Could we have already been visited by an
advanced civilization?
There is a lot of "evidence" that people often
cite. Almost all of that so-called evidence
is completely bogus. There are almost always
better explanations for whatever is
"observed" than alien visitation.
Let's be honest:
We're talking
about
UFOs --
unidentified flying objects -- and other such things.
One of the most interesting sites is the
Center
for UFO studies, founded by
J. Allen Hynek who in the 1950s and 1960s
was the US Air Force consultant on UFOs.