A recent development to confirm the existence of these electrons and positrons in intergalactic space comes from the pinpointing of "Gamma Ray Bursts" . (An article from the July 1997 Scientific American). A prediction of the Compton effect interpretation of the red shift is that there should be what is called "reverse dispersion" in signals as the light travels through this transparent intergalactic medium. This means that the shorter wavelength light should travel slightly faster through this medium than the longer wavelength light. Now, the gamma ray bursts are believed to be very distant, but very violent explosions producing very short wavelength gamma ray electromagnetic radiation. It also produces longer wavelength visible light and even longer wavelength radio waves. The recent development has been the observation that the gamma rays arrive first, followed a couple days later by the visible and then a couple more days later the radio. This is in agreement with the reverse dispersion in the light traveling billions of light years through a transparent intergalactic medium of electrons and positrons. This shows the presence of the missing 'dark matter" which not only slows the travel but also causes the red shift.
Where do these electrons come from? This has been a puzzle in the past. Intergalactic space is thought to be too cold to allow ionization of hydrogen as a source. Now that we know these gamma ray bursts are so common, we see that a source of these can be the gamma rays themselves. When high energy gamma rays collide with electrons, they change from electromagnetic radiation to matter in the form of a new electron plus a positron (the electron's antimatter counterpart). This is called "electron-positron pair production". The existence of these gamma ray bursts allows the formation of electrons and positrons to fill intergalactic space.
It is interesting to speculate about the source of these gamma ray bursts. Maybe they are the collisions of matter black holes with anti-matter black holes? Or just matter stars with anti-matter stars? These collisions result in the annihilation of matter and its conversion to energy in the form of gamma rays.
John Kierein, firstname.lastname@example.org 2852 Blue Jay Way, Lafayette,CO 80026