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Say nothing new can be learned anymore about the past by mere historical deduction from the present. Can a giant mirror-like thing out there that's let's say 2000 light years away from earth (and has been there since 4000 years ago) show us how things were on earth 4000 years ago? Could that be possible? I was thinking of this for some time and especially since it's been said that aliens would probably see dinosaurs and not humans on earth if they looked from millions of light years away, perhaps with some "super-binoculars".

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marked as duplicate by sammy gerbil, Qmechanic Apr 13 '17 at 21:34

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    $\begingroup$ Possible duplicate of A mirror in the sky to look at past Earth $\endgroup$ – sammy gerbil Apr 13 '17 at 20:14
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    $\begingroup$ This is going to need FTL capability in order to get the mirror out past the light you want to look at. Without that you can never get the mirror into the right place. $\endgroup$ – zeta-band Apr 13 '17 at 20:32
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You're last part is correct more or less, but the problem is that you'd have to drag any kind of light-collecting device to that faraway place, and once you get there, the light from the dinosaurs would be long gone. As such, we wouldn't be able to learn anything new if our history using this technique, at least so far as I can see.

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  • $\begingroup$ Wouldn't light passing close to a black hole be curved enough that some of it comes back in our direction? $\endgroup$ – zane scheepers Apr 14 '17 at 12:46
  • $\begingroup$ I'm not 100% well versed in how light curves around massive objects, but it seems to me that it would be difficult, and the object would have to already be there (or else, we would have to transport it). However, I think that these links on Quora (here and here) might be of interest. $\endgroup$ – Germ Apr 14 '17 at 13:44

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