How does a black hole know how big it should be?

  • Thread starter Slamfu
  • Start date
  • #26
2,081
104
Yeah I' ve seen that argument before. In the case of using entanglement for communications. I have no wish to misdirect this thread. Howevee to me thats like saying a particle either has all or no information till examined
 
  • #27
PeterDonis
Mentor
Insights Author
2019 Award
31,223
10,119
I have no wish to misdirect this thread. Howevee to me thats like saying a particle either has all or no information till examined
This should really be discussed in the quantum physics forum, not here; getting into it further here would indeed misdirect the thread. If you want to post this as a separate thread in the quantum physics forum, feel free to put a link here so whoever is interested can follow up.
 
  • #28
2,081
104
Agreed though there is no need to add another post to something thats already been disussed here countless times lol
 
  • #29
5,601
40
PeterDonis:
...The outside universe doesn't have to "see" any changes in the singularity; it "sees" the mass falling into the hole...,

Yes. For those trying to get a handle on BH descriptions, consider that our math
covers the BH except for the singularity at the center...that is where we have no description, not via relativity nor quantum mechanics....On the other hand, the horizon of a black hole, another type of singularity, a surface where causality between inside the BH to the outside is lost and where we think we understand the physics.

A BH is the ultimate 'roach motel': you can get in, but you can't get out!

So whatever model and space time space-time structure you consider, like Schwarzschild for example, or the more general Kerr [with some rotation] nobody knows just what happens when the radial component of the metric goes to infinity...that's the center singularity.

There is another 'singularity' when the temporal component of the metric goes to infinity....the horizon.....time appears to stop at the horizon for a distant outside observer....but this is a coordinate effect, not a physically real local effect... so another coordinate set, like those of a free falling observer continue smoothly thru the 'apparent singularity'....
 
  • #30
5,601
40
Here are excerpts of a description I don't see too often in these forums:


Black Hole Complementarity

Leonard Susskind, THE BLACK HOLE WAR (his arguments with Stephen Hawking)

In this view, all the information ever accumulated by a BH is encoded on a stretched horizon...a Planck length or so outside the event horizon and about a Planck length thick. This is a reflection of the Holographic principle: all the information on the other side of an event horizon is encoded on the surface area of that event horizon....

Of every 10,000,000,000 bits of information in the universe, all but one
are associated with the horizons of black holes. [So if you can lose information via black holes, it a really,really,really big deal.]


(p238) Today a standard concept in black hole physics is a stretched horizon which is a layer of hot microscopic degrees of freedom about one Planck length thick and a Planck length above the event horizon. Every so often a bit gets carried out in an evaporation process. This is Hawking radiation. A free falling observer sees empty space.

(p258) From an outside observer’s point of view, an in falling particle gets blasted apart….ionized….at the stretched horizon…before the particle crosses the event horizon. At maybe 100,000 degrees it has a short wavelength and any detection attempt will ionize it or not detect it!

(p270)…. eventually the [incoming] particle image is blurred as it is smeared over the stretched horizon and….and the image may (later) be recovered in long wavelength Hawking radiation.
PS; In his argument over the years with Stephen Hawking, Susskind was correct in his interpretation of BH !


Here is an online source describing BH recommended to me by others in these forums...some good insights..:

http://www.jimhaldenwang.com/black_hole.htm
Spacetime Geometry Inside [and around] a Black Hole

by Jim Haldenwang
written Nov. 12, 2004
revised July 30, 2012
 
Last edited:
  • #31
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,430
6,725
Naty, I wonder if it is correct to call the EH a "surface" since it is in no way physical and really is just a spherical coordinate r.
 
  • #32
5,601
40
I wonder if it is correct to call the EH a "surface" since it is in no way physical ....
It is a causal boundary and to me that's quite physical....but what we call it varies a lot.
In terms of the Holographic principle, 'surface' seems especially common.
 
  • #33
PeterDonis
Mentor
Insights Author
2019 Award
31,223
10,119
Naty, I wonder if it is correct to call the EH a "surface" since it is in no way physical and really is just a spherical coordinate r.
The term "surface" is pretty general; it can apply to just about any submanifold of a spacetime. The EH is the set of all points in the spacetime with r = 2m, but with no other coordinate constraints. A more precise term for it would be a "null 3-surface", meaning a submanifold with three linearly independent tangent vectors, one of which is null. (The other two are spacelike.)

As far as whether the EH is "physical", it's no less so than any other submanifold. Since it's an outgoing null surface, outgoing light rays emitted exactly at the EH stay at the EH, so there can certainly be physical things that "mark out" the EH.
 
  • #34
Nugatory
Mentor
12,988
5,699
Naty, I wonder if it is correct to call the EH a "surface" since it is in no way physical and really is just a spherical coordinate r.
It's an unambiguously specified set of points in spacetime. No matter what coordinates you're using, if you present me with the coordinates of a point, I'll be able to answer the question "is that point on the EH?" and the answer will be same no matter which coordinate system you choose. That strikes me as a pretty good operational definition of something that is "physical".
 
  • #35
5,601
40
I wonder if it is correct to call the EH a "surface" since it is in no way physical and really is just a spherical coordinate r.
I was just reading the other posts and remembered ALL the horizons we discuss in the forums have 'physical' attributes...like the Rindler horizon associated with Bells Spaceship paradox and Unruh effect....and Hawking radiation of black holes.

In fact perhaps the craziest horizon of all would be that during cosmological inflation....when the original particles [primordial perturbations] from the Big Bang were widely dispersed and sparse but were repopulated by the inflationary expansion...which only happens if a horizon is present......in other words geometrical curvature horizons induce the appearance of particles!!!.


Somehow, it appears, that an accelerating space-time or even accelerating observers, which are accompanied by horizons, induces localized mass energy...particles. Geometric circumstances create particles!


Check out this discussion with links,papers, and concepts:

https://www.physicsforums.com/showthread.php?t=590798


bapowell has an explanation with some math and says in post #17:

It's a nice exercise though to work through the evolution of a scalar field fluctuation during inflation, from its birth in the vacuum out to super horizon scales if you haven't done it. What you find once you've done this is that you end up with a spectrum of perturbations across a range of length scales.
'perturbations' ARE particles! Without such horizons we would be in an empty universe.
 
Last edited:

Related Threads on How does a black hole know how big it should be?

Replies
9
Views
1K
Replies
3
Views
662
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
2
Views
573
  • Last Post
Replies
4
Views
1K
Replies
11
Views
3K
Replies
2
Views
663
Replies
9
Views
5K
Replies
10
Views
876
  • Last Post
Replies
1
Views
2K
Top