Hawking’s result had obvious and profound implications for how we think about black holes. Instead of being a cosmic dead end, where matter and energy disappear forever, they are dynamical objects that will eventually evaporate completely. But more importantly for theoretical physics, this discovery raised a question to which we still don’t know the answer: when matter falls into a black hole, and then the black hole radiates away, where does the information go?Common sense tells us that encyclopedia information gets lost in a fire. Quantum gravity thought experiments tell theorists otherwise. Whom are you going to believe?
If you take an encyclopedia and toss it into a fire, you might think the information contained inside is lost forever. But according to the laws of quantum mechanics, it isn’t really lost at all; if you were able to capture every bit of light and ash that emerged from the fire, in principle you could exactly reconstruct everything that went into it, even the print on the book pages. But black holes, if Hawking’s result is taken at face value, seem to destroy information, at least from the perspective of the outside world. This conundrum is the “black hole information loss puzzle,” and has been nagging at physicists for decades.
In recent years, progress in understanding quantum gravity (at a purely thought-experiment level) has convinced more people that the information really is preserved.
I believe that the info is lost. I will continue to believe that until someone shows me some empirical evidence that it is not. And there is no law of quantum mechanics that says that info is never lost.
John Preskill (aka. Professor Quantum Supremacy) says otherwise. Info can't disappear because it is needed to make those quantum computers perform super-Turing feats!