The fediverse is less like Twitter and more like email. You sign up for email through a provider, like Gmail or Outlook, and they have control over your access to the other users and pay the costs of running your hardware, the same way you sign up with a particular domain on Lemmy or Mastodon. Like email, you have an inbox that receives messages, and communities are like email groups you join and send messages to. And, like email, it's based on standards that everyone has agreed on through a group called the w3 consortium.
So each instance within the fediverse can communicate with each other, but how do things like the feeds work? Since there's no algorithm is everything from Lemmy.world only going to show up on the popular feed (if I'm on that instance) or can other things like lemmy.ee or whatever also show up?
And can I comment on posts from a different instance or does that vary per instance?
Sorry, last one. I noticed there are things like music streaming and video sharing instances within the fediverse, so could Lemmy theoretically allow content from those instances to be cross-posted here?
Basically to me this feels like a super modular super media platform that has tons of parts that can plop in and out of the system as needed.
You've got it mostly right. But this part is wrong:
is everything from Lemmy.world only going to show up on the popular feed (if I’m on that instance) or can other things like lemmy.ee or whatever also show up?
(assuming you're on desktop browser) If you want to browse only lemmy.world communities, click on "local" at the top:
"Subscribed" is all communities you specifically subscribed to (on any instance in the lemmyverse) and "All" is everything on lemmy.world AND all communities anyone on lemmy.world is subscribed to.
(fwiw, my account is on a different instance, startrek.website, but I subscribed to this community, so I saw your post in my "subscribed" feed).
Not exactly, because instances don't sync communities nobody is subscribed to. That said, if you're on a large instance like .world with tons of users, it's likely you'll see pretty much anything that could be considered worth seeing.
Oook, that explains why my .world acct, and this one are so vastly different. I pretty much just see news and tech from this instance (and porn, obviously)
So what actually happens under the hood is when one instance communicates first time with another instance it builds some local cache of that remote instance. Then, when you open "All", you get everything from your local instance + things cached/requested from other instances. Admins can defederate an instance, in which case you would not see anything from it.
Since there's no algorithm is everything from Lemmy.world only going to show up on the popular feed (if I'm on that instance) or can other things like lemmy.ee or whatever also show up?
Everything federated will show up.
And can I comment on posts from a different instance or does that vary per instance?
If federated, you can both see and post both posts and comments on any instance from your home one.
could Lemmy theoretically allow content from those instances to be cross-posted here?
It could. More than that, Mastodon users currently can both subscribe to Lemmy instances and post/comment. It looks kinda weird since they mention post author/community or whomever they answer to in a comment, since they see it as if it looked like Twitter.