This is, I think, the book on quantum mechanics I've been wanting to read for 15 years—though my ability to embrace it may be due to my experience with the less-comprehensive titles I've read in the meantime. Superb, even if I did get snarled once or twice in Ball's explanations of experiments.

Interesting, though, how many shades of Kant and Wittgenstein I kept encountering. I'm not sure if that's because they've greatly influenced quantum physicists, Ball, or if I just saw them because I love them so much (in true what-I-measure-affects-what-I-see quantum style).

I also had the thought whilst reading that instead of us measuring the universe, perhaps the universe is measuring us...and trying all the time to tell us what it sees in ways we can comprehend. ( )

A refreshing new angle for me. Great that it took us through to current thinking and was about the ideas and not the personalities. Learned a lot about superposition, entanglement and decoherence - at least in flashes - way beyond my understanding in most ways but a very satisfying and interesting read. I definitely want more of these up to date books as the subject evolves. ( )

Actually, this is a really good book. I've read stacks of (popularised) books that purport to unravel the secrets of quantum theory and leave me feeling dudded at the end. I didn't come away with this feeling from Philip Ball's book, although I still feel somewhat dissatisfied. (Then Einstein and a host of other brilliant scientists seem to have come away from quantum theory feeling dissatisfied). And this is a point that Ball makes very well.
He takes us through many different interpretations of quantum behaviour ....and, I guess, the main distinction one can draw between them is A). along the lines of "shut up and calculate".....in other words just focus on the mathematical equations that purport to give us the right answers and ignore what this 'really" means in terms of particles or waves or the world that we know...and B). the other view of quantum theory which says that there must be some underlying reality behind the equations. That is, the equations actually point to some real "stuff" or the way the universe is structured.
I think it's pretty clear at the end that Ball is coming down on the side of realism........and must admit that I feel the same way myself. But with quantum behaviour one has to ask whether your own mental conditioning just pre-disposes us to this way of thinking and can it actually be justified by what we find?
Various interpretations of quantum behaviour are discussed:
1. David Hume: When A is invariably followed by B we may infer that A causes B but never be really sure about it.
2. Immanuel Kant: We have no access to the world that is not mediated by experience....we can only know the phenomenal world not "the thing in itself".
3. Max Planck...Black body radiation comes in 'lumps" ...quanta.
4. Albert Einstein 1905 .....light comes in quanta...and behaves as a particle and a wave.
5. Louis de Broglie...(French) 1924, proposed that quantum particles might display wave-like properties.
6. Erwin Schrodinger developed a wave equation..(function) that describes quantum behaviour remarkably well.
7. Max Born...(German) argued that the amplitude of the wave function squared indicates a probability.
8. Werner Heisenberg...developed matrices from the properties of objects ...showed that certain properties don't commute. Generally, Heisenberg resisted the temptation to give a physical interpretation of the maths.
9. The Niels Bohr (Copenhagen interpretation)......wave collapse when observed. Actually many variations on the basic theme that it tells you what questions you can legitimately ask.
10. Einstein, Podolsky, Rosen (EPR) proposal was that without hidden variables the Copenhagen interpretation faced a paradox....(spooky action at a distance). So, they claimed the Copenhagen interpretation was incomplete.
10. David Bohm (American) 1940's, hypothesised a particle plus a (pilot) wave which guides the particle's motion.
11. John Bell (Irish) 1964, ...repeated measurements of entangled particles ... measuring the correlation. Purely quantum correlations can be stronger than those permitted by hidden variables.
12. John Clauser and Stuart Freedman (Berkley)1970's, did laser experiments to test Bell's ideas. The experiments seem to rule out hidden variables.
13. Alain Aspect (Paris) ....entanglement fits with quantum mechanics but not hidden variables.
14, Alain Aspect, also Austrian researcher (1998) checked possibility of a signal slower than light might be influencing (the Communication loophole) ...found no change in outcome of experiment.
15. Freedom of choice experiment (pre-programming in the entangled state) 2010, Canaries Islands source of photos and detectors on different islands...also ruled out hidden variables.
16. Anton Zeilinger (Vienna) 2013, captured about 75% of the photons...thus ruling out non-representative sampling.
17. Ronald Hansen Netherlands, 2015, excluded both the communication loophole and the detection loophole at the same time by measuring entangled electrons.
