6 ms·

New black hole visualization takes viewers beyond the brink

144 points by dnetesn 2y ago

pulsartwin 2y ago
This is a great visualization. I wonder what techniques were used to create it as neither this article nor the original source seem to highlight them.
- radarsat1 2y ago
  One thing I've always wondered about these kinds of simulations is how they deal with numerical issues, since I assume they are needing to use both very small and very large numbers. Additionally, even in simple classical physics integration errors can add up very quickly, so wonder how this problem is avoided when working with these kinds of scales. Similar thoughts for things like galaxy simulations, or simulations of planet-sized collisions, etc.
  - yonatan8070 2y ago
    There are techniques for arbitrary precision math (lookup BigNum), I assume they're used there for some of the things
    - kaba0 2y ago
      That would probably be infeasibly slow. There is a whole field of CS that deals with minimizing error when doing floating point math. They just probably use decent algorithms/encoding.
  - raattgift 2y ago
    These are good questions. I'll get to the core of them after a one-paragraph rant about the aggregator linked at the top, and three paragraphs about how this bit of "science communication" (s̶c̶a̶r̶e̶ sarcasm quotes) means no answers for you about this particular visualization. I did end up peppering in a couple relevant bits of information in them though. In case it's not clear, the ordering of paragraphs below is not the order in which they were written. Preliminarily: phys.org is hot garbage. It mostly reproduces institutions' (universities, NASA) press releases with its own ads. Rarely there is original content of dubious quality. This is not the latter, it's just a NASA-written blurb. Fortunately the same content is at the original source https://science.nasa.gov/supermassive-black-holes/new-nasa-black-hole-visualization-takes-viewers-beyond-the-brink/ https://science.nasa.gov/supermassive-black-holes/new-nasa-b... -- absent that I probably wouldn't have started an answer. Unfortunately the NASA link and its link to youtube give too little information to say anything reliable about the numerical relativity (NR) "codes" (s̶c̶a̶r̶e̶ jargon quotes) for this particular visualization. Yes, it's pretty and cool; yes it will excite relativists as well as laypersons; however, how about tossing the former a little drop of technical information? The supercomputer used and how much time was spent on it is not really useful to know. I can only guess that the visualizer, Jeremy Schnittman, would want to generate data using the tools with which he's most familiar. Digging around in his publication history <https://scholar.google.com/citations?user=MiUTIQwAAAAJ https://scholar.google.com/citations?user=MiUTIQwAAAAJ> I see that he uses lots of Monte Carlo methods, often averaging over many very slightly different simulations (which might individually be wrong). I can see that for his black hole related work (mostly studying X-rays flying about just outside black holes, but also other phenomena close to but outside the horizon, or a little before the most strongly relativistic parts of black hole mergers) he prefers his own (Monte Carlo) tool Pandurata, which is described in Schnittman & Krolik 2013 <https://iopscience.iop.org/article/10.1088/0004-637X/777/1/11 https://iopscience.iop.org/article/10.1088/0004-637X/777/1/1...>. It is not at all obvious to me, especially given the scant information provided by NASA publicity, how he would safely apply these sorts of toolsets to the interior black hole metric. We aren't even told what the metric is, really; I assume Kerr with modest angular momentum, given his previous publications focus on astrophysically-reasonable Kerr black holes. There's another hint in what in the video looks like dimming at the receding limb (on the right) of the accretion disc. But this visualization could also be just Schwarzschild. Who knows? I look forward to his own professional writeup! [Other NR tools are available, e.g. <https://nrpyplus.net/ https://nrpyplus.net/> and <https://grchrombo.org/movies/ https://grchrombo.org/movies/>] Consequently I'll focus in on this part of your comment: > these kinds of scales [or] galaxy simulations [...] This is in the realm of numerical relativity and computational astrophysics respectively. There is an overlap. Although I had in mind a couple resources about your questions, they're mostly textbooks which aren't freely available. So I first visited Sebastiano Bernuzzi's always useful syllabus http://sbernuzzi.gitpages.tpi.uni-jena.de/nr/ http://sbernuzzi.gitpages.tpi.uni-jena.de/nr/ (nr is for Numerical Relativity, solving Einstein's equations with computers) and picked out two useful freely-available resources to start with. They are both called "lecture notes" but are really mini textbooks. They both have excellent bibliographies. Choptuik's 2006 "Numerical Analysis for Numerical Relativists" (PDF) http://laplace.physics.ubc.ca/People/matt/Teaching/06Mexico/mexico06.pdf http://laplace.physics.ubc.ca/People/matt/Teaching/06Mexico/... is awesome. It focuses on finite difference techniques, which dominate in numerical relativity, particularly where black holes are concerned. Like many others, Bernuzzi's 2021 3+1 Numerical Relativity <http://sbernuzzi.gitpages.tpi.uni-jena.de/nr/notes/2021/main.pdf http://sbernuzzi.gitpages.tpi.uni-jena.de/nr/notes/2021/main...> points to it in section 2.4, where you will find references to other and newer treatments of various numerical relativity methods. Other techniques get used too, finite-element, for example. For galaxy stuff, you would want a resource on e.g. smoothed particle hydrodynamics or particle-particle/particle-mesh-Ewald. ETA^2: wow, an actually useful physics SE q&a on that last bit (contrasting finite difference & finite element methods for black holes) from a little less than two years ago (direct link to imho good answer): <https://physics.stackexchange.com/a/725998 https://physics.stackexchange.com/a/725998> ETA: this is more just a bookmark for me. Even though, like Chopotuik above, it's 17 years old, <https://www.cita.utoronto.ca/~pfeiffer/talks/07Apr_Jacksonville.pdf https://www.cita.utoronto.ca/~pfeiffer/talks/07Apr_Jacksonvi...> is a really great slide deck. ETA^3: Bernuzzi "Introduction to Numerical Relativity" @ IHÉS winter 2024 https://www.youtube.com/watch?v=RcdntEBrcuM https://www.youtube.com/watch?v=RcdntEBrcuM is probably pretty good.
deadbabe 2y ago
This is incredible, would they be able to render it out as a 360 video so we could see it in VR and get a better sense of how it would feel in reality
- codegladiator 2y ago
  The second video "Flight Around Black Hole" is 360 video.
  - deadbabe 2y ago
    So how do we watch on a Quest 3?
LegionMammal978 2y ago
In a similar vein is Scott Manley's 2020 panoramic video "What Would Travelling Through A Wormhole Look Like?" [0] (and its sequel "Wormholes Get Weirder" [1]), in which he simulates a camera flying through a particular model of a wormhole [2]. Though for reasons noted in the paper, the wormhole as presented is likely non-physical. [0] https://youtu.be/V7e-1bRpweo https://youtu.be/V7e-1bRpweo [1] https://youtu.be/PVO8nvb1o2w https://youtu.be/PVO8nvb1o2w [2] https://arxiv.org/abs/1502.03809 https://arxiv.org/abs/1502.03809
revskill 2y ago
Nice. Is this using javascript to render?
m2spring 2y ago
[dead]
steve_adams_86 2y ago
I love this. I’ve been deep diving on layman general relativity and quantum mechanics for weeks now and I can’t get enough of this stuff. It’s mind blowing to me that our models of what black holes might look like seems to be getting proven over time. Absolutely crazy. As a kid I don’t think I would have guessed we’d figure so much out in my lifetime. I don’t know how it can’t fill anyone with so much wonder. I’m also amazed by the people who do this research and modelling. I struggle to comprehend all of it, let alone actively expand our understanding of it
- ryandvm 2y ago
  I'm sure you've already found them but as a layman fascinated with this stuff, Fermilab (Don) and PBS Space Time are my two favorite YouTube channels on these subjects.
  - mycall 2y ago
    The latest video [0] really explains the perspectives of diving into a black hole quite well. [0] https://www.youtube.com/watch?v=Rogm_lpVZYU https://www.youtube.com/watch?v=Rogm_lpVZYU
  - steve_adams_86 2y ago
    I haven’t! Thanks for the recommendation. I’ve mostly been listening to some of Neil Turok’s lectures lately and trying to get a more fundamental understanding, but my math and physics skills are really weak and I lose track constantly.
- rmvt 2y ago
  as someone who's been meaning to get some reading done on quantum mechanics, what materials have you been going through? every time i've seen recommendations on this topic, they always required somewhat advanced knowledge of physics and math.
hcrisp 2y ago
Cool, but I couldn't tell if it reached the point of spaghettification [0]. [0] https://en.m.wikipedia.org/wiki/Spaghettification https://en.m.wikipedia.org/wiki/Spaghettification
- The_Colonel 2y ago
  This is mentioned in the article - the point of spaghettification is marked in the video as the point of destruction, right before reaching the singularity.
