24 ms·

I stopped working on black hole information loss

461 points by nsoonhui 5y ago

pcj-github 5y ago
If a "real" (big) black hole takes billions of years to evaporate, what does it look like just before it's about to die? (and completely evaporate). Why is this "tiny black hole" not possible to reproduce experimentally? (is it?)
- Blammar 5y ago
  Start by seeing if you can make some neutronium in the lab first. When that goes off brighter than a million suns, the problem will dawn on you...
  - pcj-github 5y ago
    On the contrary, the near-final state of a black hole at EOL might be quite weak in energy.
legohead 5y ago
Isn't the way the book is broken apart and joins the current mass of the black hole the "reversible" information? That seems to be similar to her burning book -> smoke example.
- prettyStandard 5y ago
  > [B]lack holes are extremely simple. They are completely described by only three properties: their mass, angular moment, and electric charge. This is called the “no hair” theorem.
jijji 5y ago
It seems the black hole information loss paradox trying to be explained by quantum mechanics is similar to what happens in the death of humans trying to be explained by religion. There is no one that can examine either state, falling into a black hole or falling into death. Quantum mechanics and religion try to explain this, but it can most likely never be verified.
claytongulick 5y ago
Salient Ayn Rand quote: "Contradictions do not exist. Whenever you think you are facing a contradiction, check your premises. You will find that one of them is wrong."
a-dub 5y ago
> However, in practice, reversing a process is possible only in really small systems. Processes in large systems become for all practical purposes irreversible extremely quickly. If you burn your book, for example, then for all practical purposes the information in it was destroyed. However, in principle, if we could only measure the properties of the smoke and ashes well enough, we could calculate what the letters in the book once were. but that's not considering the final state, that's considering the whole process (capturing the dynamics of the change). what's the interval? all time? just the state change? if it's all time, then isn't the information there regardless of what happens later? /armchair
MrYellowP 5y ago
I really like her. She actually talks about things the right way and approaches things at a fundamental level. She's very smart and reflective of new information and critical about any consensus, like everyone should be. ... and she's not shying away from letting everyone know. "Gobbledygook". Heh.
lorepieri 5y ago
I have worked on the black hole info paradox too, and this to me looks more a rant than anything. The solution to the information paradox is expected to improve our understanding of the horizon structure, if any, and this should give us predictions detectable as gravitational waves. And we just detected the first gravitational waves! What a time to be alive :)
richardfey 5y ago
> This is a possibility that I thought about at some point myself, as I am sure many others in the field have too. I eventually came to the conclusion that it doesn’t work. So I am somewhat skeptical that their proposal actually solves the problem. But maybe I was wrong and they are right. Gerard ‘t Hooft by the way also thinks the information comes out in gravitons, though in a different way then Hsu and Calmet. So this is not an outlandish idea. "So this is not an uncommon idea." FTFY
theknocker 5y ago
__MatrixMan__ 5y ago
Can somebody point me towards the entrance to whatever rabbit hole explains why thermal information is not information? I must be missing something. You can set up a torsion balance and extract a bitstream from the way it dances in a warm gas, and each of those bits fits, albeit with some creativity, into Shannon's definition of information: Once the balance jiggles in a 1-like way, you can exclude the universes where it would've jiggled in a 0-like way from your list, thus reducing the set of candidate universes by half: one bit. Maybe we can't reconstruct the words on the book that fell into the hole without an impossible-to-achieve perspective, but that doesn't mean it's not the same amount of information. Does it?
- halter73 5y ago
  Who said thermal information is not information? I'm not an expert, but isn't the problem that a black hole's temperature is directly proportional to its mass? I assume there's a lot more information about the thing falling into the black hole other than its mass which ends up getting lost.
bluepoint 5y ago
I fully sympathize with the sentiment of the article. I also left with the impression that fundamental physics is data starved.
stakkur 5y ago
I still pause when I see how much Sabine looks like Klaus, the lead singer of the Scorpions.
grendelt 5y ago
Just admit it, you kept losing your information.
senectus1 5y ago
is it rude to post the TL;DR? >And that’s why I stopped working on the black hole information loss paradox. Not because it’s unsolvable. But because you can’t solve this problem with mathematics alone, and experiments are not possible, not now and probably not in the next 10000 years.
- fijiaarone 5y ago
  Unobservable phenomena by hypothetical objects with contradictory arbitrary rules that have no effect on reality.
  - azernik 5y ago
    A quibble - these objects are not just hypothetical. We have images and other evidence of some particularly large ones. It's the exact rules that are hypothetical.
    - ncmncm 5y ago
      But we cannot observe Hawking radiation without having, on hand, a black hole small enough to be hotter than the CMB -- or that can be enclosed and protected from it, and the enclosure itself cooled below it, and in a vacuum so hard as not to any have atoms to fall in. All tall orders.
- The_rationalist 5y ago
jvanderbot 5y ago
Do all black holes with the same mass and other 'hairless' parameters (momentum, etc) have the same temp and therefore radiation emissions? If so, can we remotely measure mass from this?
- PaulHoule 5y ago
  Except in the real world for any black hole we observe (stellar mass or larger) that temperature is much lower than the cosmic microwave background so that you won’t see it. A stellar black hole floating out between the galaxies would not be evaporating now but rather slowly gaining energy from the CMB. The universal will have to expand for a long time before it gets cooler than black holes.
  - jvanderbot 5y ago
    But, my main question: Do they all have the same temp, given all other main parameters?
    - WJW 5y ago
      That depends on if they have hair or not, but nobody knows whether they do and it would be extremely impractical to experimentally verify such a thing. That's what the article is all about. If they don't have hair then yes, you should be able to estimate mass by measuring their temperature. You would also need to know how far it is though, so that you could compensate for redshift.
      - jvanderbot 5y ago
        OK, that makes sense. In reading TFA I was just kind of blown away that temp, mass, angular momentum, etc, are all so closely tied together.
        tsimionescu 5y ago
        Note that they are so closely tied together for black holes, not necessarily for other types of objects. Black holes in the GR description are probably simpler than some elementary particles even. However, it's important to note that the GR description is itself not exactly self-consistent, as the curvature is divergent at the center of the black hole (it is infinite, I believe?).
spekcular 5y ago
This seems like a fully general (and somewhat unconvincing) argument against doing theoretical physics. The key paragraphs are: "What’s going to happen with this new solution? Most likely, someone’s going to find a problem with it, and everyone will continue working on their own solution. Indeed, there’s a good chance that by the time this video appears this has already happened. For me, the real paradox is why they keep doing it. I guess they do it because they have been told so often this is a big problem that they believe if they solve it they’ll be considered geniuses. But of course their colleagues will never agree that they solved the problem to begin with. So by all chances, half a year from now you’ll see another headline claiming that the problem has been solved. And that’s why I stopped working on the black hole information loss paradox. Not because it’s unsolvable. But because you can’t solve this problem with mathematics alone, and experiments are not possible, not now and probably not in the next 10000 years." First, let's grant that no experimental evidence will be forthcoming in thousands of years. (It's conceivable to me that some astronomers will get lucky and provide some indirect evidence of some sort, but ignore this for now.) Why do we believe that this problem can't be solved, or at least profitably investigated, with mathematics (and physical intuition, and the rest of the experimental evidence we have about black holes – it's definitely not "mathematics alone")? At least in principle, one can imagine that there is a finite set of possible solutions (corresponding to dropping various assumptions, as she mentions earlier in the article), and all but one of those can be ruled out a priori via mathematical inconsistencies, a contradiction with physical evidence from non-black hole phenomena, or other undesirable properties. Maybe there are special features of the black hole information problem that make this impossible. But this overall mode of mathematical investigation is how theoretical physics works and has always worked. Einstein discovered general relativity by tweaking assumptions and deducing the theory was likely to be true because it resolved various issues, but we had no direct test [edit: of gravitational waves] for about 100 years. It would have been unfortunate if he concluded the problem was pointless to work on because no experimental evidence would manifest within his lifetime. (Example problem fixed by Einstein: https://aether.lbl.gov/www/classes/p10/gr/PrecessionperihelionMercury.htm https://aether.lbl.gov/www/classes/p10/gr/Precessionperiheli...)
- matt_kantor 5y ago
  > Einstein discovered general relativity [...] but we had no direct test for about 100 years. General relativity was tested by the Eddington experiment in 1919: https://en.wikipedia.org/wiki/Eddington_experiment https://en.wikipedia.org/wiki/Eddington_experiment (I mostly agree with your overall point, this is just a minor quibble.)
phn 5y ago
If someone could challenge my layman understanding: Isn't the information still there, inside the black hole, but just not retrievable from the outside?
- thwd 5y ago
  Gravity is infinite at the singularity (the middle of the black hole). Everything gravitates towards that point. Our best understanding is that no information can exist here. Black holes "evaporate" over time -- by emitting Hawking radiation. This is probably where the information goes, in my layman understanding.
  - tsimionescu 5y ago
