Cosmic Consciousness: A Study in the Evolution of the Human Mind is Richard Bucke's theory that our mental states are evolving and that to date we have experienced three stages in the development of consciousness: the 'simple consciousness' of animals, the 'self-consciousness' of the vast majority of humans (reason, self awareness, imagination, etc.), and in some cases 'cosmic consciousness'; a mystical state of being beyond 'self consciousness' and the next stage of human development.
Bucke hypothesized that 'cosmic consciousness' is slowly beginning to appear in humans and will eventually spread widely throughout the human race. He posited that certain notable individuals throughout history have demonstrated that they have attained 'cosmic consciousness'.
In the book he cites examples such as Jesus, Buddha, Mohammed, Dante, St Paul, Francis Bacon, William Blake, and his close friend Walt Whitman.
Whitman, an American poet and journalist described cosmic consciousness as 'ineffable light, light rare, untellable, light beyond all signs, descriptions and languages.'
At the age of thirty-five Bucke found himself in this elevated mental state and he describes (in the third person) the manifestations leading up to it;
'1. The person, suddenly, without warning, has a sense of being immersed in a flame, or rose-colored cloud, or perhaps rather a sense that the mind is itself filled with such a cloud of haze.
2. At the same instant he is, as it were, bathed in an emotion of joy, assurance, triumph, salvation.
3. Simultaneously or instantly following the above sense and emotional experiences there comes to the person an intellectual illumination quite impossible to describe. Like a flash there is presented to his consciousness a clear conception (a vision) in outline of the meaning and drift of the universe. He does not come to believe merely; but he sees and knows that the cosmos, which to the self conscious mind seems made up of dead matter, is in fact far otherwise—is in very truth a living presence. He sees that instead of men being, as it were, patches of life scattered through an infinite sea of non-living substance, they are in reality specks of relative death in an infinite ocean of life. He sees that the life which is in man is eternal, as all life is eternal; that the soul of man is as immortal as God is; that the universe is so built and ordered that without any peradventure all things work together for the good of each and all; that the foundation principle of the world is what we call love, and that the happiness of every individual is in the long run absolutely certain.'