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Black Holes and Ambiguity

  1. Jul 14, 2011 #1
    According to a recent published article, Physicist Leonard Susskind feels, along with Niels Bohr, that rather than try to come up with a mental picture of what objective reality is, scientists should limit themselves to creating hypotheses and testing them empirically. Susskind contends that a wariness about knowing reality is justified by some contradictions and paradoxes of modern physics.

    One such paradox is the ambiguity about the fate of things that fall into a black hole. From the perspective of the object, it passes unaffected through the event horizon and is destroyed at the hole's center. An external observer, by contrast, sees the object incinerated as it passes the event horizon prior to reaching the center. Both viewpoints, although apparently irreconcilable, are considered by physicists to be valid. (1)

    I'm wondering if anybody in this forum can explain this paradox. How sure are we that one of these interpretations are not wrong? If either one is wrong, then the paradox would be resolved.

    Another question is one of epistemology: Do we really need to be sure we know what we think we know? Is physics properly a body of knowledge, or is it a methodology we can use for practical purposes?

    I tend to lean a bit to the latter viewpoint. Rather than worry about how "right" modern physics is, I see physics as a way to solve problems. If it works for that purpose, then let questions of epistemology up to philosophers.

    Jagella

    (1) Peter Byrne, Bad Boy of Physics, Scientific American, July 2011, pp 80-81
     
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  3. Jul 15, 2011 #2

    Nabeshin

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    The thing is, this isn't a paradox at all. What's wrong with the two observers coming to different conclusions about what they see? If the outside observer is smart, he can compute that for the guy who fell into the black hole, he was destroyed in a finite amount of proper time (he can say just how much!).

    Here's a less black hole-y example:
    http://en.wikipedia.org/wiki/Rindler_coordinates#The_Rindler_horizon
     
  4. Jul 15, 2011 #3
    Well, according to Special Relativity, sometimes observers do come to different conclusions about what they see. Length and time are relative to the frame of reference of the observer as I'm sure you know. Are there relativistic ramifications to what observers falling into a black hole might see versus what observers outside of the black hole might see?

    I'm not sure how your scenario resolves the paradox. What is “proper time”?

    I'm thinking that our notion that something can only be destroyed in one place is simply wrong. If Susskind is right about the destruction of an object falling into a black hole, then obviously something can be destroyed in two different places. It may not make sense to us, but the world doesn't always make sense. Quantum mechanics offers a lot of evidence that our logic doesn't always apply to the “real world.” Common sense may be OK under common circumstances, but under circumstances that are very uncommon, like that of the proximity to a black hole or on the subatomic scale, we need to rethink our ideas of what makes sense.

    It made sense to Aristotle that heavier objects fall faster than lighter objects, did it not?

    Jagella
     
  5. Jul 15, 2011 #4

    DaveC426913

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    What paradox?

    Just because two people see different things does not mean there is a paradox.

    Two people looking at a straw in a glass of water will "conclude" different things about how the straw is bent. Paradox? No.

    To think so would be to assume that the light that reaches our eyes is a True and Bona Fide Account of Actual Reality. Which we know it isn't. Photons are not oracles of reality.
     
  6. Jul 15, 2011 #5
    inre: "Photons are not oracles of reality." i am not sure why you wrote this - photons are, indeed, the ultimate oracle of reality.
     
  7. Jul 15, 2011 #6
    That's a very good point, Dave. Different people in different situations will often observe different things about an object. The key difference, though, is that we can readily explain the differences in the observed refraction of the light coming from an apparently bent straw because we understand the effects of parallax. But how do we explain the destruction of an object destroyed in two different parts of a black hole?

    I must wonder if we may be reaching the limits of human understanding. Dogs evidently cannot understand classical mechanics. Humans may not be able to understand quantum mechanics.

    Jagella
     
  8. Jul 15, 2011 #7
    They are the oracles of past reality not present reality, present reality doesnt exist as all as all perceptions are based on time.

    Example; Look at the sun, we see approximately 8 mins back; Look at the stars further away and we look further back in time.

    I thank what Dave is getting at is that we have to take into account the speed limit of the universe - apologies if I have misinterpreted you Dave.
     
  9. Jul 15, 2011 #8
    It is not destroyed in two different places. It is destroyed in a single spacetime with multiple frames of reference as I understood it.
     
  10. Jul 15, 2011 #9

    DaveC426913

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    Hm. I would have thought my point so obvious it would have been the last word on the subject...


    Really? So the straw in a glass of water is bent in reality?

    Taken at face value, photons lie about their history. Photons do not make straight lines between their destination (our eyes) and their origin (the bottom tip of the straw). When we observe the straw underwater, we take into account the fact that our very observations are distorted. We must tease out of it what is really happening based on what we know about diffractive media and light. Photons are not oracles of reality. The straw is not bent.

    This is perfectly analagous to the black hole example. Our observations are completely subject to the whims of the photons that deign to reach our eyes after whatever adventure they happen to go on. we know that the BH (or water) is mangling the paths/frequencies/etc. of the photons. Once you compensate, there's no paradox at all.
     
