Is TM the only way to transcend?

No, but surely it's the easiest and most reliable. Scientific studies show that the TM technique, designed for “automatic self-transcending,” induces the process of transcending consistently and spontaneously—for new meditators as well as long-term.
Transcending is natural—we’re all hardwired for it.
Transcending takes you deep into silent, inner wakefulness—into the wholeness of your own self, a field of non-localized or “unbounded” awareness. EEG research on TM practice shows that it creates widespread brain wave coherence, meaning, more orderly and efficient brain function, not just in localized areas of the brain but throughout. This experience integrates the different parts of your brain so that they work together better as a whole. The benefits of transcending are holistic, as watering the root is more holistic than tending single leaves or flowers.
Whenever transcending happens, the meditation process has come to an end. The meditator has gone beyond the mind’s boundaries. There is only consciousness, in its purest, most serene and orderly state. This experience is also called the state of yoga (unified awareness), sat chit ananda (never-changing bliss consciousness), turiya ("the fourth state,” unlike waking, dreaming or sleep)—on and on go the references to it in all the great traditions of meditation.
Transcending is a universal experience known to all cultures. No one tradition lays claim to transcending more than any other.
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The beauty of the Transcendental Meditation technique is that it allows transcending to happen spontaneously, effortlessly—without trying to make it happen or leaving it up to chance. During TM practice, transcending comes to you.