Answering for the world, even now, we still have many mysteries in cosmology although in the last few decades it transformed from a field with lousy experimental data to a field which the data can actively help to shift out theories.
Say even if the Buddha started the ball rolling for physics, by introducing Newtonian laws, it might take 300-400+ years to be able to reach our current scientific understanding of the cosmos. Not to mention the need for the world’s economy to undergo industrialization to be make it possible to design cheap experimental apparatus, rockets, sending telescopes up to orbit and computers to do data analysis.
It’s basically not worth thinking about the cosmos at the time of the Buddha. They would die first before they could replicate our knowledge of cosmology.
And even now, we still having a challenge to find out if the cyclic universe model is true, the ultimate fate of this universe, is there multiverses out there? Which type of multiverse?
Buddhism has a different epistemology than the materialistic view. Those things which seem important from the latter view, are not valued in Buddhism. The goal of Buddhism is the removal of suffering, and its views and methods are aimed at that.
"The time of the Gautama Buddha was a lively intellectual culture with many differing philosophical theories. KN Jayatilleke, in his “Early Buddhist Theory of Knowledge”, uses the Pali Nikayas to glean the possible epistemological views of the historical Buddha and those of his contemporaries. According to his analysis of the Saṅgārava-sutta (AN 3.60), during the Buddha’s time, Indian views were divided into three major camps with regards to knowledge:
The Traditionalists (anussavika) who regarded knowledge as being derived from scriptural sources (the Brahmins who upheld the Vedas).
The Rationalists (takki vimamsi) who only used reasoning or takka (the skeptics and materialists).
The “Experientialists” who held that besides reasoning, a kind of supra-normal yogic insight was able to bring about unique forms of knowledge (the Jains, the middle and late Upanishadic sages).
The Buddha rejected the first view in several texts such as the Kalama sutta, arguing that a claim to scriptural authority (sadda) was not a source of knowledge, as was claimed by the later Hindu Mimamsa school. The Buddha also seems to have criticized those who used reason (takka). According to Jayatilleke, in the Pali Nikayas, this term refers “primarily to denote the reasoning that was employed to construct and defend metaphysical theories and perhaps meant the reasoning of sophists and dialecticians only in a secondary sense”. The Buddha rejected metaphysical speculations, and put aside certain questions which he named the unanswerables (avyakatas), including questions about the soul and if the universe is eternal or not."—Wikipedia
The Buddhist view is that the planes of existence are destinations according to mental state, and are therefore created by the mind of the individual:
“Yet it is just within this fathom-long body, with its perception & intellect, that I declare that there is the cosmos, the origination of the cosmos, the cessation of the cosmos, and the path of practice leading to the cessation of the cosmos.”—AN 4.45
Those who want to reduce suffering have to gradually discard their former views and adjust to that way of thinking.
There are several convictions that the Buddha has left undeclared; he has set them aside and refused to comment on them. For example: the cosmos is eternal, or not eternal, or finite, or infinite; the soul and the body are the same thing, or they are different things; after death, a Realized One exists, or doesn’t exist, or both exists and doesn’t exist, or neither exists nor doesn’t exist.
“The scope of the Buddhas” appears to mean whether or not buddhas continue to exist after their physical death.
“Speculation about the world” seems to refer to, (MN63) “If you know that the world is finite, or infinite;”
IMO they are unthinkable not because they are mysterious and not logical but because there is no way one can define mystery and logic.
For example, what is mysterious and logical for one is not so for another. The basic point is that no one can come to a universal agrement about any of them. It will only end up in arguments and frustration for those who take part.