Say there is a ball of unknown radius surrounded by a bubble. The ball represents a hypothetical singular surface inside a black hole and the bubble represents the event horizon.
If you threw marbles into the bubble at different angles (let's pretend the bubble does not pop), some of the marbles will hit the ball and others will go into the bubble but miss the ball. You could determine the radius of the ball based on what marbles at what angles cause the ball's linear momentum to change.
Could you do the same thing with a black hole but from observations on how its linear momentum changes from stars entering the event horizon at different angles?
