The latter, and also "cold" nucleosynthesis. The redshift/distance relationship can also be explained in a much more visualizable and intuitive way as an inherent redshift of ancient matter's light emissions/absorptions, and that the latter have gradually been getting bluer since then. Also, Fritz Zwicky sought a reasonable explanation back in 1933, with his "tired light" hypothesis. But such ideas haven't been seriously pursued because they lacked a theoretical foundation.Drakkith said:As opposed to a 'cold' big bang? Or no big bang at all?
No, they were abandoned because their predictions don't match observation.hkyriazi said:But such ideas haven't been seriously pursued because they lacked a theoretical foundation.
That's right, as explained in detail here:Vanadium 50 said:No, they were abandoned because their predictions don't match observation.
...is a lot more than what you're describing in your OP. I suggest taking some time to work through a good modern textbook on cosmology, such as Liddle:hkyriazi said:the theoretical basis for a hot Big Bang
The theoretical basis for the hot Big Bang model is rooted in the framework of general relativity and the cosmological principle. General relativity, formulated by Albert Einstein, describes how matter and energy influence the curvature of spacetime. The cosmological principle asserts that the universe is homogeneous and isotropic on large scales, meaning it looks the same in every direction and from every location. These principles lead to the Friedmann equations, which describe how the universe expands over time. The hot Big Bang model posits that the universe was once in an extremely hot and dense state and has been expanding and cooling ever since.
Several key pieces of evidence support the hot Big Bang theory. First, the observation of the cosmic microwave background (CMB) radiation, which is the afterglow of the Big Bang, provides a snapshot of the early universe. Second, the abundance of light elements such as hydrogen, helium, and lithium observed in the universe matches predictions from Big Bang nucleosynthesis. Third, the redshift of galaxies, observed by Edwin Hubble, shows that the universe is expanding, which is consistent with the Big Bang model. Lastly, large-scale structure formation, such as the distribution of galaxies and galaxy clusters, aligns with predictions from the hot Big Bang theory.
The hot Big Bang model explains the formation of elements through a process called Big Bang nucleosynthesis. In the first few minutes after the Big Bang, the universe was hot and dense enough for nuclear reactions to occur. During this period, protons and neutrons collided to form the nuclei of the lightest elements, primarily hydrogen, helium, and small amounts of lithium and beryllium. As the universe expanded and cooled, these nuclear reactions ceased, and the relative abundances of these light elements were "frozen in." The observed proportions of these elements in the universe today match the predictions made by the Big Bang nucleosynthesis theory.
The cosmic microwave background (CMB) plays a crucial role in the hot Big Bang theory as it provides direct evidence of the universe's hot and dense early state. The CMB is the thermal radiation left over from the time when the universe became transparent to radiation, approximately 380,000 years after the Big Bang. Before this time, the universe was a hot, opaque plasma. As it expanded and cooled, electrons and protons combined to form neutral hydrogen atoms, allowing photons to travel freely. The CMB is remarkably uniform but contains slight fluctuations that correspond to the initial density variations, which eventually led to the formation of galaxies and large-scale structures. The detailed study of