On Wednesday, a team of international astronomers revealed the most compelling evidence to date – dark energy – the mystical phenomena that push our universe to expand faster are not the constant forces of nature, but the decline and flow of the universe's time.
Dark energy may not resign from our universe to a fate that is torn apart at every scale, from clusters of galaxies to nuclei, according to new measurements. Instead, its expansion fades, and ultimately the universe is stable. Or the Cosmos could even turn the course back, and was ultimately doomed to what astronomers call a big crunch.
The latest results reinforce the standard model of cosmology since last April, the best theory of scientists' history, and appetizing hints that something is injustice in the structure of the universe. Measurements from last year and this month came from collaborations running dark energy spectroscopy or digital at the telescope at Kit Peak National Astronomical Observatory in Arizona.
“It's more than a hint now,” said Michael Levy, a cosmologist and director of Digi at the Lawrence Berkeley National Laboratory. “It contradicts us with other measurements,” added Dr. Levi. “Unless Dark Energy evolves – Boy, all the ducks line up in succession.”
The presentation was made at a conference at the American Physical Society in Anaheim, California, and accompanied by a series of papers explaining the results.
“It's fair to say that this result, taken at face value, looks like the biggest hint of the nature of dark energy 25 years after discovering it,” said Adam Reese, an astrophysicist at Johns Hopkins University and an astrophysicist at the Institute of Space and Communication Sciences in Baltimore, who was not involved in the work, but shared the 2011 Nobel Prize for writing in physics.
However, even if DESI's observations challenge the standard model of cosmology, another result strengthened it, as it predicts that dark energy is constant over time. On Tuesday, the multinational team that ran the Atacama Cosmological Telescope in Chile released the most detailed images taken in the infantile universe just 380,000 years ago. (The telescope was discontinued in 2022.
Their reports, which have not yet been peer-reviewed, appear to confirm that the standard model was working as expected in the early universe. One element of that model, the Hubble constant, explains how quickly the universe is expanding, but on a certain half-century measurement, there is a contradiction that has been reduced to about 9% today. Theorists believe that when the conditions are too high for an atom to form, an additional eruption of dark energy probably occurred in the very early universe, so that this so-called Hubble tension could be resolved.
The latest Atacama results seem to exclude this idea. But they say nothing if the nature of dark energy evolved later.
Both reports sparked enthusiastic praise from other cosmologists, and at the same time confessed the cosmic confusion about what it means.
“I don't think there's a very good idea left for anything that might explain Hubble's tension at this point,” said Wendy Friedman, a cosmologist at the University of Chicago, measuring the universe and not involved in either study.
Michael Turner, a theorist at the University of Chicago, was not involved in the research either. “The good news is that there are no cracks in the eggs in the universe. The bad news is that there are no cracks in the eggs in the universe.”
Dr. Turner, who coined the term “dark energy,” added that if there is a crack, “it hasn't spread enough yet to clearly see what's next in cosmology.”
Astronomers often compare the expanding galaxies of the universe with raisins on a baking cake. As the dough rises, the raisins are carried further apart. The farther they are from each other, the faster they separate.
In 1998, two groups of astronomers measured the expansion of the universe by studying the brightness of certain types of supernova or the brightness of explosive stars. Such supernovae produce the same amount of light, making them look as spectacular as expected at even further distances. If the universe had slowed down as scientists believed at the time, the light from the distant explosion would have looked slightly brighter than it was foreseen.
Surprisingly, the two groups discovered that the supernova was fainter than expected. Instead of slowing down, the expansion of space was actually speeding up.
Energy known to physicists cannot promote accelerated expansion. Its strength should fade as it spreads even thinner throughout the balloon universe. Unless that energy comes from the universe itself.
This dark energy carries all the views of the fudge factors that Albert Einstein inserted in his theory of gravity in 1917, explaining why the universe had not collapsed with its own weight. The fudge factor, known as cosmological constants, represents a kind of cosmic repulsion that balances gravity and stabilizes the universe. When it became clear in 1929 that the universe was expanding, Einstein abandoned the cosmological constant, reportedly calling it his greatest failure.
