Poor doggie
My guess?
Gravity is the one physical force that can't be explained by physics. It doesn't follow the rules of physics as we know them. It leaks from one universe to another, too. And that's how quantum physicists knew there were more than one dimension/universe.
Maybe its something like this movie insinuates: that it is our pull to each other.
https://www.youtube.com/watch?v=_fOwJQpBl5c
or maybe its the pull through which we create our reality.
Q could use the word 'seriousness'. But he chooses 'gravity'.
Or maybe its just that traitors are hung, and its gravity that does them in.
And after all the sh*t we gave him, I <3 Ben, no homo