If we observe a galaxy at 40 billion light years distance can we say that light given off by that same galaxy today will take 40 billion years to reach us? Assuming it hasnt "moved"? basically I am asking if distance has always been constant given that space itself has "expanded." More fundamentally I am asking if when the universe was "smaller" (ie. less expanded) then was the a light year of long ago the same as a light year today.
2007-12-05 07:52:42 · 5 answers · asked by silversides27 2 in Science & Mathematics ➔ Astronomy & Space
I've wondered about this same kind of thing, myself. I've also wondered whether time itself was on the same scale as we perceive it today. I thought this might account for some of the observed red shift, since the Universe would have been more dense then. As for the alteration of dimensions and speeds from then until now, there could be a couple answers to that. Mine hits on one possibility. It may be also as you suggested: all distances between objects were smaller. Some have told me, though, that if everything was reduced in some way, including time, then it would all be relative to that age of Universe and indistinguishable from what exists now.
But back to your question: first of all, there would not be a galaxy 40 billion LY away, since the age of the Universe is estimated at 13 billion years. But you're right in thinking that where we see it now is not where it was way back when the light left it.
2007-12-05 08:05:14 · answer #1 · answered by Brant 7 · 0⤊ 0⤋
"...If we observe a galaxy at 40 billion light years distance can we say that light given off by that same galaxy today will take 40 billion years to reach us?..."
Yes, you're correct. 40-billion light years is a bit too far though; the most distant objects we can see today are about 14-billion light years distant.
"...Assuming it hasnt "moved"? basically I am asking if distance has always been constant given that space itself has "expanded." More fundamentally I am asking if when the universe was "smaller" (ie. less expanded) then was the a light year of long ago the same as a light year today..."
You have to understand that everything...stars, planets, galaxies, etc.,..are all embedded in space. Space is expanding on the largest scales of the universe therefore the distance between things in it is generally increasing. For example, say that your galaxy 40-billion light years away is more like 4-billion light years distant. Through a telescope you make an image of it this year (..2007..) You do some computations and find that the galaxy is receding from us at 9^10 km/sec. So in the 4-billion years it took the light you just now saw in your telescope to get here, that same galaxy has actually receded about 1^15 light years more. It's not located where you thought it was!
2007-12-05 16:10:49 · answer #2 · answered by Chug-a-Lug 7 · 0⤊ 0⤋
A light year is a constant measure of length, and has nothing to do with how big or fast the universe is expanding.
In the 40 million years the light takes to reach us the galaxy certainly has moved and may not even exist anymore. But the light is traveling form a specific point and time, it is not affected by anything that happens to the object emitting the light after it has been emitted.
However since the earth is traveling away for the the galaxy the distance to reach the earth over the 40 billion years will be longer but not because the source moved, it's because the target (earth) moved.
2007-12-05 15:56:37 · answer #3 · answered by Brian K² 6 · 0⤊ 0⤋
No. Given the expansion of the universe, the light will take somewhat longer to reach us. (assuming that in 40 billion years the universal expansion hasn't stopped and reversed!)
For KBW3.... Incorrect. There can be a galaxy 40 billion Ly distant REGARDless of the age of the Universe. You have assumed that the BB happened at a single point and everything expanded out from this. The BB happened everywhere at once so galaxies actually formed 40billion years away from us - and further.
2007-12-05 15:57:02 · answer #4 · answered by The Lazy Astronomer 6 · 0⤊ 0⤋
If two objects are 1 LY apart and stationary, the light will take 1 year to go from A to B.
If the two objects are rapidly traveling in opposite directions, the light will STILL only take one year to go from A to B, however it will show a red shift corresponding to it's acceleration away from B.
This is one of the strange features of light waves
2007-12-05 17:27:05 · answer #5 · answered by jordan_0_0_7 2 · 0⤊ 0⤋