This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: For close to a century, physicists have pursued a way to unite gravity with quantum mechanics. Known as quantum gravity, this goal has remained frustratingly out of reach so far.
Similarly elusive is the force of dark energy, which is believed to be driving the universe's accelerating expansion. But through new research published in Physical Review D, physicist Savvas Koushiappas of Brown University has proposed a new explanation suggesting that these two phenomena might not be separate at all. Instead, dark energy could be a natural side effect of quantum gravity, acting on the geometry of space itself.
Gravity and quantum mechanics shape the universe on vastly different scales: While quantum mechanics concerns the realm of subatomic particles, gravity shapes structures as large as galactic clusters and cosmic filaments. Individually, both of these theories have been tested to extraordinary precision through decades of painstaking experiments. However, the extreme conditions where both should apply at once, such as inside a black hole, have remained far beyond what any experiment can reach.
In his study, Koushiappas took a different approach: suggesting that we can't pin down both the size and expansion rate of the universe at the same time with perfect accuracy. This limitation is built into the fundamental uncertainty that governs the quantum world: When applied to the universe as a whole, it subtly changes the equations that describe how cosmic expansion should behave over time. This built-in uncertainty could then produce exactly the kind of accelerating expansion that cosmologists currently attribute to dark energy.
Depending on the exact mathematical details, this macroscopic imprint of quantum gravity could also replace the singularity at the instant of the Big Bang, which cosmologists have long struggled to explain. Rather than relying on a point of infinite density, Koushiappas' proposal suggests that the Big Bang followed a gentler rebound from a previously contracting universe. If Koushiappas's idea is correct, it could provide a far cleaner explanation for the origins of dark energy.
In contrast to many existing theories, this would mean that the phenomenon doesn't need to be explained by some hidden particle or exotic field waiting to be discovered: Instead, it is a property of space itself, hiding in plain sight in our observations of the universe. For now, Koushiappas acknowledges that open questions remain about his ideas. However, upcoming surveys from DESI, Euclid and the Vera C.
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