The spiritual energy of souls have to be energised at the end of each cycle because the corporeal world is sustained by our spiritual strength. The ancient Hindus had created spiritual theories based on the sciences and theories which might be 'possibilities' of how it might be. This is why they had said that the world is an illusion or that it is based on an illusion. Off course, one can use the existing sciences like how “we only see, touch and hear things based on what the brain interpretes” as one way of explaining this. The 'hologram theory' and the 'ability to create stuff through psychic power' may also be a reason why the ancient people had come up with this theory of the world being an illusion. There may also be others which people are discussing about. But our spiritual strength is also maintaining the corporeal world in existence. One might not be able to prove this because God re-energises us at the end of every cycle and so the corporeal world continues to exist. However, there is a possibility that the ancient people were trying to also say that the corporeal world is based on our spiritual strength and sustenance. This may also be a reason why the ancient people had provided for sustenance through spiritual purity. The sustenance of the corporeal world is through the mechanics of quantum physics. It is also through the use of the mechanics of quantum physics that the greys are being used in the various dimensions.