From Eternity to Here: The Quest for the Ultimate Theory of Time

This book [From Eternity to Here] declares a limited scope, and perhaps depending entirely on the depth of your interest in examining the background and nature of this scope-limited problem in minute detail, spends, at least for me, a heck of a long time discussing it. The problem that is of interest to Carroll is the apparent extremely low entropy of the initial universe (relatively high degree of order) before the big bang, and the extreme difficulty there is in coming up with a cosmological theory that can explain this low-entropic state. In the course of this we are taken through just about every consideration in regard to entropy, its history in theory, its relation to the history of the universe, through Boltzmann, quantum field theory, de Sitter space, anti de Sitter space, Hawking, black holes, the big bang, an interesting interpretation of Everett's many worlds theory, and more. The explanations are good, clear and enlightening - we learn a great deal - if one can stick with it. We end, shall we say, definitely understanding the problem. Carroll is not attempting a solution - at best an outline of possibilities. But also, by the time we are done, we wonder if in fact yet another drop of understanding can (ever) be squeezed out of the concept of entropy as an explanation of time's flow or the irreversibility of little events like broken tea cups or forming eggs. It seems wrung dry - at the limit of its explanatory power.The problem, if you are not convinced that this particular "initial low-entropy" problem is worth this much of your effort in terms of this limited scope, is Carroll's strongly implicit mindset that the current framework in which physics works will produce the solution - more thinking on entropy, quantum fields and quantum gravity and black holes and information or some new thing, like inflation - just more brilliance within the current framework. In other words, it is the problems unmentioned, the assumptions still marching on unexamined, that might have made the work more interesting as an examination of the problem of time. I list just a few here:1) Carroll notes Schrödinger's book, "What is Life?" Schrödinger was completely awestruck by the enormous counter entropy flow - the massive, inexplicable organization - that organisms represent (and all structures within them, from cells to brains), especially when considered against the entropic backdrop that should dominate all things in this universe. He could find no answer in the laws of physics; he felt there must exist organizing fields (though biologists, in a discipline sans fields, routinely seem to feel they know better than Schrödinger, assuming they have solved the problem). Carroll simply uses the occasion to note that Schrödinger's conjecture on an "aperiodic crystal" that stored information inspired Crick, as though DNA solves the whole issue, and marches on, routinely and often referring for negentropic examples along the way, to things like eggs forming as though there is no mystery lurking here at all that might apply to his problem. If you want a great eye-opener on this enormous question of Schrödinger, take a look at Gunther's  Mind, Memory, Time . Here is a thinker who launches his thought from these very thoughts of Schrödinger, and has delved very concretely and deeply into these little things like forming eggs, spiders making webs, or the inner organization of a tiny virus (one can check my review).2) Special relativity has a strange status in this book. There is a legion of physicists that expound relativity for us, ultimately discoursing at length to help the dim comprehension of us pedestrian laymen on the radical "block-tme" concept supposedly inherent in the nature of STR (there is no flow of time, all is laid out in a block - past, present, future). (For just some see  Hidden In Plain Sight: The simple link between relativity and quantum mechanics , Time Reborn: From the Crisis in Physics to the Future of the Universe ). Carroll, constantly concerned with the - what by this version of STR should be completely mythical - flow of entropy, never discusses this STR-topic at all. There is one tiny mention, and this only to the effect "if closed timelike curves could exist, we would have a definitive answer to the debate.... The eternalist block universe would win hands down..." So why not come clean here? Everyone else says the STR-based notion of block time is an inescapable conclusion. Yet Carroll apparently is unconvinced. Why? This happens to be a profound problem at the core of physics. It began with Langevin's announcement of the twin-paradox in 1918, where the "changes of time" in STR were now taken as ontological - the aging of the twin having a real, physical status. Yet physics had accepted relativity and its explanation of the Michelson-Morley results as treating the "changes of length" (i.e., space changes) in the apparatus arm as not real or ontological effects (i.e., an actual physical shortening of the arm in the direction of ether flow - as Lorentz had earlier postulated) but as simply measurement effects - effects resulting from the differing states of motion of observers, i.e., space changes are not-ontological. Yet in the Lorentz equations as embedded in Einstein's system, space changes integrally compensate for time changes, and vice versa. Space and time changes cannot have a differing ontological status. If these changes are taken as non-ontological - as measurement effects - then the relativity of simultaneity equally has no ontological status, and neither then does "block-time." Of course physics must now find the real explanation for real, physical, ontological effects like the increased life spans of mesons with increasing velocity or the retarding of clocks on jets. Bergson, by the way, in 1922 ( Duration and Simultaneity: Bergson and the Einsteinian Universe (Philosophy of science) ), deeply disturbed by the distortion to STR and our very concept of time that Langevin had introduced, attempted to straighten out physics, even to a discussion with Einstein and a interchange with the physicist Andre Metz ( Bergson and the Evolution of Physics ), but apparently lost the argument to the handy convenience of the illusory explanation of these "time changes" physics now had ready at hand. This issue happens to extend as Bergson noted - it extends to the very foundation of the GTR. Yet Carroll routinely refers to quantum field theory as a "marriage of quantum mechanics with STR," and I wonder then which interpretation of STR is even being referenced here in such a marriage. But at minimum, this issue surrounding the interpretation of STR, ultimately even GTR, cannot and should not be so nicely or subtly ignored in a work on the arrow of time.3) Both the above issues relate to that "framework" in which Carroll works so confidently and in which he envisions future solutions arising, for we come to the very (classic) metaphysic of motion in which physics yet works. Bergson challenged this metaphysic at the turn of the century ( Matter and Memory ), arguing for a temporal metaphysic in which each instant was the reflection of the entire preceding series of instants, as each current note reflects the entire preceding melody. It was a metaphysic in which motion is indivisible - or non-differentiable. Such a conception of time undercuts any notion of the reversibility of time as implied in the time-reversible equations of physics - a concept to which Carroll continually returns and struggles with. Yet the non-differentiability of space-time (with its consequent implications for motion) has been argued by Nottale (Chaos and Solitons, 1996), also essentially by Lynds (Foundations of Physics Letters, 2003), and at least considered as a real possibility by Davies (Information and the Nature of Reality). Imo, it is critical to the theory of consciousness, to the solution to Chalmers' hard problem, to other difficulties with relativity and likely to the difficulties in quantum mechanics. It is hard to imagine how one quite so easily escapes the subject of consciousness - as Carroll appears to do - when considering the origin of the universe and time itself.Not listed - the deep irreconciability between GTR and quantum mechanics (discussed by Kaku for the public) which indicates one of these theories is very wrong. Given the comments above, it is not hard to vote for GTR as the culprit, yet Carroll writes as though GTR - the very source of black holes - is unproblematic. Yet in all, an interesting work, but I would love to see a mind like Carroll's be willing to engage the many questions indicating need of a new framework.

