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It was several peer reviewed article on Arxiv but it was a few years ago that I followed the research and some of the proposed tests. However I'll take a look and if I can find the papers. If I can I'll post it. Point of detail the singularity conditions regarding the EH involve infinite redshifts and subsequent time dilation relations involving the EH. These conditions are the ones directly involved with regards to Hawking radiation. This also involves Unruh radiation https://arxiv.org/abs/0710.5373

I like indulging nice guys, Moon, so I'll start us off. Consider a constant acceleration ship, say 1g, for the confort of the occupants. "From the planetary frame of reference, the ship's speed will appear to be limited by the speed of light — it can approach the speed of light, but never reach it. If a ship is using 1 g constant acceleration, it will appear to get near the speed of light in about a year, and have traveled about half a light year in distance. For the middle of the journey the ship's speed will be roughly the speed of light, and it will slow down again to zero over a year at the end of the journey. As a rule of thumb, for a constant acceleration at 1 g (Earth gravity), the journey time, as measured on Earth, will be the distance in light years to the destination, plus 1 year. This rule of thumb will give answers that are slightly shorter than the exact calculated answer, but reasonably accurate." From Space travel under constant acceleration - Wikipedia We can then make other quick estimates to travel time "From the frame of reference of those on the ship the acceleration will not change as the journey goes on. Instead the planetary reference frame will look more and more relativistic. This means that for voyagers on the ship the journey will appear to be much shorter than what planetary observers see. At a constant acceleration of 1 g, a rocket could travel the diameter of our galaxy in about 12 years ship time, and about 113,000 years planetary time. If the last half of the trip involves deceleration at 1 g, the trip would take about 24 years. If the trip is merely to the nearest star, with deceleration the last half of the way, it would take 3.6 years." Now you might say"That's not too bad.". Only 113 000years pass on their home world to send a ship 100 000 light years. And a relatively short time to send it to a nearby star. Even doubling that time for two-way journey seems reasonable. Now comes the hard part. ( and I'm not going to attempt to quickly find/perform the calculation; I'll leave it to better, more fastidious, minds than mine ) How much Hydrogen do you need to carry, or collect along the way, in order to sustain a fusion reaction capable of sustaining a constant 1g acceleration/deceleration ?

The collapsing star is a dynamic state, and quite different from a free-falling object. There's dense stuff, and then not even Pauli-exclusion can support it. OK, so there's even more squish, at least at first. A spatial dimension rotates and is replaced by time, and that time dimension is bounded. What was the time dimension rotates out to a spatial one, one with nearly infinite extension at that. Lots of new room to spread out, but the causal light cones don't allow arbitrary travel down this big space, so I cannot say the compression ends. An example of the space available inside a black hole, Sgr-A and the black hole at the center of Andromeda share a common singularity. They're the same black hole, a region of 4D spacetime bounded by a 3D event horizon hypersurface, and in that case, the same (connected) hypersurface. It's only in a slice of coordinate space at a given time that the one object has multiple cross sections, manifesting as a pair of black holes to us, for now. None of the above is particularly an answer to the question of if there is compressed matter in an established black hole. In coordinate time, yes, it's very dense, but that's more like length contraction than pressure. None of the matter actually reaches the event horizon in coordinate time, and yes, in that state, it (the original collapsing star matter) is very much under compression. The singularity condition exists, but isn't described, precisely because the physics there is singular, sort of like asking what the perspective of a photon is like. Got a link? That sounds like pop nonsense. Is it peer reviewed? That makes more sense. Still, to be matter, it has to persist, no? Agree to all. There's also a naked singularity. You can for instance just keep dropping electrons into a black hole until the charge is more than the gravity and no more (isolated) electrons can be added by any means. Similar issues if the infalling matter adds too much angular momentum. A given mass can only have so much of that. These are examples of frame independent singularities not obscured by the coordinate singularity of the EH. Ditto with the LLM answers, which is just massaged google results. Anyway, thanks for the post. Good informative stuff in there.

Short term self-interest among plutocrats sounds like another way to say "capitalism." Or "late stage capitalism" anyway. I will try to answer your points better tomorrow.

