Recently it seems to have become fashionable among some scientists, mainly physicists, to harshly disparage philosophy in general and the philosophy and sociology of science in particular. This was not so in times gone by, especially during the time of ferment at the dawn of the twentieth century with the development of theories of relativity and quantum mechanics. While they were developing various successful computational techniques, people struggled to figure out what these theories meant because they seemed to defy our intuitions of how matter behaved at very small scales and when it was traveling very fast.
Even at that time, some eminent physicists spoke somewhat disparagingly of philosophy, such as Paul Dirac saying, “I feel that philosophy will never lead to important discoveries. It is just a way of talking about discoveries which have already been made.” But now that opinion is more widespread among scientists and in my forthcoming book I discuss this development and why it might have occurred.
But one notable exception to this disdain was Albert Einstein and throughout his life, not just in his later years when scientists tend to start philosophizing, he emphasized the importance of philosophy and felt that a scientist was impoverished by not studying it, As Matias Slavov writes, Einstein credits David Hume with giving him a key idea about the nature of time that led to his special theory of relativity.
In 1915, Albert Einstein wrote a letter to the philosopher and physicist Moritz Schlick, who had recently composed an article on the theory of relativity. Einstein praised it: ‘From the philosophical perspective, nothing nearly as clear seems to have been written on the topic.’ Then he went on to express his intellectual debt to ‘Hume, whose Treatise of Human Nature I had studied avidly and with admiration shortly before discovering the theory of relativity. It is very possible that without these philosophical studies I would not have arrived at the solution.’
More than 30 years later, his opinion hadn’t changed, as he recounted in a letter to his friend, the engineer Michele Besso: ‘In so far as I can be aware, the immediate influence of D Hume on me was greater. I read him with Konrad Habicht and Solovine in Bern.’ We know that Einstein studied Hume’s Treatise (1738-40) in a reading circle with the mathematician Conrad Habicht and the philosophy student Maurice Solovine around 1902-03. This was in the process of devising the special theory of relativity, which Einstein eventually published in 1905. It is not clear, however, what it was in Hume’s philosophy that Einstein found useful to his physics. We should therefore take a closer look.
Hume’s philosophy of time shows the fundamental relevance of the relation between an observer and a reference object. There is no evidence for absolute, self-existing time. Nor is there evidence for one universal time. There are different times, depending on the observer/reference-object relation. It is not ‘possible for time alone ever to make its appearance’, as ‘time is nothing but the manner, in which some real objects exist,’ writes Hume. Based on this dictum, in his 2007 biography of Einstein, Walter Isaacson alludes that Hume’s rejection of absolute/universal time ‘would later echo in Einstein’s theory of relativity’.
Slavov goes on to describe how Einstein and Hume’s views are in opposition to Isaac Newton and Immanuel Kant’s concept of time.
The ideas of special relativity were very much in the air when Einstein proposed his special theory. There were experimental anomalies that needed to be explained and the Lorentz transformation was already around. So one could make the case that if Einstein did not exist or propose it, someone else would come along not too long after with the same idea.
But this is not the case for Einstein’s theory of general relativity. Of the three tests of general relativity (the gravitational red shift, the bending of light by gravitational fields, and the rate of precession of the perihelion of Mercury) only the last was known as a problem and it was not seen as an insurmountable one within classical physics. His insight as to what things might look like to someone falling freely in a gravitational field led to his formulation of the Equivalence Principle and later to his General Theory that explained the Mercury problem. This insight was not obvious. As Richard Feynman said:
Einstein himself, of course, arrived at the same Lagrangian but without the help of a developed field theory, and I must admit that I have no idea how he guessed the final result. We have had troubles enough arriving at the theory – but I feel as though he had done it while swimming underwater, blindfolded, and with his hands tied behind his back!
— Feynman Lectures on Gravitation (1995) p.87. Feynman was showing how to derive the theory of general relativity. Even Feynman struggled to understand how Einstein obtained his theory of general relativity given the state of knowledge at the time.
How long might we have gone without realizing that a new theory was needed if Einstein did not have his insight? We now know that if GPS satellites do not make corrections due to the gravitational red shift, then after a day or two they will be off by about 6 miles! So that would definitely have told us that we had a problem. But would we have even reached the stage of putting satellites in space without the General Theory?
It is interesting to speculate but we cannot know. In general, it is not the case that only one person could have come up with a new theory that works well. But what can happen is the time taken for the theory to be proposed and accepted could vary greatly.