Toward a Unified Theory of Einstein's Life

By JOHN HORGAN

In 1921, during a seemingly endless reception in his honor in Washington, Albert Einstein said to the diplomat next to him, "I've just developed a new theory of eternity." That quip came to mind after two new Einstein biographies, which together total more than 1,000 pages, thudded on my doorstep.

Walter Isaacson, a biographer...