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Relativity: The Specialand General Theory

Albert Einstein · 1917 · retold from the German original

Über die spezielle und die allgemeine Relativitätstheorie (Gemeinverständlich)

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Einstein’s own account of relativity, written in 1916 for readers without higher mathematics: what space, time and motion mean once the speed of light is the same for everyone.

This is a sample: 4 of 29 sections. · Made in 170 min

From the lectures

An ideal segment corresponds to marks on a rigid rod, three aligned marks share one sightline, and moving the rod preserves its endpoint distance as an assumption to test against experience.
Physical Meaning of Geometrical Propositions

Geometry Meets Physical Measurement

To the geometrical concepts there correspond, more or less exactly, objects in nature, and these are without doubt the sole cause of the origin of those concepts.

A cloud is located above a named ground point by a vertical height, which can also be inferred from two ground sightlines without a physical pole.
The Coordinate System

From Named Place to Height

If I analyse the statement of place "in Berlin, on Potsdamer Platz", it means the following. The surface of the Earth is the rigid body to which the statement of place refers; on it, "Potsdamer Platz in Berlin" is a marked point, furnished with a name, with which the event spatially coincides.

An event inside three perpendicular coordinate planes has coordinates x, y, and z equal to its perpendicular distances from the opposite planes.
The Coordinate System

Coordinates as Distances from Planes

Measuring physics achieves this by the use of the Cartesian coordinate system. This consists of three mutually perpendicular rigid plane walls, joined together into one rigid body.

Identical clocks accompany two reference frames, with successive clock ticks paired to corresponding positions along the stone's two paths.
Space and Time in Classical Mechanics

Positions Paired With Times

A complete description of the motion, however, comes about only when one states how the body changes its place with time; that is, for every point of the path it must be stated at what time the body is there.

An indirect route from A through B to C becomes shortest when B lies between A and C, while a divided measuring rod resolves a fractional remainder.
Space and Time in Classical Mechanics

Straightness and Divided Rods

With this, a natural object has also been assigned to the straight line. Three points A, B, C of a rigid body lie on a straight line when, the points A and C being given, the point B is so chosen that the sum of the distances AB and BC is as small as possible.

How it was made

Examples for: a curious adult with school physics; add one modern instance per idea, such as GPS satellite clocks

The source

The lectures retell the German text of Project Gutenberg #77850, the 1917 Vieweg edition. The author died in 1955; the work is in the public domain. The retelling, the drawings and the voice are made by AI and checked against the book by a second model; nothing was edited by hand. How AI is used.

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