A new experiment reduces the potential properties of dark energy particles

In the United Kingdom, an experiment failed to find evidence of a particle supposed to explain most of the mass of the universe. But the search is not over.

When cosmologists observe how the universe expands, they discover that current theories of matter can not explain most of the energy of the universe. They call the unknown energy "dark energy", and theorists have tried to explain it by proposing undiscovered particles and corresponding fields. Experiments have failed to find evidence of such particles, but in physics it is not necessarily a bad thing.

"We did not exclude everything," Clare Burrage, associate professor of physics and astronomy at the University of Nottingham in the United Kingdom and author of the study, told Gizmodo. "There is still a parameter window that is probably more interesting."

Two 1998 observations of the farthest supernova revealed that not only is the universe expanding, but that expansion is accelerating. To explain this expansion, it needed a new unknown force that differentiates things, what physicists call black energy. Calculations since then have revealed that dark energy should be more than two-thirds of the total mass and energy of the universe – but we do not know what the source is.

Physicists understand the forces between the regular matter of the universe, like the electromagnetic force, as fields (where you are in the field determines how much you feel the force) with the corresponding particles (you can understand the interactions between two particles of matter like the exchange of particles of force). Thus, some theories about dark energy suggest that it is a new type of force, too weak to be observed on Earth, with a corresponding particle; these proposed particles have names such as chameleon or symmteron. Recent computer evidence has shown that chameleon theory, so named because their properties depend on the environment in which they exist, is a viable theory of black energy.

Researchers working in the UK had previously suggested that if these forces existed, they could be detected through a special kind of experience similar to that of Galileo, who dropped two bullets from the top of the leaning tower in Pisa. The researchers placed an almond-sized aluminum ball, attached to a rod, so that it could move into an extreme vacuum chamber. Then they pumped and trapped a pulse of cold rubidium atoms, then released the trap. Using a detection scheme called atomic interferometry, based on the projection of specially atom-oriented lasers, the researchers measured how the atoms moved toward the aluminum ball held in various positions, looking for the smallest differences acceleration compared to theoretical expectations.

The experiment revealed that, if there are particles of chameleon or symmetry, their effects are too light to be measured by this configuration, according to the document published in Physical Review Letters. This type of null result is important – it requires theorists and experimenters to look elsewhere for a particle explaining black energy.

These results confirm a similar set of results from a 2017 article written by a team of scientists here in the United States, with however a slightly different detection pattern. This document "is of very high quality and corroborates our previous limitations," said Gizmodo Holger Müller, leader of the University of California Berkeley's efforts in 2017, who was not involved in the new study . "They use similar, but not identical, techniques, so this is a significant enhancement of the experimental data. I must admit that this is a theoretical article by Burrage, Copeland and Hinds, "according to three scientists on this new article," which prompted us to look at chameleons ".

And it is important to continue searching. These experiments let live a few iterations of chameleons, said Burrage to Gizmodo. It is now a question of increasing the sensitivity of these experiments.