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B Event horizons frozen image

  1. Mar 23, 2016 #1
    Apparently, when viewed from a distance, the motions of a person approaching the event horizon of a black hole will appear to first slow down and then come to a complete stop as they pass through the horizon. Then, as I'm led to believe by what I've seen and read, that final 'frozen' image of the person remains forevermore, motionless and stuck at/on the horizon.

    The 'slowing down' phase makes sense if I think about the observed motion of the person's fall as being divided into consecutive instants of time (or information) and each instant being recorded on the individual frames of a film strip. Without the black hole, the movie camera projects the film strip at a frame rate such that any motion appears fluid and 'normal', but with the black hole present, the stretching out of spacetime outside the horizon is equivalent to slowing down the frame rate, thus giving the appearance of slow-motion. Eventually, at the horizon, the camera stops at the final frame, and all motion has ceased.

    What I don't get is how that final frozen image remains visible to observers long after the person has actually gone through the event horizon boundary! What is the source of that continuous image if nothing is there anymore? Wouldn't this make the black hole some kind of photo album or montage displaying a snapshot of everything that has ever fallen into it? Surely that would make the invisible black hole visible.

    I'm quite sure I've misunderstood this concept, or the film strip analogy is flawed (probably both), so I'd appreciate any info or guidance on how to visualise this process without invoking any maths.

    One further question: Using the same film strip analogy, would the observed fall into the black hole transition from smooth, fluid motion into jumpy, discrete steps of motion as the stretching of spacetime at the atomic scale decompresses the atomic-fluctuation information (in terms of photons) and makes it observable on our macroscopic scale? I guess this comes down to a question on the photon emission process.

  2. jcsd
  3. Mar 23, 2016 #2


    User Avatar
    Gold Member

    Hi. Welcome to PF. The image doesn't remain visible forever. It fades away until you can no longer see it. The source of the image are redshifted lightwaves that are just reaching your eyes.
  4. Mar 23, 2016 #3


    Staff: Mentor

    The source of an image is never "what is there" it is always "what was there". You are always looking looking at light from events on your past light cone. Many of the stars you see at night you still see even though nothing is there anymore.

    The black hole just redshifts the light infinitely.
    Last edited: Mar 23, 2016
  5. Mar 23, 2016 #4
    I guess that the last detectable thing which could be observed of an object falling in to a black hole would be a long wave radio emission.
  6. Mar 24, 2016 #5
    Ok, that's a little clearer...Thanks for your replies.
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