Do you love science and technology and sometimes wish you could contribute to a major discovery? I’ve got good news: “there’s an app for that.” With the Crayfis app, you can join a world-wide network of smartphones designed to detect ultra-high energy cosmic rays.
Cosmic rays were discovered by Victor Hess in 1912, for which he received the Nobel Prize in Physics in 1936. They are constantly raining down on us from space; typically atomic nuclei that hit the upper atmosphere leading to a huge shower of particles, some of which make it to the Earth’s surface.
Just last year a team of scientists published a result based on data from the Fermi gamma-ray space telescope indicating that lower-energy cosmic rays are associated to supernovae. However, the origin of the most energetic ones remains a mystery.
The highest energy cosmic rays are amazing, they have about as much kinetic energy as a 60 mph (~100 km/h) baseball packed into a single atomic nucleus! This is much higher energy than what is probed by the LHC, but these kinds of ultra-high energy cosmic rays are very rare. To get a feel for the numbers, the Pierre Auger Observatory, which is about the size of Rhode Island or Luxembourg, observes one of these ultra-high energy cosmic rays roughly every four weeks. What could possibly be responsible for accelerating particles to such high energies?
Untangling the mystery of these ultra-high energy cosmic rays will require observing many more, which means either a very long-running experiment or a very large area. Current arrays with large, highly-efficient devices like Auger cannot grow dramatically larger without becoming much more expensive. This motivates some out of the box thinking.
Smartphones are perfect candidates for a global cosmic ray detector. Phones these days are high-tech gadgets. The camera sensor is a lot like the pixel detectors of ATLAS and CMS, so they are capable of detecting particles from cosmic ray showers (check out the video for a quick demo). In addition, most phones have GPS to tell them where they are, wifi connections to the internet, and significant processing power. Perhaps most importantly, there are billions of smartphones already in use.
Late last year a small team led by Daniel Whiteson and Michael Mulhearn put out a paper making the case for such a world-wide network of smartphones. The paper is backed up by lab tests of the smart phone cameras and simulations of ultra-high energy cosmic ray showers. The results indicate that if we can have roughly a thousand sq. km clusters each with a thousand phones that the exposure time would be roughly equivalent to the Pierre Auger observatory. The paper quickly garnered attention as indicated by the “altmetric” summary below.
After the initial press release, more than 50,000 people signed up to the Crayfis project! That’s a great start. The Crayfis app for iOS and android are currently in beta testing and should be ready soon. I’ve joined this small project by helping develop the iOS app and the website, which are both a lot of fun. All you have to do is plug your phone in and set it camera down, probably at night when you are sleeping. If your phone thinks it has been hit by a cosmic ray, it will upload the data to the Crayfis servers. Later, we will look for groups of phones that were hit simultaneously, which indicates that its not just noise but a real cosmic ray shower.
The image below shows a screenshot of the live monitor of the Crayfis network so far — check it out, it’s fun to play with. As you can see Crayfis is already a world-wide network and may soon have the claim for the world’s largest detector.
Crayfis: A global network of smartphones
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Kyle Cranmer is a Professor of physics and data science at New York University. His blog is at theoryandpractice.org. Follow @kylecranmer
