A variation of Schrodingers cat concept ... in which it is ask if a cat is known to be in a box, is it alive or dead given our reality cannot determine the outcome (yet our perception of reality can fathom it being in only one of the two states). As an alternative we also have relative state formulation of quantum mechanics ... in which quantum matter can exist in two (or more) places at the same time (the ideal behind quantum computing and information transmission). Here the tree can continue to exist in its original upright form AND in its fallen state ... only our observation of the tree dictates its state in our [i]reality[/i]. Or the matrix alternative ... that the tree doesn't exist but is a stimulus of our imagination in order to create a distraction so that we do not become aware of the truth that we are actually hooked up to machines as a form of forced preservation.