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Could a perfect mirror/s be made to reflect one side of the Earth from the edge of the solar system and viewed with an optical or radio telescope that is in orbit?

The targeting mirrors and telescope are in orbit around Earth are aimed away at reflected Earth through the mirrors in synchronous orbit around the sun (shown in the picture below). The mirror in orbit on the telescope can be moved to see different points of reflected Earth to see about 30 seconds into the past.

In the comments: What if the Hubble was modified and aimed at the Earth? You can see stuff on a table like a blurry hammer and people.. The fact that you could see anything at all on a table is impressive. Therefore, could use to look back in time in conjunction with gunfire locators to get a visual on the exact location to get the color make and model of a car or outline of a person?

I understand the square inverse law and the further away the telescope and mirrors are from Earth the blurrier. The mirror would have to be huge or the viewing area very small. With technology, we could scan of an area on the mirror in which the Earth is reflected with a narrow aperture to take a panoramic picture?

I understand that radio telescopes do not work the same as optical telescopes, but could radio and other types of telescopes see objects in black or white on Earth farther away?

An image of a Magnetic Sail

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https://engineering.stackexchange.com/questions/12518/how-many-times-can-the-best-mirrors-reflect-in-space https://space.stackexchange.com/questions/30477/could-we-see-someone-walking-on-mars-from-earth

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  • $\begingroup$ I believe that we would have trouble making a mirror big enough, and also alignment and stuff would be tricky. Feasibility is no, but someone with math skills may be able to tell you if its theoretically possibly. $\endgroup$
    – Clay Deitas
    Commented Sep 5, 2018 at 3:53
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    $\begingroup$ Light tends to drift due to quantum weirdness, so if the distance is too great, it becomes very blurry. $\endgroup$
    – forest
    Commented Sep 5, 2018 at 3:59
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    $\begingroup$ @forest what distance is that? $\endgroup$
    – Muze
    Commented Sep 5, 2018 at 5:09
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    $\begingroup$ It'd be a lot cheaper to send up a camera & broadcast back what it captured. $\endgroup$
    – GrandmasterB
    Commented Sep 5, 2018 at 6:17
  • $\begingroup$ @Muze I have no idea. Pretty long, I guess. $\endgroup$
    – forest
    Commented Sep 5, 2018 at 8:31

5 Answers 5

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Light spreads out as it travels, proportionate to the square of the distance traveled. This is called the "inverse square law". Think about shining a light on a wall - the further away you are, the larger the circle on the wall, and the less bright it is. Less photons per square inch are arriving at the final destination.

By the time you get out to the edge of the solar system, The light is so spread out that your mirror would have to be absolutely gargantuan - Half the size of the solar system. It would also have to be curved, to avoid the light spread out any further.

As other people have mentioned - focusing issues, dust, gases and other objects in the solar system, as well as quantum weirdness are all acting against you.

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  • $\begingroup$ Yes, but at what distance would resolution be a problem. Would there be enough resolution to follow a car? You don't have to see the whole Earth at once. $\endgroup$
    – Muze
    Commented Sep 5, 2018 at 19:52
  • $\begingroup$ I believe this answer is misinformed. You don't need to make a giant mirror to compensate for the light become dimmer as it spreads out (though it certainly helps). You can just have a longer exposure time to collect more light. What you do need a bigger mirror for is to improve the resolution, though this would depend on the final optical configuration I guess. $\endgroup$
    – Snyder005
    Commented Sep 5, 2018 at 19:55
  • $\begingroup$ Wouldn't a curved mirror of this size be dangerous in terms of concentrated energy? $\endgroup$
    – Hawker65
    Commented Sep 7, 2018 at 8:59
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    $\begingroup$ @Snyder005 Wouldn't a long exposure time prevent you from seeing moving objects and defeat the whole point of CCTVing Earth? $\endgroup$
    – Hawker65
    Commented Sep 7, 2018 at 9:02
  • $\begingroup$ Depends on how long an exposure time you need. Unless you had really sensitive, extremely low-noise sensors, you're probably not getting 60 fps. Could be 1 frame per hour or day potentially. Anyways to see anything moving you'd need supreme resolution. The point was that resolution was the reason you needed the big telescope, not just because the light was dim. $\endgroup$
    – Snyder005
    Commented Sep 7, 2018 at 17:39
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No mirror (or telescope spacecraft) can view an Earthly event earlier than its launch date. The light from any event before the launch is forever beyond the reach of a spacecraft that cannot exceed the speed of light.

Alien civilizations orbiting distant stars may, in theory, be examining our distant past, and might be persuaded to share their archives with us. We should immediately begin building enormous telescopes and recording the activities of alien civilizations in order to have something to offer in exchange.

A few spacecraft have looked back at Earth and returned distant pictures. The historical value of such photos is limited because they are severely blurred, probably caused by so many people constantly moving around.

