Is Time Travel Possible?
Aristotle and St. Thomas Aquinas on Time
Time travel is certainly impossible, for two reasons supplied by Aristotle and St. Thomas respectively. For Aristotle, time travel is impossible because time is not an independent, absolute motion apart from bodies, as it was for Isaac Newton; rather, time is the numerical measure of the motion of bodies, the divisions of the dispositions of mobile bodies in motion. Time is dependent upon motion, which itself only exists within and between bodies. Thus, only the “now” truly exists, containing within itself the potencies of before and after or past and future which are not in act until they exist in the indivisible now. Although time and motion are distinct notions, they are inseparable; for this reason, it would be impossible to travel along time as if it were a geographical location since, while place and being in place are separate for bodies, and so a body can be considered independent of place (even if never truly existing outside of place), time and being in time are not separate, since time is simply the numerical measure or duration of motion. So long as a body is mobile, it is in time, and real time is only the now; indeed, the mobile body is the only assurance of the stability of time as that which perdures through change and contains the dispositions for motion. Since the measurement of time is in the mind, the tendency is to view time as independent and absolute, but this contradicts the nature of time as the measure of motion. As Glen Coughlin explains, “We tend to treat whatever we think of as if it were a thing like other things around us, as we tend to think of space as a three-dimensional thing which is immobile the way bodies are, and of material as a kind of thing like wood or air. Our thoughts of time are subject to this same inclination.” The Thomistic synthesis of the foundations of time in motion and in the mind is the concept of ens rationis cum fundamento in re, by which time “is a synthesis of real and mental being, founded in reality, existing formally in the mind.”