[[Mod. note -- Lines rewrapped to be <= 72 characters long. -- jt]]

In Scientific American Sept 2022 there are 4 articles about Black Holes.
Here I want to discuss the paper "Paradox Resolved" at page 28. This
document starts with the sentence: "A few years ago a team of chemists
unboiled an egg." For more detail select this: https://www.washingtonpost.com/news/speaking-of-science/wp/2015/01/28/how-and-why-chemists-figured-out-how-to-unboil-an-egg/
Next we can read: "The technique is of dubious utility in a kitchen, but
it neatly demonstrates the reversibility of physics. Anything in the
physical world can run both ways -- it's one of the deepest features of
the laws of physics, reflecting elemental symmetries of space, time and causality." I have a problem with this. Not so much from a mathematical
point because we can claim that Newton's Law is time reversible. But
from a physical point. A heating process requires heating equipment (or
the sun) to heat the water. A cooling process requires cooling
equipment to cool the water. That is why a heating process and a
cooling process are not time reversible. (Specific if they include
certain cyclic patterns, like the human life cycle) All these processes
are physical irreversible. Next we read: "But there's a troubling
exception: black holes." and: "The black hole does not seem to preserve information. This irreversibility, first appreciated by physicist David Finkelstein in 1958, was the earliest inkling of the black hole
information paradox -- "paradox" because how could reversible laws have irreversible effects?" The first question is: can we speak of a paradox?
To investigate you must investigate in more detail what is involved.
Consider what happens when you throw a book in an oven. It starts to
burn and slowly the book 'disappears' and what is left over is ash.
This is also a irreversible physical proces. It is impossible, assuming
that all what happens after you burn is ash, to recreate the object i.e.
the book, which was burned. Besides burning a book on earth, you can
also place the book in space ship and let the space ship collide with
the sun. Also that is an irreversible process. The space ship can also
collide with a black hole and you get exactly the same. The book is lost
and cann't recreated.

What has this to do with information? Assume, what you are reading now,
is not an e-mail but text in a book. In that case both the book and the
written text is something physical. That is what can burn and return to
ash. The contents of the text written in the english language was
information in the mind of the person who wrote the book and becomes information in your mind when you read the text. This contents is also irreversible lost when you burn the book.

Is there something what you can call "information paradox"? I don't
think so. All what happens, when something disappears in a BH, is lost
forever and can't recreated. The same for our Sun, or when you burn
something in a fire.

If you agree, than a lot what is written in the article 1: "Paradox
resolved" has to be rewritten because there they try to solve the
paradox (part of) by using entanglement. In article 2, at page 36/37
you can read that in order to solve the information paradox, Wormholes
are required. In article 3, at page 42/43 as a consequence of the
information paradox, the holographic principle is introduced.

In a laboratory the evolution of many chemical reactions evolve towards
a type of equilibrium. Suppose you have A+B --> C+D That means if you
start with 50% A and 50% B than reaction will evolve and STOP when you
get 25% A, 25%B and 25%C and 25%D. Now you can do two things: 1) Remove
C and D. Now you get 12,5% A, 12,5%B and 12,5%C and 12,5%D. 2) Remove A
and B. Now you get 12,5% A, 12,5%B and 12,5%C and 12,5%D. but the
reaction is now: C+D --> A+B This is in the opposite direction. However
to do that, human intervention is required, which is not available in
the processes part of the evolution of the Universe. And this has
nothing to do with time reversibility part of Newton's Law. And has
'nothing' to do with the behaviour of a BH.

Nicolaas Vroom https://www.nicvroom.be/

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In article <688f84fc-e19f-4db7-afb6-d2e9c2fb33afn@googlegroups.com>,
Nicolaas Vroom <nicolaas.vroom@pandora.be> writes:

In Scientific American Sept 2022 there are 4 articles about Black Holes.

"But there's a troubling exception: black holes." and: "The black hole
does not seem to preserve information. This irreversibility, first appreciated by physicist David Finkelstein in 1958, was the earliest
inkling of the black hole information paradox

Jonathan might know more about this topic, but I think that the
resolution of the "information paradox" is still not completely clear. However...

Consider what happens when you throw a book in an oven. It starts to
burn and slowly the book 'disappears' and what is left over is ash.
This is also a irreversible physical proces. It is impossible, assuming
that all what happens after you burn is ash, to recreate the object i.e.
the book, which was burned.

...I think that your description is irrelevant, because one could IN
PRINCIPLE reconstruct the book from the ashes and smoke. Impractical?
Yes? Will it ever happen? Probably not. But the claim that
information is lost forever in black holes (possibly with the caveat
that that only applies to classical black holes, not taking Hawking
evaporation into account) is the claim that it is impossible even in
principle to recover it.

Something similar might be the probability that the water in a kettle on
a fire might freeze instead of boil. According to the laws of physics,
it is possible, but EXTREMELY unlikely. Especially with thought
experiments, one has to distinguish between things which are REALLY
impossible, and things which are just really difficult and/or really improbable.

