The vibration produced by chanting Om in the physical universe corresponds to the original vibration that first arose at the time of creation. The sound of Om is also called Pranava, meaning that it sustains life and runs through Prana or breath. Om also represents the four states of the Supreme Being. The three sounds in Om (AUM) represent the waking, dream and deep sleep states and the silence which surrounds Om represents the "Turiya" state.
Because the first of the three states of consciousness is the waking state, it is represented by the sound "A" pronounced like "A" in accounting. Because the dream state of consciousness lies between the waking and the deep sleep states, it is represented by the letter "U" which lies between the "A" and "M". This "U" is pronounced like the "U" in would. The last state of consciousness is the deep sleep state and is represented by "M" pronounced as in "sum." This closes the pronunciation of Om just as deep sleep is the final stage of the mind at rest. Whenever Om is recited in succession there is an inevitable period of silence between two successive Oms. This silence represents the "fourth state" known as "Turiya" which is the state of perfect bliss when the individual self recognizes his identity with the supreme.
