In this clip from the BBC, Brian Cox is clearly talking about the currently most popular theory for what happened before the big bang. It’s called eternal inflation. In eternal inflation, the creation of our universe is not singular, so strictly speaking there isn’t any bang. According to this theory, our universe is created by a quantum fluctuation in a field called the “inflaton”. The inflaton creates this fluctuation, and that creates a bubble which then rapidly inflates, hence the name. At some point the inflation stops, and all the energy from the inflaton field is converted into matter. All the matter around us is created only at that point when the inflaton field dumps its energy. In the literature, this event is usually referred to as “reheating”.

What happened with Brian Cox’s explanation is that he made it sound as if the reheating is the big bang. I mean, listen to it yourself: “As inflation ended, the ocean of energy was converted into matter. Big Bang.” So basically he just used the word “Big Bang” for something completely different. It’s somewhat of a disease among science communicators that I’ve complained about before because it causes a lot of confusions, but let me not go there again. Maybe more importantly, even leaving aside that we don’t know whether eternal inflation is even correct, it doesn’t remove the Big Bang per se, it just removes the big bang in our universe.

In eternal inflation, there are infinitely many of those quantum fluctuations and each gives rise to a new universe. This entire multiverse of eternal inflation however must also have had a beginning at finite time, an then you can ask, well, what happened before that. So eternal inflation just moves the problem elsewhere.