The Cosmic Ray Background

History

For over a hundred years it has been known that energetic charged particles arrive at Earth from space.  We call them “cosmic rays.”  In the twentieth century it was found that some of these rays are extremely high energy protons, traveling at nearly the speed of light.  But, the source of the highest-energy protons--up to hundreds of billion-billion electron volts (hundreds of exa-electron volts, EeV)--is not known.  Since these particles are of much higher energy than any we can create with our technology, it is generally thought that they must be produced by processes related to high-energy magnetic fields, shock waves, or some other such phenomena on a galactic or intergalactic scale.  These protons arrive more or less uniformly from all directions in space, but the lack of a specific direction of origin could be either due to a large number of sources or due to their paths being bent by interactions with magnetic fields or particles as they travel through space.  Researchers have found variations in the numbers of cosmic rays arriving at Earth over time, and some of these variations have been traced to known causes such as solar wind and Earth’s magnetic field. 

Cosmic Ray Showers

 

 

Atmosperic Air Showers

It is easy to detect these extremely-high-energy protons because when each proton hits the upper atmosphere it induces a shower of high-energy “daughter” particles that in turn generate other particles.  A short while later, a very large number of particles arrives at Earth’s surface, spread over a relatively large area—up to a kilometer in radius.  Detectors for such high-energy particles are fairly easy to build, though the rate of particle detection is low for particles with the highest energies.

Scientific Speculation

Because these particles are of unknown origin, perhaps it isn't unreasonable to suspect that one of their sources might be an intelligent technological civilization somewhere else in our universe.  Recognizing that these extraordinarily energetic particles are easy to detect and are able to cross cosmic distances at nearly the speed of light, we might speculate they might have been chosen as a simple means of communication, or to be a beacon signaling the existence of that civilization.
So, we have the stage set for a scientific study which should detect natural variations in the arrival rate of cosmic rays, and we also have the possibility of detecting an intelligent signal among these events.

Modulation And Signals

Scientists studying cosmic rays have determined these rays arrive nearly uniformly from all directions (though the most recent studies suggest a bias in some directions).  Over time the rate of cosmic-ray events varies slightly, and some of these variations have been related to the annual changes in distance from the sun, solar wind intensity, and in the local magnetic fields near earth.  It appears, for example, that increasing numbers of particles emitted by the sun (the "solar wind") causes fewer cosmic rays to be detected--probably because of a shielding effect from the the solar wind.  As earth nears the sun, increasing solar wind causes a similar reduction occurs in the most energetic cosmic rays (the ones from outside our solar system).  Thus, the sun causes both regular and irregular variations in the number of particles we detect.
Data gathered by the ERGO distributed telescope system will allow students to see and study patterns of cosmic-ray events in time and space, and to observe daily, annual, and solar-activity-related patterns.  In other words, there are lots of real scientific observations and experiments, ranging from simple to complex, which can be done by students participating in the project.
What about the chance of an intelligent "signal" among all these seemingly-random cosmic-ray events?  It happens that on earth we will soon be able to create proton beams up to nearly ten tera-electron-volts with the Large Hadron Collider (LHC) at CERN in Switzerland and France.  Will we ever be able to accelerate particles to the extremely high energies observed in cosmic rays? 
The first proton beams created on Earth in the nineteen-thirties had energies up to a million electron volts or so.  We have increased the energy of proton beams by ten million times since then.  So, how long will it take us to gain another ten-million-fold energy increase?  Some physicists say another ten-million-fold increase may never be possible, because of the physical limits of magnetic fields, energy density, and so forth.  What if someone were to works on that problem for another hundred years, or thousand years?  What would a physicist living on Earth a million years from now know about generating high-energy beams?  There might be a physicist living somewhere else, a million years or longer after his own society discovered nuclear physics.  Is it out of the question that somewhere else in our galaxy, or in another galaxy, there have been experiments conducted that resulted in 100 EeV protons being shot off into space? 
If we imagine such experiments, is it reasonable to expect that these protons beams would be created in a regular pattern in time--perhaps a pattern with exquisitely precise timing?  Now, dear reader, take a leap of imagination:  imagine you're that physicist.  Would you consider the opportunity to generate these timed pulses in some sort of discernable pattern in time?  Would you be able to resist doing so?  What sort of pattern would you place upon the timing of your cosmic pulses?  Would you use regular intervals or changing intervals?  Would the time intervals between pulses of your cosmic rays be steadily changing, or would you use some sort of modulation scheme to impart information to the series of pulses—say, prime numbers or the Fibonacci series? 
Enough speculation.  Let's think about what we might detect and how we might detect it.