Our views of a black hole
Originally we thought nothing could escape from a black hole.
Then, in 1974, Stephen Hawking argued that a black hole should slowly evaporate as pairs of particles are created at the event horizon and one is swallowed and the other escapes. However, his calculations showed that this Hawking radiation depends only on the black hole's mass. Any other information about the object would be completely lost to the void, in violation of the rules of quantum theory.
Later, theorists realised that this ‘information paradox’ could be resolved if the quantum link between the two particles – a property called entanglement – is suddenly severed.
However, this would lead to a spike in energy all along the event horizon. Anything crossing the line would be instantly incinerated in a ‘firewall’. This is in direct contradiction to Einstein's general theory of relativity, which says an observer shouldn't notice anything special when crossing the line.
Parallel universes view
Some physicists argue that both the information and firewall paradoxes go away if you think of black holes from the viewpoint of the Many Worlds interpretation of quantum theory. It says that every quantum event (such as the creation of a particle pair at the event horizon) splinters the universe into multiple copies – or branches – where all possible outcomes play out. Information is preserved across all branches and Einstein's rule about a smooth passage over the event horizon only applies to each individual branch.