Quantum Space: Loop Quantum Gravity and the Search for the Structure of Space, Time, and the Universe by Jim Baggott (PDF)

Description

Combining clear discussions of both quantum theory and general relativity, this book offers one of the first efforts to explain the new quantum theory of space and time.Today we are blessed with two extraordinarily successful theories of physics. The first is Albert Einstein’s general theory of relativity, which describes the large-scale behaviour of matter in a curved spacetime. This theory is the basis for the standard model of big bang cosmology. The discovery of gravitational waves at the LIGO observatory in the US (and then Virgo, in Italy) is only the most recent of this theory’s many triumphs. The second is quantum mechanics. This theory describes the properties and behaviour of matter and radiation at their smallest scales. It is the basis for the standard model of particle physics, which builds up all the visible constituents of the universe out of collections of quarks, electrons and force-carrying particles such as photons. The discovery of the Higgs boson at CERN in Geneva is only the most recent of this theory’s many triumphs. But, while they are both highly successful, these two structures leave a lot of important questions unanswered. They are also based on two different interpretations of space and time, and are therefore fundamentally incompatible. We have two descriptions but, as far as we know, we’ve only ever had one universe. What we need is a quantum theory of gravity. Approaches to formulating such a theory have primarily followed two paths. One leads to String Theory, which has for long been fashionable, and about which much has been written. But String Theory has become mired in problems. In this book, Jim Baggott describes “the road less travelled”: an approach which takes relativity as its starting point, and leads to a structure called Loop Quantum Gravity. Baggott tells the story through the careers and pioneering work of two of the theory’s most prominent contributors, Lee Smolin and Carlo Rovelli.

User’s Reviews

Editorial Reviews: Review “…if you have enjoyed/got through popular science books about such areas as strings and superstrings, time, and the God particle, here is a fine addition to the oeuvre.” — Ian Francis, School Science Review”There is no doubt that Jim Baggott is an excellent popular science writer, and Quantum Space is the first complete and approachable account to a quantum theory that delves deep into the quest to resolve one of the great unanswered problems of modern physics: How can general relativity be made compatible with quantum mechanics? Baggott proposes Loop Quantum Gravity, which in our mind is one of the best explanations for anyone who wants to understand more about our puling universe … It’s a triumph.” — All About Space Magazine”The discovery and development of Loop Quantum Gravity has been a great adventure. Jim’s story beautifully captures its insights and excitement.” — Carlo Rovelli, author of Seven Brief Lessons on Physics About the Author Jim Baggott, Freelance science writerJim Baggott is a freelance science writer. He was a lecturer in chemistry at the University of Reading but left to work with Shell International Petroleum Company, and then as an independent business consultant and trainer. His many books include Quantum Reality: The Quest for the Real Meaning of Quantum Mechanics DS A Game of Theories (OUP, 2020), Mass: The Quest to Understand Matter from Greek Atoms to Quantum Fields (OUP, 2017), Origins: The Scientific Story of Creation (OUP, 2015), Higgs: The Invention and Discovery of the ‘God Particle’ (OUP, 2012), The Quantum Story: A History in 40 Moments (OUP, 2011), and A Beginner’s Guide to Reality (Penguin, 2005).

Reviews from Amazon users which were colected at the time this book was published on the website:

⭐Quantum Space takes a look at a less written about physical theory trying to tie together general relativity with quantum mechanics called Loop Quantum Gravity. As a field with a few key pioneers the author spends most of the book following the careers of three men, Smolin, Ashketar and Rovelli, with a focus on Smolin and Rovelli. The book definitely tries to communicate details of the theory to the casual reader and give as intuitive a feel for this esoteric subject as possible, with mixed results.The author is a chemist by training but has a strong history with science for a general audience and I have read his book on quantum theory which I found readable and informative. The author comes with an empirical view of physics and is a skeptical of some of the physics explorations of modern times that seem to be pure mathematical exercises where there are no actual predictions that can be made as the space of solutions seems unbounded. With that skepticism of string theory the author tries to discuss an alternate path to a unified theory, namely loop quantum gravity. The author gives a partial biography of Smolin and Rovelli and describes them as rogue physicists with brilliant flares focused on paving new roads in physics. The author gives the background of their early work and how they met and the early personal bonds formed. The author describes the challenges of a quantum theory of gravity and discusses how quantum field theories treat spacetime as a background vs general relativity which defines the structure of spacetime. The author discusses how loop quantum gravity attempts to quantize space rather than quantize the carrier of force of gravitation and this is a fundamentally different approach. The author gets into details of how the ideas were taken from lattice models from quantum chromodynamics but instead of that being a way to calculate approximate solutions, quantizing space was seen as a way of describing physical space exactly. The author weaves in Penros and spin networks, which turned out to be a way to further improve the model. The author discusses a lot more than just LQG and brings together developments in string theory and how the communities talked or rather didn’t communicate. He also brings up works like “Not Even Wrong” to frame what one should be trying to achieve as a physicist. I can’t say the book follows a natural path and is always coherent. The author spends time discussing particular issues plaguing all of the theories and then what kinds of solutions are considered and weaves in philosophical issues. The author seems to have strong views on the nature of quantum theory which comes out in his praise for the view of Rovelli but at results are mixed as aspects of loop quantum gravity seem just as metaphysical as string theory currently is. The author seems to be interested in promoting other modern unified theories away from super-symmetric and string theories, but in writing the way he does about loop quantum gravity towards the end, the writing turns out to sound like fantasy as well. In particular the author starts to write about how one could consider the universe as self-selecting itself for the conditions of embedded black hole formation which is not support for his empiricist view of the world.There is a lot in this book on both the history of loop quantum gravity, some of the challenges it has faced in gaining any acceptance and some of the model fixes that have been employed to get it more fully baked. It is not always easy to follow as frontier physical theories require a PhD to actually understand. Nonetheless some information can be gleaned and is a fresh departure from the abundant string theory for the general reader literature. All in all though I think the writing is a bit muddled and whereas author’s like Brian Green who are experts in the field they are writing about as well as being a good popular science writer, Jim Baggot is more the latter but not the former and it shows in how he tries to communicate some of the technical details.

