Black Holes and Information Loss

Discussion in 'Physics & Math' started by RJBeery, Mar 21, 2017.

  1. przyk squishy Valued Senior Member

    Messages:
    3,171
    No, and I never said any such thing. If we're going by the picture I linked to earlier then I already commented on its characteristics in the same post:
    So after a finite time for an outside observer, points in the interior of the black hole are neither timelike nor spacelike separated from them.
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    So do you agree that your interpretation of that picture, which you believe shows that the event horizon falls into the causal past of an observer for a time, directly contradicts Wald's definition of an event horizon which does not exist in the causal past of future null infinity?
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. przyk squishy Valued Senior Member

    Messages:
    3,171
    Wald's definition says no such thing. The definition you cited was:
    So if the event horizon is in the causal past of future null infinity then technically it doesn't count as part of the black hole region B according to this definition and is merely its boundary.

    But this is taxonomy, not logic.
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    Is every point in spacetime in yesterday's lab, which resides completely within our past lightcones and which contained an evaporating black hole, contained in the causal past of future null infinity?
     
  8. przyk squishy Valued Senior Member

    Messages:
    3,171
    Huh? The interior of the black hole, i.e., everything with the possible exception of the event horizon, is never in the past light cone of any event outside the black hole nor in the past light cone of future null infinity.

    If you had a black hole that formed in your lab and then evaporated after a while, in the way depicted on the Kruskal/Penrose diagram, then points inside the black hole would be spacelike-separated from you for a while, then they would cease to be spacelike-separated from you and they would be somewhere that is neither spacelike-separated nor timelike-separated from you and in particular not in your past light cone.

    But take a step back here: why do you care so much about Wald's definition in the first place? I don't buy that the problem you have with black holes is merely whether some definition is being applied consistently or not.
     
  9. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    What you just described is not general relativity -- spacetime is smooth. Yesterday's lab is completely contained within our past lightcones; there is no discontinuous patch which is neither spacelike, timelike or lightlike separated from the world. I'm curious -- I believe you're a physicist with a degree; have you had a university-level course on GR?
    Wald is incontrovertibly an authority on the subject. I have Misner, Wheeler and Thorne at home, I'll be happy to provide their definitions as well. Focusing on what my personal problem with black holes is isn't relevant; if I can show that a logical contradiction exists with the consensus view of event horizons using the definitions provided by general relativity then that's all that is required to make my case.
     
  10. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    Amazingly, I can't find a single mention, let alone a definition, of event horizons in Gravitation. I started to search online and came across the following though: https://arxiv.org/abs/1401.5761

    Now Hawking says a lot of things, sometimes even contradictory things, but you need to ask yourself if you are leaving your mind open to the possibility that a logical contradiction does exist regarding event horizons and evaporating black holes.
     
  11. przyk squishy Valued Senior Member

    Messages:
    3,171
    You're just making assumptions here. First of all, Riemannian manifolds are supposed to be smooth (in the sense that mathematicians who write theorems about Riemannian manifolds probably usually assume or define them to be smooth), but spacetime manifolds in GR are not always smooth everywhere, since they are sometimes predicted to contain singularities. Second, what you're talking about isn't about smoothness but about whether events in spacetime can always be connected by spacelike or timelike curves. On that, well, apparently people willing to entertain the idea of evaporating black holes just don't believe that must always be true.


    Yes.


    That wouldn't be much of a case. Suppose the evaporating black hole didn't fit Wald's definition. Then it would only mean one of two things: physicists should stop calling the evaporating black hole a "black hole" and call it something else instead or, alternatively, if they wanted to continue calling it a "black hole" they could simply retire Wald's definition. Either way, it would say nothing about contradictions in the idea itself, whatever name you give to it.

