The largest ever 3D map of the universe, featuring more than 6m galaxies, has been unveiled by scientists who said it raises questions about the nature of dark energy and the future of the universe.
The map is based on data collected by the Dark Energy Spectroscopic Instrument (Desi) in Arizona and contains three times as many galaxies as previous attempts, with many having their distances measured for the first time.
Researchers said that by using this map, they were able to measure how fast the universe expanded at different times in the past with unprecedented precision.
The results confirm that the expansion of the universe is accelerating, they added. However, the findings also raised the tantalizing possibility that dark energy—a mysterious, repulsive force driving the process—is not constant through time as previously suggested.
Dr Seshadri Nadathur, a co-author of the work and senior research fellow at the University of Portsmouth’s Institute of Cosmology and Gravitation, said: “What we see are some hints that it has in fact changed over time , which is quite exciting because this is not what the standard model of a cosmological constant dark energy would look like.”
Prof Carlos Frenk, from the University of Durham and a co-author of the research, said that if dark energy was indeed constant in time, the future of the universe was simple: it would expand on and on, forever. But if the hints found on the map stand up, it will be questioned.
“Now that all goes out the window and essentially we have to start over, and that means revising our understanding of basic physics, our understanding of the big bang itself, and our understanding of the long-range prediction for the universe.” he said, adding that the new hints left open the possibility that the universe could be undergoing a “major crisis.”
The research, which was published in a series of preprints – meaning it has yet to be peer-reviewed – reveals how the team first created the 3D map, when they measured patterns in the distribution of galaxies associated with sound waves that occurred in the early universe, known as baryon acoustic oscillations .
As the size of these patterns is known to be regular, the team was able to calibrate the distances to different galaxies on the map, allowing them to work out how fast the universe has grown over the past 11 billion years, with ‘ a precision better than 0.5% over all time, and better than 1% between 8 billion and 11 billion years ago.
Frenk said the accuracy of the measurements themselves is remarkable given that galaxies can be billions of light years away and billions of years old. “It’s amazing that we can measure anything to an accuracy of 1%, which is precision you get in the lab in physics for high-precision measurements,” he said.
Andrew Pontzen, professor of cosmology at University College London and author of the book The Universe in a Box, who was not involved in the work, said Desi was one of a series of exciting new astronomical surveys cataloging the night sky, with one of the primary goals is to measure the rate at which our expanding universe has accelerated.
“Like measuring the acceleration of a car, the map of the universe’s expansion tells us about the ‘engine’ that drives cosmic acceleration. That engine is known as dark energy,” he said.
However, Pontzen noted that our knowledge of how dark energy works was limited. “The new data, when combined with existing measurements, appear to contradict the simplest possible explanations for dark energy,” he said.
“At face value, this is an exciting step forward. But as the team themselves caution, there is still much to understand about this data and early results should be taken with a healthy grain of salt.”
