Earth may be caught in the middle of a galaxy-encompassing void, but there’s no need to panic. This may actually be the key to understanding how old the universe is and how rapidly it is expanding. The latest cosmological research is now lending credence to a controversial theory suggesting that the entire Milky Way galaxy is located near the center of a massive void.
The research, shared at the Royal Astronomical Society’s National Assembly Meeting, points to the “sound of the Big Bang” as supporting evidence. Primordial sound waves that have left a lasting imprint on the early universe appear to reinforce the idea that we live inside a void, which may explain why celestial objects far beyond our planet move much faster than expected.
Frozen Sound Waves From the Big Bang
The momentous cosmic explosion that created the universe 13.8 billion years ago didn’t release an ear-splitting sound as the name “Big Bang” might suggest. However, it did lead to the creation of sound waves that eventually stopped cold as the universe grew cooler and less dense, leaving behind valuable clues for astronomers today.
Before the universe was populated with stars and galaxies, it was a hot and dense expanse filled with plasma. Small pockets of matter that were particularly dense attracted surrounding particles. The competing forces of gravity and pressure generated by photons caused the particles to go awry, bouncing around and creating waves called baryon acoustic oscillations (BAOs).
"These sound waves traveled for only a short while before becoming frozen in place once the universe cooled enough for neutral atoms to form," said Indranil Banik, a cosmologist at the University of Portsmouth, in a press statement. "They act as a standard ruler, whose angular size we can use to chart the cosmic expansion history."
Read More: We May Finally Understand Where the Universe’s Missing Matter Has Been Hiding
The Puzzle of Hubble Tension
BAOs could be key in solving the enigma of Hubble tension, which has been at the heart of a deep-rooted debate about the expansion of the universe. Hubble tension represents a discrepancy between two models of measuring cosmic expansion: measurements of the distant, early universe in the cosmic microwave background (CMB) predict a slow rate of expansion, while measurements of the closer, more recent universe show a faster rate of expansion.
As a result, scientists have speculated why the universe appears to be expanding faster than expected. One explanation is that our galaxy is near the center of a void.
This theory proposes that the exterior of the void would have a higher density than the center, its gravity gradually pulling at the contents of the void.
"As the void is emptying out, the velocity of objects away from us would be larger than if the void were not there. This, therefore, gives the appearance of a faster local expansion rate,” said Banik in the statement.
Near the Center of a Void
For this theory to be true, Earth and our solar system would need to be close to the center of a void, about a billion light-years in radius, and with a density about 20 percent below the average for the universe as a whole.
The standard model of cosmology — suggesting that the matter across the universe is spread out in a uniform manner — clashes with the notion of a local void.
However, the researchers involved with the new research were able to come up with a model using all available BAO measurements over the last 20 years. According to Banik, “a void model is about one hundred million times more likely than a void-free model with parameters designed to fit the CMB observations taken by the Planck satellite, the so-called homogeneous Planck cosmology.”
To support this void model, the researchers will next look at light from galaxies that are no longer forming stars in an attempt to learn what kinds of stars are located there. This will help them determine an age for the galaxies, which they can then combine with redshift — how the wavelength of a galaxy’s light is stretched as it moves away from Earth — to gain a better understanding of universe expansion.
Read More: Light Emitted by a Distant Galaxy Pierces Through the Early Universe's Fog
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Euculid Consortium. Measuring the Universe with Baryon Acoustic Oscillations
NASA. NASA’s Webb, Hubble Telescopes Affirm Universe’s Expansion Rate, Puzzle Persists
Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine
