Ok so I am in an argument with my mother about the nature of black holes. She is religious and has classical physics knowledge up to degree level (she has a master's in mechanical engineering) and is very, very stubborn. Ok so she has a theory that physicists have simply arrogantly overlooked the fluid mechanical aspect of galaxies and is adamant that black holes are simply a whirlpool (yes literally just like a whirlpool) and don't have any mass at at all (I know, ****ing ludicrous right?) So how can I prove her wrong? It's frustrating me so, so bad.