An atheist would have to say that the experience you describe regarding your grandfather was all just a bunch of chemical reactions.
And a rainbow is just refraction of light! The stolid, solid atheist denies that there is anything beyond his/her own senses and by doing so denies the vey wonder that his human intelligence. Everything that we are learning from DNA and modern science says that we are animals, only minimally separated from our animal cousins. Where then does our intelligence arise? WHERE?
Jeremiah 5:21 - Hear this, you foolish and senseless people, who have eyes but do not see, who have ears but do not hear !
Yeah I understand, for those who believe, no further proof is needed, for those who dont, no evidence would ever be enough... i will simply pray god opens their eyes so they recognize it, when he reveals himself to them before they pass. This a once in a lifetime experience words barely scratch the surface of, compared to the power of being there. It was my grandfather’s final lesson from earth, for me, my sister, my mom and my grandmother! I