>one problem as i remember it is that the meter is defined as the distance that light travelsin a certain fixed period of time. problems here are that the speed of light are not constant ...
The speed of light in a vacuum is a constant. The speed of light in other media can vary. For instance, the light signal in a fiber-optic cable will travel at ca. 2/3 of the speed of light in a vacuum.
>... and also that time is also not constant and depends on the observers point of view.
Both times and measurements will vary for different observers. I don't think this is a problem: the idea is to define the meter for a non-moving observer. That is, define the meter (and the second) for your own reference frame.
> ... i believe that these issues were resolved using very precise definations of time observed, speed of light etc but it took years and i can only presume that it will also take years to get the kilogram standardised.
Yes, these things are not resolved overnight. And that is the way it should be: this should be done carefully.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
