1927 Solvay Conference
On 25th October 1927, one of the most iconic pictures of the Physicist community was taken at the Fifth Solvay International Conference on Electrons and Photons.
On 25th October 1927, one of the most iconic pictures of the Physicist community was taken at the Fifth Solvay International Conference on Electrons and Photons. This remarkable picture captures almost all of the forefathers of Quantum Theory in a single frame. 17 scientists among the 29 attendees had or later received the prestigious Nobel Prize and helped shape the world we are living in today. The list of attendees includes names like Einstein, Bohr, Schrödinger, De Broglie, Marie Curie, Lorentz, Dirac, Heisenberg, Pauli, Compton, Wien, Planck among others. 
The Fifth Conference
The conference is known for its bringing about the best of the physicists of that time. But it also defined the foundations of Quantum Theory. From this point onward, instrumentalism started to be accepted as the norm instead of scientific realism. Instrumentalism is the proposition to have looser rules based on the outcome whereas scientific realism can be deemed as a set of strict scientific rules believed to be spread throughout the universe. Einstein was a firm believer of scientific realism and could not stand the idea of a fuzzy nature of the most fundamental rule of physics. This was also the birthplace of the famous Einstein-Bohr feud where Einstein remarked "God does not play with dice" upon which Bohr replied, "Stop telling God what to do". 
The fifth Solvay Conference 1927 wasn’t the only conference to have such a grave importance. In fact, the first conference in 1911 laid the foundations of the newly formed Quantum Theory and had an invitation-only guest list that included prominent scientists like Einstein, Planck, Marie Curie, Rutherford, Lorentz, Rubens, Sommerfield, Lindermann.  There have been a total of 26 conferences on Physics and 23 other on Chemistry that brings the most influential scientists together to share their views on the proposed topic.
So when was the photo taken?
I was fascinated the first time I saw the picture and wanted to know more about the story behind it. The conference was held during 24th-29th October and I couldn't find any reference to exactly when the photo was taken, so I approached International Solvay Institutes for more information. They took the matter really seriously and forwarded the query to the Department of Archives and Special Collections. They finally concluded that the photo was probably taken on either the first day of the conference when all the participants were present, or on the second day on the 25th, following the tradition of taking the group photo on the second day of the conferences.