In the scientific search to learn more about the very early universe, a mysterious particle promises to take our knowledge to the very birth of the universe.
While yet unproven, the hypothetical particle, called an axion, might reveal for the first time the conditions of the universe just one second after the Big Bang, according to a recent study published in the journal Physical Review D.
Axions could help provide an image of the extremely young universe
Conventionally, scientists look at the electromagnetic spectrum of the universe to observe the Cosmic Microwave Background (CMB), which enables us to peer back roughly 14 billion years, a time when the universe had cooled enough for protons and electrons to combine into neutral hydrogen. Via the CMB, astronomers and cosmologists learned much about how the universe evolved. But this only takes us to roughly 400,000 years after the Big Bang, since the photons in CMB weren't released until then.
In other words, there's an empirical blindspot in our study of the universe before this era.
To deepen our knowledge of this unknown period of the universe, researchers looked to hypothetical particles called axions, which might have flashed outward in the first second of the very young universe. The new paper proposes seeking out an axion analog of the CMB, called a Cosmic axion Background (CaB). Of course, scientists have to prove the particle is real before they can use it to peer into the very ancient universe, but there are strong reasons for hope. For example, axions are a generic prediction of string theory, the leading theoretical candidate to potentially describe a new theory of quantum gravity. Axions might help answer a puzzling question about why we haven't measured the electric dipole moment for a neutron — also called the "Strong CP Problem". Additionally, axions have also garnered much attention as a possible candidate for dark matter, galvanizing researchers in a hunt for axion dark matter.
In the new paper, the scientists suggest that as scientists develop increasingly sensitive instruments in their experimental search for dark matter, they might encounter a different sign of axions, in a type of the CaB. But since the CaB possess similar qualities as dark-matter axions, experiments might leave the CaB signal out, classifying it as noise. To find the CaB via one of these instruments would kill two birds with one stone. In addition to confirming the reality of axions, scientists around the world would instantly have new fossil evidence of the environment during the very early universe. Researchers could drastically enhance our understanding of how the universe evolved, on a scale never realized before.
Dark-matter axions could solve several cosmic puzzles at once
"What we have proposed is that, by changing the way current experiments analyze data, we may be able to search for left-over axions from the early universe," said Hitoshi Murayama, Lawrence Berkeley National Laboratory senior faculty scientist and an author of the study, in an embargoed release shared with IE. "Then, we might be able to learn about the origin of dark matter, phase transition or inflation at the beginning of the universe. There are already experimental groups who have shown interest in our proposal, and I hope we can find out something new about the early universe that wasn't known before."
As if cosmology and astrophysics weren't exciting enough, this latest study lends even more empirical promise to the dark-matter program. Supposing dark matter isn't composed of axions, the ultra-sensitive instruments might still reveal an image of the unconscionably early universe, from a time when literally everything that ever was or would be was less than one second old.