The Two and the One by Romanian scholar of comparative religion Mircea Eliade (1907-1986) addresses transcendental experience across cultures. He describes tantric sex as a technique for reuniting opposites, and thus expanding spiritual perception beyond Time.
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Excerpts
[These come from the 1965 English translation.]
Certain Tantric schools teach that samarasa [state of bliss] is attainable principally by maithuna (ritual union of the sexes) and is characterised by the “staying ” or “immobilisation” of the three principal functions of a human being: Breath, seminal ejaculation and thought. The unification of opposites is expressed by the cessation of the bio-somatic processes and also of the psycho-mental flux. The immobilisation of those functions that are especially fluid is a sign that a man has left the human condition and come out on a transcendent plane…
The yogin…has succeeded in putting himself in the moment outside Time in which the Universe was not yet created…[He] has entered into non-duality and liberty…
The reunion of opposites
What is revealed to us by [this search for] the coincidentia oppositorum, the reunion of opposites, the totalisation of fragments? First of all, man’s deep dissatisfaction with his actual situation, with what is called the human condition. Man feels himself torn and separate. He often finds it difficult properly to explain to himself the nature of this separation. For sometimes he feels himself to be cut off from “something” powerful, “something” utterly other than himself. And at other times from an indefinable, timeless “state”, of which he has no precise memory, but which he does however remember in the depths of his being: a primordial state which he enjoyed before Time, before History.
This separation has take the form of a fissure, both in himself and in the World. It was the “fall”, not necessarily in the Judeo-Christian meaning of the term, but a fall nevertheless. Since it implies a fatal disaster for the human race and at the same time an ontological change in the structure of the World…
Ultimately, it is the wish to recover this lost unity that has caused man to think of the opposites as complementary aspects of a single reality…
The ego resists
Every attempt to transcend the opposites carries with it a certain danger. This is why the ideas of a coincidentia oppositorum always arouse ambivalent feelings. On the one side, man is haunted by the desire to escape from his particular situation and regain a transpersonal mode of life. On the other, he is paralysed by the fear of losing his “identity” and “forgetting” himself.
Eliade, Mircea. 1965. The two and the one. New York and Evanston: Harper & Row