mrmetanoia 2y ago
Let's get this on at the Vegas Sphere ;)
gyre007 2y ago
Honestly, this is one of the best things I’ve watch this year
CHB0403085482 2y ago
When are we gonna find a WHITE HOLE as predicted in Veritasium's video? https://www.youtube.com/watch?v=6akmv1bsz1M https://www.youtube.com/watch?v=6akmv1bsz1M
- ndsipa_pomu 2y ago
  Are you sure that the big bang wasn't one?
  - raattgift 2y ago
    Yes, we can be certain. White holes can be considered in two ways: (1) a region of spacetime into which nothing can ever cross, with a surface that is a perfect reflector; or somewhat less commonly (2) a time-reversed black hole. At scales of gigaparsecs, the universe appears to be both spatially homogeneous and isotropic, with matter denser at higher redshift. There is no way to generate this configuration of matter from a white hole. White holes are very much spatially anisotropic, that is you can point to where they are: left of you but not right of you, in front of you but not behind you, etc. The trajectories of the centres of momentum of galaxy clusters in every direction and at every redshift are diverging but not following an inertial radial. The really compelling accessible evidence against a white hole big bang is in the https://en.wikipedia.org/wiki/Lyman-alpha_forest https://en.wikipedia.org/wiki/Lyman-alpha_forest from hydrogen clouds at different redshifts being backlit by bright background (and thus earlier in the universe) sources. This "stacking" is so hard to conceive for a white hole big bang that as far as I know, nobody has actually written down a reasonable explanation for it. More technically, (general relativity) metrics at those "cosmologically large" scales are so different from the metrics of white holes that we would already have noticed. Additionally, a white hole big bang has to account for the chemistry of the earliest visible stars, whose spectral lines indicate essentially hydrogen with a tiny amount of helium and lithium. The standard cosmology's big bang nucleosynthesis's chemical abundances would have to be duplicated by a white hole big bang, and as far as I know nobody knows how to make that work. How does whatever is spit out of a white hole interior, or reflected off a white hole boundary, eventually turn into atomic hydrogen (with a smattering of heavier atoms up to 7 atomic mass units)? How does it account for the cosmic microwave background, which implies that in some region of the white hole big bang universe atoms practically everywhere were so hot as to be completely ionized? Likewise, the interior metrics of black holes are very different from metrics which reasonably describe observations at gigaparsec scales. So if one takes a "wormhole" maximal extension of a black hole spacetime and throws enormous amounts matter into the black hole end, what emerges at the white hole end is nothing like a cosmology. Nor is what's inside. So a reasonable prediction of our galaxy's future is not exiting from a white hole (with us presently inside), and a reasonable prediction of our past is not that our galaxy was spit out of a white hole (with us presently outside). As far as I know, nobody has done a convincing treatment of a non-eternal white hole in General Relativity. We've had theoretical models for forming black holes (i.e., there is a past of the black hole where there is no black hole yet, so it's non-eternal) since the 1930s (<https://en.wikipedia.org/wiki/Oppenheimer%E2%80%93Snyder_model https://en.wikipedia.org/wiki/Oppenheimer%E2%80%93Snyder_mod...>), and models for evaporating black holes since Hawking 1970, so it's quite striking there's nothing similar for white holes. There is ample astrophysical evidence supporting a range of models for non-eternal black holes and their horizons. There isn't anything seen by our telescopes that looks like it might be a white hole horizon. The accelerated expansion of the universe, discovered in 1998, kills off a bunch of vaguely related ideas, like we are in a tiny tiny fraction of a thin shell (thin as in small compared to the shell's diameter) of matter that is expanding inertially from an initial impulse (an "explosion", figuratively) acting on a dense phase of matter. By "tiny tiny" here we're talking about our visible universe occupying less than 10^-23 of the shell's thickness. This is from a family of ideas tossed around a bit before Alan Guth published his 1997 book <https://en.wikipedia.org/wiki/The_Inflationary_Universe https://en.wikipedia.org/wiki/The_Inflationary_Universe>. One could imagine a reflector onto which the