Physics has always been about asking the right questions. This is especially true for quantum theory. The most famous example is the question “is it a particle or wave”, with the implied assumption that those are the only two possibilities. On the other hand, not asking a question–for example, the “shut up and calculate” approach is just as counter-productive. Neither approach will further the knowledge base for physics. It is imperative to thoroughly think through what questions are worth asking and whether the question embeds invalid assumptions.
All we know right now about existence on a quantum scale, and we know it with an extreme level of certainty, is that the Standard Model describes the probabilities of how particles will interact with other particles or fields. If we eschew the “shut up and calculate” attitude, at least we are taking a chance that we are on a path that will result in progress. However, we know so little about what reality is on a quantum scale that the chance of asking a nonsensical question is extremely high.
I propose that trying to resolve the decoherence paradox has questions worth asking. Any time an apparent impossibility appears in science, an understanding of the paradox should always lead to a deeper understanding of reality. However, we have to be so careful of our assumptions, and we have to be sure that the question isn’t simply a matter of linguistics, our choice of definitions. I have thought at great length about the decoherence problem and see the way to pose the question that gets at the heart of the paradox:
Experiments (Aspect, et. al.) show that quantum entangled particle pairs decohere by detection at any specified distance. Everyone, including me, zeroes in on the non-causal nature of decoherence and tries to resolve that, but I think there is an underlying question that has to be answered first. No known field property maintains amplitude over that distance–every non-local field observes decreasing amplitude over distance. For example, the EM field dissipates amplitude according to the central force law. We can choose an arbitrary distance such that any EM field magnitude between entangled particles is less than any arbitrary epsilon, yet will still unfailingly maintain quantum coherence until detected. Here is the question: how could a field property continue to exert an influence on a particle when its field strength approaches the limit of 0?
Let’s now attempt to vet this question, that is, see if the question makes bad assumptions or is just a semantic issue. We are assuming that the decoherence effect propagates over distance and is mediated by a field. It could instead be a particle, but there’s no experimental evidence for that. Another approach could be that this effect takes place in an invisible sideband path, for example over an unseen dimension not in R3 + T. This would simultaneously explain the instantaneous (non-causal) aspect as well, but right now there’s no evidence for such a path. There’s several other possibilities as well, but the question itself is not flawed by making a known bad assumption. Experiment shows that the connection requires an entity, either field or particle or something else, to influence the entangled particle at distance in a non-causal way. At first glance, I don’t see a semantics problem here, this doesn’t appear to be a matter of how we define our terms.
We now should ask if the question is worth asking. What will resolving this apparent paradox accomplish? We want to gain insight into the nature of decoherence, obviously, but more than that, the quantum effect appears to demonstrate that there is evidence of a field that maintains constant magnitude, or at least that exists over the length of the decoherence path. As a result, we have to ask, does that mean that if there are a significant number of entangled particles in our universe, that the superposition of all these fields will not interfere with each other and caused decoherence failure? Asking the question this way is powerful, because EM fields would interfere and thus cause decoherence failure. Since decoherence failure does not occur in experiments as long as entangled sets of pairs do not encounter detectors, this means that EM fields are not the means by which decoherence occurs. Of course, we already knew that due to the non-causal nature of decoherence, but we now get confirmation from another direction.
But then what is the means? What field, or other entity, is responsible for decoherence? Once again, we need to look at the assumptions in this question and make sure we don’t take an invalid turn. The fact that detecting one of the entangled pair of particles determines the state of the other implies a connection. Being careful with our semantics, the word connection implies a mediating entity. What is it? Do we care or can we just go with the fact that there is a connection and not try to understand what mediates the connection?
I now have gone full circle and the original question remains. I chose to believe that this question is a valid one to ask, I don’t see bad assumptions here, I don’t think this is a semantics issue, and the question has already led to one conclusion of what cannot mediate decoherence. Now that I have a suitably framed question, next post I will explore some possible answers. Everybody and their grandmother has asked why is it noncausal, but I’m going to ask the more basic question, why doesn’t the effect disappear over distance?
Agemoz
Agemoz's Physics Blog 
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