Genre's are mostly marketing categories tbh but yeah that'd probably get labeled as fantasy, maybe science-fantasy if it was really strict about the alchemy system but generally anything remotely medieval is autolabeled fantasy if it has any magic whatsoever.
People absolutely have different criteria for something being hard sci-fi though. It generally lacks things like FTL travel or antigravity and the plot is in some way dependent on the science i.e. you couldn't change the setting without drastically changing the plot. Poul Anderson's Tau Zero is a great example of this and alot of it is known now to be counterfactual but it's still held up as a great hard sci-fi book, the key is it played in the zone of plausibility when it came out.
If you want to get into it, a more recent one is, Blindsight by Peter Watts is one I'd recommend, despite some very cringey passing references to Richard Dawkins (and I think Elon Musk iirc) it's a good hard sci-fi book.
For speculative fiction you generally want to choose something that has a low chance of being disproven before you can publish it. In general such drastic inventions of new physics are not seen as hard science fiction except in the rare cases where the author is actually a physicist or something but then they usually aren't going to speculate too wildly when they are know they almost certainly are going to be wrong. Soft sci-fi or hard magic fantasy usually fills that niche, the books have better longevity that way.
Not to pick on your hypothetical but you could easily have all the same effects by just digging a bit into materials science and/or condensed matter physics, even if you just stuck to things that we know are possible but are currently too difficult to manufacture at scale (or at all) you'd have plenty of new unique materials to build a compelling story around.
Genre's are mostly marketing categories tbh but yeah that'd probably get labeled as fantasy, maybe science-fantasy if it was really strict about the alchemy system but generally anything remotely medieval is autolabeled fantasy if it has any magic whatsoever.
People absolutely have different criteria for something being hard sci-fi though. It generally lacks things like FTL travel or antigravity and the plot is in some way dependent on the science i.e. you couldn't change the setting without drastically changing the plot. Poul Anderson's Tau Zero is a great example of this and alot of it is known now to be counterfactual but it's still held up as a great hard sci-fi book, the key is it played in the zone of plausibility when it came out.
If you want to get into it, a more recent one is, Blindsight by Peter Watts is one I'd recommend, despite some very cringey passing references to Richard Dawkins (and I think Elon Musk iirc) it's a good hard sci-fi book.
deleted by creator
For speculative fiction you generally want to choose something that has a low chance of being disproven before you can publish it. In general such drastic inventions of new physics are not seen as hard science fiction except in the rare cases where the author is actually a physicist or something but then they usually aren't going to speculate too wildly when they are know they almost certainly are going to be wrong. Soft sci-fi or hard magic fantasy usually fills that niche, the books have better longevity that way.
Not to pick on your hypothetical but you could easily have all the same effects by just digging a bit into materials science and/or condensed matter physics, even if you just stuck to things that we know are possible but are currently too difficult to manufacture at scale (or at all) you'd have plenty of new unique materials to build a compelling story around.