We Probe The Universe From A Nickel Mine, And With Lots Of Video Calls

What do a big chunk of ice at the South Pole, a mine in northern Ontario, and a mountain in Italy have in common? They’re all home to extreme underground environments, but they’re connected in another, more unexpected way. All three are host to large physics experiments searching to understand and answer the most basic questions about the world around us.

As a research scientist at SNOLAB in Sudbury, Ont., I get the chance to talk to a lot of different people about the work we do. The question often comes up: Why are we doing astrophysics–the study of space and the cosmos–from deep underground?

In particle physics, we long ago answered all of the questions that could be answered through tabletop experiments run by small groups of scientists in small laboratory spaces. Albert Michelson and Edward Morley showed that “luminiferous aether” didn’t exist, using a light source and mirrors on a bench-top stand. Marie Sklodowska Curie discovered polonium and radium in a shed next to the school of chemistry and physics at the École Normale Supérieure in Paris.

Fortunately, or unfortunately, we’re now asking bigger questions–we are looking for the nature of the universe: What gives particles their mass? What kind of particle is the neutrino? What is the rest of space made of? What is dark matter? Bigger questions require bigger experiments, which need bigger groups of people making them function.

The way to answer these questions is not just to build bigger detectors, but also to think carefully about where we put these detectors. So, scientists build detectors deep underground. We use kilometers of the earth as a dense shield to stop the particles we don’t want to detect.

The neutrinos and dark matter that we are looking for are unlikely to be stopped by the rock, so they are free to keep traveling to our detectors. The deeper we go, the more of this shielding we have.

Antarctica

Take for example IceCube, the experiment built directly into the South Pole. Looking for the highest energy neutrinos requires a cubic kilometer of ice to be buried under another 1.5 kilometers of ice.

If you’re standing on the South Pole, the bottom of the detector is 30 city blocks below you! There are over 5,000 light sensors distributed through this volume, with cables stretching to a surface control building from which the experiment is run.

This project requires over 300 people across 12 countries. Professors, students and technicians are all working on building electronics prototypes, testing techniques to drill into the oldest ice on the planet, and writing computer code to analyze all that data. There is no one country, much less one single university, that could supply all the necessary resources.

Canada

SNOLAB, Canada’s deep underground astroparticle physics laboratory, is in an active, working nickel mine over two kilometers underground. There is a rich history of particle physics experiments operating in mines, beginning in the 1960s.

Compared to experiments hosted in shuttered mines, working in an active one makes some aspects easier, because scientists don’t need to worry about operating the mine elevator (called the cage) or pumping groundwater out of the mine. But the size of the cage, and the mine tunnels (called drifts) limit the size of items that can be transported into the lab. Overall, the detectors’ increased sensitivity from all of the shielding is worth the effort.