A handwritten letter written by Albert Einstein which includes complex details of his search for a 'Theory of Everything' is to go up for auction in Jerusalem next week. The starting price will be $20,000. Written in German by the Jewish-German physicist to his friend and collaborator, the mathematician Ernst Gabor Strauss, in June 1950, the letter addresses concerns Strauss had over Einsteins attempts to develop a unified field theory. Following his breakthrough insight that space and time are one in the early years of his career, Einstein devoted the latter 30 years of his life to creating a theoretical framework in with the fundamental forces in nature, gravity and electromagnetic power, could be combined. "I am glad that you are working so hard on the question of compatibility. But I do not think your concerns are justified. I would like to formulate the proof so that your letters are taken into account," Einstein wrote in the opening to his letter. He goes on to detail a complex and lengthy scientific proof for Strauss, interpreting Strauss’ equations and solutions to distinguish real degrees of freedom from coordinate effects, in order to understand the meaning of the equations’ solutions. Einstein was ultimately unsuccessful in formatting his Theory of Everything, but his efforts left a lasting legacy in the field of quantum physics. Strauss was Einstein's assistant at the Princeton Institute for Advanced Research from 1944-1948. The pair worked on United Field Theory, with Strauss assisting Einstein in formulating mathematical models for his ideas. The two published three papers together. Born in Munich to Zionist Jewish parents, the family fled from Germany to the British Mandate of Palestine in 1933. After briefly studying at the Hebrew University, Strauss emigrated to the United States and completed his studies at Colombia University. During his career, he worked with some of the most prominent mathematicians of his era, including Paul Erdish and Richard Bellman.Meron Eren, co-owner of the Kedem Auction House which is managing the sale of the letter, said: "this is a historical item of extraordinary value that has made its way to us. Albert Einstein is considered by many to be the leading physicists of the 20th century. His theory of relativity at first met with great skepticism in the scientific world but was eventually accepted, making Einstein famous. This letter deals with the unified field theory, an incomplete theory. However, Einstein's contribution to science in this field is one of the most important in the field of science."