From where randomness comes from and why it exists? I recently began to study statistics and probability and I have two questions:


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*Where does randomness come from? What is the source of randomness? 

*Why does the randomness exist?
Is it possible to answer my question that non mathematician or non physicist can understand it? 
I searched Internet for the answer but there is very little information that non mathematician or the information is for professional physicists and mathematicians.
Also please suggest books concerning my questions that is written so that non mathematician or non physicist can understand it.
 A: Well, there's three different types of answers I can think of, with regards to what you asked. 
One case we can have is that there's some systems that are so complicated, that if you change their initial states only slightly, the system changes drastically. This is called chaos. James Gleick's book is a good one for laypeople. Any graduate level mechanics textbook should also talk about chaos, if you're going to look for that level of understanding later on. So this chaos seems to create a sort of randomness in some physical situations. But maybe that's not what you meant.
There's also randomness in quantum mechanics, where it's not possible to know precisely two related quantities simultaneously (like the momentum and position of a particle).  
Finally, there's good old experimental randomness; my physics teacher likes to think of it as "you can't know what the true result of an experiment is. You can only know what the most likely value is". For example, if you measure g (the gravitational acceleration) to be 9.8$\pm$0.01 ms$^{-2}$ (at some point on earth), you don't have the actual value of g. All you know is that the value of g is somewhere in that given range. So there's sort of a randomness to any experimental tests, because you can never know exactly what the result is. 
But, as Count Iblis pointed out, all of this "randomness" essentially boils down to quantum mechanical fluctuations. It's just easier for us to think of it in terms of different concepts. 
