Comments about "Black hole information paradox" in Wikipedia

This document contains comments about the document "Black hole information paradox" in Wikipedia

• The text in italics is copied from that url
  
• Immediate followed by some comments
  

In the last paragraph I explain my own opinion.

Contents

• 1. Principles in action
• 2. Hawking radiation
• 3. Postulated Solutions
  • 3.1 Information is irretrievably lost
• 4. Recent Developments
• 5. See also

Introduction

The article starts with the following sentence.

The black hole information paradox is an observational phenomenon that results from the combination of quantum mechanics and general relativity which suggests that physical information could permanently disappear in a black hole, allowing many physical states to devolve into the same state.

This sentence is "impossible" to understand. Almost everything related to black holes can not be directly observed.
In a certain sense you can compare a BH with a star. The surface of a star is a hot boiling substance of a very high temperature. When a comet collides with the Sun it will be disolved and disappear completely out of existance. This process is irreversible.
For a Black Hole this is the exactly same, except that the moment that this conversion starts i.e. the moment of impact, can not be observed.

This is controversial because it violates a commonly assumed tenet of science—that in principle complete information about a physical system at one point in time should determine its state at any other time.

It is in general impossible to have complete information about a physical system. The consequence is that it is impossible to predict its evolvment in the future.
If you consider a physical system globally than every physical system is influenced by the whole of the Universe, which implies because of limited knowledge of the state of the universe that its future can not accurately be predicted.

A fundamental postulate of quantum mechanics is that complete information about a system is encoded in its wave function up to when the wave function collapses.

That may be true, but what is its practical value?
What means: "complete information" Anyway what is the exact defination that "the wave system collapses" ?

The evolution of the wave function is determined by a unitary operator, and unitarity implies that information is conserved in the quantum sense.

The same as previous: What is the practical value.

This is the strictest form of determinism.

In reality in order to understand the evolution of any system the concept of determinism (meaning that it follows some strict laws) is not very helpfull.

1. Principles in action

There are two main principles in play:

• Quantum determinism means that given a present wave function, its future changes are uniquely determined by the evolution operator.
• Reversibility refers to the fact that the evolution operator has an inverse, meaning that the past wave functions are similarly unique.

The combination of the two means that information must always be preserved.

The law of conservation of energy describes that the energy in a closed system is always maintained. These law has nothing to do with the above mentioned two concepts, in the sense that neither Quantum determinism nor Reversibility can be demonstrated in any experiment, that and how they apply.

Specifically, Hawking's calculations indicated that black hole evaporation via Hawking radiation does not preserve information.

What Hawking should demonstrate is that Hawking radiation should be in conflict with the energy conservation law.

Today, many physicists believe that the holographic principle (specifically the AdS/CFT duality) demonstrates that Hawking's conclusion was incorrect, and that information is in fact preserved.

Exactly what is the holographic principle in relation to the evolution of a BH?
If that is not clear, IMO, you can not use the "holographic principle" to demonstrate that the energy conservation law is not violated.

In 2004 Hawking himself conceded a bet he had made, agreeing that black hole evaporation does in fact preserve information.

In a certain sense we create a win win situation.
The problem IMO is neither side can clearly show what his opinion is.

2. Hawking radiation

In 1975, Stephen Hawking and Jacob Bekenstein showed that black holes should slowly radiate away energy, which poses a problem.

The question is if Hawking demonstrated or predicted that BH slowly radiate or emit something i.e. energy. IMO there is nothing wrong to predict such a concept. The problem is to demonstrate this.
Part of the problem is you should define a radius for each BH. That means a "particle" belongs to the BH when it is inside this radius and does not belong to the BH when it is outside this radius.

From the no-hair theorem, one would expect the Hawking radiation to be completely independent of the material entering the black hole.

This raises a reasoning problem, because all of a sudden you have to understand the no-hair theorem.
When you consider the light that is in general emitted by the Sun, this has nothing to do how the Sun formed. IMO this is the same for any radiation emitted by a BH. You do not need the no-hair problem. Link 1

Nevertheless, if the material entering the black hole were a pure quantum state, the transformation of that state into the mixed state of Hawking radiation would destroy information about the original quantum state.

The problem with this sentence is, that in order to understand you need a good definition of what a pure quantum state and what a mixed state is.
See also Reflection 2 - Pure versus Mixed state IMO in any process in which something changes a certain amount of information is lost and new information is created. This information transformation is in the details of the process.

