# Two observers fall into separate black holes, then the black holes merge, can they meet again?

As far as I understand, both these things take finite time:

1. two black holes merging

in any sensible meaning of the term merge the two black holes do indeed merge in a finite, and very short, time.

So Black Holes Actually Merge! In 1/5th of a Second - How?

1. someone falling inside a black hole to reach the singularity

Calculating the lapsed time to fall from the horizon to the singularity of an existing black hole is a standard exercise in GR, and the result is: $$\tau \approx 6.57 \frac{M}{M_{Sun}} \mu s$$ That is, for a black hole of 10 solar masses the fall takes 65.7 microseconds!

A Hollow Black Hole

So basically, we have two observers, falling into separate black holes, and then the black holes merge. Since it takes finite time for the observers before they hit the singularity, they could theoretically observe the merger itself (which takes finite time too) from inside. Now if the merger happens so that the two event horizons open up to each other (unite) before the observers would hit their own singularity, theoretically there is a finite period of time when they are reunited into a single common (united) spacetime inside the (merged) black hole. So this is not a violation of escaping the black hole, since none of them need to escape anything. But since they are during the merger inside a common (merged) event horizon, can they meet again?

Question:

1. Two observers fall into separate black holes, then the black holes merge, can they meet again?
• Comments are not for extended discussion; this conversation has been moved to chat. Commented Oct 6, 2021 at 18:30