Do any real macroscopic black holes have a singularity?

[Wo Wala Moiz]

TL;DR Summary

Time dilation means the collapse of the star's core stops after the event horizon is formed.

Here's my reasoning.

The event horizon is the point where the escape velocity becomes greater than the speed of light.

This results in the event horizon spacetime boundary having infinite time dilation.

So, that must mean that inside the boundary of the event horizon, time dilation must, again, be infinite.

So how would the collapsing core of a star keep collapsing? Due to infinite time dilation, the moment the event horizon forms, the collapse should stop, from the perspective of the rest of the universe. And indeed, before the event horizon forms, its rate of collapse should be observed to become slower and slower.

I thus argue no actual macroscopic black hole has a singularity, and if you added enough to spin to a black hole, you wouldn't get a naked singularity, but the core of a star that would promptly begin collapsing again and eventually form another event horizon.

(That is, unless the spin added to the event horizon transferred to the collapsing core, and the increased angular momentum stops the collapse)

 

[Vanadium 50]

A singularity is not a physical thing. It is a situation where equations break down. For example, the electric field of an electron becomes infinite as r → 0. That does not mean there are no electrons.

 

[PeterDonis]

Time dilation means the collapse of the star's core stops after the event horizon is formed.

No, it does not. This is a common misconception, but it's still a misconception. This Insights article addresses it:

https://www.physicsforums.com/insights/black-holes-really-exist/

The event horizon is the point where the escape velocity becomes greater than the speed of light.

No, it's a point at which the concept of "escape velocity" as you are using it is no longer well-defined, because escape to infinity is no longer possible at all.

This results in the event horizon spacetime boundary having infinite time dilation.

No, it means that at the horizon, the concept of "time dilation" as you are using it is no longer well-defined.

So, that must mean that inside the boundary of the event horizon, time dilation must, again, be infinite.

No, it means that inside the horizon, the concept of "time dilation" as you are using it continues to not be well-defined, as at the horizon (see below).

The rest of your reasoning is invalid because it is based on invalid premises.

 

[PeterDonis]

how would the collapsing core of a star keep collapsing?

This question was answered by the classic paper of Oppenheimer and Snyder in 1939. This series of Insights articles discusses the model first presented in that paper:

https://www.physicsforums.com/insig...-model-of-gravitational-collapse-an-overview/

 

[PeterDonis]

I thus argue no actual macroscopic black hole has a singularity, and if you added enough to spin to a black hole, you wouldn't get a naked singularity, but the core of a star that would promptly begin collapsing again and eventually form another event horizon.

All this is personal speculation: even if your other claims were true (which they aren't), they still do not imply this. Please note that personal speculation is off limits here at PF.

 

[Wo Wala Moiz]

A singularity is not a physical thing. It is a situation where equations break down. For example, the electric field of an electron becomes infinite as r → 0. That does not mean there are no electrons.

Okay, what I mean is that the concept that there is a infinitely dense point in the middle of actual black, which leads to a

A singularity is not a physical thing. It is a situation where equations break down. For example, the electric field of an electron becomes infinite as r → 0. That does not mean there are no electrons.

Okay, in that case, what I meant was that the idea that there is a point of infinite density in the centre of a black hole, which is the reason for a singularity in the equations, doesn't exist in actual macroscopic black holes.

 

[Vanadium 50]

Well, you should be happy then, because GR says nothing at all like what you are talking about.

 

[Dale]

TL;DR Summary: Time dilation means the collapse of the star's core stops after the event horizon is formed.

So how would the collapsing core of a star keep collapsing?

Easy. Use any coordinates other than Schwarzschild coordinates.

 

[PeterDonis]

Moderator's note: Thread level changed to "I".

 

[PeterDonis]

Okay, what I mean is that the concept that there is a infinitely dense point in the middle of actual black

Our actual model of a black hole does not say this. So once again you are reasoning from incorrect premises.

What our actual model of a black hole says is that the singularity at $r = 0$ (1) is a spacelike line, which means it is a moment of time, not a place in space, and (2) is not actually part of the manifold, but is a limiting surface only, so the "infinite density" part is never actually realized; the density just increases without bound as the singularity is approached.

 

[Orodruin]

TL;DR Summary: Time dilation means the collapse of the star's core stops after the event horizon is formed.

Here's my reasoning.

The event horizon is the point where the escape velocity becomes greater than the speed of light.

This results in the event horizon spacetime boundary having infinite time dilation.

So, that must mean that inside the boundary of the event horizon, time dilation must, again, be infinite.

So how would the collapsing core of a star keep collapsing? Due to infinite time dilation, the moment the event horizon forms, the collapse should stop, from the perspective of the rest of the universe. And indeed, before the event horizon forms, its rate of collapse should be observed to become slower and slower.

I thus argue no actual macroscopic black hole has a singularity, and if you added enough to spin to a black hole, you wouldn't get a naked singularity, but the core of a star that would promptly begin collapsing again and eventually form another event horizon.

(That is, unless the spin added to the event horizon transferred to the collapsing core, and the increased angular momentum stops the collapse)

It seems to me that you are essentially basing all of your arguments on statements you picked up from popular scientific descriptions of what black holes are. This will generally never work out well. Popular science is typically written with verbal descriptions and analogies rather than focusing on what the theory actually says. To be successful it must be somewhat sensationalist and give the reader a feeling of understanding where there is often none. It teaches people the broad strokes of things, but does not give actual deep understanding.

Because of this, it is very common that people start arguing based on their perception of a popular description. However, this is generally doomed to be utterly nonsensical for the reasons given above. In order to be able to make arguments regarding a theory it is not sufficient to start from a popular description. You must learn what the theory actually says.

 

[Ibix]

Okay, in that case, what I meant was that the idea that there is a point of infinite density in the centre of a black hole, which is the reason for a singularity in the equations, doesn't exist in actual macroscopic black holes.

As others have noted, your model of a black hole is badly wrong, and your reasoning is based on false premises.

We do have reasons to suspect that a black hole does not contain a singularity. The short reason is that singularities are features of mathematical models, not reality. They are usually indicative of areas where the maths is going wrong somehow and we need a better theory. So we suspect that our models diverge from reality somewhere inside a black hole. What the correct description is remains a topic of active research.

It's a fascinating area, but you do need to understand general relativity and its maths to be able to reason about it. Pop scuence descriptions are evocative at best and plain wrong at worst, simply because ordinary language doesn't have the concepts needed to describe extreme circumstances like black holes.

Sean Carroll's online lecture notes are a good source to learn from, and free for download. You'll need to be comfortable with calculus and special relativity first, though.