Image credit: cratermoon
Einstein's Blackboard is the actual blackboard which physicist Albert Einstein used on May 16, 1931 during his lectures while visiting the University of Oxford in England. The writing is actually Einstein's and has been preserved to this day. The blackboard is one of the most iconic objects in the collection of the Museum of the History of Science in Oxford.
The lecture in which the blackboard was used was the second of three, delivered at Rhodes House in South Parks Road. Einstein's visit to give the Rhodes Lectures, and also to receive an honorary Doctor of Science degree from Oxford University on May 23, 1931, was hosted by the physicist Frederick Lindemann. Einstein's first lecture was on relativity, the second on cosmology, and the third on unified field theory. All the lectures were delivered in German. A brief report of the second lecture was given in The Times and in Nature. A summary of all three lectures can be found in the Archives of the Oxford Museum for the History of Science.
The equations
It has recently been pointed out that the equations on the Oxford blackboard are taken directly from a key paper on relativistic cosmology written by Einstein in April 1931 and published in the Proceedings of the Royal Prussian Academy of Science on May 9th of that year. The paper, known as The Friedmann-Einstein universe, is of historic significance because it constituted the first scientific publication in which Einstein embraced the possibility of a cosmos of time-varying radius.
In the paper, Einstein adopts Alexander Friedman's 1922 analysis of relativistic models of a universe of time-varying radius and positive curvature, but sets the cosmological constant to zero, declaring it redundant, predicting a universe that expands and contracts over time. (The work is sometimes known as the Friedman-Einstein model of the universe). With the use of Edwin Hubble's observations of a linear redshift/distance relation for the spiral nebulae,
Einstein extracts from his model estimates of ρ ~ 10−26 g/cm3, P ~ 108 light-years and t ~ 1010 years for the density of matter, the radius of the cosmos and the timespan of the cosmic expansion respectively. These values are displayed in the last three lines on the Oxford blackboard (although the units of measurement are not specifically stated for the density estimate, cgs units are implied by the other calculations).
References:
https://www.hsm.ox.ac.uk/blackboard-used-by-albert-einstein
https://www.bbc.com/news/av/uk-england-oxfordshire-41096926/the-blackboard-albert-einstein-left-in-oxford-in-the-1930s
https://curiosity.com/topics/you-can-see-a-chalkboard-covered-in-albert-einsteins-writing-at-oxford-university-curiosity/
https://en.wikipedia.org/wiki/Einstein%27s_Blackboard
