Space and Physics
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Dark matter is a hypothetical form of matter believed to be everywhere, outnumbering regular matter (what we're made of) 5-to-1. It doesn’t emit or interact with light, so it is invisible to our instruments – that’s why we call it dark. We know that it ought to be there because observations of the universe match our models only if there is a lot more matter out there. Still, it is difficult to find.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.There are a few possibilities when it comes to the nature of dark matter. It could be made of particles called weakly interacting massive particles (WIMPs), much heavier than a proton, that could be detected by the occasional collision with atoms. Or it could made of axions, particles that are so light that they weigh just a fraction of an electron.
Many labs are trying to catch WIMPs with dedicated detectors. Catching axions is a lot more difficult, but an international team has worked out an approach. Everything is both a wave and a particle (yes, technically even you), but the lighter something is, the easier one can see the wave-like nature. So the team behind a recent paper used lasers and two atomic clocks to measure the potential effect of the axions.
“Despite many theories and experiments scientists are yet to find dark matter, which we think of as the ‘glue’ of the galaxy holding everything together,” co-lead researcher Ashlee Caddell, from the University of Queensland, said in a statement.
“Our study used a different approach – analysing the data from a network of ultra-stable lasers connected by fibre optic cables, as well as from two atomic clocks aboard GPS satellites. Dark matter in this case acts like a wave, because its mass is very very low. We use the separated clocks to try to measure changes in the wave, which would look like clocks displaying different times or ticking at different rates, and this effect gets stronger if the clocks are further apart.”
The method provides the first constraints on how certain dark matter might interact with regular matter
“By comparing precision measurements across vast distances, we identified the subtle effects of oscillating dark matter fields that would otherwise cancel themselves out in conventional setups,” Caddell added. “Excitingly, we were able to search for signals from dark matter models that interact universally with all atoms, something that has eluded traditional experiments.”
There has been some circumstantial evidence from gravitational lensing, suggesting that axions are a better fit for dark matter. This method allows researchers to actually explore that range of masses.
“Scientists will now be able to investigate a broader range of dark matter scenarios, and perhaps answer some fundamental questions about the fabric of the universe,” study co-author Dr Benjamin Roberts said.
“This work also highlights the power of international collaboration and cutting-edge technology, using [Physikalisch-Technische Bundesanstalt]'s state-of-the-art atomic clocks and [University of Queensland]'s expertise in combining precision measurements and fundamental physics.”
The paper is published in Physical Review Letters.
