Washington DC [US]: A new study by Dartmouth University researchers has introduced a compelling theory that could reshape our understanding of dark matter — the elusive substance believed to make up 85% of the universe’s mass.
Published in Physical Review Letters, the study proposes that dark matter may have originated in the early universe from collisions between massless, high-energy particles. According to the mathematical model presented by physicists Robert Caldwell and Guanming Liang, these particles lost energy and instantly gained mass after pairing — marking a pivotal transformation.
While dark matter remains hypothetical, its existence is supported by unexplained gravitational effects observed in galaxies and clusters.
What makes this new theory distinct is its testability using existing observational data, particularly through signatures on the Cosmic Microwave Background (CMB) — the afterglow radiation from the Big Bang.
“Dark matter started its life as near-massless relativistic particles, almost like light,” says Robert Caldwell, professor of physics and astronomy and the paper’s senior author.
“That’s totally antithetical to what dark matter is thought to be — it is cold lumps that give galaxies their mass. Our theory tries to explain how it went from being light to being lumps.”
After the Big Bang 13.7 billion years ago, the universe was a soup of hot, fast-moving particles, similar to photons. Caldwell and Liang theorize that massless particles, due to their opposing spins, attracted each other and formed dense clusters. As they cooled, an imbalance in spin triggered a rapid drop in energy — like steam cooling into water.
“The most unexpected part of our mathematical model was the energy plummet that bridges the high-density energy and the lumpy low energy,” says Guanming Liang, the study’s lead author and a Dartmouth senior.
“At that stage, it’s like these pairs were getting ready to become dark matter,” Caldwell adds.
“This phase transition helps explain the abundance of dark matter we can detect today. It sprang from the high-density cluster of extremely energetic particles that was the early universe.”
The theory introduces a new type of particle that initiates this transformation. Caldwell and Liang note that electrons are already known to undergo a similar transition, adding plausibility to their concept.