8 ms·

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

by wanda 4y 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 4y 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 4y ago
  How does that remain true after the black hole has evaporated and there is no longer a horizon?
  - lisper 4y 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.
    - platz 4y ago
      Wall of text, didn't answer the question.
      - lisper 4y ago
        The question assumes that black holes evaporate, and we don't actually know that they do. Is that better?
        platz 4y ago
        That is a more transparent answer and direct answer, yes. Maybe if you had lead with that sentence, I wouldn't have been inclined to respond. But it also fails to address what I point out below. (as an aside, this answer is also not one that I find satisfactory on the actual topic.) Dllthomas correctly pointed out that given the two premises that (from the frame of the observer) (1) [matter takes infinite time to transit the horizon] and (2) [due to hawking radiation, black holes have a finite time span], then (2) resolves (1) when the black hole disappears. To recap, Instead of acknowledging that (2) resolves (1) you proceed to question the existence of hawking radiation and black hole evaporation, which compared to consensus is a radical view and is not warranted. Also the pivot was done in a way that seems to complicate and obfuscate rather than address the point directly (this is a common debate tactic; however I'm not sure if you were conscious of the behavior or if it was more subconscious/rationalization (more likely); you may not have even been aware you were doing it). It seems like you chose to reject consensus instead of simply accepting that (2) resolves (1), maybe because you seem to have a fixation on not ever conceding a point in a conversation. Sometimes it's ok just so say, "yeah, that's a good point". (btw if you're rejecting hawking radiation why say anything about black hole theory at all this point because it could all be wrong, no reason to speculate about it)
        lisper 4y ago
        > you seem to have a fixation on not ever conceding a point That is quite the accusation coming from someone whose entry into the conversation was "Wall of text, didn't answer the question." But let's see... > Dllthomas correctly pointed out... dllthomas did not "point out" anything, correctly or otherwise. All he did was ask the following question: "How does that remain true after the black hole has evaporated and there is no longer a horizon?" This question assumes that black holes evaporate. That assumption may be incorrect. We do not know whether or not black holes actually evaporate. In fact, we do not even know whether or not black holes actually form at all. And therefore: > (2) resolves (1) when the black hole disappears That might be true if (2) were true. Even that is arguable, but it is neither here nor there because we do not know whether or not (2) is true > compared to consensus is a radical view Yes, of course. The consensus view leads to a paradox, and so we know that the consensus view cannot possibly be correct. We also know that decades of effort have not resolved this paradox, and so it is extremely unlikely that there is a simple straightforward solution that has simply been overlooked. So the correct solution will almost certainly be a radical departure from the current consensus.
  - daxfohl 4y ago
    I think that's the point. 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. And I'm not sure whether that would be unitary or not, so it may not resolve the information paradox anyway). (Edit: I think 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?)
    - dllthomas 4y ago
      Maybe, but I think if it were easy to show that black holes (for whatever definition is important here) never actually form, the physicists would have noticed.
      - daxfohl 4y ago
        100% agree, but I'm still not seeing the flaw in the argument.
      - GoblinSlayer 4y ago
        When they are paid for research of black holes, it becomes easy to overlook their absence. They can also say they do hypothetical research, if black holes don't form by collapse maybe they form by other means, e.g. primordial black holes.
Raidion 4y ago
Totally uninformed here: Have we proved the Hawking radiation is without information (or enough of it), or is it just 'encrypted' at a level we can't distinguish from noise?
- mannykannot 4y ago
  This seems to address it (from the article): "[Hawking] radiation is thermal which means it’s random except for its temperature, and the temperature is inversely proportional to the mass of the black hole. This means two things. First, there’s no new information which comes out in the Hawking radiation..." Its mass is one of the few things we know from the outside.
  - phendrenad2 4y ago
    How do we know it's thermal? How do we know there aren't small fluctuations that are too small for us to detect millions of miles away?
    - mannykannot 4y ago
      AFAIK Hawking radiation has never been detected. It is hypothesized on the basis of current theories of quantum mechanics and gravity, and those assumptions imply a thermal distribution of energy. So, we have a reason to think that Hawking radiation occurs and has this property, while no-one so far has proposed a mechanism that would encode data on it.
    - tsimionescu 4y ago
      It's important to understand that Hawking radiation is not something we've observed and have noticed seems random. Instead, Hawking radiation is a prediction of a mathematical model. In that model, Hakwing radiation is purely random. If I remember correctly, Hawking radiation is postulated to arise because of fluctuations in the vacuum giving rise to virtual particle pairs. Normally, these would annihiliate back almost instantly. But, when such an event happens near the event horizon, one of them may fall into the black hole, leaving the other one to "escape", and appear as if the event horizon is emitting radiation. Since this radiation is caused by random fluctuations in the void outside the event horizon, it can't be correlated with anything past the even horizon, so it can't carry information about that.
SnowHill9902 4y ago
What is problematic about that? In what way does it violate the second law of thermodynamics? If anything, it seems like a great example of the natural tendency towards disorder. Also, it’s not possible to infer macroscopic prior states even with an infinitely powerful computer. When you mix water at different temperatures, entropy is irreversibly increased. It’s not possible to tell the initial temperatures just from the final state.
- jfengel 4y ago
  It's a subtle point. Several key theorems of thermodynamics rely on the ability to count unique states. If you could evolve the exact same state in two different ways, the proofs would fail. That's how thermodynamics derives indistinguishable macro states from distinguishable micro states. Throw that off and thermodynamics stops working. Since it has worked well so far they're reluctant to throw it out. Something has to go, and since they already know there's something funny going on where black holes meet quantum mechanics, that's the lowest hanging fruit.
  - SnowHill9902 4y ago
    So you are saying that if I solve the Schrödinger's equation for all the particles that make up her I could know where my wife wants to go out for dinner?
- wanda 4y ago
  > In what way does it violate the second law of thermodynamics? If you read my comment, you will find no mention of the second law of thermodynamics or any violation of said law. In fact, black holes need to evaporate in this way in order to comply with said law of thermodynamics. > When you mix water at different temperatures, entropy is irreversibly increased. It's not possible to tell the initial temperatures just from the final state. It is still water, however. You may not be able to say what temperatures W(a) and W(b) were from W(c), but you could at least say that W(c) may actually be W(ab) i.e. may be the mixture of two bodies of water W(a) and W(b). Bring the same water to a black hole and you have: W(a) went into a black hole and x came out, where x is some random heat. If you detect the heat x, what could you say about anything that may have been before? If W(a), W(b), Chair(a), Xylophone(g), Stone(f), Person(z) or anything went into the black hole, only heat x comes out in the end.
andi999 4y ago
What is the difference of this paradox to a particle entering a gas container, thermalizing, and the ejecting the particle (evaporate the gas). Thermal states is described by macroobservables only.
lamontcg 4y ago
But that just suggests that at some high enough energy that QM becomes nonlinear and singular and nonreversible and information is destroyed.

