Developed by University of Delaware physics professor Spencer Axani, CosmicWatch is a $100 pocket-sized particle detector roughly the size of a box of animal crackers. Built to track invisible muons raining down from space, the third version of the device monitors its surroundings, tolerates high radiation, and records data for educational and international astrophysics research.
Invisible particles from space stream through the Earth constantly. You cannot see, hear, feel, taste, or smell them. These subatomic particles are linked to cosmic rays—extremely energetic particles originating from exploding stars and violent events far beyond our solar system. When these cosmic rays strike atoms high up in Earth’s atmosphere, they trigger showers of secondary particles. Among them are muons, which possess enough energy to pierce the atmosphere and penetrate underground.
Detecting these high-energy interlopers used to require expensive, bulky infrastructure. Traditionally, an undergraduate physics lab course relies on a rack of electronics roughly the size of a small bookshelf to measure muons. That hardware barrier limits the experiments researchers can perform and the number of schools that can give students hands-on access to the technology. Axani changed that dynamic.
From MIT to Global Astrophysics Research
The architecture of CosmicWatch has deep roots. Axani first engineered the detector back in 2017 as a graduate student at the Massachusetts Institute of Technology (MIT). His original mission was to build a compact, energy-efficient muon detector for deployment at the IceCube observatory buried beneath the Antarctic ice sheet. At IceCube, researchers use muon detectors to help distinguish muons from neutrinos.
As the hardware evolved, Axani realized the same technology could be made portable and inexpensive enough for educational use. After joining the University of Delaware faculty in 2022, he continued refining the electronics package. The project recently reached its third version, detailed in an article published in the Journal of Instrumentation in October. These engineering upgrades let the detector monitor its surroundings, withstand high radiation levels, and gather data more quickly.
“CosmicWatch detectors allow us to do far more physics at a dramatically lower cost, in a compact and portable form, opening the door to many new kinds of experiments and outreach opportunities,” Axani explained, according to ScienceDaily.
Why Physicists Obsess Over Muons
Muons are not just academic curiosities. They act as cosmic messengers. By measuring muons, researchers can estimate properties of the originating cosmic ray, including its energy, mass, and direction. This data helps researchers study extreme cosmic events like supernovae, gamma-ray bursts, and blazars.
These particles also hold a place in the history of modern physics. Back in the early 1940s, measurements of these particles provided one of the first experimental confirmations of Albert Einstein’s theory of special relativity.
Beyond astronomy, muons offer non-destructive imaging capabilities for dense terrestrial structures. Because these particles can travel through solid materials—including walls, rock, or humans—without causing damage, they leave behind a detectable energy trail. Scientists leverage this property to image structures hidden behind large amounts of matter. A prominent example occurred in 2016, when muon technology successfully uncovered an unknown corridor inside the Great Pyramid of Giza.
Real-World Deployment Beyond the Classroom
What started as an educational outreach tool has found a role in international astrophysics research. The hardware is built from electronic components costing around $100. Whenever a muon passes through it, the device flashes and records a count. Users can later download and analyze the stored data.
The platform’s versatility has pushed it into extreme environments. Beyond high school students and university labs, the device is now being used in high-altitude balloon missions and major physics experiments. “Even though I had studied cosmic rays, I didn’t fully appreciate the rich physics behind the working of these detectors to actually ‘see’ the world and atmospheric particle production,” Sarfraz stated, as reported by ScienceDaily.