18 Juan Maldacena ...from a simple model of the quantum universe a phenomenon like gravity emerges spontaneously from the mere existence of entanglement. Or spacetime and gravity in the 3D universe look like a projection of the entanglement existing within its 2D boundary surface. (This seems to me to be worth exploring further but Ball doesn't do this).
19. Kochen and Specker 1967, pointed out that the outcomes of quantum measurements may depend on their context. (If you look at a quantum object through different windows you see different things).
20 Dagomir Kaszliowski (Uni of Singapore) has suggested that quantum non-locality and contextually are ultimately expressions of the same thing: Different facets of a more fundamental "quantum essence". He showed that non-locality and contextually seem in fact to be mutually exclusive .......can't exhibit both features at the same time.
21. Quantum objects have a wave nature which gives rise to phenomena like interference, superposition and entanglement. These behaviours become possible when there is a well defined relationship between the quantum 'waves': in effect when they are in step. This coordination is called coherence. Macroscopic , classical, objects don't display quantum interference or exist in superpositions because their wave functions are not coherent. And measurement appears to collapse coherence. And quantum decoherence is essentially a one way process. The pieces of the puzzle for all practical purposes have been scattered so widely that they are lost. For objects approaching the macroscopic scale, decoherence is to all practical purposes, instant and inevitable.
22. Wojciech Zurek, Los Alamos 1981-82 awakened interest in decoherence.
23. Serge Haroche (Paris), 1966, showed decoherence experimentally.
24. Anton Zeilinger and Markus Arndt Vienna, 1999, showed decoherence with entire molecules (buckyballs).
25. Wojciech Zurek and Bill Wooters have shown that in a double slit experiment it is possible to get some information about which path a photon took without losing all quantum interference. Measurement isn't an all or nothing process ...it's a matter of degree. Zurek calculated that a grain of dust one micrometer in size after being illuminated by the sun for one microsecond will have its location imprinted about 100 million times in the scattered photons...Some quantum states (like position) are better at creating replicas than others. Zurek et al have called this quantum Darwinism and it's what tends to get measured...and it's gathering of information that altered the picture ....not so much the role of the observer.
26. Zurek (again) ...By looking at two objects as a pair you can deduce more information than looking at each individually. This information that is encoded in the pair is a measure of their "quantum ness" and Zurek calls it quantum discord. For a classical system the discord is zero but if it's greater than zero the system has some quantum-ness.
27. Ignacio Cirac and Oriol Romero-Isart (Max Planck Institute) have outlined an experiment for putting viruses of tardigrades in superposition states. Some researchers are trying to coax superpositions states from nano mechanical resonators.
28. One argument is that classical physics emerges from quantum physics when measurements become imprecise ...as they must for large systems. (Coherence can't be seen anymore).
29. Anthony Leggett and Anupam Garg, 1985 proposed some ground rules for macro-realism: the idea that objects will behave in this realistic way. Several experimenters have recently shown the macro-realism is indeed violated for relatively small systems.
30. Hugh Everett II (1957) proposed that the entire universe is described by a universal wave function and as the universe evolves some of the superpositions break down ...so that two realities are produced from what were just potentialities.
31. Bryce de Witt 1970 publicised Everett's ideas in Physics Today. This requires parallel universes. A Multi Worlds Interpretation (MWI)..
32. Max Tegmark MIT, has suggested that all possible states exist at every instant...meaning that everything that is physically possible is realised in the parallel universes. And the act of making a decision (measurement) causes a person to split into multiple copies.
33. Some questions need to be asked about this MWI. For example how is splitting achieved when it's not implied by the Schrodinger equation. Answer: It evolves through decoherence...and more akin to salad dressing separating into layers than to bifurcation of worlds. But there must be a dizzying number of splitting events. Main advantage is that it dispenses with the mysterious collapse of the wave function.
