  The potential realization of a gravitational wave (GW) astronomy in next
years is a great challenge for the scientific community. By giving a
significant amount of new information, GWs will be a cornerstone for a better
understanding of the universe and of the gravitational physics. In this paper
the author shows that the GW astronomy will permit to solve a captivating issue
of gravitation as it will be the definitive test for the famous "Einstein frame
versus Jordan frame" controversy. In fact, we show that the motion of the test
masses, i.e. the beam splitter and the mirror in the case of an interferometer,
which is due to the scalar component of a GW, is different in the two frames.
Thus, if a consistent GW astronomy will be realized, an eventual detection of
signals of scalar GWs will permit to discriminate among the two frames. In this
way, a direct evidence from observations will solve in an ultimate way the
famous and long history of the "Einstein frame versus Jordan frame"
controversy.
