Most stars have planets. Some planets have shiny parts of their surface. So if you want to see exactly what happened some years ago somewhere on earth (say 32.5 years ago in Africa or South America, at the time of writing that means about January 1977, or 620 or 860 years ago in Europe, which are the years 1390 Toledo and Barcelona persecutions, or 1150 with the end of the second crusade, or the battle of Lisbon) all you have to do is look at stars at half the distance in light years away (stars like Alpha Centauri, Cannopus and Polaris but with less luminosity) , with a very good resolution camera, that can reconstruct even the most minute amount of light. Searching for the planets in the vicinity of these stars and for shiny surfaces, you will get the reflection of earth that day, (light traveling there and back) and if it was not too cloudy, you might be able to get a good aerial picture and even videos of events in those times.
There are several benefits for this plan:
A. It would be funded by the Queen's Historic Society along with NASA.
B. It's cost effective: The results could be put on a website, and the public, at least some, would be willing to pay for full images, before the database was stolen and put on a Warez site. (Universities would be forced to pay if research was done via the database)
C. Finally historians would be debating topics in physics and astronomy, and their would be a reason for having expensive observatories.
D. More people would be aware of light pollution, and join the campaign to restore the natural habitat of darkness to the kingdom of night.
E. Archeology could be assisted with these images. A rock kicked by someone 2000 years ago could be found today. In the last three years I have been traveling around with a book with aerial images from WWI (see link) and finding unbelievable things. It turns out that many things have not changed much, even after 100 years. And there are many proven signs that this has been so for thousands of years. The location of a plot or a road stays that way for years, even though different nations come and go...-- pashute, Jul 22 2010 I was going to show a link to the book but found this http://multimedia.h...reach/0607/m16.htmlHalfway down the video, Prof. Benjamin Kedar shows his book and life work [pashute, Jul 22 2010] Gravity Time Mirror Gravity_20Time_20Mirror [ldischler, Jul 22 2010] Search for Terrestrial Intelligence Search_20for_20Terrestrial_20Intelligencethe implausibility of your idea makes this seem almost plausible [xaviergisz, Jul 23 2010] The Squire of Gothos http://en.wikipedia...ki/Squire_of_GothosPrior Art [8th of 7, Jul 23 2010] Gravity Time Mirror Gravity_20Time_20Mirrorthese concepts were explored in this posting. [bungston, Jul 26 2010] Agony Booth http://en.wikipedia...The_Original_SeriesMirror, mirror [8th of 7, Jul 27 2010] You'd need some fearsome optics. Suppose you had a nice flat square mirror, 100km on a side, 100 light-years away and facing towards us. Let's also assume that it has the verrrrrry gentle curvature that would be needed, and tracks the earth nicely so we can make prolonged observations. Would you be able to see an image of the sun in it?
The sun gives out (according to reasonable estimates), 10^45 photons of light per second. How many of these hit the mirror? Well, a 100 light-year radius sphere has a surface area of about 10^31 square kilometers, so our 10^4 sq.km. mirror will catch about 10^45 x 10^4 /10^31 = 10^18 photons.
We've assumed that the mirror can have the necessary properties to beam these photons back to a focus at earth, so we ought to be able to see the sun easily (10^18 photons per second is lots - as much as a candle)
Could you see a candle on Earth in this mirror? A candle emits about 10^18 photons per second, so you'd be able to see only about 10^-9 photons per second; it would take on average 30 years to collect even a single photon reflected from the candle.
If you wanted to see the candle, and supposing you need at least 1 photon per second, the distance to the mirror would need to be 10^(4.5) times less, or about 1 light-day. So, you can see the sun a couple of centuries ago, or a candle the day before yesterday.
However, I suspect that no mirror would be sufficiently perfect - even quantum fluctuations in the mirror would surely lead to the returning light being scattered all over the place.
Still, [+] for prompting me to do the sums.-- MaxwellBuchanan, Jul 22 2010 Don't you mean half the distance?
Most planets have curved surfaces, and many have gas atmospheres which are going to completely scatter any patterned reflection. I'm not going to even begin to imagine what kind of camera resolution this would take, in order to capture that one photon that makes it there and back.-- RayfordSteele, Jul 22 2010 Hey!! I was working on the edit, and didn't notice I posted it already. Yes I meant half. And of course this is a TIC. :-)-- pashute, Jul 22 2010 We're assuming that some kind group of aliens has built a 100km wide concave mirror with a curvature radius of 100 light-years.-- MaxwellBuchanan, Jul 22 2010 I had a similar idea but couldn't work out the details... i like the shiny object solution +-- simonj, Jul 23 2010 Brilliant! Bun! [+]< - - - - - - - - - - >[+] !nuB !tnaillirB ))
So highly vexing that the super-computer "Deep Thought" would require yet another seven and a half million years to calculate the improbability... I like it!-- Grogster, Jul 23 2010 I think it would be a lot *easier to first build a warp drive, then a bitchin telescope, then make a quick hop ~53 light years away and turn around to see who really killed Kennedy.-- DIYMatt, Jul 23 2010 Baked.
<link>-- 8th of 7, Jul 23 2010 8th, I did not see the episode, but from the link the only similarity that I saw (or was I looking the wrong way) is a miror...-- pashute, Jul 26 2010 // I did not see the episode //
Speak not such words of Heresy !
Trelane has derived his understanding of Earth by observing it through a powerful telescope, but has failed to compensate for the time delay caused by distance.-- 8th of 7, Jul 26 2010 ...and is chastised by his mommy.
"Set your phazers on spank."-- 2 fries shy of a happy meal, Jul 27 2010 Naah, an hour or so in the Agony Booth should suffice to make the point.
<link>-- 8th of 7, Jul 27 2010 random, halfbakery