  We consider the quantum description of a toy model universe in which the
Schwarzschild-de Sitter geometry emerges from the coherent state of a massless
scalar field. Although highly idealised, this simple model allows us to find
clear hints supporting the conclusion that the reaction of the de Sitter
background to the presence of matter sources induces i) a modified Newtonian
dynamics at galactic scales and ii) different values measured for the present
Hubble parameter. Both effects stem from the conditions required to have a
normalisable quantum state.
