[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.

[oneshtein]

No, this is not an answer, because it breaks number of laws of physics, such conservation of energy. It looks like an excuse that an answer. It's just heavy stretching of the evidence until it fits the BB model of evolution of Universe.

Static Universe model of evolution doesn't requires such stretching: CMB is just light of distant galaxies. End of story.

[mrguyorama]

>No, this is not an answer, because it breaks number of laws of physics, such conservation of energy.

THE WHOLE POINT of GR is that it explains things that "classical" physics did not, while also explaining everything that classical physics did. Nothing in GR "breaks the laws of physics" because GR largely IS the laws of physics now.

If you want to throw away GR by using a "Static Universe" theory, you have to re-derive a hundred different solutions to problems you bring back into physics by doing so. Einstein literally TRIED to put a static universe into GR because he thought it felt better, and turned out to be dead wrong!

In terms of "what drives the expansion", to us, within the universe, it's just what we see. It could very well be that it's a property of whatever "substrate" or "Stuff/emptyness" that a "Universe" exists in, if "exists" even makes sense in that context. It could be a completely unknowable to us thing. There are very likely phenomena and questions that we cannot ever answer, because we simply have no way of probing them.

All we know is that the way GR says to do the math works out really well for like 99.99% of things, and if you want to come up with a model that doesn't allow space to change "size", you have a shitload of math left to do at a minimum. If you want to understand how we got here, you have 400 years of physics history to read up on. None of this is about the "correctness" of GR either. It just makes the best predictions so far, and in science, all that matters is who makes the best predictions. Want to supersede the GR model? Just predict something correctly that GR cannot, while also predicting everything else correctly.

[oneshtein]

> If you want to throw away GR by using a "Static Universe" theory, you have to re-derive a hundred different solutions to problems you bring back into physics by doing so.

GR will be a special case in a new theory, which will explain laws of Universe better, which may join together GR and QM. If a formula does a good job, then it will be used anyway. We are not throwing away Newton physics just because GR does a better job in some cases.

> In terms of "what drives the expansion", to us, within the universe, it's just what we see.

Are you talking about a "light sail" effect? Yes, EM radiation creates pressure on dust particles, which pushes them away, but gravitation doesn't let it go. The same effect happens at size of galaxy. I'm not sure about superclusters, but it looks like we are falling into Great Attractor then into Shapley Attractor with all that dust.

So yes, this is possible, but EM radiation must be stronger than gravitation.

> It just makes the best predictions so far, and in science, all that matters is who makes the best predictions.

Predictions are very important, because they allow to prove or falsify a theory, but this is a game for theoretical physicists only. There is only one reality, which can be describer in many ways. Many different formulas can fit the same data. Many different techniques can be used to achieve the same result.

Moreover, every formula works in a range, then it doesn't work. Pi is an irrational number, which cannot be reproduced correctly in reality, thus every formula or path, which contains the irrational number, can be reproduced by physical reality with limited precision only. Multiply the error by many iterations, and new physics will emerge in the same place.

The only way to prove a theory, as I see it, is to make physical demonstrations at human scale, an analog, and then study it.

Hydrodynamic quantum analogs allows us to see pilot wave at work, so no mysteries in double slit experiment anymore: it just self-interference of the pilot wave. The same can be done for space effects.

It's easier to make computer model, to make predictions, but to make a correct model, we need to understand physics first. Egg and chicken. In case of a physical demonstration, nature performs all these calculations for free, automatically. Even when they are partially correct, they are still helpful.

[ben_w]

> this is not an answer, because it breaks number of laws of physics, such conservation of energy

GR doesn't conserve energy. What follows is a bit beyond my level so I may be misremembering, but IIRC Noether's theorem is that conservation laws are always identical to some symmetries, and the symmetry for energy (time?) just isn't true in GR.

(I don't think it's even true in SR because space and time are observer dependent, but at least in SR you can get a different conserved quantity because all observers agree on a space-time interval; but as I implied in a different comment where I mentioned brilliant, this is my hobby not my profession).

[DiogenesKynikos]

> CMB is just light of distant galaxies. End of story.

The CMB is a perfect blackbody. Galaxies are far from a blackbody. Your explanation fails if one knows even a tiny amount about astronomy.

Before you criticize Big Bang cosmology, you should learn the theory. That means studying General Relativity, learning to derive the Friedmann Equations, learning about the (utterly overwhelming) observational evidence for the theory, etc. Then you'll be in a position to ask intelligent questions about the theory.

I promise you that if you learn the theory, you'll understand that the questions you're asking either don't make sense or have obvious answers. For example, conservation of energy does not hold in General Relativity. You keep saying that expansion is an ad hoc assumption that breaks physical laws. However, if you solve the Einstein Field Equations, you'll see that the universe must be either expanding or contracting. This fact bothered Einstein so much that he tried to modify General Relativity to get rid of it, something he regretted when observational evidence firmly established that the universe was indeed expanding. This was all the way back in the 1920s, and the evidence is so overwhelming now, a full century later, that it's impossible to deny.

[oneshtein]

> The CMB is a perfect blackbody. Galaxies are far from a blackbody.

CMB is not emitted by a single galaxy or even group of galaxies. It's light of trillions of supeclusters, like our Visible Universe, averaged. I expect that almost any local unevenness should be polished out when averaged over such large area and distance. We are not seeing stream of photons from individual emitters, we see random photons from extremely huge range of emitters at extremely huge range from us.

If clump together all radiation from all our Visible Universe into single stream of photons, then we will see something very similar.

> For example, conservation of energy does not hold in General Relativity.

Then something is wrong.

[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).

[oneshtein]

> Sure you do, just by sitting there.

I 100% sure that I cannot bend or stretch imaginary coordinate system outside of my imagination. Can you point to real physical process which causes stretching or bending of the mathematical abstraction?

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

I cannot see objects smaller than a star or galaxy with naked eye. However, we can see light stretched to the microwave range.

[ben_w]

> Can you point to real physical process which causes stretching or bending of the mathematical abstraction?

"General relativity" as we keep telling you.

> I cannot see objects smaller than a star or galaxy with naked eye.

Only a factor of about a trillion in the size of those two things.

> However, we can see light stretched to the microwave range.

With your eyes? No. And certainly not through your window, whose own thermal emissions relative to the CMB makes your previous claim roughly as unphysical as saying you can look through the sun's photosphere to see Jupiter during an occultation.

[oneshtein]

General Relativity is a mathematical model. Model needs mapping between physical world and model.