My usual definition of cosmology, the one I spew out much too frequently, is simply this: cosmology is the branch of astrophysics concerning the structure and history of the entire Universe (but not necessarily its origins).
Traditionally, it has been the realm of philosophy and religion. Ancient Hindu cosmology describes the origin of the Universe through the ‘Golden Egg’, and suggests that the Universe is cyclic in nature. To quote one of my own personal heroes, Carl Sagan, they believe that the Universe goes through an “endless cycle of deaths and rebirths”. Astronomers from both from ancient times and the Middle Ages interchangeably favoured Earth- and Sun-centred Universes. In the 12th century AD, the idea of infinite space and infinite universes were proposed by Islamic cosmologists. Others again were convinced that the universe was flat and sat on the shell of a giant turtle; as Stephen Hawking wrote in his Brief History of Time (1988),
“its turtles all the way down!”
Cosmology as we know it today is slightly different. Cosmologists now deal with both the very small and the very big. Their investigations range from tiny ripples in space and the primordial soup of fundamental particles in the early Universe to the clustering of galaxies on large scales to form gargantuan strings of superclusters. They also have the privilege of dealing with some pretty brain-warping concepts: the accelerating expansion of the universe; whether the universe is flat or curved in four dimensions; and whether these factors will lead to a ‘big crunch’.
What’s more, extreme technological development has allowed what is known as precision cosmology to advance rapidly in the past twenty years; cosmologists now have the power of data. However…
“Philosophers of science have repeatedly demonstrated that more than one theoretical construction can always be placed upon a given collection of data. History of science indicates that, particularly in the early developmental stages of a new paradigm, it is not even very difficult to invent such alternates.”
That’s the wisdom of Thomas Kuhn, in Chapter 7 of The Structure of Scientific Revolutions (1962). And that, I think, is where controversy comes in.
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