Einstein's Pathway to the Equivalence Principle 1905-1907

TL;DR

Between 1905 and 1907, Einstein explored extending special relativity to include gravity, leading to insights about the equivalence principle by analyzing Galileo's law of free fall and its implications for inertial and gravitational mass.

Contribution

The paper details Einstein's early development of the equivalence principle, highlighting his insight that free fall experiments could unify inertia and gravity within relativity.

Findings

Einstein recognized the significance of Galileo's law of free fall.

He proposed that free fall could serve as a basis for extending relativity.

This work laid the groundwork for the general theory of relativity.

Abstract

Between 1905 and 1907, Einstein first tried to extend the special theory of relativity in such a way so as to explain gravitational phenomena. This was the most natural and simplest path to be taken. These investigations did not fit in with Galileo's law of free fall. This law, which may also be formulated as the law of the equality of inertial and gravitational mass, was illuminating Einstein, and he suspected that in it must lie the key to a deeper understanding of inertia and gravitation. Einstein's 1907 breakthrough was to consider Galileo's law of free fall as a powerful argument in favor of expanding the principle of relativity to systems moving non-uniformly relative to each other. Einstein realized that he might be able to generalize the principle of relativity when guided by Galileo's law of free fall; for if one body fell differently from all others in the gravitational field, then with the help of this body an observer in free fall (with all other bodies) could find out that he was falling in a gravitational field.