[[Mod. note -- A few points:
1. Alas, I know very little about the information paradox.
2. Wikipedia has what looks like a nice article on it:
https://en.wikipedia.org/wiki/Black_hole_information_paradox
3. I also know very little about the history of the information paradox,
but I doubt that it's correct to credit Finkelstein (1958) with
being the first person to appreciate that black holes don't preserve
information. Finkelstein's 1958 paper discusses the causal nature
of what today we would call a black hole's event horizon, but he
only refers to "causal influences" (i.e., matter or energy), not
"information" in the sense of the information paradox.
4. To clarify, when Phillip says that *in principle* one can reconstruct
the book from the ashes and smoke, he is writing in a "Maxwell's demon"
since: all the original atoms of the book are still present in the
ashes and smoke, so one could in principle (i.e., by using nanotechnology
but without violating any laws of physics) move those atoms back
into their original "book" positions and give them back their
original room-temperature-thermal-energy velocities, thus re-forming
the chemical bonds which were broken by the combustion process
and recreating the original book.
-- jt]]

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Op zaterdag 15 oktober 2022 om 20:10:58 UTC+2 schreef Phillip Helbig (undress to reply):

In article <688f84fc-e19f-4db7...@googlegroups.com>,
Nicolaas Vroom <nicolaa...@pandora.be> writes:

"The black hole
does not seem to preserve information. This irreversibility, first appreciated by physicist David Finkelstein in 1958, was the earliest inkling of the black hole information paradox

Jonathan might know more about this topic, but I think that the
resolution of the "information paradox" is not completely clear.

The problem is we should come to an agreement what the "information
paradox" is or reject it.

However...

Consider what happens when you throw a book in an oven. It starts
to burn and slowly the book 'disappears' and what is left over is
ash. This is also an irreversible physical process.

...I think that your description is irrelevant, because one could
IN PRINCIPLE reconstruct the book from the ashes and smoke.
Impractical? Yes? Will it ever happen? Probably not.

My understanding is that all processes are irreversible. For example,
if something burns in a fire, in an oven, in a star or in a BH.
If we all agree (?), than the paradox is solved (eliminated)
This makes the understanding of all processes simpler.

Something similar might be the probability that the water in a kettle on
a fire might FREEZE (instead of boil).

How do you perform such an experiment?

According to the laws of physics, it is possible, but EXTREMELY unlikely.

All the laws of physics should be based on something that can be observed
or can be measured in nature or describes the result of an experiment.
For example, the mass of a star is in the range of...
The mass of a BH is in the range of ...

Especially with thought experiments, one has to distinguish between
things which are REALLY impossible, and things which are just really difficult and/or really improbable.

Science cannot be performed only using our mind.

[[Mod. note -- A few points:
3. I also know very little about the history of the information
paradox, but I doubt that it's correct to credit Finkelstein (1958)
with being the first person to appreciate that black holes don't
preserve information.

In this case the concept of information should be clearly described.
In its most basic concept (?) information means the meaning of the
text in a book.

not "information" in the sense of the information paradox.

The same.

4. To clarify, when Phillip says that *in principle* one can
reconstruct the book from the ashes and smoke, etc.

Consider some plankton, consider a fish who eats the plankton, consider a cormorant who eats the fish, consider an orca who eats the cormorant,
consider the orca dies, strands at the shore of the Netherlands
and is dissected at the University in Utrecht.
Is it possible to recreate the original plankton from the stomach of the
orca?
No. Neither in principle nor in practice.
In fact, if this is not possible practice, how can you claim that the
process is reversible?

When you consider, the evolution of the universe, the physical state of
the universe changes continuously. One of the most common processes are reactions or collisions. In a collision, parts collide and are destroyed
and new parts (or objects) are created. In a reaction this are chemical elements. As a result of these collisions new collisions can take place
and this is an endless chain. As a result of these reaction new
reactions can take place, also in an endless chance.
Collisions can also take place in combination with a reaction, also
in an endless chain.
What is the most important conclusion: The state of the universe can
never go back in the state it was before. That is what is observed
in the reality.

Nicolaas Vroom
https://www.nicvroom.be/

[[Mod. note -- To reiterate what I said before, Phillip Helbig's usage
of "in principle" means "with perfect nanotechnology", i.e., with the
ability to rearrange atoms and break & re-form chemical bonds as necessary.

So yes, in this "in principle" sense one could indeed reconstruct the
plankton by bringing its atoms from the dissecting room back to the
place in the Ocean where the plankton was first eaten, and recreating
all the chemical bonds etc of the molecules that mde up the plankton.

Or for a rather "easier" task, one could *in principle* bring all the
molecules in a kettle of water (which is placed in a hot environment,
e.g., over a fire) nearly to rest,
[I say "nearly" because the uncertainty principle
prevents us from bring things *exactly* to rest
(zero kinetic energy) while keeping them at a known
position.]
resulting in the kettle of water being at a very cold temperature
(way below the freezing point of water, actually very near to absolute
zero). That is, this "in principle" assumes the existence of (among
other things) a "Maxwell's demon".

While the above examples are obviously far-fetched with present technology, it's worth noting that Maxwell's demon has already be realised experimentally for nanoscale systems. There's no violation of the laws of thermodynamics
in these experiments because the "Maxwell's demon" requires a considerable power input (entropy dissipation) to operate.

An interesting example of a *macroscopic* Maxwell's demon is "stochastic cooling" as used in particle accelerators. See
https://en.wikipedia.org/wiki/Stochastic_cooling
for a nice introduction. And see
https://en.wikipedia.org/wiki/Brownian_ratchet
for an interesting piece of physics which is somewhat related.
-- jt]]

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