Cosmology - Black Holes, Wormholes and Entanglement in Scientific American of September 2022

This document contains comments about the article Black Holes, Wormholes and Entanglement by Ahmed Almheiri In Scientific American of September 2022.
Researchers cracked a paradox by considering what happens when the insides of black holes are connected by spacetime wormholes. To read this article select:



Theoretical physics has been in crisis mode ever since 1974, when Stephen Hawking argued that black holes destroy information.
A written description of the evolution of a process is information. When you burn a painting, the painting is detroyed, but not a written description or a painted copy of that painting.
Hawking showed that a black hole can evaporate, gradually transforming itself and anything it consumes into a featureless cloud of radiation.
The central issue is, if during the considered period more energy is consumed or released. Energy consumed meaning mass consumed.
During the process, information about what fell into the black hole is apparently lost, violating a sacred principle of physics.
What is this principle, which describes the behaviour of a BH?

1. A One-Way Street

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These tidal forces run to infinity in finite time, marking the abrupt end of an entire region of spacetime at the so-called black hole singularity—the place where time stops and space ceases to make sense.
This sentence tries to explain something. Unfortunate it uses words and concepts which are not clear. The result is that the text explains nothing. It becomes peotic.
What means that time stops? When I travel on a comet towards a BH at a certain moment my watch wil stop ticking because it will burn because of the heat encountered. But that does mean that time stops. Anyway we first must come to a definition what time means.

2. Something Out Of Nothing

For every calorie of energy they consume, they eventually give it back in the form of Hawking radiation—energy squeezed out of the vacuum near the event horizon.
What does the word eventually mean? How long after the energy is consumed is this energy released? In the form of what?

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3. Einstein's Enemy

The issue begins with the end of the union of the two particles straddling the event horizon. Despite being separated, they maintain a quantum union that transcends space and time—they are connected by entanglement.
What does it mean: that transcends space and time? Is that something virtual?
What means: connected ? Does that mean that the particles are connected?. Is that something similar as that the spider is connected with the three via his web?
They cited entanglement as a reason the theory must be incomplete—“spooky” is how Einstein famously described the phenomenon.
The theory behind entanglement is wrong. Einstein was also right. The "only" way to do science is by performing experiments.
A simple example of entanglement is to consider two coins in a superposition—the quantum phenomenon of being in multiple states until a measurement is made—of both coins being either heads or tails.
You should not describe a simple example, but a simple experiment. What is missing, is how these coins are brought in superposition. For example: you can shake two coins in a dice cup and place the whole on a table with the two coins covered and not visible under the dice cup. You could also use two dice cup and place both on a table with each coin covered under one dice cup. Next you can claim that the two are entangled. They are not entangled
The coins aren't facing heads and tails at the same time—that's physically impossible—but the superposition signifies that the chance of observing the pair of coins in either orientation, both heads or both tails, is a probability of one half. There is no chance of ever finding the coins in opposite orientations. Hence, the two coins are entangled ; the measurement result of one predicts the result of the other with complete certainty.
The logic behind this text is not clear.
Please read: Reflection 1.2 - An experiment to demonstrate Entanglement - using coins.
The scientists were troubled by how the two coins appeared to influence one another without having to come into physical contact.
That is correct. It is physical not possible to bring two coins in entanglement
The coins could be in separate galaxies while still maintaining the same amount of entanglement between them.
Reality is that in experiments where entanglement is involved, that how further away the particles are the less correlation there is.
See also: Reflection 1.1 - An experiment to demonstrate Entanglement - Detail
Einstein was unnerved by the apparent “spooky action at a distance” linking the results of the two separate random measurements.
The correlation between the two measurements is not caused by any “spooky action at a distance”. It is caused by the original reaction that created the two particles.
The irony is that Einstein himself is in a superposition of being both wrong and right.
Such a sentence, contains no information.
He was right to recognize the importance of entanglement in distinguishing quantum mechanics from classical physics.
That distinction is physical of no importance.
What he got wrong can be summed up with the truism “correlation does not imply causation.”
When there exist a correlation between the results of certain measurements there must be an explanation.
Although the fates of the particles are inextricably correlated, the measurement outcome of one does not cause the outcome of the other.
The explanation of the correlation is that the particles measured, are created as a result of one reaction. See also: Reflection 1 - An experiment to demonstrate Entanglement
It turns out that quantum mechanics simply allows for a new, higher degree of correlation than we are used to.
The explanation of entanglement between elementary particles lies in the reactions that created these particles.

4. Information Lost

Because Hawking radiation is composed of one half of a collection of entangled pairs, it emerges from the black hole in a completely random state — if they were coins, they would be observed to be heads or tails with equal probability.
The cause of the so called Hawking radiation is predicted as being virtual particles. These particles can be correlated. The issue is how var this correlation reaches and can be measured.
Anyway these particles are not physical connected to each other, nor can they be compared which coins.
Hence, we cannot infer anything useful about the contents of the black hole from the random measurements of the radiation.
Is that a real problem?
This means that an evaporating black hole is basically a glorified information shredder, except unlike the mechanical kind, it does a thorough job.
A sentence without any information.
We can measure the lack of information—or the randomness—in the Hawking radiation by thinking about the amount of entanglement between the radiation and the black hole.
A sentence without any information. Human involvement, like thinking, has nothing to do with this.
This pattern differs from what happens when information is preserved, as in the example of a burning book.
At elementary particle level all atoms of a book are in a very precise location. When you burn a book all what physical exists, is lost.
It does not matter if the book burns inside a black hole, our sun or in a fire.
In such a case, the entropy may rise initially, but it has to peak and fall down to zero by the end of the process.
Okay. Etc Etc.
The time at which the entropy peaks and starts to decrease is the Page time.
Okay. But what does this say about the evolution of a black hole? IMO nothing.
The destruction of information inside black holes spells disaster for physics because the laws of quantum mechanics stipulate that information cannot be obliterated.
Based on what type of experiments are the laws of qm (relevent for this discussion) based?
Maybe these laws are wrong.
This is the famous information paradox—the fact that a sprinkling of quantum mechanics onto the description of black holes leads to a seemingly insurmountable inconsistency.
See: Reflection 2 - information paradox.

