The problem is that you're trying to understand hypothetical concepts as concrete things. This is not possible. Your book is misleading you. "Might" signifies a possibility, but a highly unlikely one. That's it. Past and present tense (ie. real past and present) don't come into it.

It just so happens that "might" is a verb form of it's own, and so it is "might" in the present tense. But it also is the past tense of the verb "may." This causes much confusion for English speakers, too. (Another verb pair I can think of that easily half of all English speakers use incorrectly is "lie" and "lay." People are forever saying, "I'm going to lay down." Yech!) For a much more thorough explanation of "might" and "may," go to http://grammar.quickanddirtytips.com/may-might.aspx. I think you will find it VERY helpful.

Your question makes perfect sense.

By the way, do you understand what I'm trying to say? I'm afraid if my question makes you complicated. If it is, please feel free to feedback. It would make my language skill more improve. Thanks a lot :D.