This is philosophy and not science. It borders at best on the fringes of scientific epistemology, but that's it. <br /><br />Reality is defined very easily and readily in the sciences by events which can be observed either directly, or via instruments. If something can be detected then it can be known to exist. If it cannot be detected, despite numerous observations, then it either isn't real, or it's very hard to find, and its existence in problematic. <br /><br />So, calling something an 'illusion', except in the strictest psychological sense, is simply a philosophical discussion. It's not science and it's hardly astronomy, physics, or chemistry, either. <br /><br />"If you would discuss philosophy with me, define your terms." --Voltaire <br /> <br /><br />You must be some kind of scientist. Taking a very narrow viewpoint. Which is fine, I have no arguement with that. However, by taking a broader view, and using one's imagination (to form images in one's mind to other possibilities) is IMHO more important than disecting the world. To steal a quote from Star Trek: "To Boldly go where no man has gone before" involves imagination:<br /><br />Einstein: He had to form a mental image of riding on top of a photon, for his SR Theory.<br /><br />Stephen Hawking: Had to imagine himself at the event horizon of a black hole for his Hawking Radiation Theory.<br /><br />I did define my terms ( as in your Voltaire quote) in order to discuss philosophy with you, and your buddy Voltaire. If you missed it, I'll repeat it here:<br /><br />Illusion: The erroneous perception of reality.<br /><br />Imagination: The power of the mind to form an image of something that is not real, OR PRESENT. <br /><br />Philosophy: The investigation of causes and laws underlying reality. <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>