## How To Destroy a Black Hole 364

KentuckyFC writes

*"The critical concept that makes a black hole black is the event horizon: a theoretical boundary in space through which light and other objects can pass in one direction but not the other. Since light cannot escape the event horizon, it must be black. The event horizon is a nuisance to astrophysicists because it hides the interesting new physics that must go on inside a black hole. What they would like is a way to get rid of the event horizon so that they can see what goes on behind it. It turns out that just such a thing may be possible, say physicists. According to the mathematics of general relativity, the event horizon should disappear if a black hole were fed enough charge and angular momentum relative to its mass. However the calculations are so fiendish (PDF) that nobody knows whether the black hole would shed this extra angular momentum and charge before it could settle into a stable 'naked' state. However, the possibility that the event horizon could be destroyed raises the question of what astrophysicists would see behind this veil. According to some, black holes are regions of spacetime with infinite curvature called singularities. Many believe that 'naked' singularities cannot exist in nature. And yet there are enough question marks to suggest that this mystery is far from settled."*
## Re:look, i like making fun of star trek technobabb (Score:1, Interesting)

Rule 34 only applys if they exist... so if you can find port of a naked sigularity there's a good posability that they exist

## Naked Event Horizon (Score:4, Interesting)

It depends on scale more than anything. Small black holes almost certainly require a singularity, but a black hole the mass of a galactic cluster actually has a very low average density. So while at the event horizon space-time is very much distorted, on the inside it may not be distorted enough to overcome common everyday forces (the trick of treating a collection of mass as a point source of force doesnt work from inside that collection of mass)

## Re:Really? (Score:4, Interesting)

I would like to find a black hole that's just barely massive enough and then try this.

Finally, I think they're just trying to do a thought experiment whereby they change the shape or topology of the event horizon. Imagine a toroidal event horizon for example.

## Re:Whaazzaaaa? (Score:3, Interesting)

## Re:Something I was wondering (Score:4, Interesting)

It seems to me that in order for an established orbit to exist on the event horizon, the orbiting matter would have to be going at the speed of light. I would further presume that any matter orbiting within the event horizon would have to be /exceeding/ the speed of light.

To my knowledge, matter cannot travel at or beyond the speed of light.

## Re:But scifi writers already knew this! (Score:3, Interesting)

And yet, a small / primordial-enough black hole, after evaporating down to (and just below) its critical mass, could be seen as exploding back into flat-space, no? So the phrase could make sense?

## Re:look, i like making fun of star trek technobabb (Score:1, Interesting)

Hold it... Rule 34 states that "if it exists, there's porn of it." It says nothing about "if there's porn of it, then it exists." I'm willing to give you the benefit of the doubt since you said "there's a good possibility that they exist," but you shouldn't assume that the converse of an if-then statement has the same truth value as the original.

Exactly how you would make porn of something that doesn't exist is left as an exercise to the reader.

## Re:Would the event horizon retreat if you approach (Score:2, Interesting)

Hello,

Suppose you were falling into a black hole, and you didn't get turned into spaghetti (as might be possible if you're approaching the event horizon of a supermassive black hole). Would the event horizon seem to retreat before you? I mean, light can't escape a black hole's event horizon as we see it, but if you're falling in, wouldn't you be able to see further into the black hole as you fall?

--PM

Well, since sight depends on light reflecting off of objects to work... No, as you approached the event horizon, you still wouldn't be able to see into the black hole, as no light would be escaping (hence no visual information conveyed).

As to other point, no, the event horizon would not appear to be receding. You would seem to be approaching it normally (from your perspective), however due to time dilation, the rest of the universe would seem to be aging quite rapidly compared to you.

## Re:A little perspective here? (Score:3, Interesting)

## Re:Just wait a little while... (Score:5, Interesting)

That allows information from inside the event horizon to leak outside (which is all the astrophysicists really need) and allows the evaporation of black holes, but the event horizon would remain intact. However, we have never seen Hawking Radiation (yet) and it depends some on certain assumptions being valid. One of these assumptions is that the singularity is something "physical".

