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Is there a limit to the details we can see?

Posted on 2014-03-04
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I have always wondered what the limits of science are as far as the details we can see with "telescopes." If we could circle the moon with an array of radio telescopes, could we see in detail a planet 10 light years away? How about if we could orbit such telescopes around Jupiter, could we read some alien's newspaper? And if not, would there be anything such a "telescope" COULD tell us? Thanks!
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Question by:Eddie_Aeffect
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by:sdstuber
ID: 39904296
radio telescopes don't "see", they "listen"

So, no, you couldn't read an interstellar newspaper; but with a big enough array you have a better chance of picking up some of their radio broadcasts.

To actually visualize something we are limited by the properties of light.

With a gigantic array of ultra high precision optic telescopes you might be able to pick up some faint reflected light from a far away planet but you'd still have to deal with all of the dust and other objects between here and there that would obscure or completely occlude the visibility.  Even if you did get clear line of sight all the way to a planet, the amount of light reflected straight at us is pretty small.  Plus even if you can capture all of it, that light has to pass through the atmosphere of that remote planet, thereby creating even more distortion/occlusion from clouds, refraction, dust and other particulates.

Many of the fantastic photos that you'll see come out of NASA or other facilities are visual representations of non-visible wavelengths of the EM spectrum.  Those other wavelengths have the ability to penetrate some of the debris that visible light can't get through.  Or, even when they are blocked, the occlusion of those other wavelengths is still different than visible light, thus generating a new picture anyway.
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by:Eddie_Aeffect
ID: 39904351
Thanks for getting back to me so quickly. As you can obviously tell, I am not a scientist so I misunderstood "radio telescope" So if an optical telescope is the only way to "see" into the the distance, if you could make such a telescope with lenses the size of the moon, could you "see" any better or would the dust and such between us and what we were looking at mean it wouldn't matter if the lenses were 1000 feet across of 1000 miles?
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sdstuber earned 300 total points
ID: 39904390
A giant telescope like that would probably be able to see better, if for no other reason than because it is so big it could capture a lot more light than anything we currently have.
It would almost certainly be built with a moon-sized reflector rather than a moon-sized lens.

But, it would still be limited by interference between it and whatever it's trying to focus on.
I can give you the absolute best set of high powered binoculars to see across the room but if I stand in front of you, you still can't see beyond me.

Another thing to consider is the actual construction limits.  Using the binocular example again.  Let's say you have a tiny scratch on the lens.  That's an area of captured light that is no longer useful to you.  On a galactic scale, capturing the tiny amount of light from a distant planet means the effects of any imperfections will be magnified.  A tiny flaw or bit of dirt might be enough to completely occlude an entire planet that is many light years away.
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by:sdstuber
ID: 39904432
Also, as long as we're talking about theoretical engineering  of moon-sized telescopes, if we also assume we have a perfectly clean and defect free mirror (not possible, but let's assume it anyway)   the last thing to consider is diffraction limitations.

The wavelengths of light entering our telescope have a limitation based on their individual diffraction limits.  The math of that can be pretty complex.

If you want to research that more, some terms to look up would be diffraction limits, angular resolution, Airy disk and Rayleigh criterion.
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by:Eddie_Aeffect
ID: 39904589
Comprehensive answer given quickly! I guess there is always the difference between what is theoretically possible and what is possible with current engineering methods. My suspicion is that when the quantum computer is discovered, we will be able to "fill" in the gaps as gases and dust rotate through the universe and perhaps one day we will be able to watch alien spaceships light years away!
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by:sdstuber
ID: 39904701
There are already telescope arrays that will stitch together multiple images from different points to single image.

However, each of those sub-images is still subject to its own imperfections as well as diffraction limits.   Unless the remote ships are Deathstars (i.e. a least a small moon sized) it's exceedingly unlikely they would be visible.

As a simple test: put 2 sticks in the ground next to each other then walk away from them.  At some point you will no longer be able to distinguish them as distinct objects but only a "stick blob".  In space you won't have air as interference but you will have dust and, more importantly, you will have DISTANCE, lots and lots of distance.  So much distance that your remote objects have a relative size smaller than a wavelength of light.  That's part of the reason we've only recently been able to even detect planets.  They are so small relative to their respective suns and so far away that they are simply not distinguishable.

As we build better and better devices though we approach the limits of what light can convey and then it doesn't matter what the technology is.  It's the same reason we don't use light-based microscopes to view the tiniest objects.  Light simply isn't capable of carrying the image to us.
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by:Eddie_Aeffect
ID: 39904718
Ah, so the day of the gamma ray telescope is coming :)
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by:sdstuber
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by:Eddie_Aeffect
ID: 39904773
Amazing. But by their very nature, one the size of the moon probably wouldn't let us read an alien's newspaper. But we might be able to detect non-natural propulsion engines.
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