※ 引述《sokalula (so卡噜啦)》之铭言：
: 很多科幻题材的作品都说未来是无限多的走向
: 一切都取决你当下的决定
: 意思是说 未来有很多个
: 这样也间接的想说世界线的存在
: 但如果未来根本不会改变呢
: 唯一的未来就是你选择的那个走向呢？
: 不管你做什么选择都早就是决定好的了
: 有乡民听的懂我的意思吗
https://en.wikipedia.org/wiki/Ergodic_theory
中文番作“遍历理论”？
Ergodic theory is a branch of mathematics that studies dynamical systems with
an invariant measure and related problems. Its initial development was
motivated by problems of statistical physics
动态系统中的积分不变量。
http://news.softpedia.com/news/What-is-ergodicity-15686.shtml
Many scientists agree that ergodicity is one of the most important concepts
in statistics. So, what is it?
多数科学家同意遍历性是统计学中做重要的概念。那，它究竟是什么？
Suppose you are concerned with determining what the most visited parks in a
city are. One idea is to take a momentary snapshot: to see how many people
are this moment in park A, how many are in park B and so on. Another idea is
to look at one individual (or few of them) and to follow him for a certain
period of time, e.g. a year. Then, you observe how often the individual is
going to park A, how often he is going to park B and so on.
假设你要研究某个城市中的哪个公园最常被造访。一个方法是选一个时间点，看有多少人
在A公园，或B公园，以此类推。另一个方法是追踪一个人，例如在一年内，然后纪录
一年内他分别造访某公园的次数。
Thus, you obtain two different results: one statistical analysis over the
entire ensemble of people at a certain moment in time, and one statistical
analysis for one person over a certain period of time. The first one may not
be representative for a longer period of time, while the second one may not
be representative for all the people.
这两个方法会得出不同结果，而且各自在其母群体中代表性都不够。
The idea is that an ensemble is ergodic if the two types of statistics give
the same result. Many ensembles, like the human populations, are not ergodic.