Think of the Big Bang, and you probably imagine a moment in time when matter, energy and space itself all burst into existence at once. Yet many astrophysicists now believe that the “Big Bang” was actually two distinct events: first the inaugural instant of space and time, and second the generation of most of the “stuff” that populates that space. So, which really deserves to be called the Big Bang?
This article calls attention to a dispute I’ve noticed lately. Some physicists insist that cosmic inflation happened before the Big Bang, others that the Big Bang was the moment of everything began. Of course, if you accept the theory of eternal inflation, then there was no beginning, and the period of inflation ending is the point of the Big Bang.
Given how imprecise the term “Big Bang” actually is, how inappropriate of a term it is for describing what it applies to anyway, the debate strikes me a somewhat meaningless. (No, as the article describes, I don’t have a catchier name than “Big Bang”. That still doesn’t make it accurate.)
Personally, I’ve always thought of the Big Bang starting from the earliest moments of our universe that we can know anything about, and lasting until the cosmic microwave background was generated (after all, the CMB was often called the “afterglow” of the big bang), but I realize that isn’t how most cosmologists think about it. Of course, an argument could be made that we’re still living within the Big Bang, since everything is still expanding and cooling, although dark energy complicates that assertion.
The debate does serve one purpose however. It illuminates the stages of the early universe, which given how difficult these concepts are to describe, is actually a good thing.