Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime Kindle Edition

Sadly, it seems, the quest to make sense of quantum mechanics is not a high-status item in modern physics, and in some quarters, it is even disparaged, according to Carroll. Let this not stop the author from pursuing this matter in more detail. There are three main messages conveyed by the book: it should be understandable, real progress has been made toward understanding it, and thirdly, all of this really matters.We are introduced to some basic concepts such as the measurement problem, the wave function, probabilities, and amplitudes associated with the wave function, Schrodinger’s equation, which then leads to a discussion of what is called austere quantum mechanics or AQM. This is more commonly known as the Everett or Many-Worlds model. In a measurement, we are dealing with one wave function, which includes the object of measurement (perhaps an electron) and the measurement device. The Everett formulation basically states every version of quantum mechanics features just two things: the wave function and Schrodinger’s equation, which governs how wave functions evolve in time. These ingredients “provide a complete empirically adequate account of the world.” Reality is described by a smoothly evolving wave function and nothing else. There is a lot to learn here. We gain an understanding of Planck’s discovery of the connection of energy to frequency, which leads to Planck’s constant, the Planck length, and Planck time. In a subsequent chapter, we learn that position and momentum don’t even exist at the same time. There is a spread of possibilities for both quantities, neither having a definite value- very strange. This leads to what is called the uncertainty principle. “If position is concentrated near some location, momentum is completely undermined, and vice versa.” Then there is complementarity, which allows more than two ways of looking at a quantum system. For example, electrons can have particle-like or wave-like properties, just not at the same time. One of the degrees of freedom (explained in the book) is spin. The author’s discussion on this is interesting, if not a bit confusing to me. The next discussion is on entanglement and a feature of this is the no-signaling theorem.In section two, we delve more deeply into the Everettian world. Here every part of the universe is treated according to the rules of quantum mechanics, including the observers within it. There is a single quantum state, what Everett called the “universal wave function.” There is no Copenhagen collapse of the wave function or classical realms. The measuring apparatus itself evolves into a superposition, entangled with the state of the thing being observed. In this case, the other possible measurement outcomes exist. This is ultimately interpreted to mean branching into separate never-to-interact worlds. The collapse we see is only apparent, due to dechoerence splitting of the wave function. In a subsequent chapter the author discusses why probabilities enter into things considering that the Schrodinger equation is perfectly deterministic. In Chapter 8, we are given more insight to this many-worlds idea via a discussion between a hypothetical Alice and her father. Following this, we learn of some alternatives to the many-worlds theory. Three competitors are discussed: dynamical collapse, hidden variables, and epistemic theories. There some other theories that the author discusses, such as Bohmian mechanics, which posits hidden variables; and there is the epistemic approach, an example of which is QBism.By section III, we get into a discussion of space and the concepts of emergence and locality. We obtain an interesting take on what the “vacuum” means in quantum field theory. There is a lot to learn here if you are unfamiliar. I could probably reread some of these sections numerous times until it all sinks in. An interesting point made here is called the cosmological constant problem: the quantum contribution to the vacuum energy (including only contributions of wavelengths longer than the Planck length) gives a finite answer which is ten to the 122nd power greater than the value actually observed. Another interesting point is that empty space is “described by a stationary, unchanging quantum state, where nothing is happening from moment to moment.” This is contrary to the notion that the vacuum is full of “quantum fluctuations.” By page 268 of the book, we begin to leave the edge of what is safely understood and venture into uncharted territory. There is some discussion of black holes and entropy; we learn of the Bekenstein-Hawking entropy, for example, and that black holes have a special property: “they represent the highest-entropy states we can have in any given size region of space.” We also learn that gravity changes things. The author states that gravity leads to a “finite number of quantum degrees of freedom,” which “implies a finite-dimensional Hilbert space,” that in turn, “implies that there is some finite number of branches of the wave function.” This would make the number of worlds in the many-worlds theory finite not infinite. Piece of cake!As you can see, the reading level for this is a bit difficult unless you have some learning in the field. So, in conclusion, it seems that “we reached a point where it is no longer practical to draw a bright line between the quantum and classical realms. Everything is quantum.”

