The Big Bang as Scientific Fact

Unlike some of the other contributors to this volume, I have the luxury of dealing with a well defined topic for which a great deal of hard data are available. My charge is to argue why a reasonable person should accept the Big Bang as proven scientific fact. In his recent book Before the Beginning,the British cosmologist Sir Martin Rees wrote that he was “fairly sure” of the Big Bang - at the 90% level. Actually, I suspect that Martin was being a bit coy, for in fact it is impossible to do any constructive research in cosmology today without standing firmly on the Big Bang model. Most cosmologists, I suspect - I among them - would side with the famous Russian cosmologist Jakob Zeldovich, who said in 1982, “I am as sure of the Big Bang as I am that the Earth goes around the Sun”.

My task is specifically to motivate and defend the Big Bang model, but what exactly do I mean by the “Big Bang”? In what follows I take a narrow definition of the Big Bang as a moment in the finite past at which our Universe had very high density and (as explained later) a very high temperature. This claim is concrete, and the evidence for it is overwhelming. In defining the Big Bang so narrowly, I am deliberately sidestepping such broader questions as, did the Universe begin with the Big Bang? Did space and time begin with the Big Bang? What came before the Big Bang? These and other harder questions will be the topic of later chapters in this volume - I have the easy job of setting the stage.

Contributed by: Dr. Sandra Faber