What happens to that energy, though? Energy is conserved, even with gravitational waves, correct?
So, what happens to the energy - does some of it get converted into 'normal' potential energy by changing the (amount of gravity? gravitational fields?) of the stuff that it passes through - the weak interaction that you refer to?
And, if it interacts very weakly, does all of the energy eventually get used up this way - do GWs get 'used up' before they travel across the universe?
(Probably a meaningless question): can GWs hit the edge of the universe, and if so, what happens then?