Mysterious Dark Matter May Predate Big Bang

Dark matter, the mysterious substance that makes up roughly 80 percent of all the matter in the universe, may have been forged before our cosmos was even born. Scientists have long theorized as to what dark matter really is and how it came to exist. But now, according to a paper in the journal Physical Review Letters, researchers from the University of Texas at Austin have suggested it could have been made before the big bang. This dark matter makes up about 27 percent of the universe's total mass-energy content, 68 percent of which is made up of dark energy, with only 5 percent being "normal" matter, according to NASA.

"Dark matter is a form of matter that appears to not interact with light but we know must be there because of its gravitational influence on its surroundings—e.g., stars in galaxies rotate too fast," Ellen Sirks, a postdoctoral researcher in dark matter at the University of Sydney's School of Physics, previously told Newsweek. "We also know that there has to be approximately five to six times more of it than 'ordinary' matter—stars, planets, gas, etcetera," she said. According to the new research, dark matter may have been created during the unfathomably short period of inflation just before the big bang occurred. The big bang is the leading scientific theory explaining how the universe was born. It describes how the universe expanded from an extremely hot, dense state about 13.8 billion years ago and has been growing ever since. The universe is thought to have begun as a point of infinite density and temperature, known as a singularity, which underwent extremely rapid expansion, further expanding as it cooled. Astrophysicists have theorized that the level of dark matter present today is a result of a "freeze-out" or "freeze-in" due to interaction with a thermal bath of plasma in the universe's hot, dense past. Under the "freeze-out" scenario, dark matter particles interacted with ordinary particles and were in thermal equilibrium in the early universe. However, as the universe cooled and expanded, dark matter particles could no longer find partners to annihilate with fast enough because the interaction rate fell below the expansion rate of the universe. At some critical temperature, the annihilation of dark matter particles effectively stopped, leaving a residual abundance of dark matter particles that persists to this day. The "freeze-in" scenario suggests that dark matter particles were never in thermal equilibrium with the rest of the universe. Under this theory, dark matter particles had such weak interactions with normal matter that their annihilation was extremely rare. The researchers suggest that dark matter could have been created during the infinitesimal inflation of the universe, which lasted the tiniest fraction of the second, under a new "freeze-in" model called "warm inflation via ultraviolet freeze-in" (WIFI). "The thing that's unique to our model is that dark matter is successfully produced during inflation," study co-author Katherine Freese said in a statement. She is the director of the Weinberg Institute for Theoretical Physics and the Texas Center for Cosmology and Astroparticle Physics at the University of Texas at Austin. "In most [other] models, anything that is created during inflation is then 'inflated away' by the exponential expansion of the universe, to the point where there is essentially nothing left," Freese said. This would mean that dark matter was created much earlier than scientists previously thought. Study co-author Barmak Shams Es Haghi, a researcher at the University of Texas at Austin, said in the statement: "In our study, we focused on the production of dark matter, but WIFI suggests a broader applicability such as the production of other particles that could play a crucial role in the early universe's evolution. This highlights new opportunities for exploration in future research." Do you have a tip on a science story that Newsweek should be covering? Do you have a question about dark matter? Let us know via science@newsweek.com.

Reference

Freese, K., Montefalcone, G., & Haghi, B. S. E. (2024). Dark Matter Production during Warm Inflation via Freeze-In. Physical Review Letters, 133(21). https://doi.org/10.1103/physrevlett.133.211001