Conceptually, I think the way Lemmy and Mastodon would be able to interop is pretty straightforward: Each thread in either is basically just a tree of replies. They are just shown differently depending on the platform. Furthermore, Lemmy communities show up as Mastodon groups, and Lemmy threads show up as retoots from those groups, which I think is the most elegant solution.
The only issue that makes this interoperation unusable really is that Mastodon groups representing Lemmy communities just “retoot” every single comment, obliterating the TL of anyone who dares to follow those groups. Which as far as I know only happens because Mastodon refuses to be cooperative and properly follow the standards.
As for the other comments asking “why even care about this”: I think it’s worth as a long-term goal for the Fediverse to entirely separate the “view” aspect from the “content” aspect of platforms where reasonably possible, so that each user can browse all the content in their preferred platform. Not all fedi platforms need to conform to some absolute feature parity, but as I just said, there’s basically a one-to-one relationship between Lemmy and Mastodon content, so it is reasonable in this case. I’ve seen enough people here claim that they very much prefer the Lemmy format to read conversations.
Personally, my Mastodon account has different vibes from Lemmy, and for that reason alone there is a bunch of Lemmy communities I wouldn’t subscribe to, but would follow from Mastodon. The only reason why I don’t do that is because Mastodon’s side of the interop fucking sucks.
As far as I know (I’m not a physicist), it’s not all that clear that gravity is caused by a particle. It makes sense to assume it is, because of parallelisms with the other fundamental interactions, all of which (other than gravity) are caused by particles that have been thoroughly observed and studied.
So we kinda know what a graviton would be like and what to look for, but so far it hasn’t been found, and its existence hasn’t been conclusively determined. There are some alternative hypotheses that in fact gravitons don’t exist at all, and gravity is just a consequence of the shape of space-time, which I think is what’s going on with black holes.
(source: trust me bro I saw it on the Internet)