Dark matter is believed to be five times more prevalent in the universe than ordinary matter.
But it interacts so weakly with other matter – like the protons and electrons that make up the stuff around us – that, to date, it has defied our attempts to detect it directly. It doesn’t even interact with light, which is why we call it dark matter.
But that doesn’t mean it’s impossible to detect. We can search for dark matter in a number of ways.
We can try to produce dark matter using high-energy particle accelerators, such as the Large Hadron Collider at CERN. We can also look into regions of space where dark matter is concentrated, such as at the centres of galaxies, for signs of dark matter decaying into ordinary matter.
Finally, we can directly search for signals of dark matter by building highly sensitive detectors that can detect when a dark matter particle bumps into a particle of ordinary matter.
In January 2017, work will begin on the construction of just such a detector, a kilometre underground in the Stawell Gold Mine in Victoria.
There are many different direct searches for dark matter underway around the world, but the experiment at the Stawell Underground Physics Laboratory (SUPL) will be the first of its kind in the Southern Hemisphere.
The reason we’re putting the sensors so deep underground is to prevent them being swamped by unwanted noise from cosmic rays, the high-energy particles that constantly rain down on Earth. These cosmic rays are very energetic, so it takes a lot of material to block them and prevent them from interfering with the experiment.
So far, there has been only one claim of direct detection of dark matter from the DAMA-LIBRA experiment, deep underground in the Gran Sasso laboratory in Italy. It used thallium-doped sodium iodide crystals, which should give off a barely perceptible flash of light if dark matter collides with the ordinary matter atoms in the crystals.