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Timeline for Naked singularity: how would it behave?

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Jul 21, 2019 at 7:43 comment added Yukterez 1) It depends on the angle, as said if you approach r=0 from θ≠90° you miss the singularity and continue the path into negative r. If you transform into cartesian coordinates or use Kerr Schild you see that r=0, θ=90° is an infinitely thin ring of radius R=a, where the geodesics pass through smoothly if θ≠90°. The ring itself is also repulsive at θ=90°. 2) The pictures are Creative Commons and can be reused, and the code is also freely available at raytracing.yukterez.net and pastebin.com/u/Yukterez but the Syntax is reference.wolfram.com/language/guide/Syntax.html
Jul 19, 2019 at 15:51 comment added user4552 @Yukterez: Your work looks really nice. Is it open source? I've done some similar simulations: github.com/bcrowell/karl Thanks for the further info about what you did. But I'm still not convinced about the physics issues specifically relating to naked singularities and this question. What you can do in this sort of simulation is to trace the rays that pass through the gravitational field near the singularity, and even then you have problems with the inability to create a Cauchy surface due to the existence of CTCs. You can't simulate rays that come from or through the singularity.
Jul 19, 2019 at 0:44 comment added Yukterez @Ben Crowell, regarding your question (2): the raytracer uses Kerr Newman geodesics, I doublechecked its functionality by comparing its results to Geovis (see tinyurl.com/y3v2b5lg for the original and tinyurl.com/yyludmq8 for the reproduction), Project 599 (see tinyurl.com/yybe8ect for the original and tinyurl.com/y3smsk2z for the reproduction) and Andreas Müller (see tinyurl.com/y52j4qyw for the original and tinyurl.com/y5mwtzd2 for the reproduction), so the images should be ok. The silhouettes of the NS are also like in the cited references.
Jul 19, 2019 at 0:25 comment added Yukterez For the closed timelike curves you need to carry out some special maneuvers like in this reference: roma1.infn.it/teongrav/leonardo/bh/bhcap3.pdf#page=26 - that is something that could also be adressed, but I think it might go beyond the scope of the question. Also, the metric is of course dubious with regard to singularities, but since the question was asked hypothetically the answer is hypothetical as well.
Jul 18, 2019 at 21:51 comment added Andrew Steane I think that this answers needs to address the issue of closed timelike curves, among other things. Without paying some attention to that it is really impossible to say what goes on if one imagines passing through the ring singularity. Also, I have some vague memory of reading about some instability which is another reason to regard the Kerr metric as dubious in such conditions.
Jul 18, 2019 at 21:39 history edited Yukterez CC BY-SA 4.0
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Jul 18, 2019 at 21:34 comment added Yukterez The singularity is at r=0, θ=±90° (in Boyer Lindquist coordinates, that means in cartesian coordinates it is a ring with a radius proportional to the spin parameter). The area between the ring (-90°<θ<+90°) is not part of the singularity itself, if you fly through you do not hit the ring you only fly through without touching it
Jul 18, 2019 at 18:42 comment added user4552 [...] (4) Naked singularities can in general emit arbitrary information and unlimited energy (in GR). That means that we can't use GR to predict what comes out of them (without even worrying about tracing rays through them). (5) The superextremal Kerr-Newman solution has CTCs. That means that we can't take an initial Cauchy surface and propagate forward in time to find the solutions of wave equations or the motion of test particles.
Jul 18, 2019 at 18:41 comment added user4552 [...] ray tracing for rays that pass through the singularity, but that doesn't make sense. By definition, a singularity involves geodesic incompleteness, so you can't trace rays through it. This seemed so obviously wrong to me that it made me doubt myself, so I tried to check whether the paper had attracted published criticism or whether de Vries was a well known relativist. Google Scholar shows only one citation, which I couldn't access. De Vries got his PhD in 1994 and then immediately got a job in industry. [...]
Jul 18, 2019 at 18:32 comment added user4552 Sorry, I jumped the gun in my previous comment. However, it seems to me like there are still some issues with this answer. (1) You have some garbling in your references. Waseda is the name of the university, not the author, and the link is to a powerpoint, not to the paper in Phys Rev D. (2) It wasn't clear to me until I noticed the signatures in the corner of the images that they were ones you constructed yourself. That's cool, but it leaves us with no way to know what you actually did or whether it's correct. (3) The de Vries paper just looks wrong to me. He talks about doing optical [...]
Jul 18, 2019 at 18:11 history edited Yukterez CC BY-SA 4.0
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Jul 18, 2019 at 17:43 history edited Yukterez CC BY-SA 4.0
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Jul 18, 2019 at 17:38 history edited Yukterez CC BY-SA 4.0
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Jul 18, 2019 at 5:04 history edited Yukterez CC BY-SA 4.0
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Jul 18, 2019 at 4:57 history edited Yukterez CC BY-SA 4.0
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Jul 18, 2019 at 4:49 history edited Yukterez CC BY-SA 4.0
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Jul 18, 2019 at 4:25 comment added Yukterez A naked singularity does not have an event horizon, therefore it's called naked. Only the last image shows a black hole for comparison. The naked singulaties also bend the light of the background stars, you do not need a black hole to achieve that. Everything with energy bends light.
Jul 18, 2019 at 0:41 history edited Yukterez CC BY-SA 4.0
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Jul 18, 2019 at 0:21 comment added Emilio Pisanty Jornal URLs have no guarantee of stability either - this is why the DOI link (in this case doi.org/10.1088/0264-9381/17/1/309 ) is preferable in all cases where it is available.
Jul 17, 2019 at 23:59 history edited Yukterez CC BY-SA 4.0
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Jul 17, 2019 at 23:55 comment added Yukterez You mean the De Vriess reference? That link was dead because sci-hub changed its domain from .hk to .tw, I'll link to the iopscience source instead thanks for the hint
Jul 17, 2019 at 23:54 history edited Yukterez CC BY-SA 4.0
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Jul 17, 2019 at 23:48 history edited Yukterez CC BY-SA 4.0
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Mar 11, 2019 at 15:20 comment added Emilio Pisanty Your final link is broken. When fixing it, please note that links to papers should point to (i) landing pages (not pdfs), (ii) stable links that are robust against link rot (i.e. the DOI if it is at all available), and (iii) to legal resources. If users then want to go to piracy sites to look for their paper, that's fine, but in the interest of keeping this site as a professional venue, we link to legal resources only.
Apr 28, 2018 at 9:49 history edited Yukterez CC BY-SA 3.0
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Apr 28, 2018 at 9:43 history answered Yukterez CC BY-SA 3.0
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