Still no-one actually knows why stuff has mass which is really strange as everything is made of energy but some energy has mass while other forms of energy don't.
That's where the Higgs field theory comes in - very exciting stuff!
It's a theory that might be true but the odds say it's wrong, it may be something as simple as all energy has mass regardless of the form it takes. Which would basically explain where all that missing mass is in the universe without dark matter being needed to explain it away.
"If we hit that bullseye the rest of the dominoes will fall like a a house of cards, checkmate." Zapp Brannigan