Comments about the article in Nature: Black holes shrink but endure

Following is a discussion about this article in Nature Volume 502 / 31 October 2013 / page 603
In the last paragraph I explain my own opinion.

Black holes shrink but endure

The article (in focus / News) starts with the following text:
Theorist's idea takes on information - preservation problem
This is one of the main problems: The problem expresses the opinion of theorists.
Ellis' speculative report, posted on 17 October on the preprint server seems to undermine the seminal work of Stephen Hawking.
In 1974, Hawking calculated that owing to quantum effects, black holes are not entirely black: some particles escape the black hole's gravitational barrier, known as the event horizon.
See For detail: Black hole explosions? S. W. Hawking Pay article. and Particle Creation by Black Holes S. W. Hawking Free article.

The whole problem depends about the physical processes that happen inside a black hole and at the surface of a black hole.

The central theme is an equilibrium problem, it is like a balance. When the balance is positive the mass of the black hole will increase. When the balance is negative the mass of the black hole will decrease. The fact that the black hole exists implies that from its moment of "creation" until now the balance is positive. The question to answer is: what specific change in the neighbourhood of the black hole causes this balance to reverse?

Although many physicists are sceptical about Ellis's work, it highlights a long-running debate over the ultimate fate of black holes.
What this sentence suggests is that not all physicists agree with the outcome of the paper by S.W. Hawking. That may be true but that there is also a chance that both papers could be wrong.
Uncertainties abound because of the difficulties in reconciling quantum theory - which predicts the Hawking radiation - and Einstein's classical theory of gravitation which defines a black hole's structure.
The issue is if both theories define the physical conditions that are happening around the event horizon correct.
One of the issues is the speed of the particles involved.
The problem is near the event horizon.
Are both speeds identical?
The debate also touches on one of the most cherished beliefs about the Universe: that information is always preserved.
What do they mean with information? There is a different law and that is the law conservation of energy. But apparently that is not the issue here.
When a comet collides with the Sun are both laws valid?
IMO the law of conservation of information is not obeyed. It is impossible after collision to calculate the moment when this collision occurred and the path that the commet followed before the impact. (also the path of the Sun changed).
IMO for black holes the same is true.
If black holes evaporate, then the information they contain may die along with them.
Our Sun emits lights. Does it make sense to say that our Sun loses information? I do not think so.
By contrast, a black hole remnant would offer a way information might be preserved.
How do we know that a black hole is a "black hole" and not a "black hole remnant"? I do not think that such a distinction makes sense.
In Hawking's original view, quantum theory permits large fluctuations in energy for brief moments of time?
How are these fluctuations observed? Are they observed near black holes?
As a consequence the vacuum of space seethes with particle - anti particle pairs that continually pop in and out of existence.
How are these particle pairs observed? Are they observed near black holes?
According to Einstein any source of mass or energy distorts space.
It is important to explain how this distortion is measured.
A black hole, a body so massive that space closes in on itself.
Exactly what does this mean?
The Hawking radiation would add even more distortion.
When Hawking radiation evaporates from a black hole it decreases this distortion?
Ellis says, and so, would the ubiquitous photons from the cosmic microwave background, the bath of radiation left over from the Big Bang.
Black holes will work as a vacuum cleaner; they will diminish the amount of background radiation.
The analysis is more of an essay, says Samir Mathur, because Ellis does not perform a thorough calculation for the bending effect of the radiation.
Other physicists say that Ellis is probably incorrect.
That is probably true, but that does not mean that we know what the evolution of a black hole is.
But black hole remnants do not offer a perfect solution to the problem of information loss either. To contain all the information originally stored in a large black hole, the tiny remnants would need to have an infinite number of internal states - which would violate quantum theory, says Mathur.
The total number of states of the black hole should be the same as the number of states of its remnants. However this whole calculation is rather theoretical.
This violation of the quantum theory what does that really means? Maybe the quantum theory is not complete in this domain.
In 1997 Mathur found a potential way around this problem. He and his colleagues used string theory etc to describe all of the possible states etc.
How do you know that string theory is correct in this domain inside the event horizon?
Last year, others proposed, etc. They suggested that the particles in the Hawking radiation did not behave randomly but were instead entangled which each other etc. such that they could be messengers from the darkness...
This seems to me pure speculation.
The conventional picture holds that quantum theory makes big corrections to gravity only well inside the event horizon, near the black hole's singularity - the point at which the density of matter becomes infinite.
Is there a singularity inside the black hole? When you compare the density of matter inside a black hole with the density of the Big Bang, the density of the first should be smaller.
Ellis work, Visser says, puts a stronger spotlight on such speculations.
I think what people think what happens between the rim of the black hole and the event horizon is full of speculation. But also about the processes inside the black hole and in the environment of the event horizon.

Vanishing Act

A theorist suggests that black holes may not evaporate, but rather remain as information-bearing remnants.
               ...     |
           .         . 1--->
         .             .
        .               .
        .  ^            .
        .  |   BH    ^  .
        .  3-->      |  .
         .           | .
            .        2--->
       Picture of a black hole
 The circle repesents the event horizon 
The numbers 1 2 and 3 represent events 
  1. Virtual particle near the event horizon pop in and out of existence
  2. The emergence of a particle pair at the event horizon could result in one falling into the black hole and the other being emitted as Hawking radiation. This emission would eventually cause the black hole to evaporate.
  3. But the Hawking radiation itself may nudge the emergence of these particle pairs to a point inside the event horizon from which neither can escape. Evaporation would cease leaving a black hole remnant.
What the above picture shows is the behaviour of virtual particles created at three positions related to the Event horizon:
1) Out side the horizon. 2) At the horizon 3) Within the Event Horizon
Black holes are very heavy physical objects. Our Sun is also a heavy physical Object but much less heavier than a black hole.
Our Sun can grow in mass by collisions with smaller objects (comets). The same will happen with black holes. Stars can collide with black holes.
Heavy stars can explode. What with black holes? The Big Bang was also a huge explosion.

The biggest problem with black holes is experimental evidence how they behave. For example what happens with a space ship when if falls into a black hole. What is observed.
The same problem is with the virtual particles in the sketch. What is the speed of these particles and how do we know that they are created.

The paper by George F R Ellis

The paper in the Abstract starts with the following sentence:
This paper argues that the effect of Hawking radiation on an astro-physical black hole situated in a realistic cosmological context is not total evaporation of the black hole; rather there will always be a remnant mass.
The problem is: what is a "remnant mass". IMO you can have objects (Brown dwarfs, stars and specific Black holes) of all different sizes. How do you know that the black hole you are studying is in its remnant phase?
Using the same argument you can also question the issue how do you know that a black hole has completely vanished (evaporated away).

Reflection part 1

One interesting issue is: how do you demonstrate that inside a galaxy there is a black hole.
The best method is by observing stars around a black hole. By observing the revolution time of such a star you can calculate the mass of the black hole.
The most interesting case is: when the observer is the plane of the star. In that case during parts of its trajectory the star becomes invisible.
See Also: Milky Way galactic center black hole

This type of occultation (See Occulation) means that the star is obscured by the black hole. Such an occulation is interesting inorder to study the two moments: (1) when the star disappears and (2) when the star appears.
How closer such the star passes near the event horizon the more interesting.



Created: 25 November 2013

Back to my home page Index
Back to Nature comments Nature Index