The Witches Sabbath
Nature.com, 21 November 2011
The First Solvay Congress, Brussels, October 1911. Left-to right standing – Robert Goldschmidt, Max Planck, Heinrich Rubens, Arnold Sommerfeld, Frederick Lindemann, Maurice de Broglie, Martin Knudsen, Fritz Hasenöhrl, Georges Hostelet, Edouard Herzen, James Hopwood Jeans, Ernest Rutherford, Heike Kamerlingh Onnes, Albert Einstein, Paul Langevin. Seated – Walther Nernst, Marcel Brillouin, Ernest Solvay, Hendrik Lorentz, Emil Warburg, Jean-Baptiste Perrin (reading), Wilhelm Wien (upright), Marie Curie, Henri Poincaré.
In June 1911 was a professor of physics in Prague when he received a letter and an invitation from a wealthy Belgium industrialist. who had made a substantial fortune by revolutionizing the manufacture of sodium carbonate, offered to pay him one thousand francs if he agreed to attend a ‘Scientific Congress’ to be held in Brussels from 29 October to 4 November. He would be one of a select group of twenty-two physicists from Holland, France, England, Germany, Austria, and Denmark being convened to discuss ‘current questions concerning the molecular and kinetic theories’. and were among those invited. It was the first international meeting devoted to a specific agenda in contemporary physics: the quantum.
Planck and Einstein were among the eight asked to prepare reports on a particular topic. To be written in French, German, or English they were to be sent out to the participants before the meeting and serve as the starting point for discussion during the planned sessions. Planck would discuss his blackbody radiation theory, while Einstein had been assigned his quantum theory of specific heat. Accorded the honour of giving the final talk, there was no room on the proposed agenda for a discussion of his light-quanta – better known these days as photons.
‘I find the whole undertaking extremely attractive,’ Einstein wrote to Walter Nernst, ‘and there is little doubt in my mind that you are its heart and soul.’ Nernst with his love of motorcars was more flamboyant than the staid Planck, but was just as highly respected – in 1920 he was awarded the Nobel Prize for chemistry for what became known as the third law of thermodynamics. A decade earlier, in 1910 he was convinced that the time was ripe to launch a cooperative effort to try and get to grips with the quantum he saw as nothing more than a ‘rule with most curious, indeed grotesque properties’. Nernst put the idea to Planck who replied that such ‘a conference will be more successful if you wait until more factual material is available’. Planck argued that ‘a conscious need for reform, which would motivate’ scientists to attend the congress was shared by ‘hardly half of the participants’ envisaged by Nernst. Planck was sceptical that the ‘older’ generation would attend or would ‘ever be enthusiastic’. He advised: ‘Let one or even better two years pass by, and then it will be evident that the gap in theory which now starts to split open will widen more and more, and eventually those still remote will be sucked into it. I do not believe that one can hasten such processes significantly, the thing must and will take its course; and if you then initiate such a conference, a hundred times more eyes will be turned to it and, more importantly, it will take place, which I doubt for the present.’
Undeterred by Planck’s response, Nernst convinced Solvay to finance the conference. Interested in physics, and hoping to address the delegates about his own ideas on matter and energy, Solvay spared no expense as he booked the Hotel Metropole. In its luxurious surrounding, with all their needs catered for, Einstein and colleagues spent five days talking about the quantum and, as Lorentz said in his opening remarks, the reasons why the ‘old theories do not have the power to penetrate the darkness that surrounds us on all sides’. However, he continued, that the ‘beautiful hypothesis of the energy elements, which was first formulated by Planck and then extended to many domains by Einstein, Nernst, and others’ had opened unexpected perspectives, and ‘even those who regard it with a certain misgiving must recognize its importance and fruitfulness.’
‘We all agree that the so-called quantum theory of today, although a useful device, is not a theory in the usual sense of the word, in any case not a theory that can be developed coherently at present,’ said Einstein. ‘On the other hand, it has been shown that classical mechanics…cannot be considered a generally useful scheme for the theoretical representation of all physical phenomena.’ Whatever slim hopes he abhorred for progress at what he called ‘the Witches’ Sabbath’, Einstein returned to Prague disappointed at having learnt nothing new. ‘The h-disease looks ever more hopeless,’ he wrote to Lorentz after the conference.
Nevertheless, Einstein had enjoyed getting to know some of the other ‘witches’. Marie Curie, whom he found to be ‘unpretentious’, appreciated ‘the clearness of his mind, the shrewdness with which he marshalled his facts and the depth of his knowledge’. During the congress it was announced that she had been awarded the Nobel Prize for chemistry. She had become the first scientist to win two, having already won the Physics prize in 1903. It was a tremendous achievement that was overshadowed by the scandal that broke around her during the congress. The French press had learned that she was having an affair with a married French physicist. Paul Langevin was another delegate at the congress and the papers were full of stories that the pair had eloped. Einstein, who had seen no signs of a special relationship between the two, dismissed the newspaper reports as rubbish. Despite her ‘sparkling intelligence’, he thought Curie was ‘not attractive enough to represent a danger to anyone’.
The Solvay Congress was the end of the beginning for the quantum. It dawned on physicists that it was here to stay and they were still struggling to learn how to live with it. When the proceedings of the conference were published it brought to the attention of others, not yet aware or engaged in the struggle, what an immense challenge it was to successfully do so. The quantum would be the focus of attention at the fifth Solvay conference in 1927. What happened in the intervening years is, as they say, history.