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Black hole singularity is a surface not a point
201–210 of 239 posts
Re: Black hole singularity is a surface not a point
#202Earlier quoted context omitted.
Does time accelerate just for the astronaut approaching the black hole (meaning they would be witnessing the future) or does it accelerate for everyone (meaning approaching a black hole is going to make everything end quicker)?
My rather limited understanding is that. first there is a lot going on and due to the forces and gravitational gradients involved, matter itself probably would not survive the journey that close to the horizon. But ignoring that, When in compressed time, from the point of view of someone freefalling, timewise everything is normal, the rest of the universe has accelerated and in the case of a black hole has just aged…
Infinite time dilation means infinite Hawking radiation that will burn everything.
Re: Black hole singularity is a surface not a point
#203Earlier quoted context omitted.
If it signifies the end of time, then all the stuff in the black hole would need to no longer exist no? If anything is happening in the black hole, then time is still progressing, so nothing must be all that exists?
Time is necessary for change, not existence.
Time is change that happens in a continuous manner. It’s still possible to conceive of change happening in an unordered unpredictable way that is not like the smooth ordered time that we experience.
In a gravitational singularity spacetime breaks down. You could argue that time stops, but it’s also valid to argue that causality breaks down and we can no longer make any predictions about the future. Just because we don’t have a theory describing what could happen, doesn’t rule out that something could happen.
Re: Black hole singularity is a surface not a point
#204Earlier quoted context omitted.
As someone with basically only popsci knowledge of black holes: people claiming it would be a literal point never made much sense - fundamentally, common sense (as much as it can apply here) dictates that you cannot compress particles to an absolute point.
Common sense - the experience gained from your common everyday experience of reality - does not apply in black holes. Common sense would tell you they can't exist at all because you can't compress atoms - you have lived your entire life with atoms being entirely incompressible for the practical purpose of anything you do. Leaning on common sense to discuss fundamental physics has been wrong since round about the star…
There's indeed a problem with existence of black holes. Why would they exist? They are usually postulated into existence.
Re: Black hole singularity is a surface not a point
#205This kind of result is why GR still surprises after a century. Geometry beats intuition.
Re: Black hole singularity is a surface not a point
#206[flagged]
Re: Black hole singularity is a surface not a point
#207I have a question for any physicists here. Due to my engineering background, I know just enough physics and mathematics to completely misunderstand general relativity and quantum mechanics. However, one pattern I have noticed is that one favorite past time of physicists is looking at the mathematical models, trying to find insane ass edge cases and then trying to interpret them. With that in mind, do these equations…
Yeah. I can't do the physics myself, so I take on faith (heh) that a sufficiently fast rotating blackhole has a ring shaped singularity that can extend outside its' event horizon. This was news in the 90s and it was a plot point in at least two scifi books, though I don't think I can recommend either
I was assuming the event horizon would also have a donut shape around the ring singularity.
Re: Black hole singularity is a surface not a point
#208Earlier quoted context omitted.
I don't mean the coordinate singularity, I mean there is no more spacetime after that.
Why would that happen? In a different coordinate system (Kruskal–Szekeres coordinates) nothing special happens at the event horizon at all.
Why wouldn't it happen? From the perspective of anyone outside the black hole, nothing can ever enter it. What if that's just true?
Re: Black hole singularity is a surface not a point
#209Earlier quoted context omitted.
Why would that happen? In a different coordinate system (Kruskal–Szekeres coordinates) nothing special happens at the event horizon at all.
Why wouldn't it happen? From the perspective of anyone outside the black hole, nothing can ever enter it. What if that's just true ?
Have you considered that the apparent event horizon is not uniform for all observers?
So does spacetime exist in some frames of reference but not others because those frames disagree on the radius of the apparent event horizon?
Also note that in general an event horizon doesn’t require a singularity.
Re: Black hole singularity is a surface not a point
#210Earlier quoted context omitted.
Not quite: inside a closed surface you can't escape, but things can repeat. You can avoid a coordinate, for example by choosing not to go there, or revisit another one repeatedly. A black hole on the other hand doesn't have that: you cannot revisit old locations - attempting to do so moves you closer to the singularity.
Unless it's a spinning black hole, which contains closed timelike curves that can be reached from and can escape back to the outside universe?
Kerr spacetime contains closed timelike curves inside the inner horizon. You can reach them from the outside universe, but you can't escape back out.
Also, the region inside the inner horizon of Kerr spacetime is widely considered to be not physically reasonable, not just because of the closed timelike curves, but because the inner horizon itself is unstable--there is an infinite blueshift there which, it is believed, would cause it to be destroyed by the first tiny bit of incoming matter or radiation.