I guess we did, because it happens in black holes and armies of physicists try to 'look' for the gravity at the subatomic scale.
And, if I'm not wrong, the main purpose of CERN these days is exactly to probe gravity at small scales.
Sorry for my bad English and mostly for my bad Physics.
For me it doesn't make any sense regarding the expansion of the Universe as a distant process, a sort of time&space machine which 'degulfs' more room for the known things to occupy. My guess is the expansion is happening here now at a...