Physicists have proposed a new model of space-time that may provide the 'first observational evidence supporting string theory,' a new preprint suggests.
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.
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.
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.
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An exterior view of The Dark Energy Spectroscopic Instrument
(DESI) mounted atop the 4-meter Mayall Telescope at Kitt Peak National
Observatory in Arizona. (Image credit: DESI) |
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.