Sound changes of "wild" and "wilderness" [duplicate]

I'm having a heated a discussion with a friend and we cannot really get on the same level.

In the original pronunciation of the word wild, the "i" was the short sound that we have in the word wilderness today. How has the vowel sound in wild changed up to its present pronunciation and why hasn't the "i" in wilderness changed in the same way?

This is an alternation referred to as Trisyllabic laxing in English phonology literature. Consult the Wikipedia page for further examples. The process predates the Great Vowel Shift, which concerned only long vowels. So vowels which were made lax and short by trisyllabic laxing were effectively "shielded" from sound change.