So, let me explain why one could NEVER receive an ETI signal with particle detectors. As I mentioned yesterday, in addition to electromagnetic radiation, our galaxy is filled with charged particles known as comic rays (for historical reasons). These particles are highly energetic, traveling at relativistic speeds, so one could think to use them to communicate across galactic distances, instead of light.
But it turns out that our galaxy (like other galaxies) consists of turbulent magnetic fields distributed non-uniformly. Even our Sun has a strong magnetic field and so does the Earth. From physics 101 we know that charged particles are deflected by magnetic fields.
Charged particle in the galaxy
As you can see in the figure (Kermani and Fatemi, 2011) it is almost impossible to trace back a charged particle back to its source. Once can make similar figures tracing paths of charged particles due to the solar and earth’s magnetic field. One could never locate the origin if such a signal is ever received.
Despite of this, if someone attempts to send a signal through particles, most of them will collide in that planet’s atmosphere itself and produce unstable particles which would never reach us. One would then have to build a particle accelerator in space, which would be very expensive compared to simply building a powerful radio/optical transmitter.
If distance scales are large, the changes of these particles colliding with the interstellar matter also increases dramatically. The particle beam would thus never reach its destination. Overall, such scheme could only be implemented on April 1!