A gigantic ‘wall’ of galaxies has been found stretching across the universe
The mathematics that Albert Einstein devised in the early 20th century to describe the gravitational force of the physical universe still holds up today.
In one of the largest tests of general relativity to date, a huge team of astronomers has mapped the distribution of nearly 6 million galaxies over 11 billion years of the universe’s history.
The way gravity clumps these galaxies together along strands of the cosmic web, against the outward pull of the expansion of the universe, and the way that web evolves over time, exactly matches the predictions of Einstein’s famous theory.
It may be the biggest test of general relativity yet, covering most of the universe’s 13.8 billion-year history – meaning the theory holds up on both the largest and smallest scales.
The findings have been submitted for publication and are available in three new preprints uploaded to arXiv prior to peer review.
“General relativity has been tested very well on the scale of solar systems, but we also had to test whether our assumption works on a much larger scale,” said cosmologist Pauline Zarrouk of the French National Center for Scientific Research.
“By studying the rate at which galaxies formed, we can directly test our theories, and so far we are consistent with what general relativity predicts on a cosmological scale.”
Gravity is fundamental to the way the universe works. We don’t know what it is or why it is, only that objects with mass tend to attract other objects with mass; that the force of attraction is directly proportional to mass; and that it changes the geometry of space-time around a mass.
It also acts like a glue that holds the universe together. Large filaments of gravitational fields generated by dark matter span the entire universe in a kind of web; and most of the matter in the universe is distributed along the strands and nodes of this cosmic web.
It is predictable and measurable and so far extremely well constrained and defined by general relativity. But finding flaws in the theory could yield solutions to some remarkably thorny problems, such as the irreconcilable differences between quantum mechanics and classical physics. So scientists continue to probe to see whether the contents of the universe look exactly as general relativity says they should, at all scales.
This brings us to the Lawrence Berkeley National Laboratory-led Dark Energy Spectroscopic Instrument (DESI), a massive international collaboration currently working to map the observable universe to unlock its greatest secrets. It has been operational since 2019; the new results are based on a detailed and comprehensive analysis of only the first year of data obtained by the instrument.
The DESI Collaboration used that data to conduct a painstaking study of 5.7 million galaxies and quasars throughout the history of the universe, tracking their growth, evolution and distribution along the cosmic web from the early universe 11 billion years ago. card was mapped.
This simulation shows how adjusting gravity changes the distribution of galaxies in the universe. (collaboration Claire Lamman and Michael Rashkovetskyi/DESI)
They used general relativity to predict the growth and spread of the cosmic web, and found that the universe we live in has behaved as relativity says it should, on an epic cosmic scale. Add more gravity, or take some away, and the universe would no longer look the same.
The result follows a paper earlier this year that measured the expansion rate of the universe from cosmic remnants of acoustic waves that froze when the atomic fog that filled the early universe cleared. The DESI Collaboration hopes that continued efforts will continue to shed light on the evolution of the universe and, in turn, the mysterious forces driving it.
“This is the first time that DESI has looked at the growth of the cosmic structure,” says physicist Dragan Huterer of the University of Michigan. “We demonstrate a vast new ability to explore modified gravity and improve the limitations of dark energy models. And it’s just the tip of the iceberg.”
DESI is at the Mayall Telescope in Arizona, seen here during the 2023 Geminid shower. (KPNO/NOIRLAb/NSF/AURA/R. Sparks)
The results also put constraints on the upper limit on the mass of the neutrino, a particle so “ghostly” that we haven’t been able to weigh it precisely.
The investigation is still ongoing, as is the Collaboration’s work. The researchers are currently analyzing data from the first three years that DESI was active. By the time the instrument completes its work, it will have collected data on more than 40 million galaxies and quasars.
One of the biggest hopes is that it will help reveal the nature of dark matter, the mysterious invisible something responsible for generating additional gravity in the universe; and dark energy, the mysterious invisible something responsible for driving the variably accelerating expansion of the universe.
“Dark matter makes up about a quarter of the universe, and dark energy another 70 percent, and we don’t really know what either is,” says physicist Mark Maus of the Lawrence Berkeley National Laboratory and the University of California Berkeley.
“The idea that we can take pictures of the universe and tackle these big, fundamental questions is amazing.”
The team’s papers are now available on preprint server arXiv.
