New black hole visualization takes viewers beyond the brink
phys.org
phys.org
[0] https://youtu.be/V7e-1bRpweo
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
Do you have some proven modeling of the inside of a singularity? If so, I would be very interested in that.
I haven't been to the "edge" of our expanding universe, so I can't say anything for certain. I haven't been inside the event horizon of a black hole (or have we?), so I can't claim to say what happens on the other side of it.
What I do know is it'd be pretty sweet if black holes are entry ways into new universes and our universe is the exit point of some other universe and we are currently existing in an exit point among a massive chain / fabric of countless realities, all of which we are connected to.
So until we build chips that can reach the edge of our universe or ships that can travel to the origin of the big bang, or come up with irrefutable and provable models of what's really happening, I'm going to go with the sweetest possibility I can imagine.
Yes. A white hole is not homogeneous and isotropic. Our universe is.
> irrefutable and provable models of what's really happening
Science can never meet this requirement, because we can never collect all possible data. But that doesn't mean we can't rule out some models. We can rule out a white hole model of our universe, for the reason I gave above.
The rules—as understood through general relativity and quantum mechanics—change drastically at the scale of a singularity. No amount of observing shadows of a singularity conforming to predictions changes the ignorance regarding the interior of the singularity.
Given that these conditions are fundamentally outside of our current observational capabilities and that existing theories are known to break down under such extreme conditions, it is presumptuous to apply conventional physical models developed for ‘normal’ spacetime. Until we have a unified theory of quantum gravity that is experimentally validated, any claims about the behavior within singularities remain speculative and should be treated with appropriate skepticism.
Just because it appears from our reference frame that a black hole compresses to a point and a white hole emits from a point, does not mean that is the physical effect occurring from within the singularity. When dealing with infinite, the rules change. For all we know, beyond the event horizon, the environment could be as fantastical as a land made of ice cream and lollipops—where everything around is sweet and edible.
Doubt that?
Send a probe into the nearest black hole and somehow retrieve it. Also, locate and observe a white hole, and develop an engine with infinite thrust that can approach it. I'm sure there will be enough observational data then to make finite claims. Good luck!
Nonetheless, I suspect you are greatly overestimating the likelihood of human matter falling into a black hole.
0: https://www.forbes.com/sites/startswithabang/2019/07/02/no-b...
I can't back this up, but my theory would be near 100% of all matter ends up back in a black hole (in a very long time). If no energy is created or destroyed, whatever force is expanding the Universe will eventually un-expand it. The alternative to me seems insane - you have a closed system with finite states (insanely large numbers of finite states) that can never return to a previous state, even after near infinite time? Doesn't add up. I'm not aware of any closed-loop system (where energy is conserved) that doesn't return back to the original state.
This is not correct. First, there is no concept of "energy conservation" that applies to the universe as a whole the way you describe. Second, our best current model of the universe, based on the equations of General Relativity, says it will keep expanding forever.
> you have a closed system with finite states
Our best current model of the universe is that it is spatially infinite. So it would not have a finite number of possible states.
If the concept of energy conservation does not apply to the entire Universe, then we must ask where the additional energy created comes from or is removed. I'm not aware of evidence to suggest that it is not conserved. If there was something like this, it seems like something that could be exploited.
> Second, our best current model of the universe, based on the equations of General Relativity, says it will keep expanding forever.
I'm aware that's what is currently supported, but the collapsing Universe followed by the expanding Universe loop ties everything up nicely (cyclic model [1]).
I'm also aware that this is essentially based on the second law of thermodynamics [2], but I think as long as all processes a system undergoes are fully reversible, it should in theory be able to reverse. It would be like observing a binary counter: 0000 is the start, then we observe numbers like 0110 and 1011 and say "see, entropy is increasing indefinitely", but eventually we tick over to 1111, then 0000.
Of course if any system variable changes irreversibly (i.e. space expands infinitely), then it would not work. But given there is ongoing debate about the Hubble constant [3] and I think there is still room to believe a cyclic model could be plausible.
[1] https://en.wikipedia.org/wiki/Cyclic_model
[2] https://en.wikipedia.org/wiki/Second_law_of_thermodynamics
[3] https://en.wikipedia.org/wiki/Hubble's_law#Hubble_tension
No, we musn't, because the reason why the concept of energy conservation does not apply to the entire universe is that there is no well-defined concept of "energy of the universe as a whole" to begin with. So you can't even frame a well-defined question about whether this thing that doesn't exist is conserved or not.
> the collapsing Universe followed by the expanding Universe loop ties everything up nicely (cyclic model [1]).
