In the Beginning

Fans of The Big Bang Theory will know that “our whole universe was in a hot, dense state”— which is indeed how scientists often describe the earliest moments of the cosmos. The devil, though, is in the details. We’re pretty confident in the big bang model of cosmology (now slightly harder to google, thanks to the TV show), which says that the universe came into existence a bit less than 14 billion years ago and has been expanding and cooling ever since. But what was it, exactly, that banged? Was it a single bang? Could there have been multiple bangs leading to multiple universes? What, if anything, came before?

This is where Niayesh Afshordi and Phil Halper pick up the story in Battle of the Big Bang. Afshordi is an astrophysicist at the University of Waterloo and an associate faculty member at the Perimeter Institute for Theoretical Physics, and Halper is a science popularizer and YouTuber. They make a good pair: Afshordi handles the overall narration while drawing on the many interviews that Halper has conducted with experts over the last fifteen years or so.

Our understanding of the big bang dates back to the early twentieth century, when Albert Einstein developed his theory of gravity, known as general relativity. Soon after coming up with his equations, he tried applying them to the universe as a whole and found, surprisingly, that they didn’t seem to allow for a static universe; instead, they appeared to require the universe to be either expanding or contracting. At first, Einstein balked. Like most scientists, he believed in an unchanging, static universe. At around the same time, however, astronomers were learning how to measure the distances to far‑off galaxies. They soon discovered not only that those galaxies are moving away from our own Milky Way but that the more distant the galaxy, the faster it’s receding. (This does not mean we’re in a special place: observers in any other galaxy would find the same effect.) The universe is expanding, just as Einstein’s equations suggested.

The implications are profound. Wind back the clock, and the universe gets smaller. If you go back far enough, it must have been incredibly tiny. Eventually the notion of a cosmic explosion took root, though the term “big bang” was coined only in 1949 when the astronomer Fred Hoyle used it on a BBC Radio program. (Here Afshordi and Halper add a tidbit that I wasn’t aware of. While we’re often told that Hoyle meant the term to be disparaging, the historian Helge Kragh has suggested that he was merely trying to explain the various proposals for the universe’s origins in layman’s terms.)

The most compelling piece of evidence for the big bang was found — by accident — when radio astronomers detected a faint all‑sky glow in the mid-1960s. The universe is awash in this microwave radiation, which we now call the cosmic microwave background, or CMB. (Although the discovery of the CMB is usually credited to the American astronomers Arno Penzias and Robert Wilson, the authors point out that this microwave glow was, in fact, noticed by a Canadian astronomer, Andrew McKellar, some twenty-five years earlier. McKellar had been studying the chemistry of interstellar space and did not realize the significance of the all‑sky microwave radiation. Nonetheless, Afshordi and Halper describe him as “the first person in history to see the afterglow of the Big Bang.”)

But puzzles remained. One problem was that the CMB is very “smooth”: that is, there’s only the tiniest difference between its most and least intense regions. If the universe were small, that wouldn’t be so surprising: its various regions could have interacted with one another, smoothing everything out. But the universe is big — and it’s been around for only 14 billion years. There just hasn’t been enough time for this smoothing out to happen, across such large distances.

In the early 1980s, cosmologists put forward a possible solution: a modified version of the big bang picture called inflation. According to inflation, the universe went through a period of incredibly rapid expansion during its first split second of existence. This moment of exponential growth helps to explain why the universe is so large and yet so smooth. But inflation, depending on which version you support, delivers more than this insight: some physicists have argued that if it could happen once, why not a million times, or an infinite number of times? Inflation thus paved the way for the “eternally inflating multiverse,” one of several scenarios that physicists have been pondering in which our universe is just one of many.

The evidence for inflation is circumstantial: it’s consistent with what we see, but some other theory might be equally compatible. What would it take to prove that the universe’s hypothesized growth spurt actually happened? In 2014, astronomers using the BICEP telescope thought they had done it. (The acronym stands for Background Imaging of Cosmic Extragalactic Polarization, and yes, astronomers are really into acronyms.) Their experiment, located at the South Pole, was one of many designed to map the CMB in fine detail; the idea was to look for barely discernible patterns in the radiation called B‑modes. These subtle patterns were said to be evidence of ripples in space-time known as gravitational waves — or, more precisely, the imprint that those waves left on the CMB at the very beginning of the universe. It was not to be, however. Subsequent observations showed that the signal that BICEP measured was largely the result of dust in our own Milky Way and not a signature of early universe physics. (Had the astronomers really snagged those B‑modes, arguably clinching the case for inflation, it would have been a Nobel-worthy discovery; indeed, Brian Keating, who conceived the experiment, titled his 2018 book Losing the Nobel Prize.)

In the years that followed, the debates surrounding inflation only became more heated. In 2017, Anna Ijjas, Paul J. Steinhardt, and Avi Loeb argued in Scientific American that inflation, by predicting a possibly infinite array of universes, ends up saying nothing about the one we actually live in. (Steinhardt is an especially interesting case; an early proponent of inflation, he later turned against it because of this lack of explanatory power.) Inflation’s defenders were incensed by the critique and quickly penned a reply, recruiting such luminaries as Stephen Hawking and the Nobel laureate Steven Weinberg to sign their rebuttal.

Here the authors’ status as insiders pays off: they’ve spoken with all the key players on both sides of the inflation kerfuffle and do an admirable job of illustrating how it unfolded. Loeb, for example, “compared inflationary cosmologists to religious zealots who ‘feel offended if someone doubts their idea.’ ” (Just a few years later, he argued that the object known as ‘Oumuamua, which passed through our solar system in 2017, was likely an alien spacecraft, and he railed against those who doubted him.)

