American Scientist

BATTLE OF THE BIG BANG: The New Tales of Our Cosmic Origins. Niayesh Afshordi and Phil Halper. 360 pp. University of Chicago Press, 2025. $32.50.

Cosmologists grapple with the universe on scales not typically considered in everyday life. They attempt to make sense of unimaginably hot epochs before matter as we know it even existed, and of unimaginably cold futures where matter may decay into nothingness. At any time, cosmologists may require a detailed understanding of general relativity, quantum mechanics, or both as they ponder the evolution of matter and energy over the entire history and possible futures of the cosmos.

In their new book Battle of the Big Bang: The New Tales of Our Cosmic Origins, physicist Niayesh Afshordi and science communicator Phil Halper go beyond the history of the cosmos and explore speculative ideas about its prehistory: How did the Big Bang come to happen? What kind of physics might have preceded the Big Bang? Did the universe have a specific moment of birth, or did it always exist in some form? And how does a relatively small, closely connected, but often fractious community of scientists approach these issues—which can often seem to be beyond the boundaries of our understanding—without tearing itself apart?

These are ideas that may strike even veteran readers of popular science books as questionable or even unscientific, yet Afshordi and Halper make a convincing case that there is much to be gained by considering what happened before the classical idea of the Big Bang. Starting with a whirlwind tour through 2.5 millennia of cosmology, they quickly converge on a story that many readers may find familiar: Within the past hundred years or so, a confluence of theory (general relativity) and observations (the recession velocities of galaxies, the cosmic microwave background) pointed inexorably to the Big Bang, often referred to as the very beginning of space and time. This idea rests on well-established and observationally tested physics: At some finite time in the past, everything in our observable universe—some 40 billion light-years in radius around us today—was contained in an infinitesimally small patch of space that was unimaginably hot and dense. Questions of what preceded this Big Bang are often met with a rejoinder that such queries are meaningless, the cosmological equivalent of asking what is north of the North Pole. Afshordi and Halper proceed to demonstrate that this answer is not satisfactory.

For example, they explain how the idea of cosmological inflation—a postulated period of exponential growth of the universe that is fully enshrined as part of standard teaching of cosmology—is already an example of physics that actually precedes the hot Big Bang. In this picture, inflation really puts the “bang” in the Big Bang: In a stupendously short period of 10^-32 seconds, distances in the universe expanded in size by at least a factor of 10²⁷, the equivalent of expanding from the size of a grapefruit to the size of our observable universe today. This hypothesized period of exponential growth explains several otherwise troubling aspects of the classical Big Bang model, including the origin of cosmic structure (from quantum fluctuations during inflation) and why the universe appears to be so homogeneous and isotropic on large scales. The question of what preceded or initiated the epoch of inflation requires physicists to understand the properties of matter and energy on scales that are so small in size and so short in time that the very laws we take for granted must break down; this condition is referred to as a singularity. The authors write:

To imagine the Big Bang singularity is to ignore the contradictions of quantum mechanics and general relativity, the pillars of the physical world. Resolving this conflict by creating a theory that unifies the physics of the subatomic and the celestial, a quantum theory of gravity, remains the backdrop for much of this book.

Afshordi and Halper go to great lengths to demonstrate that many of the world’s most renowned cosmologists have wrestled with the thorny and challenging question of what preceded the well-established period of the hot Big Bang. They describe models in which the universe does indeed have a defined beginning, but also many alternate models in which it does not. For example, cyclic theories posit that the universe undergoes an infinite sequence of expansions and contractions. The ekpyrotic universe is a model in which the universe began from a merger of branes, higher-dimensional objects posited by string theory. In other string theory–inspired models, our universe does not have a singularity that marks its beginning; instead, our universe is connected to another “dual” universe that contracts as ours expands, meaning the Big Bang was a moment of transition, not a beginning in itself.

But the book does not merely catalog theories. Readers are also introduced to a dizzying cast of characters whose actions are befitting of a Shakespearean drama. We learn how theoretical physicists Neil Turok and Paul Steinhardt went from developing key ideas around inflation to arguing that inflation is a fundamentally flawed idea. Veering a bit more into the absurd, we read about Paul Frampton, who came up with a theory about a universe that cycles between expansion and contraction, but who was also involved in an international drug-smuggling ring and so had to supervise graduate students via jailhouse telephone. We meet famous Nobel laureates and scientists whose achievements have been overlooked or underappreciated, encounter fruitful scientific partnerships and bitter rivalries, and see the international and collaborative nature of modern science.

These colorful stories remind us that science is a fundamentally human endeavor performed by flawed but inquisitive and ambitious people who have made stunning progress in understanding the universe and our place in it. In an age when science and scientists are scrutinized for pursuing knowledge and its applications and when theoretical research is sometimes derided as being superfluous to the needs and wants of society, an engaging tale of some of the biggest questions imaginable and the stories of the scientists pursuing those questions is welcomed.

However, although the anecdotes about fellow scientists can be entertaining and revealing, these tales can also feel forced and distracting. Similarly, the sheer breadth of topics covered and the immense historical scope sometimes renders the writing disjointed or discursive. Perhaps necessarily, the book jumps around in time, following the flow of distinct ideas in cosmology rather than any specific chronology of discovery. Given the amount of the material covered, a reader without any previous experience with cosmology texts may find the scope somewhat overwhelming. For these readers, the appendix summarizing the many models discussed may be especially helpful.

Overall, Afshordi and Halper present a compelling scientific and personal perspective on one of the biggest—yet somehow underexplored—questions in cosmology: Does the universe have a beginning? And in true scientific fashion, the authors avoid prizing any one of the many possible answers. Rather, they present strengths and weaknesses, evidence for both pro and con (if it exists), and then allow the reader to wander through the maze of possibilities.

Battle of the Big Bang is not a retrospective but rather a forward-looking book that details controversial theories that are still very much under debate. Perhaps in the next century, we will look back on the question of the origin of the universe as settled science, or maybe scientists will still be debating some of the ideas outlined in this book along with new ones. As Afshordi and Halper make clear, however, we can be sure that scientists will not be content with stating how the universe started unless they can also answer the question of what came before.