Discovered things seem to exist independently of their discovery (think of uninhabited islands and rare species), while invented things come into existence in the very process of their invention (think of the first light bulb). But even if the first light bulb came into existence when Edison invented it, what about the idea of the light bulb? Did he invent this at the same time, or was it, as you suggest, hanging around for eons just waiting for Edison or some other genius to stumble upon it? It's a great question--and connected at root to venerable metaphysical questions to which, in my view, we still lack satisfactory answers. The issue isn't so much about how we use the concepts of invention and discovery (though this is interesting), but rather about the unsettled status of the "ideas" that we discover/invent. On the one hand, we certainly seem to talk of ideas as things that transcend particular, spatio-temporally located acts of thinking in which they might figure. We might say: George...

You're right that the use of "largest" and "smallest" involves some comparison class, even if this is only implicit. We can say that the largest postage stamp is a lot smaller than the smallest planet because we are, of course, comparing the largest stamp to other stamps, and the smallest planet (Mercury?) to other planets. (Note also that "largest" and "smallest" can be used with different implicit senses of "size". Thus, the largest blunder of my life (not buying Google when it went public) needn't be very large in any physical sense.) To make things explicit, then, your questions are (or might be?): Is there a spatially largest physical object? Is there a spatially smallest one? And you're right, unfortunately, these are really best asked of a physicist. However, answering them will, I think, depend upon certain partly philosophical issues such as whether it makes sense to speak of spatial extension when it comes to micro-particles, and whether the universe as a whole can be considered an "object".