In this book, Sean Carroll does a good job explaining quantum mechanics for persons not schooled in this subject. But when it comes to his arguments in favor of the Many-Worlds interpretation (MWI) of quantum mechanics, I believe he falls well short of what could be termed “full disclosure.”MWI is an interpretation favored by materialists because it retains determinism and seems to avoid the need for some sort of non-physical entity such as mind or consciousness to collapse wave functions. And Carroll is certainly one of the most outspoken proponents of the materialist worldview (although he labels himself a “poetic naturalist”). So it is natural that he might favor this interpretation of QM that was first postulated Hugh Everett III in the 1950s and says that every time we make an observation the world branches, and there is another copy made—one in which, for example, the electron is spinning clockwise and another where it is spinning counterclockwise. Therefore each of us exists in countless worlds, all real, but slightly different. Some of the implications of MWI are as follows:• This universe is constantly splitting into a stupendous number of branches (perhaps as many as 10 to the 100th power)—resulting from measurement-like interactions between the myriad components of the universe. Moreover, every quantum transition that takes place in every corner of the universe is splitting our local world on Earth into countless copies of itself.• Although MWI predicts an awful lot of universes, these cannot interact with one another, and therefore there is no way to know if they actually exist. Hence, it is untestable and unfalsifiable, which makes this interpretation of QM speculation, not science.• MWI denies a singular self. Our notion of self is also split, and we exist in multiple worlds. Our self can be considered a tree with countless branches. Each version is slightly different with different life experiences and outcomes. The further we go from this moment in time the greater the differences in the life histories of our various selves. Our perception of only existing in one universe is illusory. The reality is that we exist in countless worlds.• The wave function is real—not just a theoretical thing in abstract mathematical space. We might think of atoms as real, but true physical reality is the wave function. In addition, there is a wave function for the universe and it is real. Therefore, everything in the universe is entangled.• MWI appears to violate Occam’s razor, which states “entities are not to be multiplied without necessity.” On the other hand, Carroll argues it is a simplified interpretation of quantum mechanics because it eliminates the disappearance of the unobserved possibilities described by the wave function.Some of the problems with the MWI that Carroll does not talk about are as follows:• MWI presupposes a multiplicity interpretation for quantum superpositions. The basic assumption being made is that quantum superposition by default equals multiplicity. However, when you use ordinary probabilities, you are not obligated to believe that every outcome exists somewhere. For example, an electron’s wave function really may be describing a single object in a single state, rather than a multiplicity of them.• MWI tries to eliminate the need for a human element in bringing physical objects into reality by saying that splitting can occur spontaneously. However, each branch of the Many-Worlds requires a measurement at the point of bifurcation or splitting and this implies an observer. Indeed, human observation does cause splitting and the “observation problem” is not really solved by MWI. It is also obvious that spontaneous splitting is unobservable.• Experiments prove that it is not measurements that cause wave function branching (or collapse) but information about the measurement. And this information may be obtained retroactively. If measurement-like interactions are occurring all the time in the universe then exactly who is “informed” about them? This need to include the role information plays in MWI branching implies that the universal wave function postulated by the theory has a mental component.• Another problem with the MWI is that we have been split into countless worlds with their separate realities, but we are aware of only this one world. The existence of other worlds, if they were to exist, is irrelevant—we can only deal with the world we know. What this theory may actually be describing are the myriad possibilities that exist for us depending on our choices. As we make a choice, we go down one path. A different choice would lead us down another, and so forth. A choice takes us down one of the possible branches predicted by the MWI of quantum mechanics—but we only experience a single reality since it depends on the choice we make. Accordingly, there is no need for multiple realities. However, MWI is thoroughly materialistic and logically we are nothing but a bag of particles—free will is impossible. Hence, choice doesn’t enter the MWI equation.In conclusion, Carroll does not outline these faults with MWI nor point out that the theory is unfalsifiable with no scientific evidence supporting it. Hence, it would be better to call it science fiction than a scientific theory. Secondly, because it denies a singular self, MWI is best described as a metaphysical oddity. Finally, by introducing a universal wave function as the foundation for reality, it argues in favor of a cosmology of oneness, which is the hallmark of spiritual ideology. In other words, it is ironic that MWI, which is favored by many materialists because it tries to eliminate consciousness from the equation, actually hypothesizes that the universe is characterized by wholeness in which everything is connected and there are no truly separate parts—just wholeness.

Muchas gracias voy a empezar a leerlo llego 1 dia antes y esta grueso. Buen material (:

Percebi pontos relevantes nos 10 primeiros % do livros foi bom acredito que não tem tanto quanto as avaliações dizem. Fácil de ler imagino que só tenha em inglês. Recomendo de vc é mais de histórias . É introdutório e eficaz no quesito quântico caso esteja começando na área(introdutório)

A very well depicted and insightful view of the Everettian interpretation. Also, I agree, there should be more push for science to discover the 'whys' and not only the 'hows'. After all, I believe that at the core of anyone attracted by physics there is a spark of deep curiosity. Why many lost it in the process is obscure to me. The academic pretentiousness? The single minded capitalistic structure? The difficulty of mathematical enigmas and impracticality of experimentations that require full effort without distractions? Not sure, but as collectivity and individuals we should demand more. I love the way Sean Carrol approaches the topic from an informed holistic prospective that shows his incurable curiosity. As per the interpretation in itself, this is a possibility we should take into account. I wish some other advocate of different guilds wrote analogous books portraying their views in a similar fashion.

It's a shame that Sean Carroll wasn't my physics teacher. Everything explained so simply. So straight to the point. Just great!

The best explanation of quantum mechanics for the lay reader. Concepts are clearly explaiend and develop, and are nicely put into context in reference to other quantum ideas from classical ones to more modern ones. It was really fun reading it