Errors in Einstein's Reasoning (2)

Let's check "Relativity: The Special and General Theory"[2] for the explanation given by Einstein himself.

In Part I, Section 07, "The Apparent Incompatibility of the Law of Propagation of Light with the Principle of Relativity", Einstein explained this incompatibility like this:

Suppose one beam of light is sent out from the railway embankment, in the same direction where the train is moving. To an observer on the embankment, the speed of this beam is c. To an observer on the train, the speed of this beam is c-v, where v is the speed of the train. But according to the principle of relativity, the speed of light should be the same, whether the reference frame is the train or the embankment. Thus we get an incompatibility issue.

Here Einstein's reasoning is wrong. As shown in section 5 of this paper, the principle of relativity implies that all objects follow the rule of relative motion. So the observed speed c-v is the direct result of the principle of relativity, while the same light speed in all reference frames are against the principle of relativity.

To make this point clear, let's use an falling apple again.

In a orchard where a train is passing through, an apple is falling from a tree. To the person standing beside the tree, the apple is falling vertically. To a person on the train, the apple is falling along a path of parabola. Both observations are true facts, but they seem to contradict each other. Does this mean the principle of relativity is wrong?

Certainly not. The two observations are both related to the physical law, but they are not the physical law itself. In essence, any physical law represents the relation between cause and effect. In this example, the falling of the apple is caused by the gravity. If we calculate the acceleration from both observations, the results will be exactly the same number, the acceleration of gravity.