But it was too late. One feature of quantum theory, devised in 1955, predicts that empty spaces are bubbled with energy that produces repulsive forces, like Einstein's fudge factor. For the last quarter century, this constant was part of the standard model of cosmology. This model is a huge spark known as the Big Bang in the universe, born 13.8 billion years ago, and consists of 5% atomic matter, 25% dark matter and 70% dark energy. However, the model cannot say what dark matter or dark energy is indeed.
If dark energy is indeed constant for Einstein, the standard model portends a dark future. The universe continues to speed up, becoming dark and lonely forever. Distant galaxies are ultimately invisible to far away. All energy, life and thoughts are drawn from the universe.
“I'll go after something.”
Astronomers on the Desi team are trying to characterize dark energy by measuring galaxies at various times of space time. The small irregularities in the diffusion of matter throughout the primitive universe have influenced the distance between galaxies today. This is the distance expanded with space in a measurable way.
The data used for the latest digital measurements consisted of a catalog of nearly 15 million galaxies and other celestial objects. By itself, the dataset does not suggest that anything unfortunate is unfortunate to the theoretical understanding of dark energy. However, it is combined with other strategies for measuring the expansion of the universe. For example, it studied the exploding stars and the oldest light in the universe, and was released hundreds of thousands of years after the Big Bang, but the data is no longer in line with the predictions of standard models.
Enrique Pilas, a postdoctoral researcher at the University of Arizona, announced on Wednesday that it had released digital measurements, but noted that data suggests that dark energy-driven cosmic acceleration begins in time and is currently weaker than standard models predict.
The contradiction between data and theory is at most 4.2 sigma (a unit of uncertainty that physicists like), representing the 50,000 possibilities that the outcome is flukes. But the mismatch is not yet five sigmas (equivalent to one in 3.5 million chances), but rather the strict standards set by physicists to argue for discoveries.
Still, the severity appeals to suggest that something in the universe model is not well understood. Scientists may need to modify how they interpret gravity or understand the ancient light from the Big Bang. Desi Astronomers believes that the problem could be the nature of dark energy.
“Introducing dynamic dark energy will make the pieces of the puzzle better fit,” said Mustafai Shakbuzaki, a cosmologist at the University of Texas at Dallas, who led the latest digital analysis.
Wilpercival, a cosmologist at the University of Waterloo in Ontario and a spokesman for DigiCollaboration, expressed his excitement about what's on the horizon. “This is actually a little shot of the arms on the field,” he said. “Now we're chasing something.”
In the 1950s, astronomers argued that only two numbers were needed to explain cosmology. One relates to how quickly the universe is expanding, and the other explaining slowing. Things changed in the 1960s with the discovery that the universe was immersed in light from the Big Bang, known as the backdrop of the universe's microwaves. By measuring this background radiation, scientists were able to investigate early universe physics and how galaxies formed and evolved afterwards. As a result, standard models of cosmology require six parameters, including both the density of the normal and dark matter of the universe.
As cosmology becomes more accurate, additional tensions arise between predicted and measured values of these parameters, leading to the stacking of theoretical extensions to standard models. However, the latest results of the Atacama cosmological telescope – the clearest map of the cosmic microwave background to date – appears to be knocking on the doors on many of these extensions.
Desi will continue to collect data for at least another year. The ground and other telescopes in the universe take their own views of the universe. Among them are the Spherex missions that have been launched by the temporary facility in Zwick in San Diego, the European Euclidean Space Telescope and the NASA. In the future, Vera C. Rubin Observatory will begin recording Chilean night sky movies this summer, with NASA's Roman Space Telescope set to be released in 2027.
Each absorbs light from the sky, measuring fragments of the universe from various perspectives, contributing to a wider understanding of the universe as a whole. Everything acts as a continuous reminder of what a tough egg is to crack the universe.
“Each of these datasets has their own strengths,” said Alexie Leauthaud, cosmologist at the University of California, Santa Cruz and spokesman for the DESI Collaboration. “The universe is complicated, and we are trying to unravel a lot of different things.”
