What Are the Mysteries of Black Holes and Their Impact on Time and Motion?

[ladykrimson]

Hello there,

I am new to the forums, and relatively new to physics. Please bear with me as I am still learning the intricacies of the subject. I have always been fascinated with science, but I missed several opportunities to study it academically. Most of my knowledge is self-learned through documentaries, books, and searching the internet. If I am mistaken about certain things, feel free to point it out, and I will consider it a valuable learning experience.

I am fascinated with the workings of black holes. It has been a mission of mine to learn as much as I can about them. I have many speculations, but I would like to dismiss the ones that are unlikely or impossible. It could be that I am overlooking a simple law of physics that I have not yet learned, so I would be grateful for any feedback. I also have a few questions.

We suspect that even light cannot escape the gravity of a black hole because we are unable to see them or detect any non-visible light emanating from them. Is it possible that all motion inside a black hole has ceased? Perhaps the density has reached a point where motion is no longer possible.

I have heard many theories that time slows down relative to ones proximity of a black hole. Is it possible that only one's perception of time that slows? If a person performing an action could stand next to a black hole (and survive!) and we are viewing them from a further distance, time would not be slow from their perspective. Like the light from stars, it just takes a little longer for the light to reach us in order for the viewer to see the performed action. Does this sound plausible?

 

[Christov84]

Hi There,

Im not sure but id say:

The only motion that would be possible would be towards the singularity.

your perception of time stays constant. I.E your not aware time is slowing as you approach.

If you were looking outwards from a black hole(this is a bit flawed i know but bare with me) you would still "see" time moving normally.

If you could somehow move from out of the black hole and catch up with an outside observer to compare watches then you would find your clock would be way way out from theirs.

Or potentially you would see time accelerate as you then move away from the gravity source(black hole)?

 

[Chronos]

The event horizon of a black hole is the point at which the escape velocity reaches the speed of light. Photons inside the event horizon are effectively trapped. The best they can do is endlessly orbit the black hole. An observer orbiting at a safe distance could send in a probe equipped with an atomic clock [identical to the ship's clock] and 2 way radio. According to calculations, the probe should cross the event horizon at precisely midnight ship time. When the ships clock strikes midnight, the probe appears frozen in time at the event horizon. When the probe's clock strikes midnight, the ship [and the rest of the universe] appears frozen in time.

This bizarre episode of 'black hole' is brought to you by general relativity. The ship never hears the probe clock strike midnight due to gravitational redshift. The probe never hears the ship clock strike midnight because it is falling too fast for photons from the ship to catch up with it. Both the probe and ship perceive nothing remarkable about the passage of time in their own reference frame.

 

[ladykrimson]

Hi There,

Im not sure but id say:

The only motion that would be possible would be towards the singularity.

Hm. I was wondering if it was possible that the density of a black hole is not infinite.

your perception of time stays constant. I.E your not aware time is slowing as you approach.

If you were looking outwards from a black hole(this is a bit flawed i know but bare with me) you would still "see" time moving normally.

If you could somehow move from out of the black hole and catch up with an outside observer to compare watches then you would find your clock would be way way out from theirs.

Or potentially you would see time accelerate as you then move away from the gravity source(black hole)?

That is my point, precisely. Time does not accelerate or decelerate; only our perception tells us that it does.

 

[Chronos]

It is possible whatever exists at the center of a black hole is not infinitely dense. I think quantum physics forbids the existence of a 'true' singularity [a point of infinite density]. Then again, I have been known to be wrong. My wild guess is the Planck density. I'm fairly certain I can't be too far wrong. The Planck density is so close to infinite you can hardly tell the difference.

 

[ladykrimson]

It is possible whatever exists at the center of a black hole is not infinitely dense. I think quantum physics forbids the existence of a 'true' singularity [a point of infinite density]. Then again, I have been known to be wrong. My wild guess is the Planck density. I'm fairly certain I can't be too far wrong. The Planck density is so close to infinite you can hardly tell the difference.

Again, forgive me if my views are not very sound; I am still learning.

Black holes grow to be bigger over time as they absorb more material. If they had infinite density, they wouldn't grow. Would they? They would always be the same size.

 

[Nabeshin]

Again, forgive me if my views are not very sound; I am still learning.

Black holes grow to be bigger over time as they absorb more material. If they had infinite density, they wouldn't grow. Would they? They would always be the same size.

Density and mass are not the same thing.

