I feel the obvious answer should be “no” but help me think this through. It came from the previous Q on blackholes and am posting here for more visibility.

So considering two blackholes rotating about each other and eventually combining. It’s in this situation that we get gravitational waves which we can detect (LIGO experiments). But what happens in the closing moments when the blackholes are within each others event horizon but not yet combined (and so still rotating rapidly about each other). Do the gravitational waves abruptly stop? Or are we privy to this “information” about what’s going on inside an event horizon.

Thinking more generally, if the distribution of mass inside an event horizon can affect spacetime outside of the horizon then what happens in the following situation:

imagine a gigantic blackhole, one that allows a long time between passing the horizon and being crushed. You approach the horizon in a giant spacecraft and hover at a safe distance. You release a supermassive probe to descend past the horizon. The probe is supermassive in the way a mountain is supermassive. The intention is to be able to detect it’s location via perturbation in the gravity field alone. Similar to how an actual mountain causes a pendulum to hang a miniscule yet measurable distance off the vertical.

Say the probe now descends down past the horizon, at some distance off the normal. Say a quarter mile to the ‘left’ if you consider the direction of the blackholes gravitational pull.

Let’s say you had set the probes computer to perform some experiment, and a simple “yay/nay” indicated by it either staying on its current course down (yay) or it firing it’s rockets laterally so that it approaches the direct line been you and the singularity and ends up about a quarter mile ‘right’ (to indicate nay).

The question is, is the relative position of the mass of this probe detectable by examining the resultant gravitational force exerted on your spaceship? Had it remained just off of centre minutely to the ‘left’ where it started to indicate the probe communicating ‘yay’ to you, or has it now deflected minutely to the right indicating ‘nay’?

Whether the answer to this is yes or no, I’m confused what would happen in real life?

If the probes relative location is not detectable via gravity once it crosses the horizon, what happens as it approaches? Your very sensitive gravity equipment originally had a slight deviation to the left when both you and probe were outside the horizon. Does it abruptly disappear when it crosses the horizon? If so where does it go? The mass of the probe will eventually join with the mass of the singularity to make the blackhole slightly more massive. But does the gravitational pull of its mass instantly change from the location in the horizon where it crossed (about a quarter mile to the ‘left’) to now being at the singularity directly below. Anything “instant” doesn’t seem right.

Or… it’s relative position within the horizon is detectable based on you examining the very slight deviations of your super sensitive pendulum equipment on board your space craft. And you’re able to track it’s relative position as it descends, until it’s minute contribution to gravity has coalesced with the main blackhole.

But if this is the case then aren’t we now getting information from within the horizon? Couldn’t you set your probe to do experiments and then pass information back to you by it performing some rudimentary dance of manoeuvres? Which also seems crazy?

So both options seem crazy? Which is it?

(Note, this is a thought experiment. The probe is supermassive using some sort of future tech that’s imaginable but far from possible by today’s standards. Think a small planet with fusion powered engines or whatever. The point is, in principle, mass is detectable, and mass is moveable. Is this a way to peek inside a blackhole??)