John D. Norton
Department of History and Philosophy of Science, University of Pittsburgh
Pittsburgh PA 15260. Homepage: www.pitt.edu/~jdnorton
This page is available at www.pitt.edu/~jdnorton/goodies
This is an expanded version of my "What Is Einstein's Legacy to Me? Philosophy of Science" appearing in Imagine (Johns Hopkins Center for Talented Youth) Vol. 13, Issue 1, September/October, 2005.
We all know of Einstein's contribution to modern physics. Through his theories of relativity he showed us that there is a fastest possible speed and that light moves at it. He showed us that gravity is a curvature of spacetime. And he laid the foundations of modern quantum mechanics when he proposed that light really comes in little bundles of energy he called quanta. Any philosopher of science interested in the nature of space, time and matter has to take notice, for our accounts of all three were changed fundamentally by Einstein's hand.
What is less well recognized is how Einstein's work altered our understanding of the nature of science itself. To begin, he changed our ideas of how to do theoretical science. In 1905, he showed us how to make sense of the odd fact that light always propagates at exactly the same speed c, no matter how fast we go. The trick was to see that when we change our state of motion, we change our judgments of which events are simultaneous. His lucid analysis, laid out in the opening pages of his famous 1905 special relativity paper, was especially vivid. He used a thought experiment, in which asked us to imagine two clocks exchanging light signals and observers in different states of motion. The signals bounce, the clocks tick and altogether too quickly the final, astonishing result emerges.
The apparent ease with which ordinary thought experiments could yield extraordinary results was inspiring. It led many to try to copy his method They sought new theories, not in novel experiments, but in astonishing revisions of familiar notions like space and time, through carefully crafted thought experiments. These efforts rarely succeeded for those who are not Einsteins.
Another notion was read from Einstein's analysis of 1905. It was a view of which concepts may be used in science. They must be defined by the operations needed to measure the concept. So we can only use the concept of the simultaneity of two events if we can specify just how we may determine their simultaneity, by, for example, operations with light signals. This stringent demand is very effective if our goal is to force critical re-evaluation of some dubious concept. However it is as likely to cause problems where there should be none, for few of our concepts really conform to its standards.
Einstein invented neither the notion of the thought experiment nor the operational definition of a concept. He merely used them more perfectly than any who had gone before him.
The most enduring change brought by Einstein's work was to shake our sense of certainty. When Einstein entered science at the start of the 20th century, there was a strong sense of its stability. In antiquity, Euclid had described perfectly how space really is. In the 17th century, Newton had discovered the dynamics that govern time and matter. It is only from the perspective of this certainty that we can now understand the project of the influential eighteenth century philosopher Immanuel Kant. He felt compelled to devise an explanation of why all our experience must conform to the geometry of Euclid and the mechanics of Newton. The project now seems misplaced. Einstein showed us that both theories can fail when we enter the realms of the cosmically large, the very heavy, the atomically small and the very fast.
Einstein was not the only one to show us the fragility of our knowledge. But he was the first, the most effective, and the best remembered. He showed us that the old certainties had failed. So, we concluded, surely anything that replaces them could fail again.
The old confidence in our knowledge was based on the notion that experiment and experience could bear quite directly on our science. Some, like Ernst Mach, thought that all of science was or should be nothing more than compact summaries of experience. While this idea was always somewhat dubious, it could survive because even the most complicated theory of the era, Maxwell's electrodynamics, appeared to remain close to experience. For each of Maxwell's equations, one could point to experiments that seemed to be expressed just by that equation.
This sense of the closeness of theory to experience was shattered by Einstein's general theory of relativity. It required a new and complicated mathematics then unfamiliar to most physicists. Yet most of its predictions were no different than those of Newton's much simpler theory. If theories were merely summaries of experience and did not add to them, how could two theories, so much in agreement on experience, differ so much in structure?
Einstein's physics and the new physics developed by others in the twentieth century led to a sense of the fragility of theories and the powerlessness of evidence to pick out the unique truths of nature. Philosophers of science struggled to accommodate this new sense within their systems, all the while seeking to fit their ideas with Einstein's theories.
Einstein's own diagnosis of this gap between experience and theory was extreme. He proclaimed that concepts and theories are "free inventions of the human spirit" and that no method could assuredly take us from experience to the true theory. Here he contradicted the optimism of the nineteenth century during which many felt that scientific discovery could be reduced to simple recipes. John Stuart Mill continued a tradition extending back to the seventeenth century Francis Bacon. To identify the cause of some effect, he believed, one merely needed to collect cases in which the effect was present and those in which it was not. The cause could then be read directly from the systematic differences between the cases.
Later in life, Einstein came to a radical solution of the problem of responsibly practicing science while still believing that its core concepts are free inventions. Drawing on his discovery of general relativity, he concluded that the right concepts and theories could be found merely by seeking the mathematically simplest theories.
In my view, Einstein's response was too optimistic in his confidence that mathematical simplicity could be the guide to the truths of nature. Einstein was able to make no major discovery using this principle during the decades of his legendary and ultimately barren search for a unified field theory.
And Einstein's notion that concepts and theories are free inventions not fixed by experience seems too pessimistic, for science seems time and again to be able to determine the right theory on the basis of evidence. In the face of this commonplace of science, Einstein too seems to have had some difficulty maintaining his notion of free invention. He likened nature to a "well-designed word puzzle." While we may try to solve it with many words, only one "really solves the puzzle in all its parts."
This last view seems to me to capture much better the real power of evidence to point to a definite theory. If the equivalence of energy and matter expressed by E=mc2 is based on free inventions, why is there no alternative that enjoys equally powerful support from our experiences and experiments?
Some Reading
Einstein, Albert. Relativity: The Special and the General Theory. Methuen & Co., 1920.
Einstein, Albert. Ideas and Opinions. New York: Bonanza Books, 1954.
Howard, Don A., "Einstein's Philosophy of Science", The Stanford Encyclopedia of Philosophy, Edward N. Zalta (ed.) http://plato.stanford.edu/archives/spr2004/entries/einstein-philscience/.
John D. Norton is a licensed and certified dilettante whose hobby is the study of Einstein's work and thought. This hobby has so overtaken his life that he has little time for anything else and is Professor of History and Philosophy of Science and (Sept. 2005-) Director of the Center for Philosophy of Science at the University of Pittsburgh.