Philosophy

But isn't the apple growing on a tree the constant result of a dialectical process?

Describing the process as dialectical is the human part. For the universe, these processes just are, the universe doesn't care for these labels and categories that we invented to help us understand it.

Whether humans are there to witness it or not, the process still happens.

Precisely. The material process happens regardless. The fact that there is no one there to understand it through the abstract lens of dialectics changes nothing about the process itself.

abstract ideas cannot exist independently of a brain capable of comprehending them.

I find this to be an idealist premise,

Quite the opposite. It is believing that pure ideas exist somewhere out there in the ether independently of the material structure of the brain that is the very definition of idealism.

because the next logical step is to say that material reality doesn't exist outside of a brain capable of understanding matter

That does not follow at all. That would indeed be idealism. Material reality exists regardless, but it does not care for the language we invented to describe it.

If we hold that the brain is matter and the result of matter interaction is what creates ideas, then yes this premise would mean that matter doesn't exist.

Again, no, that doesn't follow. I think we're just having a semantic conflict with regards to what we mean when we say "ideas exist".

All i'm saying is that an "idea", by which we mean a specific type of pattern or process in the brain resulting from the material interaction (as you also said) between the structure of the brain and the electrical and chemical impulses in it, obviously cannot exist independently of the material substrate on which it happens, i.e. the brain. And on this i think we are both in complete agreement, we're just phrasing it differently.

everything that exists in the natural world (the one we live in) is by definition material

This is a tautology. Of course everything in the material world is by definition material.

What about animals? The dog seems to perfectly understand [...]

I can't know to what degree a dog is consciously aware and capable of abstraction or just acting on instinct because i am not a dog, so i won't comment on this.

Will consuming food to satisfy hunger stop existing in the universe if there are no more lifeforms to perform the process

This is actually a very good example because it illustrates my point: Hunger is a feeling. It's real and physical in the same way ideas are but it also depends on an organism that can feel it. Yes, the feeling of hunger can exist in an organism regardless whether that organism is capable of understanding the abstract notion of cause and effect (if ingest food, then no hunger). But if there are no more life forms to experience hunger then clearly the feeling that we call hunger won't exist anymore.

if you somehow took away all matter in the universe, made it completely empty, the laws of gravity would still exist [...] But they always apply, even when there is no gravity to pull.

The laws of gravity are a description, an abstraction that we use to understand how the universe works. They are not actually written somewhere on the fabric of spacetime. Yes they would still apply; that is: if someone capable of comprehending them appeared again those laws would still be valid descriptions of the universe. But as i said before, the universe doesn't care about the language, categories and abstractions that we use to describe how it works; it just works, it just is.

As i said, i think this all boils down to semantics. It's a question of language and how we use it.