  A question is studied whether an observer can discover quantum gravity being
in the semi-classical regime. It is shown that it is indeed possible to probe a
certain quantum gravity effect by employing an appropriately designed detector.
The effect is related to the possibility of having topologically inequivalent
geometries at once in the path integral approach.
  A CFT state which is expected to describe the eternal AdS black hole in the
large N limit is discussed. It is argued under certain assumptions that the
black hole boundary should be merely a patch of the entire AdS boundary. This
leads then to a conclusion that that CFT state is the ordinary CFT vacuum
restricted to that patch. If existent, the bulk CFT operators can behave as the
ordinary semi- classical quantum field theory in the large N limit in the weak
sense.
