Quantum computing, quantum encryption and quantum teleportation: today's physics journals sound more like Star Trek than ever. Based on the weird and counterintuitive features of quantum mechanics, these concepts have been brought to fruition in recent years by theorists and experimentalists alike. Indeed, these ideas are now leaving physics laboratories and being used by industry to make real products. Who knows what revolutions await in computation and communications from these budding breakthroughs?
But as they move from theory to application, these developments have rekindled for many physicists an interest in some long-standing questions about quantum mechanics – interpretive, philosophical questions that, on the face of it, seem light-years away from the grubby worlds of engineering and manufacturing. Can something be in two places at once? Can an object influence another more quickly than the time it takes light to travel between the two? Is it really impossible – as the uncertainty principle suggests – to fix the properties of a quantum-mechanical object such as its position and momentum at the same time?
These philosophical issues are not new. Perhaps the most famous physicist to agonize over the implications of quantum mechanics was Albert Einstein, who did not like the inherent randomness of the theory and dubbed the seeming ability of one particle to instantaneously influence another as "spooky action at a distance". But Niels Bohr also worried about such questions; so too did Werner Heisenberg and Erwin Schrödinger. In fact, most of the architects of quantum theory, toiling away during the 1910s and 1920s, thought that quantum mechanics – our description of matter and forces at the atomic scale – demanded new ways of thinking.
Yet these complex puzzles largely disappeared from view during the mid-20th century, despite Einstein's hope that some means might be found to regain a deterministic description of nature. They had not been solved – as lively discussions in recent books like Seth Lloyd's Programming the Universe make plain – but were simply sidestepped. Why was this?
A large part of the answer to that question, unexpected though it may be, is the huge impact on physics of the Second World War. The success of military projects, such as the development of the atomic bomb and radar, convinced influential policymakers that what they needed after the war as many more physicists to secure the peace. The hardening of the Cold War a few years later added new urgency. The massive training mission that ensued – bolstered in the US by tens of thousands of new federal fellowships in physics and allied fields – radically changed how physics was taught in American universities and elsewhere.
In the May issue of Physics World, David Kaiser tells how the philosophical aspects of quantum mechanics were gradually squeezed out of teaching syllabuses after the Second World War – even those of venerated physicists such as Richard Feynman, who said interpretive issues were all "in the nature of philosophical questions [and] not necessary for the further development of physics."
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