Earlier quoted context omitted.
Yes, it would be more precise if I had prepended "local" every time I said "conservation of momentum" above. With that clarification, I'm happy to stand by what I've said.
"local" seems like a fairly large assumption for something hypothesized by at least some to work through quantum mechanics, of which a central tenant is non-locality. In fact, given the consistency of qm experimental results over the past 50 or so years, it seems entirely plausible to think that it would be a field of study which could upend classical physics. All that being said I agree extreme skepticism is healthy…
Local momentum conservation is foundational to all of physics: it is embedded in Newton's laws, and you can't get much more foundational than that. As such, if anything violates it the degree of "extraordinary" would be beyond anything ever seen. Far beyond superluminal nuetrinos.
So the previous posters are correct: momentum conservation, which is generally used to mean "local momentum conservation", is as deeply foundational to physics as Newton's laws, and the kind of observable-only-by-statistical-inference non-locality seen in QM is not known to have any impact on it.
As such, it would be earth-shaking at the deepest possible levels of physics if this result were correct. That does not mean it is wrong--although that is certainly my bet and that of virtually every other working physcist--but it's important not to understate what a big deal it would be, because understanding that opens up alternative ideas regarding how to test it.
This is neither arrogance nor dismissal, but an understanding that anything that violates local momentum conservation, via QM or anything else, and also lets the rest of physcis sail blithely on, manifesting no measureable effect of any kind on any of the millions of diverse and precise experiments that have been performed, is astonishingly implausible.
Could it happen? Sure. But it's really easy for laypeople to radically underestimate the implausibility of such claims, as was done all the time in the cold fusion community.
Nor does reproduction of the effect say anything very much about either the underlying theory (such as it is) or the actual cause. Lots of things can create forces of micronewtons, and given how utterly implausible the claim is, most physicists are starting with a prior barely above epsilon. As such, the amount of evidence required to update our belief to something close to unity is going to be huge. Laypeople, who start with an unreasonably large prior because they are ignorant of how fine-tuned such novel physics would have to be to never show up anywhere else, will require less evidence.