I The Acceleration and the density of galaxies

AI Thread Summary
In the Lambda-CDM model, the density of galaxies decreases due to the expansion of the universe, but it does not completely vanish. The discussion highlights a misconception about galaxies disappearing; while they may become too dim to observe, their light continues to reach observers. The book "A Universe from Nothing" by Lawrence Krauss discusses the future visibility of galaxies, suggesting that the number of visible galaxies will diminish due to accelerated expansion. Participants seek references or papers that calculate these effects, emphasizing the importance of understanding the distinction between density and visibility. Overall, the conversation centers on the implications of cosmic expansion on galaxy visibility and density.
mbond
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In the Lambda-CDM model, the density of galaxies goes decreasing and should even vanish in the far future.

I would be grateful if someone could point me to a paper where this is calculated.
 
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It is a simple inference from the number of galaxies in a comoving volume staying constant while the size of the comoving volume increases. This just has to do with expansion itself, accelerated expansion is not required.
 
Also, as the universe expands, the density of galaxies decreases, but it never "vanishes".
 
I mean the number of visible galaxies goes vanishing because of the Acceleration. This is told in the book "A universe from nothing" by L.. Krauss, chapter "Our miserable future". Is there a paper or a reference where this is calculated?
 
mbond said:
I mean the number of visible galaxies goes vanishing because of the Acceleration. This is told in the book "A universe from nothing" by L.. Krauss, chapter "Our miserable future". Is there a paper or a reference where this is calculated?
This looks like a common misconception. Objects once seen never disappear. Apart from getting ever dimmer until eventually too hard to observe, that is. But the light is still there, reaching the observer.
Krauss has been guilty of wording this less-than-ideally in at least one other book - see e.g. this paper: https://arxiv.org/abs/astro-ph/0310808, example 13 in appendix B.
 
mbond said:
I mean the number of visible galaxies goes vanishing because of the Acceleration. This is told in the book "A universe from nothing" by L.. Krauss, chapter "Our miserable future". Is there a paper or a reference where this is calculated?
In addition to Bandersnatch's comment, nearby galaxies aren't moving apart. It isn't immediately obvious that they would ever necessarily spread out far enough to be part of the fading Bandersnatch mentions.
 
https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
The formal paper is here. The Rutgers University news has published a story about an image being closely examined at their New Brunswick campus. Here is an excerpt: Computer modeling of the gravitational lens by Keeton and Eid showed that the four visible foreground galaxies causing the gravitational bending couldn’t explain the details of the five-image pattern. Only with the addition of a large, invisible mass, in this case, a dark matter halo, could the model match the observations...
Hi, I’m pretty new to cosmology and I’m trying to get my head around the Big Bang and the potential infinite extent of the universe as a whole. There’s lots of misleading info out there but this forum and a few others have helped me and I just wanted to check I have the right idea. The Big Bang was the creation of space and time. At this instant t=0 space was infinite in size but the scale factor was zero. I’m picturing it (hopefully correctly) like an excel spreadsheet with infinite...
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