For example, do two galaxies situated in proximity reduce the atom decay rate in each other?
What happens with decay quanta escaped to infinity? Does the radius of apparent horizon effect the lifetime of the atoms in the universe?
Do atoms placed on a planet's surface decay slower than those placed at a distance from the planet? Is this decay slowing equivalent to the time slowing due to general relativity? Is it affected only be the mass of the nearby object or by dielectric constant of the material?