Capitalism isn’t necessarily to blame, at least not as much as our failure to include negative externalities into the costs paid by producers and consumers of goods and services. Manufacturer doesn’t get fined for poisoning the water. Consumer doesn’t get taxed for continuing to buy goods from that manufacturer. The cycle of water poisoning persists while healthcare needs skyrocket and economic burdens get shifted (shafted?) to everyone downstream who weren’t ever even involved in the transaction. Carbon taxes were an attempt to address this and it want capitalism that made it fail. It was politics and short term self-interest among plutocrats.

so you googled a bunch of answers so tell me google what happened to the mass of the collapsing star then.... can you answer that or did it simply disappear. That is directed at google not you lol . Would you like to see equations that directly relate to the density term in regards to the collapsing star? https://arxiv.org/pdf/2310.17647 see section 4 If Victor Toth stated that then he only looked at the vacuum solutions of the interior and ignored the coordinate assigned for the singularity R=0. Not surprising though most articles tend to ignore that part as no one feels the singularity condition should exist. I have another related article that suggests that the BH may simply be a neutron star that has collapsed just beyond its EH but is still present. As mentioned no one knows beyond the EH. So its really anyone's game until we can find a means of indirect evidence to give us more clues. Gravity waves is a viable possibility others are mentioned here. The article that has some suggestive tests via the accretion disk is here https://arxiv.org/pdf/1104.5499 there is also a section covering Hawking radiation. However one will be quite surprised at all the processes matter undergoes in that accretion disk. I recall years ago I asked my instructor " How can you possibly have infinite density or near infinite density" his answer was that although fermions cannot share the same space with the same state that restriction does not apply to bosons. " you can in fact have extremely high density and still be a vacuum solution with incredibly high temperature and density. Vacuum describes a pressure term. Its not the energy density. You get the energy density by the equations of state for the particles contained within a region. Its one thing that often confuses ppl concerning vacuum. It can be positive or negative and can describe any range of energy density. If you think about that you might consider that a star is simply a condensed matter field it can be equally treated as a field. We know in cosmology we get a similar phenomena due to the BB and its mass density terms. I didnt have time to properly respond to the quoted section earlier as I was at work. Having time now I can provide a better response. just to add the singularity at r=0 is a true singularity it cannot be removed by a change in metric choice. The event horizon itself is often described as a singularity condition however that is a coordinate singularity and not a true singularity. https://en.wikipedia.org/wiki/Kerr_metric "Rotating black holes have surfaces where the metric seems to have apparent singularities; the size and shape of these surfaces depends on the black hole's mass and angular momentum. The outer surface encloses the ergosphere and has a shape similar to a flattened sphere. The inner surface marks the event horizon; objects passing into the interior of this horizon can never again communicate with the world outside that horizon. However, neither surface is a true singularity, since their apparent singularity can be eliminated in a different coordinate system. A similar situation obtains when considering the Schwarzschild metric which also appears to result in a singularity at 𝑟=𝑟s dividing the space above and below rs into two disconnected patches; using a different coordinate transformation one can then relate the extended external patch to the inner patch (see Schwarzschild metric § Singularities and black holes) – such a coordinate transformation eliminates the apparent singularity where the inner and outer surfaces meet. Objects between these two surfaces must co-rotate with the rotating black hole, as noted above; this feature can in principle be used to extract energy from a rotating black hole, up to its invariant mass energy, Mc2." I suspect this is what Victor Toth was referring to hope that helps Mathius Balu has an excellent coverage of this http://www.blau.itp.unibe.ch/newlecturesGR.pdf He will use the BH to help explain: "artifacts of coordinate choice" I would have to dig through it though to relocate the relevant section lol and just to add flames to the proverbial fire. A rotating BH has more than one event horizon..... google is useful but unless your aware of other factors getting good answers can often mislead down the wrong google pathway. For example simply googling BH singularity will more likely than not describe the coordinate singularities regarding the EH rather than the R=0 singularity condition. This wiki has the relevant detail regarding the Gravitational singularity as the link describes it The case r = 0 is different, however. If one asks that the solution be valid for all r one runs into a true physical singularity, or gravitational singularity, at the origin. To see that this is a true singularity one must look at quantities that are independent of the choice of coordinates. One such important quantity is the Kretschmann invariant, which is given by 𝑅𝛼𝛽𝛾𝛿𝑅𝛼𝛽𝛾𝛿=12𝑟s2𝑟6=48𝐺2𝑀2𝑐4𝑟6. At r = 0 the curvature becomes infinite, indicating the presence of a singularity. At this point the metric cannot be extended in a smooth manner (the Kretschmann invariant involves second derivatives of the metric), spacetime itself is then no longer well-defined. Furthermore, Sbierski[21] showed the metric cannot be extended even in a continuous manner. For a long time it was thought that such a solution was non-physical. However, a greater understanding of general relativity led to the realization that such singularities were a generic feature of the theory and not just an exotic special case https://en.wikipedia.org/wiki/Schwarzschild_metric#Singularities_and_black_holes

