In 1907, two years of the appearance of his first paper on the theory of relativity, Einstein published in the then prestigious *Jahrbuch der Radioaktivität und Elektronik* an extensive survey article on the subject entitled On the relativity Principle and the conclusions drawn from it"^{[1]}.

In particular, in *§V. Principle of Relativity and Gravitation section 17. Accelerated Reference System and Gravitational Field*, Einstein assumes "* the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system.*"

Thirteen years later, while exposing his special relativity to a general non-mathematician reader, Einstein will qualify this principle as "*The happiest thought of my life*"

Using this principle, Einstein predicted in the same article a local version of **gravitational time dilation** and **gravitational redshift**.

Also in *§20 The effect on gravitation on electromagnetic phenomena *of the same article, Einstein was able to predict** the bending of light in presence of a gravitational field**.

**Remark 1**: This equivalence will be named properly "Hypothesis of equivalence" for the first time in 1911 .

**Remark 2**: as in this article Einstein used the Special Relativity theory equations^{[2]} and was not aware at this time of the spacetime curvature, the value of the light bending prediction was incorrect.

[1] "Über das Relativitätsprinzip und die aus demselben gezogene Folgerungen"

[2] "I had to try to modify the Newtonian theory of gravitation such as to fit its laws into the (special) theory"

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