David Deutsch, 1980's suggest that it is the only plausible interpretation of quantum theory. Ball is not convinced. Objection one: it doesn't seem plausible ...is no real objection. Objection 2: (Roland Omnes) every little measurement spawns a new world....gives too much importance to the little difference generated by quantum events. Objection 3: what can it mean to say these splittings generate copies of me. Brian Greene insists that each copy is just "you". The real you is the sum total. Lev Vaidman suggests that the "I" is defined by the complete classical description of his state of body and brain but consciousness is required and consciousness relies on experience and experience is not an instantaneous property . It takes time.You can't locate consciousness in a universe that is frantically splitting countless times every nanosecond. David Wallace has argued that the notion of "I" can only make sense if identity/consciousness is confined to a single branch of the quantum multiverse. (Seems like it's dismantling the whole notion of selfhood). Ball suggests the a convinced Everettian should always be prepared to play quantum Russian roulette where you either die or become a billionaire ...because one of your future selves will always become a billionaire. Ball suggests that people won't do this because it's "cognitively unstable " (Sean Carroll's words). Vaidman suggests that there is a "measure of existence" in which one of the many worlds "exists less" . Seems a barren proposal to Ball...and to me. What MWI denies is the existence of facts at all. It replaces them with pseudo facts. (We think this happened, even though that happened too). So no coherent notion of experience. Where are all these other worlds ....usual answer in Hilbert space... But it's a piece of maths...not a place. Asher Peres says quantum phenomena don't occur in Hilbert Space they occur in the laboratory. Tegmark puts it as " the the equations are more fundamental than words". But, Ball suggest, this is saying there are neither facts nor a "you" who is observing them. It tells us not to trust empiricism at all. And, in the end, where the MWI keeps saying everything you say is true, you have said nothing.
34. According to Ball, increasingly, it looks more logical to frame quantum mechanics as a set of rules about information: what is and is not permissible when it comes to sharing, copying, transmitting and reading it.
35. Sandu Popescu and Daniel Rohrlich (1990's) ..."super-quantum"....."Why, if things could be more strange (without breaking known laws) are they NOT so? They proposed boxes which permit more non-local exchange of information than is granted by quantum mechanics ...still without violating relativity. Ball suggest that we should be looking at how efficient communication in nature can possibly be.
36. Marcin Pawlowskiof Uni Gdansk has proposed information causality..that singles out what quantum correlations do and don't permit about information transfer. That is, it might be an axiom of quantum theory.
37. The search for fundamental quantum axioms is the project known as quantum reconstruction...rebuilding from scratch. If we could only find the right perspective, all would be clear.
38. Lucien Hardy 2001, postulated some probability rules that linked the variables characterising the state of a system to the ways we might be able to distinguish the value of these variables by measurement. They are just a modification of standard probability theory. Other workers have shown how various sets of axioms, along similar lines can give rise to characteristically quantum behaviour.
39. Jeffrey Bub of Uni of Maryland says that quantum mechanics is fundamentally a theory about the representation and manipulation of information, not a theory about the mechanics of non-classical waves or particles. (Not everyone agrees with this ...John Bell didn't). Bub's ideas come down to a question about the LOGIC that applies to quantum mechanics...if the algebra of the equations doesn't commute ....if the order matters....you get a quantum type theory. I might say here, that the logicians have long contemplated various systems of non classical logic that could embrace quantum behaviour (eg Reichenbach's (1944) proposal for a 3 valued logic...Supported by Putnam 1957: ...see Susan Haach's "Philosophy of Logics" 1978).
40. Clifton, Bub, and Halvorsen have proposed three no-go principles for quantum mechanics.and have shown that from them we can deduce a great many of the behaviours such as superposition, entanglement, uncertainty and non-locality at the heart of quantum theory.
41. Quantum Baysian or QBism was formulated by Carlton Caves, Christopher Fuchs and Ruediger Schack in early 2000's. Here all quantum mechanics refers to are beliefs about outcomes----beliefs that are individual to each observer. These beliefs do not become realised as facts until they impinge on the consciousness of the observer. So facts are specific to every observer. QBism is an expression of what John Wheeler called the 'participatory universe'..in which we play a part in the reality that we experience. I think at this stage that Ball seems to dissolve into quasi mysticism...and leaves me dissatisfied....not so much that I feel dudded but with the conviction that the physicists don't have the answers.

