I have heard it said, that if you understand yourself you understand the universe. Some say there are levels to go through in order to get to this "universal understanding". There's this one Youtuber who filmed himself on 5-MeO-DMT - his gateway drug to universal understanding. Well he was more blunt, in that he became God.
I'm pretty firmly in the naturalist camp. I've had numerous psychedelic experiences. I can see how one could think such things. But I don't think we have solid reasons to start making strong claims about the supernatural.
Here's one piece of evidence out of thousands more. Consider that the psychedelic effects of LSD can be prevented simply by blocking 5-HT2A receptors in the brain [1]. This is what you would expect if a psychedelic experience is a biochemical phenomenon occurring in the brain, like that sparked by caffeine. A more powerful and much more interesting one, yes, but not something that requires talking of "god" or "universal understanding".
Even though neuroscience intimidates me, I'm smart enough to regurgitate the summary: "The 5-HT2A receptor is central to the effects of many psychedelics, but it may not be the only receptor involved." Also I know enough about myself that I don't kknow any of these topics enough to evaluate Barbara E. Bauer, or https://psychedelicreview.com. I can keep Googling though ...
I am not sure what do you mean by 'part' and 'whole', but if by 'part' you mean a situation for example, and by 'whole' you mean the universe, well, the situation is very subjective, and you can't really know the whole.
If you are an empiricist you can't be sure about anything, you can't be even sure that your theories are describing what 'is' the world, they are just a way to look at it.
If you are rationalist, you would believe that there are some kind of innate features of your brain, now where those features came from?
You would lose information in the process of constructing any abstraction.
You can't compute the next tick of the entire universe using a process that is contained within it. That would be like saying a single page of a book can contain the entirety of the book (without changing the size of the letters, obviously). It doesn't fit.
Do you have any concrete theories of how a human can _fully_ understand the entire universe?