shell fell, and that reflector could resemble a white hole; you can get a cyclic cosmology by having the entire shell eventually reconverge on the central reflector. However, we now see the expansion of our universe is speeding up rather than slowing down, so this doesn't work. Finally, we're learning a lot more about the gravitational wave background of our universe. It is reasonable to bet that studies of the polarization of the cosmic microwave background (e.g. <https://lweb.cfa.harvard.edu/~cbischoff/bicepkeck/ https://lweb.cfa.harvard.edu/~cbischoff/bicepkeck/>) will find evidence of gravitational waves at scales large enough and uniform enough to rule out any sort of hole-like boundary (i.e., a one-way-crossing-only surface which has a spatial direction as well as being in the past) during the inflationary epoch. And we are probably already at the ruling-out point with baryon acoustic oscillation galaxy filament https://svs.gsfc.nasa.gov/13768 https://svs.gsfc.nasa.gov/13768 evidence.
davedx 2y ago
This is an awesome simulation but what I don't understand is why you wouldn't see any light from the singularity once you're inside the event horizon. Why is it completely black in there? Surely that's not correct? I get that we have no experimental evidence of what it looks like inside but surely we could simulate the photonic environment?
- beremaki 2y ago
  I am not a physicist but as I understand it everything inside the event horizon goes towards the singularity. No light can come from it for you to see the singularity
  - davedx 2y ago
    Nobody is replying with any concrete proofs or references for this, so I will remain sceptical about it :)
    - beremaki 2y ago
      Then you are skeptical about the concept of event horizon. The proof you are looking for is general relatively and all the research validating it
  - cthalupa 2y ago
    There's different answers here for different types of black holes. Effectively, significant enough charge or rotational speeds can create a second horizon where inside the black hole, allowing for stable orbits inside the event horizon. The issue is there's no real explanation we have that would explain why a black hole would have accumulated enough charge to create a large enough second horizon for there to be stable orbit for us to sit around in and look at stuff. It's more complicated with rotating black holes. https://arxiv.org/abs/1103.6140 https://arxiv.org/abs/1103.6140 and some other papers contend it's potentially possible, but I'm not sure if black holes large enough to support this sort of thing can rotate fast enough. Neither would let you see the singularity, though, because the singularity isn't really a physical thing, and even if it were, there's not really any reason to believe it would emit or reflect light. But all of this is likely nonsense when it comes to practical reality, though - the very fact the math leads us to a singularity means we're almost certainly missing something, and spacetime is really weird past Cauchy horizons - trying to extend the math to figure out what is going on behind them is probably futile. I would guess in the real world there's not really anything "interesting" here from a 'seeing stuff while alive in the black hole' perspective, but in theory there are some solutions where you could see whatever else is inside the black hole with you.
ankitg12 2y ago
Beyond the brink is another universe !!
deleted 2y ago
[deleted]
mensetmanusman 2y ago
This seems like an interesting manifestation of Gödel’s formulation about unprovable truths. The universe has set boundaries that prevent the scientific method from being completed regarding experiments in the case of black holes. This means that certain scientific truth discovery is bounded by certain lengths, timescales, and gravitational forces. Thankfully, our minds are not limited by what we can think about in the same way -thus, we can simulate what we think happens even though it is never provable by definition. :)
nojvek 2y ago
> a one-dimensional point called a singularity, where the laws of physics as we know them cease to operate. Laws of physics don't cease to operate. As in they don't stop or go to zero. We start running into near infinities and infinities. That is a poor choice of words. Below plank length, plank time, plank energy we don't have insight into the inner workings. https://www.youtube.com/watch?v=bjVfL8uNkUk https://www.youtube.com/watch?v=bjVfL8uNkUk The laws of physics are perfectly fine as we have trillions of blackholes in the universe ongoing for billions of years. It's our models that cannot describe what we cannot measure.