Technology basically facilitates tendencies and the issue is that especially younger folks are used to the instant gratification offered by things like technology (essentially everyone is carrying a dopamine machine with them at all times). I think we are a bit late in the game for that. The next generation of teachers are already not used to that anymore. In addition, the commodification of education and the increasing view of students as clients is starting to erode education in university as well. Educators in many systems across the world are struggling now to instill critical thinking skills and while it was already deteriorating over last decades, the COVID-19 pandemic has created a bit of a jump which makes things just way more visible otherwise. The reality is that we don't need an oppressive government or system to achieve those goals. That was very much a post WWII type of thinking. Now we have methods to do it voluntarily to ourselves, driven by capitalism, rather than political ideologies.

On any subject but UFOs I would agree with you. Let's do it!

But we’re talking about scientific analysis, which tries to remove such extraneous baggage from discussion (unless you are studying that particular phenomenon) Every time I have invited you to do a technical analysis of this you have declined. Which is unfortunate, because it would be interesting, but also means that this assertion is not based on actual science. Instead, it is (as some of my former students would say) a matter of pressing the “I believe” button. But one can’t pretend that this is science.

The Von Neuman hypothesis strikes me as the most neutral in its assumptions: for whatever reason, advanced civs may send out self-replicating units in the millions (and thence to billions via replication) and they just blanket all star systems in the spectral range most hospitable to life. Or not. Other filters are possible. We can't say what cost/benefit ratio is determined by a K2-plus civilization, or if anthropological fascination has anything to do with it, or what ethos they may have about contact, or if carbon-based life is seen as interesting...or just an old-fashioned and disgusting fetish that preceded the Glorious Uploading. Or quaint, and as @Moontanman mentioned, a niche hobby for some tiny fraction that studies emerging sentience. If aliens were machine intelligences, they could have some form of immortality that would open up motivations we can't conceive of, where shutting down for a ten thousand year journey would be routine. Or a nice field trip for fourth graders.

Humans are the we, our society assigns motivations and emotions to our perception of the world. The idea we would be interesting is indeed a human assessment, I have to admit I would visit an alien planet if I could and while it might be difficult for us to imagine, an advanced civilization might grant researchers who specialize in primitive cultures exclusive rights to study a new civilization. Such a study might take millenia and all the while we are being studied they do not officially contact us to prevent the study itself from influencing our behaviors as much as possible. They may share our desire to acquire knowledge and a small fraction of them study newly emerging civilizations. The reasons why they visit could be anything, indeed they could be reasons we couldn't understand, they are aliens btw. Hell there are humans who specialize in studying animal excrement... maybe that is why they anal probe so many 💩 Trying to discern their motivations is secondary at best to figuring out if this is going on at all. There is no reason to debate the whys and hows until we know if its actually happening and we can't know that until we start seriously looking at the data we have instead f dismissing it because we just can't imagine how it could be possible. Traveling slower than c is no barrier to star travel, I honestly don't see why anyone would think that, if our own civilization wanted to star travel it is conceivable. I kinda doubt you'd find anyone who wanted to spend that much money to do it but that is a capitalist view point. Not all civilizations will necessarily be motivated by profit. Personally I think the best motivator would be desire for knowledge. That one thing has motivated humans to do some really dangerous crazy stuff.. like the Moon landing.

