>Hilmar, it should be mentioned that the "speed of light" is a constant in a
specific medium. In a vacuum it is 186,000 miles per second. The speed of light changes in matter depending upon the index of refraction of the matter. Light can be slowed down below 186,000 miles per second in denser mediums.
Yes, I sometimes forgot to specify, "the speed of light in a vacuum".
Light can be slowed down to a few
meters per second; even cases of a negative speed have been observed, as well as speeds greater than the speed of light in a vacuum. (This observed speed is interpreted as an apparent speed; it can't be used to transport energy or information to the past, for instance; see
www.physicsweb.org for further information.)
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)
