Self-Indication Assumption Doomsday Argument Rebuttal - SIA Intuition: The Lost-property Metaphor

SIA Intuition: The Lost-property Metaphor

It can be hard to visualize how the Self-Indication Assumption changes the distribution because everyday cases where a null result can be returned don't change the statistics significantly. The following two examples of estimating the size of a darkened space show how the probability shift can occur:

• Cloak-room case: Imagine looking for your coat in a dark room and finding it one foot from the door; the Bayesian inference from a vague prior is that the room is less than 20 feet long (with 95% confidence).
• Lost-property case: Your coat has been filed somewhere in a huge lost-property warehouse, and as you search through its many aisles you see that they are all filled to capacity with belongings, and are various lengths. The aisle lengths are distributed according to the vague prior, except that none are more than 100 feet long. Finally, you find your coat one foot into a dark aisle, and wonder whether that aisle is more than twenty feet long.

The Bayesian inference shifts from the cloak-room case to the lost-property case, because of the chance that the coat would not be found in the aisle it was found in, and some estimate of the aisle's dimensions. Using the SIA Bayesian inference equation with = 100, n = 1, x = 20 gives the chance that the aisle is above 20 feet long in the Lost-property case:

• Cloak-room case: The confidence that the room is shorter than 20 feet long given the position of the coat = 95%
• Lost-property case: The confidence that the aisle is less than 20 feet long given exactly the same information about the coat's position in it = 65%

The confidence that the unseen space is longer than 20 feet is directly analogous to the confidence that the human race will become more than 20 times as numerous as it has been. Using an of one hundred times the current value only increases the subjective chance seven times (from 5% to 35%), but this is a very small limit for the purposes of exposition.