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PART of what turned me into a theoretical cosmology enthusiast as a child was watching the documentary A Brief History of Time and hearing about the mystery around the big bang. It showed how the equations that we use to describe space-time broke down into a singularity when we ran time all the way back to the beginning. What does this imply about the origins and history of space-time – about the ultimate cosmological tale?

When the film came out in 1991, popular science books and magazines used the term big bang to refer to the moment when our universe came to be. It was the beginning of time and the beginning of space, and thus the beginning of space-time. In a very basic way, this wasn’t super hard to relate to. For example, in my family’s own Jewish tradition, our origin story for the universe begins quite similarly.

I am now a professor of physics and when I attend physics conferences, I have a very different relationship to the idea of the big bang than I did back in the early 90s. One might expect that this is because I have gone through extensive technical training, including passing intense postgraduate exams on general relativity and quantum field theory in relativistic space-times. And it’s true, my understanding of what that mysterious singularity represented deepened.

But actually, what lay people like me didn’t know 30 years ago is that a transformation was already happening in the physics community. How people were thinking about the big bang was shifting. The big bang no longer necessarily referred to the beginning. And there may not have been a beginning at all – at least not in the traditional terms.

There have been two changes to the way physicists think about this cosmological timeline. The first is that research on inflationary models, which study the exponential expansion of space-time, indicate that inflation may be an eternal process. As in, the universe may not have had a beginning moment, and we may live in what is called an eternally inflating universe, one that was expanding exponentially even before what we call the big bang. Mathematically, this seems the most likely scenario – assuming inflation is correct.

“The universe may not have had a beginning and we may live in what is called an eternally inflating universe”

Second, these days, people often use “hot big bang” to refer to a time period, rather than a single moment. The story goes that in the early stages of our corner of space-time, what we might call the visible universe, the universe was very hot and dense. This hot big bang era was filled with an energetic goo from which atoms would eventually emerge and begin to cluster, along with dark matter, into the structures we observe today: stars, galaxies, planets and, yes, people.

In a recent email to me and my editor, one of these people structures – a thoughtful reader – sent in a question that points to this transformation in how we think about the big bang. The reader noted that, for a while, it was fashionable to publish articles about the big bang and these days there are fewer. While I can’t speak to publishing choices by the editors at this magazine or any other, I can say that in recent years, there has been more (if not total) consensus in the cosmology community about the likely scenario for the inflationary universe – that our space-time went through a period of rapid, exponential expansion. A plethora of data supports the inflationary picture, which mathematically favours an eternal scenario.

There are, of course, detractors. Paul Steinhardt, one of the early thinkers on inflation, has since become one of its most vocal critics. But even in his competitor model of the universe, the big bang is replaced by a big bounce and a cyclic universe. The key point, ultimately, is that physicists don’t like singularities, and the search has always been on for a more satisfying model. Much as the idea of a “beginning moment” might satisfy the intuition we have developed in a world where some of the most dominant religious traditions teach us that there is a definitive beginning, from a scientific point of view, the singularity is a mathematical problem to be solved.

Models of the very early universe are hard to test directly. That doesn’t stop people from trying. For example, an eternally inflating universe implies that we live in one space-time bubble of many. Astrophysicist Hiranya V. Peiris, famous for her work on the cosmic microwave background (CMB) radiation, has with co-authors proposed that CMB data can be used to test interactions between our space-time bubble and others.

If I had to theorise why it is less popular to write about this in popular publications, I’d say it is because there haven’t been any new splashy ideas about it recently. The question of whether there was a beginning, of course, remains infinitely interesting!