144 points by dnetesn 2y ago

This is a great visualization. I wonder what techniques were used to create it as neither this article nor the original source seem to highlight them.

radarsat1 2y ago
One thing I've always wondered about these kinds of simulations is how they deal with numerical issues, since I assume they are needing to use both very small and very large numbers. Additionally, even in simple classical physics integration errors can add up very quickly, so wonder how this problem is avoided when working with these kinds of scales. Similar thoughts for things like galaxy simulations, or simulations of planet-sized collisions, etc.
- yonatan8070 2y ago
  There are techniques for arbitrary precision math (lookup BigNum), I assume they're used there for some of the things
  - kaba0 2y ago
    That would probably be infeasibly slow. There is a whole field of CS that deals with minimizing error when doing floating point math. They just probably use decent algorithms/encoding.
- raattgift 2y ago
  These are good questions. I'll get to the core of them after a one-paragraph rant about the aggregator linked at the top, and three paragraphs about how this bit of "science communication" (s̶c̶a̶r̶e̶ sarcasm quotes) means no answers for you about this particular visualization. I did end up peppering in a couple relevant bits of information in them though. In case it's not clear, the ordering of paragraphs below is not the order in which they were written. Preliminarily: phys.org is hot garbage. It mostly reproduces institutions' (universities, NASA) press releases with its own ads. Rarely there is original content of dubious quality. This is not the latter, it's just a NASA-written blurb. Fortunately the same content is at the original source https://science.nasa.gov/supermassive-black-holes/new-nasa-black-hole-visualization-takes-viewers-beyond-the-brink/ https://science.nasa.gov/supermassive-black-holes/new-nasa-b... -- absent that I probably wouldn't have started an answer. Unfortunately the NASA link and its link to youtube give too little information to say anything reliable about the numerical relativity (NR) "codes" (s̶c̶a̶r̶e̶ jargon quotes) for this particular visualization. Yes, it's pretty and cool; yes it will excite relativists as well as laypersons; however, how about tossing the former a little drop of technical information? The supercomputer used and how much time was spent on it is not really useful to know. I can only guess that the visualizer, Jeremy Schnittman, would want to generate data using the tools with which he's most familiar. Digging around in his publication history <https://scholar.google.com/citations?user=MiUTIQwAAAAJ https://scholar.google.com/citations?user=MiUTIQwAAAAJ> I see that he uses lots of Monte Carlo methods, often averaging over many very slightly different simulations (which might individually be wrong). I can see that for his black hole related work (mostly studying X-rays flying about just outside black holes, but also other phenomena close to but outside the horizon, or a little before the most strongly relativistic parts of black hole mergers) he prefers his own (Monte Carlo) tool Pandurata, which is described in Schnittman & Krolik 2013 <https://iopscience.iop.org/article/10.1088/0004-637X/777/1/11 https://iopscience.iop.org/article/10.1088/0004-637X/777/1/1...>. It is not at all obvious to me, especially given the scant information provided by NASA publicity, how he would safely apply these sorts of toolsets to the interior black hole metric. We aren't even told what the metric is, really; I assume Kerr with modest angular momentum, given his previous publications focus on astrophysically-reasonable Kerr black holes. There's another hint in what in the video looks like dimming at the receding limb (on the right) of the accretion disc. But this visualization could also be just Schwarzschild. Who knows? I look forward to his own professional writeup! [Other NR tools are available, e.g. <https://nrpyplus.net/ https://nrpyplus.net/> and <https://grchrombo.org/movies/ https://grchrombo.org/movies/>] Consequently I'll focus in on this part of your comment: > these kinds of scales [or] galaxy simulations [...] This is in the realm of numerical relativity and computational astrophysics respectively. There is an overlap. Although I had in mind a couple resources about your questions, they're mostly textbooks which aren't freely available. So I first visited Sebastiano Bernuzzi's always useful syllabus http://sbernuzzi.gitpages.tpi.uni-jena.de/nr/ http://sbernuzzi.gitpages.tpi.uni-jena.de/nr/ (nr is for Numerical Relativity, solving Einstein's equations with computers) and picked out two useful freely-available resources to start with. They are both called "lecture notes" but are really mini textbooks. They both have excellent bibliographies. Choptuik's 2006 "Numerical Analysis for Numerical Relativists" (PDF) http://laplace.physics.ubc.ca/People/matt/Teaching/06Mexico/mexico06.pdf http://laplace.physics.ubc.ca/People/matt/Teaching/06Mexico/... is awesome. It focuses on finite difference techniques, which dominate in numerical relativity, particularly where black holes are concerned. Like many others, Bernuzzi's 2021 3+1 Numerical Relativity <http://sbernuzzi.gitpages.tpi.uni-jena.de/nr/notes/2021/main.pdf http://sbernuzzi.gitpages.tpi.uni-jena.de/nr/notes/2021/main...> points to it in section 2.4, where you will find references to other and newer treatments of various numerical relativity methods. Other techniques get used too, finite-element, for example. For galaxy stuff, you would want a resource on e.g. smoothed particle hydrodynamics or particle-particle/particle-mesh-Ewald. ETA^2: wow, an actually useful physics SE q&a on that last bit (contrasting finite difference & finite element methods for black holes) from a little less than two years ago (direct link to imho good answer): <https://physics.stackexchange.com/a/725998 https://physics.stackexchange.com/a/725998> ETA: this is more just a bookmark for me. Even though, like Chopotuik above, it's 17 years old, <https://www.cita.utoronto.ca/~pfeiffer/talks/07Apr_Jacksonville.pdf https://www.cita.utoronto.ca/~pfeiffer/talks/07Apr_Jacksonvi...> is a really great slide deck. ETA^3: Bernuzzi "Introduction to Numerical Relativity" @ IHÉS winter 2024 https://www.youtube.com/watch?v=RcdntEBrcuM https://www.youtube.com/watch?v=RcdntEBrcuM is probably pretty good.

