The bulk of our universe’s mass is in the form of some weird matter that can’t be seen or found using any of our normal methods that rely on interactions with the electromagnetic force. It can currently only be found through how its gravitational mass pulls on surrounding objects and bends the passage of light.

Trying to figure out what dark matter is made of is super hard and has researchers doing everything from slamming protons together at high energies to looking for tiny flashes of light from dark matter particles colliding with liquid in giant underground detectors, to even doing more math for graduate projects than I have done in my entire life.

And I have done a lot of math.

Theorists at New York University have been working on detailed models that describe how the presence of different kinds of dark matter particles would have influenced the evolution of our universe. In a new paper published in Physical Review Letters, researchers led by Cara Giovanetti demonstrate that certain kinds of dark matter particles would have affected the formation of elements during Big Bang nucleosynthesis and even left signs in the cosmic microwave background.

According to Giovanetti: Precision measurements of different parameters of the universe — for example, the amount of helium in the universe, or the temperatures of different particles in the early universe — can also teach us a lot about dark matter. Lighter forms of dark matter might make the universe expand so fast that these elements don’t have a chance to form. We learn from our analysis that some models of dark matter can’t have a mass that’s too small, otherwise, the universe would look different from the one we observe.

While this research doesn’t tell us what dark matter is, it does tell us what it isn’t, and it reminds us that the cosmic microwave background is the great test case against which theories for things small and large all must be compared.

More Information

NYU press release

“Joint Cosmic Microwave Background and Big Bang Nucleosynthesis Constraints on Light Dark Sectors with Dark Radiation,” Cara Giovanetti, Mariangela Lisanti, Hongwan Liu, and Joshua T. Ruderman, 2022 July 6, Physical Review Letters