There has been a continuous discussion on the list about the reality of SR time dilation and length contraction. Most of the commenters accept the time dilation concept since it is relatively easy to measure. Some among the group point out the paradox that they perceive as existing, but for now I want divert attention to evidence of length contraction that seems highly relevant.
I found an article in Wikipedia about the free electron laser. There is a technique for generating very high energy tunable x rays which strongly depends upon the length contraction due to electron velocities near light speed. The frequency and wavelength of the emitted radiation can be directly calculated by using the Lorentz factor. Read the article found at the following link: http://en.wikipedia.org/wiki/Free_electron_laser to see how well the mathematics works. The process uses an alternating series of magnets that are clearly spaced a large distance apart when compared to the the emitted wavelength of the synchronous radiation. If you accept that the electrons are moving at very nearly the speed of light, then the wavelength should be approximately equal to the spacing between alternate magnets unless that distance is effectively shortened by the Lorentz contraction as seen by the electrons in motion. The shortening factor directly enters into the determination of the radiation frequency. A radio wavelength structure of magnets is employed to achieve an x-ray length emission due to Lorentz contraction. Harry, this might help to explain the behavior of your train on the track questions. Think of the distance between the magnets as being similar to the space between the rail ties. Dave