This is a speculative model which at present has no evidence that favors it over our best current model. Of course we might discover more evidence in the future that would change that. If that did happen in future, then yes, we would have to reassess the "energy of the universe as a whole" question as well. I am not familiar enough with the details of cyclic models to know whether there is a well-defined "energy of the universe as a whole" in them or not.
This is not correct. Gravitationally bound systems will remain bound in a universe with a positive cosmological constant. A "Big Rip" scenario, where gravitationally bound systems get ripped apart and eventually every elementary particle is beyond the cosmological horizon of every other, requires "phantom energy", i.e., a density of dark energy that increases with time.
Light from sources at cosmological distances is redshifted, and we have several excellent lines of evidence for that, notably https://en.wikipedia.org/wiki/Lyman-alpha_forest which clearly shows that the emitted light was redshifted progressively as it reached intervening clouds of hydrogen on its way to our spectrographs.
Energy is directly proportional to wavelength. For light, E = hf, where h is Planck's constant. It's inversely proportional to wavelength, E = (hc)/λ, where c is the speed of light and λ is the wavelength. Redshifting means longer wavelengths, so less energy at the point of detection compared to the point of emission.
Energy conservation is local. At large scales, photons lose energy. Where does it go?
After you've thought about that on your own for a bit, compare your thinking with working physical cosmologist Sean Carroll's blog entry https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
The connection to what I wrote above is that General Relativity guarantees that at every single point in a general curved spacetime there is a small patch of (quasi-)static flat spacetime. That patch can be ultramicroscopic deep within a black hole, or very large (in human terms) in interplanetary space in our solar system. In that flat patch energy conservation holds, as Carroll described. Outside that patch, we can see light redshift or blueshift through spacetime; the same energy shifts happen to massive particles like cosmic ray electrons, protons and neutrinos, too. It also happens to gravitational waves.
Event horizons break time-reversal symmetry. Nothing comes back from the other side. Generically, in the presence of a relativistic quantum field (like the 17 in the standard model of particle physics), an event horizon radiates greybody radiation comparable to a blackbody with a temperature inversely proportional to the horizon area. To save words, we just use that temperature (and go back to a calculation of the exact spectrum when greater accuracy is required). Black hole event horizons are really cold. Cosmological event horizons are ridiculously cold. And really it's the apparent horizon that has a measurable temperature. There may not be an event horizon in finite time, but in many circumstances the apparent horizon is indistinguishable by experiment. We have evidence of matter crossing to the other side of these horizons (e.g. from tidal disruption events and black hole/neutron star collisions); we have decent upper limits on horizon temperatures for a small handful of black hole horizons. (And someday we will have precision laboratory evidence of Unruh event horizon temperatures).
If the universe undergoes recollapse, black holes will tend to merge into ever bigger black holes as galaxy clusters freely-fall closer together (and then interact with each other, merging into gargantuan elliptical things with silly large velocity dispersions generating all sorts of collision & merger opportunities). So you need some unknown extra step to undo the time-reversal invariance violation of black hole horizons. Have any ideas?
The bright side is that black holes hold so much entropy that you aren't in any danger of violating the second law of thermodynamics via recollapse, unless your idea does that accidentally. The entropy is easy to see in a Boltzmann sense. Given the "no hair" conjecture, a black hole is fully described by a small number of parameters. Those parameters are a macrostate. A microstate is a configuration of things that fell into the black hole imparting its mass and spin and charge(s)). Entropy is proportional to the log of all the possible microstates for that macrostate. As more matter goes into a black hole, its entropy skyrockets. (The increase in BH entropy absolutely dwarfs the decrease in vacuum entropy; since hard vacuum is a macrostate, and every reasonable volume of hard vacuum is totally substitutable for every other similar volume of hard vacuum, there's a lot of entropy there too. As we fill the vacuum with ejected stars, radiation, high-metallicity dust, and so on as we squash galaxy clusters together during recollapse, that's a loss of entropy. But still nowhere near as low an entropy as the original cold gas clouds that were around after the cosmic microwave background formed. So your idea that recollapse means low entropy is on shaky ground, especially if you are taking your "binary counter ticks back to zero" idea seriously. You can take some comfort that lots of very smart people who can do the maths and have decent physical intuitions (Penrose comes to mind) have struggled with entropy in a cyclic cosmology.
Finally, the Hubble tension at its very strongest changes the age of the the oldest galaxies from almost 14 billion years to almost double that, not whether it the universe is expanding faster now than it was between one and four billion years ago. It's not something on which you want to rest a theory of cosmic recollapse.
