My physics is pretty old, but I'll try: skimming the actual article (1), it looks like they're isolating time in the Heisenberg uncertainty principle (putting a

My physics is pretty old, but I'll try: skimming the actual article (1), it looks like they're isolating time in the Heisenberg uncertainty principle (putting all the Δ on the other side of the equality) and then following those Δ's in the other variables, which is a common use of the uncertainty principle). They imagine some displacement, then insert the result back into the uncertainty principle to see how that Δ would propagate back onto time. I was sort of excited about this because it seemed like they might be suggesting there was actually a window here to explore a quantum theory of gravity. Alas, they say "Although the methods presented here suffice to describe the entanglement of clocks arising from gravitational interaction, a full description of the physics with no background space–time would require a fundamental quantum theory of gravity". To your specific question "Who's to say that the inaccuracies are merely caused by fluctuations in spacetime?" I don't think they're claiming they found a theoretical cause to explain some observed fluctuations. In fact, they put in some notional values to see what comes out and observe "this effect is not large enough to be measured with the current experimental capabilities". Now, I think what you're getting at is the idea that you would expect the ticking of clocks to vary over space time. What they're saying is, "Of course, but we believe the problem is even more fiendish: the tick rate not only varies but it accumulates uncertainty to the point that a system which starts out as a clock can no longer be considered a clock at all. Further, [what I believe they are saying] the clock's coherence decays in a way that potentially varies with path and frame of reference. At which point, one starts wondering, why haven't we all flown apart already? And they're doing this, again, all from a theoretical standpoint. It' the same sort of thought experiment you might get if you modify Euclid's fifth axiom: all sorts of weird stuff is possible, and we don't really need experiments to show the math, although there are experiments that can be done. (1) http://www.pnas.org/content/early/2017/03/06/1616427114.full.pdf http://www.pnas.org/content/early/2017/03/06/1616427114.full...