Tension between inflation’s backers and detractors, Afshordi and Halper note, remains high. When Halper invited several of the key players to a debate, Ijjas and Steinhardt both refused. Steinhardt claimed that “the idea had done too much damage to the credibility of science and was too trivial to be worth discussing.” For his part, Afshordi says he believes “that most cosmologists side with inflation, but many are uneasy with its accompanying multiverse.”

Inflation is not the only game in town, and several competing cosmological models — all of them variations on the standard big bang view — battle it out in this book’s meaty chapters. A variety of “cyclic” models have been put forward, for instance. They suggest that what we interpret as the big bang was merely a transition from an earlier universe — an earlier phase of the multiverse, one might say — to the present one. In other words, the big bang is very much not the beginning of time. Neil Turok, who served as the director of the Perimeter Institute from 2008 to 2019, is among those who have defended such models; so too has the mathematical physicist Roger Penrose, who was awarded a Nobel Prize in 2020 for his early work on black holes. (For an idea of what it’s like to be Roger Penrose, check out Patchen Barss’s excellent biography, The Impossible Man.)

Readers will also learn about the “holographic principle,” a mind-bending idea in which a volume of space can be described as though all the information about the space were encoded on its surface (sneakily reducing the description from three dimensions down to two). While it may seem to a layperson that this move was conjured out of thin air, the authors show how it ties into earlier research on black holes by Hawking and his collaborator Jacob Bekenstein, who found that the entropy of a black hole is related to the surface area of its event horizon. (If you’ve never heard of entropy or event horizons before, this book is likely not for you.) Pie in the sky as it may sound, Afshordi notes that the holographic principle continues to inform his own efforts to make sense of the origin of the universe.

If you think the holographic principle is mind-blowing, try this out: space and time may not be fundamental; rather, they may have emerged from some more primitive entity, however many milliseconds after the initial big bang (and probably much more quickly). A key idea here is that quantum entanglement — the weird connection that can exist between certain particles regardless of how far apart they are — is linked to the structure of space-time itself. Roughly put, if two particles are quantum mechanically entangled, the result is mathematically equivalent to what you’d have if the two particles were connected by a wormhole, a hypothesized tunnel through space-time.

The book also notes more down-to-earth episodes, like the peculiar case of the English theoretical physicist Paul Frampton. In spite of making important contributions to high-energy particle physics, he was not on the ball enough to discern that the Brazilian bikini model with whom he exchanged emails in the early 2010s was (surprise!) not a Brazilian model at all. “She” tricked him into taking a bag from Belgium to Argentina; it was full of cocaine, and he ended up serving nearly five years in a South American prison. As smart as these folks are, they are also all too human.

A welcome element in this volume is the lack of idolization. While many physicists continue to speak of the late Richard Feynman in almost hagiographic terms, Afshordi and Halper acknowledge his moral shortcomings. They note that his FBI file revealed abuse allegations by his ex-wife, and they point to “the naked misogyny evident in his public writings.” (The authors don’t mention it, but apparently, as a young professor at Caltech, Feynman would pretend to be an undergraduate while hitting on young women.)

Battle of the Big Bang takes a somewhat surprising turn in the penultimate chapter, as Afshordi and Halper ponder the relationship, such as it is, between science and religion. Born and raised in Iran, Afshordi has a keen sense of how religious enthusiasm can narrow a society’s horizons — and he makes it clear that what he values about science is that it plays by (or should play by) a different set of rules. At the end of the day, observation and experiment ought to be the final arbiters when choosing among competing theories. As for actually mixing science and religion (or turning science into a religion), the authors take a hard pass. Even when a scientific idea does seem to align with a particular religious view, one should exercise caution. Consider the case of the early twentieth-century Belgian physicist Georges Lemaître, who was also a Catholic priest. Lemaître was a proponent of what he called the “primeval atom” model of the early universe, which had much in common with the big bang model that would be developed soon afterwards. Lemaître recognized that this view of the universe’s creation carried echoes of Genesis, but he also understood that there was little to be gained by pushing the comparison too far (and he got mad when Pope Pius XII did just that).

As we wait for definitive observational evidence (and it may be a prolonged wait), perhaps we can allow the beauty and elegance of our theories to guide us toward truth. Or can we? Physicists often speak of beauty and elegance, but what they have in mind may be mostly in the eye of the beholder. As Afshordi puts it, “My theorist friends point me to the amazing mathematical successes of their frameworks: canceling anomalies, dualities, or exact solutions of complex systems of equations. These frameworks offer so much to revel in, yet when I close my eyes, I see the wondrous St. Peter’s Basilica in Rome, or the breathtaking Shah Mosque in Isfahan, constructed to draw awe and inspire the faithful. But then, is the grandeur of one’s cathedral a measure of the truth in one’s theory?” (For more on the dangers of being guided by the supposed mathematical beauty of physicists’ theories, see Sabine Hossenfelder’s provocative Lost in Math: How Beauty Leads Physics Astray, from 2018.)

The origin of the universe is a problem but hardly our only one. The authors readily admit that climate change is more pressing. Yet who hasn’t wondered where humankind came from, where life came from, and, ultimately, where the whole shebang of stars and planets and galaxies came from? We may be far from truly understanding the universe’s earliest moments; even so, Afshordi and Halper relish what we have found so far and encourage the reader to delight in it also: “We have come a long way, and we should take a moment to pause and marvel at the grandeur of our playground, where hard science meets human imagination.”