einstein's report on relativity -- 9/30/20
Today's selection -- from Einstein's War by Matthew Stanley. Albert Einstein published his special theory of relativity in 1905, and by 1915 had done additional work to present his general theory of relativity to the Prussian Academy of Sciences. This theory was a leap beyond Sir Isaac Newton’s laws, and Britain’s establishment was slow to accept them, in part because of the rift between scientific communities that came with World War I. That began to change in 1917 with the Report of Relativity, authored by Britain’s Arthur Eddington:
"[By] the end of 1917 [Britain’s Arthur Eddington] had to focus all his energy on Einstein. To convert the heathen Newtonians he needed to finish his scripture, what would eventually become his Report on Relativity. But he also knew that a scientific essay by itself wasn't going to have the impact he wanted. If the eclipse expedition was to restore international science, everyone needed to be watching. Everyone needed to be invested. He had to set the stage for a scientific event that could be seen even through the clouds and smoke of the war.
"Papers given at specialist conferences wouldn't gather the attention he needed. Instead, he wrangled a spot onstage at the Royal Institution of Great Britain (usually known as the RI). The RI had been the public face of science in London for more than a century. Lecturers there spoke to packed audiences of people from all levels of education and all walks of life. It was where Michael Faraday gave his famous Christmas Lectures, including the classic 'Chemical History of a Candle.' There was no better place for Eddington to start taking the case for Einstein directly to the people.
"On February 1, 1918, the RI became Eddington's pulpit for relativity. His lecture fully embraced all the strangeness of Einstein's universe (perhaps he was inspired by his recent reading of H. G. Wells's The War of the Worlds). Listeners heard about wholly new views of space and time, mass, and energy. The speech ignited curiosity among both scientists and laypeople, priming the pump for the appearance of Eddington's Report on the Relativity Theory of Gravitation in April.
"The Report was a remarkable document: less than a hundred pages to introduce an entirely new view of the cosmos (and to set up Eddington as an expert on it). It was the culmination of eighteen months of Eddington's work to understand, digest, and translate relativity for an audience that was actively hostile to German science. He had little of Einstein's actual work to model it on. Instead, the Report is distinctly Eddington's take on relativity. He had the same equations as Einstein, de Sitter, and Hilbert. But a theory is more than just the equations. It needs a framework: to be interpreted, given meaning, and connected to everyday life. Most of the world's first encounter with relativity would not be through Einstein's framework; it would be through Eddington's.
"He explicitly wrote the document to make it as accessible as possible. The powerful but opaque Hamiltonian and Lagrangian methods, along with the complicated tensor mathematics, were exiled to a special section. Everything was laid out to get to the experimental consequences as quickly as possible. As fascinating as the theoretical aspects were, he knew that his audience needed to be persuaded that relativity was not mere speculation. It could, and would, be checked with that most powerful tool of science: looking closely at nature. That would be what determined whether, as Eddington put it a couple years later, 'Albert Einstein has provoked a revolution of thought in physical science.'
"The Report began with the Michelson-Morley experiment. Its strange null results gave Eddington a chance to question precisely what it meant to measure time or space. Once the question was open, he then presented Einstein's positivist arguments for length contraction and time dilation. The Report was where Eddington first tried out the vivid illustrations that would push his later books to the top of the bestseller lists. In one of those, Space, Time, and Gravitation, he asked the reader to imagine someone moving near the speed of light. When she consulted a mirror on board her own ship, everything looked normal. But looking out on us on the street she saw 'a strange race of men who have apparently gone through some flattening-out process; one man looks barely 10 inches across the shoulders.' Even harder than accepting this strangeness, though, was the realization that those of us on the street saw her flattened in precisely the same way.
"How to get his readers to understand this fundamental paradox? With Gulliver's Travels, of course:
Gulliver regarded the Lilliputians as a race of dwarfs; and the Lilliputians regarded Gulliver as a giant. That is natural. If the Lilliputians had appeared dwarfs to Gulliver, and Gulliver had appeared a dwarf to the Lilliputians -- but no! that is too absurd for fiction, and is an idea only to be found in the sober pages of science.
"There was no confusion for Gulliver about who seemed big and who seemed small. In Einstein's terms he might try to declare himself to be a privileged reference frame. But under relativity, no observer could be privileged over any others. So the Lilliputians could come to the same conclusion as Gulliver about the other's strange size -- each seemed absurdly small to the other. Length contraction was an inherently odd thing.
"Similarly, Eddington said, time dilation meant that two people could disagree about how long a cigar would burn for (perhaps there was some bitterness over blockade shortages hiding in that example). Clocks ran slower and slower the closer one moved to the speed of light, so 'if man wishes to achieve immortality and eternal youth, all he has to do is to cruise about space with the velocity of light. He will return to the earth after what seems to him an instant to find many centuries passed away.'
"The temptation upon hearing such outrageous claims was to try to dismiss them as, perhaps, not real. But they were fundamental to understanding relativity. Eddington appreciated that the frequency with which Einstein presented such ideas meant that 'the relativist is sometimes suspected of an inordinate fondness for paradox.' It was not mere fondness, though. Einstein's universe was genuinely different from our traditional one, and we needed to get used to it: there was no person, no place, no orientation more fundamental than any other. There was no Newtonian 'super-observer' who was always right. It was only the laws of nature themselves that were absolute."