The galaxy clusters Abell 0399 and Abell 0401 are some of the most massive objects in the universe. In a new study, researchers have discovered a 10-million-light-year-long bridge of radio waves (shown in blue in this composite image) linking them, and it’s doing crazy things to electrons. On the big roadmap of the universe, bustling clusters of galaxies are connected by long highways of plasma weaving around the wilderness of empty space. These interspace roadways are known as filaments, and they can stretch for hundreds of millions of light-years, populated only by dust, gas and busy electrons driving very close...