    > Black holes "evaporate" over time -- by emitting Hawking radiation. This is probably where the information goes, in my layman understanding. No, the Hawking radiation and evaporation is exactly what causes the problem. If black holes were forever expanding, we could simply say "they have a structure inside that we can't detect, but that structure preserves the information; but, since it's past the event horizon, it will be, even in principle, forever beyond reach of our understanding and experiment". However, if black holes eventually disappear, it means you have something like book => unknowable inside of the black hole event horizon => something observable outside. The problem now becomes that, from Hawking's discovery, the "something observable outside" is random thermal radiation, which can't contain information by definition. Hence, not just something unknowable, but a paradox (an inconsistency in the formal model).
- wanda 5y ago
  That's correct for general relativity alone, but GR isn't enough on its own. Hawking showed that the information is lost in the process of black hole evaporation as the black hole decays into anonymous radiation, and so once a black hole is gone so too is any trace of the matter it absorbed in its lifetime. It's this bit that isn't okay in quantum mechanics, and that's problematic because quantum mechanics certainly seems to be bang on the money for a great deal of other phenomena. One would have a hard time saying that QM was wrong. That's not to say that it is a complete theory, but QM has made many, highly accurate predictions that have served to edify the framework. I don't know how certain it is that black holes evaporate. It may seem tempting to think that perhaps it is this notion of evaporation that could be overturned, but then you have black holes which simply exist forever, which would be rather problematic as well.
klik99 5y ago
Sounds like they're a trisolarian agent
- geysersam 5y ago
  The opposite! Debating where effort should be spent is crucial. Trisolarians would love to see more research into unknowable multiverse stuff.
ffhhj 5y ago
We might be able to create our own BH to test theories: > The LHC will not generate black holes in the cosmological sense. However, some theories suggest that the formation of tiny 'quantum' black holes may be possible.
clord 5y ago
Doesn’t the black hole just delay the information, not destroy it? Things that “fall in” from our perspective just fade down into a static low frequency frozen image on the horizon, and the remaining trip to the horizon as seen from the outside takes infinite time. The falling perspective likewise loses timely access to information about the entire universe as the singularity fills their view. I don’t see a paradox. Just the strange behavior of time at the limit.
- wanda 5y ago
  That's not the paradoxical part. Matter goes in, sure. But before it goes in, it is something, it has a form and a composition, it is in a state and it contains information of its prior states as well. The part that is problematic is that matter that enters the black hole is only returned to the universe as anonymous radiation. The universe is stateful, and while not all processes in the universe are reversible, matter and energy do encode the states that led to their present state and thus the prior states can be inferred (by a hypothetical, powerful enough computer, for example). The problem with black holes is that the Hawking radiation from a black hole does not encode any information about its prior state.
  - lisper 5y ago
    I think you missed the GP's point, which is that matter is never "returned to the universe" because from any frame of reference outside the horizon, the matter takes infinite time to transit the horizon, so it never actually appears to enter the hole.
    - dllthomas 5y ago
      How does that remain true after the black hole has evaporated and there is no longer a horizon?
      - lisper 5y ago
        Disclaimer: we are at the hairy edge of my knowledge here, so what I am about to tell you could very well be wrong. Hawking radiation has never actually been observed. It is just something that pops out of the math if, as Sabine rightfully emphasizes in her video, you make certain assumptions. And one of those assumptions is that you have a fully-fledged black hole, i.e. an object that actually contains mass beyond the event horizon. We are used to thinking of this assumption as having actually been confirmed by observation, but it is not actually true. No one has ever actually observed a black hole, notwithstanding that we've ostensibly taken a picture of one. That image was of the radiation emitted by an accretion disk, not the black hole itself. Black holes themselves are, obviously, impossible to image. So we don't actually know whether black holes actually exist or not. The only thing we've directly observed is their gravitational effects, and the gravitational effects of an actual black hole are indistinguishable from having all of the mass of the hole actually resident just outside the event horizon. What actually happens at the horizon is beyond the reach of our current theories because there both gravity and quantum effects are significant, and we do not yet have a consistent theory of quantum gravity. Everything we think we know about black holes is actually the result of taking GR and QM and framming them together in some ad hoc way by adding simplifying assumptions which may or may not actually be true. This is the point Sabine was trying to make: the black hole information loss paradox is not a problem with physics, it's a problem with our current theories. We simply don't know how the universe actually behaves in the presence of extreme concentrations of mass/energy. The only thing that the BHILP actually tells us is that either GR or QM -- or both -- are wrong, mere approximations to the actual truth in the same way that Newtonian mechanics turned out to be an approximation to the actual truth (one that happens to work extremely well in weak gravitational fields). But no one has a clue which one is wrong or how despite 100 years of effort. And one of the reasons for this is that we have no data, and no reasonable prospects for obtaining it. So we may just have to make our peace with not knowing.
mungal 5y ago
Sabine’s niche seems to be a confident cynicism or learned skepticism and is a much appreciated addition to the space. I like Sabine’s personality and the fact she stands in defiance of the status quo of scientific outreach, namely my two least favorite tropes: “science is fun” and “let me explain something using terrible metaphors because I fail to understand the math myself”. Sabine, if you’re reading this… please create more technical content. Maybe a companion video to your more general takes. One that shows the numerical side of things. Your experience and personality already lend itself to this effort. You say “the math is insufficient” show us the math! Show us how it’s insufficient using numerical examples. Scientific outreach has a real “draw the rest of the owl” problem and I think Sabine is perfectly poised to fill the gap. There’s a George Carlin quote I’ll paraphrase ~“never talk down to your audience, they’ll catch up eventually.”
- in3d 5y ago
  I find PBS Space Time to be superior to her videos in pretty much every case. https://youtube.com/c/pbsspacetime https://youtube.com/c/pbsspacetime
- bsder 5y ago
  > Sabine’s niche seems to be a confident cynicism or learned skepticism and is a much appreciated addition to the space. I think Sabine has settled into a niche with a few other physicists of "If you don't even have a hope of testing your theory, what's the point? Let's direct those resources into things that can be tested sometime in the next century." Theoretical physics seems to have a few arenas where it has just completely left the realm of reality. It's not even like "Well, maybe we can test these in a few years when technology gets better" but more like "We would need 15 orders of magnitude more energy than exists in the universe to test this."
- zone411 5y ago
  Her video on the Simulation Hypothesis was very poor https://lech.substack.com/p/sabine-hossenfelders-video-the-simulation https://lech.substack.com/p/sabine-hossenfelders-video-the-s....
  - 5y ago
snowwrestler 5y ago
If you change assumptions to solve a big problem, you don’t necessarily need to measure the big problem to check the assumptions. General Relativity itself was first confirmed with a relatively simple measurement of star displacement during a solar eclipse. The “real solution” to the black hole information paradox will be one that solves the paradox AND provides a “small” way to test the change in assumptions that creates the big solution. This is definitely worth looking for IMO.
- im3w1l 5y ago
  Totally agree. And it may even be that the small thing comes first. That we happen to observe some weird shit in a different domain, and once we shuffle assumptions around to fit observations we get black holes for free.
- nemothekid 5y ago
  >provides a “small” way to test the change in assumptions that creates the big solution Isn't this the problem. Unless we discover some primordial black holes, all black holes we currently know about are way too cold, and will be way too cold for billions of years, to test anything. GR predicted black holes, but GR wasn't about black holes, and there were plenty of other things you could test.
  - whimsicalism 5y ago
    I think you are missing the point of the parent comment. Changing the assumptions doesn't just change how we predict black holes will behave, it should have impacts on other things that we can measure.
chubot 5y ago
Interesting, this is a slightly weaker form of a theory not being falsifiable. Any theory won’t be falsifiable in the next 10,000 years! I think it’s a good idea to make these distinctions.
fasteddie31003 5y ago
I am skeptical of any black hole research because it cannot be currently tested. I recently went down the rabbit hole on how the Event Horizon Telescope (EHT) got a picture of a black hole because this could be used as experimental evidence of how a black hole works. After looking into how the EHT was calibrated, I am extremely skeptical of their results. I'm not an Astrophysicist, but I have a lot of understanding of statistical causality and Scientific Philosophy. The EHT processes that made the image of a black hole break a lot of the scientific methods IMO. The algorithms they use to make the image of the black hole were never tested against a known celestial body to calibrate the algorithms. They took a "a posteriori" approach to their imaging algorithms, which do not produce accurate results. I noticed their unscientific approach to the imaging algorithms after when I watched "Black Holes: The Edge of All We Know", which is a first-hand account on how the EHT developed their black hole image. They were literally testing different imaging algorithms to find the one that looked most like a circle. The correct method would be to calibrate their imaging algorithms against a known celestial body to make sure their techniques produced comparable results from other instruments. Then they should have taken their calibrated imaging algorithms and gave it data from the M87 black hole, but they skipped the hole calibration step and went right into imaging the black hole, which makes me very skeptical of their results.
