At which Solvay Conference did Bohr and Einstein have their famous 1927 debate?

At which Solvay Conference did Bohr and Einstein have their famous 1927 debate? The answer is the Fifth Solvay Conference.

Held in Brussels from 24 to 29 October 1927, the meeting was devoted to “Electrons and Photons” and brought together leading figures of the emerging quantum theory. Albert Einstein challenged aspects of the Copenhagen interpretation, while Niels Bohr defended its emphasis on probability, measurement, and complementarity.

The debate was not a single formal contest with a winner announced at the end. Einstein proposed thought experiments intended to expose weaknesses in quantum mechanics, and Bohr developed responses defending the theory’s internal consistency. Their disagreements continued for decades and became one of the most famous philosophical episodes in modern physics.

This conference is sometimes confused with other Solvay meetings because the series began in 1911 and continued regularly. The Fourth Conference, held in 1924, focused on electrical conductivity; the famous Bohr–Einstein exchanges belong specifically to the Fifth, whose 29 participants included 17 Nobel laureates, present or future.