Nothing interests Michael Vogeley. That’s not to say that he is suffering from ennui. Rather, Vogeley, a cosmologist at Drexel University in Philadelphia, is intensely fascinated by the vast tracts of emptiness—the voids–that lie between clusters of galaxies and make up about 70% of space. 

Today, understanding the nature of “nothing” in physics could help resolve one of cosmology’s biggest conundrums: why the expansion of our universe is currently speeding up. (Yes, instead of slowing down, as you would expect of debris flying out from an explosive Big Bang, matter at the furthest reaches of the universe is racing away from us at an ever-faster pace.) In April 2025, Vogeley and colleagues presented “Deep Void”—a cosmic void detector that employs artificial intelligence (AI) to wade through the flood of galaxy data from telescopes and chart the tracts of cosmic nothingness. They argue that mapping the empty space between galaxies will help illuminate how and why the fabric of space between them is stretching at an ever-increasing rate. 

But unravelling the reasons behind the accelerating growth of space forces physicists and philosophers to wrestle with what exactly cosmologists mean by the term “nothing”—and whether space itself can truly expand. Is space ever really empty? Julian Barbour, a former visiting professor in physics at the University of Oxford, UK, points to a seeming absurdity in the visualization of empty space stretching. If space contains nothing, he argues, how can physicists know that its fabric is changing size? “It has no objective meaning to say that empty space is expanding,” argues Barbour. “It’s meaningless.”

Some physicists have stated that space and time blipped into existence from a profound state of Nothingness—but if so, what does that mean? “Physicists talk about ‘creation from nothing’ in contemporary cosmological contexts,” says philosopher of physics David Albert, of Columbia University in New York, New York. “But there are several obstacles to trying to hook that up to the long history of talking about ‘creation from nothing’ in Western philosophical and theological traditions.”

Philosophically, at least, “nothing” is not quite as simple as it seems. Getting to the root of its cosmic meaning could have profound consequences for our understanding of how the universe evolves.

Into the Void

Vogeley can trace the roots of his passion for voids to an exact moment in the 1980s. He was an undergraduate at Princeton, sitting in the university tearoom, when the chair of astrophysics, Jerry Ostriker, came running in, excited. “He threw an image of a slice of the universe on one of the tables, and challenged the students to explain it,” Vogeley recalls. The image, from a preprint by Harvard astronomers, charted the positions of over a thousand nearby galaxies (see image below, Lapparent, Geller & Huchra (1986)). The galaxies were not dotted randomly across the slice of the sky, but distributed along a “cosmic web,” with galaxies clustered together to create filaments and threads, separated by unexpectedly huge volumes of nothingness, spanning hundreds of millions of light-years. “These new data revealed a striking pattern, the first clear evidence of a cosmic web,” says Vogeley. 

The size of these regions, seemingly devoid of matter, had not been predicted by the best cosmological models of the day. “What was surprising was the ubiquity of large voids, their consistently low density, and the manner in which they fill space between sharply-delineated walls that connect to clusters,” says Vogeley. “The puzzle was how could you have voids that were that large?” He was immediately hooked and, upon graduating, joined the team at Harvard for his PhD, to study the mysteriously large expanses of nothingness throughout space. 

But while the bizarre voids may have appeared empty, Vogeley and his colleague, cosmologist Miguel Aragon-Calvo, at the Public University of Mexico City (UNAM), in Mexico, are quick to clarify that astronomers now know that they are not. The matter within the voids is so sparse that it does not appear in images taken with our current best telescopes. Computer simulations, however, suggest that these desolate regions of the cosmos contain some matter and a few galaxies, strung together in a wispy lace.

So, voids are more than nothing.

Shocking Supernovae

The mystery of the large size of these voids has also since been solved, thanks to revisions to our understanding of the universe’s evolution. Astronomers and physicists developed multiple possible models that could explain the appearance of the voids, but one in particular has stuck—and now forms the basis of the standard cosmological model, thanks to more precise measurements made of the universe’s expansion. 

Back in the 1980s, cosmologists had a fairly intuitive picture of the evolution of the cosmos. The idea was that an initial Big Bang explosion created space, time, and matter, hurling that matter outwards, causing the cosmos to expand. Over time, physicists expected that the gravity between the matter should exert an inward pull, causing the universe’s expansion rate to gradually slow down. In the late 1990s, however, astronomers were stunned to discover that this could not be the full story, when they tried to track the cosmic expansion rate, by measuring the location and motion of distant exploding stars, or supernovae, they found to their shock that the universe’s growth rate was actually getting faster, rather than decelerating.

Although physicists didn’t know the cause of this accelerating effect, they dubbed its source “dark energy.” Using computer simulations, they charted the evolution of the cosmos as influenced by dark energy, and the simulations showed an avalanche effect: once gravity started to pull neighboring matter together to form galaxies, those galaxies would clump together to form clusters, leaving enormous gaps between them. Voilà, a cosmic web appeared in the simulations, complete with its extensive voids of apparent nothingness. 

But while the mystery of the voids’ origins had been solved, there was now a new enigma to wrestle with: What is the dark energy pervading the cosmos? And how can dark energy be acting on empty space—on apparently nothing—and pushing it outwards?

Another article is coming where physicists wrestle with the not-so-empty nature of the quantum vacuum, questions of whether empty space even exists, at all, and how correctly conceptualizing the true nature of “nothing” in cosmology could influence our understanding of both the universe’s birth and its evolution. 

Zeeya Merali is a London-based science journalist and author of the popular physics book, A Big Bang in a Little Room.