B Spagettification and a singularity

[Ibix]

No, they don't.

Ah yes, sorry, misread the question. Same radius, different angular coordinates will bunch up because there's less area. Same angular coordinates different radius will separate just like in Newtonian gravity (qualitatively).

 

[Dale]

No, that's true. But if they cram up in the inside, don't they cram up in the outside too? Or do particles (not angularly but radially separated) cram up, seen from the outside, on the horizon?

This is what “spaghettification” means: Things get crammed up in the horizontal directions and stretched out in the vertical direction. This is basically the familiar form of tidal forces from Newtonian gravity.

 

[BoraxZ]

This is what “spaghettification” means: Things get crammed up in the horizontal directions and stretched out in the vertical direction. This is basically the familiar form of tidal forces from Newtonian gravity.

Yes. But on the inside particles get crammed in the angular directions and seen from faraway on the outside the particles seem to get crammed in the radial direction.

 

[PeterDonis]

on the inside particles get crammed in the angular directions

Which, as noted, is part of spaghettification.

seen from faraway on the outside the particles seem to get crammed in the radial direction.

Which has nothing whatever to do with spaghettification so it's off topic for this thread.

 

[Dale]

on the inside particles get crammed in the angular directions and seen from faraway on the outside the particles seem to get crammed in the radial direction.

I am not sure why you believe that, but it is untrue. Tidal forces always stretch in the vertical direction and compress in the horizontal directions, both inside and outside the horizon.

Perhaps you are thinking of some coordinate-based description. If so it is yet another reason not to take coordinates too seriously.

 

[BoraxZ]

I am not sure why you believe that, but it is untrue. Tidal forces always stretch in the vertical direction and compress in the horizontal directions, both inside and outside the horizon.

Yes, but on the outside the cramming seems to take place spatially on the horizon for radially separated particles. In the inside these particles all collect at the singularity time but get spatially separated.

Particles that are angular separated (and not radially) don't get (totally) crammed on the horizon, while in the inside they get totally crammed angularly.

 

[PeterDonis]

I am not sure why you believe that

I think he is referring to what I described in post #120. Which, as I noted, is only an optical effect. And which in any case has nothing to do with spaghettification.

 

[BoraxZ]

Perhaps you are thinking of some coordinate-based description. If so it is yet another reason not to take coordinates too seriously

Can we describe the hole without coordinates? With invariants?

 

[PeterDonis]

Can we describe the hole without coordinates? With invariants?

Of course. Many of the statements that have been made in this thread are about invariants.

 

[Dale]

I think he is referring to what I described in post #120. Which, as I noted, is only an optical effect. And which in any case has nothing to do with spaghettification.

All this obsessing over what distant observers visually see is rather pointless. But at least it isn’t obsessing over coordinates which is pointlesser

 

[BoraxZ]

All this obsessing over what distant observers visually see is rather pointless. But at least it isn’t obsessing over coordinates which is pointlesser

You got a point there!

Somehow, what we see from faraway is the opposite of what happens inside. From afar the particles seem to cram up on the Schwarzschild radius, while on the inside they cram up on the singularity time and angular directions, while their radial distances from each other have grown. Very loosely speaking.

 

[PeterDonis]

pointlesser

Is that a word? I guess it is now, since you've used it.

 

[Ibix]

pointlesser

Is that a word? I guess it is now, since you've used it.

Should be "eventlesser" in a discussion about spacetime.

 

[HansH]

I meant what vanhees71 showed in his comment. Two particles falling together freely, after which one of them (or both) accelerates away from the other to meet up again later in. Can they meet up again behind the horizon?

I think tis is still the essential part of my original question (but not answered yet I suppose, or did I mis something? could of course be after 140 answers). So constant accelarating away from eachother, how can they ever meet again?

 

[PeterDonis]

I think tis is still the essential part of my original question

Your original question was about spaghettification. That has nothing to do with the twin paradox. The twin paradox subthread is a hijack that will shortly be moved to its own thread.

 

[PeterDonis]

constant accelarating away from each other, how can they ever meet again?

Any particles involved in the spaghettification of an object as it approaches the singularity, if the spaghettification is moving them apart, will not meet again.

 

[PeterDonis]

The twin paradox subthread is a hijack that will shortly be moved to its own thread.

And now it has been:

https://www.physicsforums.com/threads/the-twin-paradox-and-black-holes.1050610/

 

[HansH]

ok thanks. my original question was indeed about spagettification, but the reason was that I was wondering if this spagettification process continues no matter how close you are to the singularity. (as I would expect and now asume you confirm that in #157, but could be that I do not understand you exactly)

 

[HansH]

probably I am a bit confused about the term 'size' and where we can speak of a 'size' of something. outside the event horizon we can speak for example of the size of an atom. With a person in freefall into a black hole Iassume the atoms still are there so also the size can be measured an also the size between 2 atoms separating due to the spagettification process. but how close can we be to the singularity before size becomes a useless definition so when is the spagettification process not able anymore to be followed by an observer (being very close nearby)?

 

[BoraxZ]

I think tis is still the essential part of my original question (but not answered yet I suppose, or did I mis something? could of course be after 140 answers). So constant accelarating away from eachother, how can they ever meet again?

All particles end up in the r=0 singularity. Spacelike separated. The r is timelike. So two particles falling in after one another end up at the same time but spatially separated. Their clocks showing different times (when synchronized before falling in).

 

[PeterDonis]

I was wondering if this spagettification process continues no matter how close you are to the singularity.

Yes, it does. Your reading of the previous post about this is correct.

probably I am a bit confused about the term 'size' and where we can speak of a 'size' of something.

Whether we can do this, and what "size" means, depends on the something and the circumstances.

At some point during the spaghettification process any kind of internal structure that determines a "size" of anything will be destroyed. For example, at some point atoms will get torn apart by it, so we can no longer speak of the size of atoms since there aren't any.

 

[PeterDonis]

two particles falling in after one another

The general topic in this thread is spaghettification, i.e., an object falls in, initially, as a single object, and the discussion is about what happens to it as it approaches the singularity--it gradually gets torn apart by increasing spacetime curvature. Two originally separate particles falling in one after the other is not quite the same scenario.

 

[BoraxZ]

The general topic in this thread is spaghettification, i.e., an object falls in, initially, as a single object, and the discussion is about what happens to it as it approaches the singularity--it gradually gets torn apart by increasing spacetime curvature. Two originally separate particles falling in one after the other is not quite the same scenario.

Yes. But aren't two particles starting at the same event, while holding one back, after which you release it, the same as an extended object?

 

[PeterDonis]

ren't two particles starting at the same event, while holding one back, after which you release it, the same as an extended object?

No. An extended object has interactions between its particles.

 

[BoraxZ]

What time is it inside the hole?

 

[BoraxZ]

No. An extended object has interactions between its particles.

Yes, that's true. But these are overcome inside so they end up spatially separated still. But less indeed.

 

[BoraxZ]

No. An extended object has interactions between its particles.

Will even a proton get ripped apart? Or maybe even quarks (when there are preons inside it)?

 

[HansH]

two particles falling in after one another end up at the same time

which time?

 

[PeterDonis]

What time is it inside the hole?

This question is not answerable. Please do not clutter the thread with pointless questions.

 

[PeterDonis]

which time?

He means the singularity, which is a moment of time.