For example, abgemacht, what makes you think you exist? What makes you think the universe exists? Incidentally both impressions arise from the same source, which is Being itself. By in a hypothetical place with no beings, no observers, I ask, whence Being?
Also, the fact of there being no observer in the past is irrelevant, all that matters is that there was an observer at any point in time in the universe, and I, as well as you, can attest that there now is. Time is as arbitrary as space.