I was reading a news story a few days ago about some folks who had been studying cosmic rays. As part of this study, they were counting electrons and positrons (antimatter electrons). It seems that they are getting way too many positrons than they expected. Supposedly, this excess of positrons may be an indication of dark matter. However, I have a better explaination.
In an alternate reality (The End of Eternity), humans on extraterrestrial colonies are destroying all of their robots, so humanity does not wind up slaves to their technology (The Robots of Dawn and others). Since these robots have positronic brains, this explains the excess of positrons that is bombarding the Earth.
Yes, I am weird
When I read the news story, I actually did think of positronic brains. I must have read too much Asimov in my youth.