Wow!
You really do like obsessing over the WRONG THINGS, Ben.
All you want to do is focus on the Universe being "eternal".
That's not what the BB cosmology about, Ben. It as nothing to do with eternal vs finite, and it has nothing to do with nothing creating something.
These are not what the BB models are about.
As I have told you in my last reply, the Big Bang models only focused on the origin and evolution of the Observable Universe.
Everything that already in the universe at present, from large structures (eg molecular clouds of gases, galaxies, stars, planets, etc) to the particles that make up atoms themselves (nucleus with protons & neutrons, plus electrons), to even smaller elementary particles (from the Standard Model, eg quarks, leptons, gauge bosons & the recent discovered Higgs), and their interactions with fundamental forces. To all the fields and energy that are also tied to the Standard Model (particle physics). Then there are more exotic particles and energy such as Dark Matter that keep galaxies and Dark Energy that drive the expansion of the Universe, counteracting the attractive forces of gravity. The BB model also explained the earliest formations of earliest stars and galaxies.
So the Big Bang models are attempts to understand what these energies, forces, fields, particles & matters are and how they form from the earliest periods, starting with the Planck Epoch, when the universe as a singularity of plasma (the hot primordial plasma soup) that was infinitely hot and dense, and when all four fundamental forces (gravitation, EM, weak nuclear & strong nuclear forces) were unified into single force at this temperature.
The expansion of the universe resulted in, the cooling of the universe, the cooling that separations of the each force to separate from the unified form, as well as cool enough that elementary particles can become discrete particles from the primordial plasma. Eventually it was cool enough for quarks to form into hadron particles - the protons & neutrons, during the Hadron Epoch. This led to the formation of the earliest and lightest atoms - hydrogen, deuterium, helium & lithium - during the Big Bang Nucleosynthesis. But these atoms were still ionized - the universe still exist as plasma, and the plasma was still hot enough that electrons won’t be bound to the atoms.
Around 378,000 years after the Big Bang, in the Recombination Epoch, the universe was cool enough for electrons to bond with atoms of which only 3 types exist, hydrogen, helium & lithium, with the hydrogen being the most abundant element in the universe.
Molecular hydrogen are the building blocks of stars, especially as they began to coalesce together in the cloud of gases, becoming more massive, until therefore gravity eventually causing the stars’ dense cores were hot enough to start fusing hydrogen into heavier elements, such as helium, carbon, oxygen or nitrogen. This process is known as Stellar Nucleosynthesis.
When the stars run out of hydrogen to fuse, the core will collapse and do one of several things, start fusing helium while the outer layer shred away from the white core (hence white dwarf stars), explode in one of the types of supernova; supernovas are responsible for forming heavier elements, from helium to all the way to iron, through thermonuclear fusion, hence the Supernova Nucleosynthesis. These heavier elements from supernovas are what responsible for formations of asteroids, planetesimals, planets and dwarf planets.
That’s what the Big Bang theory is trying to explain, the formations of fields & particles & matters, which in turn form into planets, stars and galaxies. 9 billion years after the Big Bang, our own Solar System form, from the base materials of gas cloud and debris heavier elements from older generations of stars.
The Big Bang theory is focused only on the history of the universe, that eventually make up today, including life on Earth.
While the Cyclical Universe model and Multiverse model might explain the universe being eternal, and I am fascinated by these alternative models (just curious), however I don’t think we have no way of testing them to be true. Which means, the alternatives are more speculative than reality.