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  4. Do objects ever disappear into black holes?
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Do objects ever disappear into black holes?

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Offline yor_on

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Do objects ever disappear into black holes?
« Reply #20 on: 16/09/2011 05:25:29 »
As the process slow down as seen from Earth the light will redshift. I don't know how far it can redshift before becoming impossible to measure but Raw is right. There will be a point where we can't get any more information of that object as the 'clock' stops to us observing it. And that clock do stop somewhere before passing the Even horizon as observed by us.

What I was thinking of Graham was the fact that the singularity's center will be where all mass join, I don't know what happens there with 'gravity', if it becomes measurably larger at the Event horizon as the mass disappears.
==

To me the question has to do with 'infinities'. Because that is what that center represent, all of them, no matter their apparent 'size' to us measuring the event horizon. Also it is so that space might 'deform' inside that black hole, expanding enormously to those being inside it.

That opens for a interesting question, assume that space do that, which I definitely do. What happens to the 'gravity' represented by the Event Horizon to us outside?

Will it weaken?
=

Heh, 'shrink' would be the better word there.
« Last Edit: 16/09/2011 11:42:10 by yor_on »
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Offline imatfaal

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Do objects ever disappear into black holes?
« Reply #21 on: 16/09/2011 10:03:50 »
Quote from: yor_on on 16/09/2011 05:25:29
As the process slow down as seen from Earth the light will redshift. I don't know how far it can redshift before becoming impossible to measure but Raw is right. There will be a point where we can't get any more information of that object as the 'clock' stops to us observing it. And that clock do stop somewhere before passing the Even horizon as observed by us.
Quote from: graham
It's a confusing subject. I think you are right that the BH does grow to encompass some of the matter very close to the EH (as perceived by a distant observer) though. This seems out of kilter with the formula, but then that is derived from a perfectly spherically symmetric Schwartzchild metric. I have to say I am not sure about this, but if this were not the case then you have to wonder how a BH can ever be formed because accreting matter would always take an infinite time as observed from a distance
.

I am not sure it does stop entirely - this is an artifact of using the wrong coordinate system .  It stops if you use a schwarzchild coordinates (which works fine outside black hole) - but the schwarzchild is not used for calculations actually nearing and at the black hole because of the mathematical singularity it causes (ie it pumps out an undefined answer).  So whilst the schwarzchild solution practically defined EH's it is not usuable at the EH at which point we would switch to Kruskal–Szekeres coordinates or Eddington–Finkelstein coordinates.  One thing is clear this is not settled and it is an area of great importance.

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Offline yor_on

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Do objects ever disappear into black holes?
« Reply #22 on: 16/09/2011 10:51:41 »
Yeah, it's a weird subject. But to me time is a definition that has two parts. One is your intrinsic 'arrow' that always is the same, no matter where you are. The other is based on invariant radiation, and the relations you find between that intrinsic 'clock' relative what you observe. Ah, they are the same in a way as you too is defined by 'c', at least macroscopically.

I think you can find 'times arrow' to stop, relative your own, I don't think you ever will find it to 'back up' relative yours though. Because that would destroy the universe as one common causality chain having one direction. If you imagine SpaceTime as consisting of 'clocks' ticking in every point, they all will have have one timely direction, into the 'future'. And even though some of them might be found to slow, or accelerate, relative you, none of them will start to tick into the past, not inside SpaceTime as measured there. Ultimately 'time' and 'times arrow' is about changes, with the arrow defining a causality chain.

The other side of it is superpositions.

But to fall out there needs to be a 'change'.
« Last Edit: 16/09/2011 10:53:47 by yor_on »
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Offline yor_on

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Do objects ever disappear into black holes?
« Reply #23 on: 16/09/2011 12:00:50 »
Then there is one thing more, and I guess more than that too :) All event horizons are observer dependent. That means that your definition of where it exist won't be the next observers definition. And as far as I know they all will see Hawking radiation coming from their own definition of where it is, assuming that it exist.

There is an idea of a Event Horizon though, that is determined through some universal topology/geometry, but to define that one you will need a knowledge of the whole of the universe through all time coming and passed as I understands it. Why that is, is because you can't lift out 'time' from SpaceTime, at least not in Einstein's definitions. They are one whole packet, and observer dependent.
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Offline yor_on

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Do objects ever disappear into black holes?
« Reply #24 on: 16/09/2011 12:36:14 »
Let's move this question further. Assume something falling into a black hole.

Will it reach the center?

It depends actually on your way of viewing the world. Physics do not have a certain answer to that one, it may or it may not, and actually, it may be both :)

If you trust in some hidden cosmic clock then you can't have two representations which both will come true, but if you go out from locality as defining your SpaceTime then there will exist a possibility of two answers.

Which means that to the Earth observer the guy will hang on the Event Horizon. But to the guy infalling, he will reach the center in a measurable time, according to his definition of 'time passed'.

Then we come to the question if the 'time' for the universe won't 'run out' before the free falling guy passes that Event Horizon, as the universe should start accelerating (time wise) to him. And that one is indeed tricky as it also implies that there can be no infalling matter ever reaching that Black hole before it evaporates.
==

Connecting those you can come to a definition in where it is correct that there exist two representations, but also where we find the last assumption forbidding it, as the universe will 'run out' before he meets the BH center.

Which in a way is nice, but confusing :)

Although it does keep a common causality in where we won't find two contradictory things happening, 'simultaneously' or not, macroscopically at least. But even in QM I doubt you will see two contradictory effects simultaneously. The universe seems very clever to me.
==

What it all comes down to, to me, is one question.
What is time?

Is it a local phenomena solely, where the description of a common 'seamless' universe only can exist locally, observer dependent? If it is so you automatically will have one definition, and one truth, per observer.

Then what makes us all find ourselves sharing the same 'universe' is our inability to see the other persons 'universe' simultaneously. Maybe if we could 'split' our observations into a so called 'superposition' in where all is observed from all 'points & times' simultaneously, we would find the true 'universe', but then 'times arrow' would lose all meaning.

Or you expect there to be a hidden universal clock defining all local clocks.

The difference between me discussing a 'ground state' of durations as being the same in all points, and this 'universal clock' is very subtle but in my definition we all have a same duration, as found if we could superimpose upon each other. And that beats to 'c'. And 'c' makes SpaceTime a Jello, compressing and deforming all attributes there is, including all others 'time', and distance, and all of it true, depending on you relative your cosmos.
« Last Edit: 16/09/2011 20:50:02 by yor_on »
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