Charles Hapgood was a professor at Keene State in New Hampshire. He spent 15 years investigating the mediumship of Elwood Babbitt (1921 – 2001). Hapgood made recordings of at least 100 different trance entities who spoke through the medium including Jesus, Albert Einstein, Mark Twain, and the Hindu god Vishnu. He was keen to show that the entities were different from each other and different from the medium. He found that EEGs of the medium's brain showed a completely different pattern according to which entity was in control. He also showed that different entities responded differently to a word association test.

Hapgood coauthored three books with Babbitt. The first, "Voices of Spirit" is a scientific and historical approach to the world of mediumship. The second book "The God Within - A Testament of Vishnu" and the third book "Talks With Christ and His Teachers" are primarily transcriptions of trance lectures claimed to have been given by the Vishnu Force, Jesus Christ, and other figures.