From wiki:
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.
定義:
等概率原理指出，如果有n (n > 1)種互斥(aka唔會同時發生)而可以完全羅列(aka有限數量)嘅可能性的話，而呢堆可能性除咗個名之外，並搵唔倒其他方法去分辨呢堆可能性，咁每種可能性嘅概率(aka或然率/期望值)就應等於1/n。
例子一: 擲銀仔
1. 一係公，一係字，唔會同時發生，所以係互斥
2. 一係公，一係字，只有兩種可能性 (n = 2)，所以係可以完全羅列嘅
3. "公"同"字"只係名嚟。實際上我哋搵唔倒其他嘢去分辨兩者。(其實係有...例如兩邊花紋唔同等等，但不在此論。公同字的確無任何明顯嘅資訊去分辨擲倒其一嘅概率...)
滿足咗呢3個條件，我哋就可以話，擲倒公或字呢兩種可能性嘅概率應該分別為
1/n = 1/2 = 0.5例子二: 擲骰仔
1. 一到六，唔會同時發生。互斥
2. n = 6。可以完全羅列
3. 1到6只係名嚟 (一樣無視啲坑洞先)
所以擲倒任何一個數字嘅概率應為
1/6唔駛無視任何嘢，而又可以完全滿足等概率原理嘅第三個要求嘅，當今世上恐怕就只有量子態。