- dane-pgp 5y ago
- drcode 5y ago
  I share your skepticism about the image, the problem is that without spending months learning the science & tech there is no way to substantiate our skepticism.
  - fasteddie31003 5y ago
    Just show me a calibration image of a know celestial body using the exact same algorithms and I'll be satisfied.
    - 5y ago
The_rationalist 5y ago
Aardwolf 5y ago
> They are completely described by only three properties: their mass, angular moment, and electric charge What about linear momentum, if the black hole has some velocity through space is that not also a parameter of it?
- delusional 5y ago
  I don't think linear velocity is necessary to describe a black hole. Basically, a black hole that moves behaves exactly the same as one that stands still.
  - Aardwolf 5y ago
    What's different about angular momentum in that case? Given that rotating or not rotating is also similar to moving or standing still
    - deleted 5y ago
      [deleted]
    - Koshkin 5y ago
      The (important) difference is that a rotating frame of reference is not inertial.
    - deleted 5y ago
      [deleted]
    - dark-star 5y ago
      Rotating black holes behave quite differently from static (non-rotating) black holes.
    - DiogenesKynikos 5y ago
      The laws of physics are invariant under a change in linear velocity. If you take everything in the Universe and add a constant to its velocity, and then if you yourself add that amount to your own velocity, then everything will appear exactly the same. The laws of physics are not invariant under rotation. If you take everything in the Universe and give it a nudge so that it's spinning around a particular axis, things will change. For starters, everything will fly apart, unless you also create a force field that pulls everything towards the axis of rotation (with the force increasing linearly with distance from the axis of rotation). A technical way to describe this is to say that the laws of physics have Poincaré invariance (or more properly, just Special Relativity has this invariance).[1] That's why linear momentum is viewed as a trivial property of a black hole, but angular momentum is not. 1. https://en.wikipedia.org/wiki/Poincar%C3%A9_group https://en.wikipedia.org/wiki/Poincar%C3%A9_group
morelandjs 5y ago
She's exactly right. Any science discovery that's worth its salt is falsifiable. If you can't validate your results there's a problem. It's the responsibility of every theorist to make testable predictions, and to communicate to experimentalists how they might be tested. There's frankly not enough pressure within the theory community to disregard cagey theorists that actively avoid testing their predictions, or disregard the importance of testing in general.
- bsedlm 5y ago
  This is a limitation of science. The issue I see, is how to continue to study such purely theoretical matters? Why should everything have to be testable (and thus, potentially developed into a marketable product)? It may not be science, but a lot of people still like to do that kind of theoretical work.
  - tsimionescu 5y ago
    Well, you can do maths research. That doesn't need to be testable, only self-consistent. However, number theorists don't come and say they've uncovered some grand mystery of the cosmos when they prove something about trans-finite numbers, unlike many theoretical physicists.
    - morelandjs 5y ago
      Exactly. A lot of amazing math has come out of string theory.
  - morelandjs 5y ago
    Here's the problem I see with it. Say you take multiple "top tier" theoreticians and task them with the same physical problem. Suppose they all make slightly different starting assumptions, and these assumptions lead to mutually incompatible conclusions. Which one is right? Who do we believe? The whole point of testing theories is there can only be "one truth". If you let theories run rampant without testing you end up in logically inconsistent chaos. All that said, theories should certainly be given time to grow when experimental validation is not immediately available. However, there's many in the community that take great liberty with that long leash to the detriment of physics progress.
fancyfredbot 5y ago
Reminds me of the phrase "not even wrong" https://en.m.wikipedia.org/wiki/Not_even_wrong https://en.m.wikipedia.org/wiki/Not_even_wrong
formerkrogemp 5y ago
A few of my friends in school went into physics very starry eyed and excited. They worked in academia. Then, they worked for space startups and NASA. Now they work in "business intelligence" and the tech ad business. I do enjoy Sabine's writing and perspective. I miss my friends' aspirations and enthusiasm for physics and space.
zackmorris 5y ago
This is a good post with all of the right reasons to be skeptical. However, with the really fringe stuff like this, I feel that the answers could come through intuition. On that note, her central premise is that we can't study black holes. But I'm feeling more and more convinced that the universe itself is inside of a black hole. If that's the case, then maybe we can study the inside after all. On a whim, I searched for "hawking radiation hubble constant" and stumbled onto a bunch of stuff like this (the Download PDF button works): https://www.preprints.org/manuscript/202101.0017/v2 https://www.preprints.org/manuscript/202101.0017/v2 I'm not a physicist, but if I assemble a bunch of ideas, I can make a bunch of insights like: if black holes evaporate faster as they shrink, then maybe galaxies slipping outside of our observable universe is causing it to become less massive, which is increasing its rate of expansion. Someday we may see everything shooting away from our reference point faster and faster until we ourselves pop, like reversed spaghettification. But then again, that doesn't seem quite right, because the galaxies slipping away from us faster than the speed of light probably don't experience anything catastrophic themselves. And also the galaxies might not actually be moving away, just more space has been constructed between us and them like a balloon stretching. I feel like without a solid understanding of this process, it's going to be hard to understand black holes.
Andrew_nenakhov 5y ago
Why is information loss such a big deal? Information gets lost all the time. Hit the wrong button, and the all-important file vault is gone, with all the backups, forever, information in them is lost. You might lose a job, but the universe doesn't break because of that!
- tsimionescu 5y ago
  Not sure if you are joking, but the article covers this. In principle, according to QM, information is never lost (until you make a measurement, but that's a different can of worms). In principle, in QM it is impossible to delete information. The article explains: if you burn a book, but gather detailed information about the fire and the smoke, you can reconstruct exactly what every letter on every page looked like, and every ink blot you spilled on it 10 years ago.
  - xaedes 5y ago
    Burn it to ash, collect info about the ash and reconstruct - no problem. But if you burn it in a way, that the only remains are "random thermal radiation" all the information is lost and we have a serious paradox to resolve...
    - tsimionescu 5y ago
      > But if you burn it in a way, that the only remains are "random thermal radiation" all the information is lost and we have a serious paradox to resolve... To quote the famous Spartan answer, If. That is, QM predicts this is impossible. Even if you threw the book into the Sun, you would (I must emphasize again in principle) be able to measure the radiation given off by the sun and at some point identify the words of the book.
      - kgwgk 5y ago
        > according to QM, information is never lost (until you make a measurement > you would (I must emphasize again in principle) be able to measure the radiation given off by the sun and at some point identify the words of the book Does the “information” [1] survive measurements or not? [1] “Information? Whose information? Information about what?”
visionscaper 5y ago
I don’t know much about the black hole information loss problem and I do like Sabine’s skepticism. However, saying it has no use to work on mathematical solutions in this area is taking it one step too far. Maybe, based on the solutions other (indirect) experiments can be devised, maybe it will help solve other Physics, mathematics or engineering problems in the future.
_0w8t 5y ago
One has to be skeptical even about the whole notion of the temperature of a black hole and existence of Hawking radiation. In a book from 1927 Richard Tolman tried to generalize thermodynamics to General Relativity. One of the most interesting of his results was that in GR thermal equilibrium required a temperature gradient that depended on the gravitational field. Tolmen’s result is still sometimes discussed but it is not settled if he was wrong or right. The catch is that if his reasoning was correct, then the black hole horizon from a point of view of external observer should have the temperature of 0K which in turn implied no Hawking radiation.
- wumpus 5y ago
  I did a search on arxiv and I see people are writing a small number of modern papers on that exact topic. Are you familiar enough with them to summarize?
  - _0w8t 5y ago
    I studied theoretical physics and read Tolman’s book almost 30 years ago before switching to programming. After that I have been following the topic as a hobby. As I understand, the math behind a particular generalization of thermodynamics that Tolman had used was sound. But there are other ways to try to merge the notion of temperature with GR that are considered more compatible with current attempts to merge gravity and Quantum Mechanics. We do not know which one is right. In Tolman’s approach one can not have thermal equilibrium in a stationary thermally isolated gravitation body if the temperature is constant. Isolated here is important. Think as if a star is surrounded by a membrane that no heat can penetrate and consider the resulting temperature profile. Extremely simplifying to the point of risking to give wrong impression the gravity has inherent energy gradient itself and to get isolated stationary system without energy flow the temperature must show a gradient as well. Tolman himself did not try to apply that to black holes, but it is straightforward to apply his equations in that case and that gives the absolute zero temperature at the event horizon. Again extremely simplifying in Tolman’s approach a black hole is a gigantic freezer from a point of view of external observer. That neatly solves the apparent disappearance of entropy. There is none as approaching the event horizon from a point of the external observer means loosing temperature. So entropy is lost before the horizon and there is no information paradox. Edit: for a star in a thermally isolated membrane Tolman’s approach gives that with a thermal equilibrium the temperature drops towards the center as the gravity is stronger there. Although that may sound counterintuitive, the idea is that stronger gravity slows down the time and from a point of an external observer that means colder temperature. And at black hole horizon time stops completely as seen by the external observer so the temperature is zero.
