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The basic system would consist of a big mirror in a distant
orbit around the sun pointing towards earth. The orbit
would be chosen so light travels from the earth to the
mirror and back in a couple hours up to maybe a day or
more. That distance will of course vary. When there is a
disaster, or other event on earth that is discovered
shortly after it occurred, high powered telescopes could be
used to watch the event in the reflection of the mirror
several hours after the fact. Of course more than one
mirror could be used to provide different time delays,
different angles and fuller coverage of the earth.
- Our telescopes aren't powerful enough. This could
be improved somewhat (but not fixed) by making the
mirror somewhat curved. In the extreme, the mirror could
be curved so that it focused on the earth, but then it only
focuses on a single location on earth, and only works for a
certain distance, so make it somewhat less curved.
- Constructing a mirror large enough and perfect
enough is beyond current technology.
- It would probably be more cost effective to just
have security cameras installed everywhere.
If this could work, Police investigators would request
surveillance of a certain location over a certain time
period in the past. Depending on the importance of the
crime and the availability of telescopes, a low priority
crime might be assigned a low quality telescope, resulting
in a poor image. Major events (say an assassination
terrorist attack or natural disaster might get all of the
telescopes assigned to them to capture as much data as
possible. For example, a lost airliner could be tracked
from takeoff to crash by a single telescope, but because of
its importance would probably be assigned multiple scopes
to make sure it didn't get lost again.
CSI zoom enhance
The zoom enhance scene I mentioned [xaviergisz, Feb 26 2015]
||OK, so if we want a 1hr delay, the mirror has to be
0.5 light-hours away, or 335 million miles away.
That's mid-way between Mars and Jupiter.
||Also, I'm pretty sure that you'd have to remove
Earth's atmosphere for this to work. Not just because
it's often cloudy, but because any variation in
atmospheric refraction is going to completely screw
things. Consider that stars twinkle, even though
their light is being wiggled (by the atmosphere) only
over a distance of a few 10s of kilometres. Now
multiply that distortion by about 10 million-fold.
||Satellites can currently photograph the earth
surface through the atmosphere. The telescopes
looking into the mirror need to be space based.
(definitely would need to be to look at the mirror
during the day).
||I guess the distortion would still be much worse for
a telescope effectively much farther from the
atmosphere, than a telescope looking at earth from
just past outside the atmosphere...
||There's no atmosphere beyond the atmosphere, [mb]
||Yes, [poc], I am aware of that. That's not the point I
||Suppose that the atmospheric turbulence is enough
to deflect light by 0.01 degrees. This means that a
light ray, travelling through the atmosphere to the
surface of the earth, will be shifted by quite a small
amount (ie, an angle of 0.01 degrees, over a distance
of say 30km).
||Now imagine a light ray going out through the
atmosphere, towards our mirror. It is still deflected
by the same 0.01 degrees, but it now travels (on this
deflected path) over a 300-million mile journey.
||Hence, the distance by which it has been deflected,
by the time it reaches the mirror, will be huge.
||So people would just do their crimes at night or
under cloud cover or indoors as they already do.
And planes would continue to crash at night or
during inclement weather.
||Using space as a recording medium is kind of clever.
But I'm not sure how useful this would be.
||Night: There's no reason this couldn't use infrared.
Of course it can't see indoors or in some weather,
but it would (if it was possible) help in many
||This is significantly less realistic than the magical CSI zoom and enhance. I vaguely remember one episode where there was security footage of a victim being killed, but the killer was out of frame. Not to worry, the clever CSI team simply zoomed and enhanced into the reflection of the victim's eye ball to reveal the identity of the killer.
||atmosphere: Place the mirrors of both ends outside atmosphere. Thus only the first and last lap travel through atmosphere. Remaining intermediate bouncings will occur only in clear space. This should keep distortions/absorption at minimum.
||Hmm, looks like you may be right. Perhaps the atmosphere should be removed during crimes?
||// less realistic than the magical CSI zoom and
enhance // Well, other than the atmospheric
distortion issue which may limit this to
investigations of crimes in space, there's nothing
other than current technological limits preventing
us from creating a huge moon-sized telescope that
can see that far and a reflector twice the size of
Jupiter to go with it. On the other hand there is
no technological advance that would enable
extrapolating a detailed image from a small handful
||However since CSI does have that technology, the
script writer ought to have someone snap a photo
of the moon a short time after a crime occurred.
CSI investigators could then use their zoom and
enhance to catch the killer using the mirror off the
||The CSI zoom and enhance is possible if you have a 100 gigapixel
security camera. I suppose your idea could work too, it is just a few
orders of magnitude more difficult.