A lot of cosmologists don't like infinities, so don't like singularities, but let us consider what "infinite gravity" would actually mean. It would mean you have a vertical gravitational well, with the universe being the "walls" of this well. As far as the universe is concerned. the actual hole that makes up the interesting part of the well is on the outside, just as the air in a physical well is outside the brick lining that comprise the walls. Since what we call "physical" are the objects inside the universe, it makes no logical or rational sense to talk of something that is on the outside as being "physical". You can detect it using the usual rules of topology and geometry (you can't apply any topological transformation to a torus to produce a sphere), but if you picture yourself as a Flatlander on the surface of said torus, you could NEVER observe the region on the outside that distinguishes the torus from a sphere. You could infer it existed, you could even prove that it has certain properties, but that's it.

Cosmologists and topologists don't get along, which is why space/time existed as fact in geometry long, long before any physicist accepted it was real. Einstein is said to have loathed and despised the concept, and only grudgingly accepted it had to be true after being dragged, kicking and screaming, by his theories into reaching no other answer. (You might gather from this I have a low opinion of certain branches of physics.)

But precisely because the rules of topology FORBID a torus to become a sphere, it would be impossible for a genuinely infinite-gravity singularity to evaporate completely. Instead of their evaporation speeding up as they shrank, it would have to slow down -- if they evaporated at all. Entirely the opposite of what physics expects. There's no reason for them TO evaporate, however. It is only required in cosmology to meet the requirements of the 2nd Law of Thermodynamics, but thermodynamics only applies to what exists. A hole is a region where the walls do NOT exist.

There is a third possibility. Under the standard model for space/time, time is orthogonal to space. If space is bent at 90' to all other spacial dimensions, then it is no longer space. It is time. This means that not only is there a singularity at the heart of every black hole, it would be the SAME singularity. There would have only ever been one singularity, right at T=0, and the throats of all black holes would be directly and permanently hard-linked to this. There would still be no evaporation at this end of time (it has already happened).

A fourth (and fifth) possibility is that black holes never actually form at all. There's an entire alternative model in cosmology which prohibits them outright, giving you that fourth option. Then, Professor Hawking's work on imaginary time and the curvature of time around singularities would eliminate the need for a singularity outright. If you factor time curving as well as space, then space/time never vanishes to a point. Space/time would become parabolic, giving it a minimal state, but there is no moment in which any variable hits zero or any infinite states are achieved.

There's probably others I've either not heard of, or have heard of and forgotten. But at least five different ways DO exist and are recognized in modern physics as possible in which no black hole singularity of the kind imagined would arise. That means there is simply no theoretical ground (right now) to assume that this new theory has any meaning or would make any sense.

## This doesn't really make sense (Score:2, Interesting)

## Re:In theory, yes. (Score:1, Interesting)

But this blackhole would have no center, remember.

Its center of gravity will be blank space.

Think of a bunch of stars orbiting each other rather fast in a donut.

All we need now is a highly efficient method of blocking / using the temperatures that close to several stars.

Planet-sized metamaterial invisibility cloak anyone?

## Re:Naked Event Horizon (Score:5, Interesting)

I expect some simple math based on the estimated mass and size of the universe would suggest that is not the case unless we have greatly confused some of the variables.

Estimates of the mass of the observable universe range from 3.0E+50 kilo's to 1.6E+60 kilo's. Citations. [hypertextbook.com]

Wikipedia [wikipedia.org] has it as 8.0E+52 kilos.

A black hole with the wikipedia mass has an event horizon radius of approximately 1.9E+26 meters. Compare with the radius of the observable universe, which is umm.. approximately 1.3E+26 meters. In other worse, if the wikipedia mass is correct, then we are inside a black hole assuming that the Schwarzschild equation for calculating event horizons is correct. I think the existance of dark energy has changed the game tho, such that we certainly cont be confident of the Schwarzschild radius calculation at such large scales.

## Free-fall is assumed. (Score:3, Interesting)

It is assumed that you are falling into the black hole accelerating according to the force of the gravitational pull of the black hole. So you WILL pass through the event horizon in a heartbeat.

Think of it this way:

Even if you had a magical platform that you could stand on just /outside/ the event horizon, you'd still be dead. The amount of gravity pulling down on your would not just stop your blood from flowing upwards, it would crush you into a puddle of goo on the platform.

The ONLY way you could survive the fall into the black hole would be under freefall. Any attempt to appreciably slow down your fall would result in you getting crushed. So any trip through the even horizon will be very, very fast. Probably an an appreciable fraction of the speed of light.