DangitBobby 5y ago
Doesn't the idea of "randomly emitted radiation" contradict the concept of "reversal" itself? If you know enough about a system, anything that appears random within it actually turns out to be determinstic. So I don't understand how a black hole can be said to emit "random" radiation to lose information on the first place.
- lupire 5y ago
  Non-newtownian/non-classical/non-relatistic Quantum effects are truly random. That's the core axiom of what makes "quantum" mechanics not Newtonian/classical/relativistic. It's fundamentally different from Newtownian statistical mechanics. Hawking radiation is purely random.
  - bmacho 5y ago
    > Non-newtownian/non-classical/non-relatistic Quantum effects are truly random. That's the core axiom of what makes "quantum" mechanics not Newtonian/classical/relativistic. Bohmian mechanics[1] (which is a model of QM) is fully deterministic, and Born rule emerges from the fact that we don't know some information. QM (equations, experiments) is fully consistent with a world, where the perceived randomness of a measurement is the exact same random, as in coin flips. For additional properties that QM does not satisfy (because there are known counter examples) see https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics#Comparisons https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec... [1]: https://en.wikipedia.org/wiki/De_Broglie–Bohm_theory https://en.wikipedia.org/wiki/De_Broglie–Bohm_theory
    - tsimionescu 5y ago
      Note that Bohmian mechanics (the actual mathematical formalism) is not consistent with Special Relativity, unlike regular Quantum Mechanics. It's not proven that it can't be made consistent, and some are still working on that, but so far it has remained elusive. This means that it's not really "an interpretation" of QM, it's a slightly different theory, one that is worse at predicting observed reality...
deleted 5y ago
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computator 5y ago
> You’re not missing anything if you don’t those articles. I love the irony that something is missing in her closing remark. Almost makes me wonder if it was intentional.
sytelus 5y ago
TLDR; There exist many solutions, none of them experimentally verifiable and hence the pointless debate continues.
cryptonector 5y ago
Sonic black holes have been studied experimentally. They are only weak analogs of actual black holes, so how much light they can shed on real black holes, I don't know, but it does seem to me that as long as they do have insights to reveal, we can't say that work on black hole information loss is purely mathematical. It's also possible that pure mathematical solutions will yield predictions that can be tested w/o a black hole. So I'm a bit skeptical of her take on this subject, though if work in this space is unrewarding and there's more rewarding work to do elsewhere, then that makes sense. But then, I am not a physicist! https://interestingengineering.com/sonic-black-holes-and-the-information-paradox
debdut 5y ago
Maybe in some years we create a small black hole, and since radiation is inversely proportional to mass, not only it will emit measurable emissions, it will pop out of existence or go through it's lifetime pretty quickly. Hence experiments will be possible and the paradox solution can be verified
Linda703 5y ago
Fellshard 5y ago
This may be somewhat tangential, and if it is too much so, then ignore this and move along. Isn't the key axiom - preservation of information - a presupposition, and not a formally evidenced law? As best I can tell, it's mostly been assumed as a required premise for a larger axiom - the eternality of matter.
- Strilanc 5y ago
  Here's a relevant blog post: https://scottaaronson.blog/?p=3327 https://scottaaronson.blog/?p=3327 'Is “information is physical” contentful?' In quantum mechanics, breaking unitarity (which implies conservation of information) is akin to breaking the rule in statistics that probabilities have to add up to 100%. You get things like a 300% chance of rain or a 90% chance of [null reference exception]. It's hard to overstate how deep down it is and how many things depend on it.
- twhb 5y ago
  The article does say it’s “experimentally extremely well confirmed”.
trhway 5y ago
information paradox of the modern science - reduce everything to a model of a spherical horse in a vacuum, and after that run around shouting that it isn't possible for the horse to have distinguishing features, like the horse's sex, color, breed, etc.
alophawen 5y ago
I love Sabine. I find her one of the few sober and rational voices on youtube. Maybe it is her direct and confrontative way that scares off some americans? I'd say she comes out like a sterotype german :-)
mc4ndr3 5y ago
I thought Susskind solved this.
travisgriggs 5y ago
I watched the whole video. My current physics acumen is probably in the lower half of the average HN reader. I enjoyed AP physics in high school. Took the test, got a 4. I’ve been helping my wife back in school with half life decay (as much chemistry as physics) and relished that. As a Mechanical Engineering student, I got A’s in my three required physics class. In short, I really liked physics. It helped me make sense of the world. I’m old enough, that quantum mechanics was not the public fascination it is now. Cold fusion was the big topic those days. Despite all of this early formative appreciation for physics, I have yet to really appreciate QM. It just has never helped me explain the world around me. And unlike many of the transcendental changes that occurred in the industrialized world as we got better and better at physics, whatever QM is supposed to do for me (it’s supposed to have bigger application than the double slit thing, right?), isn’t apparently obvious to me. The brief parts where Sabine is referring to QM particulars in the video, and when I skim the other articles and such I see on QM, always include a lot of phunky math, amusing names and symbols, and a sort of talk that sounds like convoluted philosophy, or an attempt to explain transubstantiation or the “mystery of the trinity.” I was amused at the end of the video. There’s a “keep your cake and eat it too” thrust. She clearly states a sort of collegiate/professional “you do you” support. At the same time she tells the viewer they don’t need to pay attention or care about it. But if we the lay masses don’t care, the PR that exists for the sake of securing funding to go on with these papers dries up. So in a round about way, she’s saying “I support my colleagues wishes to continue to pursue these studies, but you my reader shouldn’t bother to support them in any way, direct or indirect.”
- marcosdumay 5y ago
  > It just has never helped me explain the world around me. Hum... All of electronics, the entire modern chemistry, solid properties, gaseous state changes, how do you make sense of any of that without QM? (Of course, it's perfectly ok to not understand those if you don't want to. But then you can't claim that it's missing, just that you don't want to learn it.)
  - paulpauper 5y ago
    I don't think his statement is that unreasonable. the world is perceived and interfaced as macro yet the quantum is is what makes the macro. So you have to figure out where the macro becomes the quantum.
daxfohl 5y ago
Here's what I've never understood. From an outside perspective the black hole will evaporate before the thing falls in. Thus a thing can never fall in. From its perspective the hole will emit more and more intense radiation and finally evaporate just before it hits the horizon. If true, I think you can go even further and say no black hole can completely form; the collapsing matter just gets exponentially closer to being fully black until the effect of the Hawking radiation outweighs the gravitation, but it all evaporates before going fully black. No? (This latter part assumes there's some Hawking radiation or equivalent from pre-black holes as well). Now, I assume the pre-Hawking radiation would be unitary, since the only reason Hawking radiation is not unitary is because BHs don't have information, but pre-black holes are not black holes. So doesn't that solve the info paradox? Without resorting to holographs and whatnot? Where's the error?
- PaulHoule 5y ago
  See https://en.wikipedia.org/wiki/Firewall_(physics) https://en.wikipedia.org/wiki/Firewall_(physics) vs https://en.wikipedia.org/wiki/Black_hole_complementarity https://en.wikipedia.org/wiki/Black_hole_complementarity
  - daxfohl 5y ago
    Sure, but the paradoxes listed on those pages go away because the black hole never fully exists. The mass inside any volume is always just short of what would be required to make a black hole. And so of course we can expect to see crazy quantum effects at the boundaries, just like any other massively dense celestial object. However it's hidden behind insane time dilation to anyone outside. Going a bit further, it could even explain dark energy (Granted, I'm way out of my depth here): One outcome of General Relativity is that a large enough object of any density is a black hole (a black hole the size of Saturn's orbit need only be the density of water). Thus if we assume the universe is infinite and self similar, mass would have to constantly expand in order to avoid black holing.
    - peterburkimsher 5y ago
      Could a black hole exist in the same universe as a magnetic monopole? https://en.wikipedia.org/wiki/Magnetic_monopole https://en.wikipedia.org/wiki/Magnetic_monopole If energy is related to matter by E=mc², then the electromagnetic field of the monopole would also be diminished by a black hole, if one truly exists. But there might only be a single monopole. "Standard models of inflation solve the “monopole problem” by arguing that the seed from which our entire visible Universe grew was a quantum fluctuation so small that it contained only one monopole." https://www.newscientist.com/article/mg14419512-600-do-we-live-in-a-magnetic-monopole/ https://www.newscientist.com/article/mg14419512-600-do-we-li... Scientifically I'm way out of my depth, but perhaps there's a perfect universe on the other side of the black hole/white hole/wormhole. Or perhaps the perfect design is already here, and when we find bugs, we should be working to improve the world around us to make it better over time. I know I can't do that alone, but by some miracle, technology seems to be helping.
paulpauper 5y ago
Just because it's not testable does not mean it's not worthwhile. General relativity would still exist even if it could not be tested, fortunately , it is easy to empirically verify. But if the math is sound and meets certain assumptions, then it may be the correct theory. Having many mathematically sound candidates for a correct theory is better than nothing. That' why it's called theoretical physics. She seems to be ignoring that part. By her logic, theoretical physics is a waste of time.

