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Physicists provide support for retrocausal quantum theory
- stupejr 9y agoTime to start scanning for tachyon radiation
- code5fun 9y agoCmon guys really, first we come up with all this misterious dark stuff and now this...sigh
- naasking 9y ago> But by allowing for the possibility that the measurement setting for one particle can retrocausally influence the behavior of the other particle, there is no need for action-at-a-distance—only retrocausal influence. I don't quite get it. According to GR, non-locality and retrocausality are equivalent. So how is retrocausal QM different from Bohmian mechanics/pilot wave theories?
- Koshkin 9y agoI agree that retrocausality does not look at all surprising knowing GR and the long-established non-locality of QM. (Whether this is equivalent to what the pilot-wave interpretation has to say about the character of QM may require a complicated proof.)
- lucozade 9y ago> So how is retrocausal QM different from Bohmian mechanics From what I can tell from this, there's no difference in the sense that it's experimentally indistinguishable. It's different in the sense that Bohmian mechanics relies on a non-local pilot wave to match QM results. This frees the other assumption i.e. causality to get to the same answer. TBH I can't see either get much attention until someone comes up with a way to make them produce different results compared to standard QM approaches. Either that or someone finds a way to make QM calculations substantially easier using these approaches. In other words, if they produce new physics or have practical value.
- keyle 9y agoIsn't this another blanket theory that magically explains a ton of 'spooky' stuff without actually proving it? Just asking from a common's people point of view. I'm a practical person, I need tangible facts...
- rf15 9y agoThis would allow us to predict the future and potentially allow for time travel as well. Seems unlikely from the implications alone, but let's see what peer review of the details will tell us.
- naasking 9y ago> This would allow us to predict the future and potentially allow for time travel as well. It doesn't actually, they discuss this in the article. The laws of thermodynamics impose an arrow of time via boundary conditions, and something similar would apply here.
- FeepingCreature 9y agoPurely as an amateur, it seems unelegant to have something that violates causality as a mechanism, but doesn't give you a way to violate cause and effect at a higher level. It's like the universe is conspiring to keep its awesome tricks from you.
- ajuc 9y agoSo, universe is like Haskel ;) Purely functional API, but under all of that there's still imperative machine code. Also, the conspiracy may be a good thing. If you have self-replicating and mutating code on your computer you should put some sandbox around it, or it might evolve to buy more RAM on ebay. Or, more realistically - will crash the system.
- naasking 9y ago> It's like the universe is conspiring to keep its awesome tricks from you. Well that's just inevitable. You're never going to see a naked singularity, for instance.
- rf15 9y agoTrue. I also like the implication that we have another proof against T-symmetry.
- 9y ago
- woliveirajr 9y ago> First, to clarify (...) It does not mean that signals can be communicated from the future to the past(...) instead, retrocausality means (... it) can influence the properties of that particle (or another particle) in the past, even before the experimenter made their choice. In other words, a decision made in the present can influence something in the past. So, hard to explain in layman words: future can't transmit information to the past, but an action that will be taken in the present can influence some properties of a particle in the past. Take two particles, separate them enough, do some "A" thing to one of them and the other instantaneously will have the only possible state that doesn't break the universe. And one viable explanation is that when we've done the "A" thing, this information was transmitted to the particle in the past. We just couldn't measure this before (in the past) because measuring interferes with it, and that property can only be revealed at the same time that we've done the "A" thing. Is that it? Kinda of information is transmitted to the past, just can't be read before some time ?
- petters 9y agoThat explanation still seems to allow faster than light communication.
- deleted 9y ago[deleted]
- emeraldd 9y agoBased on that description would this sounds like an action in the present is putting constraints on a seemingly unrelated event that has an enforced but currently unobservable relationship in the future. Or something like that. Why do I get the feeling that this starts requiring higher dimensions? Additionally: If any particle in an entangled system get's measured along the full course of it's "enforced relationship into the future" that would be the point where the system collapses. And that's where I'd run into issues .... It would seem a more reasonable explanation that retro-causal relationships would be a fourth physical dimension for the relationship to exist along ... hmmm
- mindviews 9y ago
- mirekrusin 9y ago// WARN: because past is static, to support retrocausal influence, we're spawning alternative universes which are joined on retrocausal action choice - this slows down The Simulation and, if abused, can exhaust resources and crash.
- rf15 9y agodon't remind me that people actually believe that you can infer the existence of a simulation only with data points that are created and controlled by it.
- mirekrusin 9y agoSimulation part was a joke. But the static, unchangeable past is interesting because: 1. assumption that the past is static and can't change is not crazy and if retrocausal influence exists, it could imply Many Worlds interpretation as more plausible - there must be at least 2 different universes with static past if you can choose at present past A or past B. The joke is that branching universes creates large overhead costs (n unmerged, binary branches create 2^n universes to keep track of) in simulation that can crash it.
