One thing which comes to mind in this is - if what is shown within the borders of the rendering comprises the universe, what is to prevent usage of fantasy in the presentating? For one thing, it has to do with the fact that while this rendering is a universe of its own, to be effective in communicating, there has to be a referencing to this, our own real universe....... therefore, anything which is shown in this rendered universe can only be of value to the extent that it properly adheres to this, our own, universe's so-called 'laws of nature' - and the recognition that any other visualization is meaningless within that context... a second thing to consider is that there is a crucial difference between imaginating and fantasizing - the former utilizes the aspects of reality to formulate new ideas and applications, including some possibles yet to be - while the latter plays around with impossibles, and as such becomes psychological studies rather than contemplative works...