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Space-Time Warping

  1. Oct 21, 2013 #1
    Imaging at a Trillion Frame Per Second - Ramesh Raskar


    Although this video is extremely interesting, The part I'm most interested in occurs at about the 9:30 mark.

    Ramesh Raskar says,

    "But there is also something funny going on here .. the ripple are moving away from the camera towards the cap of the bottle when we know that light should be moving from cap to the camera?
    Well Einstein would have loved to see this femto-photo.
    It turns out that because we are recording nearly at the speed of light, there is reversal in how we observe events in the world. After a correct mathematical space-time warp, we can correct for this time distortion."

    So my question is, why do we observe a reversal in the events when photographing at almost the speed of light? I may be overthinking, but I'm curious and was wondering if anybody had an explantation. Thanks in advance for any responses!
  2. jcsd
  3. Oct 21, 2013 #2


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    Staff: Mentor

    A photo is the collection of all light that reaches the camera at a specific point (better: very short interval) in time. It is not a collection of all light emitted at a specific time.

    For regular photos, this does not make a difference, as the time needed from emitter to camera is negligible. For those high-speed videos, the effect is relevant. To determine the frame where the camera will see light somewhere, you have to add the length between light source and this point and the length between this point and the camera.

    This does not have to lead to a "reversal", but it leads to significant effects on the images.
  4. Oct 21, 2013 #3
    Ahh that makes more sense now. I was definitely overthinking the process. Thanks
  5. Oct 21, 2013 #4


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    Science Advisor

    Or the guy was over-explaining the issue.
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