In April 2006, Kaku began broadcasting "Science Fantastic" on 90 commercial radio stations in the United States. It is syndicated by Talk Radio Network and now reaches 130 radio stations and America's Talk on XM and remains the only nationally syndicated science radio program. Featured guests include Nobel laureates and top researchers in the fields of string theory, time travel, black holes, gene therapy, aging, space travel, artificial intelligence and SETI. When Kaku is busy filming for television, "Science Fantastic" goes on hiatus, sometimes for several months. Kaku is also a frequent guest on many programs, where he is outspoken in all areas and issues he considers of importance, such as the program "Coast to Coast AM" where, on November 30, 2007, he reaffirmed his belief that the existence of extraterrestrial life is a certainty. During the debut of Art Bell's new radio show "Dark Matter" on September 16, 2013, Bell referred to Kaku as "the next Carl Sagan", referring to Kaku's similar ability to explain complex science so anyone can understand it.