by wanda 4y ago

lisper 4y 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 4y ago
How does that remain true after the black hole has evaporated and there is no longer a horizon?
- lisper 4y 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.
  - platz 4y ago
    Wall of text, didn't answer the question.
    - lisper 4y ago
      The question assumes that black holes evaporate, and we don't actually know that they do. Is that better?
      - platz 4y ago
        That is a more transparent answer and direct answer, yes. Maybe if you had lead with that sentence, I wouldn't have been inclined to respond. But it also fails to address what I point out below. (as an aside, this answer is also not one that I find satisfactory on the actual topic.) Dllthomas correctly pointed out that given the two premises that (from the frame of the observer) (1) [matter takes infinite time to transit the horizon] and (2) [due to hawking radiation, black holes have a finite time span], then (2) resolves (1) when the black hole disappears. To recap, Instead of acknowledging that (2) resolves (1) you proceed to question the existence of hawking radiation and black hole evaporation, which compared to consensus is a radical view and is not warranted. Also the pivot was done in a way that seems to complicate and obfuscate rather than address the point directly (this is a common debate tactic; however I'm not sure if you were conscious of the behavior or if it was more subconscious/rationalization (more likely); you may not have even been aware you were doing it). It seems like you chose to reject consensus instead of simply accepting that (2) resolves (1), maybe because you seem to have a fixation on not ever conceding a point in a conversation. Sometimes it's ok just so say, "yeah, that's a good point". (btw if you're rejecting hawking radiation why say anything about black hole theory at all this point because it could all be wrong, no reason to speculate about it)
        lisper 4y ago
        > you seem to have a fixation on not ever conceding a point That is quite the accusation coming from someone whose entry into the conversation was "Wall of text, didn't answer the question." But let's see... > Dllthomas correctly pointed out... dllthomas did not "point out" anything, correctly or otherwise. All he did was ask the following question: "How does that remain true after the black hole has evaporated and there is no longer a horizon?" This question assumes that black holes evaporate. That assumption may be incorrect. We do not know whether or not black holes actually evaporate. In fact, we do not even know whether or not black holes actually form at all. And therefore: > (2) resolves (1) when the black hole disappears That might be true if (2) were true. Even that is arguable, but it is neither here nor there because we do not know whether or not (2) is true > compared to consensus is a radical view Yes, of course. The consensus view leads to a paradox, and so we know that the consensus view cannot possibly be correct. We also know that decades of effort have not resolved this paradox, and so it is extremely unlikely that there is a simple straightforward solution that has simply been overlooked. So the correct solution will almost certainly be a radical departure from the current consensus.
- daxfohl 4y ago
  I think that's the point. 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. And I'm not sure whether that would be unitary or not, so it may not resolve the information paradox anyway). (Edit: I think 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?)
  - dllthomas 4y ago
    Maybe, but I think if it were easy to show that black holes (for whatever definition is important here) never actually form, the physicists would have noticed.
    - daxfohl 4y ago
      100% agree, but I'm still not seeing the flaw in the argument.
    - GoblinSlayer 4y ago
      When they are paid for research of black holes, it becomes easy to overlook their absence. They can also say they do hypothetical research, if black holes don't form by collapse maybe they form by other means, e.g. primordial black holes.

