I have heard many times in those PBS or BBC dumbed-down-science-for-ordinary-dolts shows (unfortunately they're the only sources of this sort of information I have) that there was a black hole paradox at one point, wherein some people were deeply concerned over whether black holes destroy information, and eventually they decided that they don't because a black hole is actually not really quite a black hole and can't be distinguished from a bunch of mass that hasn't quite fallen in through the depth that would be its event horizon and so after the black hole expires due to the Hawking radiation effect, the information is freed back into the universe. Or at least that's what I thought of when I first heard about the paradox and then when it was resolved, it sounded like the explanation was consistent with what I thought of, but it involved multiple universes or something, so maybe not. Anyway, the thing is, I never understood why this was supposedly a problem, since when I took physics, long, long ago, no one ever said anything about the universe requiring that information be conserved. Energy is conserved. Momentum is conserved. Information, no one ever talked about. Well, they DID talk about information, of course, but they called it entropy. And entropy, meaning the disorder of a system and requiring a certain amount of information to describe (it takes few words to describe a perfect crystal, namely, but many to describe the location of atoms randomly strewn about), always increases. That's the second law of thermodynamics. So my question is, did someone connect the dots wrong here? Just because the entropy of the universe never decreases, that doesn't mean information is never destroyed. You can replace 1 bit of important information with 2 bits of trash that say nothing about what was contained in that one bit of information before it was lost. Just like I can overwrite a 1-kilobyte file with a 2-kilobyte file which had absolutely nothing to do with the 1-kilobyte file. So who decided that information was never destroyed? Does anyone actually have any observations to back up this ridiculously massive assertion, or is it just wishful thinking? And if it is the former, why wasn't I taught this back when I was in school? Or is this something they only decided on in the 80s or 90s? Another question, now that I'm thinking about it. These same dumbed-down physics shows I've seen have said that time travel wouldn't violate the laws of physics, which is why it is supposedly an open question as to whether or not it is possible to go back in time. But if all reference frames are valid, then in the reference frame of the time traveler, whose clock ticks ever forward and simply ends up in the universe at an earlier time according to some other observer, the universe has, as HIS clock ticked forward, regressed to a more ordered state. Thus this violates the second law of thermodynamics, as according to at least one observer, the time traveler or someone who stayed in the normal flow of time, the universe was less ordered at one point in time and more ordered later. How can they say it doesn't violate the laws of physics when it obviously violates the second law of thermodynamics? Is the second law of thermodynamics not considered to be a law of physics?