I have spent an entire day traveling and toiling against the turning of the earth to get to Lindau. To pass the time on the plane over the Atlantic I read Albert Einstein’s short book Relativity (the subtitles for this English version are the special and general theory or a clear explanation that anyone can understand). In Relativity Einstein shares his insights on his theory from a general scientific and philosophical point of view. He also does a lot of thought experiments with trains in scenarios such as, ‘lightning has struck the rails on our railway embankment at two places A and B far distant from each other.’ Presently I am on a train from Zurich to Lindau in the last phase of my journey so it is apt for me to consider the gedanken experiments he proposed that led to his insights. Though, I hope lightning doesn’t hit the train, but it is highly unlikely because the weather here is wonderful here just outside Zurich.
Einstein wrote Relativity in 1916 as an expository writing for the general public to consider and also with the purpose to, ‘bring some one a few happy hours of suggestive thought!’ Indeed it has. I happened upon this English translation of the fifth edition of the book in a used bookstore some time ago and grabbed it on a whim as I packed my bags. It doesn’t contain any deep insight about general relativity I have not encountered before, but it solidified the subject in my mind and it was nice to hear it from the master himself. The book was not well received originally, but I think that time has treated it well, especially because it is Einstein’s own words. His explanations aren’t crystal clear, but he treats the reader with respect and motivates the logical progression of the theory. Basically he sets the grounds for his assumptions and makes statements about the conclusions that must be drawn, for example, ‘that in general rays of light are propagated curvilinearly in gravitational fields’ and ‘all Gaussian co-ordinate systems are essentially equivalent for the formulation for the general laws of nature.’ The interesting thing is that by believing in the principle of relativity that was already in place Einstein was able to think himself to the conclusions of general relativity.
The solar eclipse on the 29th of May 1919 verified Einstein’s exact prediction of the curvature of light by matter made Einstein a celebrity. The experimental verification was carried about by the Royal Astronomical Society under difficult wartime conditions. A copy of Einstein’s 1915 work on the general theory of relativity was smuggled through war-torn Europe to Cambridge where Sir Arthur Eddington and the Royal Society began planning two expeditions to Sobral, Brazil and the island of Principe, West Africa. Ultimately it was not Eddington, but Andrew Crommelin’s photographs from Sobral that showed the positions of the bright stars in the Hyades star cluster before and during the eclipse were consistent with Einstein’s theory. After this experimental verification Einstein’s picture was in newspapers around the world and he was a genuine celebrity.
Einstein’s thought experiments led him to the revolutionary conclusions that are often summed up by saying that time-space tells matter how to move and matter tells time-space how to bend (the book opted for this nomenclature instead of space-time). The simple verification of Einstein’s experiments (other classic experimental verifications of his theory of relativity include the motion of the perihelion of Mercury, and the displacement of spectral lines via redshift) vaulted him to cult like celebrity status that is maintained today. Ultimately, Einstein did not win the Nobel Prize for his work on relativity. He received the 1921 prize for this work on the photoelectric effect. The Nobel Prize is curious like this.
* * *
Now I am in Lindau and the weather looks perfect this week. Yet, as I wait for seven trains to pass before crossing the tracks at the end of this epic day I cant help but think that if there were two ‘simultaneous’ lighting strikes an observer on the train and myself on the embankment would not agree on the simultaneity of the lightning strikes.