The Search and Discovery story on page 19 of the March 2005 issue of Physics Today opens with the statement “Cosmologists believe that half of all ordinary matter in the present epoch is hidden as a web of highly ionized intergalactic gas.”
An ionized gas is plasma, yet I could not find the word “plasma” any-where in the story. As a member of the American Physical Society’s division of plasma physics and an alumnus of the Princeton University Plasma Physics Laboratory, founded by astrophysicist Lyman Spitzer Jr, I am constantly bemused by the astrophysical community’s refusal to acknowledge the “fourth state of matter.”
Since Spitzer’s day the fields of astrophysics and plasma physics seem to have drifted apart, to the detriment of both. A first step in bringing them closer would be for astrophysicists to refrain from using the word “gas” unless they are convinced that the ionization is negligible.
