What questions are raised that we're not given answers to in Act 1, scene i?

Shakespeare begins Hamlet with a question, “Who’s there?” Who’s there, indeed.... On one level, this is a simple question, one that is asked every day in the most innocuous contexts. But on a deeper level (and everything in this play is richly rewarding on a deeper level) it is one of the basic questions of philosophy. Who is there? Who are we? What is man? Who is Hamlet? What is Hamlet? In this most philosophical of plays, we begin with a moment of covert philosophy, a question simple on the surface, but profound when pressed; and the first scene continues this focus on questioning, giving us question after question. Horatio, the quintessential scholar, skeptical and empirical, begins by questioning the reality of the ghost; eventually, he is exhorted to “question” the ghost in a more literal way – to ask the ghost questions. None of his questions are answered.