The Big Bang  (extret de la versió anglesa de wikipedia)The Big Bang is the cosmological model of the universe whose primary assertion is that the universe has expanded into its current state from a primordial condition of enormous density and temperature. The term is also used in a narrower sense to describe the fundamental “fireball” that erupted at or close to an initial timepoint in the history of our observed spacetime. Theoretical support for the Big Bang comes from mathematical models, called Friedmann models. These models show that a Big Bang is consistent with general relativity and with the cosmological principle, which states that the properties of the universe should be independent of position or orientation.Observational evidence for the Big Bang includes the analysis of the spectrum of light from galaxies, which reveal a shift towards longer wavelengths proportional to each galaxy’s distance in a relationship described by Hubble’s law. Combined with the assumption that observers located anywhere in the universe would make similar observations (the Copernican principle), this suggests that space itself is expanding. The next most important observational evidence was the discovery of cosmic microwave background radiation in 1964. This had been predicted as a relic from when hot ionized plasma of the early universe first cooled sufficiently to form neutral hydrogen and allow space to become transparent to light, and its discovery led to general acceptance among physicists that the Big Bang is the best model for the origin and evolution of the universe. (…)(…) Before observations of dark energy, cosmologists considered two scenarios for the future of the universe. If the mass density of the universe were greater than the critical density, then the universe would reach a maximum size and then begin to collapse. It would become denser and hotter again, ending with a state that was similar to that in which it started—a Big Crunch.[34] Alternatively, if the density in the universe were equal to or below the critical density, the expansion would slow down, but never stop. Star formation would cease as all the interstellar gas in each galaxy is consumed;  (…) The entropy of the universe would increase to the point where no organized form of energy could be extracted from it, a scenario known as heat death.QÜESTIONS:1. Quina  és l’afirmació bàsica de la teoria del Big Bang ?2. En què consisteix l’anomenat principi cosmològic?3. Quines dues proves físiques donen suport a la teoria del Big Bang?3. Quin comportament de l’univers es deriva de les observacions que serveixen de base a la teoria del Big Bang? 4. Quins són els dos escenaris que contemplen els cosmòlegs sobre el futur de l’univers?VOCABULARINarrower: més estret, més limitat“shift towards longer wavelengths”: canviar cap a longitud d’ones més llargues “cosmic microwave background radiation”: radiació de fons de microonesentropy: entropia, tendència al desordre i al caosheat death: mort de la calor