This would manifest as non-conservation of energy-momentum in scattering, and, as far as I know, nothing like that has been seen since neutrino was predicted by Pauli to remedy the apparent non-conservation of energy in radioactive decay. If we assume non-interacting worlds, then one should not expect to see such violations. Gravity might be an oddball, however, since different worlds are likely to have difference spacetime geometry and even topology potentially affecting each other. But this is highly speculative, as there is no adequate microscopic (quantum) gravity model out there. I have seen some wild speculations that dark energy or even dark matter could be a weak gravity-only remnant of the incomplete decoherence stopped at the Planck scale.
I don't see why differing spacetime geometries or topologies would impact other worlds. What makes gravity/geometry leak through when nothing else can?
This is a thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. The previous thread is at close to 500 comments.