There is a thing called black hole information paradoxit was the result of trying to combine general relativity and quantum mechanics.
Following the idea suggested by Albert Einstein, black holes work in a relatively simple way: no matter what you throw at them, they just crush and absorb everything, slowly growing in size and emitting some gravitational waves. What falls within, is lost forever.
However, this mechanism is not suitable for quantum mechanics. According to the principles of quantum mechanics, Everything is reversible: when you know the final state of any system, you can trace this system back to the initial state. Even if the principle is rooted in mathematics, its existence has been confirmed in microphysical systems. That obviously means that information cannot be lost. The same mathematical view says that it is somehow possible to recreate things that have been absorbed by a gravitational singularity.
So which theory is more suitable to describe a black hole? See the detailed explanation of the black hole information paradox in the video below:
