Agreed. Definition of matter should be relative. A radio wave doesn't see a wall like how we do. Also, Time seems to be one the biggest discovery of Humans even

Agreed. Definition of matter should be relative. A radio wave doesn't see a wall like how we do. Also, Time seems to be one the biggest discovery of Humans even when we don't see it, feel it, smell it, hear it, taste it. Possibly there are other such things like time yet to be discovered in this universe.