[ben_w]

> 300M years is very short period of time, unless everything cooled very very uniformly, which is not the case

~300M years is the time between the Big Bang singularity and the CMB, but not really relevant. The entire universe was everywhere as hot as the surface of a star at the time of the CMB, so any evidence of galaxies forming before that is surprising.

The surprisingly high uniformity of the temperature of the CMB — isotropic to roughly one part in 100,000 — is one of the reasons the Big Bang model replaced one of the older competing hypotheses (continuous creation IIRC).

So it is in fact the case that everything cooled very very uniformly and I'm not sure why you think otherwise?

I'm also not clear what you're saying with

> so we should see a transition somewhere

Given the CMB is itself the transition that we see.

> Sometimes, somewhere there must be a galaxy past CMB.

I think here you're mixing up space and time.

It's reasonable (please permit my use of conventional language rather than 4-vectors) to assume that a galaxy exists on the other side in space of the CMB as we see it now, but that happens at a point in time after the recombination epoch began and space became transparent, and light from that event hasn't reached us yet; when it does, the apparent distance of the CMB will be large enough for the galaxy to appear on this side.

Are you familiar with light cones and the convention of one space axis and one time axis? It might help you visualise it if you draw what's going on.

[oneshtein]

https://en.wikipedia.org/wiki/GLASS-z12

GLASS-z12 is 33.2Bly away from us. It should be behind some of the CMB produced by BB, isn't?

> Given the CMB is itself the transition that we see.

In BB model, CMB emitted by hot plasma. Where it is, that plasma?

In steady universe model, CMB is light with z=1000, emitted by distant galaxies, in range of 4Tly. It explains high uniformity of temperature. It's like the temperature of a water stream from underground: it's uniform across a climate area because underground temperature averages seasonal temperature shifting.

[ben_w]

> It should be behind some of the CMB produced by BB, isn't?

A reasonable mistake, but no.

If you look at the info box on your link, you'll see there are two different distances:

≈33.2 billion ly (10.2 billion pc) (present proper distance)

≈13.6 billion ly (4.2 billion pc) (light-travel distance)

The latter is what we're talking about when we say the CMB is about 13-point-whatever billion years old.

The difference with the other number is that the universe got bigger in the meantime, and that's where we recon it is now.

> Where it is, that plasma

The plasma itself?

Everywhere. The whole universe, including here.

The bit we see?

An echo made of light emitted at the last moment in time that it stopped being plasma — the light from the plasma that was here is now as far away from us as the plasma that caused the light we can see.

[oneshtein]

These numbers means that nothing can travel at FTL speed except this galaxy. It travelled 20Bly in 13By at the speed of 1.5 c. Extraordinary claim requires extraordinary evidence. Where is the source of energy for this FTL galaxy? Why this galaxy is not ripped apart into ball of gluon plasma?

Echo requires something to reflect of. Moreover, echo will be an order(s) of magnitude weaker and will have a stamp of the reflective surface on it properties.

[ben_w]

> These numbers means that nothing can travel at FTL speed except this galaxy

Nothing including this galaxy can beat light locally.

Look up the balloon (or raisin bread) analogy.

> echo will be an order(s) of magnitude weaker and will have a stamp of the reflective surface on it properties.

It does. That's in the CMB.

[oneshtein]

> Look up the balloon (or raisin bread) analogy.

In bread analogy, sugar is the source of energy and CO2. In balloon analogy, new air is added to balloon (with lot of turbulence). What is added to our Universe, which causes the inflation? Where we can see it?

In case of Steady Universe model, light just changes it's properties over time, for example, because gravitational waves are stretching photons and photon beams. Gravitational waves are produced by massive objects, which are orbiting each other.

[ben_w]

> What is added to our Universe, which causes the inflation?

It's a free parameter in the equations, just like the initial value for the energy in the space or the baryon number.

Or the number of space-like and time-like dimensions.

Or their inherent topology.

Not that it matters, as the point of what I suggested is that it's an analogy for all objects within the space observing the same relationship, and the implications thereof.

> Where we can see it?

In the relationship between distance and redshift. More distant objects move away faster, the further away the faster they move on average, and that relationship best matches "accelerated expansion" than any other model.

Or, more locally, it's (perhaps by coincidence) about the right level to explain the moon's orbit slowly getting bigger.

> In case of Steady Universe model, light just changes it's properties over time, for example, because gravitational waves are stretching photons and photon beams. Gravitational waves are produced by massive objects, which are orbiting each other.

Great!

Unfortunately for you, those gravitational waves can't act anything like the ones predicted by GR which we've actually observed, because those are far too weak (or spacetime too 'stiff', IIRC).

