Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [131]
The classical universe built on the foundations laid down by Newton was a deterministic, clockwork cosmos. Even after Einstein's relativistic remodelling, if the exact position and velocity of an object, particle or planet, are known at any given moment, then in principle its position and velocity can be completely determined for all time. In the quantum universe there was no room for the determinism of the classical, where all phenomena can be described as a causal unfolding of events in space and time. 'Because all experiments are subject to the laws of quantum mechanics, and therefore to equation pqh,' Heisenberg boldly asserted in the last paragraph of his uncertainty paper, 'it follows that quantum mechanics establishes the final failure of causality.'89 Any hope of restoring it was as 'fruitless and senseless' as any lingering belief in a 'real' world hidden behind what Heisenberg called 'the perceived statistical world'.90 It was a view shared by Bohr, Pauli and Born.
At Como two physicists were noticeable by their absence. Schrödinger had only weeks earlier moved to Berlin as Planck's successor and was busy settling in. Einstein refused to set foot in fascist Italy. Bohr would have to wait just a month before they met in Brussels.
PART III
TITANS CLASH OVER REALITY
'There is no quantum world. There is only an abstract quantum mechanical description.'
— NIELS BOHR
'I still believe in the possibility of a model of reality – that is to say, of a theory that represents things themselves and not merely the probability of their occurrence.'
— ALBERT EINSTEIN
Chapter 11
SOLVAY 1927
'Now, I am able to write to Einstein', Hendrik Lorentz wrote on 2 April 1926.1 Earlier that day this elder statesman of physics had been granted a private audience with the King of the Belgians. Lorentz had sought and received royal approval for Einstein's election to the scientific committee of the International Institute of Physics set up by industrialist Ernest Solvay. Once described by Einstein as 'a marvel of intelligence and exquisite tact', Lorentz had also obtained the king's permission to invite German physicists to the fifth Solvay conference scheduled for October 1927.2
'His Majesty expressed the opinion that, seven years after the war, the feelings which they aroused should be gradually damped down, that a better understanding between peoples was absolutely necessary for the future, and that science could help to bring this about', reported Lorentz.3 Aware that Germany's brutal violation of Belgian neutrality in 1914 was still fresh in the memory, the king felt 'it necessary to stress that in view of all that the Germans had done for physics, it would be very difficult to pass them over'.4 But passed over and isolated from the international scientific community they had been ever since the end of the war.
'The only German invited is Einstein who is considered for this purpose to be international', Rutherford told a colleague before the third Solvay conference in April 1921.5 Einstein decided not to attend because Germans were excluded, and instead went on a lecture tour of America to raise funds for the founding of the Hebrew University in Jerusalem. Two years later he said he would decline any invitation to the fourth Solvay conference because of the continuing prohibition on German participation. 'In my opinion it is not right to bring politics into scientific matters,' he wrote to Lorentz, 'nor should individuals be held responsible for the government of the country to which they happen to belong.'6
Unable to attend the 1921 conference because of ill health, Bohr too declined an invitation to Solvay 1924. He feared that to go might be interpreted by some as tacit approval of the policy to exclude the Germans. When Lorentz became president of the League of Nations' Committee on Intellectual Cooperation in 1925, he saw little prospect