This article is unfortunately murky. It’s confusing to state that accelerating charged particles to high speeds “therefore” produces cosmic rays. And what “charged particles”? Is the “energized” gas in fact “ionized”? “Energized” is too general a word. Finally, why are high-speed particles more easily compressed than slower-moving material?

Fredric Blum
Merion, Pa.

“Energized” means that the charged particles, existing electrons and ions, are speeded up to energies high enough to qualify as cosmic rays. Einstein’s theory of special relativity describes why a high-speed gas is especially compressible. For less-than-obvious reasons, that theory dictates that if two groups of particles have the same energy but only one is moving close to the speed of light, the latter group—in this case, ions—will exert less pressure and so will be more compressible .—R. Cowen