Users can "flag" your post and then it seems to drops faster out of sight and out of mind, and it loses it ability to acquire any comments.
Upvoting tends to bring your post up top and I've heard of posts going "viral for 24 hours on the front page of HN" which means it must all have to do with voting and comments. I haven't seen too many people claim anymore than 24 hours though. It makes sense, specifically to gain attraction from users, and of course, the more comments there are on a post, the higher it is likely to be ranked in search engines.
As far as the 24 hour period, that too makes sense, as they probably don't want the same thing being up top for too many days, weeks or months at a time, which encourages new materials all the time.
points / time^2 * penalties
So after some time the article needs a gazillion of upvotes to be in the front page.
The mods add some penalties for many reasons. For example when the article is borderline off-topic, or it's too similar to a previous article. Some penalties are automatic and some are manual.
If too many users flag the article, then the article gets a penalty. Also, if the post has much more comments than points, the article gets a penalty (this prevents flamewars).
And there are a lot of tweaks to the order.
There was a blackbox analysis done a few years ago by kens: http://www.righto.com/2013/11/how-hacker-news-ranking-really... HN discussion https://news.ycombinator.com/item?id=6799854 (920 points, 1319 days ago, 190 comments) It has more details, and some details may have changed, so use it only as an orientation an to solve your initial curiosity, but it's not set in stone.
Anyway, for an official answer you can try to contact the mods hn@ycombinator.com but some parts of the algorithm are "secret sauce", some are temporal tweaks, ...
I wonder what the penalty is for "re-posting", especially because timing seems to be key. You post at 8:30AM and get very few looks from your target audience, and then post again at 10AM and coincidentally reach a large amount of your target audience.
I wonder where the line is drawn between "spam" and "persistence"...
No no! There is a lot of great content that just streams past in /newest
As I make this post the newest submission is 0 minutes old and the oldest on that page is 27 minutes old.
When you make a post you have something like 1 hour window to attract upvotes.
Also, there are some submissions that attract upvotes that probably shouldn't - they're flaimbaity or not deeply interesting.