deadbabe 2y ago

This is incredible, would they be able to render it out as a 360 video so we could see it in VR and get a better sense of how it would feel in reality

codegladiator 2y ago
The second video "Flight Around Black Hole" is 360 video.
- deadbabe 2y ago
  So how do we watch on a Quest 3?

LegionMammal978 2y ago

In a similar vein is Scott Manley's 2020 panoramic video "What Would Travelling Through A Wormhole Look Like?" [0] (and its sequel "Wormholes Get Weirder" [1]), in which he simulates a camera flying through a particular model of a wormhole [2]. Though for reasons noted in the paper, the wormhole as presented is likely non-physical. [0] https://youtu.be/V7e-1bRpweo https://youtu.be/V7e-1bRpweo [1] https://youtu.be/PVO8nvb1o2w https://youtu.be/PVO8nvb1o2w [2] https://arxiv.org/abs/1502.03809 https://arxiv.org/abs/1502.03809

revskill 2y ago

Nice. Is this using javascript to render?

m2spring 2y ago

[dead]

steve_adams_86 2y ago

I love this. I’ve been deep diving on layman general relativity and quantum mechanics for weeks now and I can’t get enough of this stuff. It’s mind blowing to me that our models of what black holes might look like seems to be getting proven over time. Absolutely crazy. As a kid I don’t think I would have guessed we’d figure so much out in my lifetime. I don’t know how it can’t fill anyone with so much wonder. I’m also amazed by the people who do this research and modelling. I struggle to comprehend all of it, let alone actively expand our understanding of it

ryandvm 2y ago
I'm sure you've already found them but as a layman fascinated with this stuff, Fermilab (Don) and PBS Space Time are my two favorite YouTube channels on these subjects.
- mycall 2y ago
  The latest video [0] really explains the perspectives of diving into a black hole quite well. [0] https://www.youtube.com/watch?v=Rogm_lpVZYU https://www.youtube.com/watch?v=Rogm_lpVZYU
- steve_adams_86 2y ago
  I haven’t! Thanks for the recommendation. I’ve mostly been listening to some of Neil Turok’s lectures lately and trying to get a more fundamental understanding, but my math and physics skills are really weak and I lose track constantly.
rmvt 2y ago
as someone who's been meaning to get some reading done on quantum mechanics, what materials have you been going through? every time i've seen recommendations on this topic, they always required somewhat advanced knowledge of physics and math.

