The following paragraph is a scientific fact.

When we look distantly into the universe (with telescopes) we see galaxies (or whatever else you see) as they were millions years ago- in other words it is how they looked in the past (this is because of the speed of light).

So my question is could we build a technology (using current science or more speculative/theoretical science) using this scientific fact too see the earth history or past to such a level of detail that we could see historical events (e.g. individual dinosaurs) and the famous people's faces (in history books) - as if we were standing face to face with them- of the long ago past? What's the best level of detail could we theoretically see?

  • $\begingroup$ The objects we see are objects that are far away from Earth--that is why we are seeing them as they were years ago, because it took the light a long time to reach us. Earth is not far away. The light from the past has already left us. Unless there were some fantastical mirror far off in space that was aimed directly at Earth, this would not be possible. Furthermore, the mirror directors would have to have some amazing precision to direct light from Earth where it was then to Earth where it is now. It would be easier for them to just record their observations of Earth and send us their data. $\endgroup$
    – called2voyage
    Commented Sep 12, 2016 at 19:43
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    $\begingroup$ Lots of similar question s, possibly duplicates; not sure what you have in mind. See astronomy.stackexchange.com/questions/11017/… astronomy.stackexchange.com/questions/1443/… astronomy.stackexchange.com/questions/12062/… $\endgroup$
    – ProfRob
    Commented Sep 12, 2016 at 19:54
  • $\begingroup$ @Rob Jeffries I updated my question so it is more clearer to see how my question is different from those in the links above. What Im interested, for an answer, in is the level of detail (theoretical or actual) we can see Earth past history (e.g. famous faces from history). $\endgroup$
    – qwerty10
    Commented Sep 12, 2016 at 20:44
  • $\begingroup$ I don't follow. How are you going to see Earth in the past, in a way that differs from the questions I linked to? $\endgroup$
    – ProfRob
    Commented Sep 12, 2016 at 20:52
  • $\begingroup$ @Rob Jeffries Im not asking how the method would be different (or the same). As far as I understand those questions they don't give an answer to the level of detail (such as seeing a famous face as asked in the question) we could see into the past. Personally one thing what I think makes this question interesting is If the person died before the invention of photography/image recording and we didnt know what they looked like. $\endgroup$
    – qwerty10
    Commented Sep 12, 2016 at 21:21

1 Answer 1



Let's say we want to see Earth as it was 1000 years ago. Assume that someone has set up a perfect mirror 500 light-years away, so that we can actually see the light that left Earth 1000 years ago. (That's a really big assumption.)

The best telescopes in the world can't see the Apollo landing sites from Earth. We didn't get decent images of the descent stages, which were left on the surface, until the Lunar Reconnaissance Orbiter sent back photos it took from Lunar orbit. See http://www.nasa.gov/mission_pages/LRO/news/apollo-sites.html

1000 light-years is about 20 billion times as far away as the Moon. There's no way we could see people's faces at that distance with current technology -- or with any reasonable future technology. (There are physical limits on the resolution of an optical telescope of a given size.)

And all this assumes that we have that perfect mirror out there. As far as I know, nobody has set up such a mirror for us, and all the light that left Earth 1000 years ago is now 1000 light-years away, badly faded, and beyond our reach.

It's conceivable that we could develop faster-than-light travel (which may or may not be physically possible), go out there, build a telescope with a really big aperture, and point it back at Earth. But that's not likely to happen any time soon, and I wouldn't know how to determine how good an image we might be able to get.

And going back millions of years just makes the problem worse.

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    $\begingroup$ Even if your "faster-than-light travel" were possible, it would still take the thousand some odd years to get the information from the telescope back to the earth again, unless you're again going to use the "faster-than-light travel", but then what would be the point, because if you're doing that, why not just make a time-machine and travel back in time look at the earth from the moon, or low earth orbit, make a snap-chat video, and travel back into the present, post it online and call it a day. $\endgroup$
    – LaserYeti
    Commented Sep 13, 2016 at 3:58
  • $\begingroup$ @LaserYeti: I'm assuming a form of faster-than-light travel that doesn't necessarily imply time travel. (I've been watching a lot of Star Trek lately.) $\endgroup$ Commented Sep 13, 2016 at 15:26
  • $\begingroup$ I get that you didn't explicitly state "time travel," however, the principles of space-time and the speed of light tend to imply that if you move faster than all information can travel (faster than light), you're moving without the constraints of time, and therefore "time traveling." Besides, they time travel in several Star Trek episodes/movies. $\endgroup$
    – LaserYeti
    Commented Sep 13, 2016 at 16:36

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