Would you ask how an atom can travel in a vacuum? Probably not, because
the atom already is something. The same applies to light- its
electromagnetic fields are one of the basic constituents of the
universe, at least at the level we know it. They are as much something
as protons, etc.
It would be nice to someday understand ALL the different types of
particle fields as modes of behavior of some mathematical substrate
someday, but that's no more true for light than for other things.
Mike W.
(published on 10/22/2007)