hcrisp 2y ago

Cool, but I couldn't tell if it reached the point of spaghettification [0]. [0] https://en.m.wikipedia.org/wiki/Spaghettification https://en.m.wikipedia.org/wiki/Spaghettification

The_Colonel 2y ago
This is mentioned in the article - the point of spaghettification is marked in the video as the point of destruction, right before reaching the singularity.

mrmetanoia 2y ago

Let's get this on at the Vegas Sphere ;)

gyre007 2y ago

Honestly, this is one of the best things I’ve watch this year

CHB0403085482 2y ago

When are we gonna find a WHITE HOLE as predicted in Veritasium's video? https://www.youtube.com/watch?v=6akmv1bsz1M https://www.youtube.com/watch?v=6akmv1bsz1M

ndsipa_pomu 2y ago
Are you sure that the big bang wasn't one?
- raattgift 2y ago
  Yes, we can be certain. White holes can be considered in two ways: (1) a region of spacetime into which nothing can ever cross, with a surface that is a perfect reflector; or somewhat less commonly (2) a time-reversed black hole. At scales of gigaparsecs, the universe appears to be both spatially homogeneous and isotropic, with matter denser at higher redshift. There is no way to generate this configuration of matter from a white hole. White holes are very much spatially anisotropic, that is you can point to where they are: left of you but not right of you, in front of you but not behind you, etc. The trajectories of the centres of momentum of galaxy clusters in every direction and at every redshift are diverging but not following an inertial radial. The really compelling accessible evidence against a white hole big bang is in the https://en.wikipedia.org/wiki/Lyman-alpha_forest https://en.wikipedia.org/wiki/Lyman-alpha_forest from hydrogen clouds at different redshifts being backlit by bright background (and thus earlier in the universe) sources. This "stacking" is so hard to conceive for a white hole big bang that as far as I know, nobody has actually written down a reasonable explanation for it. More technically, (general relativity) metrics at those "cosmologically large" scales are so different from the metrics of white holes that we would already have noticed. Additionally, a white hole big bang has to account for the chemistry of the earliest visible stars, whose spectral lines indicate essentially hydrogen with a tiny amount of helium and lithium. The standard cosmology's big bang nucleosynthesis's chemical abundances would have to be duplicated by a white hole big bang, and as far as I know nobody knows how to make that work. How does whatever is spit out of a white hole interior, or reflected off a white hole boundary, eventually turn into atomic hydrogen (with a smattering of heavier atoms up to 7 atomic mass units)? How does it account for the cosmic microwave background, which implies that in some region of the white hole big bang universe atoms practically everywhere were so hot as to be completely ionized? Likewise, the interior metrics of black holes are very different from metrics which reasonably describe observations at gigaparsec scales. So if one takes a "wormhole" maximal extension of a black hole spacetime and throws enormous amounts matter into the black hole end, what emerges at the white hole end is nothing like a cosmology. Nor is what's inside. So a reasonable prediction of our galaxy's future is not exiting from a white hole (with us presently inside), and a reasonable prediction of our past is not that our galaxy was spit out of a white hole (with us presently outside). As far as I know, nobody has done a convincing treatment of a non-eternal white hole in General Relativity. We've had theoretical models for forming black holes (i.e., there is a past of the black hole where there is no black hole yet, so it's non-eternal) since the 1930s (<https://en.wikipedia.org/wiki/Oppenheimer%E2%80%93Snyder_model https://en.wikipedia.org/wiki/Oppenheimer%E2%80%93Snyder_mod...>), and models for evaporating black holes since Hawking 1970, so it's quite striking there's nothing similar for white holes. There is ample astrophysical evidence supporting a range of models for non-eternal black holes and their horizons. There isn't anything seen by our telescopes that looks like it might be a white hole horizon. The accelerated expansion of the universe, discovered in 1998, kills off a bunch of vaguely related ideas, like we are in a tiny tiny fraction of a thin shell (thin as in small compared to the shell's diameter) of matter that is expanding inertially from an initial impulse (an "explosion", figuratively) acting on a dense phase of matter. By "tiny tiny" here we're talking about our visible universe occupying less than 10^-23 of the shell's thickness. This is from a family of ideas tossed around a bit before Alan Guth published his 1997 book <https://en.wikipedia.org/wiki/The_Inflationary_Universe https://en.wikipedia.org/wiki/The_Inflationary_Universe>. One could imagine a reflector onto which the shell fell, and that reflector could resemble a white hole; you can get a cyclic cosmology by having the entire shell eventually reconverge on the central reflector. However, we now see the expansion of our universe is speeding up rather than slowing down, so this doesn't work. Finally, we're learning a lot more about the gravitational wave background of our universe. It is reasonable to bet that studies of the polarization of the cosmic microwave background (e.g. <https://lweb.cfa.harvard.edu/~cbischoff/bicepkeck/ https://lweb.cfa.harvard.edu/~cbischoff/bicepkeck/>) will find evidence of gravitational waves at scales large enough and uniform enough to rule out any sort of hole-like boundary (i.e., a one-way-crossing-only surface which has a spatial direction as well as being in the past) during the inflationary epoch. And we are probably already at the ruling-out point with baryon acoustic oscillation galaxy filament https://svs.gsfc.nasa.gov/13768 https://svs.gsfc.nasa.gov/13768 evidence.