    Trying to corner me (or physicists in general) with definitions like this isn't going to get you anywhere. Nobody ever said these definitions were sacrosanct. In fact, definitions can and do change over time as what physicists are interested in changes. For example: the principle of conservation of energy was proposed/discovered centuries ago. It is still believed to be true today -- but only because the definition of "energy" has been changed over the years.

    This is why it is so important to find out what the models actually are.
     
    Last edited: Apr 5, 2017
  12. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    This is true, physicists can believe whatever they want and are not constrained by any particular model but this goes beyond mere definitions -- these are definitions based upon mathematical models. If a physicist today believes that event horizons and evaporating black holes exist today then he is doing so without a mathematical model to support this belief. How is this better than woo-woo physics? The more likely scenario is that most physicists simply don't realize there is a logical contradiction...just like you.

    Please Register or Log in to view the hidden image!

     
  13. przyk squishy Valued Senior Member

    Messages:
    3,171
    You have no grounds for such an assessment.

    You are also changing the subject again. You made a specific claim that there is a logical contradiction in the idea of evaporating (and even purely classical non-evaporating) black holes. Not "I don't think there's much evidence for this idea" or "I find the theory behind them shaky" or even "this is more far-fetched than I am willing to entertain without really strong evidence". Which are opinions that someone might even reasonably be able to defend. You said "logical contradiction". You shouldn't claim something like that (and, by implication, that a large number of physicists have failed at basic logic) if you can't back it up.

    As far as the Kruskal/Penrose diagram of black hole evaporation is concerned, which is what we have to work with here, you have not shown any actual logical contradiction in it. In fact, I don't see what that could even possibly mean. There is just the diagram. How is a diagram like that supposed to contradict itself?

    Now, I haven't looked at the mathematics behind this model. So I have to admit that there could be some fundamental and obviously irreparable contradiction in the guts of that mathematics and that it is possible, however unlikely I personally think it might be, that expert researchers just haven't noticed it in the last forty years. I can't affirm what I haven't personally scrutinised. But that is irrelevant to this discussion. You have not looked at that mathematics either, so it can't be what your argument is about.
     
  14. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    This is not true. I claim that event horizons, as defined in general relativity, are logically incompatible with any sort of black holes which evaporate in finite time. Your Kruskal diagram does not show what you think it does due to the fact that this claim is contradictory to the definition of event horizons given by any number of sources. I've said many times that time and space are not fungible dimensions so a finite "time parameter" is not the same thing as occurring in finite time. Any attempt to refute this is futile because, as I said, the idea that the event horizon forms in finite time as proven by your Kruskal diagram directly contradicts general relativity. I can only type the same words so many times.

    Can event horizons exist in evaporating black holes? Sure, but not event horizons which adhere to the mathematics of general relativity. Absent another plausible mathematical model which predicts them, this subject is now pure, unsupported speculation. Woo-woo!
     
  15. przyk squishy Valued Senior Member

    Messages:
    3,171
    You haven't shown a contradiction even with Wald's definition of black holes.

    That is circular reasoning.

    That is argument by assertion.

    There is no one invariant definition of time associated with a remote event in general relativity. For the evaporating black hole diagram I actually used the most pessimistic reasonable one possible.

    You don't know the mathematics of general relativity. Certainly not enough to make claims about what is logically possible or not for a spacetime manifold.

    You haven't investigated the mathematics leading to the prediction of evaporating black holes. Certainly nowhere near enough to have an informed independent opinion on its plausibility.
     
  16. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    You're being intentionally obtuse. Wald's definition is fine, it's simply not compatible with evaporating black holes.

    You said:
    This contradicts Wald's definition that a black hole is a region which is not in the causal past of future null infinity. Do you deny this?
     
  17. The God Valued Senior Member

    Messages:
    3,546
    I have lost track of Rjbeery argument...Has anyone here understood his case about the logical contradiction? If so please state.

    I will quote him...

    ........Can event horizons exist in evaporating black holes? Sure, but not event horizons which adhere to the mathematics of general relativity......

