[jdw64]

As observations become too numerous, it seems like it can be summarized as there now being too many possible candidate explanations. As data increases and becomes clearer, more and more things don't fit the existing theories.

What are the current theories explaining the early universe? What happened to the Big Bang? I only studied astronomy up to an undergraduate level, so I don't really know.

I imagine that various non-uniform gases were scattered around, and due to spatial distortions, those uniform gas regions clumped together, forming stars and other structures. Perhaps the expansion of space wasn't uniform either—it expanded unevenly, sometimes bulging, and when space expands or contracts, energy is generated, causing spacetime changes to shake the field, and that shaking might have created matter. Maybe the dynamic interaction between changing spacetime and fields revealed the energy stored in the field in the form of particles.

What do scientists think about this in modern cosmology? My knowledge is far too limited and I lack intuition, but reading science-related articles always excites me. Maybe it's because I still have some childlike curiosity left in me

[Tazerenix]

The evidence for the big bang is generally not that if you look far enough back in a telescope, the universe looks younger, which is somewhat the layperson's confusion.

Evidence for the big bang is about measuring redshift of galaxies throughout universal history, homgeneity and thermal equilibrium of the universe and CMBR, which could only be explained by it all having been in a compressed location where it could reach thermal equilibrium at some point in the distant past.

None of that is challenged by the Webb observations about very young supermassive black holes.

In fact, the existence of supermassive black holes themselves has basically always been an unsolved problem even before Webb. The only known possible explanation (stellar collapse -> accretion -> supermassive black hole) could be ruled out even before Webb on theoretical and experimental grounds, we just have stronger evidence against it now. (To wit: if supermassive black holes form from stellar black holes by growing, you would expect to see lots of intermediate mass black holes. We see almost none. Furthermore, the process of accretion is extremely energetic, so IMBHs would be the most visible objects in the night sky. The fact we see none is doubly damning)

The mainstream position now will be big bang + some kind of primordial black hole formation during the very early stages of the universe. Work of Hawking/Penrose shows that black holes can form under generic conditions in solutions to the EFE equations. We have a general understanding of how they could come about from certain dense matter layouts in a standard GR cosmological model.

[somenameforme]

I think you're leaving out a major issue there. Homogeneity was not in favor of the big bang. It's actually a major problem - the horizon problem. [1] Parts of the universe (think opposite sides) are not causally connected. Even traveling at the speed of light, there would not be enough time for a particle in one side to reach the other since the birth of the universe. Yet the temperature within these regions is homogeneous - at a thermal equilibrium. That doesn't make any sense.

This led to the development of cosmic inflation [2], which is what largely drove me from a doe eyed young astronomy enthusiast to a highly skeptical old fart. It solves the problem in an ad hoc fashion. Just have the universal expansion go into overdrive for a bit shortly after the big bang, then slow down, then start accelerating again - and then at the end we finally get something that looks like what we see - a homogeneous system in this case.

It made some highly accurate and improbable predictions which led to widespread adoption but then ran into numerous issues requiring further ad-hoc solutions. And this process has been repeated multiple times since its original formulation, to the point that there's a library of different inflation theories now a days, all getting ever more fine-tuned. If non-casually connected regions of space acted like they were non-casually connected then all would be fine, but the homogeneity that we do have is a big problem for the big bang.

[1] - https://en.wikipedia.org/wiki/Horizon_problem

[2] - https://en.wikipedia.org/wiki/Cosmic_inflation

[wwind123]

I kind of understand your frustration about the ad-hoc nature of the Inflation theory. When I was younger I believed the truth must be simple and beautiful - if a theory is complex and ugly then it's not the real truth. But as I get older, now I think the universe is what it is. Things may or may not have a simple or elegant explanation. Theories exist to explain things and make predictions. As long they serve both purposes well, then they are the working theories.

[somenameforme]

It's not just the ad hoc nature of the hypothesis itself, but also the subsequent ad hoc retrofits and fine tuning. With enough unconstrained fine tuning you can create a signal from noise, even when no signal exists. Take for instance the geocentric universe. Ptolemy's model was completely wrong in numerous ways beyond just assuming everything revolved around the Earth, but it was sufficient to make highly accurate predictions by excessively fine tuning the model to fit observations. And as new observations contradicted the model, all you needed to do was just add more epicycles to also make them fit.

Those retrofits (or the results they explained at least) were then were used as arguments in favor of the model, which is completely nonsensical and backwards. I think the most fundamental factor in good science is falsifiability. But if we just engage in and accept ad-hoc retrofits, then models become completely unfalsifiable. And at that point, what does science even mean?

