Cosmology View

My views on Cosmology and Physics

`Book by David Michalets`

## Review of Einstein's 1920 Book on Relativity  (from Translation)

An (original) line precedes original content from the source.

A (remark) line precedes my remark from my review of the preceding original content.

My remark applies to only this section of the original.

Section VI of 35

# VI. THE THEOREM OF THE ADDITION OF VELOCITIES EMPLOYED IN CLASSICAL MECHANICS

(original)

LET us suppose our old friend the railway  carriage to be travelling along the rails with  a constant velocity v, and that a man traverses the length of the carriage in the direction of travel with a velocity w. How quickly, or, in other words, with what velocity W does the man advance relative to the embankment during the process? The only possible answer seems to result from the following consideration: If the man were to stand still for a second, he would advance relative to the embankment through a distance v equal numerically to the velocity of the carriage. As a consequence of his walking,  however, he traverses an additional distance w relative to the carriage, and hence also relative to the embankment, in this second, the distance w being numerically equal to the velocity with which he is walking. Thus in total he covers the distance W = v + w relative to the embankment in the second considered. We shall see later that this result, which expresses the theorem of the addition of velocities employed in classical mechanics, cannot be maintained; in other words, the law that we have just written down does not hold in reality. For the time being, however, we shall assume its correctness.

(remark)

In this section Einstein describes the Galilean addition of velocities. He believes he presented it correctly, but he concludes this section with
"For the time being, however, we shall assume its correctness."

In other words, the next section (VII) will describe his disagreement with this section,