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Can someone explain to a muggle like me what is "Quantum Information" concretely? I'm asking this because I don't get it why the Hawking radiation "destroying information" is so controversial. Quoting Wikipedia:

This is controversial because it violates a core precept of modern physics — that in principle the value of a wave function of a physical system at one point in time should determine its value at any other time. A fundamental postulate of the Copenhagen interpretation of quantum mechanics is that complete information about a system is encoded in its wave function up to when the wave function collapses.

If "information" means "wave function", then doesn't it mean that the particle that trespassed the event horizon collapsed? And why "information" being destroyed such a big deal? The Universe was filled with with virtual particle popping up into existence and annihilating continuously, isn't it? When they pop up into existence, information is created from nowhere, and when they annihilated that information is gone, right?

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  • $\begingroup$ There are two different concepts here: (1) unitary evolution of the wavefunction, and (2) quantum information. #1 is what you're really asking about. #2 is much more esoteric. $\endgroup$ – Ben Crowell Jun 20 '18 at 23:56
  • $\begingroup$ I guess I need to do more "homework" to grasp this stuff 😅 $\endgroup$ – moumous87 Jun 21 '18 at 8:15
  • $\begingroup$ There is no univocal definition of "quantum information". It is mostly a term used to refer to how information (the classical, "normal" one) works in a quantum mechanical context $\endgroup$ – glS Jun 21 '18 at 11:08
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No, not right. Conservation laws are fundamental to working out what exists, things can only 'pop' into existence a tiny bit, within the limits of uncertainty, which again relates to information.

The conservation of information is a well established principle of modern quantum mechanics, as just discussed here The 'Conservation of Information' myth

There were reasons to think information gets lost in black holes. Hawking radiation posed a problem, because there was no way for the ingoing mass that created the black hole, to affect the outgoing radiation. This was resolved using thermodynamic arguments that related the black hole entropy to it's surface area. The ingoing matter influences the black holes surface shae, and that information influences the form of any outgoing radiation.

Quantum mechanics is both probabalistic, and deterministic. The sum of probablities is 1, and they all happen (in many worlds).

A major school of thought holds that information is the fundamental stuff of the universe https://en.m.wikipedia.org/wiki/Digital_physics#Wheeler's_"it_from_bit" Not just special quantum information, which is about states that are in a superposition until an observation or measurement is made. But 'events' in general, rather than 'things'.

“We don't understand the world as made by stones — by things. We understand the world made by kisses, or things like kisses: happenings.” - Carlo Rovelli, quantum loop gravity theorist

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