'Naked' Singularites

What are they? How could they possibly exist?

Fuzzy recollection is that it could happen from black hole evaporation or something dealing with spin.

I think they are prohibited by the laws of nature. I seem to recall someone once speculating about such a thing being possible but I don’t see how. If light can’t escape the singularity (and therefore nothing can escape) how are you supposed to ever get information about one to you?

See http://www.straightdope.com/mailbag/mhawkingradiation.html

That is just too weird.

The day I post it there is an article on it in SD? I need to look at the front page more closely.

Still, if it did exist, what would it look like? Why would/could it destroy the universe?

I’m in a black holes course, so I’m just a student on this, but I can tell you what I learned on Friday. Geometric GR predicts things like “singularities”, where coordinates break down and you can’t describe space geometrically. It also predicts things like “horizons”, from which nothing can escape. A normal black hole is a classic example of a singularity inside a horizon. So even though physics breaks down at the singularity, you don’t have to worry about it, because it’s blocked by the horizon. The so-called Cosmic Censorship Principle is a conjecture which states that it will always work out like this; that a singularity will never exist without a horizon (“naked”). Although there are some theoretical situations in which you have a naked singularity, for instance, a black hole with a great electric charge, many assume that the Cosmic Censorship Principle is true, and that these things do not exist in the real universe.

I thought he said “Naked celebrities.” :confused:

A singularity with a charge an an angular momentum could be naked.

But what would it ‘look’ like? :slight_smile:

Moreover, why would it destroy the world? Would that be because if we could recognize a naked singularity, we would necessarily be within the horizon and therefore doomed?

Well, it could show ya, but then it’d hafta kill ya.

Hmm, the other problem I see is that it was once thought that during or just after the Big Bang, it’s possible that a great number of ‘quantum’ black holes were created. Quantum black holes are teeny black holes much too small to have been created by the process of a collapsing star.

Well, since these quantum BH’s are so small, according Hawking they would have already radiated away all thier energy long ago and have ceased to exist as BH’s.

So, either there’s already some number of naked singularities scattered around marking the graves of quantum BH’s, or quantum BH’s never existed in the first place, or BH’s do not leave behind naked singularities. So which is it?

The last one - quantum BH’s that “evaporate” due to Hawking radiation eventually just disappear with a large bang.

I’ve never understood how a singularity can not have an event horizon, i.e. how can a singularity form when the escape velocity is below c? Although maybe a way to look at it is that a naked singularity is what you see when you fall into a black hole, after you’ve passed the event horizon - then a naked singularity could be considered one where the event horizon is infinitely far away?

Also I read somewhere that the Big Bang could be thought of as a naked singularity.

Well that’s just it; we don’t know. We have no good physics to describe what happens to a photon that passes through a singularity.

Even for an observer inside the horizon, the singularity remains in the observer’s Absolute Future. So, you would not be able to see it even inside the horizon.

My Absolute Future? Wazzat?

http://physics.syr.edu/courses/modules/LIGHTCONE/schwarzschild.html

See the link for a diagram of this. The tipping of the light cone causes the time axis to become the space axis and vice versa and therefore you can no more avoid the singularity than you can avoid tomorrow. Your future light cone defines your absolute future.