# black hole, singularity...

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The discussion is about the contribution of the BH gravitational field, not of the spaceship acceleration.

Since several of you seem not to understand the concept, I can give a rigorous proof that a rod falling radially into a BH gets stretched due to the gravitational field of the BH.

That is precisely what I said.

(Proper) acceleration is absolute, meaning that it isn't relative to the gravitating body.

Right, but there is a difference between "being on a space ship" and "being on a spaceship with a prop acceleration away from the black hole", the latter of which, as swansont pointed out, was not stipulated until your last post.

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Right, but there is a difference between "being on a space ship" and "being on a spaceship with a prop acceleration away from the black hole", the latter of which, as swansont pointed out, was not stipulated until your last post.

You both miss the point, the discussion is about the contribution of the BH gravitational field. Since you three share a misunderstanding, I suggested that I provide a rigorous proof as to how the gravitational acceleration (not the gradient) also deforms the objects. By itself.

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The discussion is about the contribution of the BH gravitational field, not of the spaceship acceleration.

Right. There was no point in introducing it

Since several of you seem not to understand the concept, I can give a rigorous proof that a rod falling radially into a BH gets stretched due to the gravitational field of the BH.

The difference in the force on the two ends. I pointed that out all the way back in post #4, and others have pointed this out. Your wording implies that it would happen in a uniform field, and would break something apart outside the event horizon. Let's see the math, if that's your claim.

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Right. There was no point in introducing it

The difference in the force on the two ends. I pointed that out all the way back in post #4, and others have pointed this out. Your wording implies that it would happen in a uniform field, and would break something apart outside the event horizon. Let's see the math, if that's your claim.

Has nothing to do with force, there is no such thing a gravitational gorce in GR. It is an intrinsic property of radial motion in a gravitational field .

Edited by zztop
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There is a compressive tidal force, or set of forces, on an object at right angles to the gravitational force (Newtonian), but it would assist with spaghettification, not pancaking.

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There is a compressive tidal force, or set of forces, on an object at right angles to the gravitational force (Newtonian), but it would assist with spaghettification, not pancaking.

Correct. This effect is not what my proof is about, My proof shows the elongation in the radial direction.

I want to thank all the that keep downvoting my posts, they demonstrate the mentality of this forum. Not worth wasting my time.

Edited by zztop
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Quite a few of us on this forum CAN follow the math, ZZ.

What's more,, we understand the math and don't try to 'hide' behind it.

First you claim there are no tidal effects within an event horizon ( again, its in black and white in posts #6 and #8 ), and then post a bunch of simplistic math to 'prove' that tidal effects are related to EH size. Which was our claim to begin with.

We don't claim that there is a preferred viewpoint, that only the far-away observer's frame is significant, and that Alice will never know what happens to Bob. Bob's frame of reference is equally valid, and he WILL know what is happening as he crosses the EH on his way to the only event in his future, the meeting with the ( possible ) singularity. The two views cannot be contradictory, and can be explained by considering the signal reaching Alice from the infalling Bob.

Incidentally, you don't win arguments by down-voting your opponent.

That just makes you a sore loser.

And I find it amusing that you have the gall to complain when others do the same to you.

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Quite a few of us on this forum CAN follow the math, ZZ.

What's more,, we understand the math and don't try to 'hide' behind it.

First you claim there are no tidal effects within an event horizon ( again, its in black and white in posts #6 and #8 ), and then post a bunch of simplistic math to 'prove' that tidal effects are related to EH size. Which was our claim to begin with.

Yes, it is a simple proof that none of you was able to produce. It also happens to be correct

We don't claim that there is a preferred viewpoint, that only the far-away observer's frame is significant, and that Alice will never know what happens to Bob. Bob's frame of reference is equally valid, and he WILL know what is happening as he crosses the EH on his way to the only event in his future, the meeting with the ( possible ) singularity. The two views cannot be contradictory, and can be explained by considering the signal reaching Alice from the infalling Bob

Nothing to do with the subject being discussed, proving that you do not understand the subject, contrary to your claims.

Incidentally, you don't win arguments by down-voting your opponent.

That just makes you a sore loser.

Precisely what some of you did (in addition, you repeatedly resorted to ad-hominems). Thank you for making my point.

