So is the stuff we are seeing now in space happening now, or is it all millions of years old (see details)?

Question

I was reading this news story at Yahoo.com:

http://news.yahoo.com/s/space/20070912/sc_space/bizarreparasiticstarfound

And I was wondering if scientists have found a way to detect things that are happening now (or fairly recently) in space. Isn't everything we observe in space millions of years old (like an old movie)? How do we really know what's happening now?

If an alien civilization out there somewhere looked at us, wouldn't they see the Earth (if they could see it) as it was millions of years ago?

Answer 1

There is no such thing as time sync, we all exist ONLY in now.

The light we receive from alpha-Centuri, is about 5 years old, but some objects are millions and even billions of light years away. There is no known way to get around this. If aliens were millions of light years away from earth, and looking through a telescope, they would see the earth as it was millions of years ago.

There is a science fiction theory, that because space is curved, if you had a lens powerful enough, you could see into the past of future. The movie "PayCheck" used this theory.

Answer 2

Space is big.
Light travels at a relatively "slow" speed (300,000 km/s or 186,280 mph -- see wiki for precise numbers).

So, whenever we look at something which is far from us, we can only see the light that has made it here: in other words, we see it as it was when the light left.

We see the sun as it was 8m20s ago.

We see the nearest stars as they were over 4 years ago (years!).

We see the Andromeda galaxy (the furthest thing I can see with my eyes, without a telescope) as it was 2.4 million years ago. This galaxy is the closest major galaxy to our own. All other big galaxies are much, much further away.

That is how long it takes light to travel such distances.

According to Relativity, no information (magnetic waves, gravity, whatever else) can travel faster than light.

So we cannot see these things "as they are now".

Normally, when astronomical tables give distances to these objects, that is the distance that the light had to travel.

There is a way to calculate the distance at which the object should be today. This is called the "comoving distance". It is not very useful in astronomy, and of limited use in cosmology.

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For astronautics, calculations can be done with the exact "now" positions of planets in our solar system. The correction is only for a few hours at most, so it is easy to calculate (if you have the right equations, of course). When they send probes to other planets, they do use the correction.

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If someone at the closest star (OK, second closest, not the sun) looked at us "now", they would see us as we were a little more than 4 years ago. If we were to send a flash of light their way, the flash would take a bit more than 4 years to get there. If they were to answer right away with a return flash (or hold up a gigantic mirror), we'd see the flashback in over 8 years.

If we took a picture of them right now, our picture would show a four-year-old image. Our camera would capture the light that arrives now, meaning light that has left there 4 years ago.

Answer 3

To all intents and purposes, nothing travels faster than light. What is seen at large distances is what happened at some time in the past which is exactly proportional to the distance. So twice the distance, twice as long ago, We see the Sun as it was about 8 minutes ago, the Moon as it was a second or so ago.

"Tachyons" are a more of less hypothetical particle which are surmised to travel faster than light but there is no practical means of detecting them in enough numbers to make some kind of observational instrument as they probably do not interact much with ordinary matter.

Speed of light is about 300 million metres per second, so you see things 300 metres away (say a quarter of a mile) as they were about a millionth of a second ago.

It is not possible to have instant knowledge of goings on anywhere. While some quite recent experiments involving quantum entanglement seem to show instantaneous or near instantaneous transfer of "information" there is no practical application of this in observational astronomy, as far as I know.

This is just as impossible for any alien civilisation as it is for us unless they have had some technological breakthrough which we don't have. There is no reason to expect that any alien civilisation is vastly advanced on us, they might still be just discovering fire or masonry or inventing writing or the steam engine. We cannot know.

Answer 4

It depends how far away we're looking. If we're looking within our own solar system, then we're seeing things that aren't that far in the past (a few minutes perhaps). If we look out to nearby solar systems, we might see things that are 100 or 200 years in the past. An object would have to be pretty freakin' far to take millions of years for the light to reach Earth, but I suppose if we looked far enough, that would be the case. There is no way to see what's going on now for distant galaxies. According to Einstein, nothing can travel faster than the speed of light, so we are limited in the speed of our communication (or vision of) outer space.

Edit: The article you referenced does not mention how far away that star is, so I cannot say how far back into the past we are seeing it. However, Brandon K below me says that "everything in space is millions of light years away." That is completely untrue and absurd.

Answer 5

yes everything we see that is moving is really not at that exact point. since the galaxies are expanding, and light has a speed, any galaxies we observe are not actually in the place we are seeing them. in the time it takes light to travel to earth the galaxies are moving. so take the andromeda galaxy for example. its 2 million light years away, so the light from it takes 2 million years to get here. so we are really seeing it as it was 2 million years ago.

anything, even a car passing you is the same way. if you see a car passing you, its really a tiny, very small fraction of a millimeter ahead of where you actually see it, since light takes time to reflect off the car and to your eyes.

and um, the dude below me is wrong. if there we aliens, which if there are theyre too far away to see us. they would see it as it was however many lightyears away they are. so if they were in the andromeda galaxy they would see earth 2 million years ago. hes wrong...

Answer 6

Ok, light from stars is old. some light from stars you see is millions of years old because it takes light a long time to travel the distances from stars to earth(millions of light years).

There are no aliens, but if they looked at us right now(if they could see that far ) they would see us as we are now. Images don't travel. When you look at the moon, you don't see what it looked like a million years ago, so it's the same theory as aliens seeing us. Only light takes time to travel. Hope I win!!

Answer 7

Good question. evrerything in space is millions of light years away therfore it takes the light millions of years to travel to Earth. So some of the stars we see today may be dead (collapsed on there own gravity) because we are seeing the light from a million years ago. I guess you could consider it looking back at time.

Answer 8

It entirely depends on how far away it is. For things happening near Earth we can see them almost instantly, but most deep space objects are many light years away.

If a star 1,000 light years away blew up today, we would not know it for 1,000 years as the light would not reach us until then.

A light year is the distance light travels in one Earth year.