On the other hand, centuries later, Sadrā, chose a more radical route, by inclining towards the reality of "astī" (is-ness), as the true mode of existence, and tried to get rid of the concept of "hastī" (existence as fixed or immovable). Thus, in his philosophy, the universal movement penetrates deep into the Aristotelian "substance"/"essence", in unison with changing accident. He called this deep existential change حرکت جوهری "harekat-e jowhari" (Substantial Movement). In such a changing existence, the whole world has to go through instantaneous annihilation and recreation incessantly, while as Avicenna had predicted in his remarks on Nature, such a universal change or substantial movement would eventually entail the shortening and lengthening of time as well which has never been observed. This logical objection, which was made on Aristotle's argumentation, could not be answered in the ancient times or medieval age, but now it does not sound contradictory to the real nature of Time (as addressed in relativity theory), so by a reverse argument, a philosopher may indeed deduce that everything is changing (moving) even in the deepest core of Being.