In a gold mine at the edge of a rugged mountain range…
…scientists are going deep beneath the surface of the Earth…
…to unlock the secrets of the universe.
The entire visible universe — the stars, the planets, the chair you might be sitting on — accounts for just 15 per cent of all the mass that is there.
The rest is dark matter.
We know almost nothing about dark matter.
In fact, no-one has ever seen it.
A gold mine might seem like an unusual place to look.
But three hours west of Melbourne, in the sleepy town of Stawell, that's exactly what's happening.
What is dark matter?
"If you had eyes that could see dark matter, you would see a wind rushing through you … at 250 kilometres per second," astronomer Alan Duffy says.
"We are so used to thinking of [dark matter] as out there somewhere, holding the stars in their orbit around the Milky Way … but it's right here in this room.
"There is a gale of it blowing through us now.
"The problem with trying to find dark matter is it doesn't shine or absorb light.
"It's like a ghost, able to travel through solid walls, through the entire earth and never collide.
"It is a companion to our lives that we have never felt, tasted, touched or seen. And yet its gravity was responsible for us being here.
"Wouldn't you want to meet that companion?"
Going underground
Detecting dark matter is a sensitive business, and the conditions for any lab need to be carefully considered.
That's why the team is venturing down into a disused tunnel off the still-operational Stawell Gold Mine.
As you descend, the heat around you rises.
You can feel your clothes stick to your sweaty body as the ute takes the corners of the mine's spiralling main shaft.
There is no light, no noise, and no radioactivity.
Nothing to interfere with the experiment about to take place.
That's why physicists have chosen it as the location for the Stawell Underground Physics Laboratory, or SUPL for short.
A century of searching
Swiss astronomer Fritz Zwicky first suggested the existence of dark matter in the 1930s.
He noticed that galaxies in the Coma cluster were moving incredibly fast.
So fast, they should have gone spinning off into the universe.
But they didn't.
To explain this, Zwicky thought, there must have been some massive, unseen gravitational force filling up the cluster and holding it in place.
He called this "dark matter".
It wasn't until the 1970s that American astronomer Vera Rubin continued the search and found evidence of dark matter's existence within galaxies.
While studying the nearby galaxy Andromeda, Dr Rubin noticed it was spinning just as fast on its outer edge as it was in its middle.
That was the same in every galaxy she looked at.
She posited there was an invisible halo of matter surrounding them — accelerating the spin.
It was also Dr Rubin who estimated dark matter made up 85 per cent of all matter.
Flashes of hope
Since then, scientists have spent decades searching for visible evidence of the particle.
The Stawell lab will replicate an experiment known as DAMA/Libra, which began under a mountain in Italy in 1998.
That experiment detected something that could be dark matter at the same time each year for two decades.
Signals peaked in June and dropped in November.
The Stawell experiment, known as SABRE, which stands for Sodium-iodide with Active Background REjection, is DAMA/Libra's southern hemisphere twin, aimed at verifying its results.
The tightly controlled experiment works by using specially grown sodium iodide crystals, which are highly pure and suspended in a soup of chemicals.
Brief flashes of light are emitted when sub-atomic particles travelling through the universe hit the nuclei — or middles — of atoms within the crystals.
If a dark matter particle hits a nucleus in a crystal, it should create a tiny flash.
That flash will then be amplified so it can be picked up by a series of globes inside the detector.
Professor Duffy says replicating the same process below the equator will ensure DAMA/Libra's results can't be explained by interference from the Earth that naturally occurs across the four seasons.
If they get the same results in the southern hemisphere winter as in the northern hemisphere summer — it's dark matter.
"The world needs to know whether they are right or wrong," Professor Duffy, who is a chief investigator of the project, says.
"If they're right, Nobel Prizes for them, wonderful.
"If they're wrong, then we look somewhere else.
"Either way, it's a spectacular result."
The leading theory that explains the particles and forces that make up the world we see, known as the Standard Model of physics, cannot explain the presence of dark matter.
That is why scientists are looking for new particles.
Two of the leading candidates are axions and WIMPs.
Axions would be thousands of times lighter than any other particle scientists know about.
WIMPS (or weakly interacting massive particles) would be much heftier.
WIMPS are a promising candidate in the dark matter investigation as they wouldn't absorb or emit light — like dark matter – and they could make gamma rays when one WIMP hits another and both annihilate in a flash of energy.
SABRE will focus on WIMPs.
In Perth, researchers at the University of Western Australia are working on the ORGAN (Oscillating Resonant Group AxioN) experiment to help determine the existence of axions. A run of ORGAN earlier this year did not detect any "dark matter signals".No detection is just as valuable to researchers as a detection: It tells them where they shouldn't be looking to find dark matter.
Despite several scientific efforts to detect WIMPS, the theoretical particle has also remained elusive so far.
SABRE represents another chance to help prove or disprove its existence.
If SABRE finds dark matter, all particle and nuclear physics and fundamental science will be focused on WIMPS.
In short, it'll be a pretty big deal for humanity's collective understanding of the mass that makes up 85 per cent of the universe.
Why here?
Elisabetta Barberio has been chasing dark matter as a researcher for 10 years.
She moved into the field after working at Switzerland's Large Hadron Collider, and helping with research to confirm the existence of the Higgs Boson particle.
As the director of the University of Melbourne's particle physics research centre, she was part of the team that pushed for Stawell as the location for SABRE.
Professor Barberio said she and her colleague, Swinburne astronomer Jeremy Mould, scoured the country for a suitable site for the project.
In the northern hemisphere, this project would take place under a towering mountain or by the side of a tunnel.
"But there aren't enough of those here," Professor Barberio says.
"So we started looking at mines."
Funding was committed, but the plans gathered dust for several years as the gold mine shut while it changed owners several times.
Now, with the mine reopened, and with the support of six Australian universities and all three levels of government, the $12.6 million lab is ready to begin 20 years of scientific operations.
It will welcome scientists from across the globe to Stawell.
The actual experiment is expected to kick off in July next year.
The lab will also be used for agricultural and other scientific research over its 20-year life span.
"The equipment we are building will have spin-off technology," Professor Barberio says.
Why do we need to know?
So, why spend all this time and money?
Why go down into the depths of the Earth to realise something we can't see?
"Two hundred years ago, Benjamin Franklin was studying lightning," Professor Barberio says.
"He was just curious, and he discovered electricity.
"If his aim was just benefit to industry, he would have looked to improve candlelight.
"It is really the paradigm shift of fundamental research that you need for technology to change."
Professor Duffy says the field of particle physics is at a "crossroads".
"The last main discovery [was] the Higgs Boson — the 'God' particle," he says.
"And yet, there is this humungous amount of additional stuff out there that lies beyond the [Standard Model of physics], completely unexplained.
"When you discover what that particle is, you allow every physicist in the world a signpost [so they] know where to take the next fundamental theory of science.
"Right now, we are running in different directions trying our own ideas because no-one knows what's right.
"At the moment of discovery, we will have found more about what makes up the universe than all of science combined."
Credits:
- Reporting: Alexander Darling and Ben Knight
- Graphics: Murray Adam and Ario Rasouli
- Videography: Michael Barnett
- Video production: Melanie Counsell and Andie Noonan
- Photography: Danielle Bonica and Darryl Torpy
- Digital production: Sian Johnson and Kate Higgins
