I Clarification about the size of the Universe

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The discussion centers on the size of the universe and the implications of observing distant galaxies, which are viewed as they were in the past due to the universe's expansion. It is suggested that if we could see galaxies as they are now, the universe would appear much larger than current models indicate. The complexities of galaxy dynamics are highlighted, particularly regarding collisions and their effects on galaxy counts. Estimates of the number of galaxies rely on counting methods and density calculations, acknowledging significant error margins. Overall, the conversation emphasizes the need for a solid mathematical understanding of cosmological models to avoid speculative conclusions.
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Clarification upon size of universe
when we look at distant galaxies we are looking back in time to an ever shrinking universe. Which I would visualise as conical. If then, we could see all the galaxies as they really are right now, then surely those cones would all disappear, and the universe would be vastly bigger? e.g. by the same degree as the cones reduce over time, the universe would be at least that much greater in size. The cones in every direction would be straight instead.
Secondly some galaxies crash into others, and maybe as a result some perhaps split off – if e.g. a galaxy was traveling in a different direction, some of the velocity would push or pull some stars away from others. Even if we don’t ever get more galaxies, we would get less from collisions.
So how can we know how big the universe is now, and how many galaxies it is composed of?
 
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What research have you done on this? the age/size of the universe is a common topic so should not be hard to find good info.
 
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amorphos_b said:
Which I would visualise as conical.
Why? Where are you getting this from?

amorphos_b said:
If then, we could see all the galaxies as they really are right now, then surely those cones would all disappear, and the universe would be vastly bigger? e.g. by the same degree as the cones reduce over time, the universe would be at least that much greater in size. The cones in every direction would be straight instead.

Secondly some galaxies crash into others, and maybe as a result some perhaps split off – if e.g. a galaxy was traveling in a different direction, some of the velocity would push or pull some stars away from others. Even if we don’t ever get more galaxies, we would get less from collisions.
This all looks like personal speculation, which is off limits here.
 
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As noted above, there's quite a lot of speculation in what you wrote. Answering the answerable questions that I see:

Distance in a curved spacetime is a complicated concept. You are correct that things that look like they are (e.g.) 10 billion light years away are now further away due to expansion. Our models predict that the observable universe currently has a radius of about 45 billion light years.

Secondly, galaxy dynamics is complicated. I don't think any naive model of galaxies colliding with each other will ever tell you anything plausible. To get an estimate of the number of galaxies we simply count them. If the number density changes with distance (which it probably will, since we're looking back in time) then we can derive an estimate of the current density and multiply by the volume of the observable universe. I doubt it's an exact science, which is why the hundred billion number you quoted in your last thread has only one significant figure.
 
You could also estimate galaxy numbers from the average density of the universe, which you can estimate from the recession rates. Divide that density by the average mass of a galaxy to get the number of galaxies per unit volume. Again, the error bars will be sizeable.
 
amorphos_b said:
if we imagine that there are only 5 stars in the universe, it is rather hard to imagine that there is nothing outside of universe.
It doesn't matter how you vary the content of the universe, you never need anything outside it to explain anything. We can make accurate predictions with only the universe and the stuff in it.

A universe consisting of only five stars would not have a curved space (at least not in the sense that the term is used in cosmology - it would not even have a uniquely identifiable notion of "space"). It would be difficult to see where one could start to end up with such a thing - but you can describe it without reference to anything outside the universe.

I'm afraid you are running into a fairly common problem, which is that this kind of thing is interesting and you want to speculate about it, but you haven't studied enough maths to properly understand the models and consequently your speculation instantly wanders into the weeds. It's like the difference between listening to music and playing an instrument. Any fool can hit a button on a media player, but you have to put in some hours if you want to be able to play even in the back room of a pub.
 
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...
Why was the Hubble constant assumed to be decreasing and slowing down (decelerating) the expansion rate of the Universe, while at the same time Dark Energy is presumably accelerating the expansion? And to thicken the plot. recent news from NASA indicates that the Hubble constant is now increasing. Can you clarify this enigma? Also., if the Hubble constant eventually decreases, why is there a lower limit to its value?
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