Einstein Relatively Easy

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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"




"The essence of my theory is precisely that no independent properties are attributed to space on its own. It can be put jokingly this way. If I allow all things to vanish from the world, then following Newton, the Galilean inertial space remains; following my interpretation, however, nothing remains.."
Letter from A.Einstein to Karl Schwarzschild - Berlin, 9 January 1916

"Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the 'old one'. I, at any rate, am convinced that He is not playing at dice."
Einstein to Max Born, letter 52, 4th december 1926

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