While this is a good blog post on this topic, I would point out that Carroll does gloss over one crucial point. He says:
"[T]he best you can rigorously do is define the energy of the whole universe all at once, rather than talking about the energy of each separate piece."
What he is glossing over here is that you can't "rigorously" do this unless your standard of "rigor" is looser than it is supposed to be in GR. Any way of defining "the energy of the whole universe" will involve what are called "pseudo-tensors", which depend on particular choices of coordinates. The standard of rigor in GR is supposed to be that everything that has physical meaning is expressed in terms of tensors, i.e., objects that do not depend on particular choices of coordinates. By that standard, it is not possible to "rigorously" define "the energy of the whole universe", as I pointed out in another post upthread.
I completely agree for cosmological spacetimes. I largely agree more generally, other than thinking one shouldn't be afraid of Landau-Lifshitz and company for fear of lack of "rigour", or even resorting to vectors[1] in appropriate circumstances. Everyone should already know doing so can be a footgun. If not, someone will call them out (reviewer 2 if unlucky).
That said, it's just a blog posting aimed at non-scientists. As I know you know, Carroll has well-regarded lecture notes and now a textbook [§3.5 in the lead up to eqn 3.92 is roughly the meat of the blog post, and for the sentence you picked out cf §3.8's discussion of the use of Killing's equation, around eqns 3.178 - 3.181, defining a total energy after slicing certain spacetimes (but not the cosmological one, of course)] for anyone who wants more "rigour". :-)
Another nice -- in fact, imho better, because of how it gets to eqn (3) [and the side comment in square brackets immediately after it -- it's not a gravitational statement!] -- blog entry covering similar territory is by Michael Weiss (the diagonalargument.com one) & John C Baez: https://math.ucr.edu/home/baez/physics/Relativity/GR/energy_... Cherry picking their support for the point you make: 'These pseudo-tensors have some rather strange properties. If you choose the "wrong" coordinates, they are non-zero even in flat empty spacetime. By another choice of coordinates, they can be made zero at any chosen point, even in a spacetime full of gravitational radiation. For these reasons, most physicists who work in general relativity do not believe the pseudo-tensors give a good local definition of energy density, although their integrals are sometimes useful as a measure of total energy.'
I will admit that your notion of "rigor" is unusual to see in strongly relativistic astrophysics (e.g. NS-NS GW 170817 literature), and practically unheard of in the low speed weak field limit. So what? Is using GEM's vectors there somehow wrong just because it's a pain to deal with relatively boosted frames?
I think you're wrong that 'Any way of defining "the energy of the whole universe" will involve what are called "pseudotensors"'. There are other approaches. More germane to astrophysics -- although this is perhaps arguing more with Weiss&Baez than you? -- there is lots of work on trying to define quasilocal energy without pseudotensors. See especially e.g. the first paragraph and endnote [1] of Brown & York 1993 PRD vol 47 iss 4 <https://harvest.aps.org/v2/journals/articles/10.1103/PhysRev...> (direct PDF). And now I should really make myself time to trawl through the recent relevant work of self-styled "mathematician who pretends to be a physicist", Steve McCormick <https://www.quasilocal.com/#section2>.
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[1] For fun: "Linear algebra is easy. Just remember [that] real numbers are vectors, polynomials are vectors, integrable functions are vectors, matrices are vectors, tensors are vectors, and so on. As I said, easy." @j_bertolotti lighting a fire https://twitter.com/j_bertolotti/status/1786407421755134325 And a golden reply, "All tensors are vectors. They're not in the same vector space as the vectors they're maps for, but a tensor product of vector spaces is another vector space, satisfying all the axioms." https://twitter.com/roystgnr/status/1786449834498511130
No, that's not the issue. "GEM's vectors" still correspond to invariants--you can re-express them, if you like, as appropriate contractions of the stress-energy tensor or the Einstein tensor. Expressing them as vectors in a carefully chosen coordinate chart is just a convenience, to make the math easier to understand.
The same is not true of the "pseudo-tensors" that are used in attempts to define a "total energy of the universe as a whole". Those do not correspond to invariants. Expressing them in a carefully chosen coordinate system is not just a convenience; it's a necessity, because in other coordinate charts they either vanish or you can't even write them down at all. That's the issue.
> Brown & York 1993
The term "quasilocal" in the title should be an indicator that this method does not solve the issue I described above for the universe as a whole. It does give an alternate way of making sense of the concept of "gravitational binding energy" for a finite, bound system surrounded by vacuum, or of the idea of treating the mass of a black hole as a form of energy. But the universe as a whole is neither of these things.
Real closed loop systems are purely theoretical and the only one we know of is the Universe, so your statements about them are circular. One big unidirectional aspect of the universe is entropy - it’s a non-reversible state. Going to a previous state requires more energy than what you started with.
