The spectroscopic tool of dark energy (Desi) is installed on the Mayall telescope in Kitt Peak. Credit: KPNO/NERLELELAB/NSF/AURA/B. Tafresti
Our universe has expanded since it was born in the big bang. For decades, most cosmologists believed that the expansion of the universe was slowing down. Gravity, pulling the whole question, in the end would have passed the momentum from the big bang, stopping or even reversing the expansion.
But in 1998, Supernova’s observations revealed a surprise: the universe is not just expanding; He is accelerating. To explain this phenomenon, scientists proposed a mysterious repulsive force that pushed the galaxies, called dark energy. For the following 25 years, most hypothesized that this force was constant, an intrinsic and immutable property of the space that guided it to expand faster and faster. This force is now part of our standard model of cosmology.
Now, the recent results released on March 19 by two of the greatest cosmological surveys until today-The Dark Energy Spectroscopy Stroment (Desi) and The Dark Energy Survey (des) -Sfida that the long-standing assumption, adding to an growing corpus of tests that suggests the strength from the dark energy, after all, after everything it may not be constant. Instead, the density of dark energy can vary in cosmic time.
Related: The Supernova survey suggests that dark energy could change
Deviation suggestions
“At the beginning of the experiment, the assumption was that we would have just obtained the measurement of maximum precision confirming the constant,” says Stephanie Juneou, Astronomer at the NSF Noirlab and a member of the Desi data team. “It was actually a great surprise that we found a hint of detour.”
The tests emerge not from any single data set, but from a growing convergence through independent measurements. Desi researchers analyzed a three -dimensional map containing almost 15 million galaxies and Quasar, the most detailed spectroscopic map of the universe ever created. For themselves, Desi’s data does not significantly challenge the standard cosmological model. But if combined with external measurements, including the data of the cosmic microwave background (the Big Bang glow), the studies on supernovae and gravitational lenses, tensions begin to emerge.
In the meantime, Des scientists, who use separate methods in six years of observations, have found similar anomalies that suggest that the standard model may not tell the complete story.
“What has been most convincing for me is that the evidence comes from different directions. And it cannot be that all these different directions of different sets of data consist to give the same wrong response,” says Mustapha Ishak-Boushaki, a theoretical astrophysicist at the University of Texas in Dallas and the copy of the working group that analyzed the Desi data.
Related: Are the percentages of dark matter and dark energy stable?
Changing, not constant
The idea that dark energy can change over time is more than a provocative turn; He faces one of the deepest puzzles of modern physics. In Einstein’s equations that describe the universe, the constant Lambda cosmological (λ) – now that it is believed to represent the force of Dark Energy – offers a simple way to explain the accelerated expansion. The theory of quantum fields provides that the empty space should still contain energy, called energy under vacuum. This is a candidate for dark energy, but the theory provides that the energy of the void should act as a repulsive force more than 40 orders of magnitude stronger than the astronomers observe.
“If [dark energy] It is a cosmological constant, it was considered a dead end, “says Ishak-Boushaki.” The difference between theoretical calculations and measurements was known on the field as the most embarrassing difference that we cannot explain “.
Evolution Dark energy, however, could potentially resolve this contradiction between the small measured value of Dark Energy and the energy of the void that quantum theory provides. If the dark energy changes over time, this gives the astronomers completely new theoretical paintings to explore, from the modified theories of gravity to the energy fields that evolve naturally during cosmic history.
“With Desi, we saw the light,” says Ishak-Boushaki. “Hope is back that is not a cosmological constant, it is something different. We know what exactly is it now? No, but the door has opened for us to find it.”
Since the dark energy constitutes about 70 percent of the universe, confirming that it changes over time it would mark a profound change in our understanding of the fate of the cosmos. The constant cosmological model implies a universe that expands faster and faster, finally becoming cold and empty in a scenario sometimes nicknamed the death of heat or the great freezing. But dynamic dark energy could lead to radically different results, slowing down the expansion or accelerating it so violently that everything ends in a large catastrophic tear, causing galaxies, stars and even atoms to pieces.
The current level of statistical trust in the combined-around results to 4.2 Sigma-Si is approaching the 5-sigma threshold generally required to accept a scientific discovery. At that level, the probability that the result is a statistical fortune stroke drops to less than one in a million.
“For people like me who work there for 25 years, we didn’t expect this to happen in our life,” says Ishak-Boushaki.
More data needed
However, researchers warn that these forecasts remain speculative. Much depends on the fact that the dark energy is really changing and, in this case, what is guiding that evolution.
“I am not going to keep a funeral for the standard cosmological model,” says Jessie Muir, cosmologist at the University of Cincinnati and a member of the Team des. “I am cautiously excited. It is something to keep an eye on and really do and really try to make sure you understand.”
The next few years will be essential to explore the provisional results. Desi plans to continue collecting data until 2026, with the aim of mapping over 50 million galaxies and Quasar and potentially pushing the evolving dark energy signal beyond the 5-sigma discovery threshold. The researchers also plan to check the results with new tools and experiments, including imminent projects such as the Legacy investigation of the Vero C. Rubin Observatory on space and time and Nancy Grace Roman Space Telescope of the NASA. These tools will allow scientists to probe more deeply in space and time than ever, presenting unprecedented opportunities to study the nature of dark energy.
“It gives us the opportunity to return to the drawing table. And then we really learn, what is the true nature of a universe,” says Juneau. “I see an immense tank of new discoveries that are waiting to be made.”
Note of the editor: a previous version of this story listed Jessica Muir as a member of the Team des and Desi.
