I feel like I understand communist theory pretty well at a basic level, and I believe in it, but I just don't see what part of it requires belief in an objective world of matter. I don't believe in matter and I'm still a communist. And it seems that in the 21st century most people believe in materialism but not communism. What part of "people should have access to the stuff they need to live" requires believing that such stuff is real? After all, there are nonmaterial industries and they still need communism. Workers in the music industry are producing something that nearly everyone can agree only exists in our heads. And they're still exploited by capital, despite musical instruments being relatively cheap these days, because capital owns the system of distribution networks and access to consumers that is the means of profitability for music. Spotify isn't material, it's a computer program. It's information. It's a thoughtform. Yet it's still a means of production that ought to be seized for the liberation of the musician worker. What does materialism have to do with any of this?
We didn't discover atoms in the sense of revealing some True Thing. We slowly built successive models of a set of phenomena we identify as atoms, which we continue to revise to make more reliable in descriptive and predictive applications and from there host of other applications.
From the best of our understanding it seems like matter exists independent of our belief or observation, which works well enough that we continue to use this understanding.
OP seems to reject this in favor of something like phenomena behaving in a way that's generated from our consciousness.
This is true. I didn't mean to imply atoms are the final, completely true, and perfectly-reflective-of-reality model of matter that will be developed.
I decided to edit the comment you replied to.