A question I have puzzled over for a year now is how we define time. We chose light as the fastest thing we know (currently) as our mathematical limit, as only massless particles can only reach c our calulations of Gr and Sr are based on this. Unitl I started hearing terms of backwards in time (relatively from the observer) I had no issue with that. Now recongnizing that the tachyon is still not proven, It is as hypothecally accepted as the higgs boson etc. The properties of the tachyon is that its slowest speed is c. I started wondering how our mathematics of relativistic effects would shape were we to base our mathematics of Gr around its maximum speed, rather than stating it travels backwards in time, which is a clear violation of causality. Part of the problem I see is that human observation can only percieve in the elctromagntic spectrum, therefore our perception of time must also follow those rules shown by Gr. There have been numerous experiments that perceptually have faster than light observations the term " information cannot travel faster than light' Is often quoted to keep those effcts from violating causality, but could not the illusive tachyon carry information ? Or is the information it carries also going to be described as travelling backwards in time in violation of causality. I am curious as to how the professional physicists explain this dilemna I have. For the record I do trust Gr in its accuracies and predictions and am not atempting to debunk it, merely stating a possibility, the whole laws of causality problem in regards to tachyons and those experiments. (If I understand what little I do involve wave manipulation of light through a material giving the effect of reflected light prior to light beng sent). Speaking of tachyons, What would be its maximum speed? The speed where how we define bakwards in time matches up with the speed of light were the tachyon travelling forward? I have a hard time visualizing the limits of the tachyon on a 4-d model its like saying that if a photon were to exceed the speed of light it would reverse course back the way it came on its 4th degree bearing. Hope I make sense with that last statement.