I fear the GOP could have some success stoking fear through distorted reporting on campus violence. Amanda Marcotte made some sharp observations yesterday in Salon, on how TFG et al are doing this to further depict the Left as all lawless hooligans. https://www.salon.com/2024/05/03/donald-is-using-campus-to-stoke-right-wing-violence-for-the/ Despite all the hysteria in the punditry about campus protests against the war in Gaza, by and large, the student activists have been peaceful. Even at Columbia University, where an ill-advised police crackdown caused an inevitably angry reaction from protesters that led to a building occupation, this has been true. As former Washington Post journalist Paul Waldman explained in his newsletter, "People who have actually reported from the protests (see here or here) have by and large found them to be well-behaved." The vast majority of scary, violent images stem not from the protesters themselves, Waldman argues, but from the police crackdowns. "At the universities where the administrators had the sense to just let the students have their say, there has been almost no violence." As the cable news has breathlessly covered, there was violence this week at UCLA. But even then, it was not the leftist protesters to blame, but a gang of far-right counter-protesters who rushed in and started to attack students. As ABC 7 reported, violence only broke out "when counter-protesters tried to break down the encampment." Unfortunately, this was framed by much of the media as "clashes" between protesters and the right-wing assailants. Any good faith reading of the situation is clear: The far-right demonstrators stormed the encampment and started the violence. The student protesters were defending themselves.

But who is doing this? Who is “we”? The arguments against such travel are based on physics - e.g. travel is limited to slower - probably much slower - than c. It’s the alien proponents that are assigning motive - that humans and the earth are so fascinating that we keep being visited by them. It was not a scientific paper, and the conclusion was…what? They detected something that could not be identified. That’s not dismissing anything. It’s acknowledging that there’s not enough information to draw a definite conclusion.

How particles scatter, or form new particles etc etc always depends on their cross sections . That uses the Breit Wigner equations along with the Feymann golden rules. It not some case of a photon knowing anything. When it encounters another particle the cross sections and Feymann golden rules are used to determine the end results. Granted we also have a table that is helpful . https://en.m.wikipedia.org/wiki/Table_of_Clebsch–Gordan_coefficients

With e.g. electron/positron annihilation photons are normally produced. Photons with sufficient energy colliding could become an electron/positron pair etc as I said. Gravitons are the only possibility I see for low energy photons. A longer quote to show what I find problematic: "A photon is its own antiparticle." .... "anti-photons will annihilate with matter photons." How do photons distinguish between anti-photons and matter photons? Presumably if two high energy matter photons collide it is impossible for them to create a matter/antimatter pair. If you have a reference to there being both anti-photons and matter photons please share it. It can be the particle or anti particle which falls in. It has, loosely speaking, negative energy which reduces the energy/mass of the black hole.

My point is that when we assign human motivations to aliens we have no leg to stand on, in the Star Trek universe all or nearly all of the aliens are humanoid in both stature and motivations. I have to agree yet the devil is in the details. When your attitude is that all sighting are equally improbable you make a good point but this is simply not true. Not all sightings can be dismissed so easily, some cannot be dismissed at all. I few posts ago I posted a scientific paper about a UFO sightings but everyone has ignored it. This sighting is not so easily dismissed... still an unknown but obviously not a hubcap. The Fermi paradox and the Drake equation make some rather easily manipulated assumptions that can be used to predict almost any outcome. There could be reasons we are totally unaware of, from fear of bio contamination to simple laws a space fairing civilization might have about first contact. There is really no way to assert any reason over another. I think that if controlled hydrogen fusion is possible all those other concerns become moot. IN fact I think a pretty good argument can be made that any space fairing civilization would avoid planets and favor space habitats over colonising planets. This could led to the entire galaxy being inhabited by Von Neumann Probes colonising the galaxy via going to a star system and utilizing the asteroids and comets like bodies to build and maintain space habitats. This would also make star travel unnecessary as long as you had a star with debris around it like our Sun. We could realistically use the idea of rotating space habitats to build colonies that would when assed up amount to many times as much space as the surface of the earth. There are so many possibilities that do not limit an intelligence to just one planet but one thing you keep asserting bothers me a bit. You seem to think that Von Neumann Probes and the info they collect wouldn't be useful because ( I am assuming here) that the individual who sent the probe would be dead way before any data could be harvested from the probe. @TheVat explained why your take on this isn't as profound as you seem to think it s The possibilities of technology really do expand this discussion to new areas.