This book is an overview of the time symmetry of most physics and the reality we live in where time seems to evolve in 1 direction. Sean Carroll is a world renowned physicist and so the approach is one that is defined from the implications of our physical laws themselves rather than from a philosophical perspective based on our subjective interpretation of time. Most of the book focuses on time from the perspective of thermodynamics and the second law in particular- entropy is expected to increase through time, though relativistic time and its similarity to space is discussed, as are modern theories of the origin of the universe to try to avoid assuming the problem away theories.Let me try to talk briefly on the topics the author explores. The arrow of time is not specifically a part of classical physics (newtonian physics and electromagnetism) and this is confusing as to us, time clearly only moves forward not back. The relativistic aspects of closed spacelike curves and wormholes are addressed briefly as ideas in relativity that approach time's direction, but this isnt focused on in depthly. The author approaches the direction of time as a correspondence between entropy's strict march higher and our experience with the irreversibility of time. The ideas justifying an increase in entropy are well discussed and exponential increase in states if configuration spaces are discussed. This is with the backdrop of a static universe. Poincare's recurrence theorems in dynamical systems is brought up to describe things like the eventual recurrence of low entropy states over time and Boltzmann's retorts which amount to assuming away issues are then included. The book then discusses the change from static universe in which time has no beginning nor end to one which has a beginning and how this avoids recurrence by selecting preferred intial boundary conditions of low entropy, and then the author gets into how this too is unsatisfying as it assumes the problem away again. Quantum ideas are presented, the asymmetry of the collapse of the wave function is brought up but not taken anywhere. On a side note, I still have no clarity on how a spacelike closed curve can exist in a world with quantum mechanics (excluding a multiverse scenario) as I would think that implies there is no probability which can change an event in spacetime's trajectory and the author doesnt discuss that at all. Quantum gravity is discussed at a high level and is presented as the theory which eventually will illuminate the subject though the huge fuzziness of the subject isnt really very encouraging. The book concludes with some modern theories and directions in physics which might give consistent frameworks for worlds with strictly increasing entropy which evolve into our visible universe though is careful to admit that this is all really speculation.This is a complicated book. One can probably gloss over a lot of the content and get something out of it, but most of the contents of this book are based off a lot of deep thinking by academic minds over centuries. I for one definately have not come through this book having any stronger feeling about the nature of time, though I now have a better understanding of entropy and information theory. I also think the most clear writing on relativistic time is described in this book which takes only a small portion of the space. This is not a light read, if you make it such you probably will miss a lot of what the author is trying to communicate, im sure I missed a lot of the subtelties though i was trying to concentrate while reading. I did not come out anymore clearly on- why do we remember the past? The author often makes statements about having addressed it as a result of entropy, but I really dont find a rigorous argument in this book that convinces. The state of entropy and its direction impacts the distribution of events in a probabilistic world, it doesnt imply determinism which the arrow of time has a deterministic past from our eyes. The relative entropy of the universe now and 100 years ago being higher is not a reason why we have a memory of the past and literature from the past. The specific reason why we have a flitration of measurable sets to us that is bounded by time is not convincingly shown to be a result of increasing entropy. If it was, then I wish the author spent more time on the arguments. This book is mainly about physics and how time fits in and what time's implications are on physics and then the interpretation of that physics. It is a subject for which there will likely never be a final say, this is a bold introduction to a lot of modern ideas, but dont read it lightly as its value is in the depth of the ideas presented.

Not for the beginner as it is written at a fairly high level. For me it is perfect and one of the best I have read in a while. This was my second book from this author and both were exceptional.

A thrilling excursion to some of the most fascinating -- though yet unsolved -- issues in modern physics and cosmology, already hinted at in Kant's antinomies, among others...The road to full understanding of those perplexing themes is still long and difficult, but Carroll's maestria, enthusiasm and optimism constantly drive the reader towards hope, all along.So, embark safely !

Il miglior libro che io abbia mai letto sul problema del tempo( e ne ho letti diversi!). Si basa sopratutto sulla legge dell'entropia, spiegandone molto bene il concetto e i diversi significati.Da leggere, per chi è appassionato dei problemi più grandi e profondi del cosmo e della vita.

Book itself OK, but the font - I have a perfect sight, tested this year, this is insane. I need a loop. Its basically unreadable for me. Photo attached is appendix part (really relevant) bit the main font is not much bigger. For what, for 10 pages more if font increases?

This book is a great start if you are trying to understand the cosmology of time. I must agree that one read is not enough to understand the concepts discussed in this book. However, the author is successful in explaining rather complicated scientific concepts in layman's terms.