Cosmic Voids May Contain the Universe’s Best Secrets

Nature abhors a empty, as the saying goes, but no one told the universe that. Space is filled with cosmic voids – vast, mostly matter-free regions that have opened up between dense threads of matter that make up a cosmic web.

Far from being empty depths with little to study, these voids could hold solutions to some of the most enduring cosmic mysteries, such as the behavior of gravity, the nature of dark energy, and the so-called Hubble tension, an observational shift in the universe’s expansion rate that has been causing headaches for astronomers for years.

“With voids, we have the power to solve most of the interesting cosmological puzzles,” explains Alice Pisani, professor-researcher in cosmology working at the Marseille Center for Particle Physics (CPPM) of the National Center for Scientific Research. She adds that because there is less interference from matter, the signal-to-noise ratio is high compared to what researchers can observe.

The advent of new telescopes and advanced simulations has energized this field, inspiring a growing community of scientists around the world to specialize in voids as unique cosmological laboratories. Some experts say we might even be living in a colossal void, a position that could dramatically alter our view of the universe.

In places defined by scarcity, voids become cosmological heavyweights, where the laws of physics can be observed with unusual clarity.

“From a cosmological point of view, this is a very exciting time,” Pisani says.

What are cosmic voids?

After the Big Bang, the universe was a uniform soup of subatomic particles. But over millions of years, as matter cooled and stabilized into atoms, the faint outlines of the cosmic web began to emerge.

For billions of years, the web gravitationally attracted gas clouds, galaxy clusters and other cosmic objects to its scaffolding. As material is drawn into the web, spaces expand between its filaments, forming voids.

Small “vacuums” can open between galaxy clusters, where they may be only 10 or 20 million light years across. But the gaps can get bigger. Much bigger. The Boötes Void, also known as the Big Nothing, spans more than 300 million light years.

Calling them cosmic voids can be “misleading,” Pisani says, “because we end up thinking that a void means void. But in fact, the voids we observe are never empty. There are very small, low-mass galaxies inside these underdense regions.” The Boötes Void, for example, contains a few dozen galaxies, although that’s still far fewer than the thousands one might expect in an area of this size. similar.

Because they are relatively devoid of matter, cosmic voids remained out of sight of observations until the late 1970s. Until then, the positions of galaxies were mapped as 2D points in the sky, but the development of 3D maps of the distribution of galaxies revealed the contours of the cosmic web for the first time, revealing the presence of voids.

In recent years, a slew of new telescope surveys has sparked an explosion of new void discoveries, such as the Dark Energy Survey Instrument (DESI) in Arizona and Europe’s Euclid Space Telescope. These instruments are expected to map more than 100,000 voids in space, providing unprecedented insight into these structures. Yet these studies will only capture a fraction of the millions of voids estimated to exist in the observable universe.

“Over the last ten years, the field has really evolved significantly with new technologies,” explains Nico Schuster, cosmologist and cosmic vacuum expert at CPPM. “All of this really allows us to observe many more galaxies than before, and it finally allows us to probe the cosmic web to a much deeper depth, find more gaps and resolve them better.”