Why "Big Bang" is a bad word

In John Mather's talk last Saturday at Embry-Riddle's Elston Memorial Lecture, he covered all the standard cosmology topics (but focused on his Nobel-prize winning work with COBE, the Cosmic Background Explorer), but also showed some neat videos of how the James Webb Space Telescope will unfold once it gets to the L1 point. You can see one here.

As with all popular talks on the expanding universe, he had to contend with the perennial problem of explaining the current "standard model" of cosmology (the study of the universe and how it came to be the way it is today), known as the ΛCDM model, or the "Lambda Cold Dark Matter" model. It consists of Einstein's equations of general relativity applied to the entire universe, which, in addition to the visible matter (stars, galaxies, dust, etc) is comprised of dark matter (represented essentially by a cold gas) and dark energy (embodied in Einstein's cosmological constant Λ).

Because in every direction we look in the night sky, we see galaxies moving away from us, it is tempting to deduce that we are at the center of the universe. However, it is easy to show that an observer anywhere in the universe would see the same thing, and to draw the conclusion that there is no center. In fact, the so-called Big Bang occurred everywhere simultaneously, and the universe has always been infinite in extent. For this reason, the term "big bang" is really a misnomer, and gives non-astrophysicists the incorrect view that the "explosion" occurred at a single point and moved "outward".

It would be great to rid our lexicon of this term, but unfortunately we are stuck with it (and it clearly shows the weakness of language when describing subjects that are inherently mathematical in nature), and so every popular exposition has to set aside at least some space to explain why this we don't like it. At its core, the standard model of cosmology is based on the expanding space paradigm, in which rather than stuff expanding into already existing space, it is space itself that is expanding.  I can do no better than to quote Edward Harrison from his 1993 paper

From purist point of view one cannot but deplore the expression big bang, "loaded with inappropriate connotations" (McVittie 1974), which conjures up a false picture of a bounded universe exploding from a center in space. In modern cosmology, the universe does not expand in space, but consists of expanding space... 

And he quotes Willem de Sitter (1931), one of the founders of modern cosmology

The theory of [general] relativity brought the insight that space and time are not merely the stage on which the piece is produced, but are themselves actors playing an essential part in the plot.

For those of you who want a more technical explanation, see here, a page from the Physics FAQ, hosted by John Baez.