In Hinayana, there are the four imponderables:
- The scope of Buddhahood
- The scope of jhana
- The specifics of karma
- The origin of the universe (or the cosmos, assuming many universes exist)
These are four things they are not supposed to think about because they lead to insanity and do not lead away from suffering.
But do Mahayana Buddhists have any explanations, though, as to the true nature of these four things?
Time, gravity, light, karma; these four things seem inexplicably linked in a way I don't fully understand but vaguely imagine. Maybe I just need to find a Lama, hahaha.
You could for example read what Nagarjuna says in Mulamadhyamaka Karika
about Buddhahood in Chapter 22. Investigation of the Tathagata
about Karma in Chapter 17. Investigations of Acts and Fruits
about the origin of the universe in Chapter 27. Investigation of Views
and Chapter 11. Investigation of Extremes Before and After
several other chapters of the same work are also relevant for this question.
The issues you mention are covered in Abhidharma literature, for example in Vasubandhu's Abhidharmakosha.
In Anacker's Seven Works of Vasubandhu there is Karma Siddhi Prakarana, Investigation For The Demonstration Of Action.