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  • $\begingroup$ But we could still attempt to set up a telescope that would allow us to view imagery from here on in the future without needing video storage correct? $\endgroup$
    – user64742
    Commented Sep 8, 2018 at 2:35
  • $\begingroup$ Yes, of course. Also, two mirrors in space, reflecting each other, could store an enormous amount of data. $\endgroup$
    – A. I. Breveleri
    Commented Sep 8, 2018 at 3:10
  • $\begingroup$ The images from space probes are blurred not because of people moving around, but due to inherent limitations of their optics and sensors. $\endgroup$
    – Juraj
    Commented Aug 15, 2019 at 16:23
  • $\begingroup$ humorless @Juraj has no humor $\endgroup$
    – A. I. Breveleri
    Commented Aug 15, 2019 at 16:43
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While this wouldn't work with a mirror, there is a way it's theoretically (though not practically) possible: by using a black hole.

When light approaches a black hole, some of it ends up getting drawn in, while some of it has its trajectory bent hyperbolically and flies off elsewhere. In practice, this looks like a shining band of light outside the hole's event horizon.

With an infinitely-powerful telescope, you could find a black hole and zoom in on just the right point the edge to see light that left Earth aeons ago, got warped around the black hole, and came back toward Earth. In effect you'd have a camera pointed at the past.

(Look at Riccardo Antonelli's description for much more detail on this, plus pretty pictures, and a program to make your own!)

The real problem lies in making an infinitely-powerful telescope, as current ones aren't anywhere near powerful enough for this: we've never even seen a black hole directly yet (depending on your definition of "seen"), and there are some fundamental limitations that mean we can't just keep scaling up our current telescopes to make them stronger. But handwaving a super-powerful telescope is far from the strangest thing that's been done in science fiction.

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    $\begingroup$ Problem is, that light gets mixed up with light from other sources. You won't get any pictire out of it. $\endgroup$
    – The Square-Cube Law
    Commented Sep 5, 2018 at 12:36
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    $\begingroup$ Downvoted because the same problems that would cause a mirror to be dismissed as impossible are still present when using a black hole to "return" the light to Earth. You are effectively replacing the mirror with a black hole and introducing even more problems. In fact it's extremely more plausible to use a giant mirror than to use a black hole, so I don't see why you dismissed the mirror as impossible. $\endgroup$
    – Snyder005
    Commented Sep 5, 2018 at 19:49
  • $\begingroup$ @Snyder005 Basically because with a black hole you don't need to worry about the angle: if you choose the right spot to look at, you can see light that's approaching the black hole from any direction whatsoever. Whereas with a mirror that far away, the slightest error in angle would make the light miss Earth entirely. (A retroreflector avoids that problem, but a retroreflector also doesn't get you a nice clear image like OP wants.) $\endgroup$
    – Draconis
    Commented Sep 5, 2018 at 19:55
  • $\begingroup$ But it's easier to hand-wave the problem of mirror alignment than the problem of determining the light-path of photons from the black hole disk. By the same principal, light from all the nearby stars/galaxies will also be visible, and will be intermixed with light from Earth. The optical effects of the accretion disk would also make focusing, let alone resolving the Earth much more difficult than the mirror. $\endgroup$
    – Snyder005
    Commented Sep 5, 2018 at 20:03
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Even if we could set aside all the above-mentioned problems — blurriness, mirror size, etc. — we still couldn't 'look into the past' in the way this question seems to imply. To use your example, say we tried to connect the mirror with gunfire locators to focus it on a crime scene. Remember that our message for the mirror to focus on the crime scene can itself only travel at the speed of light. If the mirror is 30 light-seconds away, and we send our 'focus here' message 5 seconds after the guns are fired, well... when we send the 'focus here' message, the mirror is seeing what happened 30 seconds ago (i.e., 25 seconds before the gunfire). But by the time the 'focus here' message arrives, the mirror is seeing the world as it was exactly when we sent that message (i.e., 5 seconds after the gunfire). THere's no way for our message to get ahead of the light traveling outward from earth.

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  • $\begingroup$ The only moving mirrors is the ones in obit around Earth that are looking at the distant mirror in orbit around the Sun. $\endgroup$
    – Muze
    Commented Aug 11, 2019 at 22:03
  • $\begingroup$ The whole Earth is in frame on the mirrors, it is the telescope that is looking at a spot of Earth but the whole image of Earth is being captured. 1 mm of the mirror maybe 1 meter on Earth $\endgroup$
    – Muze
    Commented Aug 11, 2019 at 22:25
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Others have pointed at focus problems and so. However, spy satellites show that interesting stuff on Earth can be photographed from orbit with a fraction of second delay and with some improvements it could be raised to a few seconds with resolution enough to provide some useful evidence for some crimes happening outdoors.

However, this system has an essential flaw: the satellite must be ordered to point to the crime scene, and since the pointing order travels just as fast as light of the crime image, when officials in Earth notice the crime it's too late to point the camera.

A workaround could be to point always satellites to everywhere, but if you are going this way you don't even need the delay and you can put your cameras closer to Earth. In fact, this is already done in a lot of cities with surveillance cameras mounted on a pole - which happens to be way cheaper than a satellite or a mirror in Jupiter and gives better quality images. Interestingly, it keeps being cheaper and working finer than a satellite even if you have to install thousands of them and save the huge amount of data they yield.

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