We see the universe as it looked thousands of light years ago how do we know it's still there as we see it?

Answer 1

Actually, we don't. However, because we are within the universe, we know that it exists at least around us in some way. But we have no way of knowing what the universe is actually like "out there" since the light takes so long to reach us.

With the help of mathematics and astrophysics, we have a good understanding of what is going on "out there," even though we don't always have direct confirmation from what's visible. We can now "see" parts of the universe as it existed billions of light years ago. We can be reasonably certain that at this time (whatever that may mean relativistically) the objects we see there have long since moved through the natural cycles of their existence.

Answer 2

Sometimes planets and galaxies are so far away that it takes a very long time to reach Earth through telescopes and their technology that it appears that that planet is the way it is billions of years ago.

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Answer #2:

When you get a letter in the mail from your friend in the next town, and he says

"Today I had lunch at Al's diner.", you know he had lunch there yesterday, because

it takes a day for mail to reach you from his town. Whenever you read his words on

paper, you know that he wrote them yesterday. Did he send you a letter today ?

Maybe he did, and maybe he didn't. You have no way to know until tomorrow.

When you look in the direction of a thing and you 'see' it, the light that's entering

your eye took some time to travel from the thing to your eye, so you're seeing the

thing as it was some time ago.

-- If the thing is 12 feet from you, on the other side of the kitchen, then you see

it as it was 0.0000000122 second ago, because that's how long it takes light to

cover 12 feet.

-- If the thing is 186,282 miles from you, then you see it as it was 1 second ago.

-- If it's 238,000 miles away from you ... like on the moon ... then you see it

as it was 1.28 seconds ago.

-- If you see a giant flare erupt from the surface of the sun, 93 million miles away,

then it erupted 8 minutes ago, because the light you see took 8 minutes to get here

from the sun.

-- If you're outside at night and looking at the North Star (Polaris), you'll see it

as it was around the time the Pilgrims landed in Massachusetts, because it takes

light somewhere around 400 years to travel from Polaris to Earth. Did Polaris explode

today ? Maybe it did and maybe it didn't. We have no way to know until 400 years from now.

The farther away a star is, the dimmer it appears. With just your eyes, you can't

see anything outside of our galaxy. But a telescope can see things that are dimmer

than what your eyes can see. So if you have a telescope, you can see things that

are farther away.

-- If you have a telescope that can detect stars that are 10 million light years away

from Earth, then you see those stars as they were 10 million years ago, because it has

taken the light from them 10 million years to travel from those stars to Earth.

-- And if you can get access, for a few minutes or an hour, to one of the world-class,

professional, monster telescopes that's so sensitive that it can detect the light from

stars 10 billion light years away from us, then you see them as they were 10 billion

years ago. Those stars are most likely not even there any more. But you have no

choice. That's how long it has taken for the light to travel from those stars to Earth.