Is my thinking of the concept of lightyears correct?

So light years is how long it takes for light to reach a place (which considering how fast light is even one light year is a huge amount by our standards)

So does this mean it’s technically possible to look at the past? If we somehow made it somewhere 2000 light years away and built a powerful enough telescope (both likely not possible in for the foreseeable future I know) we could see earth as it was 2000 years in the past?

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• Sky
Lv 7
6 months ago

A light year is a measure of distance, not time. It's how far light travels in the time frame of 1 year, roughly 6 trillion miles. "Light years" is how far away other objects outside our solar system are, not long long it takes light to reach them. How long it takes for light to travel from here to there or there to here is just measured in years.

As far as looking into the past, that is correct. We see the sun as it was 8 minutes ago. We see the other planets as they were many minutes or hours ago. We see the next nearest star as it was 4 years ago. We see the Andromeda galaxy as it looked about 2.5 million years ago. And we see the most distant galaxies as they looked 12 or 13 billion years ago, because that's how long it's taken for their light to reach us. So yes, looking out into space really is looking into a window of the past, with the amount of time looking back into the past depending on how far away the particular object is. In your hypothetical scenario, yes, a huge telescope 2000 light years away would be just now seeing Earth as it was 2000 years ago, although at that distance the best it might be able to see the Earth would be a tiny fuzzy dot being swamped out by the light of the sun.

Another thing to consider: let's say we start receiving radio signals from an alien civilization on the other side of the galaxy, let's say 50,000 light years away. That civilization might not even exist any more due to any number of catastrophic reasons, and we'd never be able to let them know we got the message. When you go outside on a clear night and start thinking about these distances as you look up at the stars, it is just mind blowing to think about.

• Vincent6 months agoReport

Ya even if there is life out there it’s probably so far away we might as well be alone.

• 6 months ago

You can look into the past but the nature of entropy means that it gets ever harder to produce detailed images of planets the further you get from them. As far as Earth is concerned, that would be around twice the distance of Pluto. However, it is possible to produce images of planets a few light years away, and occasionally thousands due to gravitational lensing, although those are freak events.

• 6 months ago

Not really, no, because as light moves away from it's source, it spreads out, which means not long after the source emits the light, it is so diffuse that there is not sufficient light that could reach a camera to provide any useful information.

Plus, even the Hubble Space Telescope cannot resolve small objects on the Moon, and it's only 1.3 light seconds away.

So, even if you had a faster than light space ship, once you got 2,000 light years out from Earth, you'd be lucky to be able to capture two photons from that time that came from Earth.

• Nyx
Lv 7
6 months ago

Put it this way - are currently able to look at stuff in detail light years away?

• 6 months ago

Yes it is.

Your ideas as to how light behaves, and its characteristics, are correct.

• 6 months ago

Well, you got the gist here, a lightyear is a measure of distance, and light we see from such distant objects left that object relative to the number of lightyears away.

Consider a light nanosecond like the time it takes to see your reflection in a mirror.(about 1 meter)

Sure, if you could instantly teleport 2000 lightyears, you could see light from earth 2000 years ago.

That would take some dandy scope, but yea.

• Anonymous
6 months ago

Yes, your understanding is correct. In reality, you can not go 2000+ light years from Earth and watch the Crucifixion of Jesus.

• 6 months ago

Yes, that's essentially it. And - it works both ways. Next time you see the sun, you're seeing it *as it was* about 8 minutes, 20 seconds ago... Any of the stars you see in the sky tonight are how they looked more than 4 years - and up to a couple of hundred years - ago. You're always looking into the past... even when you look in a mirror - it takes light a finite amount of time to bounce off you, get to the mirror, then back to your eye. That's how you *looked* an instant ago.

• 6 months ago

Theoretically, one would think so. It's even been a premise in a number of SF stories. More, Bob Shaw wrote a series of stories using what was called "slowglass", which worked by slowing the passage of light through a pane of this glass -- it would show images coming through from years and decades in the past.

But the technical aspects of what you propose are not really viable. Think of light as information, something organised that we can interpret. Over long distances, this would be at the very least attenuated, if not otherwise modified by interference. So, we'd "see" what was broadcast, but it would not always make sense to us. Some of the light would be bent (by gravity) and hence not in the path we want. There are other possibilities, like objects getting between us (in the new position) and the original we want to look at.

• Anonymous
6 months ago

yes yes yes and YES. its so cool.