Observing Black Hole Collisions: Time Dilation Explained

[imsmooth]

When something approaches black hole time dilation slows the event down from our frame of reference such that nothing seems to cross the event horizon. How is it then we can observe two black holes colliding? From our frame of reference wouldn’t it seem the event never happens?

 

[A.T.]

When something approaches black hole time dilation slows the event down from our frame of reference such that nothing seems to cross the event horizon.

This is only true for an object with negligible mass, compared to the black hole mass, so the black hole horizon can be assumed to be static. For massive objects or lots of small masses falling in at the same time, the above assumption doesn't hold anymore.

 

[jbriggs444]

from our frame of reference such that nothing seems to cross the event horizon

More precisely, using one particular standard of synchronization, there is never a time over here which is judged to be simultaneous with a horizon crossing event over there.

That says more about the choice of synchronization convention than it says about whether black hole collisions can occur.