gravity-collapse structure
71Unsolved problems in physics — This is a list of some of the major unsolved problems in physics. Some of these problems are theoretical, meaning that existing theories seem incapable of explaining some observed phenomenon or experimental result. The others are experimental,… …
72Timeline of astronomy — Timeline of astronomy2500 BCMany ancient sites are thought to have astronomical significance, such as the Ancient Egyptian pyramids, Harappan shell instruments, British megaliths, and buildings in China and Latin America.In Lothal, the ancient… …
73Construction of the World Trade Center — For the post 9/11 rebuilding and ongoing construction at the World Trade Center site, see World Trade Center site. The completed World Trade Center in March 2001 The construction of the World Trade Center was conceived as an urban renewal project …
74astronomy — /euh stron euh mee/, n. the science that deals with the material universe beyond the earth s atmosphere. [1175 1225; ME astronomie ( < AF) < L astronomia < Gk. See ASTRO , NOMY] * * * I Science dealing with the origin, evolution, composition,… …
75relativity — /rel euh tiv i tee/, n. 1. the state or fact of being relative. 2. Physics. a theory, formulated essentially by Albert Einstein, that all motion must be defined relative to a frame of reference and that space and time are relative, rather than… …
76technology, history of — Introduction the development over time of systematic techniques for making and doing things. The term technology, a combination of the Greek technē, “art, craft,” with logos, “word, speech,” meant in Greece a discourse on the arts, both… …
77Seismic retrofit — Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. Other retrofit techniques are applicable to areas subject to tropical cyclones,… …
78cave — cavelike, adj. /kayv/, n., v., caved, caving. n. 1. a hollow in the earth, esp. one opening more or less horizontally into a hill, mountain, etc. 2. a storage cellar, esp. for wine. 3. Eng. Hist. a secession, or a group of seceders, from a… …
79Christianity — /kris chee an i tee/, n., pl. Christianities. 1. the Christian religion, including the Catholic, Protestant, and Eastern Orthodox churches. 2. Christian beliefs or practices; Christian quality or character: Christianity mixed with pagan elements; …
80geology — /jee ol euh jee/, n., pl. geologies. 1. the science that deals with the dynamics and physical history of the earth, the rocks of which it is composed, and the physical, chemical, and biological changes that the earth has undergone or is… …
