Albert Einstein's 100-year-old handwritten letter filled with equations sells for $71,811

A handwritten letter by Albert Einstein, believed to date back to around 1929, has sold for $71,811 at RR Auction. Addressed to mathematician Chaim Herman Muntz, the one-page document contains detailed equations exploring Hamiltonian mechanics, covariance and invariance. Written in German, the letter was sold with its original envelope, postmarked in Potsdam, offering a glimpse into Einstein's mathematical discussions nearly a century ago.