Thread by @gro_tsen

Twitter is, of course, a closed and centralized system. Both Mastodon/Fediverse and Bluesky/ATmosphere attempt to replicate (some of) its key features in such a way as to move (some) power away from the center. How do they differ? It's Complicated™. Ongoing thoughts: 🧵⤵️ •1/

‣ The Fediverse is easier to understand, because its model is very similar to email. You sign up to a server, which creates an identity for you, and you can use it to exchange messages. Except that messages are (usually) public, it works very much like email: … •2/

… your server stores your messages for you, receives replies from other servers and keeps a copy of them. Every server is a fiefdom unto itself: the user has no right, or even any real existence in the protocol, servers are responsible for everything, … •3/

… from exchanging data to maintaining user identity, to ensuring data integrity (or not). Servers can do anything: impersonate users, modify post content, change timestamps, fake replies, moderate as they wish, refuse to talk to other servers, etc. … •4/

… So while the Fediverse is said to be a “federation”, perhaps a better image is that of a bunch of lordships, each with absolute power over their dominion. They generally talk to each other, but can do whatever they want inside their domain. … •5/

… So if, as a user, you want to join the Fediverse, you need to pledge allegiance to a lord (server), who will then own all your posts and ID, like Musk does on Twitter. If you don't like this thought, you need to host your own server. I think everyone should do this. … •6/

… Also, the Fediverse works like email, but maybe Web pages are a more apt comparison: basically, a post is a Web page which others can link to: they can send you a notification to say they wrote an answer to you, and then you can set up bidirectional links. … •7/

… Each post is generally kept in several copies: on the server of the original author, but typically also on the other server if it's a reply to a post on that one, or if it has replies on that one. But servers can change what they display in any way they want. … •8/

… So there's no kind of data integrity. At all. If you reply to a post, the author of that post can modify it ex post facto. Maybe your server kept a copy of the original post, and users might see that it differs, but there's little way to tell who changed what. … •9/

… Similarly, of course, a server might post bogus replies to a post it hosts: for example, it can change the text in any way it wants. Users might click through to see the original and compare, but few people are likely to do that. •10/

‣ Discussion of the Fediverse is complicated by the fact that most of it is powered by the Mastodon software. They are different servers, but they run the same software. And Mastodon has its own additions to the basic ActivityPub protocol of the Fediverse. … •11/

… So while you can, in principle, run other software, you might encounter interoperability issues. This gives Mastodon devs enormous power on how the Fediverse actually operates. •12/

‣ Bluesky is a rather different beast. It too tries to shift the power balance away from the center, but it does it in a very different way from Mastodon/Fediverse. In short, I would say that Bluesky is less decentralized but empowers users more. •13/

Discussion of whether Bluesky is decentralized is complicated because nobody really knows what “decentralized” means, and also because Bluesky and ATproto are not the same just like Mastodon and ActivityPub are not the same. •14/

Whereas the Fediverse (ActivityPub) just has one kind of piece, viꝫ. servers, the ATmosphere has three different beasts: personal data servers (PDSs), relays, and (app) views. In short, PDSs store users' posts, relays aggregate them and views present them to others. •15/

Each has a different role and could be decentralized. Currently only PDSs are really decentralized and practical for anyone to self-host. Relays require an insane amount of storage to operate, and what views other than Bluesky might be or mean is entirely unclear. •16/

Furthermore, Bluesky still owns and controls one central piece of the ATmosphere architecture, which is the PLC (“Public Ledger of Credentials”, aka “placeholder”) identity provider, which is a kind of centralized directory of every user/agent. •17/github.com/did-method-plc…

‣ So, in many ways, the ATmosphere is far less decentralized than the Fediverse, and in practice it is still a single network with a single operator. Even if it does decentralize eventually, it is predictable that Bluesky will keep a very significant lead and advantage: … •18/

… perhaps the most apt comparison here is that Bluesky might become like what Google is on the Web: the Web's content is decentralized, but, for most users, Google acts as the entry point and a kind of centralized directory of its content/users. •19/

‣ On the other hand, Bluesky does offer a number of user features that the Fediverse in no way does. The most obvious of them is that Bluesky looks a lot like Twitter, not just in user interface, but also in functionalities, while Mastodon is worlds apart. •20/

But it's not just a matter of decorations: Bluesky can offer a search feature that works throughout the network, because, as I pointed out, it distinguishes the “relay” from the PDS, and the relays receive and index everyone's messages. •21/

So we get features on Bluesky that Twitter can easily implement in its centralized architecture like likes/reposts count, a search function that works well, hashtags and alternate feeds. (Also, the quote-post, but I'm not sure this is architecture-related or just a choice.) •22/

The Fediverse has none of these. But the Fediverse also lacks, as I pointed out earlier, any kind of data integrity, whereas this is very much baked in the AT protocol: taking inspiration from Git, it embeds a cryptographic hash in each message reference: … •23/

… so for example, if Bob replies to one of Alice's messages, Alice cannot (even if she has her own PDS) alter the message ex post facto because this would break the hash and therefore the reference. See for more on what this implies. •24/bsky.app/profile/gro-ts…

‣ Generally speaking, while the Fediverse is a very loose federation of servers (like email or the Web), Bluesky is a much more tightly integrated network (though not nearly as much as Twitter, which is just a single site); … •25/

… but on the other hand, Bluesky gives its users some existence and a much greater measure of control (whereas on the Fediverse, as I mentioned earlier, they have none except insofar as their server gives them some). … •26/

… For example, on the Fediverse, your identity as a user is inexorably tied to a server. (There is a feature to request that users start following a different account if you wish to change servers, but it's still a different account: you can't move an account.) … •27/

… And there is simply no way to move a post from one Fediverse server to another: the post is tied to the server, it only really exists on one server (even if others may have copies), and its permalink references that servers. If the server goes, the post goes with it! … •28/

… This is IMO the single greatest error with Mastodon: they didn't provide for a layer of indirection from the user's account to the server, which would have made it possible to move all of one's posts from one server to another. ATproto has this! •29/

‣ To summarize, on the Fediverse, you have full latitude in choosing your server (or setting up your own, which is IMO the only sane way to use the Fediverse), but then you're stuck with it, or at least your posts are, and you'd better hope it won't go the Twitter path, … •30/

… whereas on the ATmosphere, you basically have to use the one and only system (Bluesky, which is quite centralized), but the users have some guarantees and power wrt the system whereas on the Fediverse they are enthralled to their server. •31/

‣ To say things differently, both Mastodon/Fediverse and Bluesky/ATmosphere attempt to solve the problem stemming from the power concentration of Twitter (and what happens if a madman controls of the center), but they take very different, if complementary, approaches: … •32/

… the Fediverse splits the ❉network❉ into pieces, and tries to be a federation of fiefdoms, whereas Bluesky mostly splits the ❉roles❉, and tries to create a checks and balances system between the roles. Both are good, but serve different purposes. •33/❦ end (so far)

✱ Update: I found this (somewhat old, but still relevant) video by Justin Garrison very interesting in comparing, at a high overview level, how ActivityPub and ATproto work, and what each one's pros and cons are. I very much agree with him. •34/❦