Something Deeply Hidden is a difficult book. I had to go through it twice back to back to understand only a small fraction of all that it tries to teach and convey. Only the first two paragraphs below are a review of the book, while the rest are my reflections on what I understood, I learned, I doubt and where I disagree.The book is not for the starters. The subject matter assumes extreme pre-knowledge of the early twentieth-century quantum mechanic ideas and evolution. For those well prepared t Something Deeply Hidden is a difficult book. I had to go through it twice back to back to understand only a small fraction of all that it tries to teach and convey. Only the first two paragraphs below are a review of the book, while the rest are my reflections on what I understood, I learned, I doubt and where I disagree.The book is not for the starters. The subject matter assumes extreme pre-knowledge of the early twentieth-century quantum mechanic ideas and evolution. For those well prepared too, there is a lot in the book which could prove incomprehensible. At times, the author is deliberately vague on the concrete meaning of the Everettian interpretation, the topic at the heart of the book. At others, the discussions on highly esoteric subjects like entanglement entropy, gravity quantization, or black hole radiation are so brief that only those extremely familiar have any hope of appreciating the points made.These are the same factors that make the book a wonderful one to learn from and reflect on. There are numerous radical and intriguing points made in every section. Anything straightforward, oft-repeated or universally accepted in other popular books is almost painstakingly kept out. Even without the usual anecdotal stories of how discoveries came about or various scientists' life stories, the author can keep even the most complex subject matter quite engaging.Now on to my thoughts and importantly, disagreements based on what I understood. I am an amateur on the subject. All my knowledge is non-technical and from popular books. The arguments must be full of errors. If nothing else, the amateurish language could cause many purists to suffer heart-attacks. However, it would be an unpardonable waste if I don't put down my thoughts after reading such a gem.A. Let's start at the beginning. The world is quantum.The book makes this point thoroughly. In common parlance, at the most fundamental microscopic level, fields, particles, space, and time are all digital. Nothing is continuous or analog. Let's call these basic quantum blocks of fundamental entities generically as "quantas" for the rest of this review.B. The quantum world is also randomThere is a probabilistic nature to the behavior of these quantas, including fields. This, in itself, is not random as quantum mechanics does a fantastic job explaining the contours of the probable modes of most quantas. However, somewhere - or somewhen - quantas move away from a superposition of probable modes or potentialities to definite states or actualities. We have little knowledge of how a particular mode comes into existence at the elimination of all other potentialities and what drives the transformation.In simpler terms, our world is a giant, unpredictably shape-shifting wave function. The function is fairly well known/knowable when the world or its constituents are in their probabilistic modes. The reality we experience is a single manifestation at micro and macro levels. We have no methods to understand how potentialities transform into specific manifestations.C. Does everything have to have human language epistemology?Quantum Mechanics works. The world is perhaps quite sufficiently described in its mathematical equations. Yet, understanding it, or converting the mathematical equations into a human language form has been proven impossible. The book tries hard by relying on the Everettian "conversion" for a common man understanding. It imparts a lot of knowledge and fails in even more!Before we return to some of these problems, we need to ask the question not asked in the book: is quantum mechanics necessarily understandable beyond its mathematical equations? Not everything is explainable in every language. Math cannot describe human feelings through equations. We do not attempt rational, existential discussion on why certain DNA base pair combinations result in certain diseases. No philosophers have spent a long time asking why hydrogen and oxygen molecules combine to give a water molecule of characteristics we observe. Many practitioners strongly believe that quantum mechanical equations are also in similar ontological domains. In their views, one cannot do much better than observe and learn from the details. Asking why for every quantum equation evolution is not much different from asking why on every phenomenal emergence one experiences in physics, chemistry or biology. The attempted human language answers appear silly to all but most ardent fans. The skeptics also wonder whether these forced and imposed - always unproven if not unprovable - understandings have any ability to enhance the real science. The proponents strongly differ, mainly on account of the failure of the theory in explaining gravity. The proponents feel that epistemological progress would help narrow the search on how we move towards the more encompassing theories, the way early-twentieth-century scientists did.D. The collapse, the entanglement, the decoherence, and so many words!As explained above, the epistemologists are stuck on the quantas' transformation from probabilistic stages to actual states. Experiments have repeatedly thrown highly counter-intuitive or unorthodox outcomes that do not require changes in the mathematical expressions but make our human language based understandings appear like deeply flawed. The explanations of the earliest and most famous such epistemologists, widely referred as the Copenhagen