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Astronomy - Galaxy 30 Billion Light Years Away
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I cannot get my head round an article today saying they've found a galaxy that's 30 billion light years away. If the universe started 13.5 billion years ago and, say that's when light set out on its way to us - how can it be further away than the time it's taken for its image to get here? Somebody explained that this is because the universe is expanding, so how can we see something that's further away than the time taken for its light to reach us? I can't seem to understand this at all. Please help!!
Answers
As has been pointed out, light-years are measurements of distance, not time. We might now be seeing light from a galaxy that has taken, say, 10 billion years to get here. If the Universe was static, that would indeed tell us that the distance to that Galaxy is 10 billion light-years. However the Universe is expanding, so we need to calculate how much further...
21:44 Thu 24th Oct 2013
Maybe it wasn't so far away say 10 billion years ago and we are now seeing it now where it was 30 billion years ago: and maybe they can estimate how much further away it is based on the speed at which it's moving away from us.
But there's probably an explanation based on time slowing down at certain speeds, or something equally difficult for me to get my head around
But there's probably an explanation based on time slowing down at certain speeds, or something equally difficult for me to get my head around
I also found this claim counter-intuitive.
Were are not near an 'edge' of the universe but imagine if we were, then we'd be 13.5 billion light years from where the bang occurred and this galaxy could be 13.5 billion light years in the other direction.
So that's 27 billion light years, for starters.
Adjust by as much as you like to account for the fact that we or not are not near the edge of the univers. The rest of the discrepancy is down to the stretching of space in the 12.8 billion years since this galaxy is said to have formed (they said 700 million years after big bang).
Red shift was 7.52 or some such but I don't know how to convert that into meaningful information like "1 light year, back then, is worth 3 light years now".
Were are not near an 'edge' of the universe but imagine if we were, then we'd be 13.5 billion light years from where the bang occurred and this galaxy could be 13.5 billion light years in the other direction.
So that's 27 billion light years, for starters.
Adjust by as much as you like to account for the fact that we or not are not near the edge of the univers. The rest of the discrepancy is down to the stretching of space in the 12.8 billion years since this galaxy is said to have formed (they said 700 million years after big bang).
Red shift was 7.52 or some such but I don't know how to convert that into meaningful information like "1 light year, back then, is worth 3 light years now".
As has been pointed out, light-years are measurements of distance, not time. We might now be seeing light from a galaxy that has taken, say, 10 billion years to get here. If the Universe was static, that would indeed tell us that the distance to that Galaxy is 10 billion light-years. However the Universe is expanding, so we need to calculate how much further apart our Sun and that Galaxy have moved during that 10 billion year wait, which could easily give a figure of the order suggested in your post.
That, of course, assumes that the galaxy still exists (either in whole or in part). Many of the stars we see in the sky haven't existed for billions of years because all stars only have a finite life and we can only see them as they were when light left them.
That, of course, assumes that the galaxy still exists (either in whole or in part). Many of the stars we see in the sky haven't existed for billions of years because all stars only have a finite life and we can only see them as they were when light left them.
The rate at which space is expanding is not bounded by the speed of light -- this is because no information is being carried, space just grows indefinitely. The only things which are bounded by the speed of light are "real" things, in the sense of things that have energy or information.
To see an example of something "travelling" faster than the speed of light, stand on a beach on a windy day and measure the speed at which the wavefront meets the shore. You really need a diagram to see the point I mean, but imagine if the wave is travelling directly parallel to the shore, so that the wave front is at right angles -- then the speed at which that point moves along the shore will be the speed of the wave. If, on the other hand, the wave is hitting the beach head-on, effectively the speed at which that point moves across the beach is almost infinity! So things can travel faster than light all the time.
In this sense, then, a galaxy 30 billion light years away is perfectly possible, because the Universe needn't be (13.5billion years times the speed of light) across. As to why we can still see it, that's because distance takes on a slightly different meaning when there's Gravity. For more 'd need to go into a bit too much detail. But, basically, the 30 billion light years away measurement isn't distance as you think of it, but a different measurement altogether.
To see an example of something "travelling" faster than the speed of light, stand on a beach on a windy day and measure the speed at which the wavefront meets the shore. You really need a diagram to see the point I mean, but imagine if the wave is travelling directly parallel to the shore, so that the wave front is at right angles -- then the speed at which that point moves along the shore will be the speed of the wave. If, on the other hand, the wave is hitting the beach head-on, effectively the speed at which that point moves across the beach is almost infinity! So things can travel faster than light all the time.
In this sense, then, a galaxy 30 billion light years away is perfectly possible, because the Universe needn't be (13.5billion years times the speed of light) across. As to why we can still see it, that's because distance takes on a slightly different meaning when there's Gravity. For more 'd need to go into a bit too much detail. But, basically, the 30 billion light years away measurement isn't distance as you think of it, but a different measurement altogether.
Society:
I can say with 100% confidence that UFOs exist.
A 'UFO' is, by definition, an unidentified flying object. There have been hundreds of thousands of reports of things which have been seen flying but could not be identified. Thus, irrespective of whether they were actually weather balloons, flying lanterns, secret military devices or just boring little green men in space ships, they were all UFOs!
I can say with 100% confidence that UFOs exist.
A 'UFO' is, by definition, an unidentified flying object. There have been hundreds of thousands of reports of things which have been seen flying but could not be identified. Thus, irrespective of whether they were actually weather balloons, flying lanterns, secret military devices or just boring little green men in space ships, they were all UFOs!
We don't see anything where or how it is now but rather where and how it was when the light that is now reaching us began it journey. For objects that were moving away from us (or if you prefer, us away from it) at the time the light we now see was originally emitted, that light was red shifted and has become increasingly red shifted as it journeyed through the intermediate space which was and is expanding at an accelerating rate. Taking this expansion and the resulting redshift into consideration we can calculate the current distance of an object whose light we are now seeing although we will never be able to see it as (or where) it is now since it has long since begun receding from us at an accelerated rate far surpassing the speed of light.
...continued - We can directly observe much of the state of the early universe by the light that is now reaching us. What we can never see directly, (although there's much we can deduce based upon our current observations), is how the early universe has since unfolded in the billions of years that have elapsed between now and when what we are currently observing originally took place.
Thanks Buenchico and mibn2ceuws. I think I understand now. The light set off on its way to us 12.8 billion years ago and has just/is just arriving. But because we also know the universe expands in all directions (like spots on the skin of a balloon) and we can calculate the expansion rate, we can work out how far away it is today (i.e. assuming it still exists - which we won't know for another 12.8..er, no..another 30 billion years!). So, in other words, that galaxy is now 30 billion x 186,000x60x60x24x365 miles away.
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