To place this book in context one has to know about Einstein's vision on quantum mechanics. Einstein believed in quantum mechanics (QM) but he thought it was incomplete. In the EPR paper (Einstein, Podolsky, Rosen) of 1935 quantum entanglement was described. The wave function factored in two separate parts, so that the momentum and position of the two particles were intimately connected by some "spooky" action at a distance, exchanging information at a speed higher than the speed of light in vacuum. Einstein believed that there were some hidden local variables, not yet observable that should be taken into account. This started a war between Einstein and Bohr. This yes-no discussion between believers in Einstein and the QM adepts is still going on till the present day.

Experiments performed by groups supervised by Aspect (1982) and by Zeilinger (2007) however confirmed the existence of entanglement, hence the action at a distance. The latter was measuring polarized entangled photons at the Canary Islands Tenerife and La Palma. It was shown that there was a significant correlation between the observations, although no communication was possible. What was shown in fact was that the Bell inequality was violated. This inequality says that if variables A,B,C can take randomly any of the two values +1 or -1 (corresponding to the polarization), then AB + AC - BC ≤ 1. The experiment showed that averaging this (i.e., computing correlations), the inequality was significantly violated when A, B and C represented observations of the polarization under different circumstances characterized by parameter settings a,b and c (i.e., different orientations of the detectors): a and b on Tenerife and a and c on La Palma. Violation means that the observations are not random but there is indeed entanglement between both islands.

The book is a personal account of Hess about his attempts with his coworker Walter Philipp, and after Philipp succumbed to heart failure during a mountaineering trip in 2006, with his collaborators Hans De Raedt and Kristel Michielsen. Hess graduated in Physics in Vienna, Austria, and is now retired professor from the University of Illinois, Urbana. Philipp also was Austrian, specialized in probability theory and a colleague of Hess at the University of Illinois. Together, they have published several papers refuting the application of the Bell inequality to prove the non-locality of QM. Their main point is that the inequality only holds if all the stochastic variables are independent. However, in their opinion they are not because the hidden local variables that are not taken into account is time, or spacetime in a more general setting. This would explain the violation of the inequality in the experiment without the need for the spooky action.

Hess gives a chronological account of his collaborating conquest of the material. Their publications got opposition from the QM establishment, and not always in the most amicable or respectful way. The material of course is not very simple, but Hess avoids a mathematical treatment and explains again and again with different analogies and rephrasings that it all comes down to countering their opponents with the dependency on spacetime. To read the text, one is not required to know anything about relativity theory or quantum mechanics. Just adding plus and minus ones suffices. At some point Hess explains the basic notion of probability and stochastic variables, but that is about the most 'difficult' part. On the other hand conditional probability is not really explained and the very nature of the physical and mathematical background is largely handwaved and that leaves you as a reader somewhat in a foggy oversimplification of what is actually going on and the discussion of the successive papers seem to repeat the same thing all over and over. One could of course consult the actual papers to know their actual contents.

Another little bombshell is thrown in the QM camp when Hess discloses that Boole had an inequality equivalent to the one of Bell one century earlier. That appears in his later work with De Raedt and Michielsen. Here the discussion treats also commuting operators and macroscopic realism (the moon is there also when it is not observed). Big words, but nothing to be afraid of as an unexperienced reader.

The account is interlaced with personal anecdotes, friendships that were built up during his collaboration and the problems he and his wife had to go through when in 2006 Philipp died, he retired from the university, and they moved to live permanently in Hawaii. Also the unpleasant experience with a paper that got positive referee reports, but was nevertheless rejected for publication. The latter are all too realistic when one wants to publish results that are not streamlined with the mainstream belief. For the moment, the mainstream is formed by a majority of the believers of QM, although also Nobel prize winner Gerard 't Hooft has expressed some doubts and proposes alternatives.