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It was not a question of whether light should be pictured as waves or particles, or atoms as solar systems, but of whether the microworld could be pictured at all. The famous debate between Albert Einstein and Niels Bohr reached beyond quantum physics to the deepest foundations of science. Faced with the ever more perplexing ‘irrationalities’, Bohr, Einstein, and their followers fell into two broadly opposed camps. Bohr’s approach of ‘complementarity’ accommodated the apparent absurdities of the microworld, declared quantum concepts to be purely ‘symbolic’, and insisted that the manifestation of quantum phenomena in experiment be discussed only in the language of classical physics. He asserted that quantum theory was mathematically coherent and complete. Einstein could not accept Bohr’s ‘tranquilizing philosophy’, which dealt in probabilities rather than certainties. He insisted that physicists look more deeply for the causes of entanglement and rejected the spooky actions at a distance that this implies. Their discussion, respectful and profound, reached stasis in the mid-1930s with the apparent victory of Bohr, while attention shifted to nuclear and particle physics. But their arguments continued to reverberate, and later physicists identified testable consequences of the theory. Ingenious experiments have now confirmed its radical strangeness. Vividly capturing the personalities and interactions of a remarkable cast of characters, the prevailing socio-political circumstances, and threaded through with explanations of theory and experiment, this erudite and carefully crafted telling by Jim Baggott and John Heilbron may prove to be the definitive account of the Bohr–Einstein debate and its legacy