When someone says "it's all just an illusion" whilst referring to the manifest world, what do they actually mean?
In our waking state this physical realm seems so completely real that we build our whole lives around it. The duality we observe through the working of the "rational" mind appears to be just how things are and there is no real impulse or need to question this undeniable "reality".
There have been scientists who have looked beyond the physical, the most notable being Tesla and Einstein. Tesla was a scientific genius who not only studied the outer physical world, but also knew the importance of exploring his inner world. He followed the Indian spiritual teacher, Swami Vivekananda, who brought his deep esoteric wisdom and practice, such as meditation, to the west.
Understanding the difference between intelligence and consciousness is critical. Being highly intelligent (as many theoretical scientists are) is not necessarily accompanied by higher consciousness. Advanced spiritual practice can awaken the capacity to transcend the intellect, honing intuitive capacities that are the realm beyond thought and rational mind perceptions.
Deep meditation can also "declutch" the mind, opening the door to the experience of subtle, causal and non-dual states that leads us back to the question of the illusion. In the non-dual state of unity consciousness there is no distinction between the form and the formless as the illusion of a separate identity disintegrates where spirit and matter meet. Creating images that attempt to illustrate this is the founding philosophy behind many Sahaja images.
Image: Black kites at dusk near the Taj Mahal, Agra.