The search for dark matter
The first thing we learned in high-school science class was the concept of matter. We all know that almost everything around us is matter, including the cheesy poster outside science classrooms that says “You Matter!” Matter is any substance that has mass and takes up space. However, not all matter can be detected by our naked eyes or even the most advanced instruments. In fact, everything ever observed by human technology constitutes less than five percent of the universe—the rest is darkness.
Dark matter stealthily hides from our sight by not emitting any type of electromagnetic radiation. How, then, did scientists come to hypothesise the existence of such an elusive form of matter? It turns out that dark matter plays an indispensable role in holding the world together. In 1933, Fritz Zwicky, a Swiss astronomer working at the California Institute of Technology, measured how much visible mass there was in a certain cluster of galaxies. His result was that the quantity of visible matter was far too small to be consistent with the rotation speed of the galaxies; the galaxies would have escaped the gravitational pull of the cluster and spiralled out of control long ago. This led Zwicky to conclude that an invisible substance that generates extra gravity with its mass acts like a glue to keep galaxies intact. Another metaphor compares the universe to an ice cream: dark matter is the invisible ice cream cone, and all the ordinary things we see are the sprinkles on top.
Just a four-hour drive away from UofT, scientists at the Sudbury Neutrino Observatory (SNOLAB) conduct extraordinary experiments in hopes of learning more about dark matter. SNOLAB is buried two kilometres underground in Vale Limited’s Creighton mine, making it the deepest clean room laboratory in the world. It was designed to address, and, in 2001, eventually solved, ‘The Solar Neutrino Problem.’ The leading scientist, Arthur McDonald, was awarded the Nobel Prize in Physics for this work. The layers of rocks between SNOLAB and the surface block out unwanted radiation and distractions, creating an ideal low-background environment. One active experiment at SNOLAB is PICO, where interactions between particles are captured using bubble chambers. The detectors are located in water tanks filled with fluid previously used in household fridges. When superheated, the particles interact and cause the fluid to boil and form a bubble. The bubble is recorded on camera and microphone, to identify rare interactions of dark matter particles with ordinary matter. Indeed, every bubble contains the fragile yet beautiful key to uncovering the mysteries of dark matter.
Ever since the dawn of humanity, we have been fascinated by the unknown. Thus, the search for dark matter is not limited to the most brilliant scientists in our society—we all share the instinctual drive and insatiable desire to discover. Artists, philosophers, and historians alike have joined the open discussion around dark matter and put forth their valuable perspectives. For instance, four internationally renowned artists recently toured SNOLAB and engaged with researchers leading the search for dark matter. Their SNOLAB-inspired artworks were then displayed until earlier this month at ‘Drift: Art and Dark Matter,’ an exhibition at the UofT Art Museum. This intersection reflected on art and science’s shared mode of experimentation and creativity while addressing the issue of missing perspectives. The exhibit pointed out the important fact that SNOLAB is located on the traditional territory of the Robinson-Huron Treaty of 1850, shared by a diverse set of Indigenous communities. As we unveil the secrets of our universe, we are also searching inwards and moulding our collective identity with inclusivity and humility.
