According to the Hindu Puranas, there are fourteen worlds in the universe - the seven upper and the seven lower. The seven upper worlds are Bhuh, Bhavah, Swah, Mahah, Janah. Tapah, and Satyam; and the seven nether worlds are Atala, Vitala, Sutala, Rasatala, Talatala, Mahatala, and Patala. The region known as Bhuh is the earth where we dwell, while Swah is the celestial world to which people repair after death to enjoy the reward of their righteous actions on earth. Bhuvah is the region between the two. Janah, Tapah, and Satyam constitute Brahmaloka, or the highest heaven, where fortunate souls repair after death and enjoy spiritual communion with the personal God, and at the end of the cycle attain liberation, though a few return to earth again. The world of Mahah is located between Brahmaloka and Bhuh, Bhuuah, and Swah. Patala, the lowest of the seven nether worlds, is the realm where wicked souls sojourn after death and reap the results of their unrighteous actions on earth. Thus, from the viewpoint of Hinduism, heaven and hell are merely different worlds, bound by time, space, and causality. According to Hinduism, desires are responsible for a person's embodiment. Some of these desires can best be fulfilled in a human body, and some in an animal or a celestial body. Accordingly, a soul assumes a body determined by its unfulfilled desires and the results of its past actions. An animal or a celestial body is for reaping the results of past karma, not for performing actions to acquire a new body. Performance of karma to effect any change of life is possible only in a human body, because only human beings do good or evil consciously. Human birth is therefore a great privilege, for in a human body alone can one attain the supreme goal of life. Thus, in search of eternal happiness and immortality, the apparent soul is born again and again in different bodies, only to discover in the end that immortality can never be attained through fulfillment of desires. The soul then practices discrimination between the real and the unreal, attains desirelessness, and finally realizes its immortal nature. Affirming this fact, the Katha Upanishad says: "When all the desires that dwell in the heart fall away, then the mortal becomes immortal and here attains Brahman."