It's all illusion: the illusion of space, the illusion of mass, the illusion of light. The illusions go on and on, there is no limit to the number of illusions you can come up with.
  - Joseph P. Blodgett.

I introduce the idea from all Schools of Thought that matter is an illusion, and most likely a projection of Consciousness, by means of many quotes from renowned scientists and theologians:

"Nothing exists but thoughts! The universe is composed of impressions, ideas, pleasures, and pains."   - Sir Humphrey Davy

"Physical science, assuming that each message must have had a starting-point, postulated the existence of 'matter' to provide such starting-points. But the existence of this matter was a pure hypothesis; and matter is in actual fact as unobservable as the ether, Newtonian force, and other unobservables which have vanished from science. Early science not only assumed matter to exist, but further pictured it as existing in space and time. Again, this assumption had no adequate justification; for there is clearly no reason why the whole material universe should be restricted to the narrow framework along which messages strike our senses."  - Sir James Jeans, The new world-picture of modern physics, addressing the British Association.  

"The stream of human knowledge is impartially heading towards a non-mechanical reality. The universe begins to look more like a great thought than a great machine.  Mind no longer appears to be an accidental intruder into the realm of matter.  We are beginning to suspect that we ought rather to hail it as the creator and governor of this realm."  - Sir James Jeans, The Mysterious Universe (1930), chapter 5

"Reality is merely an illusion, albeit a very persistent one."  - Albert Einstein

"Everything we call real is made of things that cannot be regarded as real."  - Niels Bohr

"For the kabbalist, physicality does not exist in and of itself; physical existence is animated by God, whose emanation is everflowing, and without whom all physical existence would collapse in a moment." - Feldman, Jewish Mysticism and Kabbalah, p 80. 

"Truly things seen are manifest images of things unseen."  - Dionysius the Areopagite, Letter to John, Theologos, Apostle and Evangelist, Imprisoned in the Isle of Patmos.

However, it is an error to think that reality is an illusion.  I have found that people often offer to kill you to prove that reality is not an illusion.  The universe, and all it contains, visible or not, is real.  The illusion is the belief that the matter and energy comprising the universe has an independent existence from Consciousness, which is the ultimate reality.