The universe works perfectly as it is. If the laws of physics could change at some places in the universe, we wouldn't exist. At every point and at every time, the laws of physics are consistent and never change.
Which means that there can be no element lighter than Hydrogen, and there can be no place in the universe where Hydrogren is lighter than in other regions, and there was never a time (and there will never be a time) when Hydrogen was lighter than it is now. Speed of light is the same everywhere as well.
But we still don't know what the hell Dark Matter is supposed to be, so that's a nice playground. For all we know at the moment, it could very well be giant amounts of cottage cheese.