A New Theory Says Dark Matter Actually Shaped the Universe
Dark matter is understood to interact “feebly” with the visible universe, but was that always true?
Physicists have modeled the inflaton—a theoretical space scientists use to examine the period immediately post-Big Bang—to study these interactions.
It could be that dark matter’s interaction with the rest of the univerese was more equal to visible matter during this time.
In new peer-reviewed research, a team of researchers from Northeastern University stated that dark matter may have played a much bigger role in the birth of our visible universe than we thought. This is a big claim—physicists have mainly considered dark matter to be an unexplained and relatively stable part of the equation, not an active participant that shaped what our visible universe became. While scientists largely agree that dark matter is very, very weakly linked with the visible universe, these researchers have put forth a question: is there one venue where they’re both on equal footing?
It makes intuitive sense that dark matter (accounting for 95% of the universe today) must have played a part in the Big Bang that kickstarted the existence of our cosmos, but supporting that with evidence is deceptively difficult. In some math and coding classes, you learn the idea of a ‘black box function,’ where you put in a value and see what comes out, but you never see for sure process happens in the middle that makes the result pop out at the end. The Big Bang may be the ultimate black box function, and scientists can only try to reverse engineer it using more and more educated hypotheses.
In their paper, Ph.D. candidate Jinzheng Li and professor Pran Nath had to model both the Big Bang and a series of interactions in order to reverse engineer the role of dark matter. They tested the idea that the dark and visible sectors are more connected than we thought—that there could be more coupling than expected between dark matter and normal matter. In physics, coupling is when two particles of any kind are linked by one of the four fundamental forces: gravity, electromagnetism, weak interaction, or strong interaction. When you add dark matter and dark energy into the mix, there are also “feeble” interactions, which are much weaker than, well, weak.
Working with feeble interactions lets scientists consider models other than the Standard Model to try and explain the universe. It’s like substituting.0001, so you aren’t dividing by zero. And if all dark matter were feebly coupled to the visible universe, that would reinforce the idea that the visible universe has an outsize sway in terms of physics. We could continue using the Standard model, without any particularly troubling outliers in the mathematical harmony after the effects of dark matter are essentially reduced to zero.
But what if that weren’t always true? What if, at arguably the most key time, dark matter and visible matter were coupled more “democratically”—strongly enough that both sides had a more balanced say in what goes on in our universe?
To figure this out, the team examined a a theoretical space called ‘the inflaton,’ which scientists use to help understand and model the unfathomably rapid expansion (or “inflation”) of the earliest universe. If we stop assuming that dark matter only participated in feeble coupling in the inflaton, then an entire new parameter is suddenly in play. “[T]he hidden sector and the visible sectors could couple democratically to the inflaton,” the team wrote, “and in this case, the hidden sector and the visible sectors would be in thermal equilibrium at the end of reheating,” or the end of the inflaton period.
While this idea may clash with the Standard model, the researchers explain that’s part of why it should interest scientists. “[T]he analysis indicates that inclusion of hidden sectors that appear in a variety of models of particle physics beyond the standard model, and thus, their inclusion will be relevant for accurate description of physical phenomena,” they conclude.
In other words, when it comes to explaining the formation process of our universe, we should consider all the possibilities.
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