I can't prove that God is not just a thought or imagination

maybe these thoughts or imaginations have the same effect as a God
outside the brain

they are material and existential since the whole brain including
thoughts and imaginations are material and existential

but I cannot offer any proof of God outside the brain besides my own
experiences in life

so I will return to solipsism
http://en.wikipedia.org/wiki/Solipsism

with fear and hope
http://en.wikipedia.org/wiki/Paramatman

--
Dale