Edited by zztop
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Yes, it is a simple proof that none of you was able to produce. It also happens to be correct

At the second attempt, it was. You needed a nudge towards using the gradient. A fact which, to me, makes your current stance all the more surprising.

Now I like to see your math about how a person in free fall, with his head and feat experiencing the same acceleration, will be pancaked.

Edited by Bender
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At the second attempt, it was. You needed a nudge towards using the gradient. A fact which, to me, makes your current stance all the more surprising.

Now I like to see your math about how a person in free fall, with his head and feat experiencing the same acceleration, will be pancaked.

I already posted it, u need to click on the link. "Pancaking" it is not illustrative of what happens (this is the term Suskind used) , elongation is much more appropriate.

about how a person in free fall, with his head and feat experiencing the same acceleration,

Based on the above, it is clear that you do not understand GR, the different parts of the body are experiencing different accelerations (both in terms of direction and in terms of value). Hence, the "spaghettification" and the "elongation" effects. If some of you spent as much time at dancing around the issue and posting (incorrect) prose as studying GR, you would have figured it out. None of you posted one equation. None.

Edited by zztop
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Nobody challenged the spaghettification effect due to a gradient in acceleration. You claimed that there would be "pancaking" in the absence of a gradient e.g. near a massive black hole, where it is possible to have a large acceleration but a small gradient.

You have yourself provided zero math concerning that situation. The math you did produce shows that such a situation is indeed possible.

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The surface tides for a blackhole at the surface (EH) of a reasonable but undistinguished spiral galaxy (say 4million solar masses) would be a few tenths of a millimetre per second per metre *. So even two unconnected test masses would only move away from each very slowly and no spaghetification would occur outside the EH

* 6e-4 m/s^2 per metre

If I have my fermi estimations correct then at about 2e4 solar masses you would start to have problems (curl into the fetal position to avoid being stretched - although it might temporaraly fix a bad back) and at 10000 you would die. To be properly stretched at EH you would be down in the magnitude of 1000 solar masses and lower

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The surface tides for a blackhole at the surface (EH) of a reasonable but undistinguished spiral galaxy (say 4million solar masses) would be a few tenths of a millimetre per second per metre *. So even two unconnected test masses would only move away from each very slowly and no spaghetification would occur outside the EH

* 6e-4 m/s^2 per metre

If I have my fermi estimations correct then at about 2e4 solar masses you would start to have problems (curl into the fetal position to avoid being stretched - although it might temporaraly fix a bad back) and at 10000 you would die. To be properly stretched at EH you would be down in the magnitude of 1000 solar masses and lower

Elongation exists for ANY BH (it exists for any radial fall towards a gravitating body). The effect can be shown not only with the GR formalism but also with the Newtonian one. The amount of elongation is related to the Schwarzschild radius (which is related to the gravitating body mass but $r_s$ is a more elegant way of calculating). I already posted the exact proof. Once again, I want to thank all the small - minded people that keep downvoting my posts. It gives a good tally of all the people that fail to understand the subject. If you do not understand , just ask, I am more than happy to explain.

Edited by zztop
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Elongation exists for ANY BH (it exists for any radial fall towards a gravitating body). The effect can be shown not only with the GR formalism but also with the Newtonian one. The amount of elongation is related to the Schwarzschild radius (which is related to the gravitating body mass but $r_s$ is a more elegant way of calculating). I already posted the exact proof. Once again, I want to thank all the small - minded people that keep downvoting my posts. It gives a good tally of all the people that fail to understand the subject. If you do not understand , just ask, I am more than happy to explain.

What makes you think I don't understand - I gave the figures for a SMBH and some rough ideas about other forces.

The schwarzchild radius is a long way from the most elegant way of calculating it - obviously for a Schild b-hole all you need is the mass (all you ever need). Surface (EH) tides are inversely proportional to the square of the mass - so it is patently clear that as the radius is proportional to the mass then the surface tides will become insignificant for large mass blackholes.