461 points by nsoonhui 5y ago

If a "real" (big) black hole takes billions of years to evaporate, what does it look like just before it's about to die? (and completely evaporate). Why is this "tiny black hole" not possible to reproduce experimentally? (is it?)

Blammar 5y ago
Start by seeing if you can make some neutronium in the lab first. When that goes off brighter than a million suns, the problem will dawn on you...
- pcj-github 5y ago
  On the contrary, the near-final state of a black hole at EOL might be quite weak in energy.

legohead 5y ago

Isn't the way the book is broken apart and joins the current mass of the black hole the "reversible" information? That seems to be similar to her burning book -> smoke example.

prettyStandard 5y ago
> [B]lack holes are extremely simple. They are completely described by only three properties: their mass, angular moment, and electric charge. This is called the “no hair” theorem.

jijji 5y ago

It seems the black hole information loss paradox trying to be explained by quantum mechanics is similar to what happens in the death of humans trying to be explained by religion. There is no one that can examine either state, falling into a black hole or falling into death. Quantum mechanics and religion try to explain this, but it can most likely never be verified.

claytongulick 5y ago

Salient Ayn Rand quote: "Contradictions do not exist. Whenever you think you are facing a contradiction, check your premises. You will find that one of them is wrong."

a-dub 5y ago

> However, in practice, reversing a process is possible only in really small systems. Processes in large systems become for all practical purposes irreversible extremely quickly. If you burn your book, for example, then for all practical purposes the information in it was destroyed. However, in principle, if we could only measure the properties of the smoke and ashes well enough, we could calculate what the letters in the book once were. but that's not considering the final state, that's considering the whole process (capturing the dynamics of the change). what's the interval? all time? just the state change? if it's all time, then isn't the information there regardless of what happens later? /armchair

MrYellowP 5y ago

I really like her. She actually talks about things the right way and approaches things at a fundamental level. She's very smart and reflective of new information and critical about any consensus, like everyone should be. ... and she's not shying away from letting everyone know. "Gobbledygook". Heh.

lorepieri 5y ago

I have worked on the black hole info paradox too, and this to me looks more a rant than anything. The solution to the information paradox is expected to improve our understanding of the horizon structure, if any, and this should give us predictions detectable as gravitational waves. And we just detected the first gravitational waves! What a time to be alive :)

richardfey 5y ago

> This is a possibility that I thought about at some point myself, as I am sure many others in the field have too. I eventually came to the conclusion that it doesn’t work. So I am somewhat skeptical that their proposal actually solves the problem. But maybe I was wrong and they are right. Gerard ‘t Hooft by the way also thinks the information comes out in gravitons, though in a different way then Hsu and Calmet. So this is not an outlandish idea. "So this is not an uncommon idea." FTFY

theknocker 5y ago

__MatrixMan__ 5y ago

Can somebody point me towards the entrance to whatever rabbit hole explains why thermal information is not information? I must be missing something. You can set up a torsion balance and extract a bitstream from the way it dances in a warm gas, and each of those bits fits, albeit with some creativity, into Shannon's definition of information: Once the balance jiggles in a 1-like way, you can exclude the universes where it would've jiggled in a 0-like way from your list, thus reducing the set of candidate universes by half: one bit. Maybe we can't reconstruct the words on the book that fell into the hole without an impossible-to-achieve perspective, but that doesn't mean it's not the same amount of information. Does it?

halter73 5y ago
Who said thermal information is not information? I'm not an expert, but isn't the problem that a black hole's temperature is directly proportional to its mass? I assume there's a lot more information about the thing falling into the black hole other than its mass which ends up getting lost.

bluepoint 5y ago

I fully sympathize with the sentiment of the article. I also left with the impression that fundamental physics is data starved.

stakkur 5y ago

I still pause when I see how much Sabine looks like Klaus, the lead singer of the Scorpions.

grendelt 5y ago

Just admit it, you kept losing your information.

senectus1 5y ago

is it rude to post the TL;DR? >And that’s why I stopped working on the black hole information loss paradox. Not because it’s unsolvable. But because you can’t solve this problem with mathematics alone, and experiments are not possible, not now and probably not in the next 10000 years.

fijiaarone 5y ago
Unobservable phenomena by hypothetical objects with contradictory arbitrary rules that have no effect on reality.
- azernik 5y ago
  A quibble - these objects are not just hypothetical. We have images and other evidence of some particularly large ones. It's the exact rules that are hypothetical.
  - ncmncm 5y ago
    But we cannot observe Hawking radiation without having, on hand, a black hole small enough to be hotter than the CMB -- or that can be enclosed and protected from it, and the enclosure itself cooled below it, and in a vacuum so hard as not to any have atoms to fall in. All tall orders.
The_rationalist 5y ago

jvanderbot 5y ago

Do all black holes with the same mass and other 'hairless' parameters (momentum, etc) have the same temp and therefore radiation emissions? If so, can we remotely measure mass from this?

PaulHoule 5y ago
Except in the real world for any black hole we observe (stellar mass or larger) that temperature is much lower than the cosmic microwave background so that you won’t see it. A stellar black hole floating out between the galaxies would not be evaporating now but rather slowly gaining energy from the CMB. The universal will have to expand for a long time before it gets cooler than black holes.
- jvanderbot 5y ago
  But, my main question: Do they all have the same temp, given all other main parameters?
  - WJW 5y ago
    That depends on if they have hair or not, but nobody knows whether they do and it would be extremely impractical to experimentally verify such a thing. That's what the article is all about. If they don't have hair then yes, you should be able to estimate mass by measuring their temperature. You would also need to know how far it is though, so that you could compensate for redshift.
    - jvanderbot 5y ago
      OK, that makes sense. In reading TFA I was just kind of blown away that temp, mass, angular momentum, etc, are all so closely tied together.
      - tsimionescu 5y ago
        Note that they are so closely tied together for black holes, not necessarily for other types of objects. Black holes in the GR description are probably simpler than some elementary particles even. However, it's important to note that the GR description is itself not exactly self-consistent, as the curvature is divergent at the center of the black hole (it is infinite, I believe?).

spekcular 5y ago

This seems like a fully general (and somewhat unconvincing) argument against doing theoretical physics. The key paragraphs are: "What’s going to happen with this new solution? Most likely, someone’s going to find a problem with it, and everyone will continue working on their own solution. Indeed, there’s a good chance that by the time this video appears this has already happened. For me, the real paradox is why they keep doing it. I guess they do it because they have been told so often this is a big problem that they believe if they solve it they’ll be considered geniuses. But of course their colleagues will never agree that they solved the problem to begin with. So by all chances, half a year from now you’ll see another headline claiming that the problem has been solved. And that’s why I stopped working on the black hole information loss paradox. Not because it’s unsolvable. But because you can’t solve this problem with mathematics alone, and experiments are not possible, not now and probably not in the next 10000 years." First, let's grant that no experimental evidence will be forthcoming in thousands of years. (It's conceivable to me that some astronomers will get lucky and provide some indirect evidence of some sort, but ignore this for now.) Why do we believe that this problem can't be solved, or at least profitably investigated, with mathematics (and physical intuition, and the rest of the experimental evidence we have about black holes – it's definitely not "mathematics alone")? At least in principle, one can imagine that there is a finite set of possible solutions (corresponding to dropping various assumptions, as she mentions earlier in the article), and all but one of those can be ruled out a priori via mathematical inconsistencies, a contradiction with physical evidence from non-black hole phenomena, or other undesirable properties. Maybe there are special features of the black hole information problem that make this impossible. But this overall mode of mathematical investigation is how theoretical physics works and has always worked. Einstein discovered general relativity by tweaking assumptions and deducing the theory was likely to be true because it resolved various issues, but we had no direct test [edit: of gravitational waves] for about 100 years. It would have been unfortunate if he concluded the problem was pointless to work on because no experimental evidence would manifest within his lifetime. (Example problem fixed by Einstein: https://aether.lbl.gov/www/classes/p10/gr/PrecessionperihelionMercury.htm https://aether.lbl.gov/www/classes/p10/gr/Precessionperiheli...)

matt_kantor 5y ago
> Einstein discovered general relativity [...] but we had no direct test for about 100 years. General relativity was tested by the Eddington experiment in 1919: https://en.wikipedia.org/wiki/Eddington_experiment https://en.wikipedia.org/wiki/Eddington_experiment (I mostly agree with your overall point, this is just a minor quibble.)

phn 5y ago

If someone could challenge my layman understanding: Isn't the information still there, inside the black hole, but just not retrievable from the outside?

