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Observer inside a Black Hole

  1. Sep 27, 2015 #1
    There are many videos and articles about this topic (what it looks like if you fall into a black hole). I remember hearing that, inside the event horizon of a black hole, time has essentially stopped for an outside observer. However, if you fell into one that would mean that any amount of time that passes after you crossed the event horizon would account for an infinite amount of time outside the black hole. In simpler words, you would see all of time happen instantly (Is that correct so far? you don't have to read on if this is already wrong since my theory is entirely dependent on this fact.)

    But here is my problem: If hawking radiation really exists, then you can't see "all" of time happening instantly because the black hole has an expiration date ... It will eventually evaporate. So how can you ever move after you crossed the event horizon if the black hole evaporates after an instant that you are inside? Wouldn't all matter just be frozen at the position at which it enters the event horizon until the event horizon shrinks again and releases the matter inside?
     
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  3. Sep 27, 2015 #2

    pabilbado

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    The normal presentation of these gravitational time dilation effects can lead one to a mistaken conclusion: If an external observer sees me falling inside a black hole my time would look like is decreasing asymptotically. It may seem like I would see the opposite effect, seeing the universe asymptotically accelerate due to the gravitational time dilation. Until I see the universe end and then cross the black hole's horizon. This isn't the case. What I see depends on what light that reaches me does. I only see light in my past cone of light. And that's the case even if take into account the gravitational time dilation, it will change the form of my cone, but never flip it upside down so I can see the future.
    And also the problem is that classical coordinates frames won't work on an event horizon creating infinite results, what you have to use are other coordinates systems which are regular on an event horizon. (These is weird and really complex)
    So yeah you won't see the future, sorry mate :( it would have been awesome. You can check out a lot of explanations (if mine wasn't clear enough):
    http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html
    http://www.phys.vt.edu/~jhs/faq/blackholes.html#q11
    http://physics.stackexchange.com/qu...into-a-black-hole-see-the-end-of-the-universe
     
  4. Sep 27, 2015 #3
    So the gravitational time dilation doesn't really go towards infinity if you approach the event horizon. Is there any way to calculate where the observer actually is at any specific time for an outside observer?
     
  5. Sep 27, 2015 #4
    At some stage, depending on the size of the black hole, the infaller will start to become 'spagghetified' anyway.
    So unless they are subatomic in scale they are not going to be at one particular location,
    different parts of them will get spread out over quite a large range of location.
    (and if they actually are subatomic in scale then quantum effects will begin to play a part and and defining their location starts to lose meaning altogether.)
     
  6. Sep 27, 2015 #5

    pabilbado

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    Actually "Time" tends to infinity, coordinate time tends to infinity. But there is a concept called proper time which is invariant no matter what coordinate system you are using which will tend to a value T as you approach the event horizon, and that will be the time the falling object will perceive. What will happen is that no one will see you crossing the event horizon, not that you will see the end of the universe. If you want to understand further and the reasons this happens you will need to understand the geometry of general relativity. Which I am starting to grasp so I may have not explained myself correctly enough for everyone to understand what I am saying. But it really helps trying to picture an accelerating observer that will create an apparent event horizon which is easier to picture.
     
  7. Sep 27, 2015 #6
    Well of course if the observer would be a human then the black hole would have to be large enough for spaghettification to only happen after the event horizon.
    My theory is still standing... If there is a region inside a black hole where time essentially stops that would mean that the observer has to witness all of time for him to actually experience time and all that needs time to happen.
     
  8. Sep 27, 2015 #7

    Chronos

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    The external universe will actually appear redshifted to an infalling observer by as much as z=2. It is not possible to hover in place anywhere between the event horizon and signularity at the center of a black hole.
     
  9. Sep 27, 2015 #8

    Nugatory

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    No, that is not how it works. The infalling observer's experience is that he falls towards and through the event horizon and reaches the central singularity very quickly. The last light from outside that reaches his eyes before he dies at the singularity comes from events that happened only a very short time after he passed the event horizon.

    The idea that it takes infinite time to reach and fall through the event horizon is a misunderstanding of the fact that light from the infaller crossing the horizon will never (this is often misstated as "take an infinite time", but "never" is more accurate) reach the eyes of an observer outside the event horizon.

    You'll find many threads in the relativity forum here discussing these matters, and I highly recommend this paper: http://arxiv.org/abs/0804.3619
     
  10. Sep 27, 2015 #9
    I understand it now... For an outside observer it only seems like my clock has stopped because there is no light coming to him after I have crossed the event horizon. But that's just an illusion my clock hasn't completely stopped and so I will get accelerated towards the singularity in my reference frame.
     
  11. Sep 27, 2015 #10
    Thank you all for replying ^^ I think everything has been said
     
  12. Oct 15, 2015 #11
    This is a bit of an old thread, but I have a question which fits here very well. If, due to gravitational time dilation, we who are far away from a black hole perceive an objects time to nearly or complete stop, have we ever witnessed or detected an object being consumed by a black hole? Is it possible for us to see/detect this happening if the object's time is nearly stopped? If we can't, and the universe is only 13 billion years old "our time", then can we assume that everything that has ever entered a black hole, did so in the early forming stages of the universe; the first seconds or minutes?
     
  13. Oct 15, 2015 #12

    Nugatory

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    We cannot see happening, but this has nothing to do with the object's time slowing down or nearly stopping - in fact, no such thing happens (there is intense gravitational time dilation, but that's not the same as thing as "time slowing down or stopping"). We cannot see it because no matter how long we wait, light emitted from the object as it passes the event horizon will never reach us.

    If I drop you into a black hole, although I will never SEE you cross the event horizon:
    a) You will experience falling through the event horizon and then reaching the central singularity rather quickly.
    b) If I try sending you a radio message ("Dude! - I'm sorry! - I didn't mean to drop you! Please forgive me!") you will be able to reply ("You've killed me because you are a clumsy jerk! No, I don't forgive you!") only if I send it before a certain time. After that, you won't get my message until you've crossed the horizon and it's too late to reply.
    c) There is another point in time, only slightly after the one in #b, such that I have to send my message before then or you won't even receive it because you've died at the central singularity before it got to you.
     
  14. Oct 15, 2015 #13

    davenn

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    not sure how you came to that conclusion as BH's are still in the process of taking in matter if there is matter within their gravitation field to be "pulled" in
     
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