Bertrand Russell on The argument from religious experience
Russell argued that religious experiences are subjective psychological states that provide no evidence for objective theological claims.
Russell treated the argument from religious experience with the analytical precision of a logician. He acknowledged that people have profound experiences they describe as encounters with God. But he denied that the subjective intensity of an experience provides evidence for the objective truth of its content.
He pointed out that people of mutually incompatible religions report equally vivid and convincing religious experiences. A Hindu mystic's experience of Brahman and a Christian mystic's experience of Christ cannot both be veridical in the way the experiencers believe, since they describe fundamentally different realities. The most parsimonious explanation is that all such experiences are products of the human brain rather than encounters with an external divine reality.
Russell also noted that religious experiences can be reliably produced by fasting, sleep deprivation, meditation, sensory deprivation, and certain drugs — all of which alter brain chemistry. This strongly suggests that the experiences are neurological in origin rather than supernatural.
“From a scientific point of view, we can make no distinction between the man who eats little and sees heaven and the man who drinks much and sees snakes.”