Can some intelligent people explain this to me

[Deleted]

That only works if you somehow teleport a mirror to that distance.

[Valech]

Not sure if already explained.
1) Light travels at a certain speed. Despite the word "year", "Lightyear" does not describe a timeframe but a distance. 22 Lightyears is the distance it would take a beam of Light 22 years to reach.
2) Everything we see is the interpretation of light, that is reflected from any given surface and reaches our eye. That is the simple explaination why we can´t see anything in total darkness - no light = no reflections = nothing reaches our eye.
3) Logically, the light that was reflected away from what happened 22 years ago on the Apollo mission and strayed away into the vast nothingness of space is now 22 lightyears away from earth.

IF by some magical means we had a mirror at that exact spot in space and IF we had a telescope powerful enough to view that very mirror in 22 lightyears of distance we COULD see what happened on the Apollo mission.


What does that mean beyond that thought experiment? It means we look into a space, that most likely doesn´t exist anymore as we see it. With galaxies and stars being away for millions of lightyears, we look back into the past of these objects. Every Nova we witness happened millions of years ago - the very light of that event just reaching our eye at this time.


Also, there is a flaw with the initial thought experiment: We would be able to see what happened on Apollo in 22 years, since it would take the light from the mirror another 22 years to return to earth. .. Right?

[Aeula]

the speed of light travels per year as its measurement

For example if you were 65 million light years away from earth and you had a strong enough telescope to see earth from your planet, you would not see humans, you would see dinosaurs. This is because it takes 65 million years for light to travel from earth to your planet.

So technically yes. You can see back in time with a telescope. But not in a time travel sense, but more in the looking at a painting from a different era sense. In fact what we see in the night sky now is not their actual locations, as light takes time to travel. If a star is 60 million light years away, the location in the sky to us is what it was 60 million years ago and not where it is today.

Sounds like a good way to 'time travel' without worrying about changing the past. We could see what actually happened during historic events if we had enough telescopes placed all around the universe/Galaxy.

[Deleted]

Deleting my post because I think I am wrong

[Fencers]

Not sure if 22 lightyears would do the trick. Though to answer your question OP; when we look through a telescope at distant objects, we are seeing the light either emanating from or reflected off those things- stars, planets, moons, et cetera.

However, the distances are so vast that it takes "time" (time and space relative but that's another matter), for that light to reach our eyeballs. That time is the distance of an object from your eyeball/aperture.

Light travels in the vacuum of space at 299,792,458 meters per second.

Neptune is 4,345,228,800,000 meters (or 2.7 billion miles) away from Earth.

If I were to point a powerful telescope at Neptune and you happened to be this planet (impossible but work with me here) and waved at me- that image of you waving would have to travel the distance of 4,345,228,800,000 meters to reach my eyes or film. It took Voyager 2 twelve years to even get close to Neptune. That's how far Neptune is from us- taking almost 4 hours for light to go from Neptune to Earth.

By the time that image of you waving at me hits my eyes, you could be long gone. Like a satellite delay or simple webcam delay here on Earth. Or better yet- server ping. It takes time to ping a server and the higher your latency the longer it takes to react in real time. People in Australia connecting to a server in Norway are going to have a generally much higher ping than those in Norway itself because of distance. Data sent at light speed still has to travel- even though light is very fast, the distances of space are just that INCREDIBLE.

Now imagine that other celestial bodies are FURTHER than Neptune. Further than micro-planets such as Pluto. If Neptune is just 2.7 billion miles from Earth and it rogughly takes about 4 hours for light to cross that distance, revealing images from 4 hours ago on Neptune to those on Earth, 22 light years away from Earth (1.293e+14 miles!!) and looking at Earth would reveal an Earth-time that is not in line with that which you record as of 8:54AM CST April 16th, 2016.

[Ghâzh]

Pretty sure, yes. And the planets would still be orbiting where the sun was until the change in gravity reached them.

Which would also happen around the 8 minute mark. The occurrence would cause the curvature of spacetime around the sun to flatten again sending ripples moving at the speed of light towards the earth which would be experienced by the loss of sun's gravitation force. Or maybe it would be felt ever so slightly later due to the said ripple effect. Or maybe it would happen exactly at the same time since the light has to bend while moving trough the same ripples as well?