⭐I bought this book because I wanted to become familiar with LQG, the alternative theory to superstrings and other grand unification theories. Generally, I consider the book as good introduction to the topic.The book is divided to three parts. In the first one serves as refresher of current well accepted theories, namely special and general relativity and quantum mechanics (incl. standard model of particles). It seemed to me that especially chapter on general relativity is very brief. So, if somebody is not familiar with concepts like gravitational waves or frame-dragging of spacetime, I would recommend reading some other book about Einstein theory firstly.The second part is dealing with different theories having some potential to expand current quantum mechanics, like a supersymetry theory or superstring theory. Then the author is starting to describe basics concepts of LQG in this part as well.The third part is dedicated to application of LQG, e.g. the loop quantum cosmology is introduced (the problem of Big Bang singularity is solved here by means of LQG – I really enjoyed this part but I would welcome more discussion of consequences for 2nd law of thermodynamics). Also entropy of black holes from point of LQG is discussed.So far, it sounds good, however, there is some buts:1) The 13th chapter on alternative interpretation of quantum mechanics seemed to me very messy. The author is simply jumping between physics and philosophy to and fro.2) At few different points of the book, the author very highly criticises superstring theory and their proponents. I understand that he has a right to have his opinion, however, from my point of view, the criticising is more emotional than rational and there is huge amount of bitterness. For example, the author shows many pitfalls and problems in the string theory and for this reason he cosiders it to be on wrong footing but after few pages he presents similar pitfalls of LQG and simply state that further research is needed and everything would be all right. In my humble opinion of layman, I see many similarities between LQG and superstring. Maybe, they are both part of one grand theory.3) The author is also against of theory of multiverse. I understand this because multiverse theories cannot be falsified thus they are not scientific ones. But in the last chapter, he shows that LQG can produce multiverse as well.Especially points 2) and 3) shows that the author has choosen unbalanced approach. For this I gave only 3 stars. Otherwise, I would give four.

⭐This is a good book to begin learning about loop quantum gravity. There is hardly any math, (some in the notes) but the details can be quite profound and are best understood if you have some math and physics background. The history of how LQG develops is very detailed and involves many people, however the book mainly revolves about Carlo Rovelli and Lee Smolin who are some of the main contributors to LQG, (as is Roger Penrose for example). For myself it was a very good book to better understand the concepts involved in LQG since the mathematics and physics can be very complex. This is a good companion book to a more detailed study. The main downside is that it does heavily focus on Lee and Carlo a bit too much and you may disagree with some of the ideas that are heavily put forth in this relatively new theory. However I do believe, like many of the LQG people, that our fundamental concepts of space and time will need to change in the future to better understand things such as black holes, QM, and the BB, and this book definitely rocks the boat. Well worth reading and stimulating as well.

⭐I’m just about glad I read this but the experience was like munching slices of bland white bread. The story of Loop Quantum Gravity is told chronologically through the biographies of Lee Smolin and Carlo Rovelli. It’s the journey of those who started with General Relativity and tried to quantise spacetime. The nodes and links of LQG are not spacetime quanta, they’re precursor objects out of which spacetime, along with its metric field, should emerge in the low-energy limit.This is the fabrication of reality at the Planck scale, way down from observational data. The models are not without interest (especially the cosmological models) and the approach seems to have its compelling moments .. but .. but .. all the nasty things said about the theological or purely mathematical nature of String Theory also apply here, do they not?If you’re short of cash you could skip the book and read the Wikipedia article, though you are unlikely to understand it without a total familiarity with GR and QFT. The author had somehow to handwave his way over this cathedral of densely-connected abstractions: the “Quantum Space” reading experience is consequently pretty anaemic.I’m guessing that Baggott wrote this book because, with the continuing decline in the prospects for String Theory, he’s become convinced that there’s something to Loop Quantum Gravity and wants to raise its profile for a generation of new physicists wondering what on earth they should be devoting their lives to.

⭐Having read the book, I was going to give a great review. I found it readable — I quite like the interspersing of physics and biography. It presents some pretty hard physics in a very approachable way, which would be accessible to people with almost no physics background — though maybe it would too difficult if you’d never read anything about quantum mechanics before. The ideas in the book are really exciting, different and well presented.Then I read Lee Smolin’s Three Roads to Quantum Gravity, which is extensively quoted (and credited) in this book. It’s the same book! Really, all the ideas are the same, and not very much is added.If you like Jim Baggot’s other books you’ll like this one. There’s nothing wrong with it. But I’d recommend reading Three Roads to Quantum Gravity instead, especially as it is about a fifth of the price on Amazon.

⭐A useful but rather plodding summary

⭐No dislikes whatsoever. I found it very helpful for clarification of thinking about the basis of reality, especially time.

⭐Well written interesting book

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