thwd 5y ago
Gravity is infinite at the singularity (the middle of the black hole). Everything gravitates towards that point. Our best understanding is that no information can exist here. Black holes "evaporate" over time -- by emitting Hawking radiation. This is probably where the information goes, in my layman understanding.
- tsimionescu 5y ago
  > Black holes "evaporate" over time -- by emitting Hawking radiation. This is probably where the information goes, in my layman understanding. No, the Hawking radiation and evaporation is exactly what causes the problem. If black holes were forever expanding, we could simply say "they have a structure inside that we can't detect, but that structure preserves the information; but, since it's past the event horizon, it will be, even in principle, forever beyond reach of our understanding and experiment". However, if black holes eventually disappear, it means you have something like book => unknowable inside of the black hole event horizon => something observable outside. The problem now becomes that, from Hawking's discovery, the "something observable outside" is random thermal radiation, which can't contain information by definition. Hence, not just something unknowable, but a paradox (an inconsistency in the formal model).
wanda 5y ago
That's correct for general relativity alone, but GR isn't enough on its own. Hawking showed that the information is lost in the process of black hole evaporation as the black hole decays into anonymous radiation, and so once a black hole is gone so too is any trace of the matter it absorbed in its lifetime. It's this bit that isn't okay in quantum mechanics, and that's problematic because quantum mechanics certainly seems to be bang on the money for a great deal of other phenomena. One would have a hard time saying that QM was wrong. That's not to say that it is a complete theory, but QM has made many, highly accurate predictions that have served to edify the framework. I don't know how certain it is that black holes evaporate. It may seem tempting to think that perhaps it is this notion of evaporation that could be overturned, but then you have black holes which simply exist forever, which would be rather problematic as well.

klik99 5y ago

Sounds like they're a trisolarian agent

geysersam 5y ago
The opposite! Debating where effort should be spent is crucial. Trisolarians would love to see more research into unknowable multiverse stuff.

ffhhj 5y ago

We might be able to create our own BH to test theories: > The LHC will not generate black holes in the cosmological sense. However, some theories suggest that the formation of tiny 'quantum' black holes may be possible.

clord 5y ago

Doesn’t the black hole just delay the information, not destroy it? Things that “fall in” from our perspective just fade down into a static low frequency frozen image on the horizon, and the remaining trip to the horizon as seen from the outside takes infinite time. The falling perspective likewise loses timely access to information about the entire universe as the singularity fills their view. I don’t see a paradox. Just the strange behavior of time at the limit.

wanda 5y ago
That's not the paradoxical part. Matter goes in, sure. But before it goes in, it is something, it has a form and a composition, it is in a state and it contains information of its prior states as well. The part that is problematic is that matter that enters the black hole is only returned to the universe as anonymous radiation. The universe is stateful, and while not all processes in the universe are reversible, matter and energy do encode the states that led to their present state and thus the prior states can be inferred (by a hypothetical, powerful enough computer, for example). The problem with black holes is that the Hawking radiation from a black hole does not encode any information about its prior state.
- lisper 5y ago
  I think you missed the GP's point, which is that matter is never "returned to the universe" because from any frame of reference outside the horizon, the matter takes infinite time to transit the horizon, so it never actually appears to enter the hole.
  - dllthomas 5y ago
    How does that remain true after the black hole has evaporated and there is no longer a horizon?
    - lisper 5y ago
      Disclaimer: we are at the hairy edge of my knowledge here, so what I am about to tell you could very well be wrong. Hawking radiation has never actually been observed. It is just something that pops out of the math if, as Sabine rightfully emphasizes in her video, you make certain assumptions. And one of those assumptions is that you have a fully-fledged black hole, i.e. an object that actually contains mass beyond the event horizon. We are used to thinking of this assumption as having actually been confirmed by observation, but it is not actually true. No one has ever actually observed a black hole, notwithstanding that we've ostensibly taken a picture of one. That image was of the radiation emitted by an accretion disk, not the black hole itself. Black holes themselves are, obviously, impossible to image. So we don't actually know whether black holes actually exist or not. The only thing we've directly observed is their gravitational effects, and the gravitational effects of an actual black hole are indistinguishable from having all of the mass of the hole actually resident just outside the event horizon. What actually happens at the horizon is beyond the reach of our current theories because there both gravity and quantum effects are significant, and we do not yet have a consistent theory of quantum gravity. Everything we think we know about black holes is actually the result of taking GR and QM and framming them together in some ad hoc way by adding simplifying assumptions which may or may not actually be true. This is the point Sabine was trying to make: the black hole information loss paradox is not a problem with physics, it's a problem with our current theories. We simply don't know how the universe actually behaves in the presence of extreme concentrations of mass/energy. The only thing that the BHILP actually tells us is that either GR or QM -- or both -- are wrong, mere approximations to the actual truth in the same way that Newtonian mechanics turned out to be an approximation to the actual truth (one that happens to work extremely well in weak gravitational fields). But no one has a clue which one is wrong or how despite 100 years of effort. And one of the reasons for this is that we have no data, and no reasonable prospects for obtaining it. So we may just have to make our peace with not knowing.

mungal 5y ago

Sabine’s niche seems to be a confident cynicism or learned skepticism and is a much appreciated addition to the space. I like Sabine’s personality and the fact she stands in defiance of the status quo of scientific outreach, namely my two least favorite tropes: “science is fun” and “let me explain something using terrible metaphors because I fail to understand the math myself”. Sabine, if you’re reading this… please create more technical content. Maybe a companion video to your more general takes. One that shows the numerical side of things. Your experience and personality already lend itself to this effort. You say “the math is insufficient” show us the math! Show us how it’s insufficient using numerical examples. Scientific outreach has a real “draw the rest of the owl” problem and I think Sabine is perfectly poised to fill the gap. There’s a George Carlin quote I’ll paraphrase ~“never talk down to your audience, they’ll catch up eventually.”

in3d 5y ago
I find PBS Space Time to be superior to her videos in pretty much every case. https://youtube.com/c/pbsspacetime https://youtube.com/c/pbsspacetime
bsder 5y ago
> Sabine’s niche seems to be a confident cynicism or learned skepticism and is a much appreciated addition to the space. I think Sabine has settled into a niche with a few other physicists of "If you don't even have a hope of testing your theory, what's the point? Let's direct those resources into things that can be tested sometime in the next century." Theoretical physics seems to have a few arenas where it has just completely left the realm of reality. It's not even like "Well, maybe we can test these in a few years when technology gets better" but more like "We would need 15 orders of magnitude more energy than exists in the universe to test this."
zone411 5y ago
Her video on the Simulation Hypothesis was very poor https://lech.substack.com/p/sabine-hossenfelders-video-the-simulation https://lech.substack.com/p/sabine-hossenfelders-video-the-s....
- 5y ago

snowwrestler 5y ago

If you change assumptions to solve a big problem, you don’t necessarily need to measure the big problem to check the assumptions. General Relativity itself was first confirmed with a relatively simple measurement of star displacement during a solar eclipse. The “real solution” to the black hole information paradox will be one that solves the paradox AND provides a “small” way to test the change in assumptions that creates the big solution. This is definitely worth looking for IMO.

im3w1l 5y ago
Totally agree. And it may even be that the small thing comes first. That we happen to observe some weird shit in a different domain, and once we shuffle assumptions around to fit observations we get black holes for free.
nemothekid 5y ago
>provides a “small” way to test the change in assumptions that creates the big solution Isn't this the problem. Unless we discover some primordial black holes, all black holes we currently know about are way too cold, and will be way too cold for billions of years, to test anything. GR predicted black holes, but GR wasn't about black holes, and there were plenty of other things you could test.
- whimsicalism 5y ago
  I think you are missing the point of the parent comment. Changing the assumptions doesn't just change how we predict black holes will behave, it should have impacts on other things that we can measure.

chubot 5y ago

Interesting, this is a slightly weaker form of a theory not being falsifiable. Any theory won’t be falsifiable in the next 10,000 years! I think it’s a good idea to make these distinctions.

fasteddie31003 5y ago

I am skeptical of any black hole research because it cannot be currently tested. I recently went down the rabbit hole on how the Event Horizon Telescope (EHT) got a picture of a black hole because this could be used as experimental evidence of how a black hole works. After looking into how the EHT was calibrated, I am extremely skeptical of their results. I'm not an Astrophysicist, but I have a lot of understanding of statistical causality and Scientific Philosophy. The EHT processes that made the image of a black hole break a lot of the scientific methods IMO. The algorithms they use to make the image of the black hole were never tested against a known celestial body to calibrate the algorithms. They took a "a posteriori" approach to their imaging algorithms, which do not produce accurate results. I noticed their unscientific approach to the imaging algorithms after when I watched "Black Holes: The Edge of All We Know", which is a first-hand account on how the EHT developed their black hole image. They were literally testing different imaging algorithms to find the one that looked most like a circle. The correct method would be to calibrate their imaging algorithms against a known celestial body to make sure their techniques produced comparable results from other instruments. Then they should have taken their calibrated imaging algorithms and gave it data from the M87 black hole, but they skipped the hole calibration step and went right into imaging the black hole, which makes me very skeptical of their results.

