View source for Principle of indifference (nonfiction)

The '''principle of indifference''' (also called principle of insufficient reason) is a rule for assigning epistemic probabilities. Suppose that there are n > 1 mutually exclusive and collectively exhaustive possibilities. The principle of indifference states that if the n possibilities are indistinguishable except for their names, then each possibility should be assigned a probability equal to 1/n.

In Bayesian probability, this is the simplest non-informative prior. The principle of indifference is meaningless under the frequency interpretation of probability, in which probabilities are relative frequencies rather than degrees of belief in uncertain propositions, conditional upon state information.

The textbook examples for the application of the principle of indifference are coins, dice, and cards.

In a macroscopic system, at least, it must be assumed that the physical laws which govern the system are not known well enough to predict the outcome. As observed some centuries ago by [[John Arbuthnot (nonfiction)|John Arbuthnot]] (in the preface of ''Of the Laws of Chance'', 1692),

<blockquote>It is impossible for a Die, with such determin'd force and direction, not to fall on such determin'd side, only I don't know the force and direction which makes it fall on such determin'd side, and therefore I call it Chance, which is nothing but the want of art....</blockquote>

Given enough time and resources, there is no fundamental reason to suppose that suitably precise measurements could not be made, which would enable the prediction of the outcome of coins, dice, and cards with high accuracy: Persi Diaconis's work with coin-flipping machines is a practical example of this.

== In the News ==

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== Fiction cross-reference ==

* [[Gnomon algorithm]]
* [[Mathematics]]

== Nonfiction cross-reference ==

External links:

* [https://en.wikipedia.org/wiki/Principle_of_indifference Principle of indifference] @ Wikipedia


[[Category:Nonfiction (nonfiction)]]
[[Category:Logic (nonfiction)]]
[[Category:Mathematics (nonfiction)]]