interpreters, are by now comprehensively dismissed. They mumbled about the "collapse" of the "probabilistic wave function" with "observations" of a "conscious" mind into a "particular state."To a cynic, The author's favorite Many World or Everettian interpretation does little other than have a new set of words...about the "decoherence" (instead of a "collapse") of a "many world in superimpositions" (another word for probabilistic wave function) with "entanglements" with "macro environment" into "many world states" of which only one we can observe.E. What is decoherence? And what is entanglement with the macro environment?One place where many world interpretation is different is in its post-collapse outcome: the branching and the existence of many worlds after the decoherence. Let's return to this vital difference later.To eliminate the Copenhagen consciousness, Many World resorts to entanglement with the macro environment without ever defining any of the terms. Decoherence explains hardly anything more than collapse based on what I understood in the book. If any interaction with the environment causes decoherence, one or both of the following issues arise:Environment or macro environment - that causes the entanglement, which leads to the decoherence - is everywhere as such. There is no existence without environment so when do quantas actually entangle and when do they not? Why do we observe any interference in a double slit as some or the other environment element should have "entangled" the spreading wave function even in the absence of observation devices and caused the traveling quantas' wave functions to decohere the way they do with observation devices? Or why are observation devices the right enough macro "environment" with which quantas entangle and decohere but your atmosphere in the lab is not?From a decohered state, when does a single field or particle recohere and again exhibit wave-like properties? Without recoherence, everything should have decohered right at the first Big Bang moment when everything interacted with anything or everything else and it was one big, thick environment where quantas had little space to be all alone in the cohered state?F. Many Worlds: what do they do?Everettians strongly believe in branching and continuous existence of probabilistic modes post the decoherence - although no longer in superposition post the entanglement but in their splendid and parallel isolation.And they fail to see why the rest of us fail to see the futility of creations of 2^10^122 or more worlds?Our world is a state of the evolving universal wave function as it settles on a set of actualities from erstwhile probabilities. Many World either means the other potential actuality sets are in existence and evolution or simply a convenient way of thinking. The author and his Many World believing philosophers deliberately choose not to answer this simple question of belief one way or the other.If the near-infinite or infinite parallel worlds are uncountable, unobservable, and unusable, how are they any less fanciful or more useful than the Copenhageners' consciousness? One spends an enormous amount of time debating the size of the Hilbert Space rather than trying to guess the theories that might attempt to explain the collapse and the observed state after.Everettians claim that their interpretation is an austere quantum theory. It allows one to accept the quantum field equations as fully explained without the need to add any more variables. One wonders how this is different from the "shut up and calculate" practitioners when the interpretation is so much nothing more than just a set of fanciful, untestable words.Alternate theories that rely on only observations or attempt to introduce an additional probabilistic function for decoherence make far more sense.G. Entanglement entropy is not the same as ordinary entropyThe author goes at great length in drawing parallels between thermodynamic entropy with a relatively new quantum concept of entanglement entropy. There is a fascinating chapter of a discussion between Alice and her Dad where the author asserts that entanglement entropy, as driven by the entanglements responsible for decoherence, was low to start with and is continuously increasing. Despite the strong arguments, this might be a promising and extremely unbaked concept. It is anything but a proven fact like the celebrated thermodynamic counterpart.Quantum theory, as we know, is yet to accommodate gravity. It is a theory of particles in a particular space rather than one of space. It treats time differently within this space. It does not have any flexibility as it stands now to equate time to space. The author does well in stretching the theory of quantum fields to speculate on how gravity could come in. But the discussion turns extremely cumbersome due to the lack of concrete evidence as the final chapters wear on.Quantum fields don't have a single wave function as a classical field. A quantum field has modes of different waves with the modes having their own probabilistic quantum wave function. They decohere randomly to assume a specific observed classical field quation with entanglements although these field entanglements/decoherence are even less specified than the much-discussed quantum particle decoherence. In quantum entropy, the author begins by describing how quantum fields are entangled with other quantum fields and defines distance (and hence space) as the level or the extent of entanglement between fields. The approach is used to conjecture how gravity could come in with this method in the same global wave function. I hope to read the author's future work, where he further develops the details of decoherence and entanglement or entanglement entropy to overcome all the doubts I have at the end of this book. A great new subject matter, but incomplete.

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