 

[ladykrimson]

Density and mass are not the same thing.

True. Sorry...still learning.

But eventually, space will run out, will it not? There is a finite amount of space between the nucleus of an atom and the electrons that orbit them. When there is no more space, the object would cease to move, would it not?

 

[Nabeshin]

True. Sorry...still learning.

But eventually, space will run out, will it not? There is a finite amount of space between the nucleus of an atom and the electrons that orbit them. When there is no more space, the object would cease to move, would it not?

What happens when matter is crushed to densities approaching the Planck density is certainly far from clear. In fact, if we trust in the uncertainty principle, as we confine the mass to a smaller and smaller volume it actually moves faster and faster!

 

[ladykrimson]

What happens when matter is crushed to densities approaching the Planck density is certainly far from clear. In fact, if we trust in the uncertainty principle, as we confine the mass to a smaller and smaller volume it actually moves faster and faster!

So there is never a point at which motion ceases?

 

[Robot B9]

A simple (perhaps too simple?) way to think of a black hole is that it has essentially three regions.

Its "surface" would be the event horizon. We can only see stuff that is just above this surface, probably just glowing gas and particles. Anything that passes thru (going down into) the event horizon is no longer visible.

At the center is the singularity. Its just a point. Everything, all the mass of the black hole is concentrated here. It is an infinitely small point and infinitely dense.

In between the singularity and the event horizon is a sort of no mans land. Particles only travel from the event horizon to the singularity, its a one way trip. If there were no matter falling into the black hole this region would be very very empty, way beyond the empty we think vacuum is.

So that's it, a hollow ball with a tiny point at the center.

 

[Drakkith]

So there is never a point at which motion ceases?

As far as we know, there is not. Take a neutron star for example. The atoms are under so much pressure that the electrons are "forced" to combine with protons to form Neutrons. So there are no more atoms, only a very dense mass of neutrons. After that there are theories that if the mass is even gretear, the neutrons themselves will disappear as the quarks that they are composed of either combine or do other weird things and we get a quark star. At a certain mass limit, nothing can hold matter together and it becomes compressed into an infinite density in a black hole. At least, that's what we THINK happens. It is still very much under debate. (The details are under debate, not the fact that a star collapses into a black hole.)

 

[Nabeshin]

At least, that's what we THINK happens. It is still very much under debate.

I don't know if I'd say that. I think it's very widely accepted that once you compress a neutron star beyond the TOV limit, you will form an event horizon. So, for all practical purposes this object IS a black hole. Observationally, whether or not there is a true singularity is a moot point -- we cannot know, as it is shielded by an event horizon.

The 'true' nature of the singularity is what is under debate, specifically as to how quantum physics would handle such a situation. But I think the formation of the event horizon, and thus the classical observable black hole, is not really in question.

 

[Drakkith]

I don't know if I'd say that. I think it's very widely accepted that once you compress a neutron star beyond the TOV limit, you will form an event horizon. So, for all practical purposes this object IS a black hole. Observationally, whether or not there is a true singularity is a moot point -- we cannot know, as it is shielded by an event horizon.

The 'true' nature of the singularity is what is under debate, specifically as to how quantum physics would handle such a situation. But I think the formation of the event horizon, and thus the classical observable black hole, is not really in question.

Sorry, I meant that on the whole, the way a star develops into a black hole and the specifics about what happens afterwards are under debate.

 

[ladykrimson]

So there are no more atoms, only a very dense mass of neutrons. After that there are theories that if the mass is even gretear, the neutrons themselves will disappear as the quarks that they are composed of either combine or do other weird things and we get a guark star.

Hold the phone. A quark star? That is a new one for me. I will have to look those up.

Thanks for everyone's comments! I learned quite a bit!

 

[Drakkith]

Hold the phone. A quark star? That is a new one for me. I will have to look those up.

Thanks for everyone's comments! I learned quite a bit!

I only heard something about it thanks to wikipedia.

http://en.wikipedia.org/wiki/Quark_star

 

[Chronos]

Quark stars remain hypothetical, although several suspects exist. See, for example:

http://arxiv.org/abs/1010.5530
Quark nova imprint in the extreme supernova explosion SN 2006gy: the advent of the Quark Star

Hybrid stars with a quark core and degenerate neutron outer layer are also in play. Another paper:

http://arxiv.org/abs/1012.2939
Maximum Mass of the Hot Neutron Star with the Quark Core