  The direct detection of gravitational waves opens the possibility to test
general relativity and its alternatives in the strong field regime. Here we
focus on the test of the existence of extra dimensions. The classification of
gravitational waves in metric gravity theories according to their polarizations
in higher-dimensional space-time and the possible observation of these
polarizations in 3-dimensional subspace are discussed in this work. And we show
that the difference in the response of gravitational waves in detectors with
and without extra dimensions can serve as evidence for the existence of extra
dimensions.
