[xevrem]

I still don't understand what they mean by "loss". Why is this even a problem? The information isn't gone, its right -there- in the black hole, which until proven otherwise, is part of the universe.

Until someone can prove the universe cares whether the info is in a black hole or not, its not really a problem is it? If anything the universe usually shows it doesn't care what we humans think, its going to do its own thing, regardless: i.e., weak nuclear force and "symmetries"

[pdonis]

> The information isn't gone, its right -there- in the black hole

No, it isn't; it hits the singularity inside of the hole and gets destroyed. At least, that's what Hawking's original model, the one he used to predict that black holes evaporate, says.

One way of seeing why Hawking's model had to say this is to combine the following facts about the evaporating black hole and the Hawking radiation in Hawking's model:

(1) The hole itself cannot contain any information other than its mass, charge, and spin (because of the "black holes have no hair" theorem), which is far too little information to describe everything that fell into the hole.

(2) The Hawking radiation cannot contain any information about what fell into the hole because it is thermal, black-body radiation, i.e., the only information it contains is its temperature, which is related to the mass of the hole.

So the information can't be stored either inside the hole or outside the hole, which means it must be destroyed, and the only place it can be destroyed is by hitting the singularity inside the hole.

The black hole information loss problem is that the above is inconsistent with quantum unitarity. So Hawking's original model can't be right; but nobody knows what model should replace it.

[BMSmnqXAE4yfe1]

Except that later Hawking came to the conclusion that black holes do have hairs.

[effie]

> The hole itself cannot contain any information other than its mass, charge, and spin... which is far too little information

Maybe the information gets encoded in digits of value of mass expressed in some unit. There is enough digits to store any finite number of bits.

[gizmo686]

The black hole is not eternal. Once it is fully evaporated, you still need to account for the information that was contained within (or accept information loss).

[seppel]

> Once it is fully evaporated, you still need to account for the information that was contained within (or accept information loss).

One way to escape this is:

* You accept that the Hawkin radiation contains the original information.

* But it is scrambled in a reversible way, but so hard that you cannot reverse it with the energie available in the universe.

There are nice talk by Scott Aaronson about this, e.g.: https://simons.berkeley.edu/events/theoretically-speaking-se...

[cli]

I believe this was addressed in the first few paragraphs of the article: this problem is not about 'information', which is a vague phrase. Rather, it is about how black hole evaporation is fundamentally time irreversible.

[xevrem]

but wasn't the evaporation of black holes a suggested solution by hawking for information being "lost forever" in a black hole?

i.e., hawking radiation is itself unconfirmed, so its a "solution" for something that remains unproven :|

[pa7x1]

All of Quantum Mechanics respect unitary evolution, unitary evolution can be rewinded back. Black hole evaporation breaks unitary evolution, at least in the semi-classical approximation of Hawking. If you prepare a pure quantum state it will come out as mangled thermal radiation. You cannot return to the pure quantum state from the thermal radiation (i.e. we have lost information about it).

This transition is impossible in Quantum Mechanics and it would suppose a killing blow to Quantum Mechanics if true. So a better way to rephrase our worries is that if Black Holes do not respect unitary evolution then our most precise physical theory is fundamentally wrong.

[whimsicalism]

But then the black hole evaporates...