Thinking even further than that. There would be no light and no heat coming in to the atmosphere but the god blessed greenhouse effect would keep us warm for a while. How long do you reckon it would take for the life on earth to start dying?

[GennGreymane]

Sounds like a good way to 'time travel' without worrying about changing the past. We could see what actually happened during historic events if we had enough telescopes placed all around the universe/Galaxy.

Would would matter is the distance. But in theory this is a way we could "time travel"

[ranzino]

......

now you know how Ole Romer measured light speed. He and other astronomers were noticing the moons of Jupiter were sometimes late for the show or too early.

[Ghâzh]

Would would matter is the distance. But in theory this is a way we could "time travel"

No we couldn't. The problem is that we can't place those telescopes faster than light. So we can't never see beyond this starting point. If you'd send out telescopes to the space at the best we could watch things that we've already seen happen again after the point of launching said telescopes.

[GennGreymane]

No we couldn't. The problem is that we can't place those telescopes faster than light. So we can't never see beyond this starting point. If you'd send out telescopes to the space at the best we could watch things that we've already seen happen again after the point of launching said telescopes.

the telescopes themselves don't have to travel at light speed to view stuff

[Ghâzh]

the telescopes themselves don't have to travel at light speed to view stuff

No but at the best you'd see things that happened after you sent out the telescopes. What would be the point? Just place a video camera on a satellite and re-watch the tapes if you want to see things that you've already seen.

[Fencers]

How long do you reckon it would take for the life on earth to start dying?

Earth would freeze in about one week's time by most estimates- 0F. It would only drop below thereafter killing off whatever planet and animal life was left at the surface and most of the ocean's organisms. Total eco system collapse from the ocean floor up.

So about a month if lucky.

[ro9ue]

It's just traveling light and our vision based on light. The light from stars we're seeing every night is actually ancient light.

[GennGreymane]

No but at the best you'd see things that happened after you sent out the telescopes. What would be the point? Just place a video camera on a satellite and re-watch the tapes if you want to see things that you've already seen.

Ah I think I understand your point. My idea was in theory, Theoretically if we were to use a worm hole and place a telescope 65 million light years away, then its a non issue. I use the word theoretically for a reason. Technically if we has a telescope (NOW) 65 million light years away, we would not see humans, we would see dinosaurs.

[Ghâzh]

So about a month if lucky.

What about human? We could make heat figuratively speaking infinitely once the majority of humankind had died. I'd wager that a small group of people could live off easily a couple life times if they had the motivation.

Technically if we has a telescope (NOW) 65 million light years away, we would not see humans, we would see dinosaurs.

Even then we'd probably never actually get to see that since the information would take 65 million light years to reach us and we'd probably already be dead.

[ComputerNerd]

Light takes time to travel.
Therefore what we see of the universe is not what is happening currently, but as long ago as it took the light or other spectrum it is observed in to reach us.
If that is 1 light year, that is 1 year ago.
If that is 22 light years away, we will observe it as it was 22 years ago.

Plus/minus any other influences such as gravitational warping of space etc.

Edit: My explanation I suppose is a bit redundant due to many others wading in with similar explanations.

[GennGreymane]

What about human? We could make heat figuratively speaking infinitely once the majority of humankind had died. I'd wager that a small group of people could live off easily a couple life times if they had the motivation.


Even then we'd probably never actually get to see that since the information would take 65 million light years to get to us and we'd probably already be dead.

Alright you are getting me on minor technicality. Lets pretend we put it their via worm hole and have some dude take data back manually via the same worm hole.

[Deleted]

Uhm, am I wrong in coming to the conclusion you wouldn't see the moon landing, you'd see the moon 22 years ago, since the reflection itself is not part of the captured stasis of time that the light travel creates?

[Ghâzh]

Alright you are getting me on minor technicality. Lets pretend we put it their via worm hole and have some dude take data back manually via the same worm hole.

Well, minor technicality that renders the whole idea useless. Then again you could argue that you only need to look up at the night sky to time travel.

[Gheld]

To take a macro shot of something 22 light years away you would need a completely ridiculous lens setup that probably could never exist.