Physicists claim they may have found a long-awaited explanation for dark energy, the mysterious force that’s driving the accelerated expansion of the universe, a new preprint study hints.
Their calculations suggest that, at the smallest scales, space-time behaves in a profoundly quantum way, differing drastically from the smooth, continuous structure we experience in everyday life. According to their findings, the coordinates of space-time do not “commute” — meaning the order in which they appear in equations affects the outcome. This is similar to how a particle’s position and velocity behave in quantum mechanics.
One of the most striking consequences of this quantum space-time, as predicted by string theory, is that it naturally leads to cosmic acceleration. Moreover, the researchers found that the rate at which this acceleration decreases over time aligns remarkably well with the latest observations from the Dark Energy Spectroscopic Instrument (DESI).
“Viewed through the lens of our work, you could think of the DESI result as the first observational evidence supporting string theory and perhaps the first observable consequences of string theory and quantum gravity,” study co-author Michael Kavic, a professor at SUNY Old Westbury, told Live Science via email.
The mystery of the universe’s expansion
In 1998, two independent teams — the Supernova Cosmology Project and the High-Z Supernova Search Team — discovered that the universe’s expansion was not slowing down, as previously thought, but was instead accelerating. They reached this conclusion by studying distant supernovas, which appeared dimmer than expected. This acceleration implied the presence of a mysterious entity permeating space, later dubbed dark energy.
Related: ‘The universe has thrown us a curveball’: Largest-ever map of space reveals we might have gotten dark energy totally wrong
However, the origin of dark energy has remained elusive. A popular hypothesis suggests it arises from quantum fluctuations in the vacuum, similar to those seen in the electromagnetic field. Yet, when physicists attempted to compute the expansion rate based on this idea, they arrived at a value that was 120 orders of magnitude too large — a staggering discrepancy.
Recent DESI observations further complicated the picture. According to the Standard Model of elementary particles, if dark energy were simply a vacuum energy, its density should remain constant over time. However, DESI data indicate that the acceleration rate is not fixed but that it decreases over time — something the Standard Model does not predict.
Solving the mystery with string theory
To address these inconsistencies, the researchers turned to string theory, one of the leading candidates for a quantum theory of gravity. Unlike the Standard Model, which treats elementary particles as point-like, string theory proposes that they are actually tiny, vibrating, one-dimensional objects called strings. These strings, depending on their modes of vibration, give rise to different particles — including the graviton, the hypothetical quantum carrier of gravity.
In a new paper that was posted in the preprint database arXiv but has not been peer-reviewed, physicists Sunhaeng Hur, Djordje Minic, Tatsu Takeuchi (Virginia Tech), Vishnu Jejjala (University of the Witwatersrand), and Michael Kavic applied string theory to analyze space-time at the quantum level.
By replacing the Standard Model’s description of particles with the framework from string theory, the researchers found that space-time itself is inherently quantum and noncommutative, meaning the order in which coordinates appear in equations matters.
This radical departure from classical physics allowed them to derive the properties of dark energy not just from experimental data, but directly from a fundamental physical theory. Their model not only yielded a dark energy density that closely matches observational data but also correctly predicted that this energy should decrease over time, aligning with DESI’s findings.
One of the most striking aspects of their result is that the value of dark energy depends on two vastly different length scales: the Planck length, the fundamental scale of quantum gravity, which is about 10⁻³³ centimeters; and the size of the universe, which is billions of light-years across. Such a connection between the smallest and largest scales in the cosmos is highly unusual in physics and suggests that dark energy is deeply tied to the quantum nature of space-time itself.
“This hints at a deeper connection between quantum gravity and the dynamical properties of nature that had been supposed to be constant,” Kavic said. “It may turn out that a fundamental misapprehension we carry with us is that the basic defining properties of our universe are static when in fact they are not.”
Experimental tests and future prospects
Although the team’s explanation of the universe’s accelerated expansion is a significant theoretical breakthrough, independent experimental tests are needed to confirm their model. The researchers have proposed concrete ways to test their ideas.
One line of evidence “involves detecting complicated quantum interference patterns, which is impossible in standard quantum physics but should occur in quantum gravity,” Minic added.
Interference occurs when waves, such as light or matter waves, overlap and either amplify or cancel each other out, creating characteristic patterns. In conventional quantum mechanics, interference follows well-understood rules, typically involving two or more possible quantum paths. However, higher-order interference—predicted by some quantum gravity models—suggests more complex interactions that go beyond these standard patterns. Detecting such effects in the lab would be a groundbreaking test of quantum gravity.
“These are tabletop experiments that could be performed in the near future — within three to four years.”
“There are many implications of our approach to quantum gravity,” said Djordje Minic, a physicist at Virginia Tech and co-author of the paper, in an email. One line of evidence “involves detecting complicated quantum interference patterns, which is impossible in standard quantum physics but should occur in quantum gravity,” Minic added.
Interference occurs when waves, such as light or matter waves, overlap and either amplify or cancel each other out, creating characteristic patterns. In conventional quantum mechanics, interference follows well-understood rules. However, some quantum gravity models suggest more complex interactions that go beyond these standard patterns. Detecting such effects in the lab would be a groundbreaking test of quantum gravity.
“These are tabletop experiments that could be performed in the near future — within three to four years.”
In the meantime, the researchers are not waiting for experimental confirmations. They are continuing to refine their understanding of quantum space-time, as well as exploring additional avenues for testing their theory.
If confirmed, their findings would mark a major breakthrough not only in explaining dark energy but also in providing the first tangible evidence for string theory — a long-sought goal in fundamental physics.
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