PeterDonis said:
No, it doesn't. Demonstrating that an event horizon is present means demonstrating that there is a region of spacetime that is not in the causal past of future null infinity--the event horizon is then just the boundary of that region. There is no need to say anything at all about the area of the horizon, or define an "areal radius" ##r##.
In the most common derivation of the formula for the event horizon radius (##R = 2GM/c²##), either the escape velocity is simply set to the speed of light or the singularity in the Schwarzschild Metric (
equation 36 of Karl's March 1916 paper, On the gravitational field of a sphere of incompressible fluid according to Einstein's theory) is noted (as with
Science Direct 2018, "Schwarzschild Radius").
So you are right. Defining (or demonstrating) the event horizon doesn't require working with an areal radius.
But you clearly get one anyway. And in all the discussions of the Bekenstein bound, area is key.
PeterDonis said:
You can use that definition everywhere, not just outside (or at) the horizon. But using it doesn't make any difference to any invariants.
Fine, but I suggest we not treat distances in space as strictly invariant. We know it expands - but we don't know what determines that expansion.
PeterDonis said:
What does this even mean?
I.e., "Working with a Schwarzchild black hole, with event horizon at ##r_s## and a reference frame at infinity.".
The symbol for the Schwarzchild radius is often ##R##, ##r##, or ##r_s##. So, I'm just identifying which symbol I was using. And I was using the most common reference frame for specifying the coordinate. For example, not "proper" coordinates.
Sorry if this isn't the common way of flagging these things.
PeterDonis said:
What does this even mean? What sort of "description" are you talking about?
You need to show some math instead of just waving your hands.
I am refering to the
Holographic Principle which was part of common discussion in the immediate wake of the
Bekenstein Bound (1981). According to the wiki article, it became associated with string theory as well.
In a nut shell, if you don't want the universe to loose entropy, then the area enclosing any content must have the capacity to hold that entropy information. (ie, "describe" it) If the area is too small or the amount of entropy is too large, then there is a QM limit (a la Planck's distance) that throttles the entropy.
Since spheres enclose regions of entropy with a certain efficiency, there is an equation for that specific boundary. That equation (since you asked) is provided in the wiki article. It is:
## S \le \frac{ 2\pi k R E}{\hbar c} ##
where ##S## is the entropy, ##k## is the Boltzmann constant, ##R## is the radius of the sphere, and ##E## is the total mass-energy enclosed.
So, I was taking about the enclosing surface "describing" the entropy of its content. (as a 2D hologram describes a 3D image).
PeterDonis said:
In classical GR, yes. Not necessarily in all quantum models. Exactly which quantum models correctly describe quantum corrections in this regime is a major open question in this area of research. And since it is an open question, you can't make any blanket statements of the sort you are making here.
(regarding the uneventful crossing of the event horizon in the proper reference frame)
This open question is very closely related to what I am commenting on.
My point is that there is a real QM issue and that it makes no sense to treat it as strictly a problem for what happens after you cross the event horizon. The problem develops as you approach the EH and as that ##S##
approaches that ## \frac{ 2\pi k R E}{\hbar c} ##. And I am suggesting that we look for a resolution that shows its effects during that approach.
PeterDonis said:
Please give specific references. What you are describing might be a viewpoint that is given in the literature, but it's certainly not the only one.
Here are some that are worth mentioning:
* Most recently
that dark energy report (also
here). This article suggests that BH generate dark energy. Given that I see the "dark energy" expansion effect as a fruitful avenue, I also see a tie-in to this article.
* Published in 2017 by Science Direct
Argues that the Hawking Radiation source is within a BH "atmosphere": It's hardly an argument for adjusting the event horizon, but at least it's focusing on what happens as you approach that horizon.
* Published in 2018, "
Information Preservation and Weather Forecasting for Black Holes": Hawkings actually argued for some way of addressing the information paradox by replacing the "hard" event horizon with an apparent one. I'm not saying that he had the answer. But, from my point of view, he was looking in the right direction.
PeterDonis said:
This is personal speculation and is off limits here.
The only important point I was trying to make is that it should be possible to resolve the information paradox and maybe the whole event horizon geometry by looking at that Bekenstein Limit.