# Looking into the past from really far away

**URL:** <https://boards.straightdope.com/t/looking-into-the-past-from-really-far-away/408918>\
**Category:** Factual Questions\
**Created:** [June 21, 2007, 10:56pm UTC](https://boards.straightdope.com/t/looking-into-the-past-from-really-far-away/408918 "2007-06-21T22:56:14Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\
**Post date:** [June 22, 2007, 6:13pm UTC](https://boards.straightdope.com/t/looking-into-the-past-from-really-far-away/408918/21 "2007-06-22T18:13:35Z")

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Well heck, why go all that distance just to see the past? I’m pretty sure that _some_ of those little photons are going to hit something (space dust, planets, moon, the shiny part of an alien spaceship) and then reflect back toward earth. Just build yer old huge receiver-thinga-ma-bob in this solar system and decipher the reflected signal.

Glad to be of no assistance whatsoever,  
Bubba

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**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\
**Post date:** [June 22, 2007, 10:59pm UTC](https://boards.straightdope.com/t/looking-into-the-past-from-really-far-away/408918/22 "2007-06-22T22:59:36Z")

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[QUOTE=BubbaDog]  
Well heck, why go all that distance just to see the past? I’m pretty sure that _some_ of those little photons are going to hit something (space dust, planets, moon, the shiny part of an alien spaceship) and then reflect back toward earth. Just build yer old huge receiver-thinga-ma-bob in this solar system and decipher the reflected signal.

Glad to be of no assistance whatsoever,  
Bubba  
[/QUOTE]

[It’s been done.](http://www.noao.edu/outreach/press/pr05/pr0512.html)

> [@](#):
>
> A team of astronomers has found faint visible echoes of three ancient supernovae by detecting their centuries-old light as it is reflected by clouds of interstellar gas hundreds of light-years removed from the original explosions.
> 
> Located in a nearby galaxy in the southern skies of Earth, the three exploding stars flashed into short-lived brilliance at least two centuries ago, and probably longer. The oldest one is likely to have occurred more than six hundred years ago.

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**Author:** ![jackdavinci](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackdavinci/32/3259_2.png) [@jackdavinci](https://boards.straightdope.com/u/jackdavinci)\
**Post date:** [June 23, 2007, 9:17pm UTC](https://boards.straightdope.com/t/looking-into-the-past-from-really-far-away/408918/23 "2007-06-23T21:17:40Z")

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[QUOTE=Mindfield]  
Could one, given a large enough and powerful enough lens, presuming perfect, digitally assisted optics and considerable light-gathering capabilities, and with optimal astronomical conditions, observe _some kind_ of coherent, detailed imagery from the past from some considerable distance away?  
[/QUOTE]

Yes, absolutely. We already can. Right now, from Earth, we are limited to looking at places other than Earth, and with much less resolution than is useful for looking at the surfaces of planets, but that’s just a matter of degree - the principle is sound.

As for looking at Earth, barring any technology that is either actually FTL (Warp Drive) or _de facto_ FTL (teleportation), the major limit in principle is that _ **you can’t view the past of the Earth any further back than when you left it** _.

Interestingly there is a similar limit to some of the recent time travel proposals worked out by physicists - that one cannot travel back in time to a point before it was built(functional).

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