  It has been argued that the energy content in time varying spacetimes can be
obtained by using the approximate Lie symmetries of the geodesics equations in
that spacetime. When applied to cylindrical gravitational waves, it gives a
self-damping of the waves. According to this proposal the energy of the waves
go to zero asymptotically as the radial distance to the two-thirds power. If
true, this would mean that the estimates for the sensitivity of the detectors
for the various sources would have to be revised