Raidion 4y ago

Totally uninformed here: Have we proved the Hawking radiation is without information (or enough of it), or is it just 'encrypted' at a level we can't distinguish from noise?

mannykannot 4y ago
This seems to address it (from the article): "[Hawking] radiation is thermal which means it’s random except for its temperature, and the temperature is inversely proportional to the mass of the black hole. This means two things. First, there’s no new information which comes out in the Hawking radiation..." Its mass is one of the few things we know from the outside.
- phendrenad2 4y ago
  How do we know it's thermal? How do we know there aren't small fluctuations that are too small for us to detect millions of miles away?
  - mannykannot 4y ago
    AFAIK Hawking radiation has never been detected. It is hypothesized on the basis of current theories of quantum mechanics and gravity, and those assumptions imply a thermal distribution of energy. So, we have a reason to think that Hawking radiation occurs and has this property, while no-one so far has proposed a mechanism that would encode data on it.
  - tsimionescu 4y ago
    It's important to understand that Hawking radiation is not something we've observed and have noticed seems random. Instead, Hawking radiation is a prediction of a mathematical model. In that model, Hakwing radiation is purely random. If I remember correctly, Hawking radiation is postulated to arise because of fluctuations in the vacuum giving rise to virtual particle pairs. Normally, these would annihiliate back almost instantly. But, when such an event happens near the event horizon, one of them may fall into the black hole, leaving the other one to "escape", and appear as if the event horizon is emitting radiation. Since this radiation is caused by random fluctuations in the void outside the event horizon, it can't be correlated with anything past the even horizon, so it can't carry information about that.

SnowHill9902 4y ago

What is problematic about that? In what way does it violate the second law of thermodynamics? If anything, it seems like a great example of the natural tendency towards disorder. Also, it’s not possible to infer macroscopic prior states even with an infinitely powerful computer. When you mix water at different temperatures, entropy is irreversibly increased. It’s not possible to tell the initial temperatures just from the final state.

jfengel 4y ago
It's a subtle point. Several key theorems of thermodynamics rely on the ability to count unique states. If you could evolve the exact same state in two different ways, the proofs would fail. That's how thermodynamics derives indistinguishable macro states from distinguishable micro states. Throw that off and thermodynamics stops working. Since it has worked well so far they're reluctant to throw it out. Something has to go, and since they already know there's something funny going on where black holes meet quantum mechanics, that's the lowest hanging fruit.
- SnowHill9902 4y ago
  So you are saying that if I solve the Schrödinger's equation for all the particles that make up her I could know where my wife wants to go out for dinner?
wanda 4y ago
> In what way does it violate the second law of thermodynamics? If you read my comment, you will find no mention of the second law of thermodynamics or any violation of said law. In fact, black holes need to evaporate in this way in order to comply with said law of thermodynamics. > When you mix water at different temperatures, entropy is irreversibly increased. It's not possible to tell the initial temperatures just from the final state. It is still water, however. You may not be able to say what temperatures W(a) and W(b) were from W(c), but you could at least say that W(c) may actually be W(ab) i.e. may be the mixture of two bodies of water W(a) and W(b). Bring the same water to a black hole and you have: W(a) went into a black hole and x came out, where x is some random heat. If you detect the heat x, what could you say about anything that may have been before? If W(a), W(b), Chair(a), Xylophone(g), Stone(f), Person(z) or anything went into the black hole, only heat x comes out in the end.

andi999 4y ago

What is the difference of this paradox to a particle entering a gas container, thermalizing, and the ejecting the particle (evaporate the gas). Thermal states is described by macroobservables only.

lamontcg 4y ago

But that just suggests that at some high enough energy that QM becomes nonlinear and singular and nonreversible and information is destroyed.