Columbia Encyclopedia

Search results

440 results found

dark matter

(Encyclopedia)dark matter, material that is believed to make up nearly 27% of the mass of the universe but is not readily visible because it neither emits nor reflects electromagnetic radiation, such as light or ra...

measurement

(Encyclopedia)measurement, determination of the magnitude of a quantity by comparison with a standard for that quantity. Quantities frequently measured include time, length, area, volume, pressure, mass, force, and...

neutron

(Encyclopedia)neutron, uncharged elementary particle of slightly greater mass than the proton. It was discovered by James Chadwick in 1932. The stable isotopes of all elements except hydrogen and helium contain a n...

calorimetry

(Encyclopedia)calorimetry kălˌərĭmˈətrē [key], measurement of heat and the determination of heat capacity. Heat is evolved in exothermic processes and absorbed in endothermic processes; such processes includ...

Stowe, Calvin Ellis

(Encyclopedia)Stowe, Calvin Ellis stō [key], 1802–86, American educator, b. Natick, Mass., grad. Bowdoin College, 1824, and Andover Theological Seminary, 1828; husband of Harriet Beecher Stowe. He was professor ...

Empedocles

(Encyclopedia)Empedocles ĕmpĕdˈəklēz [key], c.495–c.435 b.c., Greek philosopher, b. Acragas (present Agrigento), Sicily. Leader of the democratic faction in his native city, he was offered the crown, which h...

quantum theory

(Encyclopedia)quantum theory, modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity togethe...

alpha particle

(Encyclopedia)alpha particle, one of the three types of radiation resulting from natural radioactivity. Alpha radiation (or alpha rays) was distinguished and named by E. R. Rutherford in 1909, who found by measurin...

't Hooft, Gerardus

(Encyclopedia)'t Hooft, Gerardus, 1946–, Dutch theoretical physicist, Ph.D. Univ. of Utrecht, 1972. He has been a professor at the Univ. of Utrecht since 1977. 't Hooft shared the 1999 Nobel Prize in Physics with...

gravel

(Encyclopedia)gravel, particles of rock, i.e., stones and pebbles, usually round in form and intermediate in size between sand grains and boulders. Gravel is composed of various kinds of rock, the most common const...