Comments about "Event horizon" in Wikipedia

This document contains comments about the document "Event horizon" in Wikipedia
In the last paragraph I explain my own opinion.



The article starts with the following sentence.
In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer.
The problem is what have outside observers to do with the laws of physics. See Reflection part 1
In layman's terms, it is defined as "the point of no return", i.e., the point at which the gravitational pull becomes so great as to make escape impossible.
The problem is that the physical processes which take place inside and outside a BH have nothing to do with any observer. As such the word observer should not be used.
In layman's terms, the event horizon is defined as a boundary or sphere around a BH. At each point of this sphere the gravitational pull is so great such that nothing can escape.
Light emitted from inside the event horizon can never reach the outside observer.
Also this sentence is "wrong".
Light emitted from inside the event horizon will always bounce back.
The problem is that when you agree the speed of light is not a constant.
Likewise, any object approaching the horizon from the observer's side appears to slow down and never quite pass through the horizon, with its image becoming more and more redshifted as time elapses.
This sentence requires a carefull investigation.
The problem is when an object approaches a BH its speed will increase. And when the speed increases above the speed of light the object will evaporate.
The traveling object, however, experiences no strange effects and does, in fact, pass through the horizon in a finite amount of proper time.
It depents. The problem depents about the size of the BH.
When the speed of the object increases above the speed of light the object will evaporate.
When the the object passes through the sphere defined by the size the object will merge with the BH.

1. Event horizon of a black hole

The surface at the Schwarzschild radius acts as an event horizon in a non-rotating body that fits inside this radius (although a rotating black hole operates slightly differently).
This implies that the two are the same.
The minimal mass required for a star to be able to collapse beyond these pressures is the Tolman-Oppenheimer-Volkoff limit, which is approximately three solar masses.
This limit defines a neutron star. A neutron star consists of neutrons. Something more has to happen before a neutron star becomes a BH. It is very difficult to discover in the literarture, what this "something more" physical is.
Black hole event horizons are widely misunderstood.
The issue is what is physical meaning of this event horizon? See also Reflection part 1

2. Cosmic event horizon

3. Apparent horizon of an accelerated particle

4. Interacting with an event horizon

In practice, all event horizons appear to be some distance away from any observer, and objects sent towards an event horizon never appear to cross it from the sending observer's point of view (as the horizon-crossing event's light cone never intersects the observer's world line).
The problem is that when you send an object towards a BH you will never be able to actual physical "see" that it collides with the BH, because photons can not escape from the gravitational pull of the BH. However, from a gravitational point of view it is possible to detect this collision (The same way as LIGO works). In short the concept of "event horizon" has no physical meaning.
Furthermore, the break must occur not at the event horizon, but at a point where the second observer can observe it.
THis whole discussion does not make much sense.

5. Beyond general relativity

The description of event horizons given by general relativity is thought to be incomplete
IMO the concept of event horizon is not strictly covered by GR alone. Newton's Law also supports this concept.
At present, it is expected that the primary impact of quantum effects is for event horizons to possess a temperature and so emit radiation.
The whole issue depents on the physical state inside a BH. To assume that the temperature is at absolute zero or 0 Kelvin, does not seem logical.

6. See also

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

Reflection part 1

The name "Event horizon" is a very unlucky name. The Schwarzschild radius defines a sphere. The whole idea behind this sphere is that objects which are smaller than this sphere are invisible. From a physical point of view this sphere has almost no meaning. See also Schwarzschild radius - Reflection part 1
The "Event horizon", as far as I can see it, defines the same sphere. The problem is that events that are happening within this sphere can influence the physical world outside this sphere. The best examples are colliding BH's. These collisions happen within this sphere and can be detected outside this sphere. The sole reason is gravitational radiation which is something completely different as light or photons (electro magnetic radiation). Those two should be dealt with at a different footing.


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Created: 6 September 2016

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