Submitted by **WittyUnwittingly** t3_zys5ho
in **space**

I have a relatively firm handle on all of the weird spacetime mechanics going on at/around a black hole, but something has been bugging me.

We're told that once an object crosses the event horizon, the singularity at the center becomes an unavoidable eventuality - there is no way to move in a way that puts it further from the singularity than it was before. So, what would two observers falling toward the "shared center" from opposite sides see? Their eventual collision at the singularity would be apparent, but would they be able to interact at any other point? Can they even know that the other is there?

If you framed this from a 3D geometry perspective, it's obvious that photons from one observer would never reach the other (they're all falling in toward the center, so nothing is traveling from one observer, past the center, and to the other observer). However, if you were to map all points "equidistant" from the center onto a sort of 1-dimensional spatial degree of freedom, then you'd conclude that whichever observer is closer to the center would be able to observe infalling photons from the one further out. Is this treatment of spacetime not valid here (is this not "1+3 relativistic spacetime?"), or do we just not know enough yet to give a definitive answer?

Also, don't pull any punches. Rigorous mathematical proofs and obtuse technical documents will be appreciated just as much here as ELI5s.

I figure the answer will be speculative, which is why I used the term "best guess."

Most-Hawk-4175t1_j27m7nq wroteI think a PBS spacetime show talked about something like this. Of course the answer is ridiculously complicated but I seem to remember you would basically see everything frozen in spacetime including other observers in the black hole.