David Finkelstein was the first, in 1958, who identified Schwarzschild's solution of the Einstein field equations as corresponding to a region in space from which nothing escapes. In 1959, Finkelstein and Charles W. Misner found the gravitational kink, a topological defect in the gravitational metric, whose quantum theory could exhibit spin 1/2. The simplest kink exhibited an easily understood event horizon that led him to recognize the one in the Schwarzschild metric and eliminate its coordinate singularity. In essence, Finkelstein determined that whatever falls past the Schwarzschild radius into a black hole cannot escape it; the membrane is one-directional. This important work influenced the decisions of Roger Penrose and John Archibald Wheeler to accept the physical existence of event horizons and black holes.