Replying to your lower comment
i can barely guess at how the 'hot' and 'active' tabs filter.
I don't know what active does but Hot is a pretty simple algorithm. The posts start in the same order as New (newest first), but each time a post gets an upvote, it gets a boost back toward the top of the list. How much of a boost is determined but the SP and weight of the upvote. Posts that don't get upvotes will slide down fast, while posts that continue to get upvotes will stay near the top, then eventually slide down as well.
I'm pretty sure active puts posts that were either just created, edited or had a comment added put at the top of the list, which then just continues to scroll until the next edit or comment, again just bumping to the top of the list.
Simply hitting edit and update post with no changes will put you to the top of active too.