Abstract

One type of evidence for life after death involves attempts to effect transmission of messages from a deceased person to a living one when the content of the message would have been impossible to obtain by other means. This kind of experiment is commonly criticized for the following flaw: If there is any way to check whether a putative message is correct (for instance, some record left by the deceased against which the message is to be checked), this automatically provides a possibility for the recipient to have cheated. Several variants of this idea (hand encryption and pad­lock codes) have been used in the past. The issue of authentication in computer systems is a similar type of problem and has been dealt with extensively. This paper presents a suggestion that improves on previous methods in several ways. Trap-door algorithms are a class of mathematical encoding procedures that function in one direction only. Thus, a message may be encoded and only the encoded form may be made publicly available: no record of the original message is left at all, and thus the record cannot be used for cheating. The algorithm provides an easy way to determine whether one has obtained the message, but provides no way to obtain it barring contact with the only person who knew it (the deceased). When run on a computer, this method makes it a simple matter to arrange such experiments, and owing to the mathematical nature of the algorithm, makes potential successes compelling survival evidence.