davedx 2y ago

This is an awesome simulation but what I don't understand is why you wouldn't see any light from the singularity once you're inside the event horizon. Why is it completely black in there? Surely that's not correct? I get that we have no experimental evidence of what it looks like inside but surely we could simulate the photonic environment?

beremaki 2y ago
I am not a physicist but as I understand it everything inside the event horizon goes towards the singularity. No light can come from it for you to see the singularity
- davedx 2y ago
  Nobody is replying with any concrete proofs or references for this, so I will remain sceptical about it :)
  - beremaki 2y ago
    Then you are skeptical about the concept of event horizon. The proof you are looking for is general relatively and all the research validating it
- cthalupa 2y ago
  There's different answers here for different types of black holes. Effectively, significant enough charge or rotational speeds can create a second horizon where inside the black hole, allowing for stable orbits inside the event horizon. The issue is there's no real explanation we have that would explain why a black hole would have accumulated enough charge to create a large enough second horizon for there to be stable orbit for us to sit around in and look at stuff. It's more complicated with rotating black holes. https://arxiv.org/abs/1103.6140 https://arxiv.org/abs/1103.6140 and some other papers contend it's potentially possible, but I'm not sure if black holes large enough to support this sort of thing can rotate fast enough. Neither would let you see the singularity, though, because the singularity isn't really a physical thing, and even if it were, there's not really any reason to believe it would emit or reflect light. But all of this is likely nonsense when it comes to practical reality, though - the very fact the math leads us to a singularity means we're almost certainly missing something, and spacetime is really weird past Cauchy horizons - trying to extend the math to figure out what is going on behind them is probably futile. I would guess in the real world there's not really anything "interesting" here from a 'seeing stuff while alive in the black hole' perspective, but in theory there are some solutions where you could see whatever else is inside the black hole with you.

ankitg12 2y ago

Beyond the brink is another universe !!

deleted 2y ago

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mensetmanusman 2y ago

This seems like an interesting manifestation of Gödel’s formulation about unprovable truths. The universe has set boundaries that prevent the scientific method from being completed regarding experiments in the case of black holes. This means that certain scientific truth discovery is bounded by certain lengths, timescales, and gravitational forces. Thankfully, our minds are not limited by what we can think about in the same way -thus, we can simulate what we think happens even though it is never provable by definition. :)

nojvek 2y ago

> a one-dimensional point called a singularity, where the laws of physics as we know them cease to operate. Laws of physics don't cease to operate. As in they don't stop or go to zero. We start running into near infinities and infinities. That is a poor choice of words. Below plank length, plank time, plank energy we don't have insight into the inner workings. https://www.youtube.com/watch?v=bjVfL8uNkUk https://www.youtube.com/watch?v=bjVfL8uNkUk The laws of physics are perfectly fine as we have trillions of blackholes in the universe ongoing for billions of years. It's our models that cannot describe what we cannot measure.