This is the second part in a series outlining Albert Einstein’s development of the general theory of relativity.  In Part 1 we saw that by mid-1911 Einstein¹

• knew that, in general, the equivalence principle held only locally, and likewise the Lorentz transformation, implying the need of a larger invariance group (thus, physical laws more complex than Maxwell’s equations for electrodynamics were needed for gravitation);
• had confidence in an action principle for a particle falling freely in a gravitational field;
• realized the gravitational field equations must be nonlinear because gravitational field energy is a source of gravitation;
• had calculated gravitational redshift and predicted 0.83" deflection of a light ray grazing the Sun, essentially the same as the Newtonian prediction.

Download PDF for full article. Read Part 1: 1907-1912 | Read Part 3: 1913-1915