            By 1912, however, Einstein had reached an impasse  , realizing that he needed to go beyond the mathematics that he knew and was familiar with.
<meaning-changed>             By 1912, however, Einstein had reached an impasse  , realizing that he needed to go beyond the mathematics that he knew and was familiar with.
 Conservation of energy demands that the difference in work between raising the mass and lowering the mass, , must equal or one could potentially define a perpetual motion machine. Therefore, By 1912, however, Einstein had reached an impasse , realizing that he needed to go beyond the mathematics that he knew and was familiar with.