[Tazerenix]

Yep, no doubt there are definitely issues with inflation. My main point is that the size of black holes in the early universe is largely orthogonal to the whole big bang/inflation debate. Even if the model changes, the lack of IMBH evidence means that any universal history model must have some kind of time asymmetry.

[jvs76]

I dont think about it because my days are occupied by very specific problems. Theory of Bounded Rationality and its implications apply.

[jdw64]

Right. When you don't have any breathing room, it's hard to think about anything else. That's why I take about two hours a day to just watch the news and clear my head. I'd probably forget all about it too if I were working 70-hour weeks on a contracted project, haha. Hang in there. Have a good day

[mr_toad]

> spatial distortions

Acoustic distortions. The universe was small and dense enough for sound to travel through ‘space’, which was filled with plasma. The theory is that inflation blew up these tiny distortions to the scale of the structure we see in the universe.

[ben_w]

With the caveat I'm summarising from what PBS Space Time and Dr Becky* say:

• Big Bang: we can only see back to surface of last scattering, i.e. the CMB, extrapolating backwards goes "???" at much the same point as it did a few decades back because we still have not unified quantum mechanics and general relativity

• CMB should only have isotope distribution of Big Bang nucleosynthesis, that hasn't changed in the last decades, dunno if that's what you meant by "various non-uniform gases were scattered around"?

• Variations in density of CMB do exist, key phrase is "Baryon acoustic oscillations", while they're very small magnitude they're also massive in distance scale, so they're how galactic clusters formed (that scale rather than stars directly): https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations

https://www.youtube.com/watch?v=PPpUxoeooZk

https://www.youtube.com/watch?v=LRUTnoveZs8

• Re: "Perhaps the expansion of space wasn't uniform either": I heard about specifically "Timescape Cosmology", but a quick search says that's part of a broader category of inhomogeneous cosmologies: https://en.wikipedia.org/wiki/Inhomogeneous_cosmology#Timesc...

https://www.youtube.com/watch?v=SXg6YVcdOcA

https://www.youtube.com/watch?v=JlNVZz5D6WE

• Re: "and when space expands or contracts, energy is generated": no, general relativity does not in general conserve energy, and it is related to the curvature of spacetime. Simple example is that the photons in the CMB have much less energy to us than they did to the atoms they were emitted from**: https://www.youtube.com/watch?v=04ERSb06dOg

* I assuming I'm correctly judging the level and attention to detail they're providing, given the detail they put in and references to specific research publications. My degree is Software Engineering.

** There's also a Veritasium video about this, but to me Veritasium feels like a BBC 2 evening popular science show, so I'm not as confident about recommending it.

[jdw64]

thanks!!

[tigerlily]

I took a good long look at the CMB picture, including the caption. It basically says the Universe was one big hot apparently uniform ball at one stage.

I don't know what conditions were like before that stage, but like Eric Idle says, nothing can come from nothing.

Dark energy is a horse shit name for a theory that was horse shit to begin with. The Universe is probably just inhomogeneous, like your intuition is saying.

[api]

“Dark” matter and energy are placeholder names. “Dark” means “we don’t know” which either means we can’t see or detect it or there is an alternate explanation for the effect.

It’s like a comment in your code like \\ TODO…

I don’t see why that’s that hard, or why we’d expect to instantly be able to figure everything out.

[nobodyandproud]

I think the problem is that it wasn’t just used merely as a placeholder, but to hard shutdown any discussions—often started by lay persons—about possibilities that didn’t involve brand new particle physics.

I still recall how neutrinos and black holes “couldn’t” be candidates.

To physicists, this means stellar neutrinos and blackholes (and galaxy centers). To lay persons, any category such as cold neutrinos or primordial black holes also qualify.

The sheer amount of vitriol and—I can’t think of a better term than this—“smugness” was off putting.

Before the internet, this was fine when locked away in their labs and classes; but I don’t think you understand the scale of damage neurodivergent scientists and its fans have done to the science community once they started to participate directly.

[mr_mitm]

Why do you say "probably"? We can measure and quantify the inhomogeneities very precisely, and they're tiny. This isn't a matter of opinion or intuition.

[tigerlily]

Oh, sorry I was referring to the cosmological principle [1]. The wiki page is actually quite a good summary of the whole fiasco.

[1] https://en.wikipedia.org/wiki/Cosmological_principle

[tigerlily]

I will say that the current and future telescope lineup is amazing and is bound to reveal: even more fascinating insights and mysteries!