I can’t see oxygen or clean air in general but I know it exists. I can feel it.
A person’s perception of reality is a function of the frequency of consciousness from which they view it.
Prayer, meditation, and the Holy Spirit raises our consciousness frequency. It must reach 40 Hz just to perceive beyond the physical body. I’ve jammed FM reveivers in meditation that are in the Mega Hz. I really don’t think their is an upper limit.
Look up Gamma frequencies of consciousness in EEG studies.
We know oxygen exists because of science.