[Jiggerj]

From: http://www.scienceda...80404201105.htm

"observations allow astronomers to look back in time over 10 billion years, producing images of galaxies in the Universe's infancy."

Been struggling with this idea for a while now. With the help of the Hubble's deep field images, if we can see a galaxy as it was, say, five billion years ago, and since we know that galaxies aren't stationary, then is it possible that we are also seeing that same galaxy in a different location as it was seven billion years ago, and/or three billion years ago? If not, WHY not?

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[zapatos]

If I am backing away from you and throw three balls to you from 3, 5, and 10 feet away, all thrown at the same velocity, by the time the ball from 10 feet away gets to you, the balls thrown from 3 and 5 feet are past you. They won't all get to you at the same time.

The light from the galaxy when it was 3 billion light years from you is long past you by the time the light from that same galaxy gets to you after it was sent from 10 billion light years away.

[Jiggerj]

zapatos, on 5 February 2012 - 03:20 AM, said:

If I am backing away from you and throw three balls to you from 3, 5, and 10 feet away, all thrown at the same velocity, by the time the ball from 10 feet away gets to you, the balls thrown from 3 and 5 feet are past you. They won't all get to you at the same time.

The light from the galaxy when it was 3 billion light years from you is long past you by the time the light from that same galaxy gets to you after it was sent from 10 billion light years away.

I thought of that, but we're talking billions of years for light to travel to earth. Plus, in just one field of images we see galaxies with distances of billions of years.

You use three balls as an example. What about the rear lights on a speeding car, where I can see the lights when the car is right in front of me, then a thousand feet away, then a mile away. Same car, same lights, different times.

[zapatos]

Jiggerj, on 5 February 2012 - 04:02 AM, said:

I thought of that, but we're talking billions of years for light to travel to earth. Plus, in just one field of images we see galaxies with distances of billions of years.

You use three balls as an example. What about the rear lights on a speeding car, where I can see the lights when the car is right in front of me, then a thousand feet away, then a mile away. Same car, same lights, different times.

Yes, different times for you. You don't see the lights from those three different distances at the same time. You see them at three different times.

Try to take one picture of the car that shows the light right in front of you, a thousand feet away, and a mile away, all in the same photograph.

This post has been edited by zapatos: 5 February 2012 - 04:27 AM

[Jiggerj]

zapatos, on 5 February 2012 - 04:25 AM, said:

Yes, different times for you. You don't see the lights from those three different distances at the same time. You see them at three different times.

Try to take one picture of the car that shows the light right in front of you, a thousand feet away, and a mile away, all in the same photograph.

Yeah, I can't explain the break in light as a galaxy moves through time, but the alternative is kind of scary. If we see the galaxies only as they were billions or millions of years ago, and cannot also see them as they were a million years ago, or a thousand years ago, or a hundred years ago, then those galaxies are so far away now that the stars we see are no longer there. We may be able to look up at the night sky and see how things were a long time ago, but in reality (right now) there is nothing out there to see but our own galaxy with nothing but utter darkness beyond it. <-- I don't like that thought.

[D H]

Jiggerj, on 5 February 2012 - 01:06 PM, said:

Yeah, I can't explain the break in light as a galaxy moves through time, but the alternative is kind of scary.

You've got it backwards. It's your version that is kind of scary.

Your version requires outfitting an entire galaxy with an Alcubierre-style drive, with the galaxy coming to a stop now and then to refuel. What we would see would be the galaxy during those refueling stops (which would presumably entail the consumption of an entire galactic cluster; Alcubierre drives require a preposterous amount of energy).

Fortunately we don't see anything of the sort. There are rare cases where astronomers do see multiple images of the same galaxy. It's called gravitational lensing. That gravitational lensing is very different from what you are proposing.

[John Cuthber]

"then is it possible that we are also seeing that same galaxy in a different location as it was seven billion years ago, and/or three billion years ago? If not, WHY not?"
No, because if you could see those 3 images you would need to explain why you can't see the images from 4bn, 5bn, 6bn, 6.5bn 6.002 bn and all the other possible times.

[Jiggerj]

John Cuthber, on 5 February 2012 - 06:27 PM, said:

"then is it possible that we are also seeing that same galaxy in a different location as it was seven billion years ago, and/or three billion years ago? If not, WHY not?"
No, because if you could see those 3 images you would need to explain why you can't see the images from 4bn, 5bn, 6bn, 6.5bn 6.002 bn and all the other possible times.

Okay, we are lookin up at just one galaxy as it was (say) three billions years ago. We know that the universe is expanding, and that the galaxies are moving in this expansion. So, the galaxy we are looking at is actually no longer there. Two Questions:

Where did it go?

And:

How did it automatically go from the point we are looking at now, to POOF! out of sight?

