Can anyone explain the difference between the physical, causal, astral, and mental planes?
I’m not sure about “causal” and “mental”, but the physical plane is the one we live in now. The astral is a plane we can’t perceive with our physical senses; we must develop our astral senses in order to do so. Spirits typically live there.
The biggest difference, however, is that the physical plane has lower vibrations while the astral plane has higher vibrations.