GR has known weaknesses, to be sure, but they're all annoying beyond any observations we've been able to make, and people really are looking as it's considered both important and prestigious to find a way to tie it and quantum physics together properly.

In the meanwhile, the same equations for GR describe the (just about) detectable gravitational influence your body has, and the various demonstrations of gravity influencing the flow of time and path of nearby light.

IIRC, the best atomic clocks are just about at the level where an extra 100kg sitting next to them can change the last digit relative to another otherwise identical clock, but I'm not sure how long you have to sit there.

They're definitely good enough for it to matter which floor of a building you put them on.

[DiogenesKynikos]

GLASS-z12 is way in front of the CMB.

You have to be careful with what you mean by "distance" at cosmic scales. Space is expanding with time, and there are several different definitions of "distance" that give very different results at cosmic scales.

The best "distance" measure here is simply redshift. GLASS-z12 is at redshift z=12, as the name suggests. The CMB is at redshift z=1100, so it's father away.

In fact, for very straightforward physical reasons, no light can reach us from beyond the CMB. The universe was opaque before the time of the CMB, because it was ionized and dense. Before the CMB time, photons could not travel very far at all before they hit an electron and were scattered.

[oneshtein]

Nobody pointed to a source of energy for this "expansion" of "space". Usually, coordinate system doesn't expand with time. An extraordinary claim requires extraordinary evidence.

Yes, CMB emitters are much further away, at a distance of about 4Tly, while BB claimed to be just 14By ago. Your claim, that CMB is produced by BB, requires a lot of stretching.

[DiogenesKynikos]

There's no point in arguing about this here. There's a very well defined, mathematical theory called General Relativity, which explains gravitational phenomena from Mercury's precession all the way to the expansion of the Universe.

If you take the time to learn General Relativity, and to learn how to apply it to cosmology, you will see that there are rigorous mathematical answers to the various questions you're raising.

I want to point out that this isn't esoteric stuff that only a few people understand. General Relativity and cosmology are part of a standard undergraduate physics curriculum. It only takes a few years of study, starting from Physics 101, to get to the point where you can derive the answers to all your questions from scratch.

[ben_w]

Doesn't even need that much — their questions so far are at my level, and I keep messing up the much simpler special relatively questions on brilliant.org

[oneshtein]

How GR explains claimed FTL speed of GLASS-z12? (20Bly travelled in 13By, 1.5c).

I'm listening with both ears.

[ben_w]

You've already got the answer: space expanded.

Spacetime being dynamic is kinda the point of GR.

"How" this specific expansion happens is an open question — not because nobody has any idea, but because we can't distinguish between three of them and a forth leads directly to the unsolved challenge of combining GR with quantum mechanics.

[ben_w]

> Nobody pointed to a source of energy for this "expansion" of "space".

Several have been made, the suggestions have issues.

> Usually, coordinate system doesn't expand with time.

Define "usually". Do you have experience of other universes?

> An extraordinary claim requires extraordinary evidence.

Indeed, but this comment box is too small to do the evidence justice.

Edit: that's unhelpful in retrospect, so I suggest the Youtube channel "PBS Space Time". The videos build on each other, so start at the beginning and work through the back catalogue.

> Yes, CMB emitters are much further away, at a distance of about 4Tly,

I have no idea where you got this belief from.

[oneshtein]

> Define "usually". Do you have experience of other universes?

I have experience with coordinate systems. I can bend or expand space-time on my computer all day long, to simulate reality, but I cannot do that in the real world at all.

> Indeed, but this comment box is too small to do the evidence justice.

Looking for the paper or a blog post! However, I suspect that you will just stretch evidence until it will match your model.

> I have no idea where you got this belief from.

Just by looking in the window, I see that some object are close, other are far away, then even further away, and so on, up to 4Tly. Nothing extraordinary. No Big Bangs, no FTL speeds, no hidden sources of energy of epic size, just ordinary physics.

[ben_w]

> I cannot do that in the real world at all

Sure you do, just by sitting there.

Reminds me a bit of my dad; he did radar simulation for military IFF and one of his work anecdotes was about increasing the number of decimal(!) digits of pi the software used.

He stopped boasting about that when I pointed out the extra digits were less relevant than the curvature of spacetime caused by Earth itself.

> Just by looking in the window, I see that some object are close, other are far away, then even further away, and so on, up to 4Tly

I had dreams like that once. Woke up to find I was suffering from testicular torsion.

If you seriously believe you can see 4e12 light years through your window, that's probably hallucinogens of some kind (not necessarily intentional).

[ben_w]

> ~300M years is the time between the Big Bang singularity and the CMB, but not really relevant.

Nobody else has pointed out my mistake here, the time between them is ~380ky not ~300My. My bad.