dane-pgp 5y ago
drcode 5y ago
I share your skepticism about the image, the problem is that without spending months learning the science & tech there is no way to substantiate our skepticism.
- fasteddie31003 5y ago
  Just show me a calibration image of a know celestial body using the exact same algorithms and I'll be satisfied.
  - 5y ago

The_rationalist 5y ago

Aardwolf 5y ago

> They are completely described by only three properties: their mass, angular moment, and electric charge What about linear momentum, if the black hole has some velocity through space is that not also a parameter of it?

delusional 5y ago
I don't think linear velocity is necessary to describe a black hole. Basically, a black hole that moves behaves exactly the same as one that stands still.
- Aardwolf 5y ago
  What's different about angular momentum in that case? Given that rotating or not rotating is also similar to moving or standing still
  - deleted 5y ago
    [deleted]
  - Koshkin 5y ago
    The (important) difference is that a rotating frame of reference is not inertial.
  - deleted 5y ago
    [deleted]
  - dark-star 5y ago
    Rotating black holes behave quite differently from static (non-rotating) black holes.
  - DiogenesKynikos 5y ago
    The laws of physics are invariant under a change in linear velocity. If you take everything in the Universe and add a constant to its velocity, and then if you yourself add that amount to your own velocity, then everything will appear exactly the same. The laws of physics are not invariant under rotation. If you take everything in the Universe and give it a nudge so that it's spinning around a particular axis, things will change. For starters, everything will fly apart, unless you also create a force field that pulls everything towards the axis of rotation (with the force increasing linearly with distance from the axis of rotation). A technical way to describe this is to say that the laws of physics have Poincaré invariance (or more properly, just Special Relativity has this invariance).[1] That's why linear momentum is viewed as a trivial property of a black hole, but angular momentum is not. 1. https://en.wikipedia.org/wiki/Poincar%C3%A9_group https://en.wikipedia.org/wiki/Poincar%C3%A9_group

morelandjs 5y ago

She's exactly right. Any science discovery that's worth its salt is falsifiable. If you can't validate your results there's a problem. It's the responsibility of every theorist to make testable predictions, and to communicate to experimentalists how they might be tested. There's frankly not enough pressure within the theory community to disregard cagey theorists that actively avoid testing their predictions, or disregard the importance of testing in general.

bsedlm 5y ago
This is a limitation of science. The issue I see, is how to continue to study such purely theoretical matters? Why should everything have to be testable (and thus, potentially developed into a marketable product)? It may not be science, but a lot of people still like to do that kind of theoretical work.
- tsimionescu 5y ago
  Well, you can do maths research. That doesn't need to be testable, only self-consistent. However, number theorists don't come and say they've uncovered some grand mystery of the cosmos when they prove something about trans-finite numbers, unlike many theoretical physicists.
  - morelandjs 5y ago
    Exactly. A lot of amazing math has come out of string theory.
- morelandjs 5y ago
  Here's the problem I see with it. Say you take multiple "top tier" theoreticians and task them with the same physical problem. Suppose they all make slightly different starting assumptions, and these assumptions lead to mutually incompatible conclusions. Which one is right? Who do we believe? The whole point of testing theories is there can only be "one truth". If you let theories run rampant without testing you end up in logically inconsistent chaos. All that said, theories should certainly be given time to grow when experimental validation is not immediately available. However, there's many in the community that take great liberty with that long leash to the detriment of physics progress.

fancyfredbot 5y ago

Reminds me of the phrase "not even wrong" https://en.m.wikipedia.org/wiki/Not_even_wrong https://en.m.wikipedia.org/wiki/Not_even_wrong

formerkrogemp 5y ago

A few of my friends in school went into physics very starry eyed and excited. They worked in academia. Then, they worked for space startups and NASA. Now they work in "business intelligence" and the tech ad business. I do enjoy Sabine's writing and perspective. I miss my friends' aspirations and enthusiasm for physics and space.

zackmorris 5y ago

This is a good post with all of the right reasons to be skeptical. However, with the really fringe stuff like this, I feel that the answers could come through intuition. On that note, her central premise is that we can't study black holes. But I'm feeling more and more convinced that the universe itself is inside of a black hole. If that's the case, then maybe we can study the inside after all. On a whim, I searched for "hawking radiation hubble constant" and stumbled onto a bunch of stuff like this (the Download PDF button works): https://www.preprints.org/manuscript/202101.0017/v2 https://www.preprints.org/manuscript/202101.0017/v2 I'm not a physicist, but if I assemble a bunch of ideas, I can make a bunch of insights like: if black holes evaporate faster as they shrink, then maybe galaxies slipping outside of our observable universe is causing it to become less massive, which is increasing its rate of expansion. Someday we may see everything shooting away from our reference point faster and faster until we ourselves pop, like reversed spaghettification. But then again, that doesn't seem quite right, because the galaxies slipping away from us faster than the speed of light probably don't experience anything catastrophic themselves. And also the galaxies might not actually be moving away, just more space has been constructed between us and them like a balloon stretching. I feel like without a solid understanding of this process, it's going to be hard to understand black holes.

Andrew_nenakhov 5y ago

Why is information loss such a big deal? Information gets lost all the time. Hit the wrong button, and the all-important file vault is gone, with all the backups, forever, information in them is lost. You might lose a job, but the universe doesn't break because of that!

tsimionescu 5y ago
Not sure if you are joking, but the article covers this. In principle, according to QM, information is never lost (until you make a measurement, but that's a different can of worms). In principle, in QM it is impossible to delete information. The article explains: if you burn a book, but gather detailed information about the fire and the smoke, you can reconstruct exactly what every letter on every page looked like, and every ink blot you spilled on it 10 years ago.
- xaedes 5y ago
  Burn it to ash, collect info about the ash and reconstruct - no problem. But if you burn it in a way, that the only remains are "random thermal radiation" all the information is lost and we have a serious paradox to resolve...
  - tsimionescu 5y ago
    > But if you burn it in a way, that the only remains are "random thermal radiation" all the information is lost and we have a serious paradox to resolve... To quote the famous Spartan answer, If. That is, QM predicts this is impossible. Even if you threw the book into the Sun, you would (I must emphasize again in principle) be able to measure the radiation given off by the sun and at some point identify the words of the book.
    - kgwgk 5y ago
      > according to QM, information is never lost (until you make a measurement > you would (I must emphasize again in principle) be able to measure the radiation given off by the sun and at some point identify the words of the book Does the “information” [1] survive measurements or not? [1] “Information? Whose information? Information about what?”

visionscaper 5y ago

I don’t know much about the black hole information loss problem and I do like Sabine’s skepticism. However, saying it has no use to work on mathematical solutions in this area is taking it one step too far. Maybe, based on the solutions other (indirect) experiments can be devised, maybe it will help solve other Physics, mathematics or engineering problems in the future.

_0w8t 5y ago

One has to be skeptical even about the whole notion of the temperature of a black hole and existence of Hawking radiation. In a book from 1927 Richard Tolman tried to generalize thermodynamics to General Relativity. One of the most interesting of his results was that in GR thermal equilibrium required a temperature gradient that depended on the gravitational field. Tolmen’s result is still sometimes discussed but it is not settled if he was wrong or right. The catch is that if his reasoning was correct, then the black hole horizon from a point of view of external observer should have the temperature of 0K which in turn implied no Hawking radiation.

wumpus 5y ago
I did a search on arxiv and I see people are writing a small number of modern papers on that exact topic. Are you familiar enough with them to summarize?
- _0w8t 5y ago
  I studied theoretical physics and read Tolman’s book almost 30 years ago before switching to programming. After that I have been following the topic as a hobby. As I understand, the math behind a particular generalization of thermodynamics that Tolman had used was sound. But there are other ways to try to merge the notion of temperature with GR that are considered more compatible with current attempts to merge gravity and Quantum Mechanics. We do not know which one is right. In Tolman’s approach one can not have thermal equilibrium in a stationary thermally isolated gravitation body if the temperature is constant. Isolated here is important. Think as if a star is surrounded by a membrane that no heat can penetrate and consider the resulting temperature profile. Extremely simplifying to the point of risking to give wrong impression the gravity has inherent energy gradient itself and to get isolated stationary system without energy flow the temperature must show a gradient as well. Tolman himself did not try to apply that to black holes, but it is straightforward to apply his equations in that case and that gives the absolute zero temperature at the event horizon. Again extremely simplifying in Tolman’s approach a black hole is a gigantic freezer from a point of view of external observer. That neatly solves the apparent disappearance of entropy. There is none as approaching the event horizon from a point of the external observer means loosing temperature. So entropy is lost before the horizon and there is no information paradox. Edit: for a star in a thermally isolated membrane Tolman’s approach gives that with a thermal equilibrium the temperature drops towards the center as the gravity is stronger there. Although that may sound counterintuitive, the idea is that stronger gravity slows down the time and from a point of an external observer that means colder temperature. And at black hole horizon time stops completely as seen by the external observer so the temperature is zero.

