  An overview of the experimental and observational status in gravitational
physics is given, both for the known tests of general relativity and Newtonian
gravity, but also for the increasing number of results where these theories run
into problems, such as for dark matter, dark energy, and the Pioneer and flyby
anomalies. It is argued that (1) scientific theories should be tested (2)
current theories of gravity are poorly tested in the weak-acceleration regime
(3) the measurements suggest that the anomalous phenomena have a common origin
(4) it is useful to consider the present situation under a historical
perspective and (5) it could well be that we still do not understand gravity.
Proposals for improving the current use of scientific methods are given.
  `We do not know anything - this is the first. Therefore, we should be very
modest - this is the second. Not to claim that we do know when we do not - this
is the third. That's the kind of attitude I'd like to popularize. There is
little hope for success.' (Karl Popper)