I think space is a little like an insanely low-friction version of water, i.e. a quantum foam [1] (or similar fluctuations caused by the structure of space-time). It may not be perceivable but it would mean that space could exert a drag in the same way water does. You could imagine it pulling out energy from a photon and red-shifting it, until eventually it just absorbed it. If that was true, it would also add a distance-based offset for all observations of the Universe and affects things like the Hubble constant.
That would be just one way in which a contraction may occur - nothing exciting, just all the things travelling further away worn down by the substance they travel in. Then there would be several ways to bring it all back together into a big bang.
> Real closed loop systems are purely theoretical and the only one we know of is the Universe, so your statements about them are circular.
We have simulated closed-loop systems of many kinds, I think we can make educated guesses about how they may behave. As long as all state transitions undergo a reversible function, it should eventually return to its original state?
> One big unidirectional aspect of the universe is entropy - it’s a non-reversible state.
I don't think that's entirely true. Going by the big bang, the Universe started as one large point in space-time that exploded. Not long after things started to clump together into larger and larger particles/objects, there is currently nothing to make me believe that it will not create larger and larger clumps of matter, i.e. super massive black holes.
> Going to a previous state requires more energy than what you started with.
Then where did that energy go?
Anyway, I understand this is highly theoretical and I'm not convincing anybody here, but it is nice to share some ideas.
[1] https://en.wikipedia.org/wiki/Quantum_foam
[2] https://en.wikipedia.org/wiki/Hawking_radiation#:~:text=Hawk....
As I understand it, expansion of the universe is expansion of the fabric of spacetime. It's not about objects just travelling away from each other. Thus the quantum foam friction analogy (even if true) wouldn't really apply.
> We have simulated closed-loop systems of many kinds, I think we can make educated guesses about how they may behave.
Don't mistake the incompleteness of our models for the truth. They are approximations for testing out ideas about the universe but that doesn't mean the approximations themselves exist.
> As long as all state transitions undergo a reversible function, it should eventually return to its original state?
But we know that non-reversible functions exist, both in terms of entropy and time irreversibility, & these functions happen all the time in our universe.
> Then where did that energy go?
Waste heat that can't be recovered to reverse entropy because it's already diffused throughout the universe & thus there's no local maximum to exploit. That's what the heat death of the universe refers to.
Not at all. Black holes are not magic; they don't swallow up everything.
> maybe all whiteholes are in our past, and we came from one we call Big Bang.
No, this is not correct. See my other response upthread about this.
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 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_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>. 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/>) 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 evidence.
Gravitational attraction tends to cause the trajectories of freely-falling ("floating in empty space") masses to converge. Dark energy tends to cause the trajectories of freely-falling masses to diverge. We see this in the sky: distant galaxies are freely-falling but their trajectories are away from each other (and from us).
As far as we can tell though, the "source" of dark energy is the cosmological constant. Physical interpretations usually start by slicing spacetime into spaces aligned along the cosmological time (the scale factor). In successive spatial slices ordinary matter, radiation, dark matter, and so forth all get sparser towards the future. We treat these as a sort of fluid or gas that dilutes away with the expansion of the universe, therefore the density of each fluid at a typical point differs from spatial slice to spatial slice (it's lower in the future). The cosmological constant is constant in every spatial slice. So if we were to turn it into one of these fluids, it would not dilute or thin out over time: its density at a typical point is always the same. Representing a geometrical feature (the cosmological constant) as a space-filling fluid with certain properties makes it easier to study what happens if the cosmological constant isn't constant . (Does it fluctuate? Does it get weaker or stronger over time or in the presence of overdensities of matter?)
Cosmic inflation introduces another of these fluids that like dark energy serves to separate rather than draw together the others. It's very very strong in the early part of the universe (the inflationary epoch), but disappears very early too. In some flavours of inflation, the "inflaton" field decays into standard-model matter; in others it just decays into weaker and weaker versions of itself and by the time there are electrons, positrons and photons it's basically so weak that it's undetectable.
The inflationary epoch somewhat matches your intuition that a big source of energy pushed space apart. The most important difference (at this "explain like I'm..." level) as far as I can tell is that there was no point in space that someone in the early universe could point to as the centre or source of inflation. A gravitating object has a centre of mass, and you can point to and away from that object, i.e. there is an up and down with respect to it, because it doesn't surround you like a shell. The inflaton field was strong everywhere, there was nowhere in space "outside" it.
Here is a reasonably accessible "outreach" article on cosmic inflation: https://www.ctc.cam.ac.uk/outreach/origins/inflation_zero.ph...
