Josephson's reputation for promoting unorthodox causes was cemented by his support for the ideas of water memory and cold fusion, both of which are rejected by mainstream scientists. Water memory is purported to provide a possible explanation for homeopathy ; it is dismissed by scientists as pseudoscience, although Josephson has expressed support for it since attending a conference at which French immunologist Jacques Benveniste first proposed it. Cold fusion is the hypothesis that nuclear reactions can occur at room temperature. When Martin Fleischmann, the British chemist who pioneered research into it, died in 2012, Josephson wrote a supportive obituary in the Guardian, and had published in Nature a letter complaining that its obituary had failed to give Fleischmann due credit. Antony Valentini of Imperial College London withdrew Josephson's invitation to a 2010 conference on the de Broglie-Bohm theory because of his work on the paranormal, although it was reinstated after complaints.