We don't really know yet what space is made up of. It's not dark matter, however, which is just some more stuff hanging out in space, like us. The dark matter is different from us, however, in that it doesn't interact with light, so you can't see it.
You may be thinking of dark energy, which may have some connection with whatever makes up space. Whatever our space is, however, it provides the right sort of thing for light to travel in freely. Think of a wave on a string. The string doesn't get in the way of the wave, it provides the base for the wave to exist.
Mike W.
(published on 09/30/2009)
