Here is a quote from "Cosmic Rays--Astrophysical Effects" by Stirling A. Colgate in Lerner and Trygg's Encyclopedia of Physics:

"Cosmic rays are energetic particles incident upon earth from sources that include the sun, the galaxy, and other galaxies. The most important particles are nuclei, but an electron flux of a few percent is also present. In addition to high-energy gamma rays and secondary products, neutrinos and antiprotons are also now considered as cosmic rays..."

Later in the article he says:

"A recent series of satellite measurements of the 100-Mev gamma-ray distribution in space has been interpreted as due to the creation of [pi-zero] mesons by cosmic rays of energy [approximately equal to] 1 GeV colliding with protons of the interstellar medium and then these mesons subsequently decaying to two gamma rays..."

When you say "If I detect a relativistic proton..." are you not asserting that the event was caused by a proton? Part of the uncertainty in Quantum Theory is due to the effect of the observer on the experiment. An attempt to make an observation can affect the results of the experiment. The case is somewhat like that of a myopic person trying to read an eye chart. What the person (or detector) sees is not necessarily the truth. In a football game, the umpire, although correct most of the time, sometimes makes mistakes. He is sometimes forced to "call" a play. I think the physicist is finds himself in a similar situation.

An interesting answer to the puzzle of Schrodinger's cat occurred to me recently. This is the thought experiment in which a cat is placed in a box with a vial of poison gas and left undisturbed for a while. One then wants to know if the cat is dead or alive. If someone opens the box and the cat appears to be dead, the only way that we could be certain is if he tried to revive the cat. However, any attempt to revive the cat will determine its fate, and consequently the experimenter ends up arbitrarily deciding the outcome of the experiment.

• The effect of observer. - alexander - January 25, 2001 - 18:12 UTC