I've wondered about that: The moving particle, photon, electron, neutron, is throwing off a gravity wave as it is moving if we don't have a gravity wave detector detecting that wave. So, just having the detector, maybe a second away, collapses the wave function?
My guess is that as a wave function is split into multiple parts going off in different directions and getting far apart, the particle is not yet "localized" in any of the parts. The idea that there is a particle, "localized" but we just don't yet know where it is I have a tough time accepting. Instead, until there is an interaction that transfers the energy, although maybe not the gravitational energy, there is no localization. Or, all the parts of the wave function both feel and generate gravity until the collapse from an interaction with, say, a detector.
Or, if only one part of the wave function has the particle, then when two parts of the wave function are combined, as in just Young's double slit, we should not get the interference we do get. Or, it seems we get the interference of the wave function parts, then get the detection; there never was anything localized until the detection at which time all the parts of the wave function have to collapse everywhere, instantaneously, even across 1 billion light years -- no I don't like to believe that, but I'm just looking at the interference of two parts of the wave function in Young's double slit: If the particle was really in just one of the two parts of the wave function, then tough to believe in the interference we do see.