I suppose it is also possible that life is manufactured by some advanced civilization. The manufactured beings may never reproduce except perhaps to manufacture a new one when an old one is lost. That way you could build in the capability up front to suspend biological processes for long voyages and add other features that would be beneficial for long voyages, without worrying about multiple generations or boredom.

Not quite destructive interference you can have full annihilation if the two wavefunctions are equal but opposite its realistically no different between matter and antimatter colliding with its opposite. Think of all particles are field excitations under QFT. You can get full annihilation with matter why would photons as a boson be different the antiparticle is asymmetric to the photon. Keep in mind that doesn't apply to probability wavefunctions. You have to look at the creation/annihilation operators specifically for each using QFT. Course you could further consider baryogensesis and leptogenesis which we cannot explain as that also relates.

Correct. We know of no force which can resist gravity once Neutron degeneray is exceeded in a neutron star, This is according to GR and QFT. Both of which have specific areas of applicability. When outside those areas they 'fai' by throwing up infinities; like at the center/future of a BH. IOW, points of infinite density are non-sensical predictions of badly applied models/theories. Also keep in mind that the central singularity, while being the event where geodesics end ( akin to latitude/longitude at the Earth's poles ), is not a location in space, but an event in time, and an infalling observer would be 'running into other stuff' at the end of time, not at the center. X-posted with others

Reading this Japanese philosopher on degrowth and moving away from capitalism, towards "eco socialism," I thought this might be pertinent to overpop and resource use under the present system. https://www.salon.com/2024/05/03/why-climate-change-action-requires-degrowth-to-make-our-planet-sustainable/ ...Saito's argument, as translated by Brian Bergstrom, is that climate change exists because humans as a species prioritize economic growth instead of economic sustainability. Capitalism itself, Saito asserts, is unsustainable. Even though well-meaning liberal politicians like to push for Green New Deals in the hope of continuing non-stop economic growth without the consequent ecological harm, Saito argues capitalist societies need to perpetually consume resources to remain prosperous. As a result, capitalism itself inevitably brings about planet-wide problems like climate change, habitat destruction, plastic pollution and other environmental issues. The only solution is for humanity as a whole to slow down our obsession with work, productivity and materialism. Notably, Saito stresses that the bulk of the burden to consume less falls on the wealthiest among us.

Correct its best to think of singularity as a point where the math used breaks down.

Just a note on singularities: in physics they are places/situations where the currently used theory is not valid. If "the equations do lead to the infinite density singularity" the equations fail where they predict a singularity i.e. fail to predict anything. "Singularity science" is as scientific as Scientology. There may or may not be an unknown theory of black holes with no singularity but that theory or any other will not change what goes on in black holes. Saying they contain a singularity is no more meaningful than saying there is a singularity in Donald Trump's brain. From Halc quoting Rennie "The whole point of a singularity is that our equations become singular there and cannot describe what happens." Maybe some confusion? Photons produced from matter or antimatter interactions can have the same or different polarity etc. Photons can (rarely) interact with each other but not annihilate each other (except by creating a matter/antimatter pair etc. A photon can destructively interfere with itself but this only affects its observed location, not its existence. Some cross posting...

Vacuum can have an energy density ta da lol. That energy density can easily approach infinity keep in mind my original statement had "as close as possible " that allows a QM interpretation on Planck units for cutoff though Gravity has no effective UV cutoff for the mass term. That's a large part of why gravity isn't renormalizable. The IR cutoff is already established. For the record I've had numerous discussions with some mistakes he has made in other articles of his. Sometimes I'm correct other times he is just didn't explain something accurately enough with regards to Victor Toth. Cool character though he's friendly and easily talked to.

