Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [110]
Heisenberg was 'not very pleased', he told Jordan, by Born's apparent defection to wave mechanics.29 Although he acknowledged that Schrödinger's paper was 'incredibly interesting' with its use of more familiar mathematics, Heisenberg firmly believed that when it came to physics, his matrix mechanics was a better description of the way things were at the atomic level.30 'Heisenberg from the very beginning did not share my opinion that your wave mechanics is physically more significant than our quantum mechanics', Born confided to Schrödinger in May 1927.31 By then it was hardly a secret. Nor did Heisenberg want it to be. There was too much at stake.
As spring had given way to summer in 1925 there was still no quantum mechanics, a theory that would do for atomic physics what Newtonian mechanics did for classical physics. A year later there were two competing theories that were as different as particles and waves. They both gave identical answers when applied to the same problems. What, if any, was the connection between matrix and wave mechanics? It was a question that Schrödinger began to ponder almost as soon as he finished his first ground-breaking paper. After two weeks of searching he found no link. 'Consequently,' Schrödinger wrote to Wilhelm Wien, 'I have given up looking any further myself.'32 He was hardly disappointed, as he confessed that 'matrix calculus was already unbearable to me long before I even distantly thought of my theory'.33 But he was unable to stop digging until he unearthed the connection at the beginning of March.
The two theories that appeared to be so different in form and content, one employing wave equations and the other matrix algebra, one describing waves and the other particles, were mathematically equivalent.34 No wonder they both gave exactly the same answers. The advantages of having two different but equivalent formalisms of quantum mechanics quickly became apparent. For most problems physicists encountered, Schrödinger's wave mechanics provided the easiest route to the solution. Yet for others, such as those involving spin, it was Heisenberg's matrix approach that proved its worth.
With any possible arguments about which of the two theories was correct smothered even before they could begin, attention turned from the mathematical formalism to the physical interpretation. The two theories might technically be equivalent, but the nature of physical reality that lay beyond the mathematics was altogether different: Schrödinger's waves and continuity versus Heisenberg's particles and discontinuity. Each man was convinced that his theory captured the true nature of physical reality. Both could not be right.
At the beginning there was no personal animosity between Schrödinger and Heisenberg as they began to question each other's interpretation of quantum mechanics. But soon emotions began to run high. In public and in their papers both managed, on the whole, to rein in their true feelings. In their letters, however, there was no need for tact and restraint. When he initially tried but failed to prove the equivalence of wave and matrix mechanics, Schrödinger was somewhat relieved that there might be none, since 'the mere thought makes me shudder, if I later had to present the matrix calculus to a young student as describing the true nature of the atom'.35 In his paper, 'On the Relation Between Heisenberg-Born-Jordan Quantum Mechanics and My Own', Schrödinger was at pains to distance wave mechanics from matrix mechanics. 'My theory was inspired by L. de Broglie and by brief but infinitely far-seeing remarks of A. Einstein', he explained. 'I was absolutely unaware of any genetic relationship with Heisenberg.'36 Schrödinger concluded