Question: According to the laws of physics, a object of larger mass causes time to slow down more compared to one of smaller mass. Does this mean that at a black hole's event horizon, time will stop? And if so, how can a black hole affect the space surrounding it?

Evan Keane answered on 23 Jun 2011:

This is a brilliant question! 🙂

Firstly, yes you are correct that time runs slower near something with higher mass (which means stronger gravity). Time does not stop at the event horizon of a black hole. Actually if you passed the event horizon you would notice nothing different either side of it. So there is no problem for a black hole to be able to effect the space surrounding it.

BUT for a distant observer (for instance you or I on Earth) watching somebody fall into a black hole, our view of how time passes for the person falling into the black hole is different! To us, it would appear to take an infinite amount of time for the person to reach the black hole. Basically it would appear to us like the person would never actually reach the event horizon, just get closer and closer forever (it would appear kind of like they were almost frozen just above the event horizon). This is probably where you heard of time stopping at the event horizon – but this is just from the point of view of a distant observer (who is not effected by the gravity of the black hole). For the person falling into the black hole, time would behave normally! There are loads of weird and wonderful effects like this that happen with black holes.

I HAVE A QUESTION FOR YOU (OR ANY STUDENT THAT CAN ANSWER IT!)

Q. If you are falling feet first into a black hole, and you look to your side and you see light coming straight at you, can you still escape the fall?

😀