h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Is it possible to magnify light from far away things to get a good view of what is happening there?

I'm thinking light years when I use the term far away. And I mean activity on the surface of a planet etc. when I say things.

In other words could someone a long way from the earth have a complete histroy of what's happened on the surface of our planet?

Theoretically, I don't see why not.

In practise, no. Your telescope would just have to bee too powerful.

Imagine you're talking to Galileo in the 16th Century but have the foresight to envisage the Hubble telescope.

Are you saying that a mega telescope is never going to be possible. These other, imaginary, people on the distant planet were at OUR level of development 1,000,000 years ago.

yes, that's why he said theoretically yes, but practically no.

practically given what we know - not possible.

Theoretically - given what we don't know - sure, why not?

We'd better smile for the camera then, eh?

As this is for questions: scientific and I've posed a basic one how about this...

I believe that a hologram of a lens will cause light to alter in the way that a real lens does. Is that correct?

How about having holograms of lenses as big as planets and aligned in the same way as a telescope's would be. There would me no major materials needed to float in the air. The power would be provided by a nearby sun and the machinery would be based on planets or moons.

Keep smiling they can see us!

On the first question, there are always trade-offs even if we ignore the engineering practicalities. You can only amplify what is already there, so it comes down to the amount of light you can collect. If you want a spatial resolution of 1m^2 for example, and assuming a perfect detector, you'd need to collect at least one photon reflected from each square metre of the object you want to observe.

I'm not in a position to do the maths at the moment (it being Monday and all that), but I reckon that very few photons reflected from a particular square metre of the earth's surface would reach a telescope, say, 10 light years away. There two ways to improve the situation:

1. Collect the light over an extended period of time, thereby increasing the number of photons reaching the detector. Many long-distance astronomical pictures are taken this way. But here you are merely increasing spatial resolution at the expense of temporal resolution - you can't see things move in real time if your telescope needs 20 years to collect enough light for one picture. Plus the earth is spinning.

2. Increase the effective size of the detector. The bigger the collecting area, the more light it can collect. I can't think of any fundamental limit to size, but if a telescope is big enough to observe people on a planet's surface, it is almost certainly big enough for those poeple to see, and I don't remember any reports of giant space telescopes. Unless they're all disguised as something else.

3. Some other kind of focusing mechanism, such as gravitational lensing, artificially increasing the effective size of the detector.

Perhaps dark matter is just loads of huge telescopes and lenses all pointing at us?

Exactly! Keep smiling
My cheeks are beginning to ache!

Traveller in Time looking through a leticular lens
"Holographic lenses are a reality already. Just the size required is not an option.

What about the 'natural gravity' lenses that exist already ? My guess is a black hole in line with the planet you want to observe could be used as a gigantic lens. Some drawbacks again, the mass should be extreme to create a useful magnification, as well as the gravity would fluctuate and distort the lens too much for the detail required. "

There is one problem that noone seems to have spotted. If we are presuming earth being obseved from some distant point the obsever could only ever see one side of the planet therefore only half the 'action' can ever be observed. Also the light being picked up would, for most of our history to date, be sunlight and so half the planet would be in shadow. You could use moonlight but (as explained above) the resolution would be adversly affected by the lower photon density, similarly for artificial lighting of modern times.

The only way I can complete imagine of getting a picture good enough to distiguise individual people moveing about would be enclose the planet in a dyson sphere lined with cameras and lights.

Dyson Sphere? Wazzat? Anything to do with vaccuum cleaners?

http://en.wikipedia.org/wiki/Dyson_sphere

Cool, not heard of that before.

>> Is it possible to magnify light from far away things to get a good view of what is happening there? <<

The problem is to collect enough light from the object; at about the same time. Currently, we can't even resolve the light from all parts of a star (except the Sun) in order to show it as a disc. Look at any book of astronomical photos. The bigger white blobs just indicate brighter stars. Essentially, they appear as 'point sources'.

When we come to things the size of nebulae, we can see the large scale 'detail' of galaxies etc.

In this case, time is used instead of space (a large collector). This means that the stars will have rotated to some extent during the time of the exposure needed to obtain the image. Even if the image were to be 'magnified', it would consequently show little detail. This is all reckoning without the problems of interstellar gas and dust, 'gravitational distortion' and the distortion due to the Earth's atmosphere in the case of terrestrial instruments.

Thanks for that. My question is really about using imaginative solutions to this problem that are not constrained by current technology. I understand why we can't see what is going on in other parts of the universe now, but if someone is a million years in advance of our technology what would they be able to see?

You aren't checking the front page often enough Orcus - and fancy searching wiki before looking here!

A11284959

I searched google, not wiki

>but if someone is a million years in advance of our technology what would they be able to see<

You have to be a little careful with saying such things (although don't let me stop your fun! ) - it doesn't matter how much our technology advances if you let go of a ball it will still fall to the ground.

As someone once said "you cannae change the laws of physics cap'n"

Traveller in Time with a yoyo
"Not to break them, it is how to bend them "

>but if someone is a million years in advance of our technology what would they be able to see<

Pretty much what they want - just hop on a starbus then a solarsystem taxi. A weekly ticket will be affordable.

Traveller in Time on top
"Including endless delays at the terminals . . . "