Back in 1929, Upton Sinclair wrote a book about his wife's experiments with telepathy called Mental Radio, and Albert Einstein penned the foreward. "The results of the telepathic experiments carefully and plainly set forth in this book stand surely far beyond those which a nature investigator holds to be thinkable," he wrote. Einstein was saying that telepathy operates on forces that science has not yet discovered, in contrast to gravity and electromagnetism which seem to fall off with distance, Stein explained. According to most paranormal researchers, PSI forces seem to be independent of time and distance, "and that's very unlike anything Einstein had encountered in his dealings with physics," he commented.