Frequency isn't a dimension. It is the effect of vibration, just like speed is an effect of motion.
But I am inclined to agree with the idea that the 4th dimension has something to do with dark matter. I need to read more about that
And in response to one of the posts, IMO, even time is not a dimension. Time is an auxilary concept formulated by (us) humans to make things easier. When we refer to time we are just using the interval between two events and measuring that interval based on the vibration of a caesium atom. So in effect, the base unit of time itself is based on vibration of matter. Events happen in the cosmos. Time is just our attempt at keeping track of those, but when I try to make sense of it, what it actually is, it feels more and more to be just a concept. So no, I don't think time is a dimension.
I
