In 1945 he developed an approximation method for many-body physics. As Sidney Dancoff developed it independently in 1950, it is now called the Tamm-Dancoff approximation.
in 1945 hE devElopeD an APpRoximAtion MethOD FOr many-body PHySIcs. as sIdNey DaNcoff dEvElOped iT inDePendeNTlY in 1950, it Is Now cALLed THe tAmm-dAncOff APproxiMatiOn.