Suppose two parties $A$ and $B$, some distance apart and at rest relative to each other both had control of one massive local object each.
If party $A$ lifted their local object upward relative to $B$, than the total force of gravity on $B$'s mass would angle upwards slightly.
If B then measured this shift in gravitational pull over time a communication wave could be formed between $A$ and $B$.
Wouldn't this communication channel operate instantaneously? How does this not violate the laws of causality with respect to the speed of light?