I am pretty sure that the exact proof you posted relies on a second order series simplification - but frankly I cannot be bothered to go back and look; it should definitely come with a curly almost equals and a health warning

And if we are talking about neg-reps - I only give them out for rudeness and arrogance. I haven't bothered dishing one out for a while - but bombastically making sweeping claims and then backtracking by narrowing the application of those claims is always good to gather red marks from the groundlings

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What makes you think I don't understand - I gave the figures for a SMBH and some rough ideas about other forces.

I am not talking about you.

I am pretty sure that the exact proof you posted relies on a second order series simplification - but frankly I cannot be bothered to go back and look; it should definitely come with a curly almost equals and a health warning.

No, my proof is exact, doesn't use any "simplification", there are no "curlies".

And if we are talking about neg-reps - I only give them out for rudeness and arrogance. I haven't bothered dishing one out for a while - but bombastically making sweeping claims and then backtracking by narrowing the application of those claims is always good to gather red marks from the groundlings

Edited by zztop
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...

No, my proof is exact, doesn't use any "simplification", there are no "curlies".

...

Sorry - I was looking at the posted equations rather than the links which I assumed were back up to the posts.

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Have you resolved this issue?

(acceleration proper makes you into a "pancake", not a "spaghetti")

I still don't see how acceleration proper can make someone into a pancake without a spaceship that can turn you into a pancake regardless of whether it is near a black hole or not.

I admit I downvoted one of your posts, but only because you accused me of trolling, not for anything content related. I even commended you on you math.

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Have you resolved this issue?

I still don't see how acceleration proper can make someone into a pancake without a spaceship that can turn you into a pancake regardless of whether it is near a black hole or not.

I admit I downvoted one of your posts, but only because you accused me of trolling, not for anything content related. I even commended you on you math.

Yes, I did. You need to be able to follow the proof.

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Yes, I did. You need to be able to follow the proof.

I assume you refer to the pdf you linked a couple of posts ago?

I think you can do the math, so I'm not contesting any of it, but as far as I can tell:

- there is nothing about pancaking in there

- there is a gradient in the acceleration, so it says little about a situation with only acceleration (or at least negligible gradient).

I do have a question related to what is in there: how much does this result deviate from simply doing the calculation with Newtonian mechanics, which seems to do reasonably well for calculating the Schwarzschild radius? I'm not used to this Schwarzschild metric used.

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I assume you refer to the pdf you linked a couple of posts ago?

I think you can do the math, so I'm not contesting any of it, but as far as I can tell:

- there is nothing about pancaking in there

- there is a gradient in the acceleration, so it says little about a situation with only acceleration (or at least negligible gradient).

I do have a question related to what is in there: how much does this result deviate from simply doing the calculation with Newtonian mechanics, which seems to do reasonably well for calculating the Schwarzschild radius? I'm not used to this Schwarzschild metric used.

It teaches you that the temporal distance between two endpoints of a rod increases as the radial coordinate decreases. This means that the rod gets elongated. As I already mentioned, one gets a similar (but not identical) result by using Newtonian mechanics.

Edited by zztop
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It teaches you that the temporal distance between two endpoints of a rod increases as the radial coordinate decreases. This means that the rod gets elongated. As I already mentioned, one gets a similar (but not identical) result by using Newtonian mechanics.

Are these effects complimentary? Are they similar in order of magnitude (I suppose that depends on the situation)? Does this temporal elongation cause internal forces, or does it merely appear elongated to an outside observer?

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Are these effects complimentary?

What do you mean "complementary"? The question doesn't make sense.

Are they similar in order of magnitude (I suppose that depends on the situation)?

GR defaults to Newtonian mechanics in the limit. This is well known

Does this temporal elongation cause internal forces, or does it merely appear elongated to an outside observer?

It causes internal strain. It is not an observer dependent artifact.

I already explained that this is a misleading, sloppy, unfortunate term used by Suskind.

Edited by zztop
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What do you mean "complementary"? The question doesn't make sense.

GR defaults to Newtonian mechanics in the limit. This is well known

It causes internal strain. It is not an observer dependent artifact.

I was confused because I don't see any material dependency. Do I understand correctly that the elongation here would be for a beam without any cohesion forces?

I already explained that this is a misleading, sloppy, unfortunate term used by Suskind.

So do you agree that no such effect occurs under (quasi-)uniform acceleration, regardless of how large it is?

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