Big Bang is a past horizon, though in practice our view is also limited by the opacity of the universe at early times. So our view cannot extend further backward in time, though the horizon recedes in space. If the expansion of the universe continues to accelerate, there is a future horizon as well. English astronomer Fred Hoyle is credited with coining the term "Big Bang" during a 1949 BBC radio broadcast, saying: "These theories were based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past." It
History of the Big Bang theory of the primeval atom) that the universe began with the "explosion" of the "primeval atom" — what was later called the Big Bang. Lemaître first took cosmic rays to be the remnants of the event, although it is now known that they originate within the local galaxy. Lemaître had to wait until shortly before his death to learn of the discovery of cosmic microwave background radiation, the remnant radiation of a dense and hot phase in the early universe. Hubble's Law suggested that the universe was expanding, contradicting the cosmological principle whereby the universe, when viewed on sufficiently large distance