The Big Bang Theory
Experiment
The Big Bang is a cosmological model of the initial conditions and
subsequent development of the universe. It is supported by the most
comprehensive and accurate explanations from current scientific evidence
and observation. As used by cosmologists, the term Big Bang generally
refers to the idea that the universe has expanded from a primordial hot
and dense initial condition at some finite time in the past, and continues
to expand to this day.
The scientist and Roman Catholic priest
Georges Lemaître proposed what became known as the Big Bang theory of the
origin of the Universe, although he called it his "hypothesis of the
primeval atom". The framework for the model relies on Albert Einstein's
general relativity and on simplifying assumptions (such as homogeneity and
isotropy of space). The governing equations had been formulated by
Alexander Friedmann. After Edwin Hubble discovered in 1929 that the
distances to far away galaxies were generally proportional to their
redshifts, as suggested by Lemaître in 1927, this observation was taken to
indicate that all very distant galaxies and clusters have an apparent
velocity directly away from our vantage point: the farther away, the
higher the apparent velocity. If the distance between galaxy clusters is
increasing today, everything must have been closer together in the past.
This idea has been considered in detail back in time to extreme densities
and temperatures, and large particle accelerators have been built to
experiment on and test such conditions, resulting in significant
confirmation of the theory, but these accelerators have limited
capabilities to probe into such high energy regimes. Without any evidence
associated with the earliest instant of the expansion, the Big Bang theory
cannot and does not provide any explanation for such an initial condition;
rather, it describes and explains the general evolution of the universe
since that instant. The observed abundances of the light elements
throughout the cosmos closely match the calculated predictions for the
formation of these elements from nuclear processes in the rapidly
expanding and cooling first minutes of the universe, as logically and
quantitatively detailed according to Big Bang nucleosynthesis.
Fred
Hoyle is credited with coining the phrase "Big Bang" during a 1949 radio
broadcast, as a derisive reference to a theory he did not subscribe to.
Hoyle later helped considerably in the effort to figure out the nuclear
pathway for building certain heavier elements from lighter ones. After the
discovery of the cosmic microwave background radiation in 1964, and
especially when its spectrum (i.e., the amount of radiation measured at
each wavelength) sketched out a blackbody curve, most scientists were
fairly convinced by the evidence that some Big Bang scenario must have
occurred.
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