Galaxies are seperating faster than light?

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Jun 2016
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Anything Goes

One of the problems when we get to some of these more extreme scenarios
is that there is so little hard experimental evidence
providing a framework and boundaries for the theories
that there is almost an infinity of possible ideas
with nothing much to indicate any way of defining a preference.

It can be fun to play at these boundaries,
but one has to be careful to recognise the limitations
of any of the ideas that might spring from ones imagination.

Imagination is the starting point of all science.
Science is the methodology we use to trim away the impossible, the obviously wrong, and the hopelessly improbable from the initial flood of interesting ideas.
We have to be careful, however, to not let personal biases influence the labelling of "hopelessly improbable".
The history of science is littered with examples of ideas initially labelled "hopelessly improbable", that turned out to be correct (e.g. Plate Tectonics).
 
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Aug 2019
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Screw the speed thing. Just look at the distance. You are claiming empty space expands.
 
Oct 2017
530
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Glasgow
Screw the speed thing. Just look at the distance. You are claiming empty space expands.
I'm not claiming empty space expands.

The cosmological models that include expanding space assume all space expands (empty or otherwise).

If you want to create a cosmological model that only has empty space expanding, then you'll need to invent one. To my knowledge, no such model currently exists.
 
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Oct 2017
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Glasgow
umm, galaxies are not expanding.
That certainly seems to be the case. However, galaxies are composed of matter which gravitates towards each other and the acceleration this imposes competes with the expansion of space, so it's not clear if the reason galaxies don't change their shape is due to gravity or due to something else. you're going to have to resolve this quantitatively or find someone else who has.

Why not estimate the impact of cosmological expansion on galaxies by performing some back-of-the-envelope physics calculations? Try calculating the comoving velocity of two stars, one situated at the furthest part of the galaxy and one at the nearest part, in our line of sight, and see by how much they differ. You can grab a standard cosmological model from the literature and apply it to the two objects. You'd probably also need to take into account the existing galactic dynamics, which can get quite thorny for a spiral galaxy, so perhaps assume no galactic dynamics and then assume a dwarf spheroidal one, which has much tamer dynamics than a spiral one.
 
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Aug 2019
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oh, you want to challenge my statement of spacetime not being outside of galaxies. Okay, well, I some more arguments for that.

We already know that once you are far enough away, the universe acts like a magnifying glass and objects start to increase in size in the sky.
https://scitechdaily.com/fundamental-law-of-classical-physics-reversed-in-new-research-on-giant-radio-galaxies/

https://blogs.scientificamerican.com/degrees-of-freedom/the-cosmic-magnifying-lens/

And the other is redshift from only distance. I'm claiming voids of no spacetime is causing that type of redshift.
 
Oct 2017
530
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oh, you want to challenge my statement of spacetime not being outside of galaxies.
I'm not "challenging" anything. I'm just stating that matter within galaxies is subject to gravity and this must be taken into account to determine the effect of expanding space on galaxies. The fact that galaxies don't seem to change their shape with the expanding universe is not considered a flaw of cosmological models that include expansion (in the literature, afaik). There are flaws, but that isn't one of them.

The articles you linked are interesting, but I don't see how those are relevant to anything we've talked about. They're talking about observations of distant galaxies and their properties and/or discuss the magnification effect caused by the expansion of the universe (which is a prediction of the big bang model anyway). Observations of distant objects constrain the cosmological models, so they're really interesting.

The first article you linked mentions a reference Michael D Smith and Justin Donohoe, 2019, "The morphological classification of distant radio galaxies explored with three-dimensional simulations", Monthly Notices of the Royal Astronomical Society, Volume 490, Issue 1, November 2019, Pages 1363–1382, https://doi.org/10.1093/mnras/stz2525. I'm going to read this whenever I have the time. A copy is available on the arxiv. Presumably the article refers to this because the angular size of high-redshift galaxies is a constraint on cosmological models. A quick look at the conclusions doesn't specify anything alluding to what you've been talking about "We conclude that very distant radio galaxies could appear systematically more limb-darkened due to merger-related re-direction and precession as well as due to the sensitivity limitation. However, resolution itself may not directly influence the classification since the angular diameter size remains constant beyond the red-shift of 1.5".

However, I will admit that I'm not equipped with the knowledge needed to go into detail about the models the authors are really trying to constrain with their observations. Like I said in a previous post, I don't know general relativity or the details regarding modern models of big bang cosmology (such as a lambda-CDM model), so I can't really help out with anything other than the basics. You might want to discuss this topic further with an actual cosmologist if you want better quality or more up-to-date information.
 
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Oct 2017
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Glasgow
you don't get gravity without spacetime
Well, the whole universe is space-time, so yes, of course.

By the way, are you aware that galaxies also have a non-zero gravitational influence on each other? It's important to study things like galaxy clusters, filaments and voids.
 
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topsquark

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Apr 2008
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On the dance floor, baby!
What? Nobody questions how weird this is?
You are kidding, right? You're hardly the first to notice the weirdness.... People have been making assaults on Cosmological theory since before Omar Khayyam.

It turns out that quantum fluctuations in empty space is proof spacetime is around. You aren't going to find it in empty space outside of galaxy.
I'm not being sarcastic, just making the comment: Have you been outside the galaxy to take the measurements of the quantum foam? It's all guesswork! But the guesswork is spear-headed by a basic principle without which we really can't do Cosmology: We have to assume that the laws of Physics over here are the same as the laws of Physics over there. Otherwise we can't do anything. If you disagree with that you aren't the first. But there's nothing we can do about it. GR, which handles the structure of whole universe, is the best we've got right now so we're going to use it until we find out it's wrong. So for now and probably a very very long time space-time exists everywhere. (And besides, if it's not in space-time it's unobservable anyway. You wouldn't be able to go from here to there.)

these gaps between them. Or maybe the opposite ..the bubbles are rising. Should we start screwing around with an extra dimension to explain it?
M-theory already has 11 dimensions to deal with. You really want to try for more?

Dark Matter is in a location of nothingness ..without spacetime, without the ability to have a physical state ..to be real.
Why are you talking about dark matter? I thought this conversation was about expansion? That's dark energy territory, not dark matter.

-Dan
 
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