GPS is a handy modern gadget – until you go inside, underground or underwater. Japanese researchers want to build a GPS-like system with a twist. It uses cosmic ray muons, which can easily penetrate buildings, to create highly accurate navigation systems. You can read about it in their recent article. The technology comes from MUWNS or Wireless Muometric Navigation System – quite a mouthful.
With GPS, satellites with well-known positions emit a signal that allows location determination. However, these signals are relatively weak radio waves. In this new technique, reference points are also placed in well-defined positions, but instead of sending a signal, they detect cosmic rays and transmit information about what they detect to receivers.
The receivers also pick up cosmic rays, and by determining the differences in detection, very precise navigation is possible. Like GPS, you need a well-synchronized clock and a way for the reference receivers to communicate with the receiver.
Muons penetrate deeper than other particles due to their greater mass. Cosmic rays form secondary muons in the atmosphere. About 10,000 muons reach every square meter of our planet every minute. In reality, cosmic rays impact atoms in the atmosphere and create pions, which rapidly decay into muons. Muons have short lives, but the dilation of time means that a short life traveling at 99% of the speed of light appears much longer on Earth, and this allows them to reach deep underground before disappearing.
Detecting muons may not be as difficult as you think. Even a Raspberry Pi can do it.