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## Main Question or Discussion Point

Once my understanding of the 2

Let's say there are 2 points of reference frame ##K##, we can denote these points as ##A## and ##B##. Speed of light between these points is ##c##, that doesn’t depend on chosen direction, ##A## to ##B## or ##B## to ##A##.

Let's there is inertial frame ##K'## that moves with velocity ##v## relatively to ##K##. Let's there are 2 points of reference frame ##K##’, we can denote these points as ##A’## and ##B’##. Speed of light between these points must always be ##c## and does not depend on the direction of propagation, ##A’## to ##B’## or ##B’## to ##A’##.

However, the article in Wikipedia claims that according to the 2

Why does it say „regardless of motion of light source“? It doesn't say "regardless of relative speed of observer and the source“.

Moreover, there is the following sentence in the article:

The Principle of Invariant Light Speed – "... light is always propagated in empty space with a definite velocity [speed]

What do they mean by “light in vacuum propagates with the speed ##c## in at least one system of inertial coordinates”? Are there some others

It sounds like touching a surface of a pond by a paddle of a boat . Speed of waves does not depend on the speed of a boat, but in the frame of the boat it will be different in different directions.

I feel completely lost and confused. Does Special Relativity says us there is some kind of preferred frame or even Ether? Or maybe my interpretation was wrong? What is actually meant in the second postulate?

^{nd}postulate was something like that:Let's say there are 2 points of reference frame ##K##, we can denote these points as ##A## and ##B##. Speed of light between these points is ##c##, that doesn’t depend on chosen direction, ##A## to ##B## or ##B## to ##A##.

Let's there is inertial frame ##K'## that moves with velocity ##v## relatively to ##K##. Let's there are 2 points of reference frame ##K##’, we can denote these points as ##A’## and ##B’##. Speed of light between these points must always be ##c## and does not depend on the direction of propagation, ##A’## to ##B’## or ##B’## to ##A’##.

However, the article in Wikipedia claims that according to the 2

^{nd}postulate „speed of light**in vacuum**is the same for all observers,**regardless of the motion of light source**“**https://en.wikipedia.org/wiki/Special_relativity**Why does it say „regardless of motion of light source“? It doesn't say "regardless of relative speed of observer and the source“.

Moreover, there is the following sentence in the article:

The Principle of Invariant Light Speed – "... light is always propagated in empty space with a definite velocity [speed]

*c*which is independent of the state of motion of the emitting body" (from the preface). That is, light in vacuum propagates with the speed*c*(a fixed constant, independent of direction)**, regardless of the state of motion of the light source.***in at least one system of inertial coordinates (*the "stationary system")What do they mean by “light in vacuum propagates with the speed ##c## in at least one system of inertial coordinates”? Are there some others

*moving*frames and speed of light differs from ##c## in these frames? How can this be reconciled with the relativity of simultaneity?It sounds like touching a surface of a pond by a paddle of a boat . Speed of waves does not depend on the speed of a boat, but in the frame of the boat it will be different in different directions.

I feel completely lost and confused. Does Special Relativity says us there is some kind of preferred frame or even Ether? Or maybe my interpretation was wrong? What is actually meant in the second postulate?