DangitBobby 5y ago

Doesn't the idea of "randomly emitted radiation" contradict the concept of "reversal" itself? If you know enough about a system, anything that appears random within it actually turns out to be determinstic. So I don't understand how a black hole can be said to emit "random" radiation to lose information on the first place.

lupire 5y ago
Non-newtownian/non-classical/non-relatistic Quantum effects are truly random. That's the core axiom of what makes "quantum" mechanics not Newtonian/classical/relativistic. It's fundamentally different from Newtownian statistical mechanics. Hawking radiation is purely random.
- bmacho 5y ago
  > Non-newtownian/non-classical/non-relatistic Quantum effects are truly random. That's the core axiom of what makes "quantum" mechanics not Newtonian/classical/relativistic. Bohmian mechanics[1] (which is a model of QM) is fully deterministic, and Born rule emerges from the fact that we don't know some information. QM (equations, experiments) is fully consistent with a world, where the perceived randomness of a measurement is the exact same random, as in coin flips. For additional properties that QM does not satisfy (because there are known counter examples) see https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics#Comparisons https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec... [1]: https://en.wikipedia.org/wiki/De_Broglie–Bohm_theory https://en.wikipedia.org/wiki/De_Broglie–Bohm_theory
  - tsimionescu 5y ago
    Note that Bohmian mechanics (the actual mathematical formalism) is not consistent with Special Relativity, unlike regular Quantum Mechanics. It's not proven that it can't be made consistent, and some are still working on that, but so far it has remained elusive. This means that it's not really "an interpretation" of QM, it's a slightly different theory, one that is worse at predicting observed reality...

deleted 5y ago

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computator 5y ago

> You’re not missing anything if you don’t those articles. I love the irony that something is missing in her closing remark. Almost makes me wonder if it was intentional.

sytelus 5y ago

TLDR; There exist many solutions, none of them experimentally verifiable and hence the pointless debate continues.

cryptonector 5y ago

Sonic black holes have been studied experimentally. They are only weak analogs of actual black holes, so how much light they can shed on real black holes, I don't know, but it does seem to me that as long as they do have insights to reveal, we can't say that work on black hole information loss is purely mathematical. It's also possible that pure mathematical solutions will yield predictions that can be tested w/o a black hole. So I'm a bit skeptical of her take on this subject, though if work in this space is unrewarding and there's more rewarding work to do elsewhere, then that makes sense. But then, I am not a physicist! https://interestingengineering.com/sonic-black-holes-and-the-information-paradox

debdut 5y ago

Maybe in some years we create a small black hole, and since radiation is inversely proportional to mass, not only it will emit measurable emissions, it will pop out of existence or go through it's lifetime pretty quickly. Hence experiments will be possible and the paradox solution can be verified

Linda703 5y ago

Fellshard 5y ago

This may be somewhat tangential, and if it is too much so, then ignore this and move along. Isn't the key axiom - preservation of information - a presupposition, and not a formally evidenced law? As best I can tell, it's mostly been assumed as a required premise for a larger axiom - the eternality of matter.

Strilanc 5y ago
Here's a relevant blog post: https://scottaaronson.blog/?p=3327 https://scottaaronson.blog/?p=3327 'Is “information is physical” contentful?' In quantum mechanics, breaking unitarity (which implies conservation of information) is akin to breaking the rule in statistics that probabilities have to add up to 100%. You get things like a 300% chance of rain or a 90% chance of [null reference exception]. It's hard to overstate how deep down it is and how many things depend on it.
twhb 5y ago
The article does say it’s “experimentally extremely well confirmed”.

trhway 5y ago

information paradox of the modern science - reduce everything to a model of a spherical horse in a vacuum, and after that run around shouting that it isn't possible for the horse to have distinguishing features, like the horse's sex, color, breed, etc.

alophawen 5y ago

I love Sabine. I find her one of the few sober and rational voices on youtube. Maybe it is her direct and confrontative way that scares off some americans? I'd say she comes out like a sterotype german :-)

mc4ndr3 5y ago

I thought Susskind solved this.

travisgriggs 5y ago

I watched the whole video. My current physics acumen is probably in the lower half of the average HN reader. I enjoyed AP physics in high school. Took the test, got a 4. I’ve been helping my wife back in school with half life decay (as much chemistry as physics) and relished that. As a Mechanical Engineering student, I got A’s in my three required physics class. In short, I really liked physics. It helped me make sense of the world. I’m old enough, that quantum mechanics was not the public fascination it is now. Cold fusion was the big topic those days. Despite all of this early formative appreciation for physics, I have yet to really appreciate QM. It just has never helped me explain the world around me. And unlike many of the transcendental changes that occurred in the industrialized world as we got better and better at physics, whatever QM is supposed to do for me (it’s supposed to have bigger application than the double slit thing, right?), isn’t apparently obvious to me. The brief parts where Sabine is referring to QM particulars in the video, and when I skim the other articles and such I see on QM, always include a lot of phunky math, amusing names and symbols, and a sort of talk that sounds like convoluted philosophy, or an attempt to explain transubstantiation or the “mystery of the trinity.” I was amused at the end of the video. There’s a “keep your cake and eat it too” thrust. She clearly states a sort of collegiate/professional “you do you” support. At the same time she tells the viewer they don’t need to pay attention or care about it. But if we the lay masses don’t care, the PR that exists for the sake of securing funding to go on with these papers dries up. So in a round about way, she’s saying “I support my colleagues wishes to continue to pursue these studies, but you my reader shouldn’t bother to support them in any way, direct or indirect.”

marcosdumay 5y ago
> It just has never helped me explain the world around me. Hum... All of electronics, the entire modern chemistry, solid properties, gaseous state changes, how do you make sense of any of that without QM? (Of course, it's perfectly ok to not understand those if you don't want to. But then you can't claim that it's missing, just that you don't want to learn it.)
- paulpauper 5y ago
  I don't think his statement is that unreasonable. the world is perceived and interfaced as macro yet the quantum is is what makes the macro. So you have to figure out where the macro becomes the quantum.

daxfohl 5y ago

Here's what I've never understood. From an outside perspective the black hole will evaporate before the thing falls in. Thus a thing can never fall in. From its perspective the hole will emit more and more intense radiation and finally evaporate just before it hits the horizon. If true, I think you can go even further and say no black hole can completely form; the collapsing matter just gets exponentially closer to being fully black until the effect of the Hawking radiation outweighs the gravitation, but it all evaporates before going fully black. No? (This latter part assumes there's some Hawking radiation or equivalent from pre-black holes as well). Now, I assume the pre-Hawking radiation would be unitary, since the only reason Hawking radiation is not unitary is because BHs don't have information, but pre-black holes are not black holes. So doesn't that solve the info paradox? Without resorting to holographs and whatnot? Where's the error?

PaulHoule 5y ago
See https://en.wikipedia.org/wiki/Firewall_(physics) https://en.wikipedia.org/wiki/Firewall_(physics) vs https://en.wikipedia.org/wiki/Black_hole_complementarity https://en.wikipedia.org/wiki/Black_hole_complementarity
- daxfohl 5y ago
  Sure, but the paradoxes listed on those pages go away because the black hole never fully exists. The mass inside any volume is always just short of what would be required to make a black hole. And so of course we can expect to see crazy quantum effects at the boundaries, just like any other massively dense celestial object. However it's hidden behind insane time dilation to anyone outside. Going a bit further, it could even explain dark energy (Granted, I'm way out of my depth here): One outcome of General Relativity is that a large enough object of any density is a black hole (a black hole the size of Saturn's orbit need only be the density of water). Thus if we assume the universe is infinite and self similar, mass would have to constantly expand in order to avoid black holing.
  - peterburkimsher 5y ago
    Could a black hole exist in the same universe as a magnetic monopole? https://en.wikipedia.org/wiki/Magnetic_monopole https://en.wikipedia.org/wiki/Magnetic_monopole If energy is related to matter by E=mc², then the electromagnetic field of the monopole would also be diminished by a black hole, if one truly exists. But there might only be a single monopole. "Standard models of inflation solve the “monopole problem” by arguing that the seed from which our entire visible Universe grew was a quantum fluctuation so small that it contained only one monopole." https://www.newscientist.com/article/mg14419512-600-do-we-live-in-a-magnetic-monopole/ https://www.newscientist.com/article/mg14419512-600-do-we-li... Scientifically I'm way out of my depth, but perhaps there's a perfect universe on the other side of the black hole/white hole/wormhole. Or perhaps the perfect design is already here, and when we find bugs, we should be working to improve the world around us to make it better over time. I know I can't do that alone, but by some miracle, technology seems to be helping.

paulpauper 5y ago

Just because it's not testable does not mean it's not worthwhile. General relativity would still exist even if it could not be tested, fortunately , it is easy to empirically verify. But if the math is sound and meets certain assumptions, then it may be the correct theory. Having many mathematically sound candidates for a correct theory is better than nothing. That' why it's called theoretical physics. She seems to be ignoring that part. By her logic, theoretical physics is a waste of time.