This violates Liouville's theorem and presents a physical paradox.

IMO some people make something overly complex.
IMO there is no physical paradox. The problem is in the Liouville theorem.

More precisely, if there is an entangled pure state, and one part of the entangled system is thrown into the black hole while keeping the other part outside, the result is a mixed state after the partial trace is taken into the interior of the black hole.

The problem is why do you need an entangled particle to demonstrate the Black Hole information paradox?
What is an entangled pure state and why is it important to know in relation to a BH?

Hawking remained convinced that the equations of black-hole thermodynamics together with the no-hair theorem led to the conclusion that quantum information may be destroyed.

IMO during the whole process of BH evolution it is the most obvious assumption that information is lost. Part of this loss is in the details of what has and is happening. This has nothing to do with what we humans can and cannot observe

The claim that during as part of a process information is lost is by itself already information. The opposite is no-information.

The solution to the problem that concluded the battle is the holographic principle, which was first proposed by 't Hooft but was given a precise string theory interpretation by Susskind.

This gives the impression that the holographic principle, because it solves "the problem" is correct. This is ofcourse scientifically the wrong path to follow.

In July 2004, Stephen Hawking published a paper presenting a theory that quantum perturbations of the event horizon could allow information to escape from a black hole, which would resolve the information paradox.

Also this ofcourse the wrong way to perform science. The whole issue again is how black is a black hole. Totally black means that nothing can escape. What escapes is electromagnetic radiation of particles. The description of what escapes is information, but there no information that escapes from a black hole.

3. Postulated Solutions

3.1 Information is irretrievably lost

3.2 Information gradually leaks out during the black-hole evaporation

3.3 Information suddenly escapes out during the final stage of black-hole evaporation

3.4 Information is stored in a Planck-sized remnant

3.5 Information is stored in a large remnant

3.6 Information is stored in a baby universe that separates from our own universe

3.7 Information is encoded in the correlations between future and past

4. Recent Developments

In 2014, Chris Adami, a physicist at the Michigan State University claimed to have solved the paradox. Since absolute loss of information is not allowed by quantum physics, Adami argues that the "lost" information is contained in stimulated emission that accompanies the Hawking radiation emitted by blackholes. His solution has not been confirmed.

What Adami should claim that there is no paradox. He should claim that there is something wrong with either quantum physics or general relativity or both and that in the worst case both should be modified.
He should also claim that it is not an information problem but a physical problem.

Hawking et al 5 Jan 2016 proposed new theories of information moving in and out of a black hole. The 2016 work posits that the information is saved in "soft particles", low-energy versions of photons and other particles that exist in zero-energy empty space

For Hawking the same comments are valid: He should not mention the word information. He also should not mention "zero-energy empty space". What does it mean anyway ?.
For comments about the Nature article this:

Physicists split by Hawking paper In this "News in focus" article of 28 January 2016 David Castelvecchi argues: Some welcome his latest report as afresh way to solve a BH conundrum; others are unsure of its merits.

5. See also

Following is a list with "Comments in Wikipedia" about related subjects

• No-hair theorem Comments
• Thorne–Hawking–Preskill bet Comments

Reflection 1

The BH information paradox, more specific the "energy conservation law" raises some specific questions in relation to what information is.

Consider with Lego blocks you build a house. This house you have created contains new information. In general any thing that is build or created has a certain beauty or a function. This beauty, this art work or function is new information.
Next you "destroy" what you have build or created and all this new information is destroyed.
The question is if this whole process is in agreement with the "energy conservation law". The same problem also exist when a library burns down. The burning process is in accordance with the "energy conservation law" but the issue is if that also is true for the contents of the books that are destroyed. All that information is also lost and cannot be recovered from the ashes. From a physical point of view this burning process is irreversible.
The same issues are also at stake when a comet collides with our Sun or a star is captured by a BH. All this preocesses are irreversible. The processes itself follow the "energy conservation law" but at the same time a certain amount of information of what hapenned before is lost.

Reflection 2 - Pure versus Mixed state

The Wikipedia document Quantum state gives a good description what a pure versus a mixed Quantum state is.
For that same reason you can also study the Wikipedia document: Density Matrix
The question to answer is what is the density matrix of each of the stages during the evolution of a BH.
The text link 1 discusses three entities: Material entering a BH, the BH itself and Hawking radiation.
By introducing the concept of pure and mixed state does that give any glues about the processes involved ? I do not think.

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