    This one got me completely lost and hence this query if anyone understood what he is talking about.
     
  18. przyk squishy Valued Senior Member

    Messages:
    3,171
    You haven't established any contradiction.

    Consider the proposition that both statements are true: the black hole is neither spacelike nor timelike separated from an outside observer nor in the causal past of future null infinity, and only its event horizon may be in the causal past of future null infinity.

    You have done nothing to rule this out as a logical possibility.

    I think if you were honest with yourself you would have to admit that your reasoning really amounts to "I don't see how that could be possible" or "nobody has convinced me that could be possible". Which, however convincing or exhaustive it might seem to you, is not a logical proof and thus does not establish a logical contradiction.
     
  19. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    I'm learning to parse your words, przyk. You're playing games because you've tied your ego to your position rather than sincerely seeking the truth. I asked you whether Wald's definition of black holes contradicts your assertion that the Kruskal diagram allows for event horizons to form in finite time. You respond with what I have or haven't established. It's easy to avoid being wrong when you never actually make a statement.

    - Do you believe that general relativity requires a continuous four-dimensional manifold within which differentiable coordinate systems operate (with the sole exception being the singularity)?

    - If so, do you believe that a patch of spacetime, which you've described as somehow being in our past light cone but not in the causal past of future null infinity, adheres to this requirement?
     
  20. przyk squishy Valued Senior Member

    Messages:
    3,171
    You asked me whether Wald's definition of black holes contradicts certain statements I made about the evaporating black hole which I read directly off the Kruskal diagram.

    You claimed there is an obvious contradiction with evaporating black holes. The burden of proof is on you to establish that.

    Well you're claiming things and I'm mainly just playing critic. It isn't a symmetric relationship.

    I don't have fixed beliefs about this. I would expect spacetime manifolds generally need to be differentiable (because physics behaviour is generally defined by differential equations of motion) but if someone showed me something like a manifold with a crease in it (something like a sheet of paper with a sharp fold) I wouldn't necessarily dismiss it out of hand. (We can sometimes handle this sort of thing in physics with Dirac deltas and the like.)

    I would also expect spacetime manifolds to be connected, in the sense that it should be possible to trace a continuous curve (but not necessarily a geodesic) connecting any two events in spacetime. (If a manifold isn't connected in this sense then you basically have two or more different universes that have no interaction with one another.)

    But so far as I know this isn't an issue with the evaporating black hole.

    I said that 'patch' is not in the past light cone of an external observer. If you are an external observer, then points inside the black hole start in the causal future or spacelike-separated from you. Then after a while the black hole goes somewhere (relative to you) that is not spacelike-separated from you or in your future light cone, but also not in your past light cone. I'd say you could sensibly say the black hole has evaporated and is no longer there at that point.

    To clarify something, since there has obviously been some misunderstanding: Obviously, if you're in the causal past of future null infinity (i.e., you're not in a black hole), and b) some event E is in your own past light cone, then the event E is also in the causal past of future null infinity. I am not denying that.
     
  21. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    OK, so for general relativity to be logically compatible with evaporating black holes, in your opinion, there need to be events in the spacetime fabric which are neither space-like, time-like nor light-like separated?
     
  22. The God Valued Senior Member

    Messages:
    3,546
    I still have not understood the HR connect for any contradiction.

    Well for the author of the paper, who has obviously done some work, I would refer reading of page #217 of Wald.
     
  23. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,136
    In simplistic terms, I laid out the problem long ago:

    1) HR requires an event horizon
    2) HR causes BH evaporation
    3) An evaporating BH has a finite life
    4) A BH with a finite life cannot contain an event horizon because it would be capable of existing in our past light cones (which contradicts general relativity)

    Przyk claims that #4 is false, but this would require events in the fabric of spacetime that are not space-like, time-like or light-like connected. I'm waiting for him to verify this position.
     
    Last edited: Apr 7, 2017

Share This Page