[D H]

Jiggerj, on 9 February 2012 - 10:33 PM, said:

Okay, we are lookin up at just one galaxy as it was (say) three billions years ago. We know that the universe is expanding, and that the galaxies are moving in this expansion. So, the galaxy we are looking at is actually no longer there. Two Questions:

Where did it go?

And:

How did it automatically go from the point we are looking at now, to POOF! out of sight?

Imagine that you're outside on clear, calm day and you hear the sound of a far-off passenger jet up in the sky. You look in the sky in the direction the sound appears to be coming from. There's no jet there! Did the plane disappear? Of course not. If you listen for a while the source of the sound appears to be moving. You can see the jet by looking well in front of the source of the sound. Now that you can see the jet, you can hear that there is no sound coming from where you see the jet. The sound is coming from well behind the jet. On a clear, calm day you can see and hear a jet that is 13 miles (21 kilometers) away. For such a distance, the sound you are hearing now is the sound that the jet emitted over a minute ago. You are hearing what was, not what is. You are hearing into the past.

You only hear the sound from one spot, not two or three or more. You are hearing the jet from where it was a minute ago. The sound from where it was 90 seconds ago: You heard that 30 seconds ago. That sound has already gone past. The sound from where it was 30 seconds ago, or where it is now: You haven't heard that yet. Those sound waves are still en route to you. You will hear those sounds when they reach you.

[Jiggerj]

D H, on 10 February 2012 - 10:59 AM, said:

Imagine that you're outside on clear, calm day and you hear the sound of a far-off passenger jet up in the sky. You look in the sky in the direction the sound appears to be coming from. There's no jet there! Did the plane disappear? Of course not. If you listen for a while the source of the sound appears to be moving. You can see the jet by looking well in front of the source of the sound. Now that you can see the jet, you can hear that there is no sound coming from where you see the jet. The sound is coming from well behind the jet. On a clear, calm day you can see and hear a jet that is 13 miles (21 kilometers) away. For such a distance, the sound you are hearing now is the sound that the jet emitted over a minute ago. You are hearing what was, not what is. You are hearing into the past.

You only hear the sound from one spot, not two or three or more. You are hearing the jet from where it was a minute ago. The sound from where it was 90 seconds ago: You heard that 30 seconds ago. That sound has already gone past. The sound from where it was 30 seconds ago, or where it is now: You haven't heard that yet. Those sound waves are still en route to you. You will hear those sounds when they reach you.

AHHH, I'm not explaining this well enough!
First off, the sound you're talking about is a matter of hearing something for seconds or minutes, because of it's close proximity. The galaxies are billions of light years away. I'll try this:

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[zapatos]

Jiggerj, on 10 February 2012 - 09:46 PM, said:

AHHH, I'm not explaining this well enough!
First off, the sound you're talking about is a matter of hearing something for seconds or minutes, because of it's close proximity. The galaxies are billions of light years away. I'll try this:

Ok, let's use your picture and take it to a smaller scale.

Imagine the blue dot is you. The grey dots represent your friend who is across the street, shining a flashlight at you, and walking across your field of vision. When the light from the flashlight gets to your eyes, he is no longer there. He is now further up the street (although a very small distance) because he is moving. You never see that flashlight in more than one place at once, and by the time the light gets to your eyes your friend and the flashlight are in a different position.

This is exactly the way it works on a galactic scale, only the the times and position changes are greater. It doesn't matter if the light travels for billions of years or billionths of seconds, the principle is the same.

And as far as being able to see galaxies that are 2 billion light years away, or five billion light years away in the same field of vision, that is exactly the same as seeing your friend who is 20 yards away, and the other friend who is back and to the left who is 50 yards away, in the same field of vision.

This post has been edited by zapatos: 10 February 2012 - 10:13 PM

[Jiggerj]

zapatos, on 10 February 2012 - 10:12 PM, said:

Ok, let's use your picture and take it to a smaller scale.

Imagine the blue dot is you. The grey dots represent your friend who is across the street, shining a flashlight at you, and walking across your field of vision. When the light from the flashlight gets to your eyes, he is no longer there. He is now further up the street (although a very small distance) because he is moving. You never see that flashlight in more than one place at once, and by the time the light gets to your eyes your friend and the flashlight are in a different position.

EXACTLY! But, tell me again why I can't see the flashlight when it's in a different postion? It's still shining. The distance is still close enough so that the light always remains in my field of vision.

"You never see that flashlight in more than one place at once" Right, but I do see it constantly moving across my field of vision. And if my friend moved fast enough, or if I took a picture using time-lapse photography, the light would streak.

DUH! I get it now. The hubble took a picture of the galaxies. If the hubble took ANOTHER picture we would see the galaxies in a different position.