The equations are how everybody knows. No links were provided, so I googled the question and the first 8 hits (NASA, Smithsonian, various you-tubes, reddit) all suggest matter is compressed without bound. Much of this list of bad hits is due to my search terms of "black hole infinite density". First correct answer came from of all places Quora, a site known for severe wrongness of replies. Question was: Do black holes have infinite density? Answer by Toth: "The equations that describe some of the simplest black hole solutions, including the Schwarzschild black hole are (drum roll, please)… equations of general relativity in the vacuum. Yes, that’s right. The vacuum. There is no matter. The density is zero everywhere. The Schwarzschild solution is the simplest, spherically symmetric, static vacuum solution of Einstein’s field equations." Next hit was probably the most respectable forum I can name. https://physics.stackexchange.com/questions/246061/are-black-holes-very-dense-matter-or-empty Rennie (I think) replies specifically about the Schwarzschild metric, which wasn't technically the question: "The archetypal black hole is a mathematical object discovered by Karl Schwarzschild in 1915 - the Schwarzschild metric. The curious thing about this object is that it contains no matter. Technically it is a vacuum solution to Einstein's equations. There is a parameter in the Schwarzschild metric that looks like a mass, but this is actually the ADM mass i.e. it is a mass associated with the overall geometry." The Kerr metric is also a vacuum solution, which differs only by a nonzero angular momentum. There is an Oppenheimer Snyder metric that is an 'unrealistically simplified' solution to the formation of a black hole, but it fails to describe conditions at the singularity. I was hoping at least for some indication of the whole compression vs. tension distinction. None of these metrics seem to include Hawking radiation, so they describe black holes that exist for infinite coordinate time. Rennie continues: "[Observers falling with the star collapse] see the singularity form in a finite (short!) time, but ... the Oppenheimer-Snyder metric becomes singular at the singularity, and that means it cannot describe what happens there. So we cannot tell what happens to the matter at the centre of the black hole. This isn't just because the OS metric is a simplified model, we expect that even the most sophisticated description of a collapse will have the same problem. The whole point of a singularity is that our equations become singular there and cannot describe what happens. All this means that there is no answer to your question, but hopefully I've given you a better idea of the physics involved. In particular matter doesn't mysteriously cease to exist in some magical way as a black hole forms." So my post seems to be based on information about static metrics (Schwarzschild, Kerr, others), the geometry of which shows an end to time and no matter at all, but neither do those metrics show the end to the matter that made them since these kinds of black holes are not 'made'. They exist for eternity. So Op-Sny is probably a better metric despite being 'unrealistically simplified'. A coordinate system that isn't singular at the event horizon (like Kruskal–Szekeres coordinates) shows worldlines of infalling particles just ending in time at the singularity, not persisting with the other matter persisting there. The worldline of compressed matter would not end, but only join all together with the worldlines of other particles. As you (as an observer) fall into one, tidal forces pull you apart, not compress you. This doesn't stop at the EH. So compression ever happens, then the naive description would be when you smack into that physical singularity there where everything else has gathered. None of the metrics describe that. At best they just don't answer the question at all, and on those grounds, I am reneging on the authoritarian tone of my prior replies without suggesting that the 'high density matter' description is a better description. Learned stuff today, which makes this a win topic. I hope we all have. Yes, I've seen places that compute that mass. A moon mass is still going to take an awfully long time to radiate away at CMB temperatures. Infinite time actually, at least until the CMB radiation stops adding mass as fast as HR bleeds it off.

You're taking that a bit too far. Aliens who are just like us, would require those things, but life, any kind of life, has some basic universal needs. It would need an energy/food source and to reproduce; that is all. Further, any life that emerged through an evolutionary process, would tend to optimize conditions to satisfy those needs. Their motivations, and decision making, would be based accordingly, and I don't expect that to change, even for a civilization that has been around for billions of years. But you are right. There is a slim possibility it could be ET aliens. Or time travelers, ghosts, fairies and leprechauns. But when that trivial possibility is many orders of magnitude less likely than a 'hubcap thrown in the air', it's probably OK to discount it. As to the technological obstacles to alien visitation, the Fermi Paradox/Drake Equation would have us inundated with alien civilizations, most of which should be much older than our relatively young one. Yet none have made definitive contact. You would think at least one would have, even if others are just playing hide-and-seek with us. Do you think maybe that means technological obstacles to interstellar travel are not easily dismissed ? Or maybe they're too busy with concerns about energy/food sources and reproduction, to send Von Neumann probes to other star systems to gather information which they may never recover.