There exists in physics something called the monogamy of entanglement. It is the idea that two particles who are in their maximum entangled state, their Bell state, can not by their nature be entangled with a third particle. Hawking radiation, partially explained here, involves two particles being produced that are entangled due to the energy they must carry. But if a black hole has a finite lifetime and holds a finite amount of information then the Hawking radiation must also be entangled with all previous Hawking radiation emitted. But this breaks the monogamy of entanglement as the emitted photon would be entangled with both its partner and the black hole’s past. To solve this problem it seems a sacrifice is in order.
One proposed theory is that a photon will instantly break its connection to its partner once its created. This would release an incredible amount of energy turning the area surrounding the black hole into an invisible inferno which would instantly incinerate anything unlucky enough to fall in. But Einstein’s equivalence principle, one of the key concepts in special relativity, says that free falling under gravity should be identical to floating in empty space. The existence of this incineration zone known as a “firewall” has been called outrageous and a complete impossibility. The other idea is that this fire wall doesn’t exist and it is simply an incorrect assumption that the past Hawking radiation must be entangled with the current radiation. But this would mean the black hole would lose quantum information over its lifetime. Unitarity is the idea that the sum of all probabilities for all outcomes is always 1 in other words when you add up all the chances for each outcome you must come to 100% even in a quantum regime . A loss of quantum information violates this and implies there is a possibility no event, including the event where nothing happens, could happen. This idea has been called outrageous and a complete impossibility. The people who invented this paradox Andrew Strominger, Joseph Polchinski and Cumrun Vafa have received $3 million as a prize for their breakthrough and were awarded it just three days ago. It is puzzles like these that shoe that physics is not a decaying science and we are nowhere near a complete understanding of everything there is, not even close.