Why can't light escape from a black hole? I've heard that light can't escape from a black hole. Can it? If not, why?
A black hole has an event horizon which 'marks the point of no return'. So yes, light cannot escape from a black hole.

Why? Well, think of a 'spacetime fabric'. It's the easiest way to understand the physics at work here, in my opinion.

Usually, the fabric would look like this:


(source: whyfiles.org)  

However, a black hole has so much gravity that one could say it 'rips' the spacetime fabric:


(source: ddmcdn.com)  

When the light hits this area of amazingly intense gravity, it simply cannot get out - the light travels 'along' the fabric, and since there is a rip in the fabric, one could say it simply goes away - it becomes part of the singularity.

This is a simplification, of course, but it's enough to understand at least part of the physics behind this phenonenom.