Hello Ian, Neil Bates here. I am very impressed by the literary quality of your piece, as well as the broad interdisciplinary scope and variety of picking various conceptual metaphors and points to make. Certainly something worthy of publication in a semi-popular science education forum. I must agree that issues of language in science and even basic description of experience can't be brushed aside. Too often, authors take the material of their discussions as simple clear givens. This is so despite decades of wrangling over the philosophical problems of quantum mechanics and even the scientific method. It is important in issues of the peculiar "Renninger null measurement" where we presume a "wavefunction" must have rearranged because a detector that COULD have found a particle showed a negative result. And what about unreliable detectors? Can they have ontological significance?

I haven't seen much similar to your speculations about the effective relativity of calculation. Some would say "so what" because math is conceived as a perfect Platonic thing in itself, yet foundational mathematicians still argue over discovery versus construction, the viability of unmet counterfactuals, etc.

Also: If you or other readers might take at look at my own piece, addressing the issue of the strong correlations of entanglement and how neo-mechanistic models of quantum physics aren't enough - it could use some votes on this last day. Thank you.

    Hi Jeff, I'll try to give your essay a read this week.

    Thanks for the comments! I'm not entirely sure I agree that Müller's observation is quite the same thing as that of Susskind and 't Hooft. In the latter, the one is a holographic projection of the other, whereas in Müller's view it's not a projection of any kind. They observer states are physically distinct from the objective reality that they are observing.

    Hi Simon! Thanks for the fantastic comments! I'm so glad you enjoyed the essay. Yours is on my list to read (I'm a little behind due to the semester catching up with me).

    Anyway, I do not know of an example that violates the Principle of Comprehensibility. Since I think of it a bit like I think of the Second Law, it seems that any example would be exceedingly rare (if it exists at all). If such an example did exist, my guess is that it would only exist at the quantum level much like any potential violation of the Second Law would be.

    On the other hand, I wonder if we would even know of such a violation in that most scientists would be more likely to simply dismiss any violation as experimental error on their part. It raises a lot of intriguing questions, though, when you stop to think about it.

    Hi Luca, thanks for the thought-provoking comments. I think it is very interesting to ask whether the questions we're asking need to be classical (or produce classical answers). In a sense this is related to the question of reference frames. In asking a question, we must agree on a reference frame. Normally this is considered to be a classical concept, but there is a theory of quantum reference frames that puts limits on this. So I could perhaps see that there might be problems with this at the quantum level.

    Regarding Wigner's friend, this is also very interesting. I've spent a lot of time thinking about Wigner's friend and some related ideas and there are situations where it is possible to show (using Wigner's friend-like experiments) that it is possible to know that a fact about the world exists, and yet not be able to access that fact. It's a bit like Gödel's theorems in that you can know that a truth value exists and yet not have any way to learn that truth value.

    Finally, regarding the stability of the universe, that's a good question. I don't have a good answer for that, but perhaps your essay offers some potential ideas. I'll have to take a look.

    Hi Peter, I'm not sure how we can reduce some of these fundamental limits to infinitesimals. In fact even philosophers of mathematics still struggle with infinitesimals. This is something Flavio del Santo addresses in his essay and it's worth a read. He has to step outside the entire real number paradigm to even countenance a solution to that problem. So I don't think it is as simple as reducing such limits to infinitesimals.

    Thanks for the comments Neil. I'm not surprised that this resonated with you. I know you have long tried to make a point about our language in science. I will take a look at your essay.

    Ian,

    OK, the hypothesised mechanism seems still beyond your analytical skills. Or did having to decide or - rotation exactly at an equator confuse you? No surprise as you're in the vast majority, just a little disappointing a possible answer before our eyes still seems invisible to most!.

    Best

    Peter

    YW. BTW folks, sorry if I offended anyone by mentioning the "v" word. The deadline sneaked up on me (can I say "snuck"?) and I worried about it (and is it really EST, or EDT?) Yeah, just commenting or mentioning one's own essay is an implicit invitation to that very thing, but appearances are what they are - as we might haggle over in physics.

    "As long as the universe remains relatively stable, the first condition implies the second. The fact that the universe remains relatively stable, thus ensuring that the second condition is met in the aggregate, was originally proposed as a "principle" of comprehensibility in [7]. It asserted that the nature of a physical system under investigation will always remain within the bounds of the method of investigation. That is, we expect scientific answers to scientific questions. Of course, one could object to the use of the word 'always' as there is no way to prove this. In fact it is really a statement of tendencies within physical systems akin to the Second Law of Thermodynamics. Is it better to say that the entropy of the universe only tends to increase rather than stating that it always increases? I would rather hedge my bets and assume the weaker condition even if it has never been observed to decrease. Likewise with the principle of comprehensibility. In terms of truth-conditional statements, then, we can restate this principle of comprehensibility as follows."

