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Thread: How can an object 'freeze' on the EH of a black hole?

  1. #1 How can an object 'freeze' on the EH of a black hole? 
    Forum Senior Booms's Avatar
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    fairly simple question

    supposedly to an outside observer an object passing the Event Horizon of a Black Hole will 'freeze' hanging there for ever unless the EH grows (although the object itself will have long since fallen in)


    I understand the thinking behind this, the EH is the point where light can't escape, so as an object passes it, the light it emits isn't far enough away to escape, but isn't close enough to fall in.


    this logic is sound to me, what I don't understand is how A would observe B forever, if the light is trapped then it can't reach A so A can't see it any more. to me this thinking suggests the light trapped in place itself is emiting more light.

    a more logical asusmption is that you don't see B past the EH and it would disappear


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  3. #2  
    Moderator Moderator Janus's Avatar
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    It's gravitational time dilation. For an infinitely distant observer, time slows to a stop at the event horizon.

    Gravitational time dilation can be found by:



    The radius of a black hole can be found by:



    if you plug the second equation in for "r" in the first one, you see that as your distance from the center of the black hole approaches the event horizon, the time factor increases to infinity. (an infinite time passes for the outside observer for any time experienced by you a the event horizon.


    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  4. #3  
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    Ok, here's my question though. The light that should be reflected off the object to my eye has to be moving at the speed of light. (duh) so, how can new light reflect off something that is no longer there? If time "stops" and the image is "frozen" to the observer, shouldn't we be able to see every thing that has passed the EH?

    Could I shine a different colored light on the "frozen" object and change the image?
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  5. #4  
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    The image perceived by the observer would become red shifted and at some point disappear from view, blackness would prevail, or have I missed something ?
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  6. #5  
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    Well, I dont know. According to physics, the object would appear to slow as it approached EH and then stop because crossing the EH would mean no visible light to explain what what happened. I get that part (I think)

    I'm assuming that light travels in waves and would need to continue to come at the observer after being reflected but there's no longer anything there to reflect the light.
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  7. #6  
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    Where is DrRocket when you need him ?
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