What’s interesting about this abstract or short article note is that i find it fairly comprehensible. At this point, it seems to be purely speculative or theoretical. The extra weight has yet to be actually observed. But it is in principle testable if a large enough swarm of entangled particles can be assembled. If observation or measurement collapses entanglement, then observation would reduce the weight of the observed particle. Weight is a force, while mass is a fundamental property of matter. Observation destroying some force would no violate conservation of matter-energy (any more than rendering something weightless by putting it into orbit does). The observed system would be no less massive than the entangled on: it would just exert less force on nearby measuring devices. Question: could we measure the weight of an entangled particle without destroying its entanglement? I.e. does any measurement do the trick, or just some sort of “direct” observation?
I also found it interesting that the author puts it this way: “Physicists have long known that a single quantum particle can exist in two places at the same time.” Every discussion I have ever read refers to entangled pairs of particles. Is this just semantics? Or is there a substantive difference between two separate (albeit intimately linked) particles and a single particle with two (or more) locations?
Yes, and no to both questions. :-)
Physicists speak loosely of "forces" in quantum mechanics as a holdover from Newtonian Physics, but in that context what they mean is "fundamental interactions mediated by gauge bosons." There are no actual forces, and no such thing as "weight" in quantum mechanics. The closest you get is something like <dp/dt> which is based on expectation values, not fundamental quantities. So the answer is, there is no direct observation of weight in quantum mechanics.
“Physicists have long known that a single quantum particle can exist in two places at the same time.”
Frankly, I don't really know what the meaning of that statement is in the context of the phenomenon described. An actual "particle" isn't localized. It has a wave function, which exists in a region of some spatial extent. It isn't in "one place" but it's in a heck of a lot "more places" than just two.
It's possible that the author is talking about a bosonic or fermionic system consisting of two entangled particles as if it were a single "particle," but more likely he's just confusing ordinary delocalization [the Uncertainty Principle] with entanglement [Quantum Indistinguishability]. They aren't the same thing.
Omit the statement. It either has nothing to do with entanglement, or it is objectively false. In either case, it lends nothing to the article.