    Last edited: Jul 15, 2011
  11. Jul 15, 2011 #10

    DaveC426913

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    We explain it by understanding that "the object" and "our image of the object" are not at all the same thing. Our image of the object is highly distorted in both space and time.

    Seriously, I don't know why you guys are making a big deal of this.

    Yes, observations near a black hole are highly distorted. No one is naive enough to think that, because we see the infalling object stop at the EH, that that is what really happens to it. Are they??
     
  12. Jul 15, 2011 #11

    Drakkith

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    Why exactly would an outside observer see the object incinerated at the event horizon?
     
  13. Jul 15, 2011 #12

    DaveC426913

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    An excellent question actually. Good catch. I chose to ignore it - probably shouldn't have.

    It's possible that the OP thinks there's a paradox only because they misunderstand what is actually observed.

    An outside observer would see an infalling object time dilated and red-shifted as they approached the EH. The object is asymptotically time-dilated and red-shifted to zero even while its image fades away as fewer and fewer photons climb out of the hole. (And only in principle at that. Those last few photons spread out over eternity don't really constitute much of an "image".)

    Quite the opposite of an incineration actually, more like ... infreezeration... :wink:
     
  14. Jul 15, 2011 #13
    In my opinion, the misconception of the OP is that they cannot reconcile the frame of reference of the observer and of the infalling object;

    For the external observer the infaller approaches the EH of the BH and becomes increasingly redshifted towards infinity. In our frame of reference this is totally valid.
    For the infalling observer they approach and indeed cross the "boundary" of the EH and I use the term boundary loosely. Once they cannot escape the BH they proceed (in a finite time) to head towards the singularity or whatever other predicted mathematical model of quantum gravity would hold true. (I know this isn't known)
    Both frames of reference are completely valid, and coexist. There is essentially no paradox; this is a mapping of a finite observer time to an infinite coordinate time.


    However I ask this:
    Could it be argued that inside a BH; due to the immense relativistic time dilation (from the external observers FoR) that a singularity never occurs, that from our FoR zero volume and infinite density is never reached? How does this tie in with the FoR of the infalling object?
     
  15. Jul 15, 2011 #14

    DaveC426913

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    It is meaningless to ask if something that we have no way of measuring "really" occurs.

    Simply: under circumstances in which it can be determined whether it occurs, we would determine that indeed it occurs.
     
  16. Jul 15, 2011 #15

    Drakkith

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    Dave, I love that word. Infreezeration. I think you should copyright it or something.
     
  17. Jul 15, 2011 #16
    It should be helpful for me to quote directly from the Scientific American article I cited in my opening comments:

    Leonard is not saying that observers merely see the object differently but that it suffers a different fate upon entering the black hole. Is he naive as you say? Either that or he may have cut physics' legs out from under it.

    Is this issue a “big deal”? Again, I see physics more as a means to an end than an end in itself. It is obviously useful even if we do encounter some logical quandaries as we probe the more extreme and remote parts of the cosmos. The universe doesn't care what we think: It just goes on its merry way. It has defied theologians and philosophers for millenia. It evidently has no more respect for scientists.

    Jagella
     
  18. Jul 15, 2011 #17

    DaveC426913

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    Well, I've never before heard anyone suggest that anything gets incinerated at the EH.

    That alone leads me to suspect the veracity of either the quote or, if accurate, the person being quoted.
     
  19. Jul 15, 2011 #18

    disregardthat

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    Isn't it so that an observer (as a technical term) calculates its hypothetical observation according to the theory of relativity, and by that makes up for distortions caused by gravitational fields and redshifts? So to me it shouldn't really be an issue what one would actually measure, as the only thing in consideration is what one could calculate from the measurements.

    I also have a question about an external observer watching an object falling into a black hole. Now I have read that the external observer will se the object falling closer and closer but never reaching the event horizon. But isn't this ignoring the fact that an observer actually would calculate that the object actually fell into the black hole from the measurements by taking into account the massive redshift? Though I can see how there might be some difficulty defining the event of falling into a black hole. This event doesn't really happen in any frame of reference, which leads me to the second question: Does it make sense to talk about an observer at the exact edge of a black hole horizon? Or rather, is this a valid inertial frame? It would seem to me as a valid of an inertial frame of reference as that of a photon (and thus not hypothetically capable of observing anything).
     
    Last edited: Jul 15, 2011
  20. Jul 15, 2011 #19

    DaveC426913

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    It's not ignoring it, it's demonstrating that a physcial observation is different from a calculation to explain what is expected to happen. If your model and your calculation is correct, it agrees with the observation.

    Just like the refraction of light in a glass of water.
     
  21. Jul 16, 2011 #20

    disregardthat

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    You misunderstand, my point was that one should specify the distinction (which is crucial), and without doing so is leaving out half the story. (You should see that I am in my post making the exact same point as you just did.) I would like to hear your comments on my other questions.
     
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