The foundation of all knowledge, be it about this world or about the subtle universes, is certainly a concrete experience.
Experience is either total or partial and incomplete, but it always refers to the reality of the experienced thing.
There have been many debates about the reality of the physical world. Of these, we shall mention the monist doctrine of the sage Shankaracharya (from which VEDANTA emerged) as a comparison to the tantric point of view, which will be our main topic of interest.
Shankaracharya defines Reality as being that which does not change, unlike the finite experience, which - although "real" for a moment - finally changes.
Considered from this perspective, our universe - as a changing thing - holds a relative reality. Consequently, for Shankaracharya and his followers, the world we live HERE and NOW is not real, it is merely an illusion one must surpass in order to experience the Ultimate Reality.
This point of view is true, if we look at things from the perspective of the Transcendent Absolute (BRAHMAN).
The Tantric view on these things rests upon the idea that this world is NECESSARILY real. Thus, a particular thing may be real and at the same time subject to change.
In Tantra, the divine couple Shiva and Shakti represents the Real and Total experience of the universe. In order for us to understand Reality, they are said to limit themselves and "contract" in fragments of Reality which belong to the Supreme Reality, in a gesture of divine sacrifice.
The tantric adept has to perceive his own reality, to convince himself of the reality of this world as the basis of his actions. For tantrics, this universe is real because it originates in the divine couple Shiva-Shakti.
The total experience one may have is actually the Consciousness of the Supreme, from which the Macro cosmos emerged.
The finite, limited experience has a fragmented character; consequently the knowledge obtained from this experience will not be of the whole. The essence of the limited experience is the experience we have within the confines of time and space.
However, the Ultimate experience, through its permanent nature, is placed beyond time and space, as time and space define change.
As shown before, "illusion" merely represents the experience of the Supreme Self in time and space. An important aspect of Tantra is to be aware of your actions, even the most common ones, like eating. The idea behind this focus on present action is that by doing so the past and future "disappears". What remains is the present, the eternal "now", which makes us go beyond the ordinary notion of time. This is synonymous with getting close to the Supreme Source, which transcends both Time and Space.
Advice from the famous secret treaty VIJNANA BHAIRAVA TANTRA states that one should become one with the food or drink one is consuming, filling his/her very being with it.
Furthermore, another sutra says that when singing, looking, or tasting something, one should always be completely aware, because this is how he/she will discover eternal life.
"Being in action means being free in that action." This is the point of disruption, the point at which one may reach the ultimate consciousness right here and right now.