Hi fellow PFers, long time reader here. I have a query that was motivated by a comment on another thread (“Decoherence question”). It is about the quantum properties of decohered macroscopic systems. In my (incomplete and perhaps misapprehended) understanding, a macroscopic object, say a chair, that is almost unavoidably strongly interacting with its environment, will be in a (mixed) quantum state in which its position and (linear) momentum are described by close to minimum uncertainty packets, always of course obeying the HUP. We would say that the strong interaction with the environment tends to “select” with overwhelmingly preference states in which the object is rather well localised in both configuration and momentum space. Now, although the spatial and momentum distributions are macroscopically very small, they can obviously never be null. The way I understand it, the environment is permanently monitoring both the position and momentum of the system, which should lead to the system approaching what in classical terms we would describe as Brownian motion of some sort. This is what I would expect would be the (approximate) motion of the centre of mass of the system in deep space, free from any gravitational influence. However, when the chair is resting on my (also approximately localised) floor, it seems to be at perfect rest. I´m having a hard time reconciling the non infinitely small momentum distribution with this apparent stillness. Can anyone shed some light on this issue?