results from the supernova explosion of a massive star—combined with gravitational...

In physics, spacetime, also called the space-time continuum, is a mathematical model that fuses the three dimensions of space and the one dimension of...

Nuclear fusion is a reaction in which two or more atomic nuclei, usually deuterium and tritium (hydrogen isotopes), combine to form one or more different...

The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetic, weak and strong interactions...

The law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be conserved over time. In the case...

In thermodynamics, heat is the thermal energy transferred between systems due to a temperature difference. In colloquial use, heat sometimes refers to...

Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces...

The chronology of the universe describes the history and future of the universe according to Big Bang cosmology. Research published in 2015 estimates the...

Sir Joseph John Thomson OM FRS (18 December 1856 – 30 August 1940) was a British physicist and Nobel Laureate in Physics, credited with the discovery of...

Classical mechanics is a physical theory describing the motion of objects such as projectiles, parts of machinery, spacecraft, planets, stars, and galaxies...