The protomolecule turned people into vomit zombies with a collective hive mind that could communicate instantaneously across the solar system and move an asteroid defying all laws of gravity, with the ultimate secret intent of building an interstellar wormhole.
Again, in the series (at least early on) humans are quite limited by known constraints and it would easily be considered hard scifi in many regards. But its central conceit was no less blithely nonsensical than that of TBP's - I simply can't understand how someone could put one in the hard category but disqualify the other.
I've only read two books of the Expanse, what I've read is a bit soft, but I would argue it is harder than TBP.
I think one key difference for me is that we are not told what the protomolecule is, so we can imagine it is some kind of massive DNA-like structure packed with enzymes and whatnot that can plow through biological material and reorganize it. That is a plausible start. Then, sure, it may overdo the capabilities a bit.
The sophon, though, we are told exactly what it is: it is a proton unfolded into a 2D plane on which a supercomputer is etched, which is able to configure itself in order to intercept and direct light, which is how it is able to spy on us and pull light tricks. The problem is that it is nonsensical from the start. If you can unfold a proton around a planet in such a way that it blocks all light, it is being bombarded by far more energy than it would be in a particle accelerator. It's like using paper origami to bounce asteroids, basically the same issue as the Expanse, except worse, and that's before we even get into the supercomputer stuff.
Still, point taken. The Expanse should probably not be classified as hard sci-fi either.
The protomolecule turned people into vomit zombies with a collective hive mind that could communicate instantaneously across the solar system and move an asteroid defying all laws of gravity, with the ultimate secret intent of building an interstellar wormhole.
Again, in the series (at least early on) humans are quite limited by known constraints and it would easily be considered hard scifi in many regards. But its central conceit was no less blithely nonsensical than that of TBP's - I simply can't understand how someone could put one in the hard category but disqualify the other.