various kinds of EM waves... radios "see" only radio waves (as in, the radio antenna is
shining...everything else (houses, people) are clear. metal is black -- absorbs radio waves,
but other things let them through (everything else is like glass or air).
cool, eh?
speed of light constraint is a postulate of einstein -- we do not know why this has
to be true. foundation of special relativity.
nothing moves faster than light in a vacuum
ah...twin paradox... **inertial**. had to accelerate and come back.
