Maria Popova quotes an extract from Marc Wittmann’s Altered States of Consciousness about how the science of psychedelics illuminates consciousness:
Scientific research on the effects of LSD and psilocybin has shown clearly that the states of consciousness involve striking changes in perception, emotions, and ideas, and also in the ways they are described: time, space, and the experience of self are dramatically altered. These changes are comparable only with other extreme states of consciousness such as occur in dreams, in mystical and religious ecstasy, or in acute psychotic phases in the early stage of schizophrenia. The dimensions of mystical experience include oneness of the self with the universe, the feeling of timelessness and spacelessness, the most intense feelings of happiness, and the certainty of experiencing a sacred truth which is, however, indescribable. The latter is the feeling of looking behind the veil of reality and seeing the immutable (that is, timeless and spaceless) truth of the world in its entirety.
Research into the mystical experience of the disintegration of time and the self under the influence of hallucinogens is a way toward understanding human consciousness.
Consciousness is by far the most fascinating topic of intellectual discovery (I hesitate to call it “scientific discovery”). Wittmann touches all the associated experiences that come with altered states, and how studying those are the key to understanding consciousness.