Block-based world: collision and presentation

Hello community,

I’ve started making a game for a few month and the current result is a generated world made of blocks (like in Minecraft). You can walk around, jump and collision works.
My questions is, that my collision algorithm is optimized because I’m using blocks which are all orthogonal to the coordinate system, so I don’t check the volumes and I do not use any spanning trees for optimization, because I don’t need them. If you think of a world with millions of blocks my algorithm will also work, but how does UE knows, that collision checks are actually quite simple. Another point is, that millions of blocks needn’t to be presented, because most of them are hidden behind other blocks. I’ve solved this, by adding an ‘IsTransparent()’ method to my blocks, and when a block is modified, I recalculate the neighbor blocks.

In other words, what would UE does if I add millions blocks to the scene? Can I create my game with UE?