While investigating dark matter, researchers on the XENON1T project have recorded some unexpected results: they may have encountered dark energy for the first time, by accident.
Since the acceleration of the expansion of the Universe was established in the 1990s, the hypothesis of the existence of "dark energy" has been gaining momentum in the scientific community.
The existence of an anti-gravitational force operating throughout the Universe, in fact, would not only be consistent with quantum mechanics, but would explain the accelerated expansion of our entire universe.
Dark energy, technically, is not directly detectable: a team of researchers at the University of Cambridge, however, may have encountered it for the first time. Literally by accident.
The experiment in the depths of Gran Sasso
The Cambridge research team's newly published study suggests that the strange results detected during an experiment in the depths of Gran Sasso may be the result of direct detection of dark energy.
The experiment was actually intended to detect dark matter: as Dr. Sunny Vagnozzi, author of the research, explains, "experiments like XENON1T are meant to detect dark matter directly, looking for traces of its impact with ordinary matter, but dark energy is even more elusive."
XENON1T, in the heart of the Gran Sasso, is a sort of big trap that scientists say could finally show dark matter particles. Certainly not dark energy, an eventuality no one thought of in the depths of the Gran Sasso National Laboratories.
About a year ago, the XENON1T experiment registered an unexpected signal, a sort of "excess of events" over what was expected to be detected.
As Dr. Luca Visinelli of the Frascati National Laboratories puts it, "we explored a model in which these signals could be attributed to dark energy, rather than the dark matter that the experiment was originally deputed to detect." The research team also evaluated other hypotheses, such as the axion hypothesis, but they all fell apart in the face of evidence and calculations, leaving the way open for a theoretical model that would attribute it to dark energy.
The Secret of the Universe's Expansion
"We are far from fully understanding what dark energy is," the researchers write, "but most physical models for dark energy would lead to the existence of a so-called fifth force."
Practically everything that physics cannot explain by the existence of the four forces of nature - electromagnetic, gravitational, strong nuclear and weak nuclear - could be caused by this unknown fifth force. We are again facing the great challenge of theoretical physics: the possible incompleteness of the standard model.
The existence of dark energy would explain one of the greatest mysteries of the Universe: several observations indeed indicate that the Universe consists of about 70% negative pressure energy, the so-called dark energy. The gravitational effect of dark energy would explain the acceleration of its expansion: it could be at the base of the "repulsive" mechanism from which the acceleration - proved only in 1998 - originates.
"Although they are both invisible" explains Vagnozzi "we know much more about dark matter, whose existence was already hypothesized in the twenties, while dark energy was not discovered until 1998" - the year in which the acceleration of the Universe was proved, resulting in the Nobel Prize for Physics.
Having intercepted a first signal of dark energy could pave the way for a real revolution in theoretical physics: "if the excess detected by XENON1T is really the result of dark energy," write the scientists, "then it may be possible to detect dark energy in the next decade".