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Time-lag satellite imaging

A second chance to get a picture
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Conventional CCTV surveillance relies on recording images contemporanously and reviewing them later. Often, detail is missed, or the camera pans away at a crucial moment.

It would be better if it were possible to "go back" and capture an image of an event. However, this requires "time travel", a WIBNI.

There is, however, a way that this can be achieved. Since the speed of light In vacuo is limited to 2.99 x 10^8 m/s, a satellite positioned at a suitably large distance experiences a time lag between what happens on Earth and what it "sees". A spaceborne telescope with a suitably long optical path, large objective lens, and photon-multiplication detector would be able to image quite small features, even from the immense distances involved (for a time lag of 20 minutes, about 400 million kilometres).

The problem remains that of aiming the telescope. How does it know what to point at ? By the time a radio message from earth reaches the telescope, it's too late .....

This problem is overcome by using data transmission using J S Bell's "non-local" quantum electron-pairing theory (see link), by which means (in theory) information can be instantaneously trasmitted using separated electron pairs, irrespective of the distance of separation.

Only a low rate data link would be needed to transmit aiming information. Imaging information would be returned by a conventional radio link.

A number of telescopes would be required to provide 24/7 coverage of the entire planetary surface.

8th of 7, Aug 14 2002

Bell's theorem http://www.fdavidpe...essays/healtech.htm
Non-local quantum effects. [8th of 7, Aug 14 2002, last modified Oct 21 2004]

FTL communication impossible http://math.ucr.edu...eedOfLight/FTL.html
Cannot send information faster than the speed of light [pmillerchip, Aug 14 2002, last modified Oct 21 2004]

No information transmitted http://physicsweb.o...rticle/world/13/9/3
"Superluminal" gas propagation experiments don't send information faster than light [pmillerchip, Aug 14 2002, last modified Oct 21 2004]

[link]






       ...or just a big mirror a long way away.
st3f, Aug 14 2002
  

       [admin: spelling fixed in title. sattelite -> satellite. I'll leave the rest for you, 8th]
st3f, Aug 14 2002
  

       Damn, why do I always make that same spelling mistake ?
8th of 7, Aug 14 2002
  

       Pah. Why signal the satellite to return the image when you can just build it to return every image. If you don't need the lag feed, ignore it.
phoenix, Aug 14 2002
  

       Phoenix: To get any sort of detail, the 'scope is going to have to have a narrow field of view; if you image the whole planet, then you won't see any sort of detail, even with an unachievably high resolution on the image sensor. So the thing has to "aimed" at a particular patch of land, much like existing surveillance satellites are. Hence the need for an FTL signalling channel; the lens needs to be already pointing at the desired site when the event "happens".
8th of 7, Aug 14 2002
  

       Marvellous idea, except for the teeny tiny flaw that FTL signalling is impossible (see link)...
pmillerchip, Aug 14 2002
  

       Pmillerchip: "Never say never" ..... an experiment last year using sodium vapour managed to propagate a modulated signal at 30 times C in vacuo. Photon quantum tunneling (effectively, teleportation) has been tentatively established over what is in efect a macroscopic distance (several metres).   

       You are a very brave man if you are prepared to assert that C-plus communications will "never" be possible. My recent research in this area indicates that there may be just enough elasticity in Quantum Electrodynamic theory to let FTL effects wriggle through in some way; and it has been conclusively demonstrated at CERN that causality violations do occur in some subatomic interactions. On paper, anyway. Thanks for the link, but it's not quite the whole story.
8th of 7, Aug 14 2002
  

       8th: Got a link to that sodium vapour experiment? It sounds interesting, but I couldn't find anything about it on the Web. The only vaguely relevant links I could find were ones about a caesium gas experiment that showed superluminal wavefront propagation, but didn't actually send information faster than light (see link).   

       The problem I see is that if FTL communication were possible, you could (in some frames of reference) send information back in time, with all the associated causality problems that would imply. I can't personally see how causality problems or time travel can possibly exist, but then again that's just argument from personal feeling, which is no argument at all! I guess my point of view is that extraordinary claims require extraordinary evidence, and so far I haven't seen any.   

       But I'm willing to be proved wrong...
pmillerchip, Aug 14 2002
  

       pmillerchip: I'll look for a link. They've switched from Caesium to Sodium - the experiments last year are quite promising.   

       The jury is still out on FTL communication - let's wait and see. There are a whole raft of interesting applications.
8th of 7, Aug 15 2002
  
      
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