Higher Vibratory Planes...

Unknown to us at our earthly physical level there are whole worlds of higher vibration rates, and Beings within them, which we can neither see nor touch. Since their vibration rates are higher, making their bodies less dense than ours, they are able to interpenetrate us without our even being aware of their presence. This often puzzling idea can be readily understood if we bear in mind that all "solid" matter is in fact composed of atoms with "spaces" around them.
It is of course, well known that even in the hardest substance no two atoms ever touch one another, the space between two adjacent atoms being in fact enormously larger than the two atoms themselves. Orthodox physical science long ago has posited an Ether which interpenetrates all known substances, the densest solid as well as the most rarefied gas; and just as this Ether moves with perfect freedom between the particles of densest matter, so does Etheric matter interpenetrate it in turn, and moves with perfect freedom among its particles. Thus a Being in the etheric world might be occupying the same space as a Being living in the physical world; yet each would be entirely unconscious of the other, and would in no way impede the free movement of the other.

Vibration rates existing either above or below our limited visible spectrum, though unseen, can often be experienced by those sensitive to their influences. People with heightened extrasensory perception can often see "ghosts", visible to them as a nebulous form which has the ability to pass right through them and other solid objects. Even those not accustomed to extrasensory perception may sometimes be aware of a person or place having good or bad "vibes"; this is because we can sense, on higher more intuitive levels, the vibrations being given out around us.
This difference in density and vibrational levels can also explain why it is that when we send Earth space probes to neighboring planets we appear to see no form of life. The Beings who inhabit these planets, together with the surrounding vegetation and other lifeforms, no longer exist on the dense vibratory level which remains at the planet's old physical surface. They live on a higher, more tenuous vibratory level which we cannot perceive, though it is perfectly solid to them. Their "world" is located on a higher plane surrounding the planet, a world through which our spacecraft unknowingly pass on their way to the planet's old physical crust.