I am reading the Feynman's Lectures on physics and more precisely the special theory of relativity. And I have the following questions:
1) How it was discovered and proved that the speed if light is constant?
2) If the speed of light is constant, does it mean that the speed of light is the maximum reachable speed for every object?
3) When the Lorenz transformations are explained it used graphical example how the light travel different path for the same time in two reference systems. Would be correct the same example if we replace the light with tennis ball, in example?

Question

I am reading the Feynman's Lectures on physics and more precisely the special theory of relativity. And I have the following questions:
1) How it was discovered and proved that the speed if light is constant?
2) If the speed of  light is constant, does it mean that the speed of light is the maximum reachable speed for every object?
3) When the Lorenz transformations are explained it used graphical example how the light travel different path for the same time in two reference systems. Would be correct the same example if we replace the light with tennis ball, in example?

anonymous · Answer

answer to the first and second question is 
it has been by the large amount experimental data
scientist have used particle accelerator for that purpose and they have acknowledged that at certain limit it was very impossible to increase the speed further and all these experiments are done after the Einstein special theory of relativity 
although it is constant only in the same medium

danielgenov · Answer

Yes, but let's look at the experiment of W.Bertozzi on 1965 when he accelerated electrons to speed 0.999 999 999 95 times the speed of light. So far so good. But if the speed of electron was accelerated just with 0.05 km/h it would reach the speed of light. The speed in the experiment is relative to the laboratory. BUT laboratory is placed on the earth which in turn is in relative motion to the Sun and the speed of the earth relative to the sun is much greater than 0.05km/h. And consequently the speed of the electron relative to the sun will be over the speed of light ? So, where is the mistake.

anonymous · Answer

yes it was a good contradiction to the theory 
but  from here only the fishy things started
scientists have thought that way and they have affixed the accelerator to another moving vehicle  and then conducted the same experiment have found out the same result even when they have performed  addition of the two speeds the have not reached the ultimate 'c'

further if we say that from sun reference frame then may be if we have looked it from that frame the system from sun it would have suffered time dilation and length compression 'may be' i am not sure for that

ghazi · Answer

answer to your third question... it would be false to use tennis ball for that  experiment because only mass less particle can travel at or approximately at the speed of light. like photon...answer to your second question...there is no relation between the constant speed of light and maximum achievable speed...basically if things will start moving faster than light then according to the theory of relativity object will move backwards in time ....so up to now it is not possible to travel faster than light.

vincent-lyon.fr · Answer

For your first question, look up Michelson Morley experiment. This should answer your question.

As for particles, when you near the speed of light, velocities do not add up as simply as they do in Galilean mechanics. So there is no paradox adding up the speed of the earth to that of the electrons. The total speed will prove less than the speed of light.