If I’m not reading this correctly, apologies in advance, but the gist seems to be that open timelike curves are basically no different than a gravitational field and in theory, if you send entangled particles down 2 OTC’s several times you can measure “conjugate” states to an arbitrary degree of precision in violation of the uncertainty principle.
I have no idea at all WHY that should be, but I’m hoping I at least understand the words. Here’s a quote and the link.
Better yet, a possible experiment may be in the works
Someone doesn’t know what they’re talking about. All massive particles travel along open timelike curves, and this is true regardless of whether space is curved or flat. Open timelike curves are, as you would guess from their name, not a kind of closed timelike curve (yes, even in this specialized context, “open” and “closed” are still antonyms). Unless the curve is closed (which is not, so far as we know, possible), you can’t actually retrace the same path through spacetime. Light beams, meanwhile, cannot travel on timelike curves (open or closed), since, being massless, they always travel on null curves instead.
I’m afraid to ask but is there any chance that I, personally might be currently and intimately (as I type this, wink, wink) be acquainted with this “someone?”
Or is it infinitely more likely that this is the sort of “someone” who might say, oh . . . publish an article in a place like Physical Review Letters?
Well, the authors do use a strange notion of open timelike curves. Most would just consider the term to mean ‘curves timelike everywhere which do not intersect themselves’, which is exactly the sort of trajectory every (massive) particle traverses through spacetime, and from which no violation of the uncertainty principle is possible. Instead, they propose a notion in which there is a sort of paradox-free time travel: systems can end up in one another’s past, but not in such a way as to be able to interact. From there, the violation of the uncertainty principle follows (apparently).
Now, the thing is that nobody in fact knows whether OTCs in the sense they propose are actually physically possible; as with CTCs, they may be allowed solutions of Einstein’s equations, but that doesn’t mean they describe reality. Furthermore, they use Deutsch’s proposal for dealing with time travel in quantum mechanics, which is far from being universally accepted (there’s for instance an alternative proposal, due to Seth Lloyd et al., in which I don’t think the problem arises). There are very general reasons to expect the uncertainty relation to hold even in a theory of quantum gravity: it’s a straightforward consequence of the noncommutativity of quantum mechanics, and in a sense, giving that up would mean that you don’t have a quantum theory any more. There’s a notion called ‘dispersion-free states’, which are states for which the dispersion, i.e. the ‘spread’ of its value, vanishes for all observables, and thus, no uncertainty relation holds; but such states don’t exist in any quantum theory.
It might be the researchers, or it might be the reporters who are reporting on their work. I haven’t had a chance to read any more on this than the blurb in the OP, so I can’t say which.
And yes, it’s uncommon for something that’s just flat-out wrong to get published in a prestigious journal like PRL. It does happen occasionally, though.
