<p>This is an interesting thought,but red shift was a theory that could be answered by assuming near light velocities.The belief in,this unproven idea,invokes argument of"If it is coming toward us then we will already have seen it"</p>

CC BY-SA 4.0
2020-07-07T06:02:20.570Z
What "unproven idea"?
Jim421616
CC BY-SA 3.0
2015-01-27T04:34:30.267Z
2015-01-27T04:34:30.267Z
Colin Shorey
<p>Yes this is correct for the standard model. I believe the English language explanation would be that the angular size of a galaxy does not depend on its current distance to us, but its distance when the light we currently see from it was emitted (here using "distance" synonymous with "proper distance"). Though I also believe there are other complicating factors such as the spatial geometry of the Universe.</p>

<p>Look at the first diagram in Figure 1 in <a href="http://arxiv.org/abs/astro-ph/0310808" rel="noreferrer">this paper</a>, notice how the size of the past light cone in terms of proper distance firstly increases as we go back in time, before reaching a maximum and decreasing to zero at t = 0.</p>

CC BY-SA 3.0
2015-01-25T16:16:34.157Z
Aaargh! I've actually read that paper, but didn't realize this implication. The universe is so strange. I understand Chris Impey who in a public lecture series kind of mumbled to himself: *"- I should just make up mad stuff to say in these lectures. I would get away with it."*
LocalFluff
CC BY-SA 3.0
2015-01-25T16:44:16.567Z
Those diagrams are immensely useful, there's a lot of hidden information in them! Another way of looking at it perhaps is that, though the size of gravitationally bound objects like galaxies is not hugely affected by expansion, the light as it travels from the galaxy to us will be affected by expansion causing the angular size to expand. In a Universe with a particle horizon there will always come a point where the expansion of the angular size due to cosmological expansion overwhelms the decrease in angular size due to distance.
John Davis
CC BY-SA 3.0
2015-01-25T15:39:39.273Z
2015-01-25T16:15:31.923Z
2015-01-25T16:15:31.923Z
John Davis
<p>I stumbled upon <a href="http://ned.ipac.caltech.edu/level5/March02/Sahni/Sahni4_5.html" rel="noreferrer">this text</a> which illustrates and says:</p>

<blockquote>
  <p>We find that as the object is moved to higher redshifts its angular
  size first decreases (as naively expected) but soon begins to increase
  after passing through a minimum value.</p>
</blockquote>

<p>Is this correct for the mainstream standard model? What would an English language explanation be?</p>

<distances><expansion><redshift><angular-diameter>
Do objects look larger the further away they are, beyond z=1?
LocalFluff
# Do objects look larger the further away they are, beyond z=1?

(Asked by: username_0 on 2015-01-25)

I stumbled upon [this text](http://ned.ipac.caltech.edu/level5/March02/Sahni/Sahni4_5.html) which illustrates and says:

> We find that as the object is moved to higher redshifts its angular
> size first decreases (as naively expected) but soon begins to increase
> after passing through a minimum value.

Is this correct for the mainstream standard model? What would an English language explanation be?

**Tags:** distances, expansion, redshift, angular-diameter


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## 2 answers

### Answer by username_3 on 2015-01-25. Score: 7 | Accepted answer

Yes this is correct for the standard model. I believe the English language explanation would be that the angular size of a galaxy does not depend on its current distance to us, but its distance when the light we currently see from it was emitted (here using "distance" synonymous with "proper distance"). Though I also believe there are other complicating factors such as the spatial geometry of the Universe.

Look at the first diagram in Figure 1 in [this paper](http://arxiv.org/abs/astro-ph/0310808), notice how the size of the past light cone in terms of proper distance firstly increases as we go back in time, before reaching a maximum and decreasing to zero at t = 0.

> **Comments:**
> **username_0**: Aaargh! I've actually read that paper, but didn't realize this implication. The universe is so strange. I understand Chris Impey who in a public lecture series kind of mumbled to himself: *"- I should just make up mad stuff to say in these lectures. I would get away with it."*  
> **username_3**: Those diagrams are immensely useful, there's a lot of hidden information in them! Another way of looking at it perhaps is that, though the size of gravitationally bound objects like galaxies is not hugely affected by expansion, the light as it travels from the galaxy to us will be affected by expansion causing the angular size to expand. In a Universe with a particle horizon there will always come a point where the expansion of the angular size due to cosmological expansion overwhelms the decrease in angular size due to distance.  

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### Answer by username_1 on 2015-01-27. Score: -3

This is an interesting thought,but red shift was a theory that could be answered by assuming near light velocities.The belief in,this unproven idea,invokes argument of"If it is coming toward us then we will already have seen it"

> **Comments:**
> **username_2**: What "unproven idea"?  

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