What is a Black Hole? - Stephen Hawking's final theory

5:00 I thought black holes don't destroy matter, just move it beyond it's event horizon?
Normally you could observe an object with light because it would reflect to the observer, but the gravity of a black hole is so strong that the light can't be reflected.


Googling a bit led me to wikipedia and this:
In 1973–75, Stephen Hawking and Jacob Bekenstein showed that black holes should slowly radiate away energy, which poses a problem. From the no-hair theorem, one would expect the Hawking radiation to be completely independent of the material entering the black hole. Nevertheless, if the material entering the black hole were a pure quantum state, the transformation of that state into the mixed state of Hawking radiation would destroy information about the original quantum state. This violates Liouville's theorem and presents a physical paradox.[citation needed]


I think physics girl left out the radiation to simplify things but I think it's really essential to understanding the paradox. At first I got confused about what she meant.