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.