I have been reading Albert Einstein's book titled "Relativity: The Special And The General Theory". I am still reading the Special Theory part and have not yet reached the General Theory part.
It is made clear that older theory of relativity and constancy of speed of light are not compatible with each other. So he makes an effort to examine the concepts of time and space so that there is no contradiction between this newer theory of relativity and constancy of speed of light.
Motivation behind focussing on light, other than to explain the constancy of speed of light, seems to be that we can only "sense" changes through light. That's it. There is no other way. And we have known that light takes finite time to travel.
To me, the above observation might have been motivated from Heisenberg's uncertainty principle, which assumes the exact same thing. By the time we observe something (technically, by the time light reaches us after having gotten reflected from the object), the state of the body would have changed. So there is no way we can know for certain the state of any matter. Light itself, causes the change in the position of the matter so we just can never know its exact position by the time light would have reached us.
Going back to Relativity and Einstein's book, the real deal for me starts from Chapter 10 where he talks about the Lorentz transformation. The only thing I have against this theory is that it assumes that the speed of one reference frame K' relative to the so called original reference frame K to be a "known" value. Please note that this whole theory rests on the fact that speed of light is finite and constant irrespective of frame of reference.
Now, how on earth is one to know the relative velocity of K' with respect to K? Should't that have to be taken into account as well? Speed of light should have mattered when determining the speed of K' with respect to K. In fact, that is true for any object. If we need to know its speed with respect to reference frame K, then we need to account for the finite speed of light and this will also have to include the speed of the reference K'.
Also, based on Heisenberg's uncertainty principle, there is no way to know the exact state of any matter as light is the medium through which we can know and by the time light reaches us, the state has already changed. This raises another question for me.
How can you ever assume any velocity for any body when its position is known to be uncertain?
In summary, I have two questions.
Relative velocity of K' with respect to K (in the Special Theory of Relativity) is assumed to be known and does not take the finite speed of light in determining it.
The position of any matter is assumed to be "knowable" where as it makes sense, according to Heisenberg's uncertainty principle, that it is not "knowable". How come Einstein did not bother to take care of this fact?
Somewhere, there seems to be a circular logic involved in Einstein's theory. Please clarify.