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Story Background
I have an alien that travels from ~100 light years away to Earth. He can make this trip in a matter of years though. He doesn't reveal how as he doesn't trust Earthlings since he has just come across new intelligent life.

Now, I have a guy that has created a telescope that is stationary on Earth able see in nearly perfect detail at vast distances into space. This alien now approaches my guy and gives him the coordinates to his home planet. The alien wants to show Earth his planet and people and technology they use using this "super" telescope that can look onto the surface of his planet as if we were looking look out a second story window at them.

Question
What I have read is that the sun is 93 million miles from Earth and that it takes ~8 minutes for light to travel from the Sun to Earth. So we are basically seeing the Sun from Earth 8 minutes in the past. (Which blows my mind if you ask me)

Now when the man and the alien finally look into the telescope to see his home planet, will the alien be unpleasantly surprised to see his home planet the way it was 100 years ago? (Will he see his newborn grandma?)
Or does the ability to focus (zoom in?) on something so close with the telescope fix that issue and they will see the planet as basically when he left.

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    $\begingroup$ Zooming in is not really the same thing as moving the lens closer to the light source. You can only zoom in and expect good resolution if the resolution was already there, just microscopic. The resolution at the primary lens is what you get to play with, and yes, it's from the past. $\endgroup$
    – coblr
    Jul 28, 2016 at 22:22
  • $\begingroup$ If you want a plausible answer, I would recommend removing the "I have a guy that has created a telescope that is stationary on Earth" our best pictures of the universe come from outside our atmosphere. While your alien bro might bring a terrestrial telescope capable of seeing his planet from Earth, we don't have that. $\endgroup$
    – Pork
    Jul 29, 2016 at 8:06
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    $\begingroup$ We always see things as they were, when they emitted the light. It is a bit like on a big concert, if you are 300m away from the stage, you will hear the sound a second later than it is played! - So if we mounted a giant perfect mirror in space say 5 lightyears away, then we could see ourselves from 10 years before, just as if we had thrown a ball and it came back several years later. $\endgroup$
    – Falco
    Jul 29, 2016 at 8:57
  • $\begingroup$ If 8 minutes blows your mind, try the 13.2 billion year old light that was captured in the HST's XDF. Using today's technology we have seen galaxies as they "existed just 450 million years after the universe's birth in the Big Bang." $\endgroup$
    – Mazura
    Jul 29, 2016 at 10:20

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Will he see the past?

Yes! Light emitted from stuff on the alien planet (in the form of photons) will take time to get to Earth. If you "beat it" to the Earth and look back, you will be able to receive the photons and see what was emitted.

Will the Alien Be Surprised?

Unlikely, but possible. This alien just travelled to the earth using technology far beyond what we mere humans can imagine. He will probably have a firm grasp of the speed of light and all it entails. On the other hand, he may have no idea how his own technology actually works, so it's possible he will be surprised by the time-lag.

Will he be able to actually zoom in on his planet?

No. Here is where things are weird. The maximum distance and detail you can get with a telescope is governed by the amount of light the telescope receives from the target. To view a planet 100 ly away (assuming similar luminosity to the Earth) with enough detail to look at people on the surface, you would need a MASSIVE telescope. This reddit page explains it rather well, but needless to say, such a telescope does not, and basically cannot exist.

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    $\begingroup$ It certainly can't exist by means of a traditional lens, or based on existing physics knowledge. But there's a good plausible fictional background for such a telescope in one book I read, wherein a light magnet "...reacted on light beams and pulled them in from a zone many miles in diameter and concentrated them, magnetically corrected for aberration, into a spot smaller than a dot on paper." $\endgroup$
    – Wildcard
    Jul 29, 2016 at 1:32
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    $\begingroup$ "He will definitely have a firm grasp of the speed of light and all it entails." He might just be a passenger and have no idea really how space-travel works... $\endgroup$
    – komodosp
    Jul 29, 2016 at 8:46
  • $\begingroup$ Exactly... just because you play Pokemon go doesn't mean you have a grasp of relativity to explain how GPS works and corrects for time-dilation ;-) $\endgroup$
    – Falco
    Jul 29, 2016 at 8:53
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    $\begingroup$ He may not be surprised, but I am sure he'll be amazed. And given the telescope uses a technology we don't understand, we can't say if it could zoom in to give crazy detail. If you need that to happen in your story, just have it happen. Don't explain, don't apologize. $\endgroup$
    – Tony Ennis
    Jul 29, 2016 at 11:39
  • $\begingroup$ @colmde That's fair. I assumed he had travelled to the Earth on his own, but after reading OP's question again I agree it's possible he may have been dropped off or something. Plus not everyone who drives a car themselves actually knows how the car works and everything about the physics involved. I'll make an edit. $\endgroup$
    – MozerShmozer
    Jul 29, 2016 at 17:08
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It should be noted you never are actually seeing an object, you always, technically, see light reflected off the planet. This is similar to how if you get a letter in the mail you aren't getting the letter as it's being written, you're getting a few-day instance of it in the past.

Magnifying an image with a telescope does not 'speed up' the light or any such, so the reflected light would still be just as old as if it wasn't magnified. A reflected source of light 100 light years away would, indeed, take 100 years to reach the point of observation (Earth) no matter what you do.

Assuming his telescope is that amazingly powerful to notice detail on the surface of the planet, the planet will look like it did 100 years ago, yes.

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Everything absorbs, and more importantly reflects light to a certain degree. When reflection occurs light rays are bounced back from that object in a certain pattern, and with certain colours filtered out.

So when you're looking through the telescope, and want to see the other planet what you're really looking at is the light reflected off of that planet, and light needs time to get to us. Hence "looking into the past".

Now just imagine what it must take for you to "see" the alien planet's surface:

  • Light travels down through their atmosphere
  • Light hits and object, and is reflected
  • That reflected light travels up through the atmosphere again (and is distorted by it)
  • That reflected light must now travel 100 light years in the correct direction (during this time the rays of light are distorted by gas clouds they may pass through, etc.)
  • The reflection is finally captured by your telescope :-)

Do you see how wildly unlikely that chain of events is? Furthermore, this doesn't change the fact that said reflection needed 100 years to get to you.

When you zoom in you're not somehow reaching out to the stars, and closing the distance. You're simply focusing the reflection in a different way, so that you may perceive more detail.

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If it takes light 100 years to travel from the alien planet to Earth then an observer on the earth will see the alien planet as it was 100 years ago. that doesn't change if you are looking at a continent or able to 'zoom in' and read a newspaper in the hands of an alien sat on their front porch.

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Time only exists where you are. The rung of time does not speed up or slow down because you move on the same earth spinning around.

Image you are standing on a merry go round and keep facing one direction, you do not move your feet do.

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It depends on how much "artistic license" you're taking with physics... you already have an alien traveling faster than light...

Maybe your telescope isn't a simple optical telescope and either somehow "sucks" the light from the alien planet (to get around MozerShmozer's huge telescope problem) faster than c, or uses technology similar to what the alien used to get here to send information from there to here faster than light.

Perhaps the telescope can detect tachyons (hypothetical super-light-speed particles) coming from the planet or something...

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  • $\begingroup$ Perhaps it works like an X-Ray machine, bouncing tachyons off the planet. You'll need to leave the machine running for a few [seconds - decades] but, when the tachyons get back to you, you're seeing what happened half the delay ago (instead of ~100 years ago) $\endgroup$
    – wizzwizz4
    Jul 29, 2016 at 14:46

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