5. An Eventful Horizon

Part of the challenge was that no minor tweaking of the evaporation process was sufficient to generate the Page curve and send the entropy back down to zero. What we needed was a drastic reimagining of the structure of a black hole.
The word reimgining is strange. The word revision seems better.
The main issue is: exactly why?
In a paper I published in 2013 with Donald Marolf, Joseph Polchinski and Jamie Sully (known collectively as AMPS), we tried out several ways to modify the picture of evaporating black holes using a series of Gedanken experiments—the German term for the kind of thought experiments Einstein popularized.
In general it is very difficult to use thought experiments to predict the evolution of any physical process.
Through our trials we concluded that to save the sanctity of information, one of two things had to give: either physics must be nonlocal—allowing for information to instantaneously disappear from the interior and appear outside the event horizon—or a new process must kick in at the Page time.
In physics nothing can happen instantaneous.
To preclude the increase of entropy, this process would have to break the entanglement between the particle pairs across the event horizon.
It is not clear, what is meant with breaking the entanglement between particle pairs.
Recall that the entanglement across the horizon was a result of having empty space there—the way the vacuum is maintained by a sea of entangled pairs of particles.
Words like empty space and vacuum require a clear defintion. The main problem is how is the boundary of both defined.
The black hole at the Page time would suddenly lose its interior, and spacetime would come to an end, not at the singularity deep inside the black hole but right there at the event horizon.
It is very difficult to imagine what this physical meant.
This conclusion is known as the firewall paradox, a catch-22 that meant any solution to the information paradox must come at the cost of destroying what we know about black holes.
The end of this sentence is not clear.
The final sentence of this section reads:
If there was ever a quagmire, this would be it.
My understanding is: We lost the touch with reality.

6. Fluctuating Wormholes

Eventually my colleagues and I realized that both the information paradox and the newer firewall paradox arose because our attempts to meld quantum mechanics and black hole physics were too timid.
The final part of this sentence is not clear. Specific the verb to meld.
It wasn't enough to apply quantum mechanics to only the matter present in black holes—we had to devise a quantum treatment of the black hole spacetime as well.
The why of this sentence is missing
To consider the quantum nature of spacetime, we relied on a technique designed by Richard Feynman called the path integral of quantum mechanics. The idea is based on the weird truth that, according to quantum theory, particles don't simply travel along a single path from point A to point B—they travel along all the different paths connecting the two points.
In science you should always start with either obsevations or experiments or both and secondly with a description of how these facts can be combined in one story, or law or a set of equations.
Similarly, a quantum spacetime can be in a superposition of different complicated shapes evolving in different ways.
How can spacetime be in a superposition of different shapes which evolve different?
What makes physical sense is that every process will evolve differently in time if the external influences considered are different.

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For instance, if we start and end with two regular black holes, the quantum spacetime within them has a nonzero probability of creating a short-lived wormhole that temporarily bridges their interiors.
If we consider two regular blackholes and if they exists for a long time they must rotate around each other.
The most important question is: does their distance increase or decrease.
Why mention wormholes? How are wormholes detected?
Usually the probability of this happening is vanishingly slim.
Why such a shy sentence? Why not indicate how often wormholes are observed?
When we carry out the path integral in the presence of the Hawking radiation of multiple black holes, however, the large entanglement between the Hawking radiation and the black hole interiors amplifies the likelihood of such wormholes.
Entanglement means that there is a certain correlation between Hawking radiation and the interior of a black hole. Entanglement means that the origin of the Hawking radiation and something inside the black hole are the same. That does not mean that there exists a physical link between the two. That as a result there can be wormholes is open for investigation. The most important issue is, to what extend mathematics can be used. First have to be demonstrated that there are wormholes.

7. Islands Beyond the Horizon

Why does it matter if some black holes are connected by wormholes? It turns out that they modify the answer of how much entanglement entropy there is between the black hole and its Hawking radiation.
It is very difficult to understand how black holes are physical connected.
It is also very difficult how the inside of two black holes can correlated. How is this entanglement measured?
Stars can also be physical connected, but in all these cases there is always a transport from the small towards the larger star.
The key is to measure this entanglement entropy in the presence of multiple copies of the system. This is known as the replica trick.
How is this entangle entropy measured? What is meant with multiple copies?
The relevant physical effect of these temporary wormholes is to swap out the interiors among the different black holes.
This sounds like science fiction.
Focusing on one of the black holes and its Hawking radiation, swapping out the island takes with it all the partner particles that are entangled with the outgoing Hawking radiation, and hence, technically, there is no entanglement between the black hole and its radiation.
This sounds like science fiction

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Created: 22 August 2022

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