So bottom line is that I've come away from this book with a clear conviction that none of the theories advanced so far are really satisfactory. So I am not going to find out "what is real" by reading Adam Becker's book of that title. Nor am I going to understand "spooky action at a distance" by reading George Musser's book by that name. Nor will I get the answers from Brian Green's book "the Elegant universe". I've read two of these three books l and came away dissatisfied but, at least from Philip Ball's book I come away more convinced than ever that none of these physicists really has the answer. The best hope from my perspective seems to lie with the project for quantum reconstruction (see item 37 above). One of the more telling paragraphs in the book is (p 322) that any meeting about the fundamental principles of quantum mechanics is like being in a holy city in great tumult. You will find all the religions with their priest pitted in holy war.

I haven't mentioned Ball's digression into quantum computing but he has a few interesting asides: Nobody understands how quantum computers work. Many theorists suspect that the real key to quantum speed up is entanglement not parallel worlds. p263. It remains a challenge to find problems, besides factorisation and searches that quantum computers would solve faster than classical computers. And there are so few tried and tested quantum algorithms ..and some researches think that they might be niche devices : brilliant at some things, no better than their classical counterparts at others.
Bottom line. Ball has written a really informative and helpful book. An easy five stars from me. ( )

I always try to get alternate viewpoints from as many scientists as I can. I also enjoy sorting out my understanding of quantum physics, searching for better stories, better analogies, and just... BETTER. This book is one of the BETTER. It may not be as charming as some and I don't mind how it skimps on biographies and jumps right into the SCIENCE, but it does fall short in outright describing the math. (That may be a good thing for some. Especially if you're not in the mood to crunch math.)

To be certain, this text goes beyond the everyday norm and focuses on the science. The ideas. The concerns. And it's all in the service of demystifying it all.

Quantum Physics is one of those subjects that agrees on fundamental maths but invites wildly divergent theories that make a coherent STORY of our reality. You know: Copenhagen (don't go nuts on us,) Everett (multiple-worlds), String, and more.

What we have in this book is not a biography of the physicists but an admirable attempt to make the famously weird (thank you Feynman!) as commonplace and normal as can be.

I mean, we're human, and humans are most famous for turning all things truly fantastic into the stunningly banal. :)

And this is exactly what this book tries to accomplish. Step by step, it demystifies the very small particles, removes the term spooky action, and naturalizes all things entangled.

It gives time to the various big-action theories that align the quantum with the macro, and all of this is pretty good if not as good as some other books that cover these topics, but what this book does best is describe the current technology of quantum computers. It doesn't shirk the shortcomings of our descriptions or the limitations of the process. This isn't a PR job by prospective companies trying to sell you a 100k computer.

BTW quantum computers ARE on the market now. Some developers are working on cheaper versions. What are they really good at? Factoring prime numbers.

Thank goodness! That's great for all you hackers out there! PGP MAY need a booster soon. :)

While this one doesn't always come close to the charm I'm used to in popularized physics books, I really have nothing bad to say about the contents. ( )

A great book exploring the latest thinking on the meaning of quantum mechanics, one of the the strangest and most rigorously tested theories in all of science. Philip Ball steps through some of the key concepts of quantum mechanics, such as superposition, entanglement and decoherence, explaining what the latest research has to say about them. He also reviews the main historical interpretations of quantum mechanics in the light of the latest research and shows their failings. He covers the Copenhagen interpretation put forward by Niels Bohr in the 1930's, and the many worlds view developed by Hugh Everett in the 1950's, amongst others.

Philip Ball also outlines recent developments that are taking the understanding of quantum mechanics in a different direction. In the course of this he dispels a number of myths about the theory, many of which we originated with founders of the theory in the 1930's and 1940's. For example, he explains how the uncertainty principle is not about the perturbation caused by measurement as Heisenberg originally popularised it.

I have always been fascinated by quantum mechanics, and particularly it's philosophical interpretation. This book has changed my view of how to understand the theory. A great read. ( )