我在, 我思故; 我思, 故我在

Feb. 9, 2008. Saturday
Athens, GA

概率事件如何变成必然事件？

在某一时刻，多个事件有着不同的发生概率(总概率之和为1)，但是最后只有其中的某个事件发生了，即成为变为必然事件。
那么这个概率事件怎么变为必然事件呢？
其实这个问题关键在于有两个时间点，在开始一个时间点event A 发生的概率<1,或许event A发生的概率非常非常之小，但是到后来的某个时刻event A发生了，成为必然事件。
所以当要提event A发生的概率，需要指明是在某特定时刻下，预计event A发生的概率。
This question harasses me for a long time, until I attended a lecture given by Prof. Landao on this Friday.
That lecture of Monta Carlo Sampling in statistical physics invokes me to find out one possible explanation
for that question: how a probability event becomes to be a certainty event after some time.
The answerer is that the Probability(event A) is changing along the development of time since many factors will affect the Probability(event A) in that time interval and Probability(event A)=1 at the point it happened.
Hence, we could say that Probability(event A) is a process along the development of time.
就如中国有句古话：万事具备，只欠东风。那个东风就是影响一个可能发生的概率事件成为必然事件的因素。
又如生化反应, 在刚开始的时候，那些化学物质发生反应的概率可能很小，加入催化剂（或者即使不加入催化剂，由于各物质的溶度随着反应进行，时间的推移而改变）影响着后来某一时刻这些化学物质能否完全反应。此例中，催化剂就是影响这个反应进程的一个因素。

“Never Say never” film 中讲溶液化学反应中的振荡现象，亦类似。

举抛硬币这个几乎在每本Probability Book中都会提到的例子。

The coin has two sides, one is positive side and the other is negative side. So before throwing the coin, the expected probability of occurring either the positive side  

or the negative side is 0.5. But after the coin is thrown out, your action of throwing

the coin, the air condition around the coin (e.g. wind) will affect which side of coin will be up when it falls into the earth. Actually, every behavior of the coin in the air during that process change the probability of occurring which side will be up to the ceil.

Keywords: probability, two time points, process, change, factors.