# Neutron Star to Black Hole

Discussion in 'Astronomy, Exobiology, & Cosmology' started by RajeshTrivedi, Jan 12, 2015.

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Have seen that video tashja, in fact have linked to it somewhere. When Rajesh was pushing his idea re BH density, I raised it then.
Again though, Thorne does not believe that the classical point singularity exists [says so in his book, "Black Holes and Time Warps"] and neither does any self respecting cosmologist I would hasten to add.
Most believe a surface/mass of sorts does exist between the Planck/Quantum level and the point.
His inference was a BH is 99.9% curved spacetime and so to speak of a BH density is not really applicable. [Even considering this surface at the Planck/Quantum scale.

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It's/they are theoretical thought experiments. And dont exist in reality, just as naked singularities do not.
Did you miss that river?

5. ### river

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neither do black holes and anything like it exist

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Yes he does. But as I suggested, he certainly by his book [which I have] does not accept the existence of the classical point singularity.
Note also at the 5 minute mark where he says the energy content of the BH resides mainly in the critically curved spacetime, and we all understand E=Mc2

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Would you like to explain the observed effects we see with matter/energy and spacetime orbiting these effects we see another way?
Or are you just river trolling again?

9. ### river

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Tashja...Dont get me wrong. All the replies are helpful, including my own from Professor Lewis. Each places emphasis on either of two issues, just as the many links I have given, but no where has it ever been said that the Kerr geometry and mass does not spin.
And they are hogtied to a certain extent as they are not a party to this now lengthy debate and some of the errors that have been claimed.
And if you can get more great!

I welcome them all.

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Would you like to explain the observed effects we see with matter/energy and spacetime orbiting these effects we see another way?

12. ### river

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doesn't matter

13. ### tashjaRegistered Senior Member

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Yes, but the point I'm trying to make with that video is that physicists often speak in loose terms when addressing lay audiences that they wouldn't use with their peers. Thus, Prof. Baez could be forgiven for speaking of the singularity as if it was an object. Hi reply is based on the knowledge and the language the questioner (me) is using, which, lets be real, it's amateurish at best lol. And of course, if there is any doubt about the responses, people should feel free to contact the Profs. themselves and verify it. That is why I always provide their identity.

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Agreed.

15. ### Q-reeusValued Senior Member

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Was content to lurk here, and hoping some responsible mod would have locked this hopelessly repetitive thread many pages ago. But, noting my name was dragged into it again in post #587, best to again point out something obvious but strangely twisted out of shape long ago by GR community. My definitive statement re 'gravity does/does not gravitate was:
In all the subsequent posts and polled profs comments, was given no self-consistent rebuttal. Yes luminaries like Rovelli made assertions to the effect that (still undetected) GW's 'mutually-attract' therefore self-gravitate. Problem is, he like lots of other GR experts, are at a loss to reconcile such assertions (codified in 'new GR' equations yes) with the bald fact the EFE's explicitly define field curvature as caused exclusively by all forms of non-gravitational stress-energy-momentum. Check out detail of last link I gave in above one, as confirmation of that.

Anyway, such good profs as Rovelli might care to offer a coherent explanation of why, in EFE's, the Ricci curvature outside of any matter distribution (e.g. vacuum Schwarzschild spacetime) is precisely zero!! Which explicitly, mathematically, states gravity is NOT it's own source! At least Sascha Vongehr understands that, and, rare amongst such GR experts, was prepared to say so. Plenty of super-intense gravitational field just exterior to an EH - but R = 0 = NO field self-gravitation. What's happened is folks just demanded gravity gravitates and so the original EFE's have been surreptitiously twisted out of shape and redefined in practice - without any explicit admission of that fact.

Folks like Baez might like to explain then how with R = 0 (anywhere exterior to BH EH), one can posit a self-sustaining BH gravity field - completely cut off from original source matter. PeterDonis's quite different explanation is simply clever wording - the source is in the past light-cone of the infalling matter. Right. Right.
And btw that in vacuo R = 0 in EFE's logically demands 'dragged spacetime' ala Kerr metric contains zero energy-momentum hence zero angular momentum. What one logically can have is an analogue of magnetic field - the so-called gravito-magnetic field. Which will 'drag' infalling matter into a spiral path.

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16. ### tashjaRegistered Senior Member

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Hi Q-reeus. I would love to help you, but the profs. dislike to get into never-ending online debates, though they don't seem to mind the occasional layman's question. But your arguments are of a different nature. Perhaps it's best if you take your questions directly to them. That's what I usually do.

17. ### Q-reeusValued Senior Member

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Hi tashja. Of course profs dislike being dragged into such futile debates - and welcomes become worn out. But in my case, they would have an additional reason not to respond. Enough said.

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deleted:

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19. ### Q-reeusValued Senior Member

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Fine, I'll accept that as fair context. And I suggest, for the sake of some peace and (hopefully) finality here, it be left at that.

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Agreed, In fact I deleted it just a sec ago for the sake of peace.
Agreed with your specific suggestion also that this thread should have been locked a few pages back, hopefully for like minded reasons.

21. ### wellwisherBannedBanned

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The fact remains we have never seen a black hole close enough to know for sure. When we landed probes on Mars what we thought was a done deal changed because reality data tends to do that.

If you look at a star, the space-time well contracts toward the center of gravity. Yet, this center of gravity is where reactions that have energy with the highest frequency; gamma. Space-time is slowing toward center, but mass/energy frequency is speeding up toward center.

With the sun, neutron stars and black holes, the mass/energy frequencies speed up as we go down the well, even though space-time has time slowing as we go down the well. Space-time does not take into account all the time. The distance aspect is going in the same direction, since distance/wavelength is getting smaller, while distance is contracting in space-time. But time goes the opposite way relative to space-time and mass/energy. Mass/energy contains extra time (potential) that goes beyond space-time. If this is not taking into account, it can't be right.

22. ### tashjaRegistered Senior Member

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OnlyMe, a more rigorous reply from one of our experts:

23. ### QuarkHeadRemedial Math StudentValued Senior Member

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I am sorry if I seem to be actively prolonging the life of a thread which some appear to think should already be dead, but I feel I should clear up some confusion

To use a term like "gravitational field" is bound to cause confusion when discussing a non-linear model.

Example for linear theory: Does it seem to make sense to say "There exists a magnetic field in the absence of a magnet"? Obviously not

Does it make sense to say "There exists a vector field that is everywhere zero in the absence of a magnet, and not otherwise"? To me at least it does

Likewise, I would happy with the assertion "there exists a tensor field that is everywhere zero in the absence of a gravitational source, and not otherwise"

In GR terms this corresponds to setting the source $T_{jk}=0$ and then all that is required is that the curvature field $R_{jk}=0$, since then the trace $R$ of its matrix representation is of necessity zero, and the metric field $g_{jk}$ need only be a constant.

This is because the Ricci curvature tensor depends (indirectly, through the connection) on the metric tensor which therefore, by the ordinary rules for second order partial derivatives, must be a constant.

Newtonian theory uses a scalar field (potential) $\phi$ and expresses this as $\nabla^2 \phi = 0$ implies the absence of mass, whereas GR expresses it as $R_{jk}- \frac{1}{2}R g_{jk}=0$ implies the absence of a source

Last edited: Feb 15, 2015