Seeing into the past

[sssssteve]

Let's say there was a very large mirror on a planet that is one light year away, and we built a very, VERY powerful telescope to look at it. Would we be able to see Earth as it was two years ago? Zooming in would also enable us to see events from two years ago surely.

[WaldoMcFroog]

It seems like a reasonable theoretical notion to me, taking on board all of the caveats required about whether it's physically possible to build such a mirror/ telescope or whether they would disintergrate under their own weight or something etc. etc. blah blah.

[Stav's Back]

that is a cracking question! I hope we get a nice technical answer from a know-it-all boffin scientist to clear it up

[bernardo]

Yes, exactly. (apart from the fact that we haven't got telescopes powerful enough).

[IndieSinger]

Wouldn't the light take another two years to reach us from when we set it up, though? In other words, say we (us AnswerBankers) set it up right now, then we would have to wait two years for the light (and therefore image) to bounce back at us. So on 3rd September 2006, we would be able to look at the world as it is today, 2004. So we can't look at the world in 2001, can we?

[wildwood]

Good point IndieSinger, apart from the fact that we would not be able to see any events before installation, there doesn't seems to be anything wrong with the theory.

[ludwig]

What you would have to do is just sort of wave and smile in the general direction of the planet. Then you could go away for 2 years, come back, and set up the telescope. Hopefully you would then see yourself waving and smiling back 2 years ago.

[scotsrob]

Yes, a great Q I think Steven Hawking gave up on the "back in time" theory when he realized that if a cup had fallen and smashed to pieces, when time "reverted" the cup would have to gather itself together and defy gravity by jumping back up to the table.

[Gandy]

European explorers once thought that they may sail off the edge of the world. Depending on the topology of space the light leaving earth now may end up where it began. You wouldn't need a mirror at all.

[tomd]

It's like the way it takes light 500 seconds to travel from the sun to the earth, so we're looking at an image of the sun from 8 minutes ago. It'd be kind of like a light echo, the way sound travels to a wall, reflects, and comes back for us to hear it at a later point in time.

[WHJ]

Sod all the theory - why would you want to do that sssssteve? With all the CCTV cameras around these days, we're all covered!

[keltik]

a truly amazing q, but if the mirror was big enough, you can gaurantee somebodys fingerprints will block the tiny speck our planet needs

[sssssteve]

Thanks for the answers folks, I'm reasonably sure the theory is sound, but as said already physically unviable (is that a word?...LOL)

[dstone]

I wonder if there is already a mirror in space. Perhaps some kind of gravitational anomaly that could reflect a portion of the electromagnetic spectrum. If such a feature of space exists, we may yet be able to see into Earth's past.