    By simply asking a question, we immediately establish a context which limits the scope of the inquiry. The general stability of the universe ensures that answers to our question will, to a high degree of probability, remain within the context of the question. This is the essence of comprehensibility since it allows us to develop systematic measures by which we can further probe a topic. Building an understanding requires refining the context by asking additional questions. But this also necessarily means that our knowledge is shaped by the questions we ask and how we choose to ask them, i.e. by our methodology

    "In Newton's day, testing the truth-conditional statement "time is absolute" would have produced a positive truth value given the knowledge and technology of the time. That same statement, if tested now, would elicit a negative truth value. Yet it is wrong to say that there was any change in the underlying physics between then and now. What changed was our knowledge of that physics, i.e. we increased our information. Yet even if we take Braun's view it is clear that limitations still exist and that these limitations intimately depend on context. Our inability to simultaneously measure non-commuting observables in quantum systems to arbitrary accuracy is a limit on our ability to obtain information regardless of whether or not we believe in objective truth. It arises from the context of our measurement. Comprehensibility is still the result of a combination of the mutual agreement between observers and the fact that the universe remains relatively stable. That is to say, the Principle of Comprehensibility need not be formulated in a truth-conditional form. The fact remains that in order to say we comprehend some element of the universe we must necessarily obtain some information about that element. But obtaining that information is a physical process that necessarily has a context which constrains the nature of that information; the very act of acquiring information shapes the information acquired. Physical limitations on the acquisition of knowledge are not controversial. The universe has fundamental limits baked into it. But it is these very limits that allow for the universe to be comprehensible. They are necessary in order for our seemingly finite minds to have any hope of comprehending anything. These physical limitations bear a certain resemblance to G¨odel's incompleteness theorems in that they arise from the internal structure of the system and one must break free from that structure in order to fully understand it. The universe is a vast and interconnected place of which we are but a small part, a mere mote of dust, as it were. Any attempt to comprehend it must necessarily depend on the fact that we are a part of it. Indeed the very act of comprehension is itself a part of it and is thus shaped by it. Like the god Odin from Norse mythology, who is said to have sacrificed an eye in order to attain wisdom, our quest for comprehension limits our very ability to comprehend, and the universe remains always partially veiled."

    JP: I will rate your essay just before the time for rating expires. It is a privilege to be able to read what you write and to offer comments.

    Hi Ian,

    I found the theory of quantum reference frames is very interesting (as you might imagine after having read my essay). I heard in a talk you gave at a FQXI conference, that you are working on quantum reference frame. But sadly, I could not find any paper you published on the topic.

    Thanks also for the interest and reply on my essay. I tried to gave an answer to the point you raised about the existence of semantically closed theories, if you are interested.

    Luca

    Hi Luca,

    I have a couple of papers that I co-authored on quantum reference frames that came out awhile ago. One is in PRL and the other is in PRA. I have some long-standing plans to continue this work with some other folks, but have gotten distracted by other research over the years. But I do expect to pick it up again eventually.

    Ian

    Hi Ian,

    Thank you, any feedback would be helpful. Hope your essay does well in the judging.

    Jeff

    4 days later

    I always enjoy reading Durham's essays because he is a very smart person and knows his field quite well. Noramlly, Durham writes about consciousness and free choice (see Fxqi 2019 conference in Italy), and now about comprehension, and comprehension, of course, is a part of consciousness and free choice.

    The tell for a fundamental question is in its identity. The universe is, simply, the way that it is. Likewise consciousness is simply because we are conscious...and so comprehensibility is because we comprehend. Of course, this is much too simple and so Durham feels the need, like any good philosopher, to argue endlessly about the meaning of nothing...

    Instead of free choice and consciousness, Durham states that "...each individual is free to declare whatever they wish to declare." Oh, and a single observer is also "...free to simply deny any result..." Well, the result could be wrong, right? The result could be uncertain or it could be contradicting other work.

    Is this all Durham has? Consciousness and comprehensibility are both words that mean free choice. Free choice is the key to both consciousness and comprehension and many other complex terminologies. Without unpredictable free choice, we would not be conscious nor would we ask about comprehension...

    10 days later

    Hi Ian,

    On a final note and then I let you go. First of all thanks for your interest and your reply in my blog. Time is just the hardest thing to understand. So I think it is better to leave time as external parameter until some ideas have been clarified. This does not hinder the argument.

    In a static picture one can apply the ideas of semantically closed theories on quantum reference frames. If we have a quantum reference frame, where for physical reasons, there are only finite degrees of freedom, then only limited information on the objects can be accessed. For instance if only finite SU(2) representation are possible, than such a reference frame is not able to uniquely distinguish an up and down spin in the direction of the reference frame. This is called degradation of a reference frame. It leads to a probabilistic description even for a spin collinear with the reference frame. The probability is due to an epistemic limitation on the exact (classical) distinguishability of all the 'directions' (elements of SU(2)) and the back reaction of the object on the reference frame. So it is assumed that the real symmetry is the full SU(2) but the limited resources leads to a statistical description, like statistical mechanics.

    If we demand the theory to be semantically close and the limitation is a physical one, like the finite size of the universe or the system would collapse in a black hole, then the epistemic limitation has to be taken seriously and has ontic consequences. To close the theory, I suppose the group has to be replaced by another one, that does not pretend, that there are infinite resources. I would not know, how to do that. But I can imagine that some additional quantum effect could result from this.

    In a way, when Heisenberg went to Einstein, telling him, that only observable elements should enter the theory and Einstein replied, that it is the other way round: the theory tells, what is observable. This is true for naive realistic theory. Semantically closed theories would do Heisenberg's intuition justice, that theoretical terms should be physically realizable.

    One could play a kid's game: Kid: what do you mean by spin? Me: a finite (2 dimensional) representation of the 'rotation group'. K: What is that? M: A description, that if you measure any direction, you know how probable you find an up or down result relative to that direction. K: What you mean by 'direction'? M: This is where a gyroscope points. But one needs a infinite sized gyroscope in order to distinguish all directions and having no back reaction. K: But this is absurd. The gyroscope would collapse into a black hole. Are you explaining a concept with something that cannot exist physically.

    Thanks for the conversation

    Luca

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