- deleted 9y ago[deleted]
- alasdair_ 9y agoThere doesn't seem to be anything wrong with this basic idea. As a (bad) analogy, think about how computer code can be written to detect whether or not it is running inside a virtual machine or on a "real" device. It's usually almost impossible to tell but by probing at the extremes and forcing the system to do things that never happen under common usage, it's possible. (It's also possible to break out of the system entirely and gain access to the host OS sometimes, but perhaps that's taking things too far :)
- monktastic1 9y ago
- ridewinter 9y agoThe many-worlds interpretation of quantum mechanics is the only one that's easy to understand. All others seem to bend over backwards to realistically explain quantum effects. It's so rare to find clear explanations, but they do exist. My favorite from David Deutsch, a main creator of the idea of quantum computing: To those who still cling to a single-universe world-view, I issue this challenge: explain how Shor’s algorithm works. I do not merely mean predict that it will work, which is merely a matter of solving a few uncontroversial equations. I mean provide an explanation. When Shor’s algorithm has factorized a number, using 10^500 or so times the computational resources than can be seen to be present, where was the number factorized? There are only about 10^80 atoms in the entire visible universe, an utterly minuscule number compared with 10^500. So if the visible universe were the extent of physical reality, physical reality would not even remotely contain the resources required to factorize such a large number. Who did factorize it, then? How, and where, was the computation performed?
- pron 9y agoI don't understand David Deutsch's philosophical justification. Is he suggesting that quantum computing steals computational resources from other universes? If so, in this "quantum computing as theft" view, aren't many of those universes (those similar to ours, doing a similar computation at the same time) stealing computational resources from ours at the same time, yielding the original question again?
- ridewinter 9y agoNo, nothing stolen. The quantum computer's calculations take place in parallel universes. The difficulty is arranging it so that the parallel universes are identical to eachother other than those calculations in the computer itself. That's the only way that this universe can get the answer back. That's my understanding of the many-worlds explanation of quantum computing. Nice and simple.
- petters 9y agoThe "different universes" in the multiverse are still parts of the same wavefunction. Therefore they can interact. It's just that after decoherence, they will never interact again and will stay separate.
- Lxr 9y agoI never fully understood the Bell experiments. How exactly do they discount hidden variables?
- miltondts 9y agoThey don't here is what Bell said: "There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the ‘decision’ by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster-than-light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already ‘knows’ what that measurement, and its outcome, will be."
- euyyn 9y agoOk, and barred that?
- BoiledCabbage 9y agoI could be mixing things here, but aren't the three options losing one of locality, definitiveness and non-conspiracy? https://en.wikipedia.org/wiki/Counterfactual_definiteness#Overview https://en.wikipedia.org/wiki/Counterfactual_definiteness#Ov...
- nazgul17 9y agoThe way I understood it is in a YouTube video by Looking Glass Universe. I watched it time ago, but if I remember correctly, if there were hidden variables, the distribution of outcomes of his experiment would look different compared to what it actually looks. Sorry it's a half-assed explanation :)
- rthomas6 9y agoThis reminds me a lot of the sci-fi novel Anathem by Neal Stephenson. Trying to be spoiler-free as possible, in the book, the many-worlds interpretation of quantum mechanics is the correct one, and the worlds lie on a directed acyclic graph, meaning that the flow of information can only move in one direction along the universes. So in the same way information can only travel in one direction in time (into the future), information can only travel laterally into other dimensions in one direction. So, in the book, nobody can directly influence the past, but the question of existing in multiple worlds and sending information between them, and thereby potentially exploring many possible outcomes of a situation simulatenously, is much more open. In other words, retrocausality WITH information transfer is possible when the information is flowing from one universe to another, in a certain direction.
- Tossrock 9y agospoilers I think he implies pretty heavily that the Rhetors actually CAN influence the past, through a mechanism very similar to that described in the article - "choosing" which way an event happened in the past. Their powers work at Narrative scale though, not just experimental observation.
- amoruso 9y agoJohn Cramer has been pointing this out for years (since the 1980s I think): "The Transactional Interpretation of Quantum Mechanics and Quantum Nonlocality" https://arxiv.org/abs/1503.00039 https://arxiv.org/abs/1503.00039 Also, Bell's inequality shows the state vector is nonlocal, and and that implies causality violation in relativity. Third, quantum information theory has retrocausality in the form of negative entropy: "Negative entropy in quantum information theory" https://arxiv.org/abs/quant-ph/9610005 https://arxiv.org/abs/quant-ph/9610005 Too many things pointing in the same direction. This is the right way to look at it.
- BoiledCabbage 9y agoWhat happened to John Cramer? He hit the popular science media as he was leading up to his modified delayed-choice quantum eraser for retro-causality. According to him that was a supposed paradox meaning the result of the experiment was going to have to give a result that conflicted with our theories and thus give an avenue for new discover (ie allow us to use a test that doesn't match our model). It's been a decade and no results were ever discussed. That seems bizarre to me.
- ajuc 9y agoThere's also the idea of timeless physics, as argued in https://en.wikipedia.org/wiki/Julian_Barbour#Timeless_physics https://en.wikipedia.org/wiki/Julian_Barbour#Timeless_physic... or in slightly different form in http://lesswrong.com/lw/qp/timeless_physics http://lesswrong.com/lw/qp/timeless_physics It's apparently possible to rewrite all physical equations without time coordinates and they still work. I'm not competent enough to understand all of it and to check if it's not contradicting any experiments, but I'd love to hear if it does. It seems particularly elegant (because if the state of the universe can't repeat, then why do we need time?).
- nilson 9y agosounds like ad-hoc hypothesis