Scientists have proposed that dark matter, an unidentified cosmic material that is considered one of the biggest mysteries in science, was forged in a second “Dark Big Bang” that occurred within one month of the birth of our universe, according to a recent study.
This wild new “alternate cosmology” could account for some of the most perplexing riddles about dark matter, which is about five times more abundant than the regular visible matter that makes up stars and planets, yet has still evaded direct detection.
Scientists believe that dark matter exists because we can see its gravitational effects on regular matter; for instance, galaxies are held together by dense clumps of dark matter called halos. But though its ghostly influence can be indirectly observed, attempts to actually capture a dark matter particle here on Earth have consistently failed, suggesting that this material exists in some kind of shadow realm that has only the most tenuous gravitational link with our own visible universe.
Katherine Freese and Martin Wolfgang Winkler, two physicists at the University of Texas at Austin, have now proposed that dark matter is such a bizarre outlier because it has a completely different genesis than the rest of the universe.
Our existing model of the cosmos assumes that both regular and dark matter were born in the Big Bang, a sudden moment of extreme inflation that is considered to be the start gun of the universe. Freese and Winkler upend this idea by suggesting that dark matter could be formed in a second “Dark Big Bang” that occurred within a month of the first Big Bang. What’s more, the pair propose that their model could produce a number of “exciting experimental signatures” that would be detectable to existing and future instruments, hinting that “a direct test of the Dark Big Bang origin of the dark matter could become feasible,” according to a recent study published on the preprint server arxiv.
“According to the cosmological standard model, the very early Universe went through an epoch of inflation—a rapid expansion of space driven by vacuum energy,” Freese and Winkler said in their study, which has not yet been peer-reviewed. “The origins of matter and radiation lie in the Hot Big Bang which terminates inflation and releases the vacuum energy into a hot plasma of particles. The latter contains the photons, leptons and quarks of our visible Universe, and, in the standard picture, also the dark matter.”
“However, there is no genuine reason for a common origin of visible and dark matter beyond simplicity,” the team continued. “Furthermore—despite excessive experimental searches over decades—no direct non-gravitational interactions between visible and dark matter have been detected. In this light, we will present an alternative cosmological scenario in which the visible and the dark (matter) sector are completely decoupled (other than through gravity). The Hot Big Bang only induces visible radiation and matter, but no dark matter at all.”
It’s a mind-boggling new interpretation of our cosmic origins, but the researchers said the idea of a Dark Big Bang does not appear to violate the constraints associated with models of early cosmic structure formation, provided that dark matter emerged within a few weeks of the birth of the universe.
There are a number of possible scenarios that might lead to this one-two punch at the beginning of time, but Freese and Winkler focus on what’s known as “a first-order phase transition” that led to the creation of dark matter. Essentially, in addition to producing the seeds of regular matter, the original Big Bang generated a dark quantum field that didn’t immediately decay. As the days rolled by in the universe’s infancy, regular matter cooled into atoms, a process known as Big Bang nucleosynthesis (BBN). At some point around the point of BBN, the dark quantum field did finally decay and transform its state, sparking the Dark Big Bang that created dark matter.
One of the most exciting implications of a Dark Big Bang is that it would leave traces that could be potentially detectable to modern instruments. For instance, an event of this scale would probably produce gravitational waves, which are ripples in spacetime, that might be observable in observations of ultra-dense stars known as pulsars. Indeed, Freese and Winkler suggest that a project known as the International Pulsar Timing Array (IPTA) may have already spotted potential evidence for a Dark Big Bang.
“The Dark Big Bang phase transition generates strong gravitational radiation,” the team said in their study. “[W]e investigated the sensitivity of ongoing and upcoming pulsar timing array experiments to the gravitational wave signal from the Dark Big Bang. We found that already the ongoing IPTA run (which combines several individual PTA experiments) has an exciting discovery potential for Dark Big Bangs which occur around or after BBN.”
“Intriguingly, a tentative gravitational wave signal by the NANOGrav experiment (included in the IPTA network) could already be interpreted as the first sign of the Dark Big Bang,” the researchers added.
Future instruments, such as the enormous Square Kilometer Array, could provide even more sensitivity to the search for signs of this speculative origin of dark matter. At this point, it’s hard to predict whether this unusual explanation for dark matter might ever be backed up by hard evidence, but the new study provides a tantalizing roadmap to seek the answer to one of science’s most intractable riddles.