This post has been edited by Jiggerj: 10 February 2012 - 10:38 PM

[zapatos]

Jiggerj, on 10 February 2012 - 10:31 PM, said:

EXACTLY! But, tell me again why I can't see the flashlight when it's in a different postion? It's still shining. The distance is still close enough so that the light always remains in my field of vision.

"You never see that flashlight in more than one place at once" Right, but I do see it constantly moving across my field of vision. And if my friend moved fast enough, or if I took a picture using time-lapse photography, the light would streak.

DUH! I get it now. The hubble took a picture of the galaxies. If the hubble took ANOTHER picture we would see the galaxies in a different position.

You got it!

This post has been edited by zapatos: 10 February 2012 - 11:04 PM

[JohnStu]

Definately not since in order for that to happen those galaxies must've travelled faster than speed of light which is impossible

[zapatos]

JohnStu, on 29 February 2012 - 02:59 AM, said:

Definately not since in order for that to happen those galaxies must've travelled faster than speed of light which is impossible

Can you explain please? I see nothing wrong with what we worked out and I believe he did indeed 'get it'. Or are you saying I was wrong?

[JohnStu]

zapatos, on 29 February 2012 - 03:34 AM, said:

Can you explain please? I see nothing wrong with what we worked out and I believe he did indeed 'get it'. Or are you saying I was wrong?

Okay sure. So I put my Hubble telescope here and I aim toward that corner. What I am going to see for this glimpse of time (of photo shoot) is the light I get from that direction at that instant of time. Let's say the photo I get has 3 layers of stars/galaxies. First layer is 30 million light years away. Second layer is 5 billion light years away. 3rd layer is 8 bllion light years away. If the same galaxy appear on 3 layers in the same photo shoot then it means it has travelled from 8 billion light years away to 5 billion light years away within 3 billion years. That's travelling 3 billion light years of distant over time of 3 billion years. That's 1 light year a year, which is the speed of light. Galaxies can't wrap and don't travel fast at all. In fact it's been proven they barely even move within couple billions of years.

[zapatos]

First of all, we resolved in this thread that one picture would not contain multiple pictures of the same galaxy at different locations.

JohnStu, on 29 February 2012 - 03:40 AM, said:

Okay sure. So I put my Hubble telescope here and I aim toward that corner. What I am going to see for this glimpse of time (of photo shoot) is the light I get from that direction at that instant of time. Let's say the photo I get has 3 layers of stars/galaxies. First layer is 30 million light years away. Second layer is 5 billion light years away. 3rd layer is 8 bllion light years away. If the same galaxy appear on 3 layers in the same photo shoot then it means it has travelled from 8 billion light years away to 5 billion light years away within 3 billion years. That's travelling 3 billion light years of distant over time of 3 billion years. That's 1 light year a year, which is the speed of light. Galaxies can't wrap and don't travel fast at all. In fact it's been proven they barely even move within couple billions of years.

Second, I don't know where you heard it's been proven that galaxies barely move, but...

Quote

While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, there is no such theoretical constraint when space itself is expanding. It is thus possible for two very distant objects to be expanding away from each other at a speed greater than the speed of light. Since the parts of the universe cannot be seen after their speed of expansion away from us exceeds the speed of light, the size of the entire universe could be greater than the size of the observable universe.

http://en.wikipedia....ansion_of_space

[JohnStu]

zapatos, on 29 February 2012 - 03:53 AM, said:

First of all, we resolved in this thread that one picture would not contain multiple pictures of the same galaxy at different locations.


Second, I don't know where you heard it's been proven that galaxies barely move, but...


http://en.wikipedia....ansion_of_space

Okay. I was saying "sure" to the request for an explination of what I say, not to say I disagree.

[D H]

zapatos, on 29 February 2012 - 03:53 AM, said:

Second, I don't know where you heard it's been proven that galaxies barely move, but...

http://en.wikipedia....ansion_of_space

Yep. Some of those far away galaxies are moving away from us at speeds greater than the speed of light.

Closer to home, the Milky Way and Andromeda are approaching one another at 100 to 140 km/second, about 3 to 5 times the Earth's orbital velocity about the Sun.

Quote

First of all, we resolved in this thread that one picture would not contain multiple pictures of the same galaxy at different locations.

I did not want to raise the issue of gravitational lensing until the OP "got it". Now that that has happened,



Those four blobs outside the central blob are the same object, the quasar Q2237+030, aka Einstein's cross. That central blob is the galaxy ZW 2237+030, aka Huchra's lens.




This image depicts how gravitational lensing works. If a massive object such as a galaxy or black hole is directly between us and some remote galaxy, there can be multiple straight line (null geodesic) paths light from that remote galaxy to us thanks to the way mass causes spacetime to curve.

[Airbrush]

Very nicely illustrated D H. I wonder why there are exactly 4 images of the distant quasar? Are there always 4?