[D.A.Peel]

Hello neutralino. Thank you for your criticisms. The boxed particle clock illustrates a thought experiment. Its only meant to be taken seriously in that it demonstrates what would happen should it be possible to carry out such an experiment, with such a clock, given that nothing can travel faster than the speed of light. For the sake of making it easy to imagine I could have used a make believe tennis ball. I deal with length contraction and mass increases in part 2.

Secondly, where do I say that tachyons violate causality?

a massive body can never travel at the speed of light.

Nothing with any mass at all can travel at or faster than the speed of light.

In your photon in a box experiment* you describe light taking longer to travel a longer distance, than a shorter distance. However, this has been proven by Michelson and Morely, and by many other experiments since, to not be true:

Light takes approximately 8 minutes to travel from the sun to Earth and approximately half that time to travel half that distance.

a photon travels at the speed of light as measured in all inertial frames.

But what does that have to do with light taking longer to travel to one place than another?
Got to go now.