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Looking in to the past

  1. Nov 27, 2011 #1
    ok, if when we look at a planet that is say 100000 light years away, and we can see it emitting light, and that light takes 100000 light years to reach us, then is it possible that the planet may not even be there any more? if so i f i was there looking back at erath would i be seeing into the past, like could i be seeing dinosours and stuff walking the earth?
  2. jcsd
  3. Nov 27, 2011 #2
    Yes, all our observations from the cosmos are delayed, some by very long periods of time, e.g. billions of years.

    In principle, you could see the dinosaurs. For example if the light emitted by the dinosaurs travelled out into space and was reflected at some mirror millions of lightyears away, and back towards earth. Then you'd see moving images of the dinosaurs from many millions of years ago.

    You'r only seeing old moving pictures, you cannot interact with the events taking place in this moving picture, and therefore not influence those events, of course.

    So its not really much more interesting than watching an old recording... :-)
  4. Nov 27, 2011 #3
    wow thanks for the reply :-)
  5. Nov 27, 2011 #4
    not that has got me thinking, can this be somehow reversed into seeing into the future? or am i just talking madness?
  6. Nov 27, 2011 #5
    You're welcome!

    I should probably mention something more in connection with my example of the cosmic mirror. It is of course too late now to place such a mirror in outer space. You'd have to do it beforehand. RIght now the images of the dinosaurs (the emitted light) are in principle (although increadibly/fantastically weak...) still travelling at the speed of light away from earth at many millions of lightyears away. It is impossible for us to close that gap, due to the restrictions of special relativity. We'd have to travel faster than light, which is not possible.

    Similarly, when you admire yourself in a mirror, standing 0.5m away from it, you are really watching an image of yourself that is around 3 nanoseconds old :-)
  7. Nov 27, 2011 #6
    There is no scientific evidence that suggests that this would be possible. According to the currently established laws of physics, signals such as light emanating from events only move forward in time. So a signal cannot be sent to the past, to make it possible for someone to see the future.
  8. Nov 27, 2011 #7
    when u say close the gap, do you mean that the light has long gone and is still on the move?, my question then would be can we slow light down down? if light is constant if you get me? then lets make it destination longer, say you used mirrors to deflect it 100 million times round the earth first then sent it on it way, would that not take longer to get there, i unsderstand the bit you said about you would need to have the mirror in place before hand, just asking would it be possible to slow light down , also i know 100 million times at light speed would not be enougth its just an example? thanks for your time and please tell me if u think i am waisting it and i will leave you be ha ha, thanks again for your time.
  9. Nov 27, 2011 #8
    Yup, it is possible in principle to "save" an image for future observation by letting the emanated light signal reflect e.g. between parallel mirrors. But in practice, it will be impossible, for many reasons. You'd need perfect mirrors, a near perfect vacuum, a perfect setup of perfectly stationary mirrors, etc. But in principle it is possible, if everything is "ideal". Which it never is...
  10. Nov 27, 2011 #9
    Just make a photograph, much simpler.
  11. Nov 27, 2011 #10
    ty again
  12. Nov 27, 2011 #11
    Agreed. Hence my comment above about the "light signal from the far past" not being much better than looking at a recording.
  13. Nov 27, 2011 #12
    do u think by using your (You'd need perfect mirrors, a near perfect vacuum) u could trap light in a box then u could in theory see these images from the 0.5m like looking into a mirror,..................passion where on earth ar u goona be able to take a photo of a moving dinosour? as in a real 1?
  14. Nov 27, 2011 #13
    You won't be able to capture any light from a real dinosaur by any method, since that light is too far away from us and moving away at the speed of light. But you could in principle capture light from some current event, and use it a hundred millions years later, by the methods mentioned. Again, just in principle... :-) If you want to avoid the usual simple techniques for storing images (camera etc).
  15. Nov 27, 2011 #14
    no i mean say u shined a torch in to a box of perfect mirrors and shut the box..... arrr i see.... u cant shut the box fast enough. was gonna say and trap it, i know mirrors absorb a fraction of the light there for over time it will be gone, but say perfect mirrors?
  16. Nov 27, 2011 #15
    but if you could shut that box, maybe this is for another place on here i am not sure,
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