Atheists have mystical experiences that don’t involve God.  I’ll describe several examples here.  Nietzsche had mystical experiences.  During early August 1881, at a rock beside Silvaplana Lake, in the Swiss Alps, near Sils Maria, Nietzsche had a mystical experience. Mountain imagery plays an important role in Nietzsche’s thought.  Perhaps his mystical experience was aroused by the vastness of the Alps and by reflection on the vastness of eternity. Around this time, he wrote about the eternal return and tremendous moments of ecstasy in which all of existence was absolutely affirmed.  He became aware of the extreme value of every thing as well as the extreme suffering produced by the destruction of all value by time. But the eternal return redeems existence by reproducing every valuable thing infinitely often.  He affirmed that existence is holy.

John Dewey had mystical experiences in the late 1880s.  These were intense experiences of the unity and totality of nature.  He felt himself as intensely one with the universe. These seemed to be intensely aesthetic experiences.  John McTaggart had mystical experiences.  For McTaggart, mystical experience revealed that reality is a system of spirits unified by love.  Although McTaggart believed in many spirits, he did not believe in God.  McTaggart regards love as the unifying principle of reality.  This love is the ground of being. McTaggart participates, through it, in an extreme totality.  The community of spirits is fused by love into a unified whole.

Bertrand Russell had a mystical experience in 1901.  It was triggered by watching one of his friends suffer the agonies of cancer.  During this experience he realized that only love can penetrate the utter loneliness of the self.  Russell said his experience changed him into a totally different person.  His ethical and political beliefs were suddenly inverted.  For example, he changed from imperialist to pacifist.  For the rest of his life, he retained an appreciation for the positive emotions and dispositions aroused by mysticism, but not for its production of superstition.

Arthur Koestler was an atheist writer who describes a mystical experience.  While working as a journalist during the Spanish Civil War, he was accused of being a spy and thrown into prison.  He passed the time there by etching mathematical texts into the walls with a piece of iron.  One of these texts was the Euclidean proof that there are infinitely many primes.  As he contemplated this proof, Koestler was overcome with ecstasy.  Mathematics has long been connected with mysticism; but Koestler’s experience is a vivid example of mathematical mysticism without God. The endlessness of the series of primes resembles the vastness of space or the eternity of time.  It points his mind towards infinity; but infinity is an extreme which transcends every prime.  His experience provided him with insight into the deep structure of existence.

The French thinker Pierre Hadot had mystical experiences starting in his adolescence in the 1930s and 1940s.  His experiences were almost always provoked by the perception of  the vastness of nature.  He felt his ego dissolve into the universe.  He was aware of structural features of the world: of being a part of the world, and of the world as a network of relations extending from the grass to the stars.  When he started having these experiences, Hadot was a devout Catholic. But he was shocked by his experiences, because they revealed to him that God does not exist.  His mystical experiences were anti-theistic. They eventually caused him to abandon his Catholicism.

The biologist and religious naturalist Ursula Goodenough wrote about her mystical experiences.  She is an atheist; she does not believe in any personal gods or God.  She wrote instead about her experience of Immanence or Presence.  For Goodenough, the content of mystical experience involves beauty and love.  The French philosopher Andre Comte-Sponville describes himself as a spiritual atheist.  He described his mystical experiences in great detail. His first mystical experience was aroused by the vastness of the sky.  He experienced his ego dissolving into the unity of pure existence.   He felt only absolute joy, indescribably painful love, and empty luminosity.

Richard Dawkins seems to have had mystical experiences.  After describing how one of his teachers had a religiously significant mystical experience, Dawkins says he experienced much the same thing, but without the religion.  He refers to an apparently mystical experience he had as a boy in Africa.  He was dazzled by the stars.   When he hears great music, sees great architecture, or looks at the Grand Canyon, Dawkins says he has mystical feelings.   He says deep time and deep space arouse in him feelings of the sacred and the holy.  His mystical feelings are aroused by natural extremities: by things that are extremely far, old, large, small, or detailed.  They point his thoughts towards the extremity of nature as a whole.  But these experiences do not reveal any God.  On the contrary, they reveal the glorious magnitude and detail of nature.

The American physicist Alan Lightman describes a mystical experience.  He was boating on the ocean on a summer night, from the coast of Maine to a small island where he lived.  He turned off the engine and running lights and lay back in the boat to look up at the stars when had a mystical experience.  He became intensely aware of vast scale of space and time. He felt unified with the universe. He experienced an intense dissolution.  He dissolved into the infinity of nature.  He said that, after his experience, he was still a materialistic scientist. Nevertheless, he said his experience revealed to him that nature contains absolute and sacred structures.

Eric Steinhart - Is Atheism a Belief System?