Where are you getting this from?
Alternatively, and thinking purely classically, if we do t -> -t, what happens to a perfect absorber, which takes in anything and reflects nothing impinging on it? It should spit out arbitrary things and reflect everything impinging on it. (Here I'm thinking of the Poynting vector for plane waves with their origin below the photon sphere and moving outwards vs just above the antihorizon and moving inwards -- the latter can't enter the WH).
(Maybe easier to think about if the BH absorption isn't total, like if we spin the black hole and have the plane waves (or their polarization) move against the rotation, and the WH is just time reversed -- the WH emits a bit of radiation which joins more outside the antihorizon, and the combination flies off to infinity, and not thinking too hard about the interior metric; although Wald deals with much of this in the text around eqn (12.4.18)).
That is not describing what you described.
> if we do t -> -t, what happens to a perfect absorber, which takes in anything and reflects nothing impinging on it?
It becomes a perfect emitter, which emits anything and reflects nothing impinging on it. In other words, a white hole.
To put it another way: the inside of a black hole is a region from which nothing can escape and into which everything can fall. The inside of a white hole is a region from which everything can escape and into which nothing can fall. Things coming out of a white hole are escaping from the inside. They aren't reflected.
Everything in Wald that you are referencing is describing what I just described. It is not describing what you described.
The first is right, the second is wrong. The time reverse of "no reflection" is "no reflection". It is not "reflect everything". "No reflection" means complete transmission through the surface in question. Reversing time just reverses the direction of transmission, in this case from inward (black hole) to outward (white hole).
Qualitatively what happens, in your view, when the WH touches the beam? Is it just the time reversed picture of the BH intercepting the BB? There's a part of the first spacetime where some of the light is trapped in the BH as it flies off to infinity after its encounter with the beam. Is there a part of the second spacetime in which some of the light is trapped in the WH? If so, where is it if the initial conditions are a Bonnor beam at large spacelike separation from the white hole? Does the WH cut a gap into the beam?
Alternatively, take two widely separated BHs. Grind out the Raychaudhuri equation, bearing in mind the focusing theorem. Now take two widely separated WHs. What's different? How does a circular orbit of two WHs evolve? Outgoing GWs tend to circularize elliptical binary BH orbits. Can a circular binary WH orbit decircularize? How? ("Incoming GWs from initial conditions" is not very satisfying).
The problem I think is confusing the reversal of the entire BH spacetime with a WH stitched into an ordinary Minkowski in the asymptotic limit, or into a cosmology. (Bonnor is essesntially the latter). More broadly, a WH should be able to live with future-directed null geodesics.
Of course, I could only agree with a response like, "well such a WH is almost certainly unphysical", but maybe we could ignore that in order to think about what happens when a plane wave hits a WH.
No. Nothing can get into a white hole from the outside.
> where is it if the initial conditions are a Bonnor beam at large spacelike separation from the white hole?
You are mistakenly thinking of a white hole as a "thing". It isn't. It's a region of spacetime that nothing can get inside. Or, to put it another way, it is a region of spacetime that is to the past of something else: either a black hole (if you are talking about the maximally extended Schwarzschild spacetime) or an object like a star that the white hole expanded into.
So if you "aim" anything at a white hole, you won't hit the white hole; you'll hit whatever thing the white hole is to the past of. Either a black hole, or an object that the white hole expanded into. That is what the Bonnor beam in your scenario would actually intersect.
Similar remarks would apply to your other scenarios; the actual objects you would end up dealing with would not be white holes, but whatever the white holes were to the past of.
There is a whole field of CS that deals with minimizing error when doing floating point math. They just probably use decent algorithms/encoding.
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-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> 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/777/1/1...>.
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/> and <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/ (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/... 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...> 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>
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_Jacksonvi...> is a really great slide deck.
ETA^3: Bernuzzi "Introduction to Numerical Relativity" @ IHÉS winter 2024 https://www.youtube.com/watch?v=RcdntEBrcuM is probably pretty good.
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. :)
Below plank length, plank time, plank energy we don't have insight into the inner workings.
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.
I get that we have no experimental evidence of what it looks like inside but surely we could simulate the photonic environment?
So look back and I suppose you'd see a massively phase shifted pinpoint of the universe in the line going from singularity through your eye and out of the event horizon? It wouldn't be straight out, but more like the "deorbit"
So if I'm inside the event horizon, the light that's emitted from the singularity should hit my retina, right? What am I missing?
It's more complicated with rotating black